Water vapor in nearby infrared galaxies as probed by Herschel

Chentao Yang; Yu Gao; A. Omont; Daizhong Liu; K. G. Isaak; D. Downes; P. P. van der Werf; Nanyao Lu

doi:10.1088/2041-8205/771/2/L24

paper

Water vapor in nearby infrared galaxies as probed by Herschel

arXiv:1305.6351 · doi:10.1088/2041-8205/771/2/L24

Abstract

We report the first systematic study of the submillimeter water vapor rotational emission lines in infrared (IR) galaxies based on the Fourier Transform Spectrometer (FTS) data of {\it Herschel} SPIRE. Among the 176 galaxies with publicly available FTS data, 45 have at least one H $_{2}$ O emission line detected. The H $_{2}$ O line luminosities range from $\sim 1 \times 1 0^{5}$ $L_{⊙}$ to $\sim 5 \times 1 0^{7} L_{⊙}$ while the total IR luminosities ( $L_{IR}$ ) have a similar spread ( $\sim 1 - 300 \times 1 0^{10} L_{⊙}$ ). In addition, emission lines of H $_{2}$ O $^{+}$ and H $_{2}^{18}$ O are also detected. H $_{2}$ O is found, for most galaxies, to be the strongest molecular emitter after CO in FTS spectra. The luminosity of the five most important H $_{2}$ O lines is near-linearly correlated with $L_{IR}$ , no matter whether strong active galactic nucleus signature is present or not. However, the luminosity of H $_{2}$ O( $2_{11} - 2_{02}$ ) and H $_{2}$ O( $2_{20} - 2_{11}$ ) appears to increase slightly faster than linear with $L_{IR}$ . Although the slope turns out to be slightly steeper when $z \sim 2 - 4$ ULIRGs are included, the correlation is still closely linear. We find that $L_{H_{2} O} / L_{IR}$ decreases with increasing $f_{25} / f_{60}$ , but see no dependence on $f_{60} / f_{100}$ , possibly indicating that very warm dust contributes little to the excitation of the submillimeter H $_{2}$ O lines. The average spectral line energy distribution (SLED) of the entire sample is consistent with individual SLEDs and the IR pumping plus collisional excitation model, showing that the strongest lines are H $_{2}$ O( $2_{02} - 1_{11}$ ) and H $_{2}$ O( $3_{21} - 3_{12}$ ).

6 pages, 3 figures, 2 tables, ApJ Letters in press, very minor edit

Water vapor in nearby infrared galaxies as probed by Herschel

Abstract

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