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This paper presents the third data release of the INvestigating Stellar Population In RElics (INSPIRE) project, comprising 52 ultra-compact massive galaxies (UCMGs) observed with the X-Shooter spectrograph. We measure integrated stellar velocity dispersion, [Mg/Fe] abundances, ages, and metallicities for all the INSPIRE objects. We thus infer star formation histories and confirm the existence of a degree of relicness (DoR), defined in terms of the fraction of stellar mass formed by z  = 2, the time at which a galaxy has assembled 75 per cent of its mass, and the final assembly time. Objects with a high DoR assembled their stellar mass at early epochs, while low-DoR objects show a non-negligible fraction of later formed populations and hence a spread in ages and metallicities. A higher DoR correlates with larger [Mg/Fe], supersolar metallicity, and larger velocity dispersion values. The 52 UMCGs span a large range of DoR from 0.83 to 0.06, with 38 of them having formed more than 75  per cent of their mass by z  = 2. Of these, nine are extreme relics (DoR>0.7), since they formed the totality (⁠|$\gt 99~{{\ \rm per\ cent}}$|⁠) of their stellar mass by redshift z  = 2. The remaining 14 UCMGs cannot be considered relics, as they are characterized by more extended star formation histories. With INSPIRE  we built the first sizeable sample of relics outside the local Universe, up to z ∼ 0.4, increasing the number of confirmed relics by a factor of >10, and opening up an important window to explain the mass assembly of massive galaxies in the high- z Universe. [ABSTRACT FROM AUTHOR]

We constrain the ΛCDM cosmological parameter σ8 by applying the extreme value statistics for galaxy cluster mass on the AMICO KiDS-DR3 catalogue. We sample the posterior distribution of the parameters by considering the likelihood of observing the largest cluster mass value in a sample of N obs = 3644 clusters with intrinsic richness λ* > 20 in the redshift range z ∈ [0.10, 0.60]. We obtain |$\sigma _{8}=0.90_{-0.18}^{+0.20}$|⁠ , consistent within 1σ with the measurements obtained by the Planck collaboration and with previous results from cluster cosmology exploiting AMICO KiDS-DR3. The constraints could improve by applying this method to forthcoming missions, such as Euclid and LSST, which are expected to deliver thousands of distant and massive clusters. [ABSTRACT FROM AUTHOR]

Spiral galaxies undergo strong ram-pressure effects when they fall into the galaxy cluster potential. As a consequence, their gas is stripped to form extended tails within which star formation can happen, giving them the typical jellyfish appearance. The ultraviolet imaging observations of jellyfish galaxies provide an opportunity to understand ongoing star formation in the stripped tails. We report the ultraviolet observations of the jellyfish galaxies JW39, JO60, JO194 and compare with observations in optical continuum and Hα. We detect knots of star formation in the disc and tails of the galaxies and find that their UV and Hα flux are well correlated. The optical emission line ratio maps of these galaxies are used to identify for every region the emission mechanism, due to either star formation, LINER or a mix of the two phenomena. The star-forming regions in the emission line maps match very well with the regions having significant UV flux. The central regions of two galaxies (JW39, JO194) show a reduction in UV flux which coincides with composite or LINER regions in the emission line maps. The galaxies studied here demonstrate significant star formation in the stripped tails, suppressed star formation in the central regions and present a possible case of accelerated quenching happening in jellyfish galaxies. [ABSTRACT FROM AUTHOR]

We report evidence for star formation quenching in the central 8.6 kpc region of the jellyfish galaxy JO201 that hosts an active galactic nucleus (AGN), while undergoing strong ram-pressure stripping. The ultraviolet imaging data of the galaxy disc reveal a region with reduced flux around the centre of the galaxy and a horse-shoe-shaped region with enhanced flux in the outer disc. The characterization of the ionization regions based on emission line diagnostic diagrams shows that the region of reduced flux seen in the ultraviolet is within the AGN-dominated area. The CO J2−1 map of the galaxy disc reveals a cavity in the central region. The image of the galaxy disc at redder wavelengths (9050–9250 Å) reveals the presence of a stellar bar. The star formation rate map of the galaxy disc shows that the star formation suppression in the cavity occurred in the last few 108 yr. We present several lines of evidence supporting the scenario that suppression of star formation in the central region of the disc is most likely due to the feedback from the AGN. The observations reported here make JO201 a unique case of AGN feedback and environmental effects suppressing star formation in a spiral galaxy. [ABSTRACT FROM AUTHOR]

Despite the high accuracy of photometric redshifts (zphot) derived using machine learning (ML) methods, the quantification of errors through reliable and accurate probability density functions (PDFs) is still an open problem. First, because it is difficult to accurately assess the contribution from different sources of errors, namely internal to the method itself and from the photometric features defining the available parameter space. Secondly, because the problem of defining a robust statistical method, always able to quantify and qualify the PDF estimation validity, is still an open issue. We present a comparison among PDFs obtained using three different methods on the same data set: two ML techniques, METAPHOR (Machine-learning Estimation Tool for Accurate PHOtometric Redshifts) and ANNz2, plus the spectral energy distribution template-fitting method, BPZ (Bayesian photometric redshift). The photometric data were extracted from the Kilo Degree Survey ESO Data Release 3, while the spectroscopy was obtained from the Galaxy and Mass Assembly Data Release 2. The statistical evaluation of both individual and stacked PDFs was done through quantitative and qualitative estimators, including a dummy PDF, useful to verify whether different statistical estimators can correctly assess PDF quality. We conclude that, in order to quantify the reliability and accuracy of any zphot PDF method, a combined set of statistical estimators is required. [ABSTRACT FROM AUTHOR]

We have obtained structural parameters of about 340 000 galaxies from the Kilo-Degree Survey (KiDS) in 153 deg2 of data release 1, 2, and 3. We have performed a seeing convolved 2D single Sérsic fit to the galaxy images in the four photometric bands (u, g, r, i) observed by KiDS, by selecting high signal-to-noise ratio (S/N > 50) systems in every bands. We have classified galaxies as spheroids and disc-dominated by combining their spectral energy distribution properties and their Sérsic index. Using photometric redshifts derived from a machine learning technique, we have determined the evolution of the effective radius, R e and stellar mass, M ⋆, versus redshift, for both mass complete samples of spheroids and disc-dominated galaxies up to z ∼0.6. Our results show a significant evolution of the structural quantities at intermediate redshift for the massive spheroids (log  M */M⊙ > 11, Chabrier IMF), while almost no evolution has found for less massive ones (log  M */M⊙ < 11). On the other hand, disc dominated systems show a milder evolution in the less massive systems (log  M */M⊙ < 11) and possibly no evolution of the more massive systems. These trends are generally consistent with predictions from hydrodynamical simulations and independent datasets out to redshift $$z$$ ∼ 0.6, although in some cases the scatter of the data is large to drive final conclusions. These results, based on 1/10 of the expected KiDS area, reinforce precedent finding based on smaller statistical samples and show the route towards more accurate results, expected with the the next survey releases. [ABSTRACT FROM AUTHOR]

We study the dark matter (DM) assembly in the central regions of massive early-type galaxies up to z ~ 0.65. We use a sample of ~3800 massive (log M*/M☉ > 11.2) galaxies with photometry and structural parameters from 156 deg2 of the Kilo Degree Survey (KiDS), and spectroscopic redshifts and velocity dispersions from Sloan Digital Sky Survey (SDSS). We obtain central total-to-stellar mass ratios, Mdyn/M*, and DM fractions, by determining dynamical masses, Mdyn, from Jeans modelling of SDSS aperture velocity dispersions and stellar masses, M*, from KiDS galaxy colours. We first show how the central DM fraction correlates with structural parameters, mass and density proxies, and demonstrate that most of the local correlations are still observed up to z ~ 0.65; at fixed M*, local galaxies have larger DM fraction, on average, than their counterparts at larger redshift. We also interpret these trends with a non-universal initial mass function (IMF), finding a strong evolution with redshift, which contrast independent observations and is at odds with the effect of galaxy mergers. For a fixed IMF, the galaxy assembly can be explained, realistically, by mass and size accretion, which can be physically achieved by a series of minor mergers. We reproduce both the Re-M* and Mdyn/M*-M* evolution with stellar and dark mass changing at a different rate. This result suggests that the main progenitor galaxy is merging with less massive systems, characterized by a smaller Mdyn/M*, consistently with results from halo abundance matching. [ABSTRACT FROM AUTHOR]

In this paper, we present a new method to select the faint, background galaxies used to derive the mass of galaxy clusters by weak lensing. The method is based on the simultaneous analysis of the shear signal, that should be consistent with zero for the foreground, unlensed galaxies, and of the colours of the galaxies: photometric data from the COSMic evOlution Survey are used to train the colour selection. In order to validate this methodology, we test it against a set of state-of-the-art image simulations of mock galaxy clusters in different redshift [0.23-0.45] and mass [0.5-1.55 × 1015 M⊙] ranges, mimicking medium-deep multicolour imaging observations [e.g. Subaru, Large Binocular Telescope]. The performance of our method in terms of contamination by unlensed sources is comparable to a selection based on photometric redshifts, which however requires a good spectral coverage and is thus much more observationally demanding. The application of our method to simulations gives an average ratio between estimated and true masses of ∼0.98 ± 0.09. As a further test, we finally apply our method to real data, and compare our results with other weak-lensing mass estimates in the literature: for this purpose, we choose the cluster Abell 2219 (z = 0.228), for which multiband (BVRi) data are publicly available. [ABSTRACT FROM AUTHOR]

The abundance of compact, massive, early-type galaxies (ETGs) provides important constraints to galaxy formation scenarios. Thanks to the area covered, depth, excellent spatial resolution and seeing, the ESO Public optical Kilo Degree Survey (KiDS), carried out with the VLT Survey Telescope, offers a unique opportunity to conduct a complete census of the most compact galaxies in the Universe. This paper presents a first census of such systems from the first 156 deg2 of KiDS. Our analysis relies on g-, r- and i-band effective radii (Re), derived by fitting galaxy images with point spread function (PSF)-convolved Sérsic models, high-quality photometric redshifts, zphot, estimated from machine learning techniques, and stellar masses, M*, calculated from KiDS aperture photometry. After massiveness (M* ≳ 8 × 1010M☉) and compactness (Re ≲ 1.5 kpc in g, r and i bands) criteria are applied, a visual inspection of the candidates plus near-infrared photometry from VIKING-DR1 are used to refine our sample. The final catalogue, to be spectroscopically confirmed, consists of 92 systems in the redshift range z ~ 0.2-0.7. This sample, which we expect to increase by a factor of 10 over the total survey area, represents the first attempt to select massive supercompact ETGs (MSCGs) in KiDS. We investigate the impact of redshift systematics in the selection, finding that this seems to be a major source of contamination in our sample. A preliminary analysis shows that MSCGs exhibit negative internal colour gradients, consistent with a passive evolution of these systems. We find that the number density of MSCGs is only mildly consistent with predictions from simulations at z > 0.2, while no such system is found at z < 0.2. [ABSTRACT FROM AUTHOR]

We have estimated photometric redshifts (zphot) for more than 1.1 million galaxies of the public European Southern Observatory (ESO) Kilo-Degree Survey (KiDS) data release 2. KiDS is an optical wide-field imaging survey carried out with the Very Large Telescope (VLT) Survey Telescope (VST) and the OmegaCAM camera, which aims to tackle open questions in cosmology and galaxy evolution, such as the origin of dark energy and the channel of galaxy mass growth. We present a catalogue of photometric redshifts obtained using the Multi-Layer Perceptron with Quasi-Newton Algorithm (MLPQNA) model, provided within the framework of the DAta Mining and Exploration Web Application REsource (DAMEWARE). These photometric redshifts are based on a spectroscopic knowledge base that was obtained by merging spectroscopic data sets from the Galaxy and Mass Assembly (GAMA) data release 2 and the Sloan Digital Sky Survey III (SDSS-III) data release 9. The overall 1σ uncertainty on Δz = (zspec − zphot)/(1 + zspec) is ~0.03, with a very small average bias of ~0.001, a normalized median absolute deviation of ~0.02 and a fraction of catastrophic outliers (|Δz| > 0.15) of ~0.4 per cent. [ABSTRACT FROM AUTHOR]

ABSTRACT The Capodimonte–Sternberg–Lens candidate no. 1 is an extragalactic double source detected in the Osservatorio Astronomico di Capodimonte – Deep Field. It can be interpreted either as the chance alignment of two identical galaxies at z= 0.46 or as the first case of gravitational lensing by a cosmic string. Extensive modelling shows in fact that cosmic strings are the only type of lens which (at least at low angular resolution) can produce undistorted double images of a background source. We propose an experimentum crucis to disentangle these two possible explanations. If the lensing by a cosmic string should be confirmed, it would provide the first measurements of energy scale of symmetry breaking and of the energy scale of grand unified theory. [ABSTRACT FROM AUTHOR]