The hELENa project – I. Stellar populations of early-type galaxies linked with local environment and galaxy mass

Abstract

We present the first in a series of papers in The role of Environment in shaping Low-mass Early-type Nearby galaxies (hELENa) project. In this paper we combine our sample of 20 low-mass early types (dEs) with 258 massive early types (ETGs) from the ATLAS 3D survey -all observed with the SAURON integral field unit (IFU) -to investigate early-type galaxies' stellar population scaling relations and the dependence of the population properties on local environment, extended to the low-σ regime of dEs. The ages in our sample show more scatter at lower σ values, indicative of less massive galaxies being affected by the environment to a higher degree. The shape of the age-σ relations for cluster vs. non-cluster galaxies suggests that cluster environment speeds up the placing of galaxies on the red sequence. While the scaling relations are tighter for cluster than for the field/group objects, we find no evidence for a difference in average population characteristics of the two samples. We investigate the properties of our sample in the Virgo cluster as a function of number density (rather than simple clustrocentric distance) and find that dE ages negatively correlate with the local density, likely because galaxies in regions of lower density are later arrivals to the cluster or have experienced less pre-processing in groups, and consequently used up their gas reservoir more recently. Overall, dE properties correlate more strongly with density than those of massive ETGs, which was expected as less massive galaxies are more susceptible to external influences.

Evolution of the Stellar Mass–Metallicity Relation. I. Galaxies in the z ∼ 0.4 Cluster Cl0024

“…Since galaxies with low metallicities are mainly less massive galaxies, this results in the MZR lying above that shown by Gallazzi et al (2005). The MZR with higher metallicities at the lower-mass end found here is consistent with the MZRs found in stacks of local spectra in Choi et al (2014) and in individual local early-type galaxies via integral field spectroscopy by Sybilska et al (2017). The metallicities measured by Sybilska et al (2017) were measured via spectroscopic indices using the SSP models from Vazdekis et al (2015), which is also based on the MILES library.…”

“…The metallicities measured by Sybilska et al (2017) were measured via spectroscopic indices using the SSP models from Vazdekis et al (2015), which is also based on the MILES library. Because the measurements in Choi et al (2014), Sybilska et al (2017), and this work utilize the same stellar library, it is very likely that the choice of stellar library used caused the systematic differences in the metallicity measurements from those of Gallazzi et al (2005).…”

Spectroscopic characterization of the stellar content of ultra-diffuse galaxies

“…The UDGs analysed in this work seem to display large values of [Mg/Fe] (∼ 0.4 on average). If we compare them with typical [Mg/Fe] values for dwarf systems we see that they are more similar to the values recovered in the outskirts of dwarfs (Sybilska et al 2018) or those of quenched dwarfs (Sybilska et al 2017). In addition, also the mass-metallicity relation (see Fig.…”

“…The main differences are found at the youngest ages, where we find clear signs of a quenching in the star formation that they do not detect. However, we should bear in mind that less massive galaxies (as our sample) are more susceptible to external influences than more massive systems (Sybilska et al 2017). Since the CALIFA galaxies are mainly located in low density environments (Sánchez et al 2016) and the UDGs analysed in this work lie in the Coma cluster, we may relate the existence of this quenching to either environmental effects, or the internal properties of the UDGs under analysis.…”

The Fornax 3D project: Thick disks in a cluster environment

“…A larger (initial) satellite mass could help to explain these chemical abundances, together with the dense environment where these satellites could have lived. Sybilska et al (2017) showed as dwarfs and ellipticals in clusters tend to display higher [Mg/Fe] abundances than galaxies with similar stellar masses in the field (see also Bernardi et al 2006).…”