Luis E. Campusano

Weak lensing mass distributions for 24 x-ray Abell clusters

We use the weak gravitational lensing effect to study the mass distribution and dynamical state of a sample of 24 X-ray-luminous clusters of galaxies (0.05 < z < 0.31) observed with the FORS1 instrument mounted on the VLT-Antu (Unit Telescope 1) under homogeneous sky conditions and subarcsecond image quality. The galaxy shapes were measured in the combined VIR image after deconvolution with a locally determined point-spread function, while the two-dimensional mass distributions of the clusters were computed using an algorithm based on the maximum entropy method. By comparing the mass and light distributions of the clusters in our sample, we find that their centers of mass, for the majority of the clusters, are consistent with the positions of optical centers. We find that some clusters present significant mass substructures that generally have optical counterparts. In at least one cluster (A1451), we detect a mass substructure without an obvious luminous counterpart. The radial profile of the shear of the clusters was fitted using circular and elliptical isothermal distributions, which allowed the finding of a strong correlation between the orientation of the major axis of the matter distribution and the corresponding major axes of the brightest cluster galaxy light profiles. Estimates of how close to dynamical relaxation are these clusters were obtained through comparison of our weak-lensing mass measurements with the X-ray and velocity dispersion determinations available in the literature. We find that clusters with intracluster gas colder than 8 keV show good agreement between the different mass determinations, but clusters with gas hotter than 8 keV present weak-lensing masses smaller than those inferred by the other methods and therefore have been diagnosed to be out of equilibrium. These clusters are A1451, A2163, and A2744, all of which have hints of substructure. A2744 presents the largest discrepancy between its X-ray, velocity dispersion, and weak-lensing mass determinations, which can be interpreted as being due to the interaction between the two kinematic components along the line of sight found by Girardi & Mezzeti.

A structure in the early Universe at z ∼ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology

A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume 1/3 ) � 500 Mpc (proper size, present epoch), longest dimension � 1240 Mpc, membership of 73 quasars, and mean redshift ¯ = 1.27. In terms of both size and membership it is the most extreme LQG found in the DR7QSO catalogue for the redshift range 1.0 6 z 6 1.8 of our current investigation. Its location on the sky is � 8.8 ◦ north (� 615 Mpc projected) of the Clowes & Campusano LQG at the same redshift, ¯ z = 1.28, which is itself one of the more extreme examples. Their boundaries approach to within � 2 ◦ (� 140 Mpc projected). This new, huge LQG appears to be the largest structure currently known in the early universe. Its size suggests incompatibility with the Yadav et al. scale of homogeneity for the concordance cosmology, and thus challenges the assumption of the cosmological principle.

SEEKING THE LOCAL CONVERGENCE DEPTH. V. TULLY-FISHER PECULIAR VELOCITIES FOR 52 ABELL CLUSTERS

We have obtained I-band Tully-Fisher (T-F) measurements for 522 late-type galaxies in the fields of 52 rich Abell clusters distributed throughout the sky between ~50 and 200 h-1 Mpc. Here we estimate corrections to the data for various forms of observational bias, most notably Malmquist and cluster population incompleteness bias. The bias-corrected data are applied to the construction of an I-band T-F template, resulting in a relation with a dispersion of 0.38 mag and a kinematic zero point accurate to 0.02 mag. This represents the most accurate T-F template relation currently available. Individual cluster T-F relations are referred to the average template relation to compute cluster peculiar motions. The line-of-sight dispersion in the peculiar motions is 341 ± 93 km s-1, in general agreement with that found for the cluster sample of Giovanelli and coworkers.

Signatures of Galaxy-Cluster Interactions: Spiral Galaxy Rotation Curve Asymmetry, Shape, and Extent

The environmental influences on spiral galaxy rotation curves are investigated. Our large, homogeneously collected sample of 510 cluster spiral galaxy rotation curves is used to test whether the shape of a galaxy’s rotation curve strongly depends on its location within the cluster, and thus presumably on the strength of the local intracluster medium and on the frequency and strength of tidal interactions with the cluster and cluster galaxies. The data do not corroborate such a scenario, consistent with the fact that Tully-Fisher residuals are independent of galaxy location within the cluster; while the average late-type spiral galaxy shows more rise in the outer parts of its rotation curve than does the typical early-type spiral galaxy, there is no apparent trend for either subset with cluster environment. Rotation curve asymmetry and the radial distribution of H II region tracers within galactic disks are also investigated as a function of cluster environment. Mild trends with projected cluster-centric distance are observed: (i) the (normalized) radial extent of optical line emission averaged over all spiral galaxy types shows a 4±2%; increase per Mpc of galaxy-cluster core separation, and (ii) rotation curve asymmetry falls by a factor of two between the inner and outer cluster for early-type spirals (a negligible decrease is found for late-type spirals). Such trends are consistent with spiral disk perturbations or even the stripping of the diffuse, outermost gaseous regions within the disks as galaxies pass through the dense cluster cores.

No Hubble Bubble in the Local Universe

Zehavi et al. have suggested that the Hubble flow within 70 h-1 Mpc may be accelerated by the existence of a void centered on the Local Group. Its underdensity would be ~20%, which would result in a local Hubble distortion of about 6.5%. We have combined the peculiar velocity data of two samples of clusters of galaxies, SCI and SCII, to investigate the amplitude of Hubble distortions to 200 h-1 Mpc. Our results are not supportive of that conclusion. The amplitude of a possible distortion in the Hubble flow within 70 h-1 Mpc in the SCI+SCII merged data is 0.010 ± 0.022. The largest, and still quite marginal, geocentric deviation from smooth Hubble flow consistent with that data set is a shell with ΔH0/H0 = 0.027 ± 0.023, centered at hd = 101 Mpc and extending over some 30 h-1 Mpc. Our results are thus consistent with a Hubble flow that, on distances in excess of ~50 h-1 Mpc, is remarkably smooth.

Seeking the Local Convergence Depth: The Abell Cluster Dipole Flow to 200 h–1 Mpc

We have obtained new Tully-Fisher (TF) peculiar velocity measurements for 52 Abell galaxy clusters distributed throughout the sky between ~50 and 200 h-1 Mpc. The measurements are based on I-band photometry and optical rotation curves for a sample of 522 spiral galaxies, from which an accurate TF template relation has been constructed. Individual cluster TF relations are referred to the template to compute cluster peculiar motions. The reflex motion of the Local Group of galaxies is measured with respect to the reference frame defined by our cluster sample and the distant portion of the Giovanelli et al. cluster set. We find the Local Group motion in this frame to be 565±113 km s-1 in the direction (l, b)=(267°, 26°)±10° when peculiar velocities are weighted according to their errors. After optimizing the dipole calculation to sample equal volumes equally, the vector is 509±195 km s-1 toward (255°, 33°)±22°. Both solutions agree, to within 1 σ or better, with the Local Group motion as inferred from the cosmic microwave background (CMB) dipole. Thus, the cluster sample as a whole moves slowly in the CMB reference frame, its bulk flow being at most 200 km s-1.

Seeking the Local Convergence Depth. I. Tully-Fisher Observations of the Clusters A168, A397, A569, A1139, A1228, and A1983.

We present first results of an all-sky observing program designed to improve the quality of the I band Tully-Fisher (TF) template and to obtain the reflex motion of the Local Group with respect to clusters to z = 0.06. We are obtaining between 5 and 15 TF measurements per cluster on a sample of 50 clusters at intermediate redshifts (0.02 < z < 0.06). Presentation of the data for seven Abell clusters of galaxies is given here. This data incorporates methods for estimating the true inclination of a spiral disk, an observational parameter undervalued for small angular-sized galaxies or for galaxies observed in poor seeing conditions.

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.

VLT spectroscopy of galaxies lensed by the AC 114 cluster: - Implications for the mass model and the study of low-luminosity galaxies at high-redshift

We present the first results of a spectroscopic survey of faint lensed galaxie s in the core of the galaxy cluster AC114 (z=0.312) obtained from observations w ith the FORS1 spectrograph mounted on the VLT-Antu. The galaxies were chose n in areas close to the high-z critical lines predicted by the gravitational lens model of Natarajan et al (NKSE, 1998) for this cluster, according to both lensing and photometric redshift criteria. All the target galaxies are found to correspond to background galaxies with redshifts values in the [0.7, 3.5] interval. Our spectroscopic observations confirm the predicted lensing redshifts for 3 of the multiple-image galaxies, and together with predictions of the NKSE model led to the discovery of a new 5-image configuration at redshift z=3.347. A revised NKSE model, compatible with the redshift of this new multiple-image system, was generated and employed to calculate the gravitational amplifications of all the observed galaxies. The galaxies corresponding to the multiple-image systems are found to be intrinsically fainter, between 0.5 and 1.5 magnitudes, than the limiting magnitudes of existing blank field studies. When all the observed background galaxies are considered, the resulting intrinsic absolute magnitudes range from M_B~-22 to -19. Therefore, a large gain in sensitivity towards low luminosity high-z objects can actually be obtained, in agreement with theoretical expectations. This method can be used advantageously to probe the high redshift Universe and, in particular, its application to an ensemble of massive cluster cores could constraint the faint end of luminosity function of high redshift galaxies.

SEEKING THE LOCAL CONVERGENCE DEPTH. II. TULLY-FISHER OBSERVATIONS OF THE CLUSTERS A114, A119, A194, A2295, A2457, A2806, A3193, A3381, AND A3744

We present Tully-Fisher (T-F) observations for nine rich Abell clusters of galaxies. This is the second such data installment of an all-sky survey of ~50 clusters in the redshift range 0.02 z 0.06. The data extend the T-F study of nearby clusters of Giovanelli et al.; they will be used jointly to determine an accurate I-band T-F template and to establish a cluster inertial reference frame to z ~ 0.06.