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Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

November 2013
Astronomy and Astrophysics 562

DOI:10.1051/0004-6361/201321954

Source
arXiv

Authors:

A. Karska

Nicolaus Copernicus University

Fabrice Herpin

Université Bordeaux 1

Sanami Bruderer

BÜCHI Labortechnik AG

Show all 16 authorsHide

(Abridged) We study the response of the gas to energetic processes associated with high-mass star formation and compare it with studies on low- and intermediate-mass young stellar objects (YSOs) using the same methods. The far-IR line emission and absorption of CO, H$_2$O, OH, and [OI] reveals the excitation and the relative contribution of different species to the gas cooling budget. Herschel-PACS spectra covering 55-190 um are analyzed for ten high-mass star forming regions of various luminosities and evolutionary stages at spatial scales of ~10^4 AU. Radiative transfer models are used to determine the contribution of the envelope to the far-IR CO emission. The close environments of high-mass YSOs show strong far-IR emission from molecules, atoms, and ions. Water is detected in all 10 objects even up to high excitation lines. CO lines from J=14-13 up to typically 29-28 show a single temperature component, Trot~300 K. Typical H$_2$O temperatures are Trot~250 K, while OH has Trot~80 K. Far-IR line cooling is dominated by CO (~75 %) and to a smaller extent by OI (~20 %), which increases for the most evolved sources. H$_2$O is less important as a coolant for high-mass sources because many lines are in absorption. Emission from the envelope is responsible for ~45-85 % of the total CO luminosity in high-mass sources compared with only ~10 % for low-mass YSOs. The highest-J lines originate most likely from shocks, based on the strong correlation of CO and H$_2$O with physical parameters of the sources from low- to high-masses. Excitation of warm CO is very similar for all mass regimes, whereas H$_2$O temperatures are ~100 K higher for high-mass sources than the low-mass YSOs. Molecular cooling is ~4 times more important than cooling by [OI]. The total far-IR line luminosity is about 10$^{-3}$ and 10$^{-5}$ times lower than the dust luminosity for the low- and high-mass YSOs.

Relative contributions of [O i] (dark blue), CO (yellow), H 2 O (orange), and OH (red) cooling to the total far-IR gas cooling at central position are shown from left to right horizontally for each source. The objects follow the evolutionary sequence with the most evolved sources on top.

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arXiv:1311.6644v1 [astro-ph.SR] 26 Nov 2013

Astronomy & Astrophysics

manuscript no. karska˙highmass c

ESO 2013

November 27, 2013

Far-infrared molecular lines from Low- to High-Mass

Star Forming Regions observed with

Herschel

A. Karska1,2, F. Herpin3,4, S. Bruderer1, J.R. Goicoechea5, G.J. Herczeg6, E.F. van Dishoeck1,2, I. San Jos´e-Garc´ıa2,

A. Contursi1, H. Feuchtgruber1, D. Fedele1, A. Baudry3,4, J. Braine3,4, L. Chavarr´ıa5, J. Cernicharo5, F.F.S. van der

Tak7,8, and F. Wyrowski9

1Max-Planck Institut f¨ur Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching, Germany

2Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

3Universit´e de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2 rue de l’Observatoire, BP 89, F-33271 Floirac Cedex,

France

4CNRS, LAB, UMR 5804, F-33271 Floirac Cedex, France

5Centro de Astrobiolog´ıa. Departamento de Astrof´ısica. CSIC-INTA.Carretera de Ajalvir, Km 4, Torrej´on de Ardoz. 28850, Madrid,

Spain

6Kavli Institut for Astronomy and Astrophysics, Yi He Yuan Lu 5, HaiDian Qu, Peking University, Beijing, 100871, PR China

7SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands

8Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands

9Max-Planck-Institut f¨ur Radioastronomie, Auf dem H¨ugel 69, 53121 Bonn, Germany

e-mail: karska@mpe.mpg.de

Received May 24, 2013; accepted November 26, 2013

ABSTRACT

Aims.

Our aim is to study the response of the gas to energetic processes associated with high-mass star formation andcompare it with

previously published studies on low- and intermediate-mass young stellar objects (YSOs) using the same methods. The quantiﬁed

far-infrared line emission and absorption of CO, H2O, OH, and [O i] reveals the excitation and the relative contribution of diﬀerent

atomic and molecular species to the gas cooling budget.

Methods.

Herschel-PACS spectra covering 55–190 µm are analyzed for ten high-mass star forming regions of luminosities Lbol ∼

104−106L⊙and various evolutionary stages at spatial scales of ∼104AU. Radiative transfer models are used to determine the

contribution of the quiescent envelope to the far-IR CO emission.

Results.

The close environments of high-mass protostars show strong far-infrared emission from molecules, atoms, and ions. Water is

detected in all 10 objects even up to high excitation lines, often in absorption at the shorter wavelengths and in emission at the longer

wavelengths. CO transitions from J=14 −13 up to typically 29 −28 (Eu/kB∼580 −2400 K) show a single temperature component

with a rotational temperature of Trot ∼300 K. Typical H2O excitation temperatures are Trot ∼250 K, while OH has Trot ∼80 K. Far-IR

line cooling is dominated by CO (∼75%) and to a smaller extent by [O i] (∼20 %), which becomes more important for the most

evolved sources. H2O is less important as a coolant for high-mass sources due to the fact that many lines are in absorption.

Conclusions.

Emission from the quiescent envelope is responsible for ∼45 −85 % of the total CO luminosity in high-mass sources

compared with only ∼10% for low-mass YSOs. The highest−Jlines (Jup ≥20) originate most likely from shocks, based on the strong

correlation of CO and H2O with physical parameters (Lbol,Menv) of the sources from low- to high-mass YSOs. Excitation of warm

CO described by Trot ∼300 K is very similar for all mass regimes, whereas H2O temperatures are ∼100 K higher for high-mass

sources compared with low-mass YSOs. The total far-IR cooling in lines correlates strongly with bolometric luminosity, consistent

with previous studies restricted to low-mass YSOs. Molecular cooling (CO, H2O, and OH) is ∼4 times more important than cooling

by oxygen atoms for all mass regimes. The total far-IR line luminosity is about 10−3and 10−5times lower than the dust luminosity

for the low- and high-mass star forming regions, respectively.

Key words. astrochemistry stars: formation stars: –ISM: outﬂows, shocks

1. Introduction

High-mass stars (M>8 M⊙) play a central role in the energy

budget, the shaping, and the evolution of galaxies (see review

by Zinnecker & Yorke 2007). They are the main source of UV

radiation in galaxy disks. Massive outﬂows and H ii regions are

bulence and heating of the interstellar medium (ISM). At the end

of their lives, they inject heavy elements into the ISM that form

the next generation of molecules and dust grains. These atoms

and molecules are the main cooling channels of the ISM. The

models of high-mass star formation are still strongly debated;

the two competing scenarios are turbulent core accretion and

‘competitive accretion’ (e.g. Cesaroni 2005). Molecular line ob-

servations are crucial to determine the impact of UV radiation,

outﬂows, infall and turbulence on the formation and evolution

of the high-mass protostars and ultimately distinguish between

those models.

Based on observations, the ‘embedded phase’ of high-mass

star formation may empirically be divided into several stages

(e.g. Helmich & van Dishoeck 1997; van der Tak et al. 2000;

Beuther et al. 2007): (i) massive pre-stellar cores (PSC); (ii)

high-mass protostellar objects (HMPOs); (iii) hot molecular

cores (HMC); and (iv) ultra-compact H ii regions (UCH ii). The

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

pre-stellar core stage represents initial conditions of high-mass

star formation, with no signatures of outﬂow /infall or maser

activity. During the high-mass protostellar objects stage, infall

of a massive envelope onto the central star and strong outﬂows

indicate the presence of an active protostar. In the hot molecular

core stage, large amounts of warm and dense gas and dust are

seen. The temperature of T>100 K in subregions <0.1 pc in

size is high enough to evaporate molecules oﬀthe grains. In the

ﬁnal, ultra-compact H ii regions stage, a considerable amount of

ionized gas is detected surrounding the central protostar.

The above scenario is still debated (Beuther et al. 2007), in

particular whether stages (ii) and (iii) are indeed intrinsically dif-

ferent. The equivalent sequence for the low-mass Young Stellar

Objects (hereafter YSO) is better established (Shu et al. 1987;

Andr´e et al. 1993, 2000). The ‘embedded phase’ of low-mass

protostars consists of: (i) pre-stellar core phase; (ii) Class 0; and

(iii) Class I phase. The Class 0 YSOs are surrounded by a mas-

sive envelope and drive collimated jets/outﬂows. In the more

evolved Class I objects the envelope is mostly dispersed and

more transparent for UV radiation; the outﬂows are less pow-

erful and have larger opening angles.

Low mass sources can be probed at high spatial resolution

due to a factor of 10 smaller distances, which allow us to study

well-isolated sources and avoid much of the confusion due to

clouds along the line of sight. The line emission is less aﬀected

by foreground extinction and therefore provides a good tool to

study the gas physical conditions and chemistry in the region.

The slower evolutionary timescale results in a larger number

of low-mass YSOs compared to their high-mass counterparts,

which is also consistent with observed stellar/core mass func-

tions.

While low-mass YSOs are extensively studied in the

far-infrared, ﬁrst with the Infrared Space Observatory (ISO,

Kessler et al. 1996) and now with Herschel (Pilbratt et al.

2010)1, the same is not the case for high-mass sources

(see e.g. Helmich & van Dishoeck 1997; Vastel et al. 2001;

Boonman & van Dishoeck 2003). For those, the best-studied

case is the relatively nearby Orion BN-KL region observed with

ISO’s Long- and Short-Wavelength Spectrometers (Clegg et al.

1996; de Graauw et al. 1996). Spectroscopy at long-wavelengths

(45-197 µm) shows numerous and often highly-excited H2O

lines in emission (Harwit et al. 1998), high-JCO lines (e.g., up

to J=43-42 in OMC-1 core, Sempere et al. 2000) and several OH

doublets (Goicoechea et al. 2006), while the shorter wavelength

surveys reveal the CO and H2O vibration-rotation bands and H2

pure rotational lines (van Dishoeck et al. 1998; Rosenthal et al.

2000). Fabry-Perot (FP) spectroscopy (λ/∆λ∼10,000, 30 km

s−1) data show resolved P-Cygni proﬁles for selected H2O tran-

sitions at λ < 100 µm, with velocities extending up to 100 km

s−1(Wright et al. 2000; Cernicharo et al. 2006). At the shortest

wavelengths (<45 µm) all pure rotational H2O lines show ab-

sorption (Wright et al. 2000). ISO spectra towards other high-

mass star forming regions are dominated by atomic and ionic

lines (see review by van Dishoeck 2004), similar to far-IR spec-

tra of extragalactic sources (Fischer et al. 1999; Sturm et al.

2002).

The increased sensitivity, spectral and spatial resolution

of the Photodetector Array Camera and Spectrometer (PACS)

(Poglitsch et al. 2010) onboard Herschel now allows the detailed

study of the molecular content of a larger sample of high-mass

1Herschel is an ESA space observatory with science instruments pro-

vided by European-led Principal Investigator consortia and with impor-

tant participation from NASA.

star forming regions. In particular, the more than an order of

magnitude improvement in the spectral resolution in compari-

son with the ISO-LWS grating observing mode allows the rou-

tine detections of weak lines against the very strong continuum

of high-mass sources with Herschel, with line-to-continuum ra-

tios below 1%.

The diagnostic capabilities of far-infrared lines have

been demonstrated by the recent results on low- and

intermediate-mass YSOs and their outﬂows (Fich et al. 2010;

Herczeg et al. 2012; Goicoechea et al. 2012; Manoj et al. 2013;

Wampﬂer et al. 2013; Karska et al. 2013; Green et al. 2013).

The CO ladder from J=14-13 up to 49-48 and a few tens

of H2O lines with a range of excitation energies are de-

tected towards the Class 0 sources, NGC1333 IRAS4B and

Serpens SMM1 (Herczeg et al. 2012; Goicoechea et al. 2012).

The highly-excited H2O 818 –707 line at 63.3 µm (Eu/kB=1071

K) is seen towards almost half of the Class 0 and I sources in the

Karska et al. (2013) sample, even for bolometric luminosities as

low as ∼1 L⊙. Non-dissociative shocks and to a smaller extent

UV-heating are suggested to be the dominant physical processes

responsible for the observed line emission (van Kempen et al.

2010; Visser et al. 2012; Karska et al. 2013). The contribution

from the bulk of the quiescent warm protostellar envelope to

the PACS lines is negligible for low-mass sources. Even for the

intermediate-mass source NGC7129 FIRS2, where the envelope

contribution is higher, the other processes dominate (Fich et al.

2010).

In this paper, we present Herschel-PACS spectroscopy of

10 sources that cover numerous lines of CO, H2O, OH, and

[Oi] lines obtained as part of the ‘Water in star forming re-

gions with Herschel’ (WISH) key program (van Dishoeck et al.

2011). WISH observed in total about 80 protostars at diﬀer-

ent evolutionary stages (from prestellar cores to circumstellar

disks) and masses (low-, intermediate- and high-mass) with

both the Heterodyne Instrument for the Far-Infrared (HIFI;

de Graauw et al. 2010) and PACS (Poglitsch et al. 2010). This

paper focusses only on PACS observations of high-mass YSOs.

It complements the work byvan der Tak et al. (2013), which de-

scribes our source sample and uses HIFI to study spectrally re-

solved ground-state H2O lines towards all our objects. That pa-

per also provides updated physical models of their envelopes.

The results on high-mass YSOs will be compared with those

for low- and intermediate-mass young stellar objects, analyzed

in a similar manner (Karska et al. 2013; Wampﬂer et al. 2013;

Fich et al. 2010) in order to answer the following questions: How

does far-IR line emission/absorption diﬀer for high-mass pro-

tostars at diﬀerent evolutionary stages? What are the dominant

gas cooling channels for those sources? What physical compo-

nents do we trace and what gas conditions cause the excitation

of the observed lines? Are there any similarities with the low-

and intermediate-mass protostars?

The paper is organized as follows: §2 introduces the source

sample and explains the observations and reduction methods; §3

presents results that are derived directly from the observations;

§4 focuses on the analysis of the data; §5 discusses our results

in the context of the available models and §6 summarizes the

conclusions.

2. Observations and data reduction

We present spectroscopy observations of ten high-mass star

forming regions collected with the PACS instrument on board

Herschel in the framework of the ‘WISH’ program. The sources

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

[OI]

[OIII]

[NII]

[OI]

[CII]

Fig.1. Herschel-PACS continuum-normalized spectrum of W3 IRS5 at the central position. Lines of CO are shown in red, H2O

in blue, OH in light blue, CH in orange, and atoms and ions in green. Horizontal magenta lines show spectral regions zoomed in

Figure C.1.

have an average distance of hDi=2.7 kpc, and represent vari-

ous stages of evolution, from the classical high-mass protostel-

lar objects (HMPOs) to hot molecular cores (HMCs) and ultra-

compact H ii regions (UC H ii). The list of sources and their ba-

sic properties are given in Table 1. Objects are shown in the se-

quence of increasing value of an evolutionary tracer, L0.6M−1

env,

introduced in Bontemps et al. (1996). The sequence does not al-

ways correspond well with the evolutionary stages most com-

monly assigned to the sources in the literature (last column of

Table 2), perhaps because multiple objects in diﬀerent evolu-

tionary stages are probed within our spatial resolution element

(see e.g. Wyrowski et al. 2006; Leurini et al. 2013, for the case

of G327-0.6).

PACS is an integral ﬁeld unit with a 5×5 array of spatial pix-

els (hereafter spaxels). Each spaxel covers 9.

′′4×9.

′′4, providing

a total ﬁeld of view of ∼47′′ ×47′′. The focus of this work is on

the central spaxel only. The central spaxel probes similar physi-

cal scales as the full 5 ×5 array in the 10 times closer low-mass

sources. Full 5 ×5 maps for the high-mass sources, both in lines

and continuum, will be discussed in future papers.

The range spectroscopy mode on PACS uses large grating

steps to quickly scan the full 50-210 µm wavelength range with

Table 1. Catalog information and source properties.

Object D Lbol Menv L0.6M−1

env Class

(kpc) (L⊙) (M⊙) (L0.6

⊙M−1

⊙)

G327-0.6 3.3 7.3 1042044 0.41 HMC

W51N-e1 5.1 5.2 1054530 0.59 UCH ii

DR21(OH) 1.5 1.3 104472 0.62 HMPO

W33A 2.4 3.0 104698 0.70 HMPO

G34.26+0.15 3.3 1.9 1051792 0.82 UCH ii

NGC6334-I 1.7 1.1 105750 1.41 HMC

NGC7538-I1 2.7 1.1 105433 2.45 UCH ii

AFGL2591 3.3 1.2 105373 2.99 HMPO

W3-IRS5 2.0 2.1 105424 3.68 HMPO

G5.89-0.39 1.3 4.1 104140 4.18 UCH ii

Notes. Source coordinates with references and their physical parame-

ters are taken from van der Tak et al. (2013).

Nyquist sampling of the spectral elements. The wavelength cov-

erage consists of three grating orders (1st: 102-210 µm, 2nd:

71-105 µm or 3rd: 51-73 µm), two of which are always ob-

served simultanously (one in the blue, λ < 105 µm, and one in

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.2. Herschel-PACS proﬁles of the [O i] 63.2 µm line at cen-

tral position.

the red, λ > 102 µm, parts of the spectrum). The spectral resolv-

ing power is R=λ/∆λ≈1000-1500 for the 1st order, 1500-2500

for the 2nd order, and 2500-5500 for the 3rd order (correspond-

ing to velocity resolution from ∼75 to 300 km s−1).

Two nod positions were used for chopping 3′on each side

of the source. The comparison of the two positions was made

to assess the inﬂuence of the oﬀ-source ﬂux of observed species

from the oﬀ-source positions, in particular for atoms and ions.

The [C ii] ﬂuxes are strongly aﬀected by the oﬀ-position ﬂux

and saturated for most sources – we therefore limit our analysis

of this species to the two sources with comparable results for

both nods, AFGL2591 and NGC7538-IRS1 (see Table 2).

Typical pointing accuracy is better than 2′′. However, two

sources (G327-0.6 and W33A) were mispointed by a larger

amount as indicated by the location of the peak continuum emis-

sion on maps at diﬀerent wavelengths (for the observing log see

Table A.1 in the Appendix). In order to account for the non-

centric ﬂux distribution on the integral ﬁeld unit due to mis-

pointing and to improve the continuum smoothness, for these

sources two spaxels with maximum continuum levels are used

(spaxel 11 and 21 for G327 and 23 and 33 for W33A). Summing

a larger number of spaxels was not possible due to a shift of line

proﬁles from absorption to emission. The spatial extent of line

emission /absorption will be analyzed in future papers.

We performed the basic data reduction with the Herschel

Interactive Processing Environment v.10 (HIPE, Ott 2010). The

ﬂux was normalized to the telescopic background and cali-

brated using Neptune observations. Spectral ﬂatﬁelding within

HIPE was used to increase the signal-to-noise (for details, see

Herczeg et al. 2012; Green et al. 2013). The overall ﬂux calibra-

tion is accurate to ∼20%, based on the ﬂux repeatability for

multiple observations of the same target in diﬀerent programs,

cross-calibrations with HIFI and ISO, and continuum photome-

try. Custom IDL routines were used to further process the dat-

acubes. The line ﬂuxes were extracted from the central spaxel

(except G327-0.6 and W33A, see above) using Gaussian ﬁts

with ﬁxed line width (for details, see Herczeg et al. 2012). Next,

they were corrected for the wavelength-dependent loss of radi-

ation for a point source (see PACS Observer’s Manual2). That

approach is not optimal for the cases where emission is extended

beyond the central spaxel, but that is mostly the case for atomic

lines, which will be presented in a companion paper by Kwon

et al. (in preparation, hereafter Paper II). The uncertainty intro-

duced by using the point-source correction factors for extended

sources depends on the amount of emission in the surrounding

ring of spaxels. The continuum ﬂuxes are calculated using all 25

spaxels, except G327-0.6 where 1 spaxel was excluded due to

saturation. In most cases, the tabulated values are at wavelengths

near bright lines. They are calculated using spectral regions on

both sides of the lines (but masking any features) and inter-

polated linearly to the wavelength of the lines. The ﬂuxes are

presented in Table B.1 in the Appendix. Our continuum ﬂuxes

are included in the spectral energy distribution ﬁts presented in

van der Tak et al. (2013), who used them to derive physical mod-

els for all our sources. Those models and associated envelope

masses are used in this work in Sections 5.1 and 5.3.

3. Results

Figure 1 shows the full normalized PACS spectrum with line

identiﬁcations for W3 IRS5, a high-mass protostellar object

with the richest molecular emission among our sources. Carbon

monoxide (CO) transitions from J=14-13 to J=30-29 are de-

tected, all in emission (see blow-ups of high-JCO lines in

Figures C.1 and C.2). Water vapor (H2O) transitions up to Eup ∼

1000 K are detected (e.g. 716 −625 at 66.1 µm, see blow-ups in

Figure C.1). At wavelengths shortwards of ∼90 µm many H2O

lines are seen in absorption, but those at longer wavelengths are

primarily in emission.

Seven hydroxyl (OH) doublets up to Eup ≈618 K are seen3.

All lines within the 2Π3/2ladder (119, 84, and 65 µm doublets;

see Figure 1 in Wampﬂer et al. 2013) are strong absorption

lines. The 2Π1/2ladder lines (163 and 71 µm) are seen in emis-

sion. The cross-ladder transitions at 79 µm (OH 1/2,1

/2-3/2,3/2,

Eup ≈180 K) and 96 µm (OH 3/2,1

/2-5/2,3

/2,Eup ≈270 K) are

absorption and emission lines, respectively. Only the ground-

rotational lines of methylidyne (CH) are detected at 149 µm

in absorption. The [O i] transitions at 63 µm and 145 µm are

both strong emission lines in W3 IRS5. That is not always the

case for other sources in our sample. The [O i] line at 63 µm,

where the velocity resolution of PACS is at its highest (∼90

km s−1), shows a variety of proﬁles (see Figure 2): pure ab-

sorption (G327-0.6, W51Ne1, G34.26, W33A), regular P-Cygni

proﬁles (AFGL2591, NGC6334-I), hints of inverse P-Cygni pro-

ﬁles in DR21(OH) and pure emission (W3 IRS5, NGC7538-I1,

G5.89). The [O i] line at 145 µm, however, is always detected

in emission. The P-Cygni proﬁles resolved at velocity scales of

∼100 km s−1resemble the high-velocity line wings observed

in ro-vibrational transitions of CO in some of the same sources

(Mitchell et al. 1990; Herczeg et al. 2011), suggested to origi-

2http://herschel.esac.esa.int/Docs/PACS/html/pacs om.html

3The highest-excited OH doublet at 71 µm is not considered further

in the analysis, because the 70-73 µm region observed with PACS is

aﬀected by spectral leakage and thus is badly ﬂux-calibrated.

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.3. Normalized spectral regions of all our sources at the central position at 64-68, 148-157, and 169-182 µm. Objects are shown

in the evolutionary sequence, with the most evolved ones on top. Lines of CO are shown in red, H2O in blue, OH in light blue, CH

in orange, and NH3and C3in green. Spectra are shifted vertically to improve the clarity of the ﬁgure.

nate in the wind impacting the outﬂow cavities. Note however

that not all absorption needs to be associated with the source:

it can also be due to foreground absorption (e.g. outﬂow lobe

or the ISM). For example, ISO Fabry Perot and new Herschel/

HIFI observations of H2O and OH in Orion also showline wings

in absorption /emission extending to velocities up to ∼100 km

s−1(Cernicharo et al. 2006; Goicoechea et al. 2006, Choi et al.

in prep.), but the ISO-LWS Fabry-Perot observations of Orion

did not reveal P-Cygni proﬁles in the [O i] 63 µm line.

A comparison of selected line-rich parts of the spectra for all

our sources is presented in Figure 3. The spectra are normalized

by the continuum emission to better visualize the line absorption

depths. However, the unresolved proﬁles of PACS underestimate

the true absorption depths and cannot be used to estimate the

optical depths.

The 64-68 µm segment covers the highly-excited H2O lines

at 66.4, 67.1, and 67.3 µm (Eup ≈410 K); high-JCO lines at

65.7 (J=40-39) and 67.3 (J=39-38); and the OH 2Π3/2J=

9/2−7/2(Eup ≈510 K) doublet at 65 µm. The low-lying H2O

lines are detected for all sources. The high-JCO lines are not

detected in this spectral region. The OH doublet is detected for

6 out of 10 sources (see also Figure C.3 in the Appendix).

The main lines seen in the 148-157 µm region are: CH

2Π3/2J=3/2–2Π1/2J=1

/2transition at 149 µm (in absorption),

CO 17-16, and H2O 322 −313 line at 156.2 µm (Eup ≈300

K). Weak absorption lines at ∼155 −156 µm seen towards the

hot core G327-0.6 are most likely C3ro-vibrational transitions

(Cernicharo et al. 2000, Paper II).

The most commonly detected lines in the 170-182 µm spec-

tral region include the CO 15-14 line and the H2O lines at 174.6,

179.5 and 180.5 µm (Eup ≈100-200 K). The proﬁles of H2O

lines change from object to object: the H2O 212 −101 line at

179.5 µm is in absorption for all sources except W3 IRS5; the

H2O 221 −112 at 180.5 µm is in emission for the three most

evolved sources (top 3 spectra on Figure 3). The ammonia line

at ∼170 µm, NH3(3,2)a-(2,2)s, is detected towards 4 sources

(G327-0.6, W51N-e1, G34.26, and NGC6334-I). An absorption

line at ∼181 µm corresponds to H18

2O 212 −101 and/or H3O+

1−

1−1+

1lines (Goicoechea & Cernicharo 2001). Extended dis-

cussion of ions and molecules other than CO, H2O, and OH will

appear in Paper II.

Line proﬁles of H2O observed with HIFI show a vari-

ety of emission and absorption components that are not re-

solved by PACS (Chavarr´ıa et al. 2010; Kristensen et al. 2012;

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.4. Relative contributions of [O i] (dark blue), CO (yellow),

H2O (orange), and OH (red) cooling to the total far-IR gas cool-

ing at central position are shown from left to right horizontally

for each source. The objects follow the evolutionary sequence

with the most evolved sources on top.

van der Tak et al. 2013). The only H2O lines observed in com-

mon by the two instruments within the WISH program are the

ground-state transitions: 212 −101 at 179.5 µm (1670 GHz) and

221−112 at 180.5 µm (1661 GHz), both dominated by absorptions

and therefore not optimal to estimate to what extent a complex

water proﬁle is diluted at the PACS spectral resolution. However,

HIFI observations of the lines between excited rotational states,

which dominate our detected PACS lines, are generally in emis-

sion at the longer wavelengths probed by HIFI. In the case of

12CO 10–9, the line proﬁles of YSOs observed with HIFI con-

sist of a broad outﬂow and a narrow quiescent component with

the relative fraction of the integrated intensity of the narrow to

broad components being typically 30-70% for low-mass sources

(Yıldız et al. 2013). For the single case of a high-mass YSO, W3

IRS5, this fraction is about 50% (San Jos´e-Garc´ıa et al. 2013).

To summarize, PACS spectra of high-mass sources from our

sample show detections of many molecular lines up to high ex-

citation energies. CO, H2O, OH, and CH lines are seen towards

all objects, whereas weaker lines of other molecules are detected

towards less than half of the sources. CO lines are always seen

in emission, CH in absorption, whereas other species show dif-

ferent proﬁles depending on the transition and the object. Table

C.1 shows the CO line ﬂuxes for all lines in the PACS range.

4. Analysis

4.1. Far-IR line cooling

Emission lines observed in the PACS wavelength range are used

to calculate the contribution of diﬀerent species to the total line

cooling from high-mass protostars. Our goal is to compare the

cooling of warm gas by molecules and atoms with the cooling

by dust and connect them with the evolutionary stages of the

objects. Relative contributions to the cooling between diﬀerent

molecules are also determined, which can be an indicator of the

physical processes in the environments of young protostars (e.g.

Nisini et al. 2002; Karska et al. 2013).

We deﬁne the total far-IR line cooling (LFIRL) as the sum

of all emission line luminosities from the ﬁne-structure [Oi]

lines (at 63 and 145 µm) and the detected molecules, follow-

ing Nisini et al. (2002) and Karska et al. (2013). [Cii], the most

important line coolant of diﬀuse interstellar gas, is also expected

to be a signiﬁcant cooling agent in high-mass star forming re-

gions and extragalactic sources. It is not explicitly included in

our analysis, however,because the calculated ﬂuxes are strongly

aﬀected by oﬀ-source emission and often saturated (see also

Section 2). The emitted [C ii] luminosity is shown below for only

two sources, where reliable ﬂuxes were obtained. Cooling in

other ionic lines such as [O iii], [N ii], and [N iii] is also excluded,

due to the oﬀ-position contamination and the fact that those

lines trace a diﬀerent physical component than the molecules

and [O i]. Since the only molecules with emission lines are CO,

H2O, and OH, the equation for the total far-IR line cooling can

be written as: LFIRL =LOI +LCO +LH2O+LOH.

Table 2 summarizes our measurements. The amount of cool-

ing by dust is described by the bolometric luminosity and equals

∼104-105L⊙for our sources (van der Tak et al. 2013). The to-

tal far-IR line cooling ranges from ∼1 to ∼40 L⊙, several or-

ders of magnitude less than the dust cooling. Relative contri-

butions of oxygen atoms and molecules to the gas cooling are

illustrated in Figure 4. Atomic cooling is the largest for the more

evolved sources in our sample (see Table 1), in particular for

NGC7538 IRS1 and AFGL2591, where it is the dominant line

cooling channel. For those two sources, additional cooling by

[C ii] is determined and amounts to ∼10-25% of LFIRL (Table 2).

Typically, atomic cooling accounts for ∼20 % of the total line

far-IR line cooling. Molecular line cooling is dominated by CO,

which is responsible for ∼15 up to 85% of LFIRL, with a median

contribution of 74%. H2O and OH median contributions to the

far-IR cooling are less than 1%, because many of their transitions

are detected in absorption. Assuming that the absorptions arise

in the same gas, as found for the case of Orion (Cernicharo et al.

2006), they therefore do not contribute to the cooling, but heat-

ing of the gas. Still, the contribution of H2O to the total FIR

cooling increases slightly for more evolved sources, from ∼5%

(DR21(OH)) to 30% (W3IRS5), whereas no such trend is seen

for OH.

4.2. Molecular excitation

Detections of multiple rotational transitions of CO, H2O and

OH allow us to determine the rotational temperatures of the

emitting or absorbing gas using Boltzmann diagrams (e.g.

Goldsmith & Langer 1999). For H2O and OH, the densities are

likely not high enough to approach a Boltzmann distribution and

therefore the diagrams presented below are less meaningful.

Emission line ﬂuxes are used to calculate the number of

emitting molecules, Nu, for each molecular transition using

Equation (1), assuming that the lines are optically thin. Here,

Fλdenotes the ﬂux of the line at wavelength λ,dis the distance

to the source, Ais the Einstein coeﬃcient, cis the speed of light

and his Planck’s constant:

Nu=4πd2Fλλ

hcA (1)

The base 10 logarithm of Nuover degeneracy of the upper level

guis shown as a function of the upper level energy, Eu, in

Boltzmann diagrams (Figures 5 and 6). The rotational temper-

ature is calculated in a standard way, from the slope bof the

linear ﬁt to the data in the natural logarithm units, Trot =−1/b.

Because the size of the emitting region is not resolved by our

instrument, the calculation of column densities requires addi-

tional assumptions and therefore only the total numbers of emit-

ting molecules is determined. The formula for the total number

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Table 2. Far-IR line cooling by molecules and atoms in units of L⊙.

Source Lbol LFIRL Lmol LOI LCO LH2O LOH LCII

(L⊙)(L⊙) (L⊙) (L⊙)

G327-0.6 7.3 1042.1(0.7) 1.8(0.6) 0.3(0.1) 1.8(0.6) – – –

W51N-e1 5.2 10537.8(10.8) 30.2(8.9) 7.6(1.8) 25.3(6.8) 2.5(1.1) 2.4(1.0) –

DR21(OH) 1.3 1041.4(0.4) 1.3(0.4) 0.09(0.03) 1.2(0.3) 0.09(0.04) – –

W33A 3.0 1040.7(0.2) 0.6(0.2) 0.05(0.02) 0.6(0.2) 0.02(0.01) 0.04(0.01) –

G34.26+0.15 1.9 1059.6(2.9) 7.7(2.4) 1.9(0.5) 7.7(2.4) – – –

NGC6334-I 1.1 1054.2(1.3) 4.2(1.2) 0.04(0.03) 3.4(1.0) 0.7(0.2) 0.06(0.03) –

NGC7538-IRS1 1.1 10513.6(3.3) 2.6(0.8) 11.0(2.5) 1.8(0.5) 0.6(0.2) 0.2(0.1) 2.0(0.4)

AFGL2591 1.2 1056.1(1.8) 2.7(0.8) 3.4(0.9) 1.6(0.5) 1.0(0.4) 0.11(0.04) 1.9(0.4)

W3-IRS5 2.1 10522.0(6.0) 17.8(5.0) 4.2(1.0) 10.5(2.5) 6.1(2.2) 1.2(0.4) –

G5.89-0.39 4.1 1048.8(2.2) 5.1(1.3) 3.7(0.9) 3.9(0.9) 0.8(0.3) 0.5(0.2) –

Notes. Columns show: (1) bolometric luminosity, Lbol, (2) total FIR line cooling, LFIRL (Lmol+LOI), (3) molecular cooling, Lmol, and (4) cooling

by oxygen atoms, LOI. Cooling by individual molecules is shown in column (5) CO, (6) H2O, and (7) OH. Absence of emission lines that would

contribute to the cooling are shown with ”–” (absorption lines are detected for H2O and OH). Errors are written in brackets and include 20%

calibration error on individual line ﬂuxes.

of emitting molecules, Ntot, is derived from the expression for

total column density, Ntot =Q·exp(a), where Qis the partition

function for the temperature and ais the y-intercept. Correcting

for a viewing angle, Ω = d2/πR2, and multiplying by the gas

emitting area of radius R, yields:

Ntot =Q·exp(a)·d2(2)

For details, see e.g. Karska et al. (2013) and Green et al. (2013).

For absorption lines, column densities, Nl, are calcu-

lated from line equivalent widths, Wλ, using Equation 3 (e.g.

Wright et al. 2000).

Nl=8πcWλgl

λ4Agu(3)

This relation assumes that the lines are optically thin, the cover-

ing factor is unity and the excitation temperature Tex ≪hc/kλ

for all lines.

Some of the emission /absorption lines are likely P-Cygni

proﬁles (Cernicharo et al. 2006) that are not resolved with PACS

and which we assume to be pure emission /absorbing lines.

The natural logarithm of Nlover the degeneracy of the lower

level, gl, is shown on the Boltzmann diagrams as a function of

the lower level energy, El(Figures 6, 7 and 9). Rotational tem-

peratures and total column densities are calculated in the same

way as for the emission lines (see above).

In the following sections, the excitation of CO, H2O, and

OH are discussed separately. Table 3 summarizes the values

of rotational temperatures, Trot, and total numbers of emitting

molecules or column densities, for those species.

4.2.1. CO

Figure 5 shows CO rotational diagrams for all our sources.

CO detections, up to J=30-29 (Eu=2565 K), are well de-

scribed by single rotational temperatures in the range from 220

K (AFGL2591 and NGC7538 IRS1) to ∼370 K (W3IRS5 and

G34.26+0.15) and the average of Trot,CO ∼300(23)±60 K.4The

highest temperatures are seen for objects where high-JCO tran-

sitions with Eu>2000 K are detected.

4The value in the brackets (23) shows the average error of rotational

temperatures for diﬀerent sources, whereas ±60 is the standard devia-

tion of rotational temperatures.

Temperatures of ∼300 K are attributed to the ‘warm’

component in low-mass YSOs (e.g. Goicoechea et al. 2012;

Karska et al. 2013; Green et al. 2013), where they are calculated

using transitions from Jup =14 (Eu=580 K) to 24 (Eu=1660

K). In those sources, a break around Eu∼1800 K in the ro-

tational diagram is noticable (see vertical line on Figure 5) and

Jup ≥25 transitions are attributed to the ‘hot’ component. Such

a turning point is not seen on the diagrams of our high-mass

sources with detections extending beyond the J=24 −23 tran-

sition.

In NGC7538 IRS1, a possible break is seen around Eu∼

1000 K. A two component ﬁt to the data results in rotational

temperatures Trot1 ∼160±10 K and Trot2 ∼370±35 K. The lat-

ter temperature is consistent within errors with the ‘warm’ com-

ponent seen towards low-mass sources. The colder tempera-

ture resembles the ∼70 −100 K ‘cool’ component seen in

Jup ≤14 transitions (e.g. Goicoechea et al. 2012; Karska et al.

2013; van der Wiel et al. 2013), detected at wavelengths longer

than the PACS range.

The absence of the hot component towards all our sources

is not signiﬁcant according to the calculated upper limits. In

addition to limited S/Nand line-to-continuum ratio, there are

other eﬀects that may prevent the hot component from being

detected. These include the fact that the continuum becomes

more optically thick at the shorter wavelengths (see also below)

and/or a smaller ﬁlling factor of the hot component in the PACS

beam compared with low-mass sources. More generally, both

the ‘warm’ and ‘hot’ components could still be part of a single

physical structure such as proposed in Neufeld (2012).

The average logarithm of the number of emitting (warm)

CO molecules, log10N, is similar for all objects, and equals

52.4(0.1)±0.5. Values of log10Nin the range from 51.6 to 53.1

are derived. DR21(OH), one of the lowest bolometric luminos-

ity sources in our sample, exhibits one of the lowest N(CO) con-

tents, whereas the highest CO content is found for W51N-e1, the

most luminous source.

4.2.2. H2O

Figure 6 shows rotational diagrams of H2O calculated for ﬁve

sources with H2O lines detected both in emission and in absorp-

tion. Because the emitting region is not resolved by our observa-

tions, the diagrams calculated using the emission and absorption

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.5. Rotational diagrams of CO for all objects in our sample. The base 10 logarithm of the number of emitting molecules from a

level u,Nu, divided by the degeneracy of the level, gu, is shown as a function of energy of the upper level in kelvins, Eup. Detections

are shown as ﬁlled circles, whereas three sigma upper limits are shown as empty circles. Blue lines show linear ﬁts to the data and

the corresponding rotational temperatures. The vertical red line in the G34.26+0.15 panel shows the dividing line between the warm

and hot components as seen in rotational diagrams of low-mass YSOs. Errors associated with the ﬁt are shown in brackets.

lines are shown separately. Figure 7 shows H2O diagrams for the

three sources where all H2O lines are seen in absorption. The rotational diagrams show a substantial scatter, larger

than the errors of individual data points, caused by large opac-

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.6. Rotational diagrams of H2O calculated using emission lines (left column) and absorption lines (right column), respectively.

For emission line diagrams, the logarithm with base 10 of total number of molecules in a level u,N, divided by the degeneracy of

the level, gu, is shown as a function of energy of the upper level in Kelvins, Elow. For absorptions lines, the natural logarithm of the

column density in a level l,Nl, divided by the degeneracy of the level, gl, is shown in y-axis. A one component linear ﬁt is shown

with the corresponding value of rotational temperature and error of the ﬁt in brackets. A solid line is used for the cases where at least

10 lines are detected. In the W3 IRS5 emission panel, para-H2O lines are shown in grey and ortho-H2O lines in black, respectively.

ities, subthermal excitation (see Herczeg et al. 2012 and below) and possible radiation excitation by far-IR dust emission pump-

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Table 3. CO, H2O, and OH rotational excitation

Source Warm CO H2O (em.) H2O (abs.) RaOH 2Π3/2bOHc

Trot(K) log10 NTrot(K) log10NTrot (K) lnNlow (arc sec) Trot(K) Trot (K)

G327-0.6 295(60) 51.9(0.3) .. . ... 210(80) 34.5(0.5) .. . 105(12) 77(29)

W51N-e1 330(15) 52.9(0.1) 320(120) 50.1(0.5) 200(90) 34.0(0.5) 3.4 66(-) 54(29)

DR21(OH) 290(15) 51.7(0.1) .. . .. . .. . . .. ... 98(27) 79(30)

W33A 245(40) 51.6(0.2) .. . .. . .. . . .. ... .. . .. .

G34.26+0.15 365(15) 52.3(0.1) .. . .. . 270(210) 34.0(0.6) .. . 89(5) 71(15)

NGC6334-I 370(20) 51.9(0.1) .. . .. . 180(40) 34.6(0.3) .. . 93(-) 71(50)

NGC7538-IRS1 220(20) 51.7(0.2) 400(90) 48.2(0.2) 170(70) 33.1(0.5) 1.1 52(-) 54(37)

AFGL2591 220(20) 51.7(0.2) 460(110) 49.1(0.2) 160(130) 33.9(1.1) 1.6 105(29) 89(21)

W3-IRS5 375(10) 52.4(0.1) 260(40) 49.3(0.2) 220(160) 34.1(0.6) 3.2 109(3) 83(22)

G5.89-0.39 295(10) 52.2(0.1) 250(40) 49.1(0.2) 250(190) 34.6(0.6) 3.0 96(1) 77(16)

Notes. Rotational temperatures of H2O and OH within the 2Π3/2ladder are calculated using at least 10 and 3 lines /doublets, respectively, and

are shown in boldface. Non-detections are marked with dots. For OH temperatures determined using only 2 transitions, the associated error is not

given and marked with ”-”.

(a)Size of the H2O emitting region assuming that all H2O lines trace the same physical component (see Section 4.2.2.). (b)Rotational temperature

of OH calculated using the OH 2Π3/2ladder transitions only, see Figure 9 and Section 4.2.3. (c)Rotational temperature of OH calculated using all

lines detected in absorption.

Fig.7. Rotational diagrams of H2O calculated using absorption

lines. A single component ﬁt is used to calculate the temperature

shown in the panels.

ing. The determination of rotational temperatures is therefore

subject to signiﬁcant errors when only a limited number of lines

is detected. In Table 3 H2O temperatures calculated using at least

10 lines are indicated in boldface. Ro-vibrational spectra of H2O

from ISO-SWS towards massive protostars (four of them in com-

mon with our sample) show rotational temperatures of H2O as

high as 500 K, in agreement within the errors with our measure-

ments (Boonman & van Dishoeck 2003).

The largest number of H2O lines is detected in the two most

evolved sources – G5.89-0.39 and W3 IRS5. Single component

ﬁts to 12 and 37 water emission lines, respectively, give similar

rotational temperatures of ∼250 K (see Figure 6), with no sys-

tematic diﬀerences between o-H2O and p-H2O lines. Rotational

temperatures determined for the remaining sources, with at least

5 detections of H2O in emission, are higher, Trot ∼300 −450 K,

but are less accurate.

Fig.8. Top: Rotational diagram of H2O calculated assuming a

kinetic temperature T=1000 K, H2density n=106cm−3,

H2O column density 2 ·1016 cm−2, and line width ∆V=5 km

s−1. Lines observed in absorption in NGC6334-I are shown in

blue. Fits are done to all lines in the PACS range included in

the LAMDA database (Sch¨oier et al. 2005) (in black) and to the

NGC6334-I lines (in blue). Darker shades denote optically thin

lines. Bottom: The same as above, but assuming a H2O column

density 1012 cm−2, such that all lines are optically thin.

Rotational temperatures calculated from a single component

ﬁt to the absorption line diagrams are ∼200 K for all sources.

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.9. Rotational diagrams of OH calculated using absorption lines, similar to Figure 7 for H2O. The single component ﬁt to all

OH transitions detected in absorption is shown with a solid line with the corresponding temperature. A separate single component

ﬁt is done for the OH 2Π3/2ladder transitions and drawn in a dashed line. The respective rotational temperatures are tabulated in

Table 3.

They are in good agreement with the values obtained from the

emission diagrams for G5.89-0.39 and W3 IRS5, suggesting that

all H2O lines originate in the same physical component (see e.g.

Cernicharo et al. 2006). In such a scenario, the column densi-

ties should also agree, and the comparison of the total number

of molecules calculated from emission lines and columns deter-

mined from the absorption lines yields the size of the emitting

region, R. The radius of the H2O emitting area under that con-

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

dition equals ∼3 arcsec for G5.89-0.39 and W3 IRS5 (see Table

3). To assess the eﬀects of optical depth and subthermal exci-

tation on the derived temperatures from the absorption lines,

equivalent widths of lines are calculated using the radiative

transfer code Radex (van der Tak et al. 2007) and translated to

column densities using Equation (2). The adopted physical con-

ditions of Tkin =1000 K and n=106cm−3are typical of

warm, shocked region where water is excited (Goicoechea et al.

2012). The models were calculated using all H2O lines in the

PACS range included in the LAMDA database (Sch¨oier et al.

2005). The latest available H2O collisional coeﬃcients are used

(Daniel et al. 2011, and references therein).

Figure 8 shows the ‘theoretical’ rotational diagrams calcu-

lated for low and high column densities. A single component ﬁt

to all lines in the high column density model gives a tempera-

ture of ∼120 K, consistent with subthermal excitation, and a

total column density of 1.2·1015 cm−2(lnNlow ∼34.7), an order

of magnitude lower than the input column. A separate ﬁt to the

lines detected in NGC6334-I (shown in blue) gives a tempera-

ture of ∼180 K and a slightly higher column density (1.9·1015

cm−2). These observed lines are typically highly optically thick

with τ∼few tens, up to 100.

In the low column density model all lines are optically thin.

A ﬁt to all lines gives a temperature of ∼120 K, similar to the

high column density model. The level populations are clearly

subthermal (Trot ≪Tkin), resulting in the scatter in the diagram.

These examples illustrate the diﬃculty in using the inferred ro-

tational temperatures to characterize a complex environment of

high-mass star forming regions.

The continuum opacity at PACS wavelengths is typically of

the order of a few in the observed sources, as indicated by the

source structures derived by van der Tak et al. (2013), and be-

comes higher at shorter wavelengths. This implies that the ab-

sorbing H2O is on the frontside of the source. Also, any emission

at short wavelengths must originate outside the region where the

dust is optically thick.

4.2.3. OH

Figure 9 presents rotational diagrams of OH calculated using ab-

sorption lines. A single component is ﬁtted to all detected lines.

A separate ﬁt is done for the lines originating in the 2Π3/2lad-

der, which are mostly collisionally excited. This ﬁt excludes the

intra-ladder 79 µm doublet, connecting with the ground state,

that readily gets optically thick (Wampﬂer et al. 2013). A pos-

sible line-of-sight contribution by unrelated foreground is ex-

pected in the ground-state 119 µm line, which is included in

the ﬁt. The resulting rotational temperatures for each source are

shown in Table 3, separately for those two ﬁts.

The average rotational temperature for the 2Π3/2ladder is

very similar for all objects and equals 100(12)±7 K. The

inclusion of all OH doublets results in lower temperatures,

Trot,OH ∼79(22)±6 K.

5. Discussion: from low to high mass

5.1. Origin of CO emission

Several physical components have been proposed as a source

of far-IR CO emission in isolated low-mass young stel-

lar objects: (i) the inner parts of the quiescent envelope,

passively heated by a central source (Ceccarelli et al. 1996;

Doty & Neufeld 1997); (ii) gas in cavity walls heated by UV

Table 4. Input parameters for the C18O envelope emission

modela

Object X0XinbTev FWHM 16O/18Oc

(K) (km s−1)

G327-0.6 3.8 10−7– – 5.0 387

W51N-e1 3.0 10−7– – 4.7 417

DR21(OH) 1.3 10−6– – 2.4 531

NGC6334-I 0.5 10−72.0 10−735 4.2 437

G5.89-0.39 0.1 10−75.0 10−740 4.5 460

NGC7538-I1 2.1 10−87.5 10−735 2.1 614

Notes. (a)Parameters for the remaining sources will be presented in

San Jos´e-Garc´ıa et al. (in prep.). (b)A jump abundance proﬁle is used

to model NGC6334-I, G5.89-0.39 and NGC7538 IRS1. (c)The ratio de-

pends on the source’s distance from the Galaxy center (Wilson & Rood

1994).

photons (van Kempen et al. 2009, 2010; Visser et al. 2012); (iii)

currently shocked gas along the outﬂow walls produced by the

protostellar wind-envelope interaction (van Kempen et al. 2010;

Visser et al. 2012; Karska et al. 2013).

The quiescent envelope of high-mass protostars is warmer

and denser than for low-mass YSOs and therefore its contribu-

tion to the far-IR CO emission is expected to be larger. In this

section, we determine this contribution for a subsample of our

sources using the density and temperature structure of each en-

velope obtained by van der Tak et al. (2013).

In this work, the continuum emission for all our objects is

modeled using a modiﬁed 3D Whitney-Robitaille continuum ra-

diative transfer code (Robitaille 2011; Whitney et al. 2013). For

simplicity, the van der Tak et al. models do not contain any cavity

or disk, and assume a spherically symmetric power law density

structure of the envelope, n∝r−p, where pis a free parame-

ter. The size and mass of the envelope, and the power law ex-

ponent, p, are calculated by best-ﬁt comparison to the spectral

energy distributions and radial emission proﬁles at 450 and 850

µm (Shirley et al. 2000). The models solve for the dust tempera-

ture as function of radius and assume that the gas temperature is

equal to the dust temperature. For more detailed discussion, see

van der Tak et al. (2013).

The envelope temperature and density structure from

van der Tak et al. (2013) is used as input to the 1D radiative

transfer code RATRAN (Hogerheijde & van der Tak 2000) in

order to reproduce simultaneously the strenghts of optically

thin C18O lines from J=2-1 to 9-8 (following the procedure

in Yıldız et al. 2010, 2012). The free parameters include C18O

constant abundance X0and the line width, FWHM. For three

sources, a ‘jump’ abundance proﬁle structure is needed, de-

scribed by the evaporation temperature Tev and inner abun-

dance Xin. The parameters derived from the ﬁts are sum-

marized in Table 4; the C18O observations are taken from

San Jos´e-Garc´ıa et al. (2013), while the modeling details and re-

sults for all our objects will be presented in I. San Jos´e-Garc´ıa

(in prep.).

The parameters from Table 4 are used as inputs for the

RATRAN models of 12CO. The integrated 12CO line emission

obtained from RATRAN is convolved with the telescope beam

and compared with observed line ﬂuxes.

Figure 10 compares the envelope model for NGC7538 IRS1

with the 12CO Jup =14 to 22 observations from Herschel/PACS,

CO 3-2 (in 14” beam, San Jos´e-Garc´ıa et al. 2013) and CO 7-

6 (in 8” beam, Boonman et al. 2003) from the James Clerk

Maxwell Telescope. By design, the model ﬁts the line proﬁle

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Table 5. Far-IR CO emission: observations and envelope models

Object LCO(obs) LCO(env)

(L⊙) (L⊙) (%)

High-mass YSOsa

G327-0.6 1.9 1.6 84

W51N-e1 25.8 14.6 56

DR21(OH) 1.2 0.7 58

NGC6334-I 3.4 2.4 71

G5.89-0.39 3.9 1.8 46

NGC7538-I1 2.1 1.6 77

Low-mass YSOsb

NGC1333 I2A 4.1 10−30.3 10−37

HH46 6.9 10−30.5 10−37

DK Cha 5.1 10−30.1 10−32

Notes. (a)Observed CO luminosities are calculated using detected tran-

sitions only, from J=14-13 to 30-29, depending on the source (see

Table C.1). The corresponding envelope CO luminosities are calculated

using the same transitions. (b)Results from Visser et al. (2012). The ob-

served CO emission is taken to be the total CO emission originating

from all modeled physical components.

of C18O 9-8 (San Jos´e-Garc´ıa et al. 2013, from Herschel/HIFI)

shown in the bottom of Figure 10. The pure envelope model

slightly underproduces the 13 CO 10-9 line, because it does not

include any broad entrained outﬂow component (Tex ∼70 K,

Yıldız et al. 2013). Adding such an outﬂow to the model (see

Mottram et al. 2013) provides an excellent ﬁt to the total line

proﬁle. For the case of 12CO, the pure envelope model repro-

duces the 3-2 and 7-6 lines within a factor of two, with the dis-

crepancy again being due to the missing outﬂow in the model.

This envelope model reproduces the CO integrated intensities

for transitions up to Jup =18, but the larger JCO ﬂuxes are

underestimated by a large factor.

Comparison of the observed and modeled integrated 12CO

line emission for the remaining sources from Table 4 is shown

in Figure 11. As found for the case of NGC7538 IRS1, the con-

tribution of the quiescent envelope emission can be as high as

70-100% of that of the J=15-14 line but decreases sharply for

the higher-Jtransitions. Only 3-22% of CO J=22-21 line emis-

sion is reproduced by the envelope models. In total ∼50 −100

% of observed total FIR CO luminosity can be explained by the

envelope emission (see Table 5).

This contribution is much larger than for low-mass YSOs,

where the quiescent envelope is responsible for only up to 7%

of the total CO emission (Visser et al. 2012). Still, even for the

high-mass sources, an additional physical component is needed

to explain the excitation of the highest-JCO lines. The broad

line proﬁles of high-J(J≥10) CO lines (San Jos´e-Garc´ıa et al.

2013) argue in favor of a shock contribution to the far-IR emis-

sion in 12CO. There may also be a contribution from UV-heating

of the outﬂow cavities by the photons from the protostellar

accretion shocks or produced by high velocity shocks inside

the cavities as found for low-mass YSOs (Visser et al. 2012)

but this component is best distinguished by high-J13CO lines

(van Kempen et al. 2009). Physical models similar to those de-

veloped for low-mass sources by Visser et al. (2012), which in-

clude the diﬀerent physical components, are needed to compare

the relative contribution of the envelope emission, shocks, and

UV-heating in the high-mass sources, but this is out of the scope

of this paper.

Fig.10. Top: Comparison of integrated line ﬂuxes of 12CO ob-

served by Herschel/PACS and from the ground (black dots with

errorbars) and the predictions of the quiescent envelope pas-

sively heated by the luminosity of the source (red crosses) for

NGC7538-IRS1. Bottom: The same model compared with the

JCMT 12CO 3-2 and Herschel/HIFI 13CO 10-9 and C18O 9-8

observed line proﬁles. Additional model including an outﬂow

component is shown in blue dashed line.

5.2. Molecular excitation

The basic excitation analysis using Boltzmann diagrams in

Section 4.2 shows remarkably similar rotational temperatures of

each molecule for all our high-mass sources, irrespective of their

luminosity or evolutionary stage. The average values of those

temperatures are: 300 K for CO, 220 K for H2O, and 80 K for

OH.

Figure 12 presents our results in the context of low-

and intermediate-mass YSOs studies by (Fich et al. 2010;

Herczeg et al. 2012; Goicoechea et al. 2012; Manoj et al. 2013;

Wampﬂer et al. 2013; Karska et al. 2013; Green et al. 2013;

Lee et al. 2013). Rotational temperatures from the Water In Star

forming regions with Herschel (WISH), the Dust, Ice and Gas in

Time (DIGIT), and the Herschel Orion Protostar Survey (HOPS)

programs are shown separately. OH rotational temperatures of

NGC1333 I4B, Serpens SMM1, and L1448 are taken from the

literature, whereas temperatures for the two additional low-

mass YSOs and four intermediate-mass YSOs are calculated

in Appendix B based on the line ﬂuxes from Wampﬂer et al.

(2013).

Rotational temperatures of CO are remarkably similar for

most sources in the luminosity range from 10−1to 106L⊙and

equal to ∼300 −350 K. For the high-mass sources, this refers

to the shocked component, not the quiescent envelope compo-

nent discussed in §5.1. In order to explain such temperatures

in low-mass YSOs, two limiting solutions on the physical con-

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.11. Comparison of integrated line ﬂuxes of CO observed

by PACS only (black dots with errorbars) and the predictions of

the quiescent envelope passively heated by the luminosity of the

source (red crosses).

ditions of the gas have been proposed: (i) CO is subthermally

excited in hot (Tkin ≥103K), low-density (n(H2)≤105cm−3)

gas (Neufeld 2012, Manoj et al. 2013); or (ii) CO is close to

LTE in warm (Tkin ∼Trot) and dense (n(H2)>ncrit ∼106cm−3)

gas (Karska et al. 2013). The low-density scenario (i) in the case

of even more massive protostars studied in this work is rather

unlikely. Even though no 13CO lines are detected in our PACS

spectra, three of our high-mass protostars were observed in the

fundamental v=1−0 vibration-rotation bands of CO and

13CO (Mitchell et al. 1990). The Boltzmann distribution of high-

Jpopulations of 13CO, indicated by a single component on ro-

tational diagrams, implies densities above 106cm−3for W33A

and NGC7538-I1 and >107cm−3for W3 IRS5.

Rotational temperatures of H2O increase for the more mas-

sive and more luminous YSOs from about 120 K to 220 K

(Figure 12). The similarity between the temperatures obtained

from the absorption and emission lines argues that they arise

in the same physical component in high-mass YSOs (see also

Cernicharo et al. 2006). Due to the high critical density, the wa-

ter lines are most likely subthermally excited in both low- and

high-mass YSOs (see above discussion in Section 4.2.2), but in

the denser environment of high-mass protostars, the gas is closer

to LTE and therefore the rotational temperatures are higher. High

optical depths of H2O lines drive the rotational temperatures to

higher values, both for the low- and high-mass YSOs. Lines are

in emission, when the angular size of the emitting region (∆ΩL)

Fig.12. Rotational temperatures of CO, H2O, and OH for low-

to high mass star forming regions. WISH, DIGIT and HOPS

team’s results obtained with PACS are shown in blue, red, and

navy blue, respectively. Dotted lines show the median values

of the rotational temperature from each database; for the case

of WISH, the median is calculated separately for objects with

Lbol <103L⊙and Lbol >103L⊙, except for OH where

intermediate-mass YSOs covering 103>Lbol >50 L⊙are also

shown separately. The CO and H2O excitation of intermediate-

mass sources has not yet been surveyed with Herschel.

multiplied by the blackbody at excitation temperature is larger

than the continuum ﬂux at the same wavelength,

∆ΩL×Bν(Tex)>Fcont,ν (4)

and are in absorption in the opposite case.

Rotational temperatures of OH show a broad range of values

for low-mass YSOs (from about 50 to 150 K), whereas they are

remarkably constant for intermediate mass YSOs (∼35 K; see

Appendix D) and high-mass YSOs (∼80 K). The low tempera-

tures found towards the intermediate mass YSOs may be a result

of the diﬀerent lines detected towards those sources rather than

a diﬀerent excitation mechanism.

5.3. Correlations

Figure 13 shows relations between selected line luminosities of

CO, H2O, and [O i] transitions and the physical parameters of

the young stellar objects. Our sample of objects is extended to

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

the low-mass deeply embedded objects studied with PACS in

Herczeg et al. (2012); Goicoechea et al. (2012); Wampﬂer et al.

(2013); Karska et al. (2013) and intermediate-mass objects from

Fich et al. (2010); Wampﬂer et al. (2013). This allows us to

study a broad range of luminosities, from ∼1 to 106L⊙, and

envelope masses, from 0.1 to 104M⊙.

The typical distance to low-mass sources is 200 pc, whereas

to high-mass sources – 3 kpc. For this comparison, the full PACS

array maps of low-mass regions are taken (∼50′′), which corre-

sponds to spatial scales of 104AU; only a factor of 3 smaller than

the central spaxel (∼10′′ ) observation of high-mass objects. On

the other hand, the physical sizes of the low-mass sources are

smaller than those of high-mass sources by a factor that is com-

parable to the diﬀerence in average distance of low- and high-

mass sources, so one could argue that one should compare just

the central spaxels for both cases. Using only the central spaxel

for the low-mass YSOs does not aﬀect the results, however (see

Figure 9 in Karska et al. 2013).

The choice of CO, H2O, OH, and [O i] transitions is based on

the number of detections of those lines in both samples and their

emission proﬁles. The strengths of the correlations are quanti-

ﬁed using the Pearson coeﬃcient, r. For the number of sources

studied here, the 3 σcorrelation corresponds to r≈0.6 and 5 σ

correlation to r≈0.95.

Figure 13 shows strong, 5 σcorrelations between the se-

lected line luminosities and bolometric luminosities as well as

envelope masses. The more luminous the source, the larger is its

luminosity in CO, H2O, and [O i] lines. Similarly, the more mas-

sive is the envelopesurrounding the growing protostar,the larger

is the observed line luminosity in those species. The strength of

the correlations over such broad luminosity ranges and envelope

masses suggests that the physical processes responsible for the

line emission are similar.

In the case of low-mass young stellar objects, Karska et al.

(2013) linked the CO and H2O emission seen with PACS with

the non-dissociative shocks along the outﬂow walls, most likely

irradiated by the UV photons. The [O i] emission, on the other

hand, was attributed mainly to the dissociative shocks at the

point of direct impact of the wind on the dense envelope. In the

high-mass sources the envelope densities and the strength of ra-

diation are higher, but all in all the origin of the emission can be

similar.

5.4. Far-IR line cooling

Figure 14 compares the total far-IR cooling in lines, its molec-

ular and atomic contributions, and the cooling by dust for the

YSOs in the luminosity range from ∼1 to 106L⊙.

The far-IR line cooling, LFIRL, correlates strongly (5σ) with

the bolometric luminosity, Lbol, in agreement with studies on

low-mass YSOs (Nisini et al. 2002; Karska et al. 2013). Under

the assumption that LFIRL is proportional to the shock energy, the

strong correlation between Lbol and LFIRL has been interpreted

by Nisini et al. (2002) as a result of the jet power/velocity being

correlated with the escape velocity from the protostellar surface

or an initial increase of the accretion and ejection rate.

The ratio of molecular and atomic line cooling, Lmol /Latom, is

similar for YSOs of diﬀerent luminosities, although a large scat-

ter is present. Cooling in molecules is about 4 times higher than

cooling in oxygen atoms. If cooling by [C ii] was included in the

atomic cooling, the Lmol/Latom ratio would decrease for the high-

mass sources. In low-mass YSOs, the [C ii] emission accounts

for less than 1% of the total cooling in lines (Goicoechea et al.

2012, for Ser SMM1). In the high-mass sources, this contribu-

Fig.13. Correlations of line emission with bolometric luminos-

ity (left column) and envelope mass (right column) from top to

bottom: CO 14-13, H2O 303-212, [O i] at 145 µm and OH 163 µm

line luminosities. Low- and intermediate-mass young stellar ob-

jects emission is measured over 5×5 PACS maps. Red and blue

circles show Class 0 and Class I low-mass YSOs from Karska et

al. (2013). Navy diamonds show intermediate mass YSOs from

Wampﬂer et al. (2013; O and OH lines) and from Fich et al.

(2010; CO and H2O line). High-mass YSOs ﬂuxes are measured

in the central position and shown in black. Pearson coeﬃcient r

is given for each correlation.

tion is expected to be higher due to the carbon ionizing and CO

dissociating FUV radiation. In Section 4.1 we estimate the [C ii]

cooling in two high-mass sources to 10-25% of LFIRL .

The ratio of cooling by gas (molecular and atomic lines)

and dust (Lbol) decreases from 1.3·10−3to 6.2·10−5from low to

high-mass YSOs. It reﬂects the fact that H2O, and to a smaller

extent OH, contributes less to the line luminosity in the high-

mass sources, because many of its lines are detected in absorp-

tion. The detection of H2O and OH lines in absorption proves

that IR pumping is at least partly responsible for the excita-

tion of these molecules and the resulting emission lines (e.g.

Goicoechea et al. 2006; Wampﬂer et al. 2013). In the case where

collisions play a marginal role, even the detected emission lines

of those species do not necessarily cool the gas.

The above numbers do not include cooling from molecules

outside the PACS wavelength range. This contribution can be

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.14. From top to bottom: (1) Total far-IR line cooling; (2)

Ratio of molecular to atomic cooling; (3) Gas to dust cooling

ratio, LFIRL/Lbol, where LFIRL =Lmol +Latom; as a function of

bolometric luminosity. Low-mass YSOs are shown in red (Class

0) and blue (Class I), whereas high-mass ones are in black.

signiﬁcant for CO, where for low-mass sources the low-Jlines

are found to increase the total CO line luminosity by about 30%

(Karska et al. 2013). Thus, the CO contribution to the total gas

cooling is likely to be even larger than suggested by Table 2.

6. Conclusions

We have characterized the central position Herschel/PACS spec-

tra of 10 high-mass protostars and compared them with the re-

sults for low- and intermediate-mass protostars analyzed in a

similar manner. The conclusions are as follows:

1. Far-IR gas cooling of high-mass YSOs is dominated by CO

(from ∼15 to 85% of total far-IR line cooling, with median

contribution of 74%) and to smaller extent by [O i] (with me-

dian value ∼20 %). H2O and OH median contributions to

the far-IR cooling are less than 1%. In contrast for low-mass

YSOs, the H2O, CO, and [O i] contributions are compara-

ble. The eﬀective cooling by H2O is reduced because many

far-IR lines are in absorption. The [O i] cooling increases for

more evolved sources in both mass regimes.

2. Rotational diagrams of CO in the PACS range show a single,

warm component, corresponding to rotational temperature of

∼300 K, consistent with low-mass YSOs. Upper limits on

high−JCO do not exclude the existence of an additional,

hot component in several sources of our sample.

3. Emission from the quiescent envelope accounts for

∼45-85 % of the total CO luminosity observed in the

PACS range. The corresponding values for the cooler and

less dense envelopes of low-mass YSOs are below 10%.

Additional physical components, most likely shocks, are

necessary to explain the highest−JCO lines.

4. Rotational diagrams of H2O are characterized by Trot ∼250

K for all sources both from emission and absorption data.

This temperature is about 100 K higher than for low-mass

sources, likely due to the higher densities in high-mass

sources. The diagrams show scatter due to subthermal ex-

citation and optical depth eﬀects.

5. OH rotational diagrams are described by a single rota-

tional temperatures of ∼80 K, consistent with most low-mass

YSOs, but higher by ∼45 K than for intermediate-mass ob-

jects. Similar to H2O, lines are sub-thermally excited.

6. Fluxes of the H2O 303 −212 line and the CO 14 −13 line

strongly correlate with bolometric luminosities and envelope

masses over 6 and 7 orders of magnitude, respectively. This

correlation suggests a common physical mechanism respon-

sible for the line excitation, most likely the non-dissociative

shocks based on the studies of low-mass protostars.

7. Across the large luminosity range from ∼1 to 106L⊙, the

far-IR line cooling strongly correlates with the bolometric

luminosity, in agreement with studies on low-mass YSOs.

The ratio of molecular and atomic line cooling is ∼4, similar

for all those YSOs.

8. Because several H2O lines are in absorption, the gas to dust

cooling ratio decreases from 1.3·10−3to 6.2·10−5from low

to high-mass YSOs.

Acknowledgements. Herschel is an ESA space observatory with science in-

struments provided by European-led Principal Investigator consortia and with

important participation from NASA. AK acknowledges support from the

Christiane N¨usslein-Volhard-Foundation, the L′Or´eal Deutschland and the

German Commission for UNESCO via the ‘Women in Science’ prize. JRG, LC,

and JC thank the Spanish MINECO for funding support from grants AYA2009-

07304, AYA2012-32032 and CSD2009-00038 and AYA. JRG is supported by a

Ramo´on y Cajal research contract. Astrochemistry in Leiden is supported by the

Netherlands Research School for Astronomy (NOVA), by a Royal Netherlands

Academy of Arts and Sciences (KNAW) professor prize, by a Spinoza grant and

grant 614.001.008 from the Netherlands Organisation for Scientiﬁc Research

(NWO), and by the European Community’s Seventh Framework Programme

FP7/2007-2013 under grant agreement 238258 (LASSIE).

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Appendix A: Details of PACS observations

Table A.1 shows the observing log of PACS observations used

in this paper. The observations identiﬁcations (OBSID), obser-

vation day (OD), date of observation, total integration time, pri-

mary wavelength ranges, and pointed coordinates (RA, DEC)

are listed. All spectra were obtained in Pointed /Chop-Nod ob-

serving mode. Additional remarks are given for several sources.

G327-0.6 and W33A observations were mispointed. NGC6334-

I, W3IRS5, and NGC7538-IRS1 spectra were partly satu-

rated and re-observed (re-obs). Two observations of W51N-e1,

G34.26, G5.89, and AFGL2591 were done using diﬀerent point-

ing.

Appendix B: Continuum measurements

Table B.1 shows the continuum ﬂuxes for all our sources mea-

sured using the full PACS array. The ﬂuxes were used in

the spectral energy distributions presented by van der Tak et al.

(2013).

Appendix C: Tables with ﬂuxes and additional

ﬁgures

Table C.1 shows line ﬂuxes and 3 σupper limits of CO lines

toward all our objects in units of 10−20 W cm−2. For details, see

the table caption.

Figure C.1 show blow-ups of selected spectral regions of W3

IRS5 with high-JCO, H2O, and OH lines. Figures C.2 and C.3

show blow-ups of selected CO and OH transitions towards all

sources.

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Table A.1. Log of PACS observations

Source OBSID OD Date Total time Wavelength ranges RA DEC Remarks

(s) (µm) (h m s) (o′ ′′ )

G327-0.6 1342216201 659 2011-03-04 6290 102-120 15 53 08.8 -54 37 01.0 mispointed

1342216202 659 2011-03-04 4403 55-73 15 53 08.8 -54 37 01.0 mispointed

W51N-e1 1342193697 327 2010-04-06 4589 55-73 19 23 43.7 +14 30 28.8 diﬀ. point.

1342193698 327 2010-04-06 4969 102-120 19 23 43.7 +14 30 25.3 diﬀ. point.

DR21(OH) 1342209400 551 2010-11-15 4401 55-73 20 39 00.8 +42 22 48.0

1342209401 551 2010-11-16 6280 102-120 20 39 00.8 +42 22 48.0

W33A 1342239713 1018 2012-02-25 4403 55-73 18 14 39.1 -17 52 07.0 mispointed

1342239714 1018 2012-02-25 3763 102-120 18 14 39.1 -17 52 07.0 mispointed

1342239715 1018 2012-02-25 2548 174-210 18 14 39.1 -17 52 07.0 mispointed

G34.26+0.15 1342209733 542 2010-11-07 4589 55-73 18 53 18.8 +01 14 58.1 diﬀ. point.

1342209734 542 2010-11-07 4969 102-120 18 53 18.7 +01 15 01.5 diﬀ. point.

NGC6334-I 1342239385 1013 2012-02-21 4403 55-73 17 20 53.3 -35 47 00.0 saturated

1342239386 1013 2012-02-21 3763 102-120 17 20 53.3 -35 47 00.0 saturated

1342239387 1013 2012-02-21 2548 174-210 17 20 53.3 -35 47 00.0 saturated

1342252275 1240 2012-10-05 3771 102-120 17 20 53.3 -35 46 57.2 re-obs

NGC7538-I1 1342211544 589 2010-12-24 6290 102-120 23 13 45.3 +61 28 10.0 saturated

1342211545 589 2010-12-24 4403 55-73 23 13 45.3 +61 28 10.0 saturated

1342258102 1329 2013-01-02 3771 102-120 23 13 45.2 +61 28 10.4 re-obs

AFGL2591 1342208914 549 2010-11-14 6280 102-120 20 29 24.7 +40 11 19.0 diﬀ. point.

1342208938 550 2010-11-15 4403 55-73 20 29 24.9 +40 11 21.0 diﬀ. point.

W3-IRS5 1342191146 286 2010-02-24 6345 102-120 2 25 40.6 +62 05 51.0 saturated

1342191147 286 2010-02-24 4102 55-73 2 25 40.6 +62 05 51.0 saturated

1342229091 860 2011-09-21 4403 55-73 2 25 40.6 +62 05 51.0 saturated

1342229092 860 2011-09-21 4499 102-120 2 25 40.6 +62 05 51.0 re-obs

1342229093 860 2011-09-21 2249 55-73 2 25 40.6 +62 05 51.0 re-obs

G5.89-0.39 1342217940 691 2011-04-05 4969 102-120 18 00 30.5 -24 04 00.4 diﬀ. point.

1342217941 691 2011-04-05 4589 55-73 18 00 30.5 -24 04 04.4 diﬀ. point.

Table B.1. Full-array continuum measurements in 103Jy

λ(µm) Continuum (103Jy)

G327-0.6aW51N-e1 DR21(OH) W33A G34.26 NGC6334I NGC7538I1 AFGL2591 W3IRS5 G5.89

56.8 2.2 11.0 1.7 1.9 7.9 16.1 8.6 5.5 23.0 17.7

59.6 2.6 12.3 2.0 2.1 8.2 17.2 8.9 5.7 23.8 18.8

62.7 3.0 13.3 2.5 2.2 9.2 18.2 9.3 5.8 24.0 19.7

63.2 3.0 13.6 2.6 2.3 9.4 18.3 9.3 5.8 24.2 19.9

66.1 3.5 14.3 3.0 2.5 10.6 19.3 9.6 6.0 24.8 20.2

69.3 3.8 15.2 3.4 2.5 10.9 19.8 9.6 6.0 24.4 20.7

72.8 4.6 17.8 4.1 3.0 13.2 20.5 9.7 5.9 24.8 15.7

76.0 4.9 18.6 4.5 2.9 14.0 20.9 9.6 5.6 24.4 15.8

79.2 5.3 18.9 4.8 3.0 14.4 20.9 9.5 5.6 23.3 15.7

81.8 5.6 19.2 5.1 3.2 14.8 21.1 9.6 5.7 23.1 15.7

86.0 6.1 19.8 5.5 3.2 15.6 21.6 9.6 5.5 22.2 15.7

90.0 >3.2 20.1 5.9 3.4 16.0 21.8 9.9 5.5 21.8 15.3

93.3 >3.3 19.7 6.4 3.3 15.9 21.7 9.6 5.5 20.9 14.7

108.8 8.2 18.8 7.8 3.9 16.1 23.7 10.0 5.3 19.4 13.1

113.5 8.1 18.5 7.8 3.9 15.9 23.0 9.8 5.2 18.2 12.5

118.0 >7.1 18.1 7.9 3.8 15.6 22.2 9.5 5.0 17.3 11.9

125.4 >7.2 17.5 7.9 3.7 15.2 21.2 9.0 4.7 15.8 11.0

130.4 >7.2 16.7 7.8 3.6 14.6 20.2 8.5 4.4 14.6 10.2

136.0 8.1 16.1 7.7 3.5 14.1 19.2 8.1 4.2 13.4 9.6

145.5 8.0 14.7 7.6 3.3 13.0 17.4 7.3 3.8 11.7 8.4

158.5 7.7 12.6 6.9 3.0 11.1 15.1 6.3 3.3 9.5 6.8

164.0 7.5 11.7 6.6 2.9 10.3 14.1 5.8 3.0 8.6 6.1

169.1 7.2 11.0 6.0 2.7 9.7 13.6 5.4 2.8 7.9 5.7

175.8 6.9 10.0 5.9 2.7 8.9 12.3 5.0 2.6 7.0 5.0

179.5 6.6 9.5 5.6 2.4 8.5 11.6 4.7 2.4 6.5 4.7

186.0 5.6 8.7 4.8 2.4 7.8 10.2 4.0 2.0 5.5 4.2

Notes. The calibration uncertainty of 20% of the ﬂux should be included for comparisons with other modes of observations or instruments. (a)One

spaxel at N-W corner of the PACS map is saturated around 100 µm region due to the strong continuum; therefore the tabulated values are the lower

limits to the total continuum ﬂux from the whole map.

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Table C.1. CO line ﬂuxes in 10−20 W cm−2

Trans. λlab (µm) Central position ﬂux (10−20 W cm−2)

G327-0.6aW51N-e1 DR21(OH) W33AaG34.26+0.15 NGC6334-I NGC7538-I1 AFGL2591 W3IRS5 G5.89-0.39

CO 14-13 185.9990 8.52(0.48) 40.93(1.26) 29.93(0.67) 7.96(0.23) 23.05(1.14) 40.07(1.60) 17.79(0.52) 10.86(0.45) 76.67(1.38) 80.36(0.74)

CO 15-14 173.6310 9.34(0.36) 50.65(1.83) 22.65(1.07) 4.91(0.32) 26.30(1.07) 52.70(2.39) 14.54(0.33) 7.72(0.57) 86.13(1.76) 103.91(1.41)

CO 16-15 162.8120 8.82(0.51) 43.10(1.43) 24.71(0.92) 4.12(0.18) 22.71(1.06) 43.88(1.59) 11.78(0.39) 8.00(0.27) 99.73(1.08) 105.49(1.76)

CO 17-16 153.2670 3.00(0.76) 36.94(1.54) 16.19(1.21) 2.74(0.24) 18.52(1.63) 31.37(2.46) 8.60(0.56) 5.67(0.38) 86.40(1.31) 96.31(1.67)

CO 18-17 144.7840 2.13(0.48) 27.78(1.89) 17.40(1.13) 4.35(0.39) 18.27(1.53) 20.93(2.02) 5.82(0.47) 5.02(0.53) 83.05(1.69) 82.73(1.67)

CO 19-18 137.1960 6.76(0.64) 24.18(1.81) 13.82(1.07) 3.41(0.37) 20.16(1.68) 36.07(2.02) 4.96(0.42) 3.02(0.58) 79.39(1.54) 60.19(2.14)

CO 20-19 130.3690 6.68(0.81) 25.73(1.42) 15.02(0.93) 3.54(0.52) 21.93(1.93) 37.25(2.19) 5.31(0.54) 4.34(0.64) 77.08(2.27) 59.14(1.27)

CO 21-20 124.1930 3.96(1.24) 22.77(3.15) 11.38(0.87) <0.75 18.69(2.02) 34.56(5.43) 4.62(0.72) 2.97(0.61) 60.64(2.13) 51.31(2.90)

CO 22-21 118.5810 4.61(1.16) 20.31(3.29) 9.79(1.23) <0.77 21.66(3.21) 35.05(5.02) 3.97(0.89) <0.90 63.44(2.81) 44.98(3.84)

CO 24-23 108.7630 <1.78 <7.05 5.18(1.40) <0.54 18.86(5.45) 12.89(3.28) <1.68 <0.86 49.51(3.75) 21.89(3.45)

CO 27-26 96.7730 <0.86 4.71(0.79) 3.68(0.56) <1.50 4.34(1.22) 9.46(1.76) <2.49 <1.01 23.29(2.65) 6.16(0.81)

CO 28-27 93.3490 <1.75 6.28(1.21) <0.94 <0.91 5.06(1.35) 11.75(1.99) <4.97 <1.04 24.72(1.75) 9.71(1.63)

CO 29-28 90.1630 <1.24 5.23(1.54) <1.23 <1.25 3.67(1.30) 10.80(5.36) <6.35 <1.70 20.23(1.94) 5.38(3.49)

CO 30-29 87.1900 <1.10 3.59(0.72) <1.00 <1.72 4.48(1.10) <7.00 <2.10 <1.57 14.38(2.03) 6.32(2.59)

CO 32-31 81.8060 <1.19 <5.84 <1.19 <1.43 <2.31 <4.63 <1.84 <2.03 <9.49 <3.70

CO 33-32 79.3600 <3.99 <11.04 <1.70 <2.28 <3.76 <18.46 <2.09 <1.99 <3.40 <13.59

CO 34-33 77.0590 <1.88 <4.57 <1.83 <1.83 <3.17 <2.71 <1.40 <2.16 <5.27 <6.93

CO 35-34 74.8900 <2.06 <2.90 <0.99 <1.27 <2.03 <3.09 <2.50 <1.20 <1.83 <18.61

CO 36-35 72.8430 <0.55 <0.63 <0.29 <0.70 <1.17 <1.74 <0.69 <0.37 <7.03 <3.00

CO 38-37 69.0740 <1.36 <1.06 <1.93 <0.67 <1.77 <1.21 <3.23 <2.09 <2.16 <2.74

CO 39-38 67.3360 <1.20 <0.84 <0.40 <1.86 <0.80 <2.50 <2.40 <0.89 <1.99 <3.54

CO 40-39 65.6860 <0.57 <2.40 <0.43 <1.05 <2.40 <1.94 <2.17 <0.94 <2.63 <2.91

CO 41-40 64.1170 <1.06 <1.11 <0.57 <1.80 <1.54 <2.91 <1.59 <1.80 <5.56 <4.60

CO 42-41 62.6240 <1.03 <2.74 <0.44 <1.08 <2.50 <2.19 <1.91 <2.34 <4.01 <5.01

CO 43-42 61.2010 <0.90 <1.39 <0.58 <1.05 <1.20 <4.59 <2.10 <2.41 <4.94 <6.21

CO 44-43 59.8430 <0.67 <1.61 <0.39 <0.68 <1.41 <3.38 <2.30 <1.54 <2.85 <3.49

CO 45-44 58.5470 <0.96 <1.24 <0.55 <1.41 <1.42 <1.34 <1.69 <1.08 <6.77 <4.89

CO 46-45 57.3080 <2.33 <10.54 <1.03 <1.81 <4.01 <6.49 <3.75 <2.65 <6.46 <8.54

CO 47-46 56.1220 <0.76 <1.08 <0.50 <2.29 <1.85 <2.51 <1.39 <1.71 <5.78 <4.79

Notes. The uncertainties are 1σmeasured in the continuum on both sides of each line; calibration uncertainty of 20%of the ﬂux should be included for comparisons with other modes of observations

or instruments. 3σupper limits calculated using wavelength dependent values of full-width high maximum for a point source observed with PACS are listed for non-detections. CO 23-22 and CO

31-30 ﬂuxes are not listed due to severe blending with the H2O 414-303 line at 113.537 µm and the OH 7

2,3

2-5

2,3

2line at 84.4 µm, which are often in absorption. CO 25-24, CO 26-25 and CO 37-36

transitions are located in the regions of overlapping orders, where the ﬂux calibration is unreliable. (a)A mispointed observation. The ﬂuxes are calculated from a sum of two spaxel closest to the

true source position, see Section 2.

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Table D.1. OH rotational excitation and number of emitting

molecules Nubased on emission lines for low- and intermediate-

mass sources

Source Trot(K) log10N

Low-mass YSOs

NGC1333 I4A 270(700) 52.4(0.9)

L1527 80(40) 51.5(0.6)

Ced110 I4 380(1400) 51.4(0.9)

IRAS15398 85(90) 51.5(1.0)

L483 200(380) 52.0(0.9)

L1489 140(150) 51.6(0.7)

TMR1 490(2150) 52.0(0.8)

TMC1 170(290) 51.7(0.9)

HH46 160(350) 52.6(1.1)

Intermediate-mass YSOs

NGC2071 37(10) 55.7(0.8)

Vela IRS17 35(10) 55.1(0.7)

Vela IRS19 36(15) 55.1(1.1)

NGC7129 FIRS2 170(270) 53.9(0.9)

L1641 S3MMS1 36(10) 54.7(0.8)

Notes. Rotational diagrams are shown in Figures D.1 and D.2. Objects

with at least 3 detected doublets in Wampﬂer et al. (2013) are presented.

Rotational temperatures of OH calculated with error less than 100 K are

shown in boldface.

Appendix D: OH in low and intermediate mass

sources

Figures D.1 and D.2 show rotational diagrams of OH for low-

and intermediate-mass young stellar objects based on the ﬂuxes

presented in Wampﬂer et al. (2013). Only the sources with at

least 3 detected doublets in emission (out of 4 targeted in total)

are shown in diagrams. Rotational temperatures and total num-

bers of emitting molecules are summarized in Table D.1. In case

of low-mass YSOs, a single component ﬁt is usually not a good

approximation (with the exception of L1527 and IRAS15398).

In the intermediate-mass YSOs, on the other hand, such approx-

imation holds and results in a very similar rotational tempera-

tures of OH Trot ∼35 K for all sources except NGC7129 FIRS2.

Fig.D.2. OH rotational diagrams (from emission lines) for

intermediate-mass young stellar objects (ﬂuxes from Wampﬂer

et al. 2013).

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.C.1. Close-ups of several of the H2O, CO and OH lines in W3IRS5 are shown in Figure 1. The rest wavelength of each line is

indicated by dashed lines: blue for H2O, red for CO and light blue for OH. Identiﬁcations of the undetected lines in the presented

spectral regions are shown in brackets.

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.C.2. Close-ups of several transitions of CO lines in the PACS wavelength range towards all sources. The spectra are continuum

subtracted and shifted vertically for better visualization.

A. Karska et al. 2013: Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

Fig.C.3. Normalized spectra of OH doublets for all our sources at central position. Doublets at 71 and 98 µm are excluded because

of poor calibration of those spectral regions observed with PACS. OH doublet at 84.4 µm is a blend with the CO 31-30 line, whereas

OH at 65.13 µm can be aﬀected by H2O 625-514 at 65.17 µm.

Fig.D.1. OH rotational diagrams (from emission lines) for low-mass young stellar objects (ﬂuxes from Wampﬂer et al. 2013).

High-resolution SOFIA/EXES Spectroscopy of Water Absorption Lines in the Massive Young Binary W3 IRS 5

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Full-text available

Aug 2023

We present in this paper mid-infrared (5–8 μ m) spectroscopy toward the massive young binary W3 IRS 5, using the Echelon Cross Echelle Spectrograph (EXES) spectrometer in high-resolution mode ( R ∼ 50,000) from the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA). Many (∼180) ν 2 = 1–0 and (∼90) ν 2 = 2–1 absorption rovibrational transitions are identified. Two hot components over 500 K and one warm component of 190 K are identified through Gaussian fittings and rotation diagram analysis. Each component is linked to a CO component identified in the IRTF/iSHELL observations ( R = 88,100) through their kinematic and temperature characteristics. Revealed by the large scatter in the rotation diagram, opacity effects are important, and we adopt two curve-of-growth analyses, resulting in column densities of ∼10 ¹⁹ cm ⁻² . In one analysis, the model assumes a foreground slab. The other assumes a circumstellar disk with an outward-decreasing temperature in the vertical direction. The disk model is favored because fewer geometry constraints are needed, although this model faces challenges as the internal heating source is unknown. We discuss the chemical abundances along the line of sight based on the CO-to-H 2 O connection. In the hot gas, all oxygen not locked in CO resides in water. In the cold gas, we observe a substantial shortfall of oxygen and suggest that the potential carrier could be organics in solid ice.

High-resolution SOFIA/EXES Spectroscopy of Water Absorption Lines in the Massive Young Binary W3 IRS 5

Preprint

Jun 2023

We present in this paper mid-infrared (5-8~$\mu$m) spectroscopy toward the massive young binary W3~IRS~5, using the EXES spectrometer in high-resolution mode ($R\sim$50,000) from the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA). Many ($\sim$180) $\nu_2$=1--0 and ($\sim$90) $\nu_2$=2-1 absorption rovibrational transitions are identified. Two hot components over 500 K and one warm component of 190 K are identified through Gaussian fittings and rotation diagram analysis. Each component is linked to a CO component identified in the IRTF/iSHELL observations ($R$=88,100) through their kinematic and temperature characteristics. Revealed by the large scatter in the rotation diagram, opacity effects are important, and we adopt two curve-of-growth analyses, resulting in column densities of $\sim10^{19}$ cm$^{-2}$. In one analysis, the model assumes a foreground slab. The other assumes a circumstellar disk with an outward-decreasing temperature in the vertical direction. The disk model is favored because fewer geometry constraints are needed, although this model faces challenges as the internal heating source is unknown. We discuss the chemical abundances along the line of sight based on the CO-to-H$_2$O connection. In the hot gas, all oxygen not locked in CO resides in water. In the cold gas, we observe a substantial shortfall of oxygen and suggest that the potential carrier could be organics in solid ice.

Exploring the Chemical Space of C3H2NO Isomers and Bimolecular Reactions with Hydrogen Cyanide and Formaldehyde: Insights into the Emergence of Life

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May 2023

The emergence of life remains one of the most intriguing scientific questions, and understanding the chemical processes that led to it is essential. Recent discoveries of C3H2NO isomers in the interstellar medium have motivated further exploration of this molecular formula. Here, we use density functional theory to explore the potential energy surface of C3H2NO isomers, including acyclic and cyclic structures, and identify twelve low-lying isomers. We then investigate bimolecular reaction with HCN and H2CO using an artificial force-induced automated search and transition state search for the minimal energy routes. Our results predict the formation of Oxiran- 2-ylazanide and (Z)2-aminoacetaldehyde as the kinetically and thermodynamically controlled products, respectively. These results provide insights into the potential formation of biomarkers such as N-methyleneformamide in the interstellar medium, which have been found in recent years. Our study contributes to prebiotic chemistry and offers a critical step toward understanding the chemical processes that led to the emergence of life in the universe.

Exploring the Chemical Space of C3H2NO Isomers and Bimolecular Reactions with Hydrogen Cyanide and Formaldehyde: Insights into the Emergence of Life

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The Detection of Deuterated Water in the Large Magellanic Cloud with ALMA

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We report the first detection of deuterated water (HDO) toward an extragalactic hot core. The HDO 2 11 –2 12 line has been detected toward hot cores N 105–2 A and 2 B in the N 105 star-forming region in the low-metallicity Large Magellanic Cloud (LMC) dwarf galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA). We have compared the HDO line luminosity ( L HDO ) measured toward the LMC hot cores to those observed toward a sample of 17 Galactic hot cores covering three orders of magnitude in L HDO , four orders of magnitude in bolometric luminosity ( L bol ), and a wide range of Galactocentric distances (thus metallicities). The observed values of L HDO for the LMC hot cores fit very well into the L HDO trends with L bol and metallicity observed toward the Galactic hot cores. We have found that L HDO seems to be largely dependent on the source luminosity, but metallicity also plays a role. We provide a rough estimate of the H 2 O column density and abundance ranges toward the LMC hot cores by assuming that HDO/H 2 O toward the LMC hot cores is the same as that observed in the Milky Way; the estimated ranges are systematically lower than Galactic values. The spatial distribution and velocity structure of the HDO emission in N 105–2 A is consistent with HDO being the product of the low-temperature dust grain chemistry. Our results are in agreement with the astrochemical model predictions that HDO is abundant regardless of the extragalactic environment and should be detectable with ALMA in external galaxies.

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE. II. A detailed kinematic analysis of the DR21 Main outflow

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Oct 2023

Context. Molecular outflows are believed to be a key ingredient in the process of star formation. The molecular outflow associated with DR21 Main in Cygnus-X is one of the most extreme molecular outflows in the Milky Way in terms of mass and size. The outflow is suggested to belong to a rare class of explosive outflows formed by the disintegration of protostellar systems. Aims. We aim to explore the morphology, kinematics, and energetics of the DR21 Main outflow, and to compare those properties to confirmed explosive outflows in order to unravel the underlying driving mechanism behind DR21. Methods. We studied line and continuum emission at a wavelength of 3.6 mm with IRAM 30 m and NOEMA telescopes as part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program. The spectra include ( J = 1−0) transitions of HCO ⁺ , HCN, HNC, N 2 H ⁺ , H 2 CO, and CCH, which trace different temperature and density regimes of the outflowing gas at high velocity resolution (~0.8 km s ⁻¹ ). The map encompasses the entire DR21 Main outflow and covers all spatial scales down to a resolution of 3″ (~0.02 pc). Results. Integrated intensity maps of the HCO ⁺ emission reveal a strongly collimated bipolar outflow with significant overlap of the blueshifted and redshifted emission. The opening angles of both outflow lobes decrease with velocity, from ~80 to 20° for the velocity range from 5 to 45 km s ⁻¹ relative to the source velocity. No evidence is found for the presence of elongated, “filament-like” structures expected in explosive outflows. N 2 H ⁺ emission near the western outflow lobe reveals the presence of a dense molecular structure, which appears to be interacting with the DR21 Main outflow. Conclusions. The overall morphology as well as the detailed kinematics of the DR21 Main outflow are more consistent with a typical bipolar outflow than with an explosive counterpart.

Velocity-resolved high-J CO emission from massive star-forming clumps

Article

Full-text available

Oct 2023

Context. Massive star formation is associated with energetic processes, which result in significant gas cooling via far-infrared (IR) lines. Velocity-resolved observations can constrain the kinematics of the gas, allowing the identification of the physical mechanisms responsible for gas heating. Aims. Our aim is to quantify far-IR CO line emission towards high-mass star-forming regions, identify the high-velocity gas component associated with outflows, and estimate the physical conditions required for the excitation of the observed lines. Methods. Velocity-resolved SOFIA/GREAT spectra of 13 high-mass star-forming clumps of various luminosities and evolutionary stages are studied in highly excited rotational lines of CO. For most targets, the spectra are from frequency intervals covering the CO 11−10 and 16−15 lines towards two sources, also the CO 13−12 line was observed with SOFIA/4GREAT. Angular resolutions at the line frequencies range from 14″ to 20″, corresponding to spatial scales of ~0.1–0.8 pc. Radiative transfer models were used to determine the physical conditions giving rise to the emission in the line wings. Results. All targets in our sample show strong high-J CO emission in the far-IR, characterised by broad line wings associated with outflows, thereby significantly increasing the sample of high-mass objects with velocity-resolved high-J CO spectra. Twelve sources show emission in the line wings of the CO 11−10 line ( E u / k B =365 K), and eight sources in the CO 16−15 line ( E u /k B =752 K). The contribution of the emission in the line wings to the total emission ranges from ~28% to 76%, and does not correlate with the envelope mass or evolutionary stage. Gas excitation temperatures cover a narrow range of 120–220 K for the line wings, and 110–200 K for the velocity-integrated line emission, assuming local thermodynamics equilibrium (LTE). For the two additional sources with the CO 13−12 line ( E u / k B =503 K) data, wing emission rotational temperatures of ~130 K and 165 K were obtained using Boltzmann diagrams. The corresponding non-LTE radiative transfer models indicate gas densities of 10 ⁵ −10 ⁷ cm ⁻³ and CO column densities of 10 ¹⁷ −10 ¹⁸ cm ⁻² in the line wings, similar to physical conditions in deeply embedded low- and high-mass protostars. The velocity-integrated CO line fluxes correlate with the bolometric luminosity over 7 orders of magnitude, including data on the low-mass protostars from the literature. This suggests that similar processes are responsible for the high-J CO excitation over a significant range of physical scales. Conclusions. Velocity-resolved line profiles allow the detection of outflows towards massive star-forming clumps spanning a broad range of evolutionary stages. The lack of clear evolutionary trends suggest that mass accretion and ejection prevail during the entire lifetime of star-forming clumps.

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Full-text available

Apr 2023

Context. Far-infrared (FIR) line emission provides key information about the gas cooling and heating due to shocks and UV radiation associated with the early stages of star formation. Gas cooling via FIR lines might, however, depend on metallicity. Aims. We aim to quantify the FIR line emission and determine the spatial distribution of the CO rotational temperature, ultraviolet (UV) radiation field, and H 2 number density toward the embedded cluster Gy 3–7 in the CMa– l 224 star-forming region, whose metallicity is expected to be intermediate between that of the Large Magellanic Cloud and the Solar neighborhood. By comparing the total luminosities of CO and [OI] toward Gy 3–7 with values found for low- and high-mass protostars extending over a broad range of metallicities, we also aim to identify the possible effects of metallicity on the FIR line cooling within our Galaxy. Methods. We studied SOFIA/FIFI-LS spectra of Gy 3–7, covering several CO transitions from J = 14–13 to 31-30, the OH doublet at 79 μm, the [O I ] 63.2 and 145.5 μm, and the [C II ] 158 μm lines. The field of view covers a 2′ × 1′ region with a resolution of ~7″–18″. Results. The spatial extent of CO high- J ( J up ≥14) emission resembles that of the elongated 160 μm continuum emission detected with Herschel, but its peaks are offset from the positions of the dense cores. The [O I ] lines at 63.2 μm and 145.5 μm follow a similar pattern, but their peaks are found closer to the positions of the cores. The CO transitions from J = 14–13 to J = 16–15 are detected throughout the cluster and show a median rotational temperature of 170 ± 30 K on Boltzmann diagrams. Comparisons to other protostars observed with Berschel show a good agreement with intermediate-mass sources in the inner Galaxy. Assuming an origin of the [O I ] and high- J CO emission in UV-irradiated C– shocks, we obtained pre-shock H 2 number densities of 10 ⁴ –10 ⁵ cm ⁻³ and UV radiation field strengths of 0.1–10 Habing fields ( G 0 ). Conclusions. Far-IR line observations reveal ongoing star formation in Gy 3–7, dominated by intermediate-mass Class 0/I young stellar objects. The ratio of molecular-to-atomic far-IR line emission shows a decreasing trend with bolometric luminosities of the protostars. However, it does not indicate that the low-metallicity has an impact on the line cooling in Gy 3–7.

A Herschel study of the high-mass protostar IRAS20126+4104

Article

Full-text available

Feb 2023

We performed Herschel observations of the continuum and line emission from the high-mass star-forming region IRAS 20126+4104, which hosts a well-studied B-type (proto)star powering a bipolar outflow and is associated with a Keplerian circumstellar disk. The continuum images at six wavelengths allowed us to derive an accurate estimate of the bolometric luminosity and mass of the molecular clump enshrouding the disk. The same region has been mapped in 12 rotational transitions of carbon monoxide, which were used in synergy with the continuum data to determine the temperature and density distribution inside the clump and improve upon the mass estimate. The maps of two fine structure oxygen far-IR lines were used to estimate the volume density of the shocked region at the surface of the southern lobe of the outflow and the mass-loss rate. Our findings lend further support to the scenario previously proposed by various authors, confirming that at the origin of the bolometric luminosity and bipolar outflow from IRAS 20126+4104 is a B-type star located at the centre of the Keplerian disk.

L1448-MM Observations by the Herschel Key Program

Article

Full-text available

Sep 2013

We present Herschel/PACS observations of L1448-MM, a Class 0 protostar with a prominent outflow. Numerous emission lines are detected at 55 < lambda < 210 micrometer including CO, OH, H2O, and [O I]. We investigate the spatial distribution of each transition to find that lines from low energy levels tend to distribute along the outflow direction while lines from high energy levels peak at the central spatial pixel. Spatial maps reveal that OH emission lines are formed in a relatively small area, while [O I] emission is extended. According to the rotational diagram analysis, the CO emission can be fitted by two (warm and hot) temperature components. For H2O, the ortho-to-para ratio is close to 3. The non-LTE LVG calculations suggest that CO and H2O lines could instead be formed in a high kinetic temperature (T > 1000 K) environment, indicative of a shock origin. For OH, IR-pumping processes play an important role in the level population. The molecular emission in L1448-MM is better explained with a C-shock model, but the atomic emission of PACS [O I] and Spitzer/IRS [Si II] emission is not consistent with C-shocks, suggesting multiple shocks in this region. Water is the major line coolant of L1448-MM in the PACS wavelength range, and the best-fit LVG models predict that H2O and CO emit (50-80)% of their line luminosity in the PACS wavelength range.

High-J CO survey of low-mass protostars observed with Herschel-HIFI

Article

Full-text available

Jun 2013

The evolution of deeply embedded young stellar objects (YSOs) has traditionally been traced through dust continuum spectral energy distributions (SEDs), but the use of CO excitation as an evolutionary probe has not yet been explored due to lack of high-J CO observations. The aim is to constrain the physical characteristics (excitation, kinematics, column density) of the warm gas toward 26 low-mass Class 0 and I YSOs using spectrally-resolved Herschel Space Observatory data of high-J lines of CO. Data are complemented by ground-based observations from APEX and the JCMT to compare those with the colder gas traced by lower-J CO lines. This is the first large spectrally resolved high-J CO survey conducted for these types of sources. The median excitation temperatures for 12CO, 13CO and C18O derived from single-temperature fits to the J_u=2-10 integrated intensities are ~70K, 48K and 37K, respectively, with no significant difference between Class 0 and I sources and no trend with M_env or L_bol. Thus, in contrast with the continuum SEDs, the spectral line energy distributions (SLEDs) do not show an evolution during the embedded stage. In contrast, the integrated line intensities of all CO isotopologs show a clear decrease with evolutionary stage as the envelope is dispersed. The H2O 110-101/CO 10-9 intensity ratio does not change significantly with velocity, in contrast with the H2O/CO 3-2 ratio, indicating that CO 10-9 is the lowest transition for which the line wings probe the same warm shocked gas as H2O. Modeling of the full suite of C18O lines indicates an abundance profile for Class 0 sources that is consistent with a freeze-out zone below 25 K and evaporation at higher temperatures, with but some fraction of the CO transformed into other species in the cold phase. In contrast, observations for two Class I sources in Ophiuchus are consistent with a constant high CO abundance profile.

Astronomical Data Analysis Software and Systems XIX

Article

Jan 2010

S. Ott

Water in star-forming regions with Herschel (WISH)

Article

Jun 2013

Context. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow. Aims. We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. Methods. We present velocity-resolved Herschel HIFI spectra of multiple water-transitions observed towards 29 nearby Class 0/I protostars as part of the WISH guaranteed time key programme. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components. Results. Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H-2 densities of order 10(5) -10(8) cm(-3) and H2O column densities of order 10(16) -10(18) cm(-2). H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order 10-200 AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order 1-30 AU. Conclusions. Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors. We propose that this is due to the differences in shock properties and geometry between these positions. Class I sources have similar excitation conditions to Class 0 sources, but generally smaller line-widths and emitting region sizes. We suggest that it is the velocity of the wind driving the outflow, rather than the decrease in envelope density or mass, that is the cause of the decrease in H2O intensity between Class 0 and I sources.

Waterfalls Around Protostars

Article

Jul 2013

Water is uniquely sensitive to motion of any kind within the protostellar environment due to its large Einstein A coefficient. As part of the 'Water in star-forming regions with Herschel' (WISH) survey, infall signatures were detected in the HIFI water spectra observed towards 5 Class 0/I protostars observed. The combination of observations of multiple water transitions and full 1-D non-LTE radiative transfer models of protostellar envelopes provides a self-consistent way to probe the physics and chemistry of infalling envelope material.

Rotational excitation of 45 levels of ortho/para-H 2O by excited ortho/para-H 2 from 5 K to 1500 K: State-to-state, effective, and thermalized rate coefficients

Article

Dec 2011

Aims: This work deals with the rotational excitation of ortho/para-H2O with para/ortho-H2 so that thermalized de-(excitation) rate coefficients up to 1500 K for the first 45th level of ortho/para-H2O are provided. Results are available in BASECOL with state-to-state rate coefficients, their fitting coefficients, and effective rate coefficients. In addition, we provide a routine that combines all data in order to create thermalized rate coefficients. Methods: Calculations were performed with the close coupling (CC) method over the whole energy range, using the same 5D potential energy surface (PES) as the one employed in previous papers. The current CC results were compared with thermalized quasi-classical trajectory (QCT) calculations using the same PES and with previous quantum calculations obtained between T = 20 K and T = 140 K with a different PES. The relative strengths of water excitation rate coefficients when water is excited with ortho-H2 versus para-H2 was also analyzed. Results: For collision with para-H2, the rotation-rotation process is found to be the dominant process for inelastic transfer for some water transitions, implying that calculations must include the j2 = 2 level. An important result of this paper is that j2 = 1 and j2 = 2 effective rate coefficients are very similar so that either j2 = 1 or j2 = 2 need to be calculated for astrophysical applications. In addition, at high temperature ratios of j2 = 2 (1) over j2 = 0, effective rate coefficients converge towards one to within a few percent. This study confirms that j2 = 3 effective rate coefficients are within 20% to j2 = 1 effective rate coefficients. Conclusions: For astrophysical applications, these results imply that future collisional excitation of light molecules with H2 should be carried out with para-H2, including j2 = 2, so as to obtain correct effective j2 = 0 effective rate coefficients and using the j2 = 2 effective rate coefficients for all excited j2 effective rate coefficients. In contrast, collisional excitation of heavy molecules with H2 might be restricted to para-H2 with j2 = 0 and to ortho-H2 with j2 = 1, using the j2 = 1 rate coefficients for all excited j2 effective rate coefficients. These conclusions should simplify the future methodological choice for collisional excitation calculations applied to interstellar/circumstellar media.

Physical and chemical variations within the W�3 star-forming region: II. The 345�GHz spectral line survey

Article

Aug 1997

Results are presented of the 345 GHz spectral survey toward three sources in the W 3 Giant Molecular Cloud: W 3 IRS4, W 3 IRS5 and W 3(H2O). Nearly 90% of the atmospheric window between 334 and 365 GHz has been scanned using the James Clerk Maxwell Telescope (JCMT(1)) down to a noise level of similar to 80 mK per resolution element. These observations are complemented by a large amount of data in the 230 GHz atmospheric window. From this data set physical conditions and beam-averaged column densities are derived for more than 14 chemically different species (over 24 different isotopes). The physical parameters derived in Paper I (Helmich et al. 1994) are confirmed by the analysis of the excitation of other species, although there is evidence that the silicon- and sulfur-bearing molecules exist in a somewhat denser and warmer environment. The densities are high, greater than or equal to 10(6) cm(-3), in the three sources and the kinetic temperatures for the bulk of the gas range from 55 K for IRS4 to 220 K for W 3(H2O). The chemical differences between the three sources are very striking: silicon- and sulfur-bearing molecules such as SiO and SO2 are prominent toward IRS5, whereas organic molecules like CH3OH, CH3OCH3 and CH3OCHO are at least an order of magnitude more abundant toward W 3(H2O). Vibrationally excited molecules are also detected toward this source. Only simple molecules are found toward IRS4. The data provide constraints on the amount of deuterium fractionation and the ionization fraction in the observed regions as well. These chemical characteristics are discussed in the context of an evolutionary sequence, in which IRS5 is the youngest, W 3(H2O) somewhat older and IRS4, although still enigmatic, the oldest.

ISO-SWS observations of pure rotational H_2O absorption lines toward Orion-IRc2

Article

Jun 2000

First detections of thermal water vapor absorption lines have been made toward Orion IRc2 using the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). Grating spectra covering wavelengths 25-45 mu m yield 19 pure rotational lines, originating from energy levels 200-750 K above ground. Fabry-Perot spectra of 5 transitions resolve the line profiles and reveal the H2O gas kinematics. The fact that all lines are seen in absorption is in striking contrast with data from the ISO Long Wavelength Spectrometer (LWS), where the H_2O lines appear in emission. At least one line displays a P-Cygni type profile, which suggests that the water is located in an expanding shell centered on or near IRc2. The expansion velocity is 18 km s-1, in agreement with the value inferred from H2O maser observations by Genzel et al. (1981). Because the continuum is intense and likely formed in or near the water-containing gas, the excitation of the observed transitions is dominated by radiative processes. A simple, generalised curve-of-growth method is presented and used to analyze the data. A mean excitation temperature of 72 K and a total H_2O column density of 1.5x 1018 cm-2 are inferred, each with an estimated maximum uncertainty of 20%. Combined with the H_2 column density derived from ISO observations of the pure rotational H_2 lines, and an assumed temperature of 200-350 K, the inferred H_2O abundance is 2-5x 10-4 in the warm shocked gas. This abundance is similar to that found recently by Harwit et al. (1998) toward Orion using data from the LWS, but higher than that found for most other shocked regions by, for example, Liseau et al. (1996). Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

The physical conditions in the PDR of W49N

Article

Sep 2001

We present ISO-LWS and ground-based SEST observations which probe the Photo Dissociation Region (PDR) of W49N. The ISO-LWS observations consist of low resolution ( ~ 200) grating spectra between 43 mu m and 197 mu m, and high resolution ( ~ 104) Fabry-Pérot spectra of the [CII] 158 mu m and [OI] 63 and 145 mu m lines. The SEST observations consist of C16O J = 1 -> 0 and C18O J = 2 -> 1 maps of the region. Using all these observations and with the help of a detailed PDR model, we have determined the physical and chemical structure of the PDR of W49N. We find that only a tiny fraction, 2.5%, of the cloud gas is in the atomic form. This gas has an average density n=104 cm-3 and a temperature T ~ 130 K. The PDR is created by a FUV field G0 =3 x 105 times brighter than the average FUV interstellar field, which is emitted by the stars associated with the several HII regions inside the cloud. The photoelectric heating efficiency is very low, ~ 10-4, relative to other known PDRs, probably because of the relatively high G0/n ratio. Overall, W49N seems to be one of the youngest giant molecular clouds actively forming stars in the Galaxy, since most of the cloud material is still molecular and dense and not yet dispersed by the several embedded newly formed massive protostars. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) with the participation of ISAS and NASA.

Evolution in the Far-Infrared Spectra of Low-Mass Young Embedded Sources

Article

Jul 2002

The far-infrared spectra (45-197 mum) of 28 low-luminosity young embedded objects have been studied in order to search for possible evolutive trends in the observed spectral features. The low-resolution spectra from 45 to 197 mum of 17 Class 0 and 11 Class I sources taken with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory have been used for this analysis. The most prominent features presented by these spectra are the [O I] 63 and 145 mum fine-structure lines and pure rotational lines from the abundant molecules CO, H2O, and OH. Clear differences are found, however, between the spectra of the two classes of objects. Water lines, which are prominent in the spectra of Class 0 sources, are not observed in Class I objects, with an upper limit

Far-infrared molecular lines from Low- to High-Mass Star Forming Regions observed with Herschel

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