Publications (7)0 Total impact
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Article: Dark matter halo properties from galaxy-galaxy lensing
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ABSTRACT: We present results for a galaxy-galaxy lensing study based on imaging data from the Canada-France-Hawaii Telescope Legacy Survey Wide. From a 12 million object multi-colour catalogue for 124 deg^2 of photometric data in the u*g'r'i'z' filters we compute photometric redshifts (with a scatter of \sigma_{\Delta z/(1+z)} = 0.033 and an outlier rate of \eta=2.0 per cent for i'<=22.5) and extract galaxy shapes down to i'=24.0. We select a sample of lenses and sources with 0.05 < z_d <= 1 and 0.05 < z_s <= 2. We fit three different galaxy halo profiles to the lensing signal, a singular isothermal sphere (SIS), a truncated isothermal sphere (BBS) and a universal density profile (NFW). We derive velocity dispersions by fitting an SIS out to 100 h^{-1} kpc to the excess surface mass density \Delta\Sigma and perform maximum likelihood analyses out to a maximum scale of 2 h^{-1} Mpc to obtain halo parameters and scaling relations. We find luminosity scaling relations of \sigma_{red} ~ L^{0.24+-0.03} for the red lens sample, \sigma_{blue} ~ L^{0.23+-0.03} for blue lenses and \sigma ~ L^{0.29+-0.02} for the combined lens sample with zeropoints of \sigma*_{red}=162+-2 km/s, \sigma*_{blue}=115+-3 km/s and \sigma*=135+-2 km/s at a chosen reference luminosity L*_{r'} = 1.6 \times 10^10 h^{-2} L_{r',sun}. The steeper slope for the combined sample is due to the different zeropoints of the blue and red lenses and the fact that blue lenses dominate at low luminosities and red lenses at high luminosities. The mean effective redshifts for the lens samples are <z_{red}>=0.28 for red lenses, <z_{blue}>=0.35 for blue lenses and =0.34 for the combined lens sample.03/2013; -
Article: X-Ray Groups of Galaxies in the Aegis Deep and Wide Fields
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ABSTRACT: We present the results of a search for extended X-ray sources and their corresponding galaxy groups from 800-ks Chandra coverage of the All-wavelength Extended Groth Strip International Survey (AEGIS). This yields one of the largest X-ray selected galaxy group catalogs from a blind survey to date. The red-sequence technique and spectroscopic redshifts allow us to identify 100$%$ of reliable sources, leading to a catalog of 52 galaxy groups. The groups span the redshift range $z\sim0.066-1.544$ and virial mass range $M_{200}\sim1.34\times 10^{13}-1.33\times 10^{14}M_\odot$. For the 49 extended sources which lie within DEEP2 and DEEP3 Galaxy Redshift Survey coverage, we identify spectroscopic counterparts and determine velocity dispersions. We select member galaxies by applying different cuts along the line of sight or in projected spatial coordinates. A constant cut along the line of sight can cause a large scatter in scaling relations in low-mass or high-mass systems depending on the size of cut. A velocity dispersion based virial radius can more overestimate velocity dispersion in comparison to X-ray based virial radius for low mass systems. There is no significant difference between these two radial cuts for more massive systems. Independent of radial cut, overestimation of velocity dispersion can be created in case of existence of significant substructure and also compactness in X-ray emission which mostly occur in low mass systems. We also present a comparison between X-ray galaxy groups and optical galaxy groups detected using the Voronoi-Delaunay method (VDM) for DEEP2 data in this field.02/2013; -
Article: Weak lensing mass estimates of galaxy groups and the line-of-sight contamination
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ABSTRACT: Weak lensing is an important technique to determine the masses of galaxy groups. However, the distortion imprint on the shape of the background galaxies is affected by all the mass content along the line-of-sight. Using COSMOS shear mock data we study the shear profile of 165 groups and investigate the level at which the neighbouring groups can enhance or suppress the shear signal from the main halo. Our mock data are based on CFHT and Subaru observations and the information on the galaxy groups is taken from the COSMOS X-ray catalogue of extended sources. The expected gravitational shear field of these groups is calculated assuming that the haloes follow NFW density profiles. We conclude that, on average, the signal-to-noise for a detection of the main halo is affected by ~15%x\sqrt{ngal/30} with respect to the signal-to-noise the same halo would have if it was isolated in the sky. Groups with neighbours that are close in projected distance (<1') are the most affected, but haloes located at larger angular distances also cause a measurable shear signal, which can be interpreted as uncorrelated large-scale structure. The average bias in the mass excess estimate of individual groups that is introduced by the external haloes is zero with an rms of ~6-72%, depending on the aperture size used. The shear signal introduced by large-scale structure acts as an external source of noise. The averaged uncertainty introduced is \sigma_{\gamma_t}^{LSS}~0.006 per component for an aperture size of ~5', which corresponds to 1.8% of the one-component intrinsic ellipticity value. This large-scale structure noise error becomes equal to intrinsic ellipticity noise if there are measurements for ~3000 galaxies within a certain aperture, a number that is already achieved by current deep surveys such as COSMOS and, therefore, should not be ignored.11/2011; -
Article: The Massive Galaxy Cluster XMMU J1230.3+1339 at z ~ 1: Colour-magnitude relation, Butcher-Oemler effect, X-ray and weak lensing mass estimates
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ABSTRACT: We present results from the multi-wavelength study of XMMU J1230.3+1339 at z ~ 1. We analyze deep multi-band wide-field images from the Large Binocular Telescope, multi-object spectroscopy observations from VLT, as well as space-based serendipitous observations, from the GALEX and Chandra X-ray observatories. We apply a Bayesian photometric redshift code to derive the redshifts using the FUV, NUV and the deep U, B, V, r, i, z data. We achieve an accuracy of $\triangle z/(1+z)$ = 0.07 (0.04) and the fraction of catastrophic outliers is $\eta$ = 13 (0)%, when using all (secure) spectroscopic data, respectively. The i - z against z colour-magnitude relation of the photo-z members shows a tight red-sequence with a zero point of 0.935 mag, and slope equal to -0.027. We observe evidence for a truncation at the faint end of the red-cluster-sequence and the Butcher-Oemler effect, finding a fraction of blue galaxies $f_b \approx$ 0.5. Further we conduct a weak lensing analysis of the deep 26' $\times$ 26' r-band LBC image. The observed shear is fitted with a Single-Isothermal-Sphere and a Navarro-Frenk-White model to obtain the velocity dispersion and the model parameters, respectively. Our best fit values are, for the velocity dispersion $\sigma_{SIS}$ = 1308 $\pm$ 284, concentration parameter c = 4.0$^{+14}_{-2}$ and scale radius r$_{s}$ = 345$^{+50}_{-57}$ kpc. Combining our mass estimates from the kinematic, X-ray and weak lensing analyses we obtain a total cluster mass of $M^{tot}_{200}$ = (4.56 $\pm$ 2.3) $\times$ 10$^{14}$ M$_{\sun}$. This study demonstrates the feasibility of ground based weak lensing measurements of galaxy clusters up to z ~ 1. Comment: 29 pages, 34 figures, 6 tables, full resolution pdf-file available at http://www.usm.uni-muenchen.de/people/mike/XMMUJ1230_MNRAS.pdf, submitted to MNRAS, shortened abstract09/2010; -
Article: CARS: the CFHTLS-Archive-Research Survey; I. Five-band multi-colour data from 37 sq. deg. CFHTLS-Wide observations
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ABSTRACT: We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual multi-colour survey based on public archive images from the CFHT-Legacy-Survey. Our main scientific interests in CARS are optical searches for galaxy clusters from low to high redshift and their subsequent study with photometric and weak-gravitational lensing techniques. As a first step of the project we present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide component. Our aims are to create astrometrically and photometrically well calibrated co-added images. Second goal are five-band (u*, g', r', i', z') multi-band catalogues with an emphasis on reliable estimates for object colours. These are subsequently used for photometric redshift estimates. The article explains in detail data processing, multi-colour catalogue creation and photometric redshift estimation. Furthermore we apply a novel technique, based on studies of the angular galaxy cross-correlation function, to quantify the reliability of photo-z's. The accuracy of our high-confidence photo-z sample (10-15 galaxies per sq. arcmin) is estimated to $\sigma_{\Delta_z/(1+z)}\approx 0.04-0.05$ up to i'<24 with typically only 1-3% outliers. Interested users can obtain access to our data by request to the authors. Comment: 31 pages, 18 figures, 6 tables; accepted for publication by A&A main journal11/2008; -
Article: A counter-rotating core in the dwarf elliptical galaxy VCC 510
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ABSTRACT: We present optical long-slit spectra of the Virgo dwarf elliptical galaxy VCC 510 at high spectral and spatial resolution. Heliocentric velocities and velocity dispersions as functions of galaxy radius are derived by deconvolving line-of-sight velocity distributions. A maximum rotation v_rot=8 km/s inside half the effective radius (re~20 arcsec) and a mean, radially flat velocity dispersion sigma=44 km/s are measured. The core extending over the inner 2 arcsec (~140 pc) is found to rotate in the opposite sense with v_rot(core) ~ -1/2 v_rot. VCC 510 (M_B ~ -15.7) is therefore by far the faintest and smallest galaxy with a counter-rotating core known. From the main body rotation and the velocity dispersion profile we deduce that VCC 510 is anisotropic and clearly not entirely supported by rotation. By comparison of Lick absorption-line indices with stellar population models we derive an old luminosity-weighted age (10 Gyr) and sub-solar metallicity ([Z/H]=-0.4) inside the effective radius. There is tentative evidence that the counter-rotating core might be younger and less alpha/Fe enhanced. From the stellar population parameters we obtain a total stellar mass-to-light ratio of ~3.6 (M/L_B)_sun which is significantly lower than a rough dynamical estimate obtained from the kinematics through the virial theorem (~15). This discrepancy hints toward the possible presence of dark matter in the centre of VCC 510. We discuss the origin of the counter-rotating core and exclude fly-by encounters as a viable possibility. Gas accretion or galaxy merging provide more likely explanations. VCC 510 is therefore the direct observational evidence that such processes do occur in cluster satellite galaxies on dwarf galaxy scales. Comment: 4 pages, two figures, accepted by A&A Letters11/2005; -
Article: CARS: the CFHTLS-Archive-Research Survey
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ABSTRACT: Context. We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual multi-colour survey that is based on public archive images from the Deep and Wide components of the CFHT-Legacy-Survey (CFHTLS). Our main scientific interests in the CFHTLS Wide-part of CARS are optical searches for galaxy clusters from low to high redshift and their subsequent study with photometric and weak-gravitational lensing techniques.Aims. As a first step in the CARS project, we present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide component. Our aims are first to create astrometrically and photometrically well-calibrated co-added images from publicly available CFHTLS data. Second, we offer five-band ($u^*g'r'i'z'$) multi-band catalogues with an emphasis on reliable estimates for object colours. These are subsequently used for photometric redshift estimates.Methods. We consider all those CFHTLS-Wide survey pointings that were publicly available on January 2008 and that also have five-band coverage in $u^*g'r'i'z'$. The data were calibrated and processed with our GaBoDS/THELI image processing pipeline. The quality of the resulting images was thoroughly checked against the Sloan-Digital-Sky Survey (SDSS) and already public high-end CFHTLS data products. From the co-added images we extracted source catalogues and determined photometric redshifts using the public code Bayesian Photometric Redshifts (BPZ). Fifteen of our survey fields directly overlap with public spectra from the VIMOS VLT deep (VVDS), DEEP2 and SDSS redshift surveys, which we used for calibration and verification of our redshift estimates. Furthermore we applied a novel technique, based on studies of the angular galaxy cross-correlation function, to quantify the reliability of photo-$z$'s.Results. With this paper we present 37 sq. degrees of homogeneous and high-quality five-colour photometric data from the CFHTLS-Wide survey. The median seeing of our data is better than $0\farcs 9$ in all bands and our catalogues reach a $5\sigma$ limiting magnitude of about $i'_{\rm AB}\approx$ 24.5. Comparisons with the SDSS indicate that most of our survey fields are photometrically calibrated to an accuracy of $0.04$ mag or better. This allows us to derive photometric redshifts of homogeneous quality over the whole survey area. The accuracy of our high-confidence photo-$z$ sample (10-15 galaxies per sq. arcmin) is estimated with external spectroscopic data to $\sigma_{\Delta_z/(1+z)}\approx$ 0.04-0.05 up to $i'_{\rm AB}$ < 24 with typically only 1-3% outliers. In the spirit of the Legacy Survey we make our catalogues available to the astronomical community. Our products consist of multi-colour catalogues and supplementary information, such as image masks and JPEG files to visually inspect our catalogues. Interested users can obtain the data by request to the authors.http://dx.doi.org/10.1051/0004-6361:200810426.
