Investigating quenching in Recently Quenched Elliptical galaxies with HI studies

TL;DR

RQEs represent a transitional phase between star-forming and quiescent galaxies, and this paper probes their quenching by measuring HI content in 155 central RQEs, plus analogous preRQEs and postRQEs. The study finds that RQEs retain substantial HI reservoirs (f_gas ≥ 17%), challenging gas-depletion quenching scenarios, and identifies a halo mass threshold at log M_halo = 12.1 that delineates different evolutionary pathways. The authors propose two quenching trajectories: (a) rapid quenching via major mergers followed by brief AGN/LINER activity and passive evolution, and (b) rapid quenching followed by rejuvenation through minor mergers before settling into long-term quenched ellipticals. The results highlight the interplay between cold and hot-mode gas accretion, feedback, and environment in shaping quenching, and call for future SKA observations to unravel the physical mechanisms.

Abstract

Recently Quenched Elliptical galaxies (RQEs) represent a critical phase in the transition from star-forming to quiescent galaxies. However, the mechanisms driving their quenching remain elusive. We conduct a multi-wavelength analysis of 155 RQEs, along with their precursors (preRQEs) and descendants (postRQEs), focusing on their neutral hydrogen (HI) content and star formation properties. Contrary to conventional quenching models emphasizing gas depletion, RQEs retain substantial HI reservoirs ($f_{\text{gas}} \geq 17\%$), suggesting that quenching is not primarily driven by gas exhaustion. We identify a critical halo mass threshold at $\log M_{\text{halo}} = 12.1 M_{\odot}$, delineating different evolutionary pathways for RQEs. This threshold aligns with the transition from cold-mode to hot-mode gas accretion in theoretical models. RQEs in lower-mass halos ($\log M_{\text{halo}} < 12.1 M_{\odot}$) likely experience rapid quenching, possibly initiated by major mergers, followed by brief AGN activity and sustained LINER emission. We propose two evolutionary pathways: (a) rapid quenching via major mergers followed by AGN/LINER activity and passive evolution, and (b) rapid quenching followed by rejuvenation through minor mergers before evolving into more massive, long-term quenched ellipticals. These results challenge the conventional understanding of galaxy quenching, especially in low-density environments where RQEs typically reside. Our findings suggest that while RQEs may follow a rapid quenching pathway, their evolution is influenced by interactions between gas accretion modes, feedback mechanisms, and environmental factors. Future observations with advanced radio interferometers like SKA will be crucial for elucidating the quenching mechanisms in RQEs and their role in galaxy evolution.

Figures (1)

• Figure 1: Distribution of stellar mass, halo mass, redshift, and central light concentration (reflecting the prominence of the central bulge) for RQEs and comparable subpopulations. The figure presents boxplots comparing the properties of RQEs with preRQEs and postRQEs. The boxes represent the IQR (interquartile range), illustrating the distribution of the central $50\%$ of the population. Whiskers extend to 1.5 times the IQR, and outliers are shown as points beyond the whiskers. Medians are annotated within the boxes, and Q1 and Q3 values are indicated, highlighting the distribution and any differences or similarities among the subpopulations. Dashed lines indicate selection cuts (related to RQEs) to which preRQEs and postRQEs were matched.