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.

Fast radio bursts (FRBs) are mysterious radio bursts with a time scale of approximately milliseconds. Two populations of FRB, namely repeating and non-repeating FRBs, are observationally identified. However, the differences between these two and their origins are still cloaked in mystery. Here we show the time-integrated luminosityduration (L ν -w int,rest ) relations and luminosity functions (LFs) of repeating and nonrepeating FRBs in the FRB Catalogue project. These two populations are obviously separated in the L ν -w int,rest plane with distinct LFs, i.e., repeating FRBs have relatively fainter L ν and longer w int,rest with a much lower LF. In contrast with non-repeating FRBs, repeating FRBs do not show any clear correlation between L ν and w int,rest . These results suggest essentially different physical origins of the two. The faint ends of the LFs of repeating and non-repeating FRBs are higher than volumetric occurrence rates of neutron-star mergers and accretion-induced collapse (AIC) of white dwarfs, and are consistent with those of soft gamma-ray repeaters (SGRs), type Ia supernovae, magnetars, and white-dwarf mergers. This indicates two possibilities: either (i) faint non-repeating FRBs originate in neutron-star mergers or AIC and are actually repeating during the lifetime of the progenitor, or (ii) faint non-repeating FRBs originate in any of SGRs, type Ia supernovae, magnetars, and white-dwarf mergers. The bright ends of LFs of repeating and non-repeating FRBs are lower than any candidates of progenitors, suggesting that bright FRBs are produced from a very small fraction of the progenitors regardless of the repetition. Otherwise, they might originate in unknown progenitors.

We present a multi-wavelength analysis of the very fast X-ray transient MAXI J0158-744, which was detected by MAXI/GSC on 2011 November 11. The subsequent exponential decline of the Xray flux was followed with Swift observations, all of which revealed spectra with low temperatures (∼100eV) indicating that MAXI J0158-744 is a new Supersoft Source (SSS). The Swift X-ray spectra near maximum show features around 0.8 keV that we interpret as possible absorption from O viii, and emission from O, Fe, and Ne lines. We obtained SAAO and ESO optical spectra of the counterpart early in the outburst and several weeks later. The early spectrum is dominated by strong Balmer and He i emission, together with weaker He ii emission. The later spectrum reveals absorption features that indicate a B1/2IIIe spectral type, and all spectral features are at velocities consistent with the Small Magellanic Cloud. At this distance, it is a luminous SSS (> 10 37 erg s −1 ) but whose brief peak luminosity of > 10 39 erg s −1 in the 2-4 keV band makes it the brightest SSS yet seen at "hard" X-rays. We propose that MAXI J0158-744 is a Be-WD binary, and the first example to possibly enter ULX territory. The brief hard X-ray flash could possibly be a result of the interaction of the ejected nova shell with the B star wind in which the white dwarf (WD) is embedded. This makes MAXI J0158-744 only the third Be/WD system in the Magellanic Clouds, but it is by far the most luminous. The properties of MAXI J0158-744 give weight to previous suggestions that SSS in nearby galaxies are associated with early-type stellar systems.

We analyse the stellar and hot gas content of 18 nearby, low-mass galaxy clusters, detected in redshift space and selected to have a dynamical mass 3 × 1014 < M/M⊙ < 6 × 1014 (h= 0.7), as measured from the 2dF Galaxy Redshift Survey. We combine X-ray measurements from both Chandra and XMM with ground-based near-infrared observations from CTIO, Anglo-Australian Telescope and Canada–France–Hawaii Telescope to compare the mass in hot gas and stars to the dynamical mass and state of the clusters. Only 13 of the clusters are detected in X-ray emission, and for these systems we find that a range of 7–20 per cent of their baryonic mass, and <3 per cent of their dynamical mass, is detected in starlight, similar to what is observed in more massive clusters. In contrast, the five undetected clusters are underluminous in X-ray emission, by up to a factor of 10, given their stellar mass. Although the velocity distribution of cluster members in these systems is indistinguishable from a Gaussian, all show subtle signs of being unrelaxed: either they lack a central, dominant galaxy, or the bright galaxy distribution is less concentrated and/or more elongated than the rest of the sample. Thus we conclude that low-mass clusters and groups selected from the velocity distribution of their galaxies exhibit a dichotomy in their hot gas properties. Either they are detected in X-ray, in which case they generally lie on the usual scaling relations, or they are completely undetected in X-ray emission. The non-detections may be partly related to the apparently young dynamical state of the clusters, but it remains a distinct possibility that some of these systems are exceptionally devoid of hot emitting gas as the result of its expulsion or rarefaction