The global star formation rate has decreased significantly since z∼ 1, for reasons that are not well understood. Red‐sequence galaxies, dominating in galaxy clusters, represent the population that have had their star formation shut off, and may therefore be the key to this problem. In this work, we select 127 rich galaxy clusters at 0.17 ≤z≤ 0.36, from 119 deg2 of the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) optical imaging data, and construct the r′‐band red‐sequence luminosity functions (LFs). We show that the faint end of the LF is very sensitive to how red‐sequence galaxies are selected, and an optimal way to minimize the contamination from the blue cloud is to mirror galaxies on the redder side of the colour–magnitude relation. The LFs of our sample have a significant inflexion centred at , suggesting a mixture of two populations. Combining our survey with low‐redshift samples constructed from the Sloan Digital Sky Survey, we show that there is no strong evolution of the faint end of the LF (or the red‐sequence dwarf‐to‐giant ratio) over the redshift range 0.2 ≲z≲ 0.4, but from z∼ 0.2 to ∼0 the relative number of red‐sequence dwarf galaxies has increased by a factor of ∼3, implying a significant build‐up of the faint end of the cluster red sequence over the last 2.5 Gyr.

We describe new JWST/NIRSpec observations of galaxies at 𝑧 7 taken as part of the CEERS survey of the EGS field. Previous observations of this area have revealed associations of Ly𝛼 emitters at redshifts (𝑧 = 7.5, 7.7, 8.7) where the IGM is thought mostly neutral, leading to suggestions that these systems are situated in large ionized bubbles. We identify 21 𝑧 7 galaxies with robust redshifts in the CEERS dataset, including 10 in the Ly𝛼 associations. Their spectra are indicative of very highly ionized and metal poor gas, with line ratios (O32 = 17.84 and Ne3O2 = 0.89) and metallicity (12 + log [O/H] = 7.84) that are rarely seen at lower redshifts. We find that the most extreme spectral properties are found in the six 𝑧 7 Ly𝛼 emitting galaxies in the sample. Each have hard ionizing spectra indicating that their visibility is likely enhanced by efficient ionizing photon production. Ly𝛼 velocity offsets are found to be very large ( 300 km s −1 ), likely also contributing to their detectability. We find that Ly𝛼 in 𝑧 7 galaxies is 6 − 12× weaker than in lower redshift samples with matched rest-frame optical spectral properties. If the bubbles around the Ly𝛼 emitters are relatively small ( 0.5 − 1 pMpc), we may expect such significant attenuation of Ly𝛼 in these ionized regions. We discuss several other effects that may contribute to weaker Ly𝛼 emission at 𝑧 7. Deep spectroscopy of fainter galaxies in the vicinity of the Ly𝛼 emitters will better characterize the physical scale of the ionized bubbles in this field.

Fast radio bursts (FRBs) are millisecond transients of unknown origin(s) occurring at cosmological distances. Here we, for the first time, show time-integrated-luminosity functions and volumetric occurrence rates of non-repeating and repeating FRBs against redshift. The time-integrated-luminosity functions of non-repeating FRBs do not show any significant redshift evolution. The volumetric occurrence rates are almost constant during the past ∼10 Gyr. The nearly-constant rate is consistent with a flat trend of cosmic stellar-mass density traced by old stellar populations. Our findings indicate that the occurrence rate of non-repeating FRBs follows the stellar-mass evolution of long-living objects with ∼Gyr time scales, favouring e.g. white dwarfs, neutron stars, and black holes, as likely progenitors of non-repeating FRBs. In contrast, the occurrence rates of repeating FRBs may increase towards higher redshifts in a similar way to the cosmic star formation-rate density or black hole accretion-rate density if the slope of their luminosity function does not evolve with redshift. Short-living objects with ≲ Myr time scales associated with young stellar populations (or their remnants, e.g., supernova remnants, young pulsars, and magnetars) or active galactic nuclei might be favoured as progenitor candidates of repeating FRBs.

Using the optical data from the Wide component of the Canada–France–Hawaii Telescope (CFHT) Legacy Survey, and new ultraviolet (UV) data from GALEX, we study the colours and specific star formation rates (SSFRs) of ∼ 100 galaxy clusters at 0.16 < z < 0.36, over areas extending out to radii of r∼ 7 Mpc. We use a multicolour, statistical background subtraction method to study the galaxy population at this radius; thus our results pertain to those galaxies which constitute an excess over the average field density. We find that the average SSFR and its distribution of the star‐forming galaxies (with at z∼ 0.2 and at z∼ 0.3) have no measurable dependence on the clustercentric radius and are consistent with the field values. However, the fraction of galaxies with SFR above these thresholds, and the fraction of optically blue galaxies, are lower for the overdense galaxy population in the cluster outskirts compared with the average field value, at all stellar masses and at all radii out to at least 7 Mpc. Most interestingly, the fraction of blue galaxies that are forming stars at a rate below our UV detection limit is much higher in all radial bins around our cluster sample compared with the general field value. This is most noticeable for massive galaxies ; while almost all blue field galaxies of this mass have detectable star formation, this is true for less than 20 per cent of the blue cluster galaxies, even at 7 Mpc from the cluster centre. Our results support a scenario where galaxies are pre‐processed in locally overdense regions in a way that reduces their SFR below our UV detection limit, but not to zero.

We present the analysis of a new near-infrared (NIR) spectrum of a recently discovered z = 6.621 quasar PSO J006+39 in an attempt to explore the early growth of supermassive black holes (SMBHs). This NIR (rest-frame ultraviolet, UV) spectrum shows blue continuum slope and rich metal emission lines in addition to Lyα line. We utilize the Mg line width and the rest frame luminosity L 3000Å to find the mass of SMBH (M BH ) to be ∼ 10 8 M ⊙ , making this one of the lowest mass quasars at high redshift. The power-law slope index (α λ ) of the continuum emission is −2.94 ± 0.03, significantly bluer than the slope of α λ = −7/3 predicted from standard thin disc models. We fit the spectral energy distribution (SED) using a model which can fit local SMBHs, which includes warm and hot Comptonisation powered by the accretion flow as well as an outer standard disc. The result shows that the very blue slope is probably produced by a small radial (∼ 230 gravitational radius, R g ) extent of the standard accretion disc. All plausible SED models require that the source is super-Eddington (L bol /L Edd 9), so the apparently small disc may simply be the inner funnel of a puffed up flow, and clearly the SMBH in this quasar is in a rapid growth phase. We also utilize the rest-frame UV emission lines to probe the chemical abundance in the broad line region (BLR) of this quasar. We find that this quasar has super solar metallicity through photoionization model calculations.