GASS 3505: the prototype of H i-excess, passive galaxies

Abstract

We present our multiwavelength analysis of a prototype H I-excess galaxy, GASS 3505, selected based on having a large gas content (M HI = 10 9.9 M ) compared to its little associated star formation activity (∼0.1 M yr −1 ) in the GALEX Arecibo SDSS Survey (GASS). Very Large Array (VLA) observations show that the H I in GASS 3505 is distributed in a regularly rotating, extended (∼50 kpc radius) gas ring. In the SDSS optical image GASS 3505 appears as a bulge-dominated galaxy, however deep optical imaging reveals low surface brightness ( 25 mag arcsec −2 ) stellar emission around the central bulge. Direct evidence for accretion is detected in form of an extended (∼60 kpc) stellar stream, showing that GASS 3505 has experienced a minor merger in the recent past. We investigate the possibility that the H I ring in GASS 3505 was accreted in such a merger event using N-body and smoothed particle hydrodynamic (SPH) simulations. The best model that reproduces the general properties (i.e., gas distribution and kinematics, stellar morphology) of the galaxy involves a merger between the central bulge and a gas-rich (M = 10 9 M and M HI /M = 10) disk galaxy. However, small discrepancies in the observed and modeled properties could suggest that other sources of gas have to be involved in the build-up of the gas reservoir. This work is the first step toward a larger program to investigate the physical mechanisms that drive the large scatter in the gas scaling relations of nearby galaxies.

Cold gas and dust: Hunting spiral-like structures in early-type galaxies

“…Our conclusion is supported by the fact that extended H I in several of these galaxies often comes from the external sources, as implied by the lack of a correlation between H I mass and stellar mass in ETGs (Serra et al 2012) and by the frequent kinematical misalignment between H I and stars (Serra et al 2014). Our results are also consistent with previous studies, such as Davis et al (2015), who find that the origin of the cold gas is most likely due to the minor mergers in their sample ETGs (see also Geréb et al 2016). Kaviraj et al (2012) also stress that dust contribution from stellar mass loss is not enough to create the observed dust alone.…”

xCOLD GASS: The Complete IRAM 30 m Legacy Survey of Molecular Gas for Galaxy Evolution Studies

“…The longest molecular gas depletion times we measure are 10 10 < yr, while atomic gas depletion times can be in excess of 10 11 yr. This illustrates clearly how galaxies may have large reservoirs of cold atomic gas that are not associated with the star formation process, as may be the case, for example, in early-type galaxies (Serra et al 2011(Serra et al , 2014Geréb et al 2016) and in low-mass galaxies.…”

H i galaxies with little star formation: an abundance of LIERs

“…An archetype H i-excess galaxy, GASS 3505, with H i mass (M H I )= 10 9.9 M and a surprisingly inefficient SFR of ∼ 0.1 M yr −1 , was found to be associated with a 50 kpc gas ring. Evidence of recent star formation was observed in regions of high H i column densities (> 10 20 cm −2 ), but not in regions of low H i column densities, suggesting that low H i column density is likely the main factor for the low SFR (Geréb et al 2016). It has also been proposed that the high specific angular momentum of H i-excess galaxies prevents the gas in these galaxies from collapsing inwards (Hallenbeck et al 2014;Boissier et al 2016;Obreschkow et al 2016;Lutz et al 2017).…”

“…We also compare this sample to the ATLAS 3D H i survey (Serra et al 2012), which undertook a 21-cm survey of Medians for the H i-WISE sample were estimated using only galaxies that met the last three sample selection criteria. For comparison, we also plot the H i and stellar properties of well studied galaxy GASS 3503 (purple diamond; Geréb et al 2016) and the ETGs from ATLAS 3D H i survey (pink; Serra et al 2012). By construction, the sample has a lower sSFR than the H i-WISE sample.…”