Ikema (Miyako Ryukyuan)

We quantify the evolution of the stellar mass functions (SMFs) of star-forming and quiescent galaxies as a function of morphology from z ~ 3 to the present. Our sample consists of ~ 50000 galaxies in the CANDELS fields (~880 arcmin2), which we divide into four main morphological types, i.e. pure bulge-dominated systems, pure spiral disc-dominated, intermediate two-component bulge+disc systems and irregular disturbed galaxies. Our main results are:1) Star-formation: At z ~ 2, 80% of the stellar mass density of star-forming galaxies is in irregular systems. However, by z ~ 0.5, irregular objects only dominate at stellar masses below 109 Msun. A majority of the star-forming irregulars present at z ~ 2 undergo a gradual transformation from disturbed to normal spiral disc morphologies by z ~ 1 without significant interruption to their star formation. Rejuvenation after a quenching event does not seem to be common except perhaps for the most massive objects, because the fraction of bulge-dominated star-forming galaxies with M*/Msun > 1010.7 reaches 40% at z < 1. 2) Quenching: We confirm that galaxies reaching a stellar mass of M* ~ 1010.8 Msun (M*) tend to quench. Also, quenching implies the presence of a bulge: the abundance of massive red discs is negligible at all redshifts over 2 dex in stellar mass. However, the dominant quenching mechanism evolves. At z > 2, the SMF of quiescent galaxies above M* is dominated by compact spheroids. Quenching at this early epoch destroys the disc and produces a compact remnant unless the star-forming progenitors at even higher redshifts are significantly more dense. At 1 < z < 2, the majority of newly quenched galaxies are discs with a significant central bulge. This suggests that mass quenching at this epoch starts from the inner parts and preserves the disc. At z < 1, the high-mass end of the passive SMF is globally in place and the evolution mostly happens at stellar masses below 1010 Msun. These low-mass galaxies are compact, bulge-dominated systems, which were environmentally quenched: destruction of the disc through ram-pressure stripping is the likely process

Success and failure in secondary education: socio-economic background effects on secondary school outcome in the Netherlands, 1927-1998

In the Netherlands, educational attainment is the result of a sequence of separate educational transitions. Because of the tracked nature of the Dutch educational system, students do not make binary stay-or-leave-decisions at each transition. After having entered one track of secondary education, students can change tracks during the entire secondary course. The initial track and the secondary school outcome therefore are incongruent for a significant proportion of the Dutch students. As social background partly predicts initial track placement, track changes and successful termination of the course, we suggest distinguishing conditional and unconditional effects of family background in the transition to secondary school outcome. This paper complements findings of previous research by taking into account the tracked structure of the Dutch educational system and the entire sequence of transitions in secondary education. For the empirical analysis, repeated cross-sections from the Family Survey Dutch Population (1992, 1998, 2000 and 2003) are used. Multinomial logistic regressions reveal that inequality in the outcome of secondary education is partly explained by the fact that initial track placement is socially selective and because this initial inequality is even enhanced by track changes during secondary education. The remaining ‘conditional’ effect of parental education, however, indicates that parental education works on top of this selection to prevent drop out. Inequality in secondary school outcome thus is a cumulative result of social background effects in a sequence of educational transitions throughout secondary education. Decreasing inequality over time is entirely explained by decreasing inequality in the transition from primary to secondary education.

Fast, Slow, Early, Late: Quenching Massive Galaxies at z ∼ 0.8

We investigate the stellar populations for a sample of 161 massive, mainly quiescent galaxies at 〈zobs〉 = 0.8 with deep Keck/DEIMOS rest-frame optical spectroscopy (HALO7D survey). With the fully Bayesian framework Prospector, we simultaneously fit the spectroscopic and photometric data with an advanced physical model (including nonparametric star formation histories, emission lines, variable dust attenuation law, and dust and active galactic nucleus emission), together with an uncertainty and outlier model. We show that both spectroscopy and photometry are needed to break the dust–age–metallicity degeneracy. We find a large diversity of star formation histories: although the most massive (M⋆ > 2 × 1011 M⊙) galaxies formed the earliest (formation redshift of zf ≈ 5–10 with a short star formation timescale of τSF ≲ 1 Gyr), lower-mass galaxies have a wide range of formation redshifts, leading to only a weak trend of zf with M⋆. Interestingly, several low-mass galaxies have formation redshifts of zf ≈ 5–8. Star-forming galaxies evolve about the star-forming main sequence, crossing the ridgeline several times in their past. Quiescent galaxies show a wide range and continuous distribution of quenching timescales (τquench ≈ 0–5 Gyr) with a median of $\langle {\tau }_{\mathrm{quench}}\rangle ={1.0}_{-0.9}^{+0.8}\,\mathrm{Gyr}$ and of quenching epochs of zquench ≈ 0.8–5.0 ($\langle {z}_{\mathrm{quench}}\rangle ={1.3}_{-0.4}^{+0.7}$). This large diversity of quenching timescales and epochs points toward a combination of internal and external quenching mechanisms. In our sample, rejuvenation and "late bloomers" are uncommon. In summary, our analysis supports the "grow-and-quench" framework and is consistent with a wide and continuously populated diversity of quenching timescales