Stellar content of extremely red quiescent galaxies atz> 2

Abstract

Context. A set of 20 extremely red galaxies at 2.5 ≤ z phot. ≤ 3.8 with photometric features of old passive-evolving galaxies without dust, with stellar masses of ∼ 10 11 M ⊙ , have colors that could be related to passive-evolving galaxies with mean ages larger than 1 Gyr. This suggests they have been formed, on average, when the Universe was very young (< 1 Gyr). Aims. We provide new estimates for the stellar content of these 20 galaxies, with a deeper analysis for two of them that includes spectroscopy. Methods. We obtained, with the GRANTECAN-10.4 m, ultraviolet rest-frame spectra of two galaxies and analyzed them together with photometric data. The remaining 18 galaxies are analyzed only with photometry. We fit the data with models of a single-burst stellar population (SSP), combinations of two SSPs, as well as with extended star formation. Results. Fits based on one SSP do not provide consistent results for the blue and red wavelengths. Moreover, the absence in the spectra of a break at ∼ 2 × 10 3 Å indicates that a rather young component is necessary. Using two SSPs we can match the photometric and spectroscopic data, with the bulk of the stellar population being very old (several Gyr) and the remaining contribution (< 5% of stellar mass fraction) from a young, likely residual star formation component with age 0.1 Gyr. Exponentially decaying extended star formation (τ) models improve slightly the fits with respect to the single burst model, but they are considerably worse than the two SSP based fits, further supporting the residual star formation scenario. Conclusions. The fact that one SSP cannot match these early-type galaxies highlights the limitations for the use of age estimators based on single lines or breaks, such as the Balmer break used in cosmic chronometers, thus questioning this approach for cosmological purposes.

Timing the formation and assembly of early-type galaxies via spatially resolved stellar populations analysis

“…Trager et al 2000a), light profile concentration (e.g. Graham et al 2001) and recurrent appearance of old galaxies at high redshifts (Lonoce et al 2015;Kriek et al 2016;López-Corredoira et al 2017) ought to indicate that ETGs were formed very rapidly, in gas rich, high star formation rate events beyond z ∼ 2, or even earlier (Wellons et al 2015). This would imply that the bulk of stars within ETGs were formed in situ, in a monolithic-like fashion, leading to the observed scaling relations between stellar population properties and galaxy mass.…”

Constraining late-time transitions in the dark energy equation of state

“…On the other hand, we emphasise that this compilation of Hubble parameter measurements is heterogeneous: some of the measurements come from galaxy clustering and baryon acoustic oscillations (henceforth BAO) observations, while others come from the so-called cosmic chronometers or differential age method (Jimenez & Loeb 2002). We note that it is not currently clear that possible systematics issues of the cosmic chronometers method are well understood and under control (Liu et al 2016;Lopez-Corredoira et al 2017;Concas et al 2017;Lopez-Corredoira & Vazdekis 2018).…”

Nonparametric reconstruction of interaction in the cosmic dark sector

“…However, they are subject to other sources of systematic uncertainties, such as the modelling of stellar ages carried out through the stellar population synthesis techniques (SPS). Given a pair of ensembles of passivelyevolving galaxies at two different redshift it is possible to infer ∆z ∆t from observations under the assumption of a concrete SPS model [82][83][84]. Thus H(z) can directly be computed using equation (32), the quantity we are interested in.…”