E. Puddu

Luminosity function of clusters of galaxies

The composite galaxy luminosity function (hereafter LF) of 39 Abell clusters of galaxies is derived by computing the statistical excess of galaxy counts in the cluster direction with respect to control elds. Due to the wide eld coverage of the digitised POSS-II plates, we can measure eld counts around each cluster in a fully homogeneous way. Furthermore, the availability of virtually unlimited sky coverage allows us to directly compute the LF errors without having to rely on the estimated variance of the background. The wide eld coverage also allows us to derive the LF of the whole cluster, including galaxies located in the cluster outskirts. The global composite LF has a slope 1:1 0:2 with minor variations from blue to red lters, and M 21:7; 22:2; 22: 4m ag (H0 =5 0 km s 1 Mpc 1 )i ng;r and i lters, respectively (errors are detailed in the text). These results are in quite good agreement with several previous determinations and in particular with the LF determined for the inner region of a largely overlapping set of clusters, but derived making use of a completely dierent method for background subtraction. The similarity of the two LFs suggests the existence of minor dierences between the LF in the cluster outskirts and in the central region, or a negligible contribution of galaxies in the cluster outskirts to the global LF.

New evidence for a linear colour–magnitude relation and a single Schechter function for red galaxies in a nearby cluster of galaxies down to M*+ 8

The colour and luminosity distributions of red galaxies in the cluster Abell 1185 (z = 0.0325) were studied down to M ∗ + 8 in the B, V and R bands. The colour‐magnitude (CM) relation is linear without evidence for significant bending down to absolute magnitudes that are seldom probed in the literature (MR =− 12.5 mag). The CM relation is thin (±0.04 mag) and its thickness is quite independent of the magnitude. The luminosity function (LF) of red galaxies in Abell 1185 is adequately described by a Schechter function, with a characteristic magnitude and a faint end slope that also well describe the LF of red galaxies in other clusters. There is no passband dependence of the LF shape other than an obvious M ∗ shift due to the colour of the considered population. Finally, we conclude that, based on colours and luminosity, red galaxies form a homogeneous population over four decades in stellar mass, providing a second piece of evidence against faint red galaxies being a recent cluster population.

Scaling relations of the colour-detected cluster RzCS 052 at z= 1.016 and some other high-redshift clusters

We report on the discovery of the z = 1.016 cluster RzCS 052 using a modified red-sequence method, follow up spectroscopy and X-ray imaging. This cluster has a velocity dispersion of 710 ± 150 km s -1 , a virial mass of 4.0 x 10 14 M ⊙ (based on 21 spectroscopically confirmed members) and an X-ray luminosity of (0.68 ± 0.47) x 10 44 erg s -1 in the [1-4] keV band. This optically selected cluster appears to be of richness class 3 and to follow the known L X -σ v relation for high-redshift X-ray selected clusters. Using these data, we find that the halo occupation number for this cluster is only marginally consistent with what was expected assuming a self-similar evolution of cluster scaling relations, suggesting perhaps a break of them at z ∼ 1. We also rule out a strong galaxy merging activity between z = 1 and today. Finally, we present a Bayesian approach to measuring cluster velocity dispersions and X-ray luminosities in the presence of a background: we critically reanalyse recent claims for X-ray underluminous clusters using these techniques and find that the clusters can be accommodated within the existing L X -σ v relation.

Towards a census of supercompact massive galaxies in the Kilo Degree Survey

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 Sersic models, high-quality photometric redshifts, zphot, estimated from machine learning techniques, and stellar masses, M⋆, calculated from KiDS aperture photometry. After massiveness ({M_{⋆}}≳ 8 × 10^{10} M_{⊙}) and compactness ({R_e}≲ 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.

A weak-lensing analysis of the Abell 383 cluster

Aims. We use deep CFHT and SUBARU uBVRIz archival images of the Abell 383 cluster (z = 0.187) to estimate its mass by weak-lensing. Methods. To this end, we first use simulated images to check the accuracy provided by our Kaiser-Squires-Broadhurst (KSB) pipeline. These simulations include shear testing programme (STEP) 1 and 2 simulations, as well as more realistic simulations of the distortion of galaxy shapes by a cluster with a Navarro-Frenk-White (NFW) profile. From these simulations we estimate the effect of noise on shear measurement and derive the correction terms. The R-band image is used to derive the mass by fitting the observed tangential shear profile with an NFW mass profile. Photometric redshifts are computed from the uBVRIz catalogs. Different methods for the foreground/background galaxy selection are implemented, namely selection by magnitude, color, and photometric redshifts, and the results are compared. In particular, we developed a semi-automatic algorithm to select the foreground galaxies in the color-color diagram, based on the observed colors. Results. Using color selection or photometric redshifts improves the correction of dilution from foreground galaxies: this leads to higher signals in the inner parts of the cluster. We obtain a cluster mass M vir = 7.5 +2.7 -1.9 × 10 14 M ⊙ : this value is ~20% higher than previous estimates and is more consistent the mass expected from X-ray data. The R-band luminosity function of the cluster is computed and gives a total luminosity L tot = (2.14 ± 0.5) x 10 12 L ⊙ and a mass-to-luminosity ratio M/L ~ 300 M ⊙ /L ⊙ .

Morphology of low-redshift compact galaxy clusters – I. Shapes and radial profiles

The morphology of clusters of galaxies may be described with a set of parameters which contain information concerning the formation and evolutionary history of these systems. In this paper we present a preliminary study of the morphological parameters of a sample of 28 compact Abell clusters extracted from Digitized Palomar Sky Survey data, measured with a procedure based on the use of the CIAO-SHERPA software, developed at the Centre for Astrophysics for X-ray data analysis. The morphology of galaxy clusters is parametrized by their apparent ellipticity, position angle of the major axis, centre coordinates, core radius and β-model power-law index. Our procedure provides estimates of these parameters (and of the related uncertainties) by simultaneously fitting them all, overcoming some of the difficulties induced by sparse data and low-number statistics typical of this kind of analysis. The cluster parameters were fitted in a 6 x 6 Mpc 2 region, measuring the background in a 4 < R < 5 Mpc annulus. We also explore the correlations between shape and profile parameters and other cluster properties. Our results can be summarized as follows: one-third of this compact cluster sample has core radii smaller than 100 kpc, i.e. near the limit that our data allow us to resolve, possibly consistent with cusped models. The remaining clusters span a broad range of core radii up to ∼1500 kpc, including some apparently regular clusters with well-resolved core radii. More than 80 per cent of this sample has ellipticity higher than 0.2. The alignment between the cluster and the major axis of the dominant galaxy is confirmed at a high significance level, while no correlation is observed with other bright cluster members. No significant correlation is found between cluster richness and ellipticity. Instead, cluster richness is found to correlate, albeit with large scatter, with the cluster core radius. Finally, in contrast to claims in previous works, a flat universe seems to be favoured, and in any case is not excluded, by the power-law index β of our number density profiles.

The Capodimonte Deep field : Presentation of the survey and first follow-up studies

We present the Capodimonte Deep Field (OACDF), a deep field covering an area of 0.5 square degrees in the B, V, R optical bands plus six medium-band filters in the wavelength range 773--913 nm. The field reaches the following limiting AB magnitudes: B~25.3, V~24.8 and R~25.1 and contains about 50000 extended sources in the AB magnitude range 18 < R < 25 . Hence, it is intermediate between deep pencil beam surveys and very wide but shallow surveys. The main scientific goal of the OACDF is the identification and characterization of early-type field galaxies at different look-back times in order to study different scenarios of galaxy formation. Parallel goals include the search for groups and clusters of galaxies and the search for rare and peculiar objects (gravitational lenses, QSOs, halo White Dwarfs). In this paper we describe the OACDF data reduction, the methods adopted for the extraction of the photometric catalogs, the photometric calibration and the quality assessment of the catalogs by means of galaxy number counts, spectroscopic and photometric redshifts and star colors. We also present the first results of the search for galaxy overdensities. The depth of the OACDF and its relatively large spatial coverage with respect to pencil beam surveys make it a good tool for further studies of galaxy formation and evolution in the redshift range 0--1, as well as for stellar studies.

KiDS-450: cosmological constraints from weak lensing peak statistics – I. Inference from analytical prediction of high signal-to-noise ratio convergence peaks

This paper is the first of a series of papers constraining cosmological parameters with weak lensing peak statistics using similar to 450 deg(2) of imaging data from the Kilo Degree Survey (KiDS-450). We measure high signal-to-noise ratio (SNR: nu) weak lensing convergence peaks in the range of 3 < nu < 5, and employ theoretical models to derive expected values. These models are validated using a suite of simulations. We take into account two major systematic effects, the boost factor and the effect of baryons on the mass-concentration relation of dark matter haloes. In addition, we investigate the impacts of other potential astrophysical systematics including the projection effects of large-scale structures, intrinsic galaxy alignments, as well as residual measurement uncertainties in the shear and redshift calibration. Assuming a flat Lambda cold dark matter model, we find constraints for S-8 = sigma(8)(Omega(m)/0.3)(0.5) = 0.746(-0.107)(+0.046) according to the degeneracy direction of the cosmic shear analysis and Sigma(8) = s8(Omega(m)/0.3) 0.38 = 0.696(-0.050)(+0.048) based on the derived degeneracy direction of our high-SNR peak statistics. The difference between the power index of S-8 and in Sigma(8) indicates that combining cosmic shear with peak statistics has the potential to break the degeneracy in sigma(8) and Omega(m). Our results are consistent with the cosmic shear tomographic correlation analysis of the same data set and similar to 2s lower than the Planck 2016 results.

Astronomy textbook images: do they really help students?

In this paper we present a study on the difficulties secondary school students experience in interpreting textbook images of elementary astronomical phenomena, namely, the changing of the seasons, Sun and lunar eclipses and Moon phases. Six images from a commonly used textbook in Italian secondary schools were selected. Interviews of 45?min about the astronomical concepts related to the images were carried out with eighteen students attending the last year of secondary school (aged 17?18). Students? responses were analyzed through a semiotic framework based on the different types of visual representation structures. We found that the wide range of difficulties shown by students come from na?ve or alternative ideas due to incorrect or inadequate geometric models of the addressed phenomena. As a primary implication of this study, we suggest that teachers should pay attention to specific iconic features of the discussed images, e.g., the compositional structure and the presence of real/symbolic elements.

Data reduction and astrometry strategies for wide-field images: an application to the Capodimonte Deep Field

The Capodimonte Deep Field (OACDF) is a multi-colour imaging survey on two 0.5×0.5 square degree fields performed in the BVRI bands and in six medium-band filters (700 - 900 nm) with the Wide Field Imager (WFI) at the ESO 2.2 m telescope at La Silla, Chile. In this contribution the adopted strategies for the OACDF data reduction are discussed. Preliminary scientific results of the survey are also presented.The Capodimonte Deep Field (OACDF) is a multi-colour imaging survey on two 0.5x0.5 square degree fields performed in the BVRI bands and in six medium-band filters (700 - 900 nm) with the Wide Field Imager (WFI) at the ESO 2.2 m telescope at La Silla, Chile. In this contribution the adopted strategies for the OACDF data reduction are discussed. Preliminary scientific results of the survey are also presented.