A High-resolution, 3D Neutral Hydrogen Survey

neutral_hydrogen_survey.jpgThe COSMOS H I Large Extragalactic Survey (CHILES) Very Large Array (VLA) deep field is the first high-resolution, three-dimensional survey of neutral hydrogen (HI) 21cm emission over a substantial cosmic volume. In this initial contribution, Hess et al. present a study of 16 neutral hydrogen (HI)-detected galaxies found in 178 hours of Very Large Array observations from Epoch 1 of the COSMOS H I Large Extragalactic Survey (CHILES). They focus on two redshift ranges between 0.108 ≤ z ≤ 0.127 and 0.162 ≤ z ≤ 0.183 which are among the worst affected by radio frequency interference (RFI). While this represents only 10% of the total frequency coverage and 18% of the total expected time on source compared to what will be the full CHILES survey, they demonstrate that their data reduction pipeline recovers high-quality data even in regions severely impacted by RFI. They also report on our in-depth testing of an automated spectral line source finder to produce H I total intensity maps which we present side-by-side with significance maps to evaluate the reliability of the morphology recovered by the source finder. The team recommends that this become a common place manner of presenting data from upcoming H Isurveys of resolved objects. They use the COSMOS 20k group catalogue and extract the filamentary structure using the topological DisPerSE algorithm to evaluate the H I morphology in the context of both local and large-scale environments and we discuss the shortcomings of both methods. Many of the detections show disturbed H I morphologies suggesting they have undergone a recent interaction which is not evident from deep optical imaging alone. Overall, the sample showcases the broad range of ways in which galaxies interact with their environment. This is a first look at the population of galaxies and their local and large-scale environments observed in H I by CHILES at redshifts beyond the z = 0.1 Universe. These VLA observations provide crucial insight into the physics of the gaseous evolution of the neutral atomic gas in galaxies, and guidance for future deeper surveys with next generation radio arrays. 

Image: CHILES VLA image of an HI group at z = 0.12 (Hess et al., 2018).

Publication: Kelley M. Hess (Netherlands Institute for Radio Astronomy) et al., CHILES: HI Morphology and Galaxy Environment at z=0.12 and z=0.17, Monthly Notices of the Royal Astronomical Society, 484, 2234 (20 December 2018).

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