The HI gas content of galaxies around Abell 370, a galaxy cluster at z = 0.37

TL;DR

This study measures the atomic hydrogen gas content of 324 galaxies around Abell 370 at z=0.37, revealing substantial gas quantities and evolutionary trends in galaxy clusters over 4 billion years.

Contribution

It provides the first detailed measurement of HI gas in galaxies at z=0.37 using coadded signals, highlighting evolution in gas content compared to local clusters.

Findings

Average HI mass is (6.6 +- 3.5)x10^9 solar masses for all galaxies.

Galaxies further from the cluster core have higher HI content.

HI gas quantities are up to 8 times higher than in the nearby Coma cluster.

Abstract

We used observations from the Giant Metrewave Radio Telescope to measure the atomic hydrogen gas content of 324 galaxies around the galaxy cluster Abell 370 at a redshift of z = 0.37 (a look-back time of ~4 billion years). The HI 21-cm emission from these galaxies was measured by coadding their signals using precise optical redshifts obtained with the Anglo-Australian Telescope. The average HI mass measured for all 324 galaxies is (6.6 +- 3.5)x10^9 solar masses, while the average HI mass measured for the 105 optically blue galaxies is (19.0 +- 6.5)x10^9 solar masses. The significant quantities of gas found around Abell 370, suggest that there has been substantial evolution in the gas content of galaxy clusters since redshift z = 0.37. The total amount of HI gas found around Abell 370 is up to ~8 times more than that seen around the Coma cluster, a nearby galaxy cluster of similar size. Despite this higher gas content, Abell 370 shows the same trend as nearby clusters, that galaxies close to the cluster core have lower HI gas content than galaxies further away. The Abell 370 galaxies have HI mass to optical light ratios similar to local galaxy samples and have the same correlation between their star formation rate and HI mass as found in nearby galaxies. The average star formation rate derived from [OII] emission and from de-redshifted 1.4 GHz radio continuum for the Abell 370 galaxies also follows the correlation found in the local universe. The large amounts of HI gas found around the cluster can easily be consumed by the observed star formation rate in the galaxies over the ~4 billion years (from z = 0.37) to the present day.