-
M. Galametz,
S. Hony,
F. Galliano,
S. C. Madden,
M. Albrecht,
C. Bot,
D. Cormier,
C. Engelbracht,
Y. Fukui,
F. P. Israel, [......], K. Misselt,
E. Montiel,
K. Okumura,
P. Panuzzo,
J. Roman- Duval,
M. Rubio,
M. Sauvage,
J. P. Seale,
M. Sewilo,
J. Th. van Loon
[show abstract]
[hide abstract]
ABSTRACT: We present a study of the infrared/submm emission of the LMC star forming
complex N158-N159-N160. Combining observations from the Spitzer Space Telescope
(3.6-70um), the Herschel Space Observatory (100-500um) and LABOCA (870um)
allows us to work at the best angular resolution available now for an
extragalactic source. We observe a remarkably good correlation between SPIRE
and LABOCA emission and resolve the low surface brightnesses emission. We use
the Spitzer and Herschel data to perform a resolved Spectral Energy
Distribution (SED) modelling of the complex. Using MBB, we derive a global
emissivity index beta_c of 1.47. If beta cold is fixed to 1.5, we find an
average temperature of 27K. We also apply the Galliano et al. (2011) modelling
technique (and amorphous carbon to model carbon dust) to derive maps of the
star formation rate, the mean starlight intensity, the fraction of PAHs or the
dust mass surface density of the region. We observe that the PAH fraction
strongly decreases in the HII regions. This decrease coincides with peaks in
the mean radiation field intensity map. The dust surface densities follow the
FIR distribution, with a total dust mass of 2.1x10^4 Msolar (2.8 times less
than when using graphite grains) in the resolved elements we model. We find a
non-negligible amount of dust in the molecular cloud N159 South (showing no
massive SF). We also investigate the drivers of the Herschel/PACS and SPIRE
submm colours as well as the variations in the gas-to-dust mass ratio (G/D) and
the XCO conversion factor in the region N159. We finally model individual
regions to analyse variations in the SED shape across the complex and the 870um
emission in more details. No measurable submm excess emission at 870um seems to
be detected in these regions.
02/2013;
-
M ~L Boyer,
S Srinivasan,
J ~T Loon,
I McDonald,
M Meixner,
D Zaritsky,
K ~D Gordon,
F Kemper,
B Babler,
M Block,
S Bracker,
C ~W Engelbracht,
J Hora,
R Indebetouw,
M Meade, K Misselt,
T Robitaille,
M Sewilo,
B Shiao,
B Whitney
aj. 05/2012; 143:127.
-
F. Galliano,
S. Hony,
J. -P. Bernard,
C. Bot,
S. C. Madden,
J. Roman-Duval,
M. Galametz,
A. Li,
M. Meixner,
C. W. Engelbracht,
V. Lebouteiller, K. Misselt,
E. Montiel,
P. Panuzzo,
W. T. Reach,
R. Skibba
[show abstract]
[hide abstract]
ABSTRACT: Aims: In this paper, we perform detailed modelling of the Spitzer and
Herschel observations of the LMC, in order to: (i) systematically study the
uncertainties and biases affecting dust mass estimates; and to (ii) explore the
peculiar ISM properties of the LMC.
Methods: To achieve these goals, we have modelled the spatially resolved SEDs
with two alternate grain compositions, to study the impact of different
submillimetre opacities on the dust mass. We have rigorously propagated the
observational errors (noise and calibration) through the entire fitting
process, in order to derive consistent parameter uncertainties.
Results: First, we show that using the integrated SED leads to
underestimating the dust mass by ~50 % compared to the value obtained with
sufficient spatial resolution, for the region we studied. This might be the
case, in general, for unresolved galaxies. Second, we show that Milky Way type
grains produce higher gas-to-dust mass ratios than what seems possible
according to the element abundances in the LMC. A spatial analysis shows that
this dilemma is the result of an exceptional property: the grains of the LMC
have on average a larger intrinsic submm opacity (emissivity index beta~1.7 and
opacity kappa_abs(160 microns)=1.6 m2/kg) than those of the Galaxy. By studying
the spatial distribution of the gas-to-dust mass ratio, we are able to
constrain the fraction of unseen gas mass between ~10, and ~100 % and show that
it is not sufficient to explain the gas-to-dust mass ratio obtained with Milky
Way type grains. Finally, we confirm the detection of a 500 microns extended
emission excess with an average relative amplitude of ~15 %, varying up to 40
%. This excess anticorrelates well with the dust mass surface density. Although
we do not know the origin of this excess, we show that it is unlikely the
result of very cold dust, or CMB fluctuations.
10/2011;
-
I McDonald,
M ~L Boyer,
J ~T Loon,
A ~A Zijlstra,
J ~L Hora,
B Babler,
M Block,
K Gordon,
M Meade,
M Meixner, K Misselt,
T Robitaille,
M Sewilo,
B Shiao,
B Whitney
VizieR Online Data Catalog. 05/2011; 219:30023.
-
I McDonald,
M ~L Boyer,
J ~T Loon,
A ~A Zijlstra,
J ~L Hora,
B Babler,
M Block,
K Gordon,
M Meade,
M Meixner, K Misselt,
T Robitaille,
M Sewilo,
B Shiao,
B Whitney
apjs. 04/2011; 193:23.
-
Lynn Redding Carlson,
Marta Sewiło,
Margaret Meixner,
Krista Alexandra Romita,
Barbara Whitney,
J. L. Hora,
M. Cignoni,
Elena Sabbi,
Antonella Nota,
Marco Sirianni,
Linda J. Smith,
Karl Gordon,
B. Babler,
S. Bracker,
J. S. Gallagher III,
M. Meade, K. Misselt,
A. Pasquali,
and B. Shiao
[show abstract]
[hide abstract]
ABSTRACT: We present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical (HST/ACS F555W, F814W, and SMARTS/ANDICAM V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8 μm and MIPS 24 μm). Combining this with Infrared Survey Facility near-infrared photometry (J, H, Ks ), we compare the young main sequence (MS) and pre-main sequence (PMS) populations prominent in the optical with the current young stellar object (YSO) populations revealed by the infrared. We analyze the MS and PMS population with isochrones in color-magnitude diagrams to derive ages and masses. The optical data reveal ~565 PMS candidates, low-mass Stage III YSOs. We characterize ~40 YSOs by fitting their spectral energy distributions to a grid of models (Robitaille et al.) to derive luminosities, masses, and evolutionary phase (Stages I-III). The higher resolution HST images reveal that ~70% of the YSO candidates are either multiples or protoclusters. For YSOs and PMS sources found in common, we find a consistency in the masses derived. We use the YSO mass function to derive a present-day star formation rate of ~0.2-1.0 M ☉ yr–1 kpc–2, similar to the rate derived from the optical star formation history suggesting a constant star formation rate for this region. We demonstrate a progression of star formation from the optical star cluster center to the edge of the star-forming dust cloud. We derive lifetimes of a few 105 years for the YSO Stages I and II.
The Astrophysical Journal 03/2011; 730(2):78. · 6.02 Impact Factor
-
Lynn Redding Carlson,
Marta Sewilo,
Margaret Meixner,
Krista A. Romita,
Barbara Whitney,
Joseph L. Hora,
M. Cignoni,
E. Sabbi,
A. Nota,
M. Sirianni,
L. J. Smith,
K Gordon,
B. Babler,
S. Bracker,
J. S. Gallagher III,
M. Meade, K. Misselt,
A. Pasquali,
B. Shiao
[show abstract]
[hide abstract]
ABSTRACT: We present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical HST/ACS (F555W, F814W) and SMARTS/ANDICAM (V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8 micron and MIPS 24 micron). Combining this with IRSF (InfraRed Survey Facility) near-infrared photometry (J, H, Ks), we compare the young main sequence (MS) and pre-main sequence (PMS) populations prominent in the optical with the current young stellar object (YSO) populations revealed by the infrared (IR). We analyze the MS and PMS population with isochrones in color-magnitude diagrams to derive ages and masses. The optical data reveal ~565 PMS candidates, low mass Stage III YSOs. We characterize ~40 YSOs by fitting their spectral energy distributions (SEDs) to a grid of models (Robitaille et al. 2007) to derive luminosities, masses and evolutionary phase (Stage I-III). The higher resolution HST images reveal that ~70% of the YSO candidates are either multiples or protoclusters. For YSOs and PMS sources found in common, we find a consistency in the masses derived. We use the YSO mass function to derive a present-day star-formation rate of ~0.2-1.0 Msun/yr/kpc^2, similar to the rate derived from the optical star formation history suggesting a constant star formation rate for this region. We demonstrate a progression of star formation from the optical star cluster center to the edge of the star forming dust cloud. We derive lifetimes of a few 10^5 years for the YSO Stages I and II. Comment: 55 pages, 18 Figures; High resolution images available form author Accepted to ApJ
12/2010;
-
M. Meixner,
F. Galliano,
S. Hony,
J. Roman-Duval,
T. Robitaille,
P. Panuzzo,
M. Sauvage,
K Gordon,
C. Engelbracht, K. Misselt, [......],
B. Sargent,
M. Sewiło,
J. D. Simon,
R. Skibba,
L. J. Smith,
S. Srinivasan,
A. G. G. M. Tielens,
J. Th. van Loon,
B. Whitney,
P. M. Woods
[show abstract]
[hide abstract]
ABSTRACT: The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) of the Magellanic Clouds will use dust emission to investigate the life cycle of matter in both the Large and Small Magellanic Clouds (LMC and SMC). Using the Herschel Space Observatory's PACS and SPIRE photometry cameras, we imaged a 2x8 square degree strip through the LMC, at a position angle of ~22.5 degrees as part of the science demonstration phase of the Herschel mission. We present the data in all 5 Herschel bands: PACS 100 and 160 {\mu}m and SPIRE 250, 350 and 500 {\mu}m. We present two dust models that both adequately fit the spectral energy distribution for the entire strip and both reveal that the SPIRE 500 {\mu}m emission is in excess of the models by 6 to 17%. The SPIRE emission follows the distribution of the dust mass, which is derived from the model. The PAH-to-dust mass (f_PAH) image of the strip reveals a possible enhancement in the LMC bar in agreement with previous work. We compare the gas mass distribution derived from the HI 21 cm and CO J=1-0 line emission maps to the dust mass map from the models and derive gas-to-dust mass ratios (GDRs). The dust model, which uses the standard graphite and silicate optical properties for Galactic dust, has a very low GDR = 65(+15,-18) making it an unrealistic dust model for the LMC. Our second dust model, which uses amorphous carbon instead of graphite, has a flatter emissivity index in the submillimeter and results in a GDR = 287(+25,-42) that is more consistent with a GDR inferred from extinction. Comment: To be published in Astronomy & Astrophysics, Herschel First Results Issue
06/2010;
-
M. L. Boyer,
B. Sargent,
J. Th. van Loon,
S. Srinivasan,
G. C. Clayton,
F. Kemper,
L. J. Smith,
M Matsuura,
Paul M. Woods,
M. Marengo, [......],
K. D. Gordon,
S. Hony,
R. Indebetouw, K. Misselt,
K Okumura,
P. Panuzzo,
D. Riebel,
J. Roman-Duval,
M. Sauvage,
G. C. Sloan
[show abstract]
[hide abstract]
ABSTRACT: Massive evolved stars can produce large amounts of dust, and far-infrared (IR) data are essential for determining the contribution of cold dust to the total dust mass. Using Herschel, we search for cold dust in three very dusty massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red supergiant. We model the spectral energy distributions using radiative transfer codes and find that these three stars have mass-loss rates up to 10^-3 solar masses/year, suggesting that high-mass stars are important contributors to the life-cycle of dust. We found far-IR excesses in two objects, but these excesses appear to be associated with ISM and star-forming regions. Cold dust (T < 100 K) may thus not be an important contributor to the dust masses of evolved stars. Comment: accepted to A&A as part of the Herschel first results special issue
05/2010;
-
B. Lawton,
K. D. Gordon,
B. Babler,
M. Block,
A. D. Bolatto,
S. Bracker,
L. R. Carlson,
C. W. Engelbracht,
J. L. Hora,
R. Indebetouw, [......],
M. Meade,
M. Meixner, K. Misselt,
M. S. Oey,
J. M. Oliveira,
T. Robitaille,
M. Sewilo,
B. Shiao,
U. P. Vijh,
and B. Whitney
[show abstract]
[hide abstract]
ABSTRACT: H II regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. To study the H II regions, we compute the bolometric infrared flux, or total infrared (TIR), by integrating the flux from 8 to 500 μm. The TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and re-emitted across the mid-to-far-infrared (IR) spectrum. We aim to determine the monochromatic IR band that most accurately traces the TIR and produces an accurate obscured SFR over large spatial scales. We present the spatial analysis, via aperture/annulus photometry, of 16 Large Magellanic Cloud (LMC) and 16 Small Magellanic Cloud (SMC) H II region complexes using the Spitzer Space Telescope's IRAC (3.6, 4.5, 8 μm) and MIPS (24, 70, 160 μm) bands. Ultraviolet rocket data (1500 and 1900 Å) and SHASSA Hα data are also included. All data are convolved to the MIPS 160 μm resolution (40 arcsec full width at half-maximum), and apertures have a minimum radius of 35''. The IRAC, MIPS, UV, and Hα spatial analysis are compared with the spatial analysis of the TIR. We find that nearly all of the LMC and SMC H II region spectral energy distributions (SEDs) peak around 70 μm at all radii, from ~10 to ~400 pc from the central ionizing sources. As a result, we find the following: the sizes of H II regions as probed by 70 μm are approximately equal to the sizes as probed by TIR (70 pc in radius); the radial profile of the 70 μm flux, normalized by TIR, is constant at all radii (70 μm ~ 0.45TIR); the 1σ standard deviation of the 70 μm fluxes, normalized by TIR, is a lower fraction of the mean (0.05-0.12 out to ~220 pc) than the normalized 8, 24, and 160 μm normalized fluxes (0.12-0.52); and these results are the same for the LMC and the SMC. From these results, we argue that 70 μm is the most suitable IR band to use as a monochromatic obscured star formation indicator because it most accurately reproduces the TIR of H II regions in the LMC and SMC and over large spatial scales. We also explore the general trends of the 8, 24, 70, and 160 μm bands in the LMC and SMC H II region SEDs, radial surface brightness profiles, sizes, and normalized (by TIR) radial flux profiles. We derive an obscured SFR equation that is modified from the literature to use 70 μm luminosity, SFR(M ☉ yr–1) = 9.7(0.7) × 10–44 L 70(ergs s–1), which is applicable from 10 to 300 pc distance from the center of an H II region. We include an analysis of the spatial variations around H II regions between the obscured star formation indicators given by the IR and the unobscured star formation indicators given by UV and Hα. We compute obscured and unobscured SFRs using equations from the literature and examine the spatial variations of the SFRs around H II regions.
The Astrophysical Journal 05/2010; 716(1):453. · 6.02 Impact Factor
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S Kim,
E. Kwon,
S. C. Madden,
M. Meixner,
S. Hony,
P. Panuzzo,
M. Sauvage,
J. Roman-Duval,
K. D. Gordon,
C. Engelbracht, [......],
M. Galametz,
A. Hughes,
A Kawamura,
T Onishi,
D. Paradis,
A. Poglitsch,
W. T. Reach,
T. Robitaille,
M. Rubio,
A. G. G. M. Tielens
[show abstract]
[hide abstract]
ABSTRACT: We present clumps of dust emission from Herschel observations of the Large Magellanic Cloud (LMC) and their physical and statistical properties. We catalog cloud features seen in the dust emission from Herschel observations of the LMC, the Magellanic type irregular galaxy closest to the Milky Way, and compare these features with HI catalogs from the ATCA+Parkes HI survey. Using an automated cloud-finding algorithm, we identify clouds and clumps of dust emission and examine the cumulative mass distribution of the detected dust clouds. The mass of cold dust is determined from physical parameters that we derive by performing spectral energy distribution fits to 250, 350, and 500 micronm emission from SPIRE observations using DUSTY and GRASIL radiative transfer calculation with dust grain size distributions for graphite/silicate in low-metallicity extragalactic environments. The dust cloud mass spectrum follows a power law distribution with an exponent of gamma=-1.8 for clumps larger than 400 solar mass and is similar to the HI mass distribution. This is expected from the theory of ISM structure in the vicinity of star formation. Comment: 4 pages, 4 figures, to appear in A&A special issue
05/2010;
-
K. D. Gordon,
F. Galliano,
S. Hony,
J. -P. Bernard,
A. Bolatto,
C. Bot,
C. Engelbracht,
A. Hughes,
F. P. Israel,
F. Kemper, [......],
M. Meixner, K. Misselt,
K Okumura,
P. Panuzzo,
M. Rubio,
W. T. Reach,
J. Roman-Duval,
M. Sauvage,
R. Skibba,
A. G. G. M. Tielens
[show abstract]
[hide abstract]
ABSTRACT: The properties of the dust grains (e.g., temperature and mass) can be derived from fitting far-IR SEDs (>100 micron). Only with SPIRE on Herschel has it been possible to get high spatial resolution at 200 to 500 micron that is beyond the peak (~160 micron) of dust emission in most galaxies. We investigate the differences in the fitted dust temperatures and masses determined using only <200 micron data and then also including >200 micron data (new SPIRE observations) to determine how important having >200 micron data is for deriving these dust properties. We fit the 100 to 350 micron observations of the Large Magellanic Cloud (LMC) point-by-point with a model that consists of a single temperature and fixed emissivity law. The data used are existing observations at 100 and 160 micron (from IRAS and Spitzer) and new SPIRE observations of 1/4 of the LMC observed for the HERITAGE Key Project as part of the Herschel Science Demonstration phase. The dust temperatures and masses computed using only 100 and 160 micron data can differ by up to 10% and 36%, respectively, from those that also include the SPIRE 250 & 350 micron data. We find that an emissivity law proportional to lambda^-1.5 minimizes the 100-350 micron fractional residuals. We find that the emission at 500 micron is ~10% higher than expected from extrapolating the fits made at shorter wavelengths. We find the fractional 500 micron excess is weakly anti-correlated with MIPS 24 micron flux and the total gas surface density. This argues against a flux calibration error as the origin of the 500 micron excess. Our results do not allow us to distinguish between a systematic variation in the wavelength dependent emissivity law or a population of very cold dust only detectable at lambda > 500 micron for the origin of the 500 micron excess. Comment: 5 pages, 3 figurers, A&A, in press
05/2010;
-
S. Hony,
F. Galliano,
S. C. Madden,
P. Panuzzo,
M. Meixner,
C. Engelbracht, K. Misselt,
M. Galametz,
M. Sauvage,
J. Roman-Duval, [......],
A. Bolatto,
K Okumura,
C. -H. R. Chen,
R. Indebetouw,
F. P. Israel,
E. Kwon,
A. Li,
F. Kemper,
M. S. Oey,
M. Rubio
[show abstract]
[hide abstract]
ABSTRACT: We study the structure of the medium surrounding sites of high-mass star formation to determine the interrelation between the HII regions and the environment from which they were formed. The density distribution of the surroundings is key in determining how the radiation of the newly formed stars interacts with the surrounds in a way that allows it to be used as a star formation tracer. We present new Herschel/SPIRE 250, 350 and 500 mum data of LHA 120-N44 and LHA 120-N63 in the LMC. We construct average spectral energy distributions (SEDs) for annuli centered on the IR bright part of the star formation sites. The annuli cover ~10-~100 pc. We use a phenomenological dust model to fit these SEDs to derive the dust column densities, characterise the incident radiation field and the abundance of polycyclic aromatic hydrocarbon molecules. We see a factor 5 decrease in the radiation field energy density as a function of radial distance around N63. N44 does not show a systematic trend. We construct a simple geometrical model to derive the 3-D density profile of the surroundings of these two regions. Herschel/SPIRE data have proven very efficient in deriving the dust mass distribution. We find that the radiation field in the two sources behaves very differently. N63 is more or less spherically symmetric and the average radiation field drops with distance. N44 shows no systematic decrease of the radiation intensity which is probably due to the inhomogeneity of the surrounding molecular material and to the complex distribution of several star forming clusters in the region. Comment: Accepted for publication in A&A letters (Herschel special issue)
05/2010;
-
M Sewilo,
R Indebetouw,
L ~R Carlson,
B Whitney,
C -H ~R Chen,
M Meixner,
T Robitaille,
J ~T Loon,
J ~M Oliveira,
E Churchwell, [......],
P Panuzzo,
M Sauvage,
J Roman-Duval,
K Gordon,
C Engelbracht, K Misselt,
K Okumura,
T Beck,
J Hora,
P ~M Woods
VizieR Online Data Catalog. 04/2010; 351:89073.
-
M. L. Boyer,
J. Th. van Loon,
I. McDonald,
K. D. Gordon,
B. Babler,
M Block,
S. Bracker,
C. Engelbracht,
J. Hora,
R. Indebetouw,
M. Meade,
M. Meixner, K. Misselt,
M. Sewilo,
B. Shiao,
B. Whitney
[show abstract]
[hide abstract]
ABSTRACT: Using Spitzer IRAC observations from the SAGE-SMC Legacy program and archived Spitzer IRAC data, we investigate dust production in 47 Tuc, a nearby massive Galactic globular cluster. A previous study detected infrared excess, indicative of circumstellar dust, in a large population of stars in 47 Tuc, spanning the entire Red Giant Branch (RGB). We show that those results suffered from effects caused by stellar blending and imaging artifacts and that it is likely that no stars below about 1 mag from the tip of the RGB are producing dust. The only stars that appear to harbor dust are variable stars, which are also the coolest and most luminous stars in the cluster. Comment: Accepted for publication in ApJL
02/2010;
-
K Romita,
L ~R Carlson,
M Sewilo,
M Meixner,
E Sabbi,
K Gordon,
A Nota,
M Sirianni,
L ~J Smith,
C Leither, [......],
R Indebetouw,
D Kato,
J ~S Gallagher,
B Babler,
M Meade,
M ~S Oey,
M Cignoni,
M Tosi,
U Vijh,
R Walterbos
American Astronomical Society Meeting Abstracts #215; 01/2010
-
M Terrazas,
B Whitney,
M Meade,
B Babler,
R Indebetouw,
J Hora,
S Bracker,
C Engelbracht,
K Gordon,
M Block, K Misselt,
M Meixner,
M Sewilo,
B Shiao
American Astronomical Society Meeting Abstracts #215; 01/2010
-
M Meixner,
S Hony,
S Madden,
K Gordon,
C Engelbracht,
A ~G ~G ~M Tielens,
A Bolatto,
J Duval,
B Babler, K Misselt, [......],
M Sauvage,
S Srinivasan,
T Robitaille,
J Loon,
B Whitney,
J Oliveira,
J Hora,
C Bot,
R Skibba,
HERITAGE Team
American Astronomical Society Meeting Abstracts #215; 01/2010
-
D Rubin,
S Hony,
S ~C Madden,
A ~G ~G ~M Tielens,
M Meixner,
R Indebetouw,
W Reach,
A Ginsburg,
S Kim,
K Mochizuki, [......],
C ~W Engelbracht,
B -Q For,
K Gordon,
J ~L Hora,
C Leitherer,
M Meade, K Misselt,
M Sewilo,
U Vijh,
B Whitney
[show abstract]
[hide abstract]
ABSTRACT: Context. Photoelectric heating is a dominant heating mechanism for many phases of the interstellar medium. We study this mechanism throughout the Large Magellanic Cloud (LMC).
Aims. We aim to quantify the importance of the [C II] cooling line and the photoelectric heating process of various environments in the LMC and to investigate which parameters control the extent of photoelectric heating.
Methods. We use the BICE [C II] map and the Spitzer/SAGE infrared maps. We examine the spatial variations in the efficiency of photoelectric heating: photoelectric heating rate over power absorbed by grains, i.e. the observed [C II] line strength over the integrated infrared emission. We correlate the photoelectric heating efficiency and the emission from various dust constituents and study the variations as a function of H emission, dust temperatures, and the total infrared luminosity. The observed variations are interpreted in a theoretical framework. From this we estimate radiation field, gas temperature, and electron density.
Results. We find systematic variations in photoelectric efficiency. The highest efficiencies are found in the diffuse medium, while the lowest coincide with bright star-forming regions (~1.4 times lower). The [C II] line emission constitutes 1.32% of the far infrared luminosity across the whole of the LMC. We find correlations between the [C II] emission and ratios of the mid infrared and far infrared bands, which comprise various dust constituents. The correlations are interpreted in light of the spatial variations of the dust abundance and by the local environmental conditions that affect the dust emission properties. As a function of the total infrared surface brightness, S_(TIR), the [C II] surface brightness can be described as: S_([C II]) = 1.25 S^(0.69)_(TIR)[10^(-3) erg s^(-1) cm^(-2) sr^(-1)], for S_(TIR) ≳ 3.2 x 10^(-4) erg s^(-1) cm^(-2) sr^(-1). We provide a simple model of the photoelectric efficiency as a function of the total infrared luminosity. We find a power-law relation between radiation field and electron density, consistent with other studies. The [C II] emission is well-correlated with the 8 µm emission, suggesting that the polycyclic aromatic hydrocarbons play a dominant role in the photoelectric heating process.
åp. 02/2009; 494:647-661.
-
Uma P. Vijh,
M. Meixner,
B. Babler,
M. Block,
S. Bracker,
C. W. Engelbracht,
B. For,
K. Gordon,
J. Hora,
R. Indebetouw,
C. Leitherer,
M. Meade, K. Misselt,
M. Sewilo,
S. Srinivasan,
and B. Whitney
[show abstract]
[hide abstract]
ABSTRACT: We present initial results and source lists of variable sources in the Large Magellanic Cloud (LMC) for which we detect thermal infrared variability from the Surveying the Agents of a Galaxy's Evolution (SAGE) survey, which had two epochs of photometry separated by 3 months. The SAGE survey mapped a 7° × 7° region of the LMC using the Infrared Array Camera (IRAC) and the MIPS instruments on board Spitzer. Variable sources are identified using a combination of the IRAC 3.6, 4.5, 5.8, 8.0 μ bands and the MIPS 24 μ bands. An error-weighted flux difference between the two epochs is used to assess the variability. Of the ~3 million sources detected at both epochs, we find ~2000 variable sources for which we provide electronic catalogs. Most of the variable sources can be classified as asymptotic giant branch (AGB) stars. A large fraction (>66%) of the extreme AGB stars are variable and only smaller fractions of carbon-rich (6.1%) and oxygen-rich (2.0%) stars are detected as variable sources. We also detect a population of variable young stellar object candidates.
The Astronomical Journal 01/2009; 137(2):3139. · 4.03 Impact Factor
