DIISC Survey: Deciphering the Interplay Between the Interstellar Medium, Stars, and the Circumgalactic Medium Survey

TL;DR

The DIISC Survey investigates how the properties of the circumgalactic medium, interstellar medium, and star-forming regions are interconnected, revealing a strong inverse correlation between Lyman alpha absorption strength and the normalized impact parameter related to the galaxy's HI disk.

Contribution

This survey provides new insights into the relationship between the CGM and the galaxy's gas disk, emphasizing the importance of HI radius as a predictor of Lyman alpha absorption.

Findings

Strong inverse correlation between Lyman α equivalent width and impact parameter normalized by HI radius.

HI radius normalization better predicts Lyman α absorption than virial radius.

Neutral gas distribution in the CGM is more linked to the galaxy's gas disk than to stellar or dark matter components.

Abstract

We present the Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) Survey. This survey is designed to investigate the correlations in properties between the circumgalactic medium (CGM), the interstellar medium (ISM), stellar distributions, and young star-forming regions. The galaxies were chosen to have a QSO sightline within 3.5 times the HI radii probing the disk-CGM interface. The sample contains 34 low-redshift galaxies with a median stellar mass of 10$^{10.45}~\rm M_{\odot}$ probed at a median impact parameter of $\rho=55~kpc$. The survey combines ultraviolet spectroscopic data from the Cosmic Origins Spectrograph aboard the Hubble Space Telescope with HI 21 cm hyperfine transition imaging with the Very Large Array (VLA), ultraviolet imaging from Galaxy Evolution Explorer (GALEX), and optical imaging and spectroscopy with the MMT and Vatican Advanced Technology Telescope. We describe the specific goals of the survey, data reduction, high-level data products, and some early results. We present the discovery of a strong inverse correlation, at a confidence level of 99.99%, between Lyman $\alpha$ equivalent width, $\rm W_{Ly\alpha}$, and impact parameter normalized by the HI radius ($\rho/R_{HI}$). We find $\rho/R_{HI}$ to be a better empirical predictor of Lyman $\alpha$ equivalent width than virial radius normalized impact parameter ($\rho/R_{vir}$) or parameterizations combining $\rho,~R_{vir}$, stellar mass, and star formation rate. We conclude that the strong anticorrelation between the Lyman $\alpha$ equivalent width and $\rho/R_{HI}$ indicates that the neutral gas distribution of the CGM is more closely connected to the galaxy's gas disk rather than its stellar and dark matter content.