2022A&A...666L...3G


Query : 2022A&A...666L...3G

2022A&A...666L...3G - Astronomy and Astrophysics, volume 666, L3 (2022/10-1)

Importance of radiative pumping for the excitation of the H2O submillimeter lines in galaxies.

GONZALEZ-ALFONSO E., FISCHER J., GOICOECHEA J.R., YANG C., PEREIRA-SANTAELLA M. and STEWART K.P.

Abstract (from CDS):

H2O submillimeter emission is a powerful diagnostic of the molecular interstellar medium in a variety of sources, including low- and high-mass star-forming regions of the Milky Way, and from local to high-redshift galaxies. However, the excitation mechanism of these lines in galaxies has been debated, preventing a basic consensus on the physical information that H2O provides. Radiative pumping due to H2O absorption of far-infrared photons emitted by dust and collisional excitation in dense shocked gas have both been proposed to explain the H2O emission. Here we propose two basic diagnostics to distinguish between the two mechanisms: First, the ortho-H2O 321 - 212 75 μm and the para-H2O 220 - 111 101 μm rotational lines in shock-excited regions are expected to be in emission, while when radiative pumping dominates, the two far-infrared lines are expected to be in absorption. Second, the radiative pumping scenario predicts, based on the statistical equilibrium of H2O level populations, that the apparent isotropic net rate of far-infrared absorption in the 321 ← 212 (75 μm) and 220 ← 111 (101 μm) lines should be higher than or equal to the apparent isotropic net rate of submillimeter emission in the 321 → 312 (1163 GHz) and 220 → 211 (1229 GHz) lines, respectively. Applying both criteria to all 16 galaxies and several Galactic high-mass star-forming regions in which the H2O 75 μm and submillimeter lines have been observed with Herschel/PACS and SPIRE, we show that in most (extra)galactic sources, the H2O submillimeter line excitation is dominated by far-infrared pumping, combined in some cases with collisional excitation of the lowest energy levels. Based on this finding, we revisit the interpretation of the correlation between the luminosity of the H2O 988 GHz line and the source luminosity in the combined Galactic and extragalactic sample.

Abstract Copyright: © E. González-Alfonso et al. 2022

Journal keyword(s): radiative transfer - line: formation - ISM: molecules - galaxies: ISM - infrared: galaxies - submillimeter: galaxies

Simbad objects: 26

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Number of rows : 26
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 NGC 253 SyG 00 47 33.134 -25 17 19.68   8.03   6.94 8.1 ~ 3344 2
2 M 77 Sy2 02 42 40.7091669408 -00 00 47.859690204 9.70 9.61 8.87 10.1 9.9 ~ 4610 2
3 LEDA 17155 Sy2 05 21 01.3994605776 -25 21 45.321827832   15.47 14.75     ~ 501 0
4 NAME Orion-KL SFR 05 35 14.16 -05 22 21.5           ~ 2299 1
5 NAME IRAS F08572+3915 NW LIN 09 00 25.364 +39 03 54.23     16.66     ~ 421 1
6 M 82 AGN 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 5869 6
7 NAME NGC 3690 East AGN 11 28 33.07 +58 33 54.2   11.8       ~ 631 4
8 ESO 320-30 EmG 11 53 11.722 -39 07 48.72   13.30   11.86   ~ 186 1
9 NGC 4355 Sy2 12 26 54.6206739120 -00 52 39.421212996   14.21 13.37     ~ 492 2
10 Mrk 231 Sy1 12 56 14.2341182928 +56 52 25.238373852   14.68 13.84     ~ 1990 3
11 NGC 4945 Sy2 13 05 27.279 -49 28 04.44   9.31 14.40 7.55   ~ 1478 2
12 2MASX J13150638-5509225 Sy2 13 15 06.383 -55 09 22.60   17.3       ~ 149 0
13 Mrk 273 Sy2 13 44 42.1781 +55 53 12.819   15.68 14.91     ~ 916 3
14 Z 49-57 GiC 15 13 13.0927 +07 13 31.850   15.5       ~ 238 1
15 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2963 4
16 NGC 6240 Sy2 16 52 58.9 +02 24 03   14.31 13.37     ~ 1640 2
17 LEDA 60189 LIN 17 23 21.943 -00 17 00.96   15.1       ~ 425 0
18 NAME Galactic Circumnuclear Disk PoG 17 45 40.0 -29 00 28           ~ 162 0
19 NAME Sgr A* X 17 45 40.03599 -29 00 28.1699           ~ 4400 3
20 NAME Sgr B2 (North) Rad 17 47 20.2 -28 22 21           ~ 675 1
21 NAME Sgr B2 Main Rad 17 47 20.5 -28 23 06           ~ 408 1
22 W 31c HII 18 10 29.1 -19 56 05           ~ 341 0
23 GCNM 23 Y*O 18 29 49.63 +01 15 21.9           ~ 273 2
24 W 49n HII 19 10 13.2 +09 06 12           ~ 470 3
25 W 51 SNR 19 23 50 +14 06.0           ~ 1278 1
26 NGC 7469 Sy1 23 03 15.6 +08 52 26 12.60 13.00 12.34     ~ 2101 3

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