Joint Optical-HI mock catalogs and prospects for upcoming HI surveys

TL;DR

This paper introduces a method for creating joint optical-HI mock catalogs to predict and analyze upcoming HI surveys, enhancing our understanding of galaxy evolution through combined data modeling.

Contribution

It presents a novel approach to generate optical-HI joint mock catalogs for upcoming radio surveys, enabling better predictions and analysis of HI science and galaxy evolution.

Findings

Joint catalogs improve predictions for HI detection and stacking outcomes.

Combining stacking with direct detections constrains the HI mass function.

The method provides a benchmark for HI science in future surveys.

Abstract

Atomic hydrogen (HI) regulates star formation as cold gas fuels star formation. It represents a key phase of matter in the baryon cycle involving accretion, feedback, outflows, and gas recycling. Redshifted $21$ cm line emission originating from galaxies serves as a key tracer for investigating HI gas and its dynamics in the interstellar medium (ISM) and circumgalactic medium (CGM), and enables the study of galaxy evolution. Nonetheless, direct detections of HI are currently limited to $z \leq 0.4$ due to the inherently weak $21$ cm emission line. Ongoing and upcoming large radio surveys aim to detect $21$ cm emission from galaxies up to $z \gtrsim 1$ with unprecedented sensitivity. In current work, we present a novel approach for creating optical-HI joint mock catalogs for upcoming SKA precursor surveys: MIGHTEE-HI and LADUMA with MeerKAT and WALLABY with ASKAP. Incorporation of optical properties along with HI in our mock catalogs makes these a powerful tool for making predictions for upcoming surveys and provides a benchmark for exploring the HI science (e.g., conditional HIMF and optical-to-HI scaling relations) expected from these surveys. As a case study, we show the use of the joint catalogs for predicting the expected outcome of stacking detection for average HI mass in galaxies that are below the threshold for direct detection. We show that combining stacking observations with the number of direct detections puts a strong constraint on the HI mass function, especially in the regime where the number of direct detections is small, as often happens near the farther edge of HI surveys. This intermediate step may be used to set priors for the full determination of the HI mass function.