E. S. Cypriano

Star formation efficiency in galaxy clusters

Context. The luminous material in clusters of galaxies exists in two forms: the visible galaxies and the X-ray emitting intra-cluster medium. The hot intra-cluster gas is the major observed baryonic component of clusters, about six times more massive than the stellar component. The mass contained within visible galaxies is approximately 3% of the dynamical mass. Aims. Our aim was to analyze both baryonic components, combining X-ray and optical data of a sample of five galaxy clusters (Abell 496, 1689, 2050, 2631 and 2667), within the redshift range 0.03 < z < 0.3. We determined the contribution of stars in galaxies and the intra-cluster medium to the total baryon budget. Methods. We used public XMM-Newton data to determine the gas mass and to obtain the X-ray substructures. Using the optical counterparts from SDSS or CFHT we determined the stellar contribution. Results. We examine the relative contribution of galaxies, intra-cluster light and intra-cluster medium to baryon budget in clusters through the stellar-to-gas mass ratio, estimated with recent data. We find that the stellar-to-gas mass ratio within r500 (the radius within which the mean cluster density exceeds the critical density by a factor of 500), is anti-correlated with the ICM temperature, which range from 24% to 6% while the temperature ranges from 4.0 to 8.3 keV. This indicates that less massive cold clusters are more prolific star forming environments than massive hot clusters.

Velocity Dispersion, Mass, and the Luminosity Function of the Fossil Cluster RX J1416.4+2315

We study the properties of the fossil cluster RX J1416.4+2315 through g- and i-band imaging and spectroscopy of 25 member galaxies. The system is at a mean redshift of 0.137 and has a velocity dispersion of 584 km s-1. Superposed onto one quadrant of the cluster field is a group of five galaxies at a mean redshift of 0.131, which, if included as part of the cluster, increases the velocity dispersion to 846 km s-1. The central object of RX J1416.4+2315 is a normal elliptical galaxy with no cD envelope. The luminosity function of the system, estimated by the number counts and statistical background correction in the range -22.6 < M < -16.6, is well fitted by a Schechter function with M = -21.2 ± 0.8 and α = -1.2 ± 0.2 (H0 = 70 km s-1 Mpc-1, ΩM = 0.3, ΩΛ = 0.7). The luminosity function obtained from the spectroscopically confirmed members in both the g and i bands agrees with the photometric results. The mass of the system, M ~ 1.9 × 1014 h M⊙, its M/L of 445 h70 M⊙ L, and LX of 11 × 1043 h ergs s-1 (bolometric) suggest that this system is the second example of a known fossil cluster, after RX J1552.2+2013, confirmed in the literature.

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.

AN OPTICAL AND X-RAY STUDY OF THE FOSSIL GROUP RX J1340.6+4018*

Fossil groups are systems with one single central elliptical galaxy and an unusual lack of luminous galaxies in the inner regions. The standard explanation for the formation of these systems suggests that the lack of bright galaxies is due to galactic cannibalism. In this study, we show the results of an optical and X-ray analysis of RX J1340.6+4018, the prototype fossil group. The data indicate that RX J1340.6+4018 is similar to clusters in almost every sense (dynamical mass, X-ray luminosity, M/L, and luminosity function) except for the lack of L* galaxies. There are claims in the literature that fossil systems have a lack of small mass halos, compared to predictions based on the lambda cold dark matter scenario. The observational data gathered on this and other fossil groups so far offer no support for this idea. Analysis of the SN Ia/SN II ejecta ratio in the inner and outer regions shows a marginally significant central dominance of SN Ia material. This suggests that either the merger which originated in the central galaxy was dry or the group has been formed at early epochs, although better data are needed to confirm this result.

Searching High-Redshift Large-Scale Structures: Photometry of Four Fields around Quasar Pairs at z ~ 1

We have studied the photometric properties of four fields around the high-redshift quasar pairs QP 1310+0007, QP 1355-0032, QP 0110-0219, and QP 0114-3140 at z ~ 1 with the aim of identifying large-scale structures (galaxy clusters or groups) around them. This sample was observed with the Gemini Multi-Object Spectograph (GMOS) at the Gemini North and South telescopes in the g, r, i, and z bands, and our photometry is complete to a limiting magnitude of i ~ 24 mag (corresponding to ~M + 2 at the redshift of the pairs). Our analysis reveals that QP 0110-0219 shows very strong and QP 1310+0007 and QP 1355-0032 show some evidence for the presence of rich galaxy clusters in direct vicinity of the pairs. On the other hand, QP 0114-3140 could be an isolated pair in a poor environment. This work suggest that z ~ 1 quasar pairs are excellent tracers of high-density environments, and the same technique may be useful to find clusters at higher redshifts.

The Compact Group of Galaxies HCG 31 in an Early Phase of Merging

We have obtained high spectral resolution (R = 45900) Fabry-Perot velocity maps of the Hickson Compact Group HCG 31 in order to revisit the important problem of the merger nature of the central object A+C and to derive the internal kinematics of the candidate tidal dwarf galaxies in this group. Our main findings are: (1) double kinematic components are present throughout the main body of A+C, which strongly suggests that this complex is an ongoing merger (2) regions

Star formation in H i tails: HCG 92, HCG 100 and six interacting systems

A2

Witnessing the Formation of a Galaxy Cluster at z = 0.485: Optical and X-Ray Properties of RX J1117.4+0743 ([VMF 98] 097)*

and E, to the east and south of complex A+C, present rotation patterns with velocity amplitudes of

The merger history of the complex cluster Abell 1758: a combined weak lensing and spectroscopic view

sim 25 km s^{-1}

Weak lensing and spectroscopic analysis of the nearby dissociative merging galaxy cluster Abell 3376

and they counterrotate with respect to A+C, (3) region F, which was previously thought to be the best example of a tidal dwarf galaxy in HCG 31, presents no rotation and negligible internal velocity dispersion, as is also the case for region