We present the evolution in the number density and stellar mass functions of photometrically selected post-starburst galaxies in the UKIDSS Deep Survey (UDS), with redshifts of 0.5 < z < 2 and stellar masses log(M/M ⊙ )> 10. We find that this transitionary species of galaxy is rare at all redshifts, contributing ∼5% of the total population at z ∼ 2, to <1% by z ∼ 0.5. By comparing the mass functions of quiescent galaxies to post-starburst galaxies at three cosmic epochs, we show that rapid quenching of star formation can account for 100% of quiescent galaxy formation, if the post-starburst spectral features are visible for ∼250 Myr. The flattening of the low mass end of the quiescent galaxy stellar mass function seen at z ∼ 1 can be entirely explained by the addition of rapidly quenched galaxies. Only if a significant fraction of post-starburst galaxies have features that are visible for longer than 250 Myr, or they acquire new gas and return to the star-forming sequence, can there be significant growth of the red sequence from a slower quenching route. The shape of the mass function of these transitory post-starburst galaxies resembles that of quiescent galaxies at z ∼ 2, with a preferred stellar mass of log(M/M ⊙ )∼ 10.6, but evolves steadily to resemble that of star-forming galaxies at z < 1. This leads us to propose a dual origin for post-starburst galaxies: (1) at z > ∼ 2 they are exclusively massive galaxies that have formed the bulk of their stars during a rapid assembly period, followed by complete quenching of further star formation; (2) at z < ∼ 1 they are caused by the rapid quenching of gas-rich star-forming galaxies, independent of stellar mass, possibly due to environment and/or gas-rich major mergers.

We have analysed the 24um properties of a radio-selected sample in the Subaru-XMM/Newton Deep Field in order to explore the behaviour of the FIR/radio relation at high redshifts. Statistically, the correlation is described by q24, the ratio between the observed flux densities at 24um and 1.4GHz, respectively. Using 24um data results in considerably more scatter in the correlation than previous work using data at 60-70um. Nevertheless, we do observe a steady correlation as a function of redshift, up to z~3.5, suggesting its validity back to primeval times. We find q24 = 0.30 +/- 0.56 for the observed and q24 = 0.71 +/- 0.47 for the k-corrected radio sample, based on sources with 300uJy < S(1.4GHz) < 3.2mJy and 24um detections. A suitable k-correction given by a M82-like mid-IR template suggests no extreme silicate absorption in the bulk of our radio sample. Using thresholds in q24 to identify radio-excess sources, we have been able to characterise the transition from radio-loud AGN to star-forming galaxies and radio-quiet AGN at faint (<1mJy) radio flux densities. Our results are in broad agreement with previous studies which show a dominant radio-loud AGN population at >1mJy. The rest-frame U-B colours of the expected radio-excess population have redder distribution than those that follow the correlation. This is therefore a promising way to select obscured Type-2 AGN, with a radio loud nature, missed by deep X-ray observations. Spectroscopic follow-up of these sources is required to fully test this method.Comment: The paper contains 7 figures and 1 table. In press at MNRA

We present the results of a search for galaxy clusters in Subaru-XMM Deep Field. We reach a depth for a total cluster flux in the 0.5-2 keV band of 2x10^{-15} ergs cm^{-2} s^{-1} over one of the widest XMM-Newton contiguous raster surveys, covering an area of 1.3 square degrees. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, 3 sources are identified as X-ray counterparts of radio lobes, and in 3 further sources, X-ray counterpart of radio lobes provides a significant fraction of the total flux of the source. In the area covered by NIR data, our identification success rate achieves 86%. We detect a number of radio galaxies within our groups and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with the predictions of concordance cosmology and current knowledge of the X-ray cluster properties, concluding that a reduction of concordance sigma_8 value by 5% is required in order to match the prediction of the model and the data. This conclusion still needs verification through the completion of cluster follow-up.Comment: 15 pages, MNRAS sub

We present spectroscopic and 11‐band photometric redshifts for galaxies in the 100‐μJy Subaru/XMM–NewtonDeep Field radio source sample. We find good agreement between our redshift distribution and that predicted by the Square Kilometre Array (SKA) Simulated Skies project. We find no correlation between K‐band magnitude and radio flux, but show that sources with 1.4‐GHz flux densities below ∼1 mJy are fainter in the near‐infrared than brighter radio sources at the same redshift, and we discuss the implications of this result for spectroscopically incomplete samples where the K–z relation has been used to estimate redshifts. We use the infrared–radio correlation to separate our sample into radio‐loud and radio‐quiet objects and show that only radio‐loud hosts have spectral energy distributions consistent with predominantly old stellar populations, although the fraction of objects displaying such properties is a decreasing function of radio luminosity. We calculate the 1.4‐GHz radio luminosity function (RLF) in redshift bins to z= 4 and find that the space density of radio sources increases with lookback time to z≈ 2, with a more rapid increase for more powerful sources. We demonstrate that radio‐loud and radio‐quiet sources of the same radio luminosity evolve very differently. Radio‐quiet sources display strong evolution to z≈ 2 while radio‐loud active galactic nuclei below the break in the RLF evolve more modestly and show hints of a decline in their space density at z > 1, with this decline occurring later for lower‐luminosity objects. If the radio luminosities of these sources are a function of their black hole spins then slowly rotating black holes must have a plentiful fuel supply for longer, perhaps because they have yet to encounter the major merger that will spin them up and use the remaining gas in a major burst of star formation.

Context. The advent of deep multiwavelength extragalactic surveys has led to the necessity for advanced and fast methods for photometric analysis. In fact, codes which allow analyses of the same regions of the sky observed at different wavelengths and resolutions are becoming essential to thoroughly exploit current and future data. In this context, a key issue is the confusion (i.e. blending) of sources in low-resolution images.Aims. We present -, a publicly available software package developed within the  project. - is aimed at extracting accurate photometry from low-resolution images, where the blending of sources can be a serious problem for the accurate and unbiased measurement of fluxes and colours.Methods. - can be considered as the next generation to , providing significant improvements over and above it and other similar codes (e.g. ). - gathers data from a high-resolution image of a region of the sky, and uses this information (source positions and morphologies) to obtain priors for the photometric analysis of the lower resolution image of the same field. - can handle different types of datasets as input priors, namely i) a list of objects that will be used to obtain cutouts from the real high-resolution image; ii) a set of analytical models (as .fits stamps); iii) a list of unresolved, point-like sources, useful for example for far-infrared (FIR) wavelength domains.Results. By means of simulations and analysis of real datasets, we show that - yields accurate estimations of fluxes within the intrinsic uncertainties of the method, when systematic errors are taken into account (which can be done thanks to a flagging code given in the output). - is many times faster than similar codes like  and  (up to hundreds, depending on the problem and the method adopted), whilst at the same time being more robust and more versatile. This makes it an excellent choice for the analysis of large datasets. When used with the same parameter sets as for  it yields almost identical results (although in a much shorter time); in addition we show how the use of different settings and methods significantly enhances the performance.Conclusions. - proves to be a state-of-the-art tool for multiwavelength optical to far-infrared image photometry. Given its versatility and robustness, - can be considered the preferred choice for combined photometric analysis of current and forthcoming extragalactic imaging surveys.

We present a Bayesian full-spectral-fitting analysis of 75 massive ($M_* \gt 10^{10.3} \, \mathrm{M_\odot }$) UVJ-selected galaxies at redshifts of 1.0 < z < 1.3, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multiwavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the bagpipes code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We first constrain the stellar mass versus stellar age relationship, finding a steep trend towards earlier average formation time with increasing stellar mass (downsizing) of $1.48^{+0.34}_{-0.39}$ Gyr per decade in mass, although this shows signs of flattening at $M_* \gt 10^{11} \, \mathrm{M_\odot }$. We show that this is consistent with other spectroscopic studies from 0 < z < 2. This relationship places strong constraints on the AGN-feedback models used in cosmological simulations. We demonstrate that, although the relationships predicted by simba and illustristng agree well with observations at z = 0.1, they are too shallow at z = 1, predicting an evolution of ≲0.5 Gyr per decade in mass. Secondly, we consider the connections between green-valley, post-starburst, and quiescent galaxies, using our inferred SFH shapes and the distributions of galaxy physical properties on the UVJ diagram. The majority of our lowest-mass galaxies ($M_* \sim 10^{10.5} \, \mathrm{M_\odot }$) are consistent with formation in recent (z < 2), intense starburst events, with time-scales of ≲500 Myr. A second class of objects experience extended star-formation epochs before rapidly quenching, passing through both green-valley and post-starburst phases. The most massive galaxies in our sample are extreme systems: already old by z = 1, they formed at z ∼ 5 and quenched by z = 3. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.

We investigate galactic-scale outflows in the redshift range 0.71 z 1.63, using 413 K-band selected galaxies observed in the spectroscopic follow-up of the UKIDSS Ultra-Deep Survey (UDSz). The galaxies have an average stellar mass of ∼10 9.5 M ⊙ and span a wide range in rest-frame colours, representing typical star-forming galaxies at this epoch. We stack the spectra by various galaxy properties, including stellar mass, [O II] equivalent width, star-formation rate, specific star-formation rate and rest-frame spectral indices. We find that outflows are present in virtually all spectral stacks, with velocities ranging from 100-1000 km s −1 , indicating that large-scale outflowing winds are a common property at these redshifts. The highest velocity outflows (>500 km s −1 ) are found in galaxies with the highest stellar masses and the youngest stellar populations. Our findings suggest that high velocity galactic outflows are mostly driven by star-forming processes rather than AGN, with implied mass outflow rates comparable to the rates of star formation. Such behaviour is consistent with models required to reproduce the high-redshift mass-metallicity relation.

We present a new method to classify the broad band optical-NIR spectral energy distributions (SEDs) of galaxies using three shape parameters (super-colours) based on a Principal Component Analysis of model SEDs. As well as providing a compact representation of the wide variety of SED shapes, the method allows for easy visualisation of information loss and biases caused by the incomplete sampling of the rest-frame SED as a function of redshift. We apply the method to galaxies in the UKIDSS Ultra Deep Survey with 0.9 < z < 1.2, and confirm our classifications by stacking rest-frame optical spectra for a fraction of objects in each class. As well as cleanly separating a tight red-sequence from star-forming galaxies, three unusual populations are identifiable by their unique colours: very dusty star-forming galaxies with high metallicity and old mean stellar age; post-starburst galaxies which have formed 10% of their mass in a recent unsustained starburst event; and metal-poor quiescent dwarf galaxies. We find that quiescent galaxies account for 45% of galaxies with log M * /M > 11, declining steadily to 13% at log M * /M = 10. The properties and mass-function of the poststarburst galaxies are consistent with a scenario in which gas-rich mergers contribute to the growth of the low and intermediate mass range of the red sequence.