HI Rich but Low Star Formation galaxies in MaNGA: Physical Properties and Comparison to Control Samples

TL;DR

This study identifies and analyzes a rare class of HI-rich, low star formation rate galaxies in MaNGA, revealing diverse physical mechanisms such as gas accretion, AGN feedback, and bar quenching responsible for their properties.

Contribution

It introduces a new sample of HI-rich, low SFR galaxies and compares their physical properties to control samples, highlighting multiple processes influencing star formation suppression.

Findings

Evidence of recent external gas accretion in some galaxies

Presence of AGN feedback indicators in certain cases

Some galaxies have high angular momentum, large radius HI discs

Abstract

Gas rich galaxies are typically star-forming. We make use of HI-MaNGA, a program of HI follow-up for the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey of the Sloan Digital Sky Surveys to construct a sample of unusual neutral hydrogen (HI, 21cm) rich galaxies which have low Star Formation Rates (SFRs); using infra-red color from the Wide-field Infrared Survey Explorer (WISE) as a proxy for specific SFR. Out of a set of 1575 MaNGA galaxies with HI-MaNGA detections, we find 83 (5%) meet our selection criteria to be HI rich with low SFR. We construct two stellar mass-matched control samples: HI rich galaxies with typical SFR (High SF Control) and HI poor galaxies with low SFR (Low HI Control). We investigate the properties of each of these samples, comparing physical parameters such as ionization state maps, stellar and ionized gas velocity and dispersion, environment measures, metallicity, and morphology to search for the reasons why these unusual HI rich galaxies are not forming stars. We find evidence for recent external accretion of gas in some galaxies (via high counter-rotating fractions), along with some evidence for AGN feedback (from a high cLIER and/or red geyser fraction), and bar quenching (via an enhanced strong bar fraction). Some galaxies in the sample are consistent with simply having their HI in a high angular momentum, large radius, low density disc. We conclude that no single physical process can explain all HI rich, low SFR galaxies.