The Westerbork Coma Survey: A blind, deep, high-resolution HI survey of the Coma cluster

TL;DR

This survey used the Westerbork telescope to detect and analyze the atomic hydrogen content of galaxies in the Coma cluster, revealing interactions with the environment that affect star formation and gas content.

Contribution

It provides the first deep, high-resolution HI survey of the Coma cluster, identifying new HI sources and analyzing their properties in relation to the cluster environment.

Findings

75% of HI-selected galaxies have enhanced star formation and are HI deficient.

Over half of the detected galaxies show disturbed HI morphologies.

The results suggest rapid HI stripping or a boost in HI-to-H2 conversion triggering starbursts.

Abstract

We present the blind Westerbork Coma Survey probing the HI content of the Coma galaxy cluster with the Westerbork Synthesis Radio Telescope. The survey covers the inner $\sim$ 1 Mpc around the cluster centre, extending out to 1.5 Mpc towards the south-western NGC 4839 group. The survey probes the atomic gas in the entire Coma volume down to a sensitivity of $\sim$ 10$^{19}$ cm$^{-2}$ and 10$^8$ M$_{\odot}$. Combining automated source finding with source extraction at optical redshifts and visual verification, we obtained 40 HI detections of which 24 are new. Over half of the sample displays perturbed HI morphologies indicative of an ongoing interaction with the cluster environment. With the use of ancillary UV and mid-IR, data we measured their stellar masses and star formation rates and compared the HI properties to a set of field galaxies spanning a similar stellar mass and star formation rate range. We find that $\sim$ 75 % of HI-selected Coma galaxies have simultaneously enhanced star formation rates (by $\sim$ 0.2 dex) and are HI deficient (by $\sim$ 0.5 dex) compared to field galaxies of the same stellar mass. According to our toy model, the simultaneous HI deficiency and enhanced star formation activity can be attributed to either HI stripping of already highly star forming galaxies on a very short timescale, while their H$_2$ content remains largely unaffected, or to HI stripping coupled to a temporary boost of the HI-to-H$_2$ conversion, causing a brief starburst phase triggered by ram pressure before eventually quenching the galaxy.