A multiwavelength survey of HI-excess galaxies with surprisingly inefficient star formation

Abstract

We present the results of a multiwavelength survey of H I-excess galaxies, an intriguing population with large H I reservoirs associated with little current star formation. These galaxies have stellar masses M > 10 10 M , and were identified as outliers in the gas fraction vs. NUV−r color and stellar mass surface density scaling relations based on the GALEX Arecibo SDSS Survey (GASS). We obtained H I interferometry with the GMRT, Keck optical long-slit spectroscopy and deep optical imaging (where available) for four galaxies. Our analysis reveals multiple possible reasons for the H I excess in these systems. One galaxy, AGC 10111, shows an H I disk that is counter-rotating with respect to the stellar bulge, a clear indication of external origin of the gas. Another galaxy appears to host a Malin 1-type disk, where a large specific angular momentum has to be invoked to explain the extreme M HI /M ratio of 166%. The other two galaxies have early-type morphology with very high gas fractions. The lack of merger signatures (unsettled gas, stellar shells and streams) in these systems suggests that these gas-rich disks have been built several Gyr-s ago, but it remains unclear how the gas reservoirs were assembled. Numerical simulations of large cosmological volumes are needed to gain insight into the formation of these rare and interesting systems.

xGASS: passive discs do not host unexpectedly large reservoirs of cold atomic hydrogen

“…If confirmed, this may have important implications on our view of galaxy quenching, as already discussed by Peng & Renzini (2019). However, these results appear in contradiction with the bulk of conclusions so far reached by other analysis of the same xGASS and ALFALFA datasets (e.g., Catinella et al 2010;Huang et al 2012;Brown et al 2015;Saintonge et al 2016;Geréb et al 2018;C18).…”

“…In this paper, we focus on the case of disk galaxies with E-mail: luca.cortese@uwa.edu.au (LC) large Hi reservoirs that are not feeding star formation. Examples of gas-rich passive disks do exist (Geréb et al 2018), and have been known for decades (Pickering et al 1997), but so far only a small number of such objects has been reported. Indeed, while Hi content correlates less strongly with star formation rate (SFR) than H 2 , SFR remains one of the global galaxy properties more tightly linked to Hi mass, with just a weak secondary dependence on stellar structure (Catinella et al 2010;Brown et al 2015;Cook et al 2019).…”

Group pre-processing versus cluster ram-pressure stripping: the case of ESO156−G029

“…Based on the q value, we can conclude that ESO156-G029 has a high angular momentum and thus low star formation efficiency. The properties of ESO156-G029 are similar to the galaxies studied by Geréb et al (2018) and H i eXtreme galaxies (HIX, Lutz et al 2017, although ESO156-G029 shows signs of a disturbance. In the following sections we explore whether ram-pressure and galaxy interaction may have had an effect on ESO156-G029.…”

UGC 1378 – a Milky Way sized galaxy embedded in a giant low surface brightness disc

“…UGC 1378's gas-to-stellar mass ratio, its H disc size and mass are similar to the "Bluedisk" galaxies. UGC 1378's H mass fraction is lower than that of the galaxies in the Geréb et al (2018) and HIghMass (Huang et al 2014) samples. UGC 1378's properties are summarized in Table 1.…”