Compact Elliptical Galaxies in Different Local Environments: A Mixture of Galaxies with Different Origins?

Abstract

We present the stellar populations of 138 compact elliptical galaxies (cEs) in the redshift range of z < 0.05 using the Sloan Digital Sky Survey (SDSS) DR12. Our cEs are divided into those with [cE(w)] and without [cE(w/o)] a bright (M r < −21 mag) host galaxy. We investigated the stellar population properties of cEs based on the Lick line indices extracted from SDSS spectra. cE(w)s show [Z/H] and [α/Fe] distributions skewed toward higher values compared to those of the cE(w/o)s. No statistically significant difference in age distribution was found between the cE(w)s and cE(w/o)s. In the mass–metallicity distribution, cE(w)s deviate from the relation observed for early-type galaxies at a given stellar mass, whereas cE(w/o)s conform to the relation. Based on the different features in the stellar populations of cE(w)s and cE(w/o)s, we can propose two different cE formation channels tracing different original masses of the progenitors. cE(w)s would be the remnant cores of the massive progenitor galaxies whose outer parts are tidally stripped by a massive neighboring galaxy (i.e., a nurture origin). In contrast, cE(w/o)s are likely the faint end of early-type galaxies maintaining in situ evolution in an isolated environment with no massive galaxy nearby (i.e., a nature origin). Our results reinforce the propositions that cEs comprise a mixture of galaxies with two types of origins depending on their local environment.

A search for active galactic nuclei in low-mass compact galaxies

“…This supports what has been seen from the study of their stellar populations and kinematic: cEs are mixed-bag of both origins (e.g. Ferré-Mateu et al 2018a;Kim et al 2020;Ferré-Mateu et al 2021).…”

“…We thank Soo-Chang Rey and Suk Kim for providing their list of cEs from Kim et al (2020) and Aaron Romanowsky for insightful discussions. AFM has received financial support through the Postdoctoral Junior Leader Fellowship Programme from 'La Caixa' Banking Foundation (LCF/BQ/LI18/11630007).…”

“…Chilingarian et al 2009;Huxor et al 2011;Paudel et al 2013;Chilingarian & Zolotukhin 2015;Ferré-Mateu et al 2018a) to the existence of them in isolated places that would make the stripping process impossible (e.g. Paudel & Ree 2014;Ferré-Mateu et al 2018a;Kim et al 2020). In terms of simulations, Bekki et al (2001), Pfeffer & Baumgardt (2013); Pfeffer et al (2016) and Goodman & Bekki (2018) have reproduced the stripping path for UCDs, whereas Martinović & Micic (2017), Du et al (2019) and Urrutia Zapata et al (2019) have shown that both being formed in-situ as low-mass galaxies but also being the result of stripping larger galaxies can reproduce the observed properties of cEs.…”

“…Some works have already tried to address these different origins via the study of their kinematics, stellar populations and other relevant properties (e.g. Chilingarian et al 2008;Chilingarian et al 2009;Norris et al 2014;Janz et al 2015;Chilingarian & Zolotukhin 2015;Ferré-Mateu et al 2018a;Kim et al 2020;Ferré-Mateu et al 2021).…”

Compact elliptical galaxies hosting active galactic nuclei in isolated environment

“…In the nearby universe, compact elliptical galaxies (cEs) are a rare class of non-star-forming objects that are typically characterized by compact sizes (100 − 900 pc), low stellar masses (10 8 − 10 10 M ), and very high stellar densities. Only a few hundred cEs are currently known (Chilingarian et al 2009;Norris et al 2014;Chilingarian & Zolotukhin 2015;Kim et al 2020). They conform to the low-mass regime of the mass-size relation defined by massive early-type galaxies.…”