Submillimeter H₂O and H₂O⁺emission in lensed ultra- and hyper-luminous infrared galaxies atz ~ 2–4

Abstract

We report rest-frame submillimeter H 2 O emission line observations of 11 ultra-or hyper-luminous infrared galaxies (ULIRGs or HyLIRGs) at z ∼ 2-4 selected among the brightest lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we have detected 14 new H 2 O emission lines. These include five 3 21 -3 12 ortho-H 2 O lines (E up /k = 305 K) and nine J = 2 para-H 2 O lines, either 2 02 -1 11 (E up /k = 101 K) or 2 11 -2 02 (E up /k = 137 K). The apparent luminosities of the H 2 O emission lines are µL H 2 O ∼ 6-21 × 10 8 L (3 < µ < 15, where µ is the lens magnification factor), with velocity-integrated line fluxes ranging from 4-15 Jy km s −1 . We have also observed CO emission lines using EMIR on the IRAM 30m telescope in seven sources (most of those have not yet had their CO emission lines observed). The velocity widths for CO and H 2 O lines are found to be similar, generally within 1 σ errors in the same source. With almost comparable integrated flux densities to those of the high-J CO line (ratios range from 0.4 to 1.1), H 2 O is found to be among the strongest molecular emitters in high-redshift Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H 2 O (L H 2 O ) and infrared (L IR ) that L H 2 O ∼L IR 1.1-1.2 , with our new detections. This correlation could be explained by a dominant role of far-infrared pumping in the H 2 O excitation. Modelling reveals that the far-infrared radiation fields have warm dust temperature T warm ∼ 45-75 K, H 2 O column density per unit velocity interval N H 2 O /∆V 0.3 × 10 15 cm −2 km −1 s and 100 µm continuum opacity τ 100 > 1 (optically thick), indicating that H 2 O is likely to trace highly obscured warm dense gas. However, further observations of J ≥ 4 H 2 O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H 2 O + emission in three sources. A tight correlation between L H 2 O and L H 2 O + has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H 2 O + and H 2 O suggests that cosmic rays generated by strong star formation are possibly driving the H 2 O + formation.

Probing the Full CO Spectral Line Energy Distribution (SLED) in the Nuclear Region of a Quasar-starburst System at z = 6.003

“…J0439+1634 was detected in the H 2 O(3 2,1 − 3 1,2 ) emission, and suggest a L H2O(32,1−31,2) /L CO(6−5) ratio of 1.23 ± 0.22. Adopting a mean H 2 O(3 2,1 −3 1,2 )/H 2 O(2 0,2 −1 1,1 ) of 1.4 estimated from SMGs in Yang et al (2016), we estimate the L H2O /L CO (6−5) ratio in J0439+1634 of 0.86 ± 0.17, which is comparable to the value of J2310+1855.…”

“…We find in the velocity maps that CO (8 − 7), (9 − 8) and H2O(20,2 − 11,1) generally follow the velocity gradient observed from [C II] 158µm (Wang et al 2013) from northeast to southwest. (Yang et al 2016) and APM 08279+5255 (Bradford et al 2011) from left to right. Note that all the luminosities plotted are intrinsic luminosities that have been corrected for lensing.…”

“…Recent studies found linear relations between the infrared luminosity and the H 2 O(2 0,2 − 1 1,1 ) luminosity in local and high redshift infrared bright systems, suggesting the excitation of this water transition is dominated by infrared pumping (van der Werf et al 2011;Yang et al 2016;Jarugula et al 2019). We first compare the H 2 O detection of J2310+1855 to the local and high redshift (U)LIRGs.…”

HIFI Spectroscopy of H2O Submillimeter Lines in Nuclei of Actively Star-forming Galaxies

“…This implies that the modest spectral resolution of the Herschel/ SPIRE spectroscopy results in severe limitations for the detections of low-excitation lines and limits the construction of excitation models, since emission and absorption from different ISM components along the line of sight are averaged. Recently, water has been detected in high-z sources with both high spectral and spatial resolution afforded by ALMA and NOEMA (e.g., Omont et al 2011Omont et al , 2013Combes et al 2012;Yang et al 2016). The results confirm that H O 2 lines are among the strongest molecular lines in high-z ultraluminous starburst galaxies, with intensities almost comparable to those of the high-J CO lines (e.g., Omont et al 2013;Yang et al 2016).…”

“…Recently, water has been detected in high-z sources with both high spectral and spatial resolution afforded by ALMA and NOEMA (e.g., Omont et al 2011Omont et al , 2013Combes et al 2012;Yang et al 2016). The results confirm that H O 2 lines are among the strongest molecular lines in high-z ultraluminous starburst galaxies, with intensities almost comparable to those of the high-J CO lines (e.g., Omont et al 2013;Yang et al 2016). In order to obtain a better understanding of observed water spectra in the early universe, a comprehensive analysis of water line shapes in the local universe is required.…”