First detection of the 448 GHz ortho-H₂O line at high redshift: probing the structure of a starburst nucleus at z = 3.63

Abstract

Submillimeter rotational lines of H 2 O are a powerful probe in warm gas regions of the interstellar medium (ISM), tracing scales and structures ranging from kiloparsec disks to the most compact and dust-obscured regions of galactic nuclei. The ortho-H 2 O(4 23 -3 30 ) line at 448 GHz, which was recently detected in a local luminous infrared galaxy (Pereira-Santaella et al. 2017), offers a unique constraint on the excitation conditions and ISM properties in deeply buried galaxy nuclei since the line requires high far-infrared optical depths to be excited. In this letter, we report the first high-redshift detection of the 448 GHz H 2 O(4 23 -3 30 ) line using ALMA, in a strongly lensed submillimeter galaxy (SMG) at z = 3.63. After correcting for magnification, the luminosity of the 448 GHz H 2 O line is ∼ 10 6 L . In combination with three other previously detected H 2 O lines, we build a model that "resolves" the dusty ISM structure of the SMG, and find that it is composed of a ∼ 1 kpc optically thin (optical depth at 100 µm τ 100 ∼ 0.3) disk component with dust temperature T dust ≈ 50 K emitting a total infrared power of 5 × 10 12 L with surface density Σ IR = 4 × 10 11 L kpc −2 , and a very compact (0.1 kpc) heavily dust-obscured (τ 100 1) nuclear core with very warm dust (100 K) and Σ IR = 8 × 10 12 L kpc −2 . The H 2 O abundance in the core component, X H 2 O ∼ (0.3-5) × 10 −5 , is at least one order of magnitude higher than in the disk component. The optically thick core has the characteristic properties of an Eddington-limited starburst, providing evidence that radiation pressure on dust is capable of supporting the ISM in buried nuclei at high redshifts. The multi-component ISM structure revealed by our models illustrates that dust and molecules such as H 2 O are present in regions characterized by highly differing conditions and scales, extending from the nucleus to more extended regions of SMGs.

Planck’s Dusty GEMS

“…This could correspond to a multiphase ISM, with one or multiple very dense (n > 10 5 cm −3 ) and spatially-concentrated nuclear cores emitting HCN, HCO + , and HNC lines and hosting the Eddington-limited starburst identified in C17a, which is distributed over an extended, gas-rich and lower surface brightness disk-like component dominating the low-to mid-J CO emission. Such ISM structures are common in low-redshift ULIRGs and a similar scenario has been recently proposed by Yang et al (2020) for a z = 3.6 SMG with dense-gas conditions probed by H 2 O lines.…”

ALMA [N ii] 205 μm Imaging Spectroscopy of the Lensed Submillimeter Galaxy ID 141 at Redshift 4.24

“…The Sérsic index (n S0 ) of the source galaxy is 0.95, which is between 0.5 (corresponding to a Gaussian light profile) and 1.0 (corresponding to an exponential disk); this indicates the morphology of the source is close to an exponential disk or a combination of the typical Gaussian and exponential disk profile. A dust morphology comprised of a core plus a disk structure is also found in SMG G09v1.97 at z=3.63 (Yang et al 2020). The half-light radius of the source is 0 18, which is equivalent to 1.24 kpc in physical units.…”

Detection of H2O and OH+ in z>3 Hot Dust-Obscured Galaxies

“…Detections of H 2 O transitions in high-z and lensed sub-mm galaxies confirm that they are among the strongest molecular lines in starburst galaxies and also show similar line profiles and spatial distribution as the high-J CO emission (e.g. Lis et al 2011;van der Werf et al 2011;Bradford et al 2011;Combes et al 2012;Lupu et al 2012;Bothwell et al 2013;Omont et al 2013;Riechers et al 2013;Weiß et al 2013;Yang et al 2016;Oteo et al 2017;Yang et al 2019;Apostolovski et al 2019;Casey et al 2019;Jarugula et al 2019;Yang et al 2020). Furthermore, there is a correlation between the line luminosity and the IR luminosity, extending over three orders of magnitude (e.g.…”