Search

The connection between quenching mechanisms, which rapidly turn star-forming systems into quiescent, and the properties of the galaxy population remains difficult to discern. In this work we investigate the physical properties of MaNGA and SAMI galaxies at different stages of their star formation history. Specifically, we compare galaxies with signatures of recent quenching (Quenched) – |$\rm H \, \alpha$| in absorption and low Dn (4000) – with the rest of the low star-forming and active population (Retired and Ageing, respectively). The analysis is performed in terms of characteristics such as the total stellar mass, half-light radius, velocity-to-dispersion ratio, metallicity, and environment. We find that the Ageing population comprises a heterogeneous mixture of galaxies, preferentially late-type systems, with diverse physical properties. Retired galaxies, formerly Ageing or Quenched systems, are dominated by early-type high-mass galaxies found both at low and dense environments. Most importantly, we find that recently quenched galaxies are consistent with a population of compact low-mass satellite systems, with higher metallicities than their Ageing analogues. We argue that this is compatible with being quenched after undergoing a star-burst phase induced by environmental processes (e.g. ram pressure). However, we also detect a non-negligible fraction of field central galaxies likely quenched by internal processes. This study highlights that, in order to constrain the mechanisms driving galaxy evolution, it is crucial to distinguish between old (Retired) and recently quenched galaxies, thus requiring at least two estimates of the specific star formation rate over different time-scales. [ABSTRACT FROM AUTHOR]

We study recent changes on the star-formation history (SFH) of galaxies by means of the ageing diagram (AD), tracing the fraction of stars formed during the last ∼20 Myr through the equivalent width of the |$\rm H\alpha$| line and ∼1−3 Gyr through the dust-corrected optical colour (g − r)0or the Balmer break. We provide a physical characterization by using Pipe3D estimates of the SFH of Calar Alto Legacy Integral Field Area and Mapping Nearby Galaxies at Apache Point Observatory galaxies, in combination with the predictions from IllustrisTNG-100. Our results show that the AD may be divided into four domains that correlate with the stellar mass fractions formed in the last 20 Myr and 3 Gyr: ageing systems, whose star formation rate changes on scales of several Gyr, account for |$70-80{{\ \rm per\ cent}}$| of the galaxy population. Objects whose SFH was abruptly truncated in the last ∼1 Gyr arrange along a detached quenched sequence that represents |$\sim 5-10{{\ \rm per\ cent}}$| by (volume-corrected) number for 109 < M */M⊙ < 1012. Undetermined systems represent an intermediate population between the ageing and quenched regimes. Finally, Retired galaxies, dominated by old stellar populations, are located at the region in the AD where the ageing and quenched sequences converge. Defining different star formation activity levels in terms of the birth rate parameter |$b\equiv \frac{SFR}{\langle SFR \rangle }$|⁠ , we find that galaxies transit from the ageing to quenched sequences on scales ∼500 Myr. We conclude that the AD provides a useful tool to discern recently quenched galaxies from the dominant ageing population. [ABSTRACT FROM AUTHOR]

We modelled dust grain-size distributions for carbonaceous and silicates dust, as well as for free-flying iron nanoparticles in the environment of a γ-ray burst (GRB) afterglow, GRB 180325A. This GRB, at a redshift (⁠|$z$|⁠) of 2.2486, has an unambiguous detection of the 2175 Å extinction feature with R V  = 4.58 and A V  = 1.58 mag. In addition to silicates, polycyclic aromatic hydrocarbons (PAH), and graphite, we used iron nanoparticles grain-size distributions for the first time to model the observed extinction curve of GRB 180325A. We fit the observed extinction for four model permutations, using 232 sets of silicates, graphite, carbon abundance in hydrocarbon molecules (b C), and fraction of iron abundance in free-flying nanoparticles (Y Fe). These four different permutations were chosen to test iron nanoparticles significance and carbon abundance in hydrocarbons. Our results indicate that iron nanoparticles contribution is insignificant and there is a degeneracy of carbon abundances, with the range (0.0 ≤ b C ≤ 0.7) × 10−5 providing the best-fit to the observed extinction curve of GRB 180325A. We therefore favour the simplest model of silicates and PAHs. The silicates are dominant and contribute to the entire wavelength range of the GRB extinction curve while graphite contributes towards both the 2175 Å bump and the ultraviolet (UV) extinction. The afterglow peak luminosity (1.5 × 1051 erg s−1) indicates dust destruction may have taken place. We conclude that further investigations into other potential contributors of extinction are warranted, particularly for steep UV extinction. [ABSTRACT FROM AUTHOR]

For years, the extragalactic community has divided galaxies in two distinct populations. One of them, featuring blue colours, is actively forming stars, while the other is made up of 'red-and-dead' objects with negligible star formation. Yet, are these galaxies really dead? Here, we would like to highlight that, as previously reported by several independent groups, state-of-the-art cosmological numerical simulations (EAGLE, IllustrisTNG, MAGNETICUM, and SIMBA) predict the existence of a large number of quenched galaxies that have not formed any star over the last few Gyr. In contrast, observational measurements of large galaxy samples in the nearby Universe (GAMA, SDSS) suggest that even the most passive systems still form stars at some residual level close to sSFR ∼ 10−12 yr−1. Unfortunately, extremely low star formation poses a challenge for both approaches. We conclude that, at present, the fraction of truly dead galaxies is still an important open question that must be addressed in order to understand galaxy formation and evolution. [ABSTRACT FROM AUTHOR]