HI in Group Interactions: HCG 44

TL;DR

This study uses deep HI observations of galaxy group HCG 44 to reveal extended neutral gas structures, providing insights into group interactions, gas survival, and informing future telescope surveys.

Contribution

It presents the first high-sensitivity, large-field HI mapping of HCG 44, detecting a massive, extended tidal tail and discussing its implications for galaxy group evolution.

Findings

Detected a 450 kpc HI tail containing 1.1x10^9 M_Sun of gas.

The tail extends twice as far and has more mass than previously observed.

The HI clouds in the tail have survived over 1 Gyr after being stripped.

Abstract

Extending deep observations of the neutral atomic hydrogen (HI) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example and we have combined HI data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (N_HI < 2x10^18 cm^-2) to the neutral gas over a large field-of-view beyond the compact group itself. We find the giant HI tail north of HCG 44 contains 1.1x10^9 M_Sun of gas and extends 450 kpc from the compact group: twice as much mass and 33% further than previously detected. However, the additional gas is still unable to account for the known HI deficiency of HCG 44. The tail likely formed through a strong tidal interaction and HI clouds in the tail have survived for 1 Gyr or more after being stripped. This has important implications for understanding the survival of neutral clouds in the intragroup and circumgroup medium, and we discuss their survival in the context of simulations of cold gas in hot halos. HCG 44 is one of a growing number of galaxy groups found to have more extended HI in the intragroup and circumgroup medium than previously measured. Our results provide constraints for simulations on the properties of galaxy group halos, and reveal a glimpse of what will be seen by future powerful HI telescopes and surveys.