The GADOT Galaxy Survey: Dense Gas and Feedback in Herschel-Selected Starburst Galaxies at Redshifts 2 to 6

TL;DR

This study uses ALMA and NOEMA observations to analyze dense gas and feedback processes in Herschel-selected starburst galaxies at redshifts 2-6, revealing prevalent outflows, shock excitation, and correlations with dust temperature.

Contribution

It provides new insights into the molecular gas excitation and feedback mechanisms in high-redshift starbursts, highlighting the role of galactic winds and shock excitation in galaxy evolution.

Findings

OH+ absorption is detected in 89% of the sample.

Evidence of outflows and inflows in most galaxies.

Shock excitation of warm, dense gas is more common than in nearby galaxies.

Abstract

We report the detection of 23 OH+(1-0) absorption, emission, or P-Cygni-shaped lines and CO(9-8) emission lines in 18 Herschel-selected z=2-6 starburst galaxies with ALMA and NOEMA, taken as part of the Gas And Dust Over cosmic Time (GADOT) Galaxy Survey. We find that the CO(9-8) luminosity is higher than expected based on the far-infrared luminosity when compared to nearby star-forming galaxies. Together with the strength of the OH+ emission components, this may suggest that shock excitation of warm, dense molecular gas is more prevalent in distant massive dusty starbursts than in nearby star-forming galaxies on average, perhaps due to an impact of galactic winds on the gas. OH+ absorption is found to be ubiquitous in massive high-redshift starbursts, and is detected toward 89% of the sample. The majority of the sample shows evidence for outflows or inflows based on the velocity shifts of the OH+ absorption/emission, with a comparable occurrence rate of both at the resolution of our observations. A small subsample appears to show outflow velocities in excess of their escape velocities. Thus, starburst-driven feedback appears to be important in the evolution of massive galaxies in their most active phases. We find a correlation between the OH+ absorption optical depth and the dust temperature, which may suggest that warmer starbursts are more compact and have higher cosmic ray energy densities, leading to more efficient OH+ ion production. This is in agreement with a picture in which these high-redshift galaxies are "scaled-up" versions of the most intense nearby starbursts.