Local massive quiescent disk galaxies are commonly believed to be gas poor. A research team comprising investigators from KIAA (led by Yingjie Peng) and SHAO (Feng Yuan) uses data from large sky surveys, showing that, on the contrary, massive quiescent central disk galaxies in the nearby universe often have a remarkably large amount of cold atomic hydrogen gas. Massive quiescent central disk galaxies are quenched because of their significantly reduced molecular gas content, lower dust content, and lower star formation efficiency. This work is published in the Astrophysical Journal Letters [1] and is featured as the American Astronomical Society (AAS) NOVA research highlight [2]. The associated paper is among the top 3 most voted papers on voxcharta in 2019 [3].
Identifying the physical mechanism responsible for star formation quenching is one of the most debated open questions. In general, the level of star formation in the galaxy is controlled by its cold gas reservoir and star formation efficiency. Investigating the cold gas content in galaxies will provide direct observational evidence of how quenching may happen.
Based on the data from SDSS, ALFALFA, GASS, and COLD GASS surveys, the team found that quiescent central disk galaxies exhibit similarly symmetric characteristic double-horn H I profiles as star-forming systems (Figure 1, left panel), strongly suggesting that both galaxy types have regularly rotating H I disks. The almost constant H I gas mass of ∼1010Mʘ (Figure 1, right panel), across the entire observable range of SFR, corresponds to H I disks with radii of ∼30 kpc. Thus, the H I gas in quenched disks may be stored in an outer ring such as in the prototypical case of the S0 galaxy NGC 1543.
These observational evidence give new insights into the quenching mechanism of star forming galaxies. Since the H I gas is distributed on very large scales, once the central H2 gas is consumed by star formation, expelled by outflows, or ionized/photo-dissociated by UV radiation from AGNs, the timescale for the H I gas with high angular momentum in the outer disk to migrate inward may be very long in the absence of perturbations. Therefore, during the quenching process, the rotationally supported outer H I disk remains largely unchanged. The SFR decreases, driven by the decreasing H2 gas mass in the central region and progressively suppressed H2 star formation efficiency (Figure 1, right panel), with the gas remaining atomic rather than replenishing the star-forming molecular phase. The implications of these findings for the quenching of star formation in disk galaxies are further explored in C. Zhang et al. (2020, in preparation [4]) from the same team.
[1]. Nearly all Massive Quiescent Disk Galaxies Have a Surprisingly Large Atomic Gas Reservoir
C. Zhang, Y. Peng, L.C. Ho, R. Maiolino, A. Dekel, Q. Guo, F. Mannucci, D. Li, F. Yuan, A. Renzini, J. Dou, K. Guo, Z. Man, Q. Li, The Astrophysical Journal Letters, 884, 52 (2019)
[2]. [1] is featured on the American Astronomical Society (AAS) NOVA research highlights
https://aasnova.org/2019/10/30/plenty-of-gas-left-in-giant-dead-disk-galaxies/
[3]. [1] is among the top 3 most voted papers on voxcharta out of more than 20,000 published papers in 2019
[4]. Mass and Environment as Drivers of Galaxy Evolution. IV. On the Quenching of Massive Central Disk Galaxies in The Local Universe
C. Zhang, Y. Peng,…, F. Yuan et al., 2020, to be submitted.