2012ApJ...751...10P

Query : 2012ApJ...751...10P

2012ApJ...751...10P - Astrophys. J., 751, 10 (2012/May-3)

The molecular gas in luminous infrared galaxies. II. Extreme physical conditions and their effects on the XcoFactor.

PAPADOPOULOS P.P., VAN DER WERF P., XILOURIS E., ISAAK K.G. and GAO Y.

Abstract (from CDS):

In this work, we conclude the analysis of our CO line survey of luminous infrared galaxies (LIRGs: LIR ≳ 1011 L☉) in the local universe (Paper I) by focusing on the influence of their average interstellar medium (ISM) properties on the total molecular gas mass estimates via the so-called Xco= M(H2)/L_co, 1-0_factor. One-phase radiative transfer models of the global CO spectral line energy distributions (SLEDs) yield an Xco distribution with co> ∼ (0.6±0.2) M☉(K km/s pc2)–1 over a significant range of average gas densities, temperatures, and dynamic states. The latter emerges as the most important parameter in determining Xco, with unbound states yielding low values and self-gravitating states yielding the highest ones. Nevertheless, in many (U)LIRGs where available higher-J CO lines (J = 3-2, 4-3, and/or J = 6-5) or HCN line data from the literature allow a separate assessment of the gas mass at high densities ( ≥ 104/cm3) rather than a simple one-phase analysis, we find that near-Galactic Xco∼ (3-6) M☉(K km/s pc2)–1 values become possible. We further show that in the highly turbulent molecular gas in ULIRGs, a high-density component will be common and can be massive enough for its high Xco to dominate the average value for the entire galaxy. Using solely low-J CO lines to constrain Xco in such environments (as has been the practice up until now) may have thus resulted in systematic underestimates of molecular gas mass in ULIRGs, as such lines are dominated by a warm, diffuse, and unbound gas phase with low Xco but very little mass. Only well-sampled high-J CO SLEDs (J = 3-2 and higher) and/or multi-J observations of heavy rotor molecules (e.g., HCN) can circumvent such a bias, and the latter type of observations may have actually provided early evidence of it in local ULIRGs. The only way that the global Xco of such systems could be significantly lower than Galactic is if the average dynamic state of the dense gas is strongly gravitationally unbound. This is an unlikely possibility that must nevertheless be examined, with lines of rare isotopologues of high gas density tracers (e.g., H13CN, high-J 13CO lines) being very valuable in yielding (along with the lines of the main isotopes) such constraints. For less IR-luminous, disk-dominated systems, we find that the galaxy-averaged Xco deduced by one-phase models of global SLEDs can also underestimate the total molecular gas mass when much of it lies in an star-formation-quiescent phase extending beyond a central star-forming region. This is because such a phase (and its large Xco) remains inconspicuous in global CO SLEDs. Finally, detailed studies of a subsample of galaxies find ULIRGs with large amounts (∼109 M☉) of very warm ( ≥ 100 K) and dense gas ( ≳ 105/cm3), which could represent a serious challenge to photon-dominated regions as the main energy portals in the molecular ISM of such systems.

Abstract Copyright: ∼

Journal keyword(s): galaxies: active - galaxies: ISM - galaxies: starburst - ISM: molecules - radiation mechanisms: general - techniques: spectroscopic

Errata: erratum vol. 758, art. 71 (2012)

Simbad objects: 43

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Number of rows : 43
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024 		#notes
1 NPM1G +40.0002 Sy2 00 08 20.3675391072 +40 37 55.922085984     16.8     ~ 45 0
2 NGC 157 Sy2 00 34 46.7879913696 -08 23 47.273597952   11.0 19.00 10.03 10.7 ~ 352 0
3 M 31 AGN 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 12666 1
4 Mrk 1502 Sy1 00 53 34.9331107632 +12 41 35.929269132   14.41 14.03     ~ 1169 1
5 NGC 828 rG 02 10 09.5469097104 +39 11 25.233638244   13.0       ~ 165 1
6 NGC 985 Sy1 02 34 37.882 -08 47 17.02   14.64 14.28 12.9   ~ 412 0
7 M 77 Sy2 02 42 40.7091669408 -00 00 47.859690204 9.70 9.61 8.87 10.1 9.9 ~ 4608 2
8 2MASX J02513583+4315117 LIN 02 51 35.8187772168 +43 15 11.772126504   18.09 17.36     ~ 56 0
9 IRAS 03359+1523 G 03 38 47.1918750504 +15 32 53.853117504   16.3       ~ 107 0
10 ZW VII 31 G 05 16 46.384 +79 40 12.63   15.8       ~ 151 0
11 LEDA 17155 Sy2 05 21 01.3994605776 -25 21 45.321827832   15.47 14.75     ~ 499 0
12 NAME Ori A MoC 05 38 -07.1           ~ 3015 0
13 NAME Ori B MoC 05 41 43.0 -01 54 44           ~ 1378 0
14 NAME Orion Molecular Cloud MoC 05 56 -01.8           ~ 1101 1
15 IC 443 SNR 06 17 00.0000000 +22 34 11.998901           ~ 1237 1
16 2MASX J08065079+5235074 EmG 08 06 50.8068272808 +52 35 07.225461240           ~ 22 0
17 NAME IRAS F08572+3915 NW LIN 09 00 25.364 +39 03 54.23     16.66     ~ 420 1
18 UGC 4881 IG 09 15 55.5 +44 19 58   14.9       ~ 169 0
19 UGC 5101 Sy2 09 35 51.6045544584 +61 21 11.589382368   15.20 15.50     ~ 573 4
20 M 82 AGN 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 5865 6
21 NGC 3310 AGN 10 38 45.85707 +53 30 11.8940   12.45 12.15     ~ 774 1
22 LEDA 33083 LIN 10 59 18.128 +24 32 34.74   15.7       ~ 275 1
23 IC 694 AG? 11 28 27.312 +58 34 42.29   18.2       ~ 252 2
24 NGC 3690 IG 11 28 31.0 +58 33 41   13.19 12.86     ~ 978 4
25 NAME Antennae IG 12 01 53.170 -18 52 37.92           ~ 1694 0
26 LEDA 39024 LIN 12 13 46.107 +02 48 41.50           ~ 355 1
27 Mrk 231 Sy1 12 56 14.2341182928 +56 52 25.238373852   14.68 13.84     ~ 1989 3
28 IC 883 SBG 13 20 35.4 +34 08 22   14.8       ~ 401 1
29 NGC 5135 Sy2 13 25 44.059 -29 50 01.24   12.58 13.35 11.53 12.2 ~ 475 1
30 M 51 Sy2 13 29 52.698 +47 11 42.93   9.26 8.36 8.40   ~ 4332 4
31 Mrk 273 Sy2 13 44 42.1781 +55 53 12.819   15.68 14.91     ~ 914 3
32 3C 293.0 BLL 13 52 17.8719816576 +31 26 46.487381604   16.10 15.10     ~ 472 3
33 LEDA 52270 Sy1 14 37 38.2867288488 -15 00 24.087592692   16.58 16.40     ~ 277 1
34 Z 49-57 GiC 15 13 13.0927 +07 13 31.850   15.5       ~ 238 1
35 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2961 4
36 NGC 6240 Sy2 16 52 58.9 +02 24 03   14.31 13.37     ~ 1638 2
37 LEDA 60189 LIN 17 23 21.943 -00 17 00.96   15.1       ~ 425 0
38 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 14436 0
39 SNR G034.6-00.5 SNR 18 56 10.650 +01 13 21.30           ~ 965 2
40 NAME South America H2G 22 51 49.307 -17 52 23.96   16.97       ~ 328 3
41 NGC 7469 Sy1 23 03 15.6 +08 52 26 12.60 13.00 12.34     ~ 2098 3
42 IC 5283 GiP 23 03 17.9800776408 +08 53 36.838944528   15.2       ~ 120 1
43 LEDA 90429 SyG 23 39 01.274 +36 21 08.77   16.17       ~ 217 1

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