L. Sodré

Quasar Variability in the Framework of Poissonian Models

Quasar optical monitoring campaigns are reaching a new standard of quality as a result of long-term, accurate CCD observations. In this paper we review the basic Poissonian formulation of quasar variability, using it as a mathematical tool to extract relevant parameters such as the energy, rate, and lifetimes of the flares through the analysis of observed light curves. It is shown that in this very general framework the well-established anticorrelation between variability amplitude and wavelength can only be understood as an effect of an underlying spectral component that remains stable on long timescales and is redder than the variable component. The formalism is applied to the B and R light curves of 42 PG quasars collected by the Wise Observatory group. Variability indices for these data are obtained with a structure function analysis. The mean number of living flares is constrained to be in the range between ~ 5 and 100, while their rates are found to be of order ? ~ 1-100 yr-1. Monochromatic optical flare energies E? ~ 1046-1048 ergs ?-1 and lifetimes ? of ~0.5-3 yr are derived. Lower limits of typically 25% are established for the contribution of a nonvariable component in the R band. The substantial diversity in these properties among quasars invalidates simple versions of the Poissonian model in which flare energies, lifetimes, and the background contribution are treated as universal invariants. Light-curve simulations confirm the applicability of the method. Few significant correlations between variability indices and multiwavelength properties of the quasars exist, confirming the results of Giveon and colleagues in 1999. The good correlation between the EW(H?) and the long-term variability amplitude is interpreted in a scenario in which only the variable component participates in the ionization of the line emitting gas. This idea is consistent with the observed trends of the variability amplitude with ?, EW(He II), and the X-ray-optical spectral index. The parameter estimates derived under the framework of Poissonian models are applicable to several scenarios for the nature of quasar variability and can help in guiding, testing, and discriminating between detailed physical models.

Gemini and Chandra observations of Abell 586, a relaxed strong-lensing cluster

We analyze the mass content of the massive strong-lensing cluster Abell 586 (z = 0.17). We use optical data (imaging and spectroscopy) obtained with the Gemini Multi-Object Spectrograph (GMOS) mounted on the 8 m Gemini North telescope, together with publicly available X-ray data taken with the Chandra space telescope. Employing different techniques—velocity distribution of galaxies, weak gravitational lensing, and spatially resolved X-ray spectroscopy—we derive mass and velocity dispersion estimates from each of them. All estimates agree well with each other, within a 68% confidence level, indicating a velocity dispersion of 1000-1250 km s-1. The projected mass distributions obtained through weak lensing and X-ray emission are strikingly similar, having nearly circular geometry. We suggest that Abell 586 is probably a truly relaxed cluster whose last major merger occurred more than ~4 Gyr ago.

Morphological properties of superclusters of galaxies

We studied superclusters of galaxies in a volume-limited sample extracted from the Sloan Digital Sky Survey Data Release 7 and from mock catalogues based on a semi-analytical model of galaxy evolution in the Millennium Simulation. A density field method was applied to a sample of galaxies brighter than Mr =− 21+ 5l ogh100 to identify superclusters, taking into account selection and boundary effects. In order to evaluate the influence of the threshold density, we have chosen two thresholds: the first maximizes the number of objects (D1) and the second constrains the maximum supercluster size to ∼120 h −1 Mpc (D2). We have performed a morphological analysis, using Minkowski Functionals, based on a parameter, which increases monotonically from filaments to pancakes. An anticorrelation was found between supercluster richness (and total luminosity or size) and the morphological parameter, indicating that filamentary structures tend to be richer, larger and more luminous than pancakes in both observed and mock catalogues. We have also used the mock samples to compare supercluster morphologies identified in position and velocity spaces, concluding that our morphological classification is not biased by the peculiar velocities. Monte Carlo simulations designed to investigate the reliability of our results with respect to random fluctuations show that these results are robust. Our analysis indicates that filaments and pancakes present different luminosity and size distributions.

JPCAM: A 1.2 GPIXEL CAMERA FOR THE J-PAS SURVEY

JPCam is a 14-CCD mosaic camera, using the new e2v 9k-by-9k 10microm-pixel 16-channel detectors, to be deployed on a dedicated 2.55m wide-field telescope at the OAJ (Observatorio Astrofisico de Javalambre) in Aragon, Spain. The camera is designed to perform a Baryon Acoustic Oscillations (BAO) survey of the northern sky. The J-PAS survey strategy will use 54 relatively narrow-band (~13.8nm) filters equi-spaced between 370 and 920nm plus 3 broad-band filters to achieve unprecedented photometric red-shift accuracies for faint galaxies over ~8000 square degrees of sky. The cryostat, detector mosaic and read electronics is being supplied by e2v under contract to J-PAS while the mechanical structure, housing the shutter and filter assembly, is being designed and constructed by a Brazilian consortium led by INPE (Instituto Nacional de Pesquisas Espaciais). Four sets of 14 filters are placed in the ambient environment, just above the dewar window but directly in line with the detectors, leading to a mosaic having ~10mm gaps between each CCD. The massive 500mm aperture shutter is expected to be supplied by the Argelander-Institut fur Astronomie, Bonn. We will present an overview of JPCam, from the filter configuration through to the CCD mosaic camera. A brief outline of the main J-PAS science projects will be included.

Retired galaxies: not to be forgotten in the quest of the star formation – AGN connection

We propose a fresh look at the Main Galaxy Sample of the Sloan Digital Sky Survey by packing the galaxies in stellar mass and redshift bins. We show how important it is to consider the emission-line equivalent widths, in addition to the commonly used emission-line ratios, to properly identify retired galaxies (i.e. galaxies that have stopped forming stars and are ionized by their old stellar populations) and not mistake them for galaxies with low-level nuclear activity. We find that the proportion of star-forming galaxies decreases with decreasing redshift in each mass bin, while that of retired galaxies increases. Galaxies with

What drives the Balmer extinction sequence in spiral galaxies? clues from the sloan digital sky survey

M_\star > 10^{11.5} M_\odot

Design of the J-PAS and J-PLUS filter systems

have formed all their stars at redshift larger than 0.4. The population of AGN hosts is never dominant for galaxy masses larger than

Assessing the reliability of friends-of-friends groups on the future Javalambre Physics of the Accelerating Universe Astrophysical Survey

10^{10} M_\odot

BeppoSAX observation of the cluster Abell 970

. We warn about the effects of stacking galaxy spectra to discuss galaxy properties. We estimate the lifetimes of active galactic nuclei (AGN) relying entirely on demographic arguments --- i.e. without any assumption on the AGN radiative properties. We find upper-limit lifetimes of about 1--5 Gyr for detectable AGN in galaxies with masses between

The cluster of galaxies Abell 970

10^{10}