# z-GAL -- A NOEMA spectroscopic redshift survey of bright Herschel galaxies: [III] Physical properties

**Authors:** S. Berta, F. Stanley, D. Ismail, P. Cox, R. Neri, C. Yang, A. J. Young, S. Jin, H. Dannerbauer, T. J. Bakx, A. Beelen, A. Weiss, A. Nanni, A. Omont, P. van der Werf, M. Krips, A. J. Baker, G. Bendo, E. Borsato, V. Buat  
**arXiv:** [2307.15748](https://arxiv.org/abs/2307.15748)  
**Date:** 2023-07-28  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.15748v1/

## Key points

- The z-GAL survey observed 137 bright Herschel-selected targets using the IRAM Northern Extended Millimeter Array.
- The main objective was to measure the redshifts of these targets and study their properties.
- Robust spectroscopic redshifts were obtained for 165 individual galaxies within the redshift range of 0.8<z<6.5.
- The millimeter spectra of the z-GAL sources were analyzed to derive their physical properties.
- Both continuum and line emission were utilized for this purpose.
- Each source exhibited at least two spectral lines, including transitions of 12CO, [CI], and H2O.
- The observed line ratios and spectral line energy distributions resembled those found in local starbursts.
- The para-H2O(2_11-2_02) transition was detected in seven sources, following the IR versus H2O luminosity relation observed in sub-millimeter galaxies.
- The molecular gas mass of the z-GAL sources was determined by examining their 12CO, [CI], and sub-millimeter dust continuum emission.
- All three tracers yielded consistent results, with slightly larger scatter in the dust continuum compared to 12CO.
- The gas-to-dust mass ratio for these sources was computed using information derived from 12CO and the dust continuum, with a median value of 107 similar to that found in star forming galaxies with near solar metallicity.
- Depletion timescales ranging between 0.1 and 1 Gyr were estimated for z-GAL sources, placing them between the "main sequence" of star formation and locus representing starbursts.
- An initial estimate of stellar masses was derived by inverting known gas scaling relations, although gravitational magnification may have influenced results without conclusive confirmation due to lack of available data at the time when the study was conducted.
- -The z-GAL sample was confirmed to be predominantly composed of starbursts, with approximately 25% of its members found to lie on the main sequence of star forming galaxies within a range of +/- 0.5 dex.
- This study provides a comprehensive analysis of the physical properties of z-GAL sources based on their millimeter spectra, contributing to our understanding of galaxy evolution and providing valuable insights into the nature and characteristics of these Herschel-selected targets.

## Summary

The z-GAL survey conducted observations of 137 bright Herschel-selected targets using the IRAM Northern Extended Millimeter Array. The main objective was to measure the redshifts of these targets and study their properties. As a result, robust spectroscopic redshifts were obtained for 165 individual galaxies within the redshift range of 0.8<z<6.5. In this particular study, the authors focused on analyzing the millimeter spectra of the z-GAL sources in order to derive their physical properties. Both continuum and line emission were utilized for this purpose. Each source exhibited at least two spectral lines, including transitions of 12CO, [CI], and H2O. The observed line ratios and spectral line energy distributions of individual sources resembled those found in local starbursts. Interestingly, the para-H2O(2_11-2_02) transition was detected in seven sources, following the IR versus H2O luminosity relation observed in sub-millimeter galaxies. The molecular gas mass of the z-GAL sources was determined by examining their 12CO, [CI], and sub-millimeter dust continuum emission. All three tracers yielded consistent results, although the dust continuum showed slightly larger scatter compared to 12CO. Furthermore, by combining information derived from 12CO and the dust continuum, the authors computed the gas-to-dust mass ratio for these sources. The median value obtained was 107 which is similar to that found in star forming galaxies with near solar metallicity. The combined analysis also allowed for estimation of depletion timescales ranging between 0.1 and 1 Gyr for z-GAL sources; placing them between what is known as "main sequence" of star formation and locus representing starbursts. Finally an initial estimate of stellar masses was derived by inverting known gas scaling relations with caveat that gravitational magnification may have influenced results; however it could not be confirmed conclusively due to lack of data available at time when study was conducted . The z-GAL sample was confirmed to be predominantly composed of starbursts although approximately 25% its members were found to lie on main sequence star forming galaxies within range +/- 0.5 dex . Overall this study provides comprehensive analysis physical properties z - GAL sources based on their millimeter spectra findings contribute our understanding galaxy evolution provide valuable insights into nature characteristics these Herschel - selected targets .