CO, H₂O, H₂O⁺ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales

Abstract

Using the Atacama Large Millimeter/submillimeter Array (ALMA), we report high angular-resolution observations of the redshift z =3.63 galaxy H-ATLAS J083051.0+013224 (G09v1.97), one of the most luminous strongly lensed galaxies discovered by the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). We present 0 . 2-0 . 4 resolution images of the rest-frame 188 and 419 µm dust continuum and the CO(6-5), H 2 O(2 11 -2 02 ), and J up = 2 H 2 O + line emission. We also report the detection of H 18 2 O(2 11 -2 02 ) in this source. The dust continuum and molecular gas emission are resolved into a nearly complete ∼ 1 . 5 diameter Einstein ring plus a weaker image in the center, which is caused by a special dual deflector lensing configuration. The observed line profiles of the CO(6-5), H 2 O(2 11 -2 02 ), and J up = 2 H 2 O + lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the CO, H 2 O, and H 2 O + line emission at sub-kiloparsec scales. The reconstructed dust emission in the source plane is dominated by a compact disk with an effective radius of 0.7 ± 0.1 kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is µ ∼ 10-11, the magnification of the line emission varies from 5 to 22 across different velocity components. The line emission of CO(6-5), H 2 O(2 11 -2 02 ), and H 2 O + have similar spatial and kinematic distributions. The molecular gas and dust content reveal that G09v1.97 is a gas-rich major merger in its pre-coalescence phase, with a total molecular gas mass of ∼ 10 11 M . Both of the merging companions are intrinsically ultra-luminous infrared galaxies (ULIRGs) with infrared luminosities L IR reaching 4 × 10 12 L , and the total L IR of G09v1.97 is (1.4 ± 0.7) × 10 13 L . The approaching southern galaxy (dominating from V = −400 to −150 km s −1 relative to the systemic velocity) shows no obvious kinematic structure with a semi-major half-light radius of a s = 0.4 kpc, while the receding galaxy (0 to 350 km s −1 ) resembles an a s = 1.2 kpc rotating disk. The two galaxies are separated by a projected distance of 1.3 kpc, bridged by weak line emission (−150 to 0 km s −1 ) that is co-spatially located with the cold dust emission peak, suggesting a large amount of cold interstellar medium (ISM) in the interacting region. As one of the most luminous star-forming dusty high-redshift galaxies, G09v1.97 is an exceptional source for understanding the ISM in gas-rich starbursting major merging systems at high redshift.

Planck’s Dusty GEMS

“…6. Lower limits are near the upper regime of SMGs, and more comparable to the elevated ratio in G09v1.97 ), a strongly lensed major merger of two ULIRGs at z = 3.634, characterized at high angular resolution by Yang et al (2019). Secondly, we obtain similar brightness levels for HNC and HCN lines in the GEMS.…”

A hyper luminous starburst at z = 4.72 magnified by a lensing galaxy pair at z = 1.48

“…The errors quoted in the redshift measurements are underestimated, as the uncertainties from the line profiles are not included. Indeed, as discussed in different studies based on simulations (for instance, Hezaveh et al 2012; Serjeant 2012) and observa- tions (for instance, Riechers et al 2008;Dye et al 2015;Yang et al 2017Yang et al , 2019aApostolovski et al 2019), the magnification can significantly vary along the velocity channels from blue to red and thus heavily distort the intrinsic line profile. This differential lensing effect may also cause different line profiles in different images.…”

“…Another aspect of gravitational lensing is that the deflection of the light emitted by a background source allows us to probe the mass distribution of the foreground source acting as the lens, constraining dark matter (DM) sub-halo structures (Hezaveh et al 2016) as well as the initial mass function (IMF; Cañameras et al 2017), for instance. Finally, gravitational lensing boosts the angular resolution with which we can observe background sources allowing spatially resolved studies of the ISM of high redshift galaxies (for instance, Swinbank et al 2015;Cañameras et al 2018;Litke et al 2019;Yang et al 2019a;Apostolovski et al 2019).…”

High-redshift star formation in the Atacama large millimetre/submillimetre array era

“…Recently, ALMA has enabled high-resolution observations of this molecule. A high-resolution observation of thermal H 2 O in an extragalactic source was achieved with the 0.9 00 detection in the strongly lensed source SDP.81 during the ALMA 2014 Long Baseline Campaign [280], recently superseded with approximately 0.4 00resolution observations of the strongly lensed merger G09v1.97 at z = 3.63 by Yang et al [281].…”