2008A&A...484..205D


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.04CET12:12:36

2008A&A...484..205D - Astronomy and Astrophysics, volume 484, 205-223 (2008/6-2)

Extinction and dust/gas ratio in LMC molecular clouds.

DOBASHI K., BERNARD J.-P., HUGHES A., PARADIS D., REACH W.T. and KAWAMURA A.

Abstract (from CDS):

The goal of this paper is to measure the dust content and distribution in the Large Magellanic Cloud (LMC) by comparing extinction maps produced in the near-infrared wavelengths and the spatial distribution of the neutral and molecular gas, as traced by HI and CO observations. In order to derive an extinction map of the LMC, we have developed a new method to measure the color excess of dark clouds, using the 2MASS all-sky survey. Classical methods to measure the color excess (including the NICE method) tend to underestimate the true color excess if the clouds are significantly contaminated by unreddened foreground stars, as is the case in the LMC. We propose a new method that uses the color of the X percentile reddest stars and which is robust against such contamination. Using this method, it is possible to infer the positions of dark clouds with respect to the star distribution by comparing the observed color excess as a function of the percentile used and that predicted by a model. On the basis of the resulting extinction map, we perform a correlation analysis for a set of dark molecular clouds. Assuming similar infrared absorption properties for the dust in the neutral and molecular phases, we derive the absorption-to-column density ratio (AV)/(NH) and the CO-to-H2 conversion factor XCO. We show that (AV)/(NH) increases from the outskirts of the LMC towards the 30 Dor star-forming region. This can be explained either by a systematic increase of the dust abundance, or by the presence of an additional gas component not traced by HI or CO, but strongly correlated to the Hi distribution. If dust abundance is allowed to vary, the derived XCO factors for the selected regions are several times lower than those derived from a virial analysis of the CO data. This could indicate that molecular clouds in the LMC are not gravitationally bound, or that they are bounded by substantial external pressure. However, the XCO values derived from absorption can be reconciled with the virial results assuming a constant value for the dust abundance and the existence of an additional, unseen gas component. These results are in agreement with those derived for the LMC from diffuse far-infrared emission.

Abstract Copyright:

Journal keyword(s): ISM: dust, extinction - galaxies: Magellanic Clouds - infrared: ISM

Simbad objects: 28

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Number of rows : 28

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9707 1
2 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 5866 1
3 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 3647 0
4 [FKM2008] LMC N J0447-6713 MoC 04 47 35.9 -67 13 44           ~ 5 0
5 [FKM2008] LMC N J0449-6826 MoC 04 49 24.2 -68 26 50           ~ 5 0
6 [FKM2008] LMC N J0451-6704 MoC 04 51 58.0 -67 04 19           ~ 4 0
7 [FKM2008] LMC N J0453-6909 MoC 04 53 44.3 -69 09 22           ~ 5 0
8 [FKM2008] LMC N J0455-6634 MoC 04 55 49.8 -66 34 17           ~ 5 0
9 [FKM2008] LMC N J0513-6936 MoC 05 13 07.2 -69 36 15           ~ 6 0
10 [FKM2008] LMC N J0514-7010 MoC 05 14 17.0 -70 10 28           ~ 4 0
11 [FKM2008] LMC N J0516-6807 MoC 05 16 11.6 -68 07 14           ~ 7 0
12 [FKM2008] LMC N J0521-7000 MoC 05 21 10.3 -70 00 23           ~ 5 0
13 [FKM2008] LMC N J0521-6847 MoC 05 21 33.4 -68 47 33           ~ 5 0
14 [FKM2008] LMC N J0522-6756 MoC 05 22 33.5 -67 56 59           ~ 4 0
15 [FKM2008] LMC N J0523-6820 MoC 05 23 00.9 -68 20 43           ~ 5 0
16 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 15209 1
17 [FKM2008] LMC N J0525-6918 MoC 05 25 36.0 -69 18 16           ~ 5 0
18 [FKM2008] LMC N J0531-6830 MoC 05 31.7 -68 34           ~ 11 0
19 [FKM2008] LMC N J0532-6742 MoC 05 32 15.7 -67 42 35           ~ 5 0
20 [FKM2008] LMC N J0535-6735 MoC 05 35 31.6 -67 35 05           ~ 3 0
21 RMC 136 Cl* 05 38 42.396 -69 06 03.36           ~ 1778 1
22 [FKM2008] 186 MoC 05 39 00.20 -69 08 00.0           ~ 6 0
23 [FKM2008] LMC N J0539-6932 MoC 05 39 00.5 -69 32 13           ~ 5 0
24 [FKM2008] LMC N J0540-7008 MoC 05 40 07.2 -70 08 20           ~ 9 0
25 [FKM2008] 216 MoC 05 44.3 -69 24           ~ 16 0
26 [FKM2008] LMC N J0547-6953 MoC 05 47 55.1 -69 53 09           ~ 5 0
27 NAME Coalsack Nebula DNe 12 31 19 -63 44.6           ~ 246 0
28 Ass Cyg OB 7 As* 21 08 +47.6           ~ 198 0

    Equat.    Gal    SGal    Ecl

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2021.03.04-12:12:36

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