Witnessing the star formation quenching in L* ellipticals

Abstract

We study the evolution of L* elliptical galaxies in the color-magnitude diagram in terms of their star-formation history and environment, in an attempt to learn about their quenching process. We have visually extracted 1109 L* galaxies from a sample of 36500 galaxies that were spectroscopically selected from Stripe82 of the Sloan Digital Sky Survey. From this sample we have selected 51 ellipticals based on their surface-brightness profile being well-fitted by a single S$\acute{e}$rsic profile with S$\acute{e}$rsic indices 3 < n < 6. Our sample consists of 12 blue-cloud L* ellipticals (BLE), 11 green-valley L* ellipticals (GLE), and 28 red-sequence L* ellipticals (RLE). We find that most of the RLEs and GLEs have been quenched only recently, or are still forming stars, based on their [O iii] and Hα emission, while the BLEs are forming stars vigorously. The star-formation in BLEs is found to be extended over the galaxy and not confined to their central region. In about 40 per cent of the L* ellipticals (ten BLEs, four GLEs and five RLEs), star-formation quenching seems to have started only recently, based on the lower [O iii] emission compared to the [O ii] and Hα emission, at a given metallicity. We also find that the galaxy color is correlated with the cosmic-web environment, with the BLEs tending to reside in lower-density regions, the RLEs preferring denser, clustered regions, and the GLEs found in either. One possible scenario is that as the star-forming ellipticals migrate into the clusters, their star formation is suffocated by the hot intra-cluster medium.

Post-processing of galaxies due to major cluster mergers

“…This is supported by the higher fraction of blue ETGs for A3560, which, despite showing characteristics of relaxed clusters, is part of the broader Shapley Supercluster system and hence connected with the cosmic web network. Furthermore, Dhiwar et al (2023) find that blue ETGs with Milky Way-like stellar masses (logM * /M ∼ 10) reside in low-density environments, making them a probable population of the cosmic filament-like environment now observed as a part of the newly forming post-merger system. Despite lacking specific stellar population information for these galaxies, our forthcoming follow-up work (Kelkar et al, in prep.…”

A Simple Spectroscopic Technique to Identify Rejuvenating Galaxies

“…A popular way to categorize galaxies is via the D n 4000-Hδ plane (e.g., Kauffmann et al 2003;Borgne et al 2006;Kauffmann 2014;Maltby et al 2016;Wu et al 2018;Dhiwar et al 2023). To investigate how different types of galaxy populations are located in the D n 4000-Hδ plane, we also include model quiescent and post-starburst populations here for comparison purposes.…”

Rapid Quenching of Galaxies at Cosmic Noon

“…Wild et al (2016) also used photometric data (using a supercolor selection) to identify post-starbursts and concluded that the post-starburst phase accounts for 25%-50% of the growth of the red sequence at z ∼ 1. In summary, quite a significant fraction of quiescent galaxies can be explained by the PSB phase (e.g., Snyder et al 2011;Wild et al 2016;Dhiwar et al 2023), especially at higher redshifts, highlighting the importance of the rapid quenching phase.…”