Modeling the H2O submillimeter emission in extragalactic sources

Abstract

Recent observational studies have shown that H2O emission at (rest) submillimeter wavelengths is ubiquitous in infrared galaxies, both in the local and in the early Universe, suggestive of far-infrared pumping of H2O by dust in warm regions. In this work, models are presented that show that (i) the highest-lying H2O lines (E_{upper}>400 K) are formed in very warm (T_{dust}>~90 K) regions and require high H2O columns (N_{H2O}>~3x10^{17} cm^{-2}), while lower lying lines can be efficiently excited with T_{dust}~45-75 K and N_{H2O}~(0.5-2)x10^{17} cm^{-2}; (ii) significant collisional excitation of the lowest lying (E_{upper}<200 K) levels, which enhances the overall L_{H2O}-L_{IR} ratios, is identified in sources where the ground-state para-H2O 1_{11}-0_{00} line is detected in emission; (iii) the H2O-to-infrared (8-1000 um) luminosity ratio is expected to decrease with increasing T_{dust} for all lines with E_{upper}<~300 K, as has recently been reported in a sample of LIRGs, but increases with T_{dust} for the highest lying H2O lines (E_{upper}>400 K); (iv) we find theoretical upper limits for L_{H2O}/L_{IR} in warm environments, owing to H2O line saturation; (v) individual models are presented for two very different prototypical galaxies, the Seyfert 2 galaxy NGC 1068 and the nearest ultraluminous infrared galaxy Arp 220, showing that the excited submillimeter H2O emission is dominated by far-infrared pumping in both cases; (vi) the L_{H2O}-L_{IR} correlation previously reported in observational studies indicates depletion or exhaustion time scales, t_{dep}=Sigma_{gas}/Sigma_{SFR}, of <~12 Myr for star-forming sources where lines up to E_{upper}=300 K are detected, in agreement with the values previously found for (U)LIRGs from HCN millimeter emission...

13 pages, 13 figures

References in corpus (6)

• A Dust-Obscured Massive Maximum-Starburst Galaxy at a Redshift of 6.34
• SMA Imaging of CO(3-2) Line and 860 micron Continuum of Arp 220 : Tracing the Spatial Distribution of Luminosity
• Black hole in the West Nucleus of Arp 220
• Far-Infrared Properties of Spitzer-selected Luminous Starbursts
• A gravitationally lensed water maser in the early Universe
• High-excitation OH and H_2O lines in Markarian 231: the molecular signatures of compact far-infrared continuum sources

Cited by in corpus (26)

• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• Molecular outflows in local ULIRGs: energetics from multi-transition OH analysis
• Molecular line emission in NGC1068 imaged with ALMA: II. The chemistry of the dense molecular gas
• Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z~2-4 as probed by multi-J CO lines
• A Hard X-ray Test of HCN Enhancements as a Tracer of Embedded Black Hole Growth
• Microwave Background Temperature at a Redshift of 6.34 from H2O Absorption
• Submillimeter H2O and H2O+ emission in lensed ultra- and hyper-luminous infrared galaxies at z ~ 2-4
• Bright [CII] 158$\mu$m emission in a quasar host galaxy at $z=6.54$
• An ALMA multi-line survey of the ISM in two quasar host-companion galaxy pairs at $z>6$
• HIFI Spectroscopy of ${\mathrm{H}}_2\mathrm{O}$ submm Lines in Nuclei of Actively Star Forming Galaxies
• Probing the full CO spectral line energy distribution (SLED) in the nuclear region of a quasar-starburst system at $z=6.003$
• CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales
• The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120-5453
• Close-up view of a luminous star-forming galaxy at z=2.95
• HERUS: A CO Atlas from SPIRE Spectroscopy of local ULIRGs
• First detection of the 448 GHz ortho-H2O line at high redshift: probing the structure of a starburst nucleus at z = 3.63
• Inflowing gas onto a compact obscured nucleus in Arp 299A: Herschel spectroscopic studies of H2O and OH
• A proto-pseudobulge in ESO 320-G030 fed by a massive molecular inflow driven by a nuclear bar
• The ionization rates of galactic nuclei and disks from Herschel/HIFI observations of water and its associated ions
• The ramp-up of interstellar medium enrichment at z>4
• Smoke on the water: CO and H2O in a circumnuclear disc around a quasar at redshift 2.64
• Unveiling the warm dense ISM in $z>6$ quasar host galaxies via water vapor emission
• The importance of radiative pumping on the emission of the H_2O submillimeter lines in galaxies
• Detection of H2O and OH+ in z>3 Hot Dust-Obscured Galaxies
• Herschel and Odin observations of H2O, CO, CH, CH+, and NII in the barred spiral galaxy NGC 1365. Bar-induced activity in the outer and inner circumnuclear tori
• Herschel water maps towards the vicinity of the black hole Sgr A*