1997A&A...328..471I


Query : 1997A&A...328..471I

1997A&A...328..471I - Astronomy and Astrophysics, volume 328, 471-482 (1997/12-2)

H2 and its relation to CO in the LMC and other Magellanic irregular galaxies.

ISRAEL F.P.

Abstract (from CDS):

H2 column densities towards CO clouds in the LMC and SMC are estimated from their far-infrared surface brightness and HI column density. The newly derived H2 column densities imply N(H2)/I(CO) conversion factors (in units of 1021mol/cm2/(K.km/s)) XLMC=1.3±0.2 and XSMC=12±2. LMC and SMC contain total (warm) H2 masses of 1.0±0.3x108M and 0.75±0.25x108M respectively. Local H2/HI mass ratios similar to those in LMC and SMC are found in the magellanic irregulars NGC 55, 1569, 4214, 4449 and 6822 and in the extragalactic HII region complexes NGC 604, 595 and 5461 in M 33 and M 101 respectively. In these HII regions and in NGC 4449, we find X=1-2; in NGC 55, 4214 and 6822 X=3-6 again in units of 1021mol/cm2/(K.km/s). The post-starburst galaxy NGC 1569 has a very high value similar to that of the SMC. The CO-H2 conversion factor X is found to depend on both the ambient radiation field intensity per nucleon σFIR/NH and metallicity [O]/[H]: logX∝0.9±0.1log(σFIR)/(NH)-3.5±0.2log([O])/([H]). Neglecting dependency on radiation field, a reasonable approximation is also provided by logX∝-2.7±0.3log([O])/([H]). Milky Way values are consistent with these relations. This result is interpreted as the consequence of selective photodissociation of CO subjected to high radiation field energy densities and poor (self)shielding in low-metallicity environments, and especially the preferential destruction of diffuse CO in `interclump' gas. Although locally H2 may be the dominant ISM-component, the average global H2/HI mass ratio is 0.2±0.04 and the average H2 gas mass fraction is 0.12±0.02. Magellanic irregulars have warm molecular gas fractions very similar to those of our Galaxy, whereas other global properties (mass, luminosity, metallicity, CO luminosity) are very different.

Abstract Copyright:

Journal keyword(s): Galaxies: individual: LMC, SMC - Galaxies: ISM - irregular - Magellanic Clouds - Infrared: ISM: continuum - ISM: molecules

Simbad objects: 70

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Number of rows : 70
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NGC 55 GiG 00 14 53.602 -39 11 47.86 8.54 8.58 7.87 7.84   ~ 739 2
2 NGC 248 Cl* 00 45 24.07 -73 22 44.4           ~ 46 0
3 LHA 115-N 16 Em* 00 46 19.8 -73 23 33           ~ 25 0
4 [RGM91] SW-1 MoC 00 46 30 -73 21.1           ~ 4 0
5 LHA 115-N 17 Em* 00 46 35.9 -73 31 35           ~ 23 0
6 LHA 115-N 26 PN 00 48 08.624 -73 14 54.62 14.70 15.22 14.31   14.57 ~ 54 1
7 LHA 115-N 25 Cl* 00 48 09.12 -73 14 19.1           ~ 38 1
8 LIN 106 Em* 00 48 09.2567602656 -73 14 15.990591768   13.93 13.75 14.70 14.47 O8V 32 0
9 [RGM91] SW-2 MoC 00 48 17 -73 13.6           ~ 3 0
10 LHA 115-N 32 Y*O 00 49 39.4 -72 48 47           ~ 28 0
11 LHA 115-N 37 EmO 00 50 44.3 -72 46 40           ~ 25 0
12 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10194 1
13 [RGM91] NE-1 MoC 00 58 14 -71 51.3           ~ 3 0
14 [RGM91] NE-2 MoC 00 58 18 -72 06.3           ~ 2 0
15 SNR B0057-72.2 SNR 00 59 27.40 -72 10 10.7   12.37 12.57     ~ 225 0
16 LHA 115-N 72 HII 01 01 30.7 -71 51 08           ~ 14 0
17 [RGM91] NE-3 MoC 01 03 07 -71 58.9           ~ 3 0
18 SNR B0102-72.3 SNR 01 04 01.2 -72 01 52           ~ 367 1
19 NGC 595 HII 01 33 33.53 +30 41 29.8           ~ 197 0
20 NGC 604 HII 01 34 32.1 +30 47 01           ~ 568 0
21 NGC 1569 IG 04 30 49.186 +64 50 52.52 11.72 11.86 11.03     ~ 1196 3
22 LMC-CO 3 MoC 04 51.9 -69 15           ~ 5 0
23 NGC 1748 As* 04 54 24.6 -69 11 01   12.750 12.3     ~ 58 2
24 LHA 120-N 83B HII 04 54 25.2 -69 11 00           ~ 47 1
25 LHA 120-N 11 HII 04 56 51.4 -66 24 24           ~ 244 0
26 LMC-CO 6 MoC 04 57.7 -66 23           ~ 5 0
27 LMC-CO 11 MoC 05 08.1 -69 09           ~ 4 0
28 LHA 120-N 105A HII 05 09 34.3 -68 53 45           ~ 52 1
29 NGC 1858 Cl* 05 09 56.09 -68 54 06.2   9.76 9.88     ~ 79 3
30 LMC-CO 13 MoC 05 10.7 -68 55           ~ 4 0
31 LMC-CO 15 MoC 05 13.2 -69 33           ~ 4 0
32 LHA 120-N 113 HII 05 13 21.7 -69 21 33           ~ 103 1
33 LHA 120-N 30 HII 05 14 34.4 -67 34 03           ~ 16 0
34 LMC-CO 18 MoC 05 20.3 -70 00           ~ 4 0
35 LHA 120-N 44 EmO 05 22 06.9 -67 56 46           ~ 179 1
36 LMC-CO 19 MoC 05 22.3 -67 53           ~ 6 0
37 LMC-CO 20 MoC 05 22.8 -68 29           ~ 3 0
38 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 15990 1
39 LHA 120-N 132 HII 05 24 17 -69 39.9           ~ 12 0
40 NGC 1948 As* 05 24 20.00 -66 24 12.0   10.81 10.61     ~ 102 0
41 LMC-CO 22 MoC 05 25.2 -69 47           ~ 2 0
42 LMC-CO 23 MoC 05 26.1 -66 15           ~ 5 0
43 LHA 120-N 144 HII 05 26 42.5 -68 49 34           ~ 66 0
44 LMC-CO 26 MoC 05 31.1 -71 05           ~ 4 0
45 NGC 2018 As* 05 31 24.00 -71 04 24.0   10.91 10.89     ~ 103 1
46 [FKM2008] LMC N J0531-6830 MoC 05 31.7 -68 34           ~ 11 0
47 LHA 120-N 148 HII 05 32 10.9 -68 28 23           ~ 33 0
48 LMC-CO 29 MoC 05 32.4 -67 46           ~ 3 0
49 NGC 2014 As* 05 32 24 -67 41.3   9.17 8.97     ~ 75 0
50 LHA 120-N 150 HII 05 33 42.18 -68 45 59.2           ~ 15 0
51 LHA 120-N 64B HII 05 37 00 -66 21.0           ~ 11 0
52 LMC-CO 31 MoC 05 37.5 -66 21           ~ 3 0
53 NGC 2060 SNR 05 37 51.4466169456 -69 10 23.947092084   9.69 9.59     ~ 336 2
54 LMC-CO 32 MoC 05 37.9 -69 07           ~ 4 0
55 NAME 30 Dor Nebula SFR 05 38 36.0 -69 05 11           ~ 1099 2
56 LHA 120-N 159 HII 05 39 46.650 -69 45 39.94           ~ 261 2
57 LMC-CO 34 MoC 05 39.8 -71 16           ~ 4 0
58 LMC-CO 35 MoC 05 40.0 -70 11           ~ 5 0
59 LMC-CO 33 MoC 05 40.0 -69 46           ~ 6 0
60 LHA 120-N 176 HII 05 40 48.5 -70 10 06           ~ 12 0
61 LHA 120-N 214 EmO 05 40 54 -71 14.7           ~ 16 0
62 LHA 120-N 216 HII 05 40 57.3 -70 54 41           ~ 9 0
63 LMC-CO 36 MoC 05 41.0 -70 39           ~ 3 0
64 [FKM2008] 216 MoC 05 44.3 -69 24           ~ 16 0
65 LHA 120-N 167 HII 05 44 24.2 -69 22 43           ~ 20 0
66 NGC 4228 SBG 12 15 39.174 +36 19 36.80 10.63 10.30 9.93 9.74   ~ 912 1
67 NGC 4449 EmG 12 28 11.118 +44 05 36.81 10.11 9.98 9.64 9.45   ~ 1071 1
68 NGC 5461 HII 14 03 40.96 +54 19 02.4           ~ 178 0
69 NGC 6822 G 19 44 56.199 -14 47 51.29   18 8.1     ~ 1496 0
70 LHA 120-N 18A EmO ~ ~           ~ 2 0

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2022.05.20-20:04:37

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