arXiv subjects

C. Adami

Publications and source records attributed to C. Adami.

At least 199 records · Page 11Linked to original sources

arXiv2004

Large scale diffuse light in the Coma cluster: a multi-scale approach

We have obtained wide field images of the Coma cluster in the B, V, R and I bands with the CFH12K camera at CFHT. In order to search for large scale diffuse emission, we have applied to these images an iterative multi scale wavelet analysis and reconstruction technique which allowed to model all the sources (stars and galaxies) and subtract them from the original images. We found various concentrations of diffuse emission present in the central zone around the central galaxies NGC4874 and NGC4889. We characterize the positions, sizes and colors of these concentrations. Some sources do not seem to have strong star formation, while another one probably exhibits spiral-like color. One possible origin for the star forming diffuse emission sources is that in the region of the two main galaxies NGC4874 and NGC4889 spiral galaxies have recently been disrupted and star formation is still active in the dispersed material. We also use the characteristics of the sources of diffuse emission to trace the cluster dynamics. A scenario in which the group around NGC 4874 is moving north is consistent with our data.

astro-ph↗

arXiv2004

The XMM-LSS Survey. First high redshift galaxy clusters: relaxed and collapsing systems

We present five newly found galaxy clusters at z>0.6 from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at z=0.613 and σ_V=867^{+80}_{-60} km/s, XLSSC 002 at z=0.772 and σ_V=524^{+267}_{-116} km/s and XLSSC 003 at z=0.839 and σ_V=780^{+137}_{-75} km/s. These three clusters have X-ray bolometric luminosities L_X \sim 1-3 \times 10^{44} erg/s and temperatures 2-4 keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between L_X, T and σ_V, within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an overdensity of galaxies of a colour R-z'=1.4 that matches the redshift of the central galaxy z=0.87, although it cannot unambiguously be confirmed by the spectroscopic observations alone. The highest redshift candidate cluster pertaining to this paper, XLSSC 005, is most likely a double cluster complex at a redshift around unity, associated with an extended X-ray source with probable substructure.

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arXiv2004

Bias in the Estimation of Global Luminosity Functions

We discuss a bias present in the calculation of the global luminosity function (LF) which occurs when analysing faint galaxy samples. This effect exists because of the different spectral energy distributions of galaxies, which are in turn quantified by the k-corrections. We demonstrate that this bias occurs because not all galaxy types are visible in the same absolute magnitude range at a given redshift and it mainly arises at high redshift since it is related to large k-corrections. We use realistic simulations with observed LFs to investigate the amplitude of the bias. We also compare our results to the global LFs derived from Hubble Deep Field-North and -South (HDF) surveys. We conclude that, as expected, there is no bias in the global LF measured in the absolute magnitude range where all galaxy types are observable. Beyond this range the faint-end slope of the global LF can be over/under-estimated depending on the adopted LF estimator. The effect is larger when the reference filter in which the global LF is measured, is far from the rest-frame filter in which galaxies are selected. The fact that LF estimators are differently affected by this bias implies that the bias is minimal when the different LF estimators give measurements consistent with one another at the faint-end. For instance, we show that the estimators are discrepant in the same way both in the simulated and HDF LFs. This suggests that the HDF LFs are affected by the presently studied bias. The best solution to avoid this bias is to derive the global LF in the reference filter closest to the rest-frame selection filter.

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arXiv2003

The VIRMOS deep imaging survey: III. ESO/WFI deep U-band imaging of the 0226-04 deep field

In this paper we describe the U-band imaging of the F02 deep field, one of the fields in the VIRMOS Deep Imaging Survey. The observations were done at the ESO/MPG 2.2m telescope at La Silla (Chile) using the 8k x 8k Wide-Field Imager (WFI). The field is centered at alpha(J2000)=02h 26m 00s and delta(J2000)=-04deg 30' 00", the total covered area is 0.9 deg**2 and the limiting magnitude (50% completeness) is U(AB) ~ 25.4 mag. Reduction steps, including astrometry, photometry and catalogue extraction, are first discussed. The achieved astrometric accuracy (RMS) is ~ 0.2" with reference to the I-band catalog and ~ 0.07" internally (estimated from overlapping sources in different exposures). The photometric accuracy including uncertainties from photometric calibration, is < 0.1 mag. Various tests are then performed as a quality assessment of the data. They include: (i) the color distribution of stars and galaxies in the field, done together with the BVRI data available from the VIMOS survey; (ii) the comparison with previous published results of U-band magnitude-number counts of galaxies.

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arXiv2003

Early results from the VIMOS VLT Deep Survey

The VIMOS VLT Deep Survey (VVDS) is underway to study the evolution of galaxies, large scale structures and AGNs, from the measurement of more than 100000 spectra of faint objects. We present here the results from the first epoch observations of more than 20000 spectra. The main challenge of the program, the redshift measurements, is described, in particular entering the ``redshift desert'' in the range $1.5<z<3$ for which only very weak features are observed in the observed wavelength range. The redshift distribution of a magnitude limited sample brighter than $I_{AB}=24$ is presented for the first time, showing a peak at a low redshift $z\sim0.7$, and a tail extending all the way above $z=4$. The evolution of the luminosity function out to $z=1.5$ is presented, with the LF of blue star forming galaxies carrying most of the evolution, with L* changing by more than two magnitudes for this sub-sample.

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arXiv2003

Comparison of two optical cluster finding algorithms for the new generation of deep galaxy surveys

We present a comparison between two optical cluster finding methods: a matched filter algorithm using galaxy angular coordinates and magnitudes, and a percolation algorithm using also redshift information. We test the algorithms on two mock catalogues. The first mock catalogue is built by adding clusters to a Poissonian background, while the other is derived from N-body simulations. Choosing the physically most sensible parameters for each method, we carry out a detailed comparison and investigate advantages and limits of each algorithm, showing the possible biases on final results. We show that, combining the two methods, we are able to detect a large part of the structures, thus pointing out the need to search for clusters in different ways in order to build complete and unbiased samples of clusters, to be used for statistical and cosmological studies. In addition, our results show the importance of testing cluster finding algorithms on different kinds of mock catalogues to have a complete assessment of their behaviour.

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arXiv2003

Environmental Effects on the Kinematics of Virgo Cluster Galaxies

We present results from an ongoing survey dedicated to the ionized gas kinematics of Virgo cluster spiral galaxies using Fabry-Perot interferometry. Our goal is to study the environmental effects on galaxy evolution in the Virgo cluster. We report here on the Halpha distribution map and velocity field of NGC 4438, the prototype of an interacting galaxy near the centre of the cluster.

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arXiv2003

The VLA-VIRMOS Deep Field I. Radio observations probing the microJy source population

We have conducted a deep survey (r.m.s noise 17 microJy) with the Very Large Array (VLA) at 1.4 GHz, with a resolution of 6 arcsec, of a 1 square degree region included in the VIRMOS VLT Deep Survey. In the same field we already have multiband photometry down to I(AB)=25, and spectroscopic observations will be obtained during the VIRMOS VLT survey. The homogeneous sensitivity over the whole field has allowed to derive a complete sample of 1054 radio sources (5 sigma limit). We give a detailed description of the data reduction and of the analysis of the radio observations, with particular care to the effects of clean bias and bandwidth smearing, and of the methods used to obtain the catalogue of radio sources. To estimate the effect of the resolution bias on our observations we have modelled the effective angular-size distribution of the sources in our sample and we have used this distribution to simulate a sample of radio sources. Finally we present the radio count distribution down to 0.08 mJy derived from the catalogue. Our counts are in good agreement with the best fit derived from earlier surveys, and are about 50 % higher than the counts in the HDF. The radio count distribution clearly shows, with extremely good statistics, the change in the slope for the sub-mJy radio sources.

astro-ph↗

arXiv2002

Ab Initio Modeling of Ecosystems with Artificial Life

Artificial Life provides the opportunity to study the emergence and evolution of simple ecosystems in real time. We give an overview of the advantages and limitations of such an approach, as well as its relation to individual-based modeling techniques. The Digital Life system Avida is introduced and prospects for experiments with ab initio evolution (evolution "from scratch"), maintenance, as well as stability of ecosystems are discussed.

physics.bio-ph↗

arXiv2002

The ESO Nearby Abell Cluster Survey. XI. Segregation of cluster galaxies and subclustering

We study luminosity and morphology segregation of over 3000 cluster galaxies in an ensemble cluster of 59 rich, nearby galaxy clusters observed in the ESO Nearby Cluster Survey (ENACS). Within this sample we identify those galaxies that are in substructures. We compare the distribution of projected clustercentric distance, R, and 'normalized' relative line-of-sight velocity, v, of several subsamples, using the 2D Kolmogorov-Smirnov test. We find evidence of luminosity segregation only for the ellipticals outside substructure and brighter than M_R = -22.0 +/- 0.1 (h0=100 km/s/Mpc). We confirm the well-known segregation of early- and late-type galaxies. The early and late spirals (Sa--Sb and Sbc--Ir respectively) outside substructure also appear to have different (R,v)-distributions. In each morphological class, the galaxies within substructure have different (R,v)-distributions from the galaxies that are not in substructure. Among the samples of galaxies that are not in substructure, at least 3 ensembles can and must be distinguished: [E+S0], S_early, and [S_late+ELG]. The [E+S0] ensemble is most centrally concentrated and has a fairly low velocity dispersion that hardly varies with radius. The [S_late+ELG] ensemble is least concentrated and has the highest velocity dispersion, which increases significantly towards the centre. The (R,v)-distribution of S_early galaxies is intermediate between those of the two other ensembles. Among the galaxies within substructure the S0 and [S_late+ELG] galaxies have different (R,v) distributions. We discuss briefly the implications of our results for processes of galaxy destruction and transformation within clusters. [ABRIDGED]

astro-ph↗

arXiv2001

Group analysis in the SSRS2 catalog

We present an automated method to detect populations of groups in galaxy redshift catalogs. This method uses both analysis of the redshift distribution along lines of sight in fixed cells to detect elementary structures and a friend-of-friend algorithm to merge these elementary structures into physical structures. We apply this method to the SSRS2 galaxy redshift catalog. The groups detected with our method are similar to group catalogs detected with pure friend-of-friend algorithms. They have similar mass distribution, similar abundance versus redshift, similar 2-point correlation function and the same redshift completeness limit, close to 5000 km/s. If instead of SSRS2, we use catalogs of new generation, it would lead to a completeness limit of z$\sim$0.7. We model the luminosity function for nearby galaxy groups by a Schechter function with parameters M*=(-19.99+/-0.36)+5logh and alpha=-1.46 +/- 0.17 to compute the mass to light ratio. The median value of the mass to light ratio is 360 h M/L and we deduce a relation between mass to light ratio and velocity dispersion sigma (M/L=3.79 +/- 0.64)sigma -(294 +/- 570)). The more massive the group, the higher the mass to light ratio, and therefore, the larger the amount of dark matter inside the group. Another explanation is a significant stripping of the gas of the galaxies in massive groups as opposed to low mass groups. This extends to groups of galaxies the mild tendency already detected for rich clusters of galaxies. Finally, we detect a barely significant fundamental plane for these groups but much less narrow than for clusters of galaxies.

astro-ph↗

arXiv2001

The XMM-Newton $Ω$ Project

The abundance of high-redshift galaxy clusters depends sensitively on the matter density $\OmM$ and, to a lesser extent, on the cosmological constant $Λ$. Measurements of this abundance therefore constrain these fundamental cosmological parameters, and in a manner independent and complementary to other methods, such as observations of the cosmic microwave background and distance measurements. Cluster abundance is best measured by the X-ray temperature function, as opposed to luminosity, because temperature and mass are tightly correlated, as demonstrated by numerical simulations. Taking advantage of the sensitivity of XMM-Newton, our Guaranteed Time program aims at measuring the temperature of the highest redshift (z>0.4) SHARC clusters, with the ultimate goal of constraining both $\OmM$ and $Λ$.

astro-ph↗

arXiv2001

Central Matter Distributions in Rich Clusters of Galaxies from z~0 to z~0.5

We have analyzed the galaxy number density and luminosity density profiles of rich clusters of galaxies from redshifts z=0 to z=0.5. We show that the luminosity profile computed with bright galaxies is significantly cusped in the center of the clusters, whatever the redshift. This is in agreement with the dark matter profiles predicted by numerical simulations. The galaxy number density profile for the bright galaxies is fitted equally well with a core model or a cusped model. In contrast, the luminosity and the galaxy number density profiles of the fainter galaxies are significantly better fitted by a core rather than a cusp model. We did not detect any statistically significant different fits when applied to data in range from z=0 to z=0.5. The difference in profile between faint and bright galaxies may be due to the rapid (relative to the age of the universe at z=0 versus z=0.5) destruction of the faint galaxies by tidal forces and merging events in the denser central regions of the clusters. This process could erase the cusp by turning faint galaxies into diffuse light. In this case, the galaxies (with a cusp visible in the bright galaxy number density and mainly in luminosity profiles) would trace the total mass distribution.

astro-ph↗

arXiv2000

The Bright SHARC Survey: The Cluster Catalog

We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 sq.deg and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on-going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identified thirty-seven clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696<z<0.83 and a luminosity range of 0.065<Lx<8.3e44 erg/s [0.5-2.0 keV] (assuming Ho = 50 km/s/Mpc and qo=0.5). Twelve of the clusters have redshifts greater than z=0.3, eight of which are at luminosities brighter than Lx=3e44 erg/s. Seventeen of the 37 optically confirmed Bright SHARC clusters have not been listed in any previously published catalog. We also report the discovery of three candidate ``fossil groups'' of the kind proposed by Ponman et al. (1994).

astro-ph↗

arXiv2000

Dynamical and content evolution of a sample of clusters from z~0 to z~0.5

In this paper, we present an analysis of the dynamics and segregation of galaxies in rich clusters from z~0.32 to z~0.48 taken from the CFHT Optical PDCS (COP) survey and from the CNOC survey (Carlberg et al. 1997). Our results from the COP survey are based upon the recent observational work of Adami et al. (2000) and Holden et al. (2000) and use new spectroscopic and photometric data on six clusters selected from the Palomar Distant Cluster Survey (PDCS; Postman et al. 1996). We have compared the COP and CNOC samples to the ESO Nearby Abell Cluster Survey (ENACS: z~0.07). Our sample shows that the z<0.4 clusters have the same velocity dispersion versus magnitude, morphological type and radius relationships as nearby Abell clusters. The z~0.48 clusters exhibit, however, departures from these relations. Furthermore, there appears to be a higher fraction of late-type (or bluer, e.g. Butcher and Oemler, 1984) galaxies in the distant clusters compared to the nearby ones. The classical scenario in which massive galaxies virialize before they evolve from late into early type explain our observations. In such a scenario, the clusters of our sample began to form before a redshift of ~0.8 and the late-type galaxy population had a continuous infall into the clusters.

astro-ph↗

arXiv2000

The Bright SHARC Survey: The Selection Function and its Impact on the Cluster X-ray Luminosity Function

We present the results of a set of simulations designed to quantify the selection function of the Bright SHARC survey for distant clusters. The statistical significance of the simulations relied on the creation of thousands of artificial clusters with redshifts and luminosities in the range 0.25<z<0.95 and 0.5<L_X<10x10^44 erg/s (0.5-2.0 keV). We created 1 standard and 19 varied distribution functions, each of which assumed a different set of cluster, cosmological and operational parameters. The parameters we varied included the values of Omega_0, Omega_Lambda, Beta, core radius and ellipticity. We also investigated how non-standard surface brightness profiles; cooling flows; and the ROSAT pointing target, influence the selection function in the Bright SHARC survey. For our standard set we adopted the parameters used during the derivation of the Bright SHARC Cluster X-ray Luminosity Function (CXLF), i.e. Omega_0=1, Omega_Lambda=0 and an isothermal Beta model with beta=0.67, r_c=250 kpc and e=0.15. We found that certain parameters have a dramatic effect on our ability to detect clusters, e.g. the presence of a NFW profile or a strong cooling flow profile, or the value of r_c and beta. Other parameters had very little effect, e.g. the type of ROSAT target and the cluster ellipticity. We show also that all the tested parameters have only a small influence on the computed luminosity of the clusters except the presence of a strong cooling flow. We conclude that the CXLF presented in Nichol et al. (1999) is robust (under the assumption of standard parameters), but stress the importance of cluster follow-up in order to better constrain the morphology of the distant clusters found in the Bright SHARC and other surveys.

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arXiv2000

Uncertainties on Clusters of Galaxies Distances

We investigate in this paper the error on the cluster redshift estimate as a function of: (1) the number of galaxy structures along the line of sight; (2) the morphology of the clusters (regular/substructures); (3) the nature of the observed galaxies (cD/normal galaxies); (4) the number of observed galaxies; and (5) the distance of the clusters. We find that if we use cD galaxies we have errors of less than 2% (at the 1-$σ$ level) for the cluster distances except when the clusters are very complex. In those cases when we use five redshift measurements along the cluster lines of sight to compute the mean redshift, the mean redshift estimate error is less than 5% for the clusters closer than z=0.30. The same error of 5% for clusters in z=[0.30;0.60] requires about 12 redshifts measurements.

astro-ph↗

arXiv2000

CFHT Optical PDCS Survey II: Evolution in the Space Density of Clusters of Galaxies

We present the first dynamical study of the optically selected Palomar Distant Cluster Survey (PDCS). We show that eleven out of twelve PDCS clusters we observed are real over-densities of galaxies. Most clusters have velocity dispersions appropriate for clusters of galaxies. However, we find a fraction (1/3) of objects in the PDCS which have velocity dispersions in the range of groups of galaxies (200 +/- 100 km/s) but have richnesses appropriate for clusters of galaxies. We measure the richness function, X-ray luminosity function (using both the detections and upper limits), and the mass function derived from our velocity dispersions. We confirm that the space density, as a function of richness, of clusters of galaxies in the PDCS is ~5 times that of the Abell catalog. Excluding the above fraction of 1/3 of objects with low velocity dispersions, we measure a space density ~3 times that of the Abell catalog for equivalent mass clusters of galaxies. Our space density estimates are in agreement with other low-redshift, optically-selected cluster surveys such as the EDCC, APM and EDCC2, which raises the possibility that the Abell catalog is incomplete. Our X-ray luminosity function agrees with other measurements based on both X-ray and optically selected samples, so we find that the PDCS does not miss clusters of galaxies that would be found in an X-ray selected survey. Our resulting mass function, centered around 10e14 Msun/h, agrees with the expectations from such surveys as the Canadian Network for Observational Cosmology cluster survey, though errors on our mass measurements are too large to constrain cosmological parameters.

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