Do the stellar populations of the brightest two group galaxies depend on the magnitude gap?

Abstract

We investigate how the stellar populations of the inner regions of the first and the second brightest group galaxies (respectively BGGs and SBGGs) vary as a function of magnitude gap, using an SDSS-based sample of 550 groups with elliptical BGGs. The sample is complete in redshift, luminosity and for ∆M 12 up to 2.5 mag, and contains 59 large-gap groups (LGGs, with ∆M 12 > 2.0 mag). We determine ages, metallicities, and SFHs of BGGs and SBGGs using the STARLIGHT code with two different single stellar population models (which lead to important disagreements in SFHs), and also compute [α/Fe] from spectral indices. After removing the dependence with galaxy velocity dispersion or with stellar mass, there is no correlation with magnitude gap of BGG ages, metallicities, [α/Fe], and SFHs. The lack of trends of BGG SFHs with magnitude gap suggests that BGGs in LGGs have undergone more mergers than those in small-gap groups, but these mergers are either dry or occurred at very high redshift, which in either case would leave no detectable imprint in their spectra. We show that SBGGs in LGGs lie significantly closer to the BGGs (in projection) than galaxies with similar stellar masses in normal groups, which appears to be a sign of the earlier entry of the former into their groups. Nevertheless, the stellar population properties of the SBGGs in LGGs are compatible with those of the general population of galaxies with similar stellar masses residing in normal groups.

Fossil group origins

“…However, a significant fraction of their mass was accreted via later dry mergers (Méndez-Abreu et al 2012). The similar properties of the stellar populations of BGGs in FSs and non-FSs also point toward a similar formation (La Barbera et al 2009;Eigenthaler & Zeilinger 2013;Trevisan et al 2017). Nevertheless, the merging process in the BGGs of FSs has been especially effective because these galaxies are among the brightest galaxies observed in the Universe (Aguerri et al 2011;Méndez-Abreu et al 2012;Zarattini et al 2014).…”

The Observed Evolution of the Stellar Mass - Halo Mass Relation for Brightest Central Galaxies

“…For each bin, as in GM&M18 and GM&M19, we apply a m gap completeness criterion based on the binning of the BCG and 4th brightest galaxy's absolute magnitudes against the BCG's apparent magnitude and m gap to determine the apparent magnitude limit of the sample (a redshift dependent limit) (Colless 1989;Garilli et al 1999;La Barbera et al 2010;Trevisan et al 2017;Golden-Marx & Miller 2018). Additionally, since the halo mass distribution can be approximated as Gaussian, the peak indicates the mass that the sample becomes incomplete.…”

The properties and environment of very young galaxies in the local Universe

“…We obtained 𝑟 vir by first deducing 𝑟 200,m (of spheres that are 200 times denser than the mean density of the Universe from the 𝑀 200,m masses given in the Yang et al catalogue (which are based on abundance matching with the group luminosities). We then calculated the 𝑟 vir , following appendix A of Trevisan, Mamon & Khosroshahi (2017a) for the conversion from quantities relative to the mean density to those relative to the critical density, and the corresponding virial masses, 𝑀 vir = (Δ v /2) 𝐻 2 (𝑧) 𝑟 3 vir /𝐺. To assign the galaxies to their nearest group, we compute the distances, 𝑑, between the galaxies and the group centres, assuming two regimes.…”