2010A&A...512A..68G


Query : 2010A&A...512A..68G

2010A&A...512A..68G - Astronomy and Astrophysics, volume 512, A68-68 (2010/3-1)

The molecular interstellar medium of the Local group dwarf NGC 6822. The molecular ISM of NGC 6822.

GRATIER P., BRAINE J., RODRIGUEZ-FERNANDEZ N.J., ISRAEL F.P., SCHUSTER K.F., BROUILLET N. and GARDAN E.

Abstract (from CDS):

Do molecular clouds collapse to form stars at the same rate in all environments? In large spiral galaxies, the rate of transformation of H2 into stars varies little. However, the SFE in distant objects (z∼1) is much higher than in the large spiral disks that dominate the local universe. Some small Local Group galaxies share at least some of the characteristics of intermediate-redshift objects, such as size or color. Recent work has suggested that the star formation efficiency (SFE, defined as the star formation rate per unit H2) in local Dwarf galaxies may be as high as in the distant objects. A fundamental difficulty in these studies is the independent measure of the H2 mass in metal-deficient environments. At 490kpc, NGC 6822 is an excellent choice for this study; it has been mapped in the CO(2-1) line using the multibeam receiver HERA on the 30m IRAM telescope, yielding the largest sample of giant molecular clouds (GMCs) in this galaxy. Despite the much lower metallicity, we find no clear difference in the properties of the GMCs in NGC 6822 and those in the Milky Way except lower CO luminosities for a given mass. Several independent methods indicate that the total H2 mass in NGC 6822 is about 5x106M in the area we mapped and less than 107M in the whole galaxy. This corresponds to a N(H2)/ICO≃4x1021cm–2/(K.km/s) over large scales, such as would be observed in distant objects, and half that in individual GMCs. No evidence was found for H2 without CO emission. Our simulations of the radiative transfer in clouds are entirely compatible with these N(H2)/ICO values. The SFE implied is a factor 5-10 higher than what is observed in large local universe spirals. The CO observations presented here also provide a high-resolution datacube (1500a.u. for the assumed 100 pc distance, 0.41km/s velocity resolution) of a local molecular cloud along the line of sight.

Abstract Copyright:

Journal keyword(s): galaxies: individual: NGC 6822 - Local Group - galaxies: evolution - galaxies: ISM - ISM: clouds - stars: formation

Nomenclature: Table 2: [GBR2010] GMC NGC6822 NN (Nos 1-15).

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 - 2023
#notes
1 IC 10 G 00 20 23.16 +59 17 34.7   13.6 9.5     ~ 1074 0
2 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 12039 1
3 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10475 1
4 M 33 GiG 01 33 50.8965749232 +30 39 36.630403128 6.17 6.27 5.72     ~ 5578 1
5 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 16422 1
6 NGC 2403 AGN 07 36 51.3381434280 +65 36 09.650825640 9.31 8.84 8.38 8.19   ~ 1717 1
7 NGC 4414 GiG 12 26 27.1276893168 +31 13 24.626206488 11.12 10.96 10.12     ~ 547 2
8 M 51 GiP 13 29 52.698 +47 11 42.93   9.26 8.36 8.40   ~ 4141 4
9 [H25] V HII 19 44 52.84 -14 43 09.8           ~ 59 0
10 [GBR2010] GMC NGC6822 2 MoC 19 44 53.1 -14 43 10           ~ 1 0
11 [GBR2010] GMC NGC6822 1 MoC 19 44 54.6 -14 43 11           ~ 1 0
12 NGC 6822 G 19 44 56.199 -14 47 51.29   18 8.1     ~ 1507 0
13 [GBR2010] GMC NGC6822 7 MoC 19 44 56.7 -14 42 12           ~ 1 0
14 [GBR2010] GMC NGC6822 10 MoC 19 44 57.8 -14 47 44           ~ 1 0
15 [GBR2010] GMC NGC6822 9 MoC 19 44 58.3 -14 47 17           ~ 1 0
16 [GBR2010] GMC NGC6822 6 MoC 19 44 59.8 -14 47 54           ~ 1 0
17 [GBR2010] GMC NGC6822 8 MoC 19 44 59.9 -14 47 10           ~ 1 0
18 [GBR2010] GMC NGC6822 5 MoC 19 45 00.1 -14 47 47           ~ 1 0
19 [GBR2010] GMC NGC6822 4 MoC 19 45 00.3 -14 47 46           ~ 1 0
20 [GBR2010] GMC NGC6822 13 MoC 19 45 01.07 -14 42 07.0           ~ 1 0
21 [GBR2010] GMC NGC6822 12 MoC 19 45 01.47 -14 43 24.0           ~ 1 0
22 [GBR2010] GMC NGC6822 3 MoC 19 45 03.3 -14 47 12           ~ 1 0
23 KD D26 HII 19 45 05.2 -14 43 13           ~ 48 0
24 [GBR2010] GMC NGC6822 14 MoC 19 45 19.87 -14 41 59.0           ~ 1 0
25 [GBR2010] GMC NGC6822 11 MoC 19 45 22.1 -14 44 41           ~ 1 0
26 [GBR2010] GMC NGC6822 15 MoC 19 45 23.53 -14 47 14.0           ~ 1 0
27 NGC 6946 H2G 20 34 52.332 +60 09 13.24   10.5       ~ 2413 2
28 NAME Local Group GrG ~ ~           ~ 7849 0

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2022.12.09-20:47:35

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