The gaseous natal environments of GPS and CSS sources with ASKAP -- FLASH

TL;DR

This study uses ASKAP's FLASH survey to investigate the gaseous environments of GPS and CSS radio sources, revealing neutral hydrogen gas and interactions that influence galaxy and black hole evolution.

Contribution

It presents the first phase results of FLASH, detecting HI absorption in GPS/CSS sources and linking gas-rich interactions to AGN activity.

Findings

Detected HI absorption in several GPS/CSS sources

Identified galaxy interactions potentially fueling AGN

Provided initial insights into gas kinematics around young radio sources

Abstract

GPS and CSS sources are thought to represent a young and/or confined sub-population of radio-loud active galactic nuclei (AGN) that are yet to evacuate their surrounding ambient interstellar gas. By studying the gaseous environments of these objects we can gain an insight into the inter-dependent relationship between galaxies and their supermassive black holes (SMBHs). The First Large Absorption Survey in HI (FLASH) will build a census of the neutral atomic hydrogen (HI) gas in galaxies at intermediate cosmological redshifts. FLASH is expected to detect at least several hundred HI absorbers associated with GPS and CSS sources. These absorbers provide an important probe of the abundance and kinematics of line-of-sight neutral gas towards radio AGN, in some cases revealing gas associated with infalling clouds and outflows. Observations are now complete for the first phase of the FLASH Pilot Survey and early analysis has already yielded several detections, including the GPS source PKS2311$-$477. Optical imaging of this galaxy reveals an interacting system that could have supplied the neutral gas seen in absorption and triggered the radio-loud AGN. FLASH will provide a statistically significant sample with which the prevalence of such gas-rich interactions amongst compact radio galaxies can be investigated.