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Yiming Li,
Alison F. Crocker,
Daniela Calzetti, Christine D. Wilson,
Robert C. Kennicutt,
Eric J. Murphy,
Bernhard R. Brandl,
B. T. Draine,
M. Galametz,
B. D. Johnson, [......],
C. W. Engelbracht,
B. Groves,
C. -N. Hao,
G. Helou,
J. Hinz,
L. K. Hunt,
O. Krause,
H. Roussel,
M. Sauvage,
J. D. T. Smith
[show abstract]
[hide abstract]
ABSTRACT: We use the near--infrared Br\gamma hydrogen recombination line as a reference
star formation rate (SFR) indicator to test the validity and establish the
calibration of the {\it Herschel} PACS 70 \mu m emission as a SFR tracer for
sub--galactic regions in external galaxies. Br\gamma offers the double
advantage of directly tracing ionizing photons and of being relatively
insensitive to the effects of dust attenuation. For our first experiment, we
use archival CFHT Br\gamma and Ks images of two nearby galaxies: NGC\,5055 and
NGC\,6946, which are also part of the {\it Herschel} program KINGFISH (Key
Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use the
extinction corrected Br\gamma emission to derive the SFR(70) calibration for
H{\sc ii} regions in these two galaxies. A comparison of the SFR(70)
calibrations at different spatial scales, from 200 pc to the size of the whole
galaxy, reveals that about 50% of the total 70\mu m emission is due to dust
heated by stellar populations that are unrelated to the current star formation.
We use a simple model to qualitatively relate the increase of the SFR(70)
calibration coefficient with decreasing region size to the star formation
timescale. We provide a calibration for an unbiased SFR indicator that combines
the observed H\alpha with the 70 \mu m emission, also for use in H{\sc ii}
regions. We briefly analyze the PACS 100 and 160 \mu m maps and find that
longer wavelengths are not as good SFR indicators as 70\mu m, in agreement with
previous results. We find that the calibrations show about 50% difference
between the two galaxies, possibly due to effects of inclination.
04/2013;
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Luigi Spinoglio,
Miguel Pereira-Santaella,
Gemma Busquet,
Maximilien R. P. Schirm, Christine D. Wilson,
Jason Glenn,
Julia Kamenetzky,
Naseem Rangwala,
Philip R. Maloney,
Tara J. Parkin,
George J. Bendo,
Suzanne C. Madden,
Mark G. Wolfire,
Alessandro Boselli,
Asantha Cooray,
Mathew J. Page
[show abstract]
[hide abstract]
ABSTRACT: The first complete submillimetre spectrum (190-670um) of the Seyfert 2 galaxy
NGC1068 has been observed with the SPIRE Fourier Transform Spectrometer onboard
the {\it Herschel} Space Observatory. The sequence of CO lines (Jup=4-13),
lines from water, the fundamental rotational transition of HF, two o-H_2O+
lines and one line each from CH+ and OH+ have been detected, together with the
two [CI] lines and the [NII]205um line. The observations in both single
pointing mode with sparse image sampling and in mapping mode with full image
sampling allow us to disentangle two molecular emission components, one due to
the compact circum-nuclear disk (CND) and one from the extended region
encompassing the star forming ring (SF-ring). Radiative transfer models show
that the two CO components are characterized by density of n(H_2)=10^4.5 and
10^2.9 cm^-3 and temperature of T=100K and 127K, respectively. The comparison
of the CO line intensities with photodissociation region (PDR) and X-ray
dominated region (XDR) models, together with other observational constraints,
such as the observed CO surface brightness and the radiation field, indicate
that the best explanation for the CO excitation of the CND is an XDR with
density of n(H_2) 10^4 cm^-3 and X-ray flux of 9 erg s^-1 cm^-2, consistent
with illumination by the active galactic nucleus, while the CO lines in the
SF-ring are better modeled by a PDR. The detected water transitions, together
with those observed with the \her \sim PACS Spectrometer, can be modeled by an
LVG model with low temperature (T_kin \sim 40K) and high density (n(H_2) in the
range 10^6.7-10^7.9 cm^-3).
08/2012;
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Erin Mentuch Cooper, Christine D. Wilson,
Kelly Foyle,
George Bendo,
Jin Koda,
Marten Baes,
Médéric Boquien,
Alessandro Boselli,
Laure Ciesla,
Asantha Cooray,
Steve Eales,
Maud Galametz,
Vianney Lebouteiller,
Tara Parkin,
Hélène Roussel,
Marc Sauvage,
Luigi Spinoglio,
Matthew W. L. Smith
[show abstract]
[hide abstract]
ABSTRACT: Using infrared imaging from the Herschel Space Observatory, observed as part
of the VNGS, we investigate the spatially resolved dust properties of the
interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales
of 1 kpc. Spectral energy distribution modelling of the new infrared images in
combination with archival optical, near- through mid-infrared images confirms
that both galaxies underwent a burst of star formation ~370-480 Myr ago and
provides spatially resolved maps of the stellar and dust mass surface
densities. The resulting average dust-to-stellar mass ratios are comparable to
other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at
log M(dust)/M(star)= -2.5+/-0.2 and NGC 5195 at log M(dust)/M(star)=
-3.5+/-0.3. The dust-to-stellar mass ratio is constant across NGC 5194
suggesting the stellar and dust components are coupled. In contrast, the mass
ratio increases with radius in NGC 5195 with decreasing stellar mass density.
Archival mass surface density maps of the neutral and molecular hydrogen gas
are also folded into our analysis. The gas-to-dust mass ratio, 94+/-17, is
relatively constant across NGC 5194. Somewhat surprisingly, we find the dust in
NGC 5195 is heated by a strong interstellar radiation field, over 20 times that
of the ISRF in the Milky Way, resulting in relatively high characteristic dust
temperatures (~30 K). This post-starburst galaxy contains a substantial amount
of low-density molecular gas and displays a gas-to-dust ratio (73+/-35) similar
to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such
high temperatures as there is no star formation in the galaxy and its active
galactic nucleus is 5-10 times less luminous than the one in NGC 5194, which
exhibits only a modest enhancement in the amplitude of its ISRF.
06/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We have used high resolution (~2.3") observations of the local (D = 46 Mpc)
luminous infrared galaxy Arp 299 to map out the physical properties of the
molecular gas which provides the fuel for its extreme star formation activity.
The 12CO J=3-2, 12CO J=2-1 and 13CO J=2-1 lines were observed with the
Submillimeter Array and the short spacings of the 12CO J=2-1 and J=3-2
observations have been recovered using James Clerk Maxwell Telescope single
dish observations. We use the radiative transfer code RADEX to estimate the
physical properties (density, column density and temperature) of the different
regions in this system. The RADEX solutions of the two galaxy nuclei, IC 694
and NGC 3690, are consistent with a wide range of gas components, from warm
moderately dense gas with T_{kin} > 30 K and n(H_{2}) ~ 0.3 - 3 x 10^{3}
cm^{-3} to cold dense gas with T_{kin} ~ 10-30 K and n(H_{2}) > 3 x 10^{3}
cm^{-3}. The overlap region is shown to have a better constrained solution with
T_{\rm{kin}}$ ~ 10-50 K and n(H_{2}) ~ 1-30 x 10^{3} cm^{-3}. We estimate the
gas masses and star formation rates of each region in order to derive molecular
gas depletion times. The depletion times of all regions (20-60 Myr) are found
to be about 2 orders of magnitude lower than those of normal spiral galaxies.
This rapid depletion time can probably be explained by a high fraction of dense
gas on kiloparsec scales in Arp 299. We estimate the CO-to-H_{2} factor,
\alpha_{co} to be 0.4 \pm 0.3 (3 x 10^{-4}/ x_{CO}) M_{sol} (K km s^{-1}
pc^{2})^{-1} for the overlap region. This value agrees well with values
determined previously for more advanced merger systems.
04/2012;
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Stephen Eales,
Matthew W. L. Smith,
Robbie Auld,
Maarten Baes,
George J. Bendo,
Simone Bianchi,
Alessandro Boselli,
Laure Ciesla,
David Clements,
Asantha Cooray, [......],
Haley Gomez,
Jacopo Fritz,
Tom Hughes,
Suzanne Madden,
Laura Magrini,
Michael Pohlen,
Luigi Spinoglio,
Joris Verstappen,
Catherine Vlahakis, Christine D. Wilson
[show abstract]
[hide abstract]
ABSTRACT: It has often been suggested that an alternative to the standard CO/21-cm
method for estimating the mass of the interstellar medium (ISM) in a galaxy
might be to estimate the mass of the ISM from the continuum dust emission. In
this paper, we investigate the potential of this technique using Herschel
observations of ten galaxies in the Herschel Reference Survey and in the
Herschel Virgo Cluster Survey. We show that the emission detected by Herschel
is mostly from dust that has a temperature and emissivity index similar to that
of dust in the local ISM in our galaxy, with the temperature generally
increasing towards the centre of each galaxy. We calibrate the dust method
using the CO and 21-cm observations to provide an independent estimate of the
mass of hydrogen in each galaxy, solving the problem of the uncertain `X
factor' for the molecular gas by minimizing the dispersion in the ratio of the
masses estimated using the two methods. With the calibration for the dust
method and the estimate of the X-factor produced in this way, the dispersion in
the ratio of the two gas masses is 30%, which gives an upper limit on the
fundamental accuracy of the dust method. The calibration we obtain for the dust
method is very similar to an independent Herschel measurement for M31 and to
the calibration for the Milky Way from Planck measurements.
02/2012;
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Junko Ueda,
Daisuke Iono,
Glen Petitpas,
Min S. Yun,
Paul T. P. Ho,
Ryohei Kawabe,
Rui-Qing Mao,
Sergio Martín,
Satoki Matsushita,
Alison B. Peck,
Yoichi Tamura,
Junzhi Wang,
Zhong Wang, Christine D. Wilson,
and Qizhou Zhang
[show abstract]
[hide abstract]
ABSTRACT: We present a ~1'' (100 pc) resolution 12CO (3-2) map of the nearby intermediate-stage interacting galaxy pair NGC 4038/9 (the Antennae galaxies) obtained with the Submillimeter Array. We find that half the CO (3-2) emission originates in the overlap region where most of the tidally induced star formation had been previously found in shorter wavelength images, with the rest being centered on each of the nuclei. The gross distribution is consistent with lower resolution single-dish images, but we show for the first time the detailed distribution of the warm and dense molecular gas across this galaxy pair at resolutions comparable to the size of a typical giant molecular complex. While we find that 58% (33/57) of the spatially resolved Giant Molecular Associations (a few × 100 pc) are located in the overlap region, only ≤30% spatially coincides with the optically detected star clusters, suggesting that the bulk of the CO (3-2) emission traces the regions with very recent or near future star formation activity. The spatial distribution of the CO (3-2)/CO (1-0) integrated brightness temperature ratios mainly ranges between 0.3 and 0.6, which suggests that on average the CO (3-2) line in the Antennae is not completely thermalized and similar to the average values of nearby spirals. A higher ratio is seen in both nuclei and the southern complexes in the overlap region. A higher radiation field associated with intense star formation can account for the nucleus of NGC 4038 and the overlap region, but the nuclear region of NGC 4039 shows relatively little star formation or active galactic nucleus activity and cannot be easily explained. We show kinematical evidence that the high line ratio in NGC 4039 is possibly caused by gas inflow into the counter-rotating central disk.
The Astrophysical Journal 12/2011; 745(1):65. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The FIR/submm window is one of the least-studied regions of the
electromagnetic spectrum, yet this wavelength range is absolutely crucial for
understanding the physical processes and properties of the ISM in galaxies. The
advent of the Herschel Space Observatory has opened up the entire FIR/submm
window for spectroscopic studies. We present the first FIR/submm spectroscopic
results on both nearby and distant galaxies obtained in the frame of two
Herschel key programs: the Very Nearby Galaxies Survey and the Herschel ATLAS.
12/2011;
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Ramin A Skibba,
Charles W Engelbracht,
Daniel Dale,
Joannah Hinz,
Stefano Zibetti,
Alison Crocker,
Brent Groves,
Leslie Hunt,
Benjamin D Johnson,
Sharon Meidt, [......],
Edward Montiel,
Hans-Walter Rix,
Héì Ene Roussel,
Karin Sandstrom,
Marc Sauvage,
Eva Schinnerer,
J D Smith,
Fabian Walter, Christine D Wilson,
Mark Wolfire
[show abstract]
[hide abstract]
ABSTRACT: Using new far-infrared imaging from the Herschel Space Observatory with ancillary data from ultraviolet (UV) to submillimeter (submm) wavelengths, we estimate the total emission from dust and stars of 62 nearby galaxies in the KINGFISH survey in a way that is as empirical and model-independent as possible. We collect and exploit these data in order to measure from the spectral energy distributions (SEDs) precisely how much stellar radiation is intercepted and re-radiated by dust, and how this quantity varies with galaxy properties. By including SPIRE data, we are more sensitive to emission from cold dust grains than previous analyses at shorter wavelengths, allowing for more accurate estimates of dust temperatures and masses. The dust/stellar flux ratio, which we measure by integrating the SEDs, has a range of nearly three decades (from 10 −2.2 to 10 0.5). The inclusion of SPIRE data shows that estimates based on data not reaching these far-IR wavelengths are biased low by 17% on average. We find that the dust/stellar flux ratio varies with morphology and total infrared (IR) luminosity, with dwarf galaxies having faint luminosities, spirals having relatively high dust/stellar ratios and IR luminosities, and some early-types having low dust/stellar ratios. We also find that dust/stellar flux ratios are related to gas-phase metallicity (log(f dust /f *) = −0.66 ± 0.08 and −0.22 ± 0.12 for metal-poor and intermediate-metallicity galaxies, respectively), while the dust/stellar mass ratios are less so (differing by ≈ 0.2 dex); the more metal-rich galaxies span a much wider range of the flux ratios. In addition, the substantial scatter between dust/stellar flux and dust/stellar mass indicates that the former is a poor proxy of the latter. Comparing the dust/stellar flux ratios and dust temperatures, we also show that early-types tend to have slightly warmer temperatures (by up to 5 K) than spiral galaxies, which may be due to more intense interstellar radiation fields, or possibly to different dust grain compositions. Finally, we show that early-types and early-type spirals have a strong correlation between the dust/stellar flux ratio and specific star formation rate, which suggests that the relatively bright far-IR emission of some of these galaxies is due to ongoing (if limited) star formation as well as to the radiation field from older stars, which is heating the dust grains.
09/2011;
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Tracey Hill,
Frederique Motte,
Pierre Didelon,
Sylvain Bontemps,
Vincent Minier,
Martin Hennemann,
Nicola Schneider,
Philippe Andre,
Alexander Men'shchikov,
Loren D. Anderson, [......],
Nicolas Peretto,
Stefano Pezzuto,
Helene Roussel,
Marc Sauvage,
Thierry Sousbie,
Leonardo Testi,
Derek Ward-Thompson,
Glenn J. White, Christine D. Wilson,
Annie Zavagno
[show abstract]
[hide abstract]
ABSTRACT: We present the first Herschel PACS and SPIRE results of the Vela C molecular
complex in the far-infrared and submillimetre regimes at 70, 160, 250, 350, and
500 um, spanning the peak of emission of cold prestellar or protostellar cores.
Column density and multi-resolution analysis (MRA) differentiates the Vela C
complex into five distinct sub-regions. Each sub-region displays differences in
their column density and temperature probability distribution functions (PDFs),
in particular, the PDFs of the `Centre-Ridge' and `South-Nest' sub-regions
appear in stark contrast to each other. The Centre-Ridge displays a bimodal
temperature PDF representative of hot gas surrounding the HII region RCW 36 and
the cold neighbouring filaments, whilst the South-Nest is dominated by cold
filamentary structure. The column density PDF of the Centre-Ridge is flatter
than the South-Nest, with a high column density tail, consistent with formation
through large-scale flows, and regulation by self-gravity. At small to
intermediate scales MRA indicates the Centre-Ridge to be twice as concentrated
as the South-Nest, whilst on larger scales, a greater portion of the gas in the
South-Nest is dominated by turbulence than in the Centre-Ridge. In Vela C,
high-mass stars appear to be preferentially forming in ridges, i.e., dominant
high column density filaments.
08/2011;
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Naseem Rangwala,
Philip R. Maloney,
Jason Glenn, Christine D. Wilson,
Adam Rykala,
Kate Isaak,
Maarten Baes,
George J. Bendo,
Alessandro Boselli,
Charles M. Bradford, [......],
Peter Imhof,
Julia Kamenetzky,
Suzanne C. Madden,
Erin Mentuch,
Nicola Sacchi,
Marc Sauvage,
Maximilien R. P. Schirm,
M. W. L. Smith,
Luigi Spinoglio,
Mark Wolfire
[show abstract]
[hide abstract]
ABSTRACT: We present Herschel SPIRE-FTS observations of Arp~220, a nearby ULIRG. The
FTS continuously covers 190 -- 670 microns, providing a good measurement of the
continuum and detection of several molecular and atomic species. We detect
luminous CO (J = 4-3 to 13-12) and water ladders with comparable total
luminosity; very high-J HCN absorption; OH+, H2O+, and HF in absorption; and CI
and NII. Modeling of the continuum yields warm dust, with T = 66 K, and an
unusually large optical depth of ~5 at 100 microns. Non-LTE modeling of the CO
shows two temperature components: cold molecular gas at T ~ 50 K and warm
molecular gas at T ~1350 K. The mass of the warm gas is 10% of the cold gas,
but dominates the luminosity of the CO ladder. The temperature of the warm gas
is in excellent agreement with H2 rotational lines. At 1350 K, H2 dominates the
cooling (~20 L_sun/M_sun) in the ISM compared to CO (~0.4 L_sun/M_sun). We
found that only a non-ionizing source such as the mechanical energy from
supernovae and stellar winds can excite the warm gas and satisfy the energy
budget of ~20 L_sun/M_sun. We detect a massive molecular outflow in Arp 220
from the analysis of strong P-Cygni line profiles observed in OH+, H2O+, and
H2O. The outflow has a mass > 10^{7} M_sun and is bound to the nuclei with
velocity < 250 km/s. The large column densities observed for these molecular
ions strongly favor the existence of an X-ray luminous AGN (10^{44} ergs/s) in
Arp 220.
06/2011;
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Daisuke Iono, Christine D. Wilson,
Min S. Yun,
Andrew J. Baker,
Glen R. Petitpas,
Alison B. Peck,
Melanie Krips,
T. J. Cox,
Satoki Matsushita,
J. Christopher Mihos,
and Ylva Pihlstrom
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed comparison of the CO (3-2) emitting molecular gas between a local sample of luminous infrared galaxies (U/LIRGs) and a high-redshift sample that comprises submm selected galaxies (SMGs), quasars, and Lyman Break Galaxies (LBGs). The U/LIRG sample consists of our recent CO (3-2) survey using the Submillimeter Array while the CO (3-2) data for the high-redshift population are obtained from the literature. We find that the and L FIR relation is correlated over five orders of magnitude, which suggests that the molecular gas traced in CO (3-2) emission is a robust tracer of dusty star formation activity. The near unity slope of 0.93 ± 0.03 obtained from a fit to this relation suggests that the star formation efficiency is constant to within a factor of 2 across different types of galaxies residing in vastly different epochs. The CO (3-2) size measurements suggest that the molecular gas disks in local U/LIRGs (0.3-3.1 kpc) are much more compact than the SMGs (3-16 kpc), and that the size scales of SMGs are comparable to the nuclear separation (5-40 kpc) of the widely separated nuclei of U/LIRGs in our sample. We argue from these results that the SMGs studied here are predominantly intermediate stage mergers, and that the wider line widths arise from the violent merger of two massive gas-rich galaxies taking place deep in a massive halo potential.
The Astrophysical Journal 04/2009; 695(2):1537. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present ~2'' resolution CO (3-2), HCO+(4-3), and 880 μm continuum images of the luminous infrared galaxy NGC 6240 obtained at the Submillimeter Array. We find that the spatially resolved CO (3-2), HCO + (4-3), and the 880 μm emission peaks between the two nuclear components that are both known to harbor AGNs. Our large velocity gradient (LVG) analysis performed on each velocity channel suggests that the peak of the molecular gas emission traced in our observations is warm (T = 20-100 K), dense (nH2 = 105.0-105.4 cm-3), and moderately optically thin (τ = 0.2-2) in the central 1 kpc. We also find large column densities of ~1023 cm-2. Such extreme conditions are observed over ~300 km s-1 centered around the CO-derived systemic velocity. The derived molecular gas mass from the CO (3-2) emission and a CO-to-H2 conversion factor commonly used for ULIRGs is (6.9 ± 1.7) × 109 M☉, and this is consistent with the mass derived from previous CO (2-1) observations. The gas is highly turbulent in the central kpc (ΔvFWZI ~ 1175 km s-1). Furthermore, possible inflow or outflow activity is suggested from the CO (3-2) velocity distribution. We tentatively state that 3.5 × 108 M☉ of isolated CO (3-2) emission seen west of the northern disk may be associated with outflows from starburst superwinds, but the gas outflow scenario from one of the central AGN is not completely ruled out. Piecing all of the information together, the central region of NGC 6240 harbors 2 AGNs, ~1010 M☉ of molecular gas mass, 5 × 107 M☉ of dust mass, and has possible evidence of inflow and outflow activity.
The Astrophysical Journal 12/2008; 659(1):283. · 6.02 Impact Factor
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Christine D. Wilson,
Glen R. Petitpas,
Daisuke Iono,
Andrew J. Baker,
Alison B. Peck,
Melanie Krips,
Bradley Warren,
Jennifer Golding,
Adam Atkinson,
Lee Armus,
T. J. Cox,
Paul Ho,
Mika Juvela,
Satoki Matsushita,
J. Christopher Mihos,
Ylva Pihlstrom,
and Min S. Yun
[show abstract]
[hide abstract]
ABSTRACT: We present new data obtained with the Submillimeter Array for a sample of 14 nearby luminous and ultraluminous infrared galaxies. The galaxies were selected to have distances DL < 200 Mpc and far-infrared luminosities log LFIR > 11.4. The galaxies were observed with spatial resolutions of order 1 kpc in the CO J = 3–2, CO J = 2–1,13CO J = 2–1, and HCO+ J = 4–3 lines as well as the continuum at 880 μm and 1.3 mm. We have combined our CO and continuum data to measure an average gas-to-dust mass ratio of 120 ± 28 (rms deviation 109) in the central regions of these galaxies, very similar to the value of 150 determined for the Milky Way. This similarity is interesting given the more intense heating from the starburst and possibly accretion activity in the luminous infrared galaxies compared to the Milky Way. We find that the peak H2 surface density correlates with the far-infrared luminosity, which suggests that galaxies with higher gas surface densities inside the central kiloparsec have a higher star formation rate. The lack of a significant correlation between total H2 mass and far-infrared luminosity in our sample suggests that the increased star formation rate is due to the increased availability of molecular gas as fuel for star formation in the central regions. In contrast to previous analyses by other authors, we do not find a significant correlation between central gas surface density and the star formation efficiency, as traced by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that it is the star formation rate, not the star formation efficiency, that increases with increasing central gas surface density in these galaxies.
The Astrophysical Journal Supplement Series 12/2008; 178(2):189. · 13.46 Impact Factor
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Satoki Matsushita,
Daisuke Iono,
Glen R. Petitpas,
Richard C. -Y. Chou,
Mark A. Gurwell,
Todd R. Hunter,
Jeremy Lim,
Sebastien Muller,
Alison B. Peck,
Kazushi Sakamoto,
Satoko Sawada-Satoh,
Martina C. Wiedner,
David J. Wilner, Christine D. Wilson
[show abstract]
[hide abstract]
ABSTRACT: We have used the Submillimeter Array (SMA) to make the first interferometric
observations (beam size ~1") of the 12CO J=6-5 line and 435 micron (690 GHz)
continuum emission toward the central region of the nearby ULIRG Arp 220. These
observations resolve the eastern and western nuclei from each other, in both
the molecular line and dust continuum emission. At 435 micron, the peak
intensity of the western nucleus is stronger than the eastern nucleus, and the
difference in peak intensities is less than at longer wavelengths. Fitting a
simple model to the dust emission observed between 1.3 mm and 435 micron
suggests that dust emissivity power law index in the western nucleus is near
unity and steeper in the eastern nucleus, about 2, and that the dust emission
is optically thick at the shorter wavelength. Comparison with single dish
measurements indicate that the interferometer observations are missing ~60% of
the dust emission, most likely from a spatially extended component to which
these observations are not sensitive. The 12CO J=6-5 line observations clearly
resolve kinematically the two nuclei. The distribution and kinematics of the
12CO J=6-5 line appear to be very similar to lower J CO lies observed at
similar resolution. Analysis of multiple 12CO line intensities indicates that
the molecular gas in both nuclei have similar excitation conditions, although
the western nucleus is warmer and denser. The excitation conditions are similar
to those found in other extreme environments, including M82, Mrk 231, and BR
1202-0725. Simultaneous lower resolution observations of the 12CO, 13CO, and
C18O J=2-1 lines show that the 13CO and C18O lines have similar intensities,
which suggests that both of these lines are optically thick, or possibly that
extreme high mass star formation has produced in an overabundance of C18O.
11/2008;
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[show abstract]
[hide abstract]
ABSTRACT: This paper presents 12CO J=3-2, 13CO J=3-2, C18O J=3-2, and 13CO J=2-1 spectra of the irregular starburst galaxy M82 taken with the 15 m James Clerk Maxwell Telescope. All maps exhibit a double peaked morphology, despite evidence that the higher J transitions are optically thick. This morphology suggests that the double peaked structure is not the result of an edge-on torus of molecular gas as is commonly assumed. We observe line ratio gradients that can best be explained by a temperature gradient increasing from NE to SW in conjunction with a density gradient that increases in the opposite sense. These gradients may have been caused by the interaction with M81, resulting in increased star formation that both heats and depletes the molecular gas in the SW lobe of M82. Comment: 8 pages + 2 colour figures; accepted for ApJ Letters
06/2000;
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[show abstract]
[hide abstract]
ABSTRACT: This paper presents CI, CO J=4-3, and CO J=3-2 maps of the barred spiral galaxy M83 taken at the James Clerk Maxwell Telescope. Observations indicate a double peaked structure which is consistent with gas inflow along the bar collecting at the inner Lindblad resonance. This structure suggests that nuclear starbursts can occur even in galaxies where this inflow/collection occurs, in contrast to previous studies of barred spiral galaxies. However, the observations also suggest that the double peaked emission may be the result of a rotating molecular ring oriented nearly perpendicular to the main disk of the galaxy. The CO J=4-3 data indicate the presence of warm gas in the nucleus that is not apparent in the lower-J CO observations, which suggests that CO J=1-0 emission may not be a reliable tracer of molecular gas in starburst galaxies. The twelve CI/CO J=4-3 line ratios in the inner 24'' x 24'' are uniform at the 2 sigma level, which indicates that the CO J=4-3 emission is originating in the same hot photon-dominated regions as the CI emission. The CO J=4-3/J=3-2 line ratios vary significantly within the nucleus with the higher line ratios occurring away from peaks of emission along an arc of active star forming regions. These high line ratios (>1) likely indicate optically thin gas created by the high temperatures caused by star forming regions in the nucleus of this starburst galaxy. Comment: 15 pages with 10 figures. To appear in the August 10 1998 issue of The Astrophysical Journal
03/1998;
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[show abstract]
[hide abstract]
ABSTRACT: The FIR/submm window is amongst the least explored spectral regions of the electromagnetic spectrum. It is, however, a key to study the general properties of the interstellar medium of galaxies, as it contains important spectral line diagnostics from the neutral, ionized and molecular ISM. The Herschel Space Observatory, successfully launched on 14 May 2009, is the first observatory to cover the entire FIR/submm range between 57 and 672 μm. We discuss the main results from the ISO era on FIR spectroscopy of galaxies and the enormous science potential of the Herschel mission through a presentation of its spectroscopic extragalactic key programs.
New Astronomy Reviews.
