arXiv subjects

Dario Trevese

Publications and source records attributed to Dario Trevese.

9 recordsLinked to original sources

arXiv2011

The large-scale structure in the Chandra Deep Field South

We have studied the large scale distribution of matter in the Chandra Deep Field South on the basis of photometric redshifts and we have identifed several over-densities between redshift 0.6 and 2.3. We analyse two of these structures using the deepest X-ray observations ever obtained: 4 Ms with the Chandra satellite and 2.5 Ms with XMM-Newton. We set a very faint upper limit on the X-ray luminosity of a structure at redshift 1.6, and we find an extended X-ray emission from a structure at redshift 0.96 of which we can estimate the gas temperature and make a comparison with the scaling relations between the X-ray luminosity and mass or temperature of high redshift galaxy clusters.

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arXiv2007

XMM-Newton observation of the cluster ZW 1305.4+2941 in the field SA 57

We report the details of an XMM observation of the cluster of galaxies ZW 1305.4+2941 at the intermediate redshift of z=0.241, increasing the small number of interesting X-ray constraints on properties of ~3 keV systems above z=0.1. Based on the 45 ks XMM observation, we find that within a radius of 228 kpc the cluster has an unabsorbed X-ray flux of 2.07 +/- 0.06 x 10^{-13} erg/cm^2/s, a temperature of kT = 3.17 +/-0.19 keV, in good agreement with the previous ROSAT determination, and an abundance of 0.93 (+0.24,-0.29} solar. Within r_500 = 723 +/- 6 kpc the rest-frame bolometric X-ray luminosity is L_X (r_500)= 1.25 +/- 0.16 x 10^{44} erg/s. The cluster obeys the scaling relations for L_X, T and the velocity dispersion derived at intermediate redshift for kT < 4 keV, for which we provide new fits for all literature objects. The mass derived from an isothermal NFW model fit is, M_vir = 2.77 +/- 0.21 x 10^{14} solar masses, with a concentration parameter, c = 7.9 +/- 0.5.

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arXiv2006

A new (2+1)D cluster finding algorithm based on photometric redshifts: large scale structure in the Chandra Deep Field South

Aims: We study galaxy clustering and explore the dependence of galaxy properties on the the environment up to a redshift z~1, on the basis of a deep multi-band survey in the Chandra Deep Field South. Methods: We have developed a new method which combines galaxy angular positions and photometric redshifts to estimate the local galaxy number-density. This allows both the detection of overdensities in the galaxy distribution and the study of the properties of the galaxy population as a function of the environmental density. Results: We detect two moderate overdensities at z~0.7 and z~1 previously identified spectroscopically. We find that the fraction of red galaxies within each structure increases with volume density, extending to z~1 previous results. We measure ``red sequence'' slopes consistent with the values found in X-ray selected clusters, supporting the notion that the mass-metallicity relation hold constant up to z~1. Conclusions: Our method based on photometric redshifts allows to extend structure detection and density estimates up to the limits of photometric surveys, i.e.considerably deeper than spectroscopic surveys. Since X-ray cluster detection at high redshift is presently limited to massive relaxed structures, galaxy volume density based on photometric redshift appears as a valuable tool in the study of galaxy evolution.

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arXiv2004

A Project for a New Echo-Mapping Campaign at Intermediate Redshift

AGN masses can be estimated by "single epoch" spectral measurements through a mass-luminosity- linewidth relation calibrated by echo mapping measurements of a reference sample of low redshift ($z < 0.3$) and low luminosity ($M_B > -26$) AGNs. To analyze the possible dependence of this relation on luminosity we selected a sample of bright, intermediate redhift ($z \sim 1$) objects and we started a spectrophotometric monitoring campaign with a typical sampling time of about one month. Variability observations of lines with shorter wavelength than H$_β$ will also provide new information on the structure of the broad line region. Cross-correlation analysis of continuum and line variations will require years of monitoring. We present a preliminary analysis of the data collected during the first year of observations and we discuss the adequacy of the spectrophotometric accuracy attained and future prospects of this project.

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arXiv2003

Spectral Slope Variability of BL Lac Objects in the Optical Band

Light curves of eight BL Lac objects in the BVRI bands have been analyzed. All of the objects tend to be bluer when brighter. However spectral slope changes differ quantitatively from those of a sample of QSOs analyzed in a previous paper (Trevese & Vagnetti 2002) and appear consistent with a different nature of the optical continuum. A simple model representing the variability of a synchrotron component can explain the spectral changes. Constraints on a possible thermal accretion disk component contributing to the optical luminosity are discussed.

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arXiv2001

Host Galaxies and the Spectral Variability of Quasars

Brightness variability of QSOs is associated with variations of the spectral energy distribution in the optical-UV range. The observed change of the spectral shape depends on the contribution of the host galaxy. Simulations, taking into account luminosities and spectra expected for the host galaxies, are compared with the observed spectral variability of a complete QSO sample.

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arXiv2001

Continuum Variability of Active Galactic Nuclei in the Optical-UV Range

The variability of the continuum spectral energy distribution has been analyzed for a complete magnitude-limited sample of quasars in Selected Area 57, observed at two epochs in the photographic $U$, $B_J$, $F$ and $N$ bands with the Mayall 4m telescope at Kitt Peak. Changes $δα$ of the spectral slope $α$ appear correlated with brightness variations $δlog f_ν$ indicating an average hardening of the spectrum in the bright phases. This confirms that the correlation of variability with redshift, found in a single observing band, is due to intrinsic spectral changes. The average observed $δα- δlog f_ν$ relation is consistent with the spectral change due to temperature variation of a black body of about $2.5 \cdot 10^4 K$.

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arXiv2000

Spectral Variability of QSOs in the Optical Band

A new analysis of the variability of the spectral slope of PG QSOs has been performed, on the basis of recent literature data in the B and R photometric bands. Preliminary results confirm our previous findings concerning the increase of variability with the rest-frame observing frequency. We also find a correlation of the spectral slope with luminosity, consistent with temperature changes of an emitting black body.

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arXiv1997

Variable Extended Objects in SA 57

We have isolated a sample of 14 candidate variable objects with extended image structure to Bj = 22.5 in 0.284 deg^2 of Selected Area 57. The majority of candidates are blue (U-B<0) and relatively compact. At fainter magnitudes, there is a steep rise in the number of variable objects. These objects are also compact and blue, and some of them are likely to be truly stellar. Twelve of the Bj <= 22.5 candidates have been observed spectroscopically over limited ranges of wavelength and a variety of resulting signal-to-noise. Five candidates display spectra consistent with Seyfert-like activity. In most cases where we have not been able to confirm a Seyfert spectroscopic type, the spectra are of insufficient quality or coverage to rule out such a classification. The majority of candidates have luminosities less than 10% of the nominal demarkation between QSOs and AGN (M(B) = -23). The surface density of confirmed M(B) > -23 AGN to Bj = 22, including stellar sources, is ~40/deg^2, in good agreement with other surveys at this depth. The confirmed AGN in extended sources make up 36% of this population. Thus, the application of a variability criterion to images with extended structure enhances the completeness of the census of active nuclei. If the majority of our candidates are bona fide AGN, the surface density could be as high as 82/deg^2 for M(B) > -23, and 162/deg^2 for all luminosities to Bj = 22, with extended sources contributing up to 33% of the total. (abridged)

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