We present the data from an extensive, moderately deep (b_J_~19.5) spectroscopic survey of ~600 galaxies within four regions of the sky located near the South Galactic Pole. About 75% of the measured galaxies are in an approximately 3x1.5sq.deg region dominated by the rich cluster of galaxies Klemola 44 (Abell 4038). The other three small areas cover about 1sq.deg each. Here, we discuss in detail the observing and data reduction strategies, and the completeness of and errors in the measured redshifts. The data collected are being used for: (i) a study of the large-scale redshift distribution of the galaxies in each field, and (ii) a thorough dynamical investigation of Klemola 44. Results from these analyses will be presented in forthcoming papers.
Based on spectroscopy and multiband wide-field observations of the gravitationally lensed quasar HE 0435-1223, we determine the probability distribution function of the external convergence {kappa}_ext_ for this system. We measure the under/overdensity of the line of sight towards the lens system and compare it to the average line of sight throughout the Universe, determined by using the CFHTLenS (The Canada France Hawaii Lensing Survey) as a control field. Aiming to constrain {kappa}_ext_ as tightly as possible, we determine under/overdensities using various combinations of relevant informative weighting schemes for the galaxy counts, such as projected distance to the lens, redshift and stellar mass. We then convert the measured under/overdensities into a {kappa}_ext_ distribution, using ray-tracing through the Millennium Simulation. We explore several limiting magnitudes and apertures, and account for systematic and statistical uncertainties relevant to the quality of the observational data, which we further test through simulations. Our most robust estimate of {kappa}_ext_ has a median value {kappa}^med^_ext_=0.004 and a standard deviation {sigma}_{kappa}_=0.025. The measured {sigma}_{kappa}_ corresponds to 2.5 per cent relative uncertainty on the time delay distance, and hence the Hubble constant H_0_ inferred from this system. The median {kappa}^med^_ext_ value varies by ~0.005 with the adopted aperture radius, limiting magnitude and weighting scheme, as long as the latter incorporates galaxy number counts, the projected distance to the main lens and a prior on the external shear obtained from mass modelling. This corresponds to just ~0.5 per cent systematic impact on H_0_. The availability of a well-constrained {kappa}_ext_ makes HE 0435-1223 a valuable system for measuring cosmological parameters using strong gravitational lens time delays.
As a prerequisite for cosmological studies using adaptive optics techniques, we have begun to identify and characterize faint sources in the vicinity of bright stars at high Galactic latitudes. The initial phase of this work has been a program of K_s_ imaging conducted with SOFI at the ESO NTT. From observations of 42 southern fields evenly divided between the spring and autumn skies, we have identified 391 additional stars and 1589 galaxies lying at separations <60" from candidate guide stars in the magnitude range 9.0<R<12.4. When analyzed as a "discrete deep field" with 131-arcmin^2^ area, our dataset gives galaxy number counts that agree with those derived previously over the range 16<K_s_<20.5. This consistency indicates that in the aggregate, our fields should be suitable for future statistical studies. We provide our source catalogue as a resource for users of large telescopes in the southern hemisphere.
The gravitational lens system CLASS B2108+213 has two radio-loud lensed images separated by 4.56 arcsec. The relatively large image separation implies that the lensing is caused by a group of galaxies. In this paper, new optical imaging and spectroscopic data for the lensing galaxies of B2108+213 and the surrounding field galaxies are presented. These data are used to investigate the mass and composition of the lensing structure.
We discuss the X-ray and optical properties of the massive galaxy cluster MACSJ1206.2-0847 (z=0.4385), discovered in the Massive Cluster Survey (MACS). Our Chandra observation of the system yields a total X-ray luminosity of 2.4x10^45^erg/s (0.1-2.4keV) and a global gas temperature of 11.6+/-0.7keV, very high values typical of MACS clusters. In both optical and X-ray images, MACSJ1206.2-0847 appears close to relaxed in projection, with a pronounced X-ray peak at the location of the brightest cluster galaxy (BCG); we interpret this feature as the remnant of a cold core. A spectacular giant gravitational arc, 15-arcsec in length, bright (V~21) and unusually red (R-K=4.3), is seen 20-arcsec west of the BCG; we measure a redshift of z=1.036 for the lensed galaxy. From our Hubble Space Telescope image of the cluster, we identify the giant arc and its counter image as a sevenfold imaged system. An excess of X-ray emission in the direction of the arc coincides with a mild galaxy overdensity and could be the remnant of a minor merger with a group of galaxies. We derive estimates of the total cluster mass as well as of the mass of the cluster core using X-ray, dynamical and gravitational-lensing techniques. For the mass enclosed by the giant arc (r<119kpc), our strong-lensing analysis based on Hubble Space Telescope imaging yields a very high value of 1.1x10^14^M_{sun}_, inconsistent with the much lower X-ray estimate of 0.5x10^14^M_{sun}_. Similarly, the virial estimate of 4x10^15^M_{sun}_ for the total cluster mass, derived from multi-object spectroscopy with Canada-France-Hawaii Telescope (CFHT) and the VLT of 38 cluster members, is significantly higher than the corresponding X-ray estimate of 1.7x10^15^M_{sun}_. We take the discrepancy between X-ray and other mass estimates to be indicative of pronounced substructure along the line of sight during an ongoing merger event, an interpretation that is supported by the system's very high velocity dispersion of 1580km/s.
We present galactic spectroscopic data from a pencil beam of 10.75'x7.5' centered on the X-ray cluster RXJ0054.0-2823 at z=0.29. We study the spectral evolution of galaxies from z=1 down to the cluster redshift in a magnitude-limited sample at R<=23, for which the statistical properties of the sample are well understood. We divide emission-line galaxies into star-forming galaxies, Low Ionization Nuclear Emission line Regions (LINERs), and Seyferts by using emission-line ratios of [OII],H{beta}, and [OIII], and derive stellar fractions from population synthesis models. We focus our analysis on absorption and low-ionization galaxies.
We present a catalog of morphological and color data for galaxies with 21<I_814<25mag in the Hubble Deep Field (Williams et al. 1996, in Science with the Hubble Space Telescope II). Galaxies have been inspected and (when possible) independently visually classified on the MDS and DDO systems. Measurements of central concentration and asymmetry are also included in the catalog. The fraction of interacting and merging objects is seen to be significantly higher in the Hubble Deep Field than it is among nearby galaxies. Barred spirals are essentially absent from the deep sample. The fraction of early-type galaxies in the Hubble Deep Field is similar to the fraction of early-types in the Shapley-Ames Catalog, but the fraction of galaxies resembling archetypal grand-design late-type spiral galaxies is dramatically lower in the distant HDF sample.
We present aperture-matched point-spread function (PSF)corrected BVi'z'JH photometry and Bayesian photometric redshifts (BPZ) for objects detected in the Hubble Ultra Deep Field (UDF), 8042 of which are detected at the 10 level (e.g., i'<29.01 or z'<28.43). Most of our objects are defined identically to those in the public STScI catalogs, enabling a straightforward object-by-object comparison. We have combined detections from i', z', J+H, and B+V+i'+ z' images into a single comprehensive segmentation map. Using a new program called SExSeg, we are able to force this segmentation map into SExtractor for photometric analysis. The resulting photometry is corrected for the wider NIC3 PSFs using our ColorPro software. We also correct for the ACS z'-band PSF halo. Offsets are applied to our NIC3 magnitudes, which are found to be too faint relative to the ACS fluxes. Based on BPZ spectral energy distribution (SED) fits to objects of known spectroscopic redshift, we derived corrections of -0.30+/-0.03mag in J and -0.18+/-0.04mag in H. Our offsets appear to be supported by a recent recalibration of the UDF NIC3 images combined with nonlinearity measured in NICMOS itself. The UDF reveals a large population of faint blue galaxies (presumably young starbursts), bluer than those observed in the original Hubble Deep Fields.
We investigate the distribution and velocity field of galaxies situated in a band of 100x20 degrees centered on M87 and oriented along the Local supercluster plane. Our sample amounts 2158 galaxies with radial velocities less than 2000 km/s. Of them, 1119 galaxies (52%) have distance and peculiar velocity estimates. About 3/4 of early-type galaxies are concentrated within the Virgo cluster core, most of the late-type galaxies in the band locate outside the virial radius. Distribution of gas-rich dwarfs with M_HI_> M* looks to be insensitive to the Virgo cluster presence. Among 50 galaxy groups in the equatorial supercluster band 6 groups have peculiar velocities about 500-1000km/s comparable with virial motions in rich clusters. The most cryptic case is a flock of nearly 30 galaxies around NGC4278 (Coma I cloud), moving to us with the mean peculiar velocity of -840km/s. This cloud (or filament?) resides at a distance of 16.1Mpc from us and approximately 5Mpc away from the Virgo center. Galaxies around Virgo cluster exhibit Virgocentric infall with an amplitude of about 500 km/s. Assuming the spherically symmetric radial infall, we estimate the radius of the zero-velocity surface to be R0=(7.0+/-0.3)Mpc that yields the total mass of Virgo cluster to be (7.4+/-0.9)x10^14^ solar masses, in tight agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark mater beyond its virial core.
The evolution of galaxies is influenced by the environment in which they reside. This effect should be strongest for the lowest-mass and lowest-luminosity galaxies. To study dwarf galaxies in extremely low density environments, we have compiled a deep catalogue of dwarf galaxies in the nearby Lynx-Cancer void. This void hosts some of the most metal-poor dwarfs known to date. It borders the Local Volume at negative supergalactic Z(SGZ) coordinates and has a size of more than 16Mpc. With a distance to its centre of only 18Mpc, it is close enough to allow a search for the faintest dwarfs. Within the void 75 dwarf (-11.9>M_B_>-18.0) and four subluminous (-18.0>M_B_>-18.4) galaxies have been identified. We present the parameters of the void galaxies and a detailed analysis of the completeness of the catalogue as a function of magnitude and surface brightness.