arXiv subjects
Publications and source records attributed to R. Pello.
We have imaged the inner square arcminute of the well known lensing and cooling flow cluster A2390 (z = 0.23) down to a sensitivity of 65 and 130 microJy at 6.75 and 15 micronmetre, respectively. We report the first evidence of an active star-forming region in a cooling flow (at those wavelengths) and strong emission in the mid-IR from lensed galaxies located at z=0.9.
This paper addresses the problem of detecting high-redshift clustering in deep photometric surveys. We have used photometric redshifts to select different samples of galaxies in the HDF, in order to study their clustering properties within the 2.5<z<4.5 domain, in redshift bins of 0.5, using different techniques. A strong clustering signal is found for redshift bins including z~3.4 and leading to a present correlation length of r_0 = 4.1 +- 0.8 h^-1 Mpc (q_0=0.1) assuming linear evolution. An excess appears in the correlation function of chip 2 with respect to the fit. This excess could be associated to the main structure detected in this field, which contains 20% of the objects identified at 3.4<z<3.9. Its dimensions are 3 h^-1 Mpc x 0.5 h^-1 Mpc. The galaxies at 3.4<z<3.9 exhibit a SFR of a few solar masses per year, but their comoving density is a factor of ~50 higher than the population of star-forming galaxies reported by Steidel et al. (1996b). The resulting star formation rate density is at least 1.1 10^-2 h Msun/yr/Mpc^3 (1.8 10^-2 h Msun/yr/Mpc^3) with q_0=0.1(0.5), slightly higher than the results by Madau et al. (1996) at 2.5<z<3.5, and then incompatible with a global decrease of the star formation in this redshift domain. These results on star formation and clustering are consistent with a hierarchical scenario for galaxy formation.
We present a detailed model of the absolute number counts, color and redshift distributions of gravitational arclets observed in clusters of galaxies. The framework adopted for galaxy evolution is chosen to fairly reproduce the observed number counts and redshift distribution of field galaxies. Then, the spectrophotometric evolutionary code is coupled with an accurate modelling of two clusters-lens mass distributions (A2218 and A370). We investigate the influence of the mass modelling on the counts and we show that simple cluster-scale potentials can no longer be used for arcs statistics. The main result is that arcs at redshifts between 0.5 and 1 are correctly predicted by the modelling as observed. Nevertheless, an important population of high redshift arclets (z>1.0) is also revealed by the simulations, which is not observed in spectroscopic surveys of arclets. We discuss the nature of this disagreement, probably due to uncertainties in the evolutionary models. The spatial distribution of arclets in number density and the local mean redshift at each point of the image are derived and can be used to optimize the search for high redshift galaxies.
We present an optical and near-infrared survey of galaxies in nearby clusters aimed at determining fundamental quantities of galaxies, such as multivariate luminosity function and color distribution for each Hubble type. The main characteristics of our survey are completeness in absolute magnitude, wide wavelength coverage and faint limiting magnitudes.
This paper describes new results on the identification of the complex gravita- tional lens responsible for the double quasar Q2345+007. A gravitational shear field was detected recently about 45'' away from the QSO, centered on an excess of faint blue galaxies. We present deep photometric data in the near-IR (J & K'), which are used together with optical BRI photometry to build spectral ener- gy distributions for all the objects, and to derive a photometric redshift esti- mate by comparison with synthetic spectrophotometric data. We propose a statis- tical method to analyse the distribution in z. An excess of galaxies at z about 0.75 is detected in this field, with a 2D distribution showing a maximum located at the center of the weak-shear field. The z inferred for this overdensity (a distant cluster of galaxies) corresponds to an absorption system in the spectrum of the quasar B. Most cluster-member candidates at z=0.75 are undergoing a star- formation process or are burst systems 1 to 3 Gyr old. We also discuss the exis- tence of other possible excesses of galaxies at different z planes.
A mass model of the rich cluster A2218 is presented based on optical and new near-infrared images of arc(let)s and the ROSAT/HRI X-ray map. A lensing model is proposed with two dark matter clumps, centered on the two bright galaxies around which the various arcs are observed. Two of them, close to the most massive clump around the brightest galaxy, are required to be fold images, given their position angle with respect to the major axis. A third image for each of the two arcs is then predicted to be on the opposite side of the major axis. Both images are indeed found at the expected positions, with consistent magnitudes, colors and shapes. One of the arcs has a known redshift of $0.7$, and the model predicts that the other arc should be at higher redshift, $z \approx 3$. Photometric data in UBrzJK' indicates that a redshift close to 3 is indeed probable for this arc. The dark matter halo is found to be sharply peaked on the giant central galaxy. The ROSAT/HRI X-ray map shows a strongly clumped image, poorly correlated with the cD light and the mass model on scales below $\sim$ 200$h_{50}^{-1}$kpc, but similar to the distribution of galaxies and the mass model when smoothed on this scale. The large degree of central substructure implied helps to account for the discrepancy previously found (in the two massive clusters A2218 \& A1689) between the mass derived from the gravitational lenses and that derived from the X-ray profile and temperature distributions, in a model of hydrostatic equilibrium. Most of the discrepancy can probably be explained by bulk motions and acceleration of the gas, and projection effects enhancing the lensing power of the cluster.