arXiv subjects

Gijs Verdoes Kleijn

Publications and source records attributed to Gijs Verdoes Kleijn.

At least 37 records · Page 2Linked to original sources

arXiv2016

Dependence of GAMA galaxy halo masses on the cosmic web environment from 100 square degrees of KiDS weak lensing data

Galaxies and their dark matter haloes are part of a complex network of mass structures, collectively called the cosmic web. Using the tidal tensor prescription these structures can be classified into four cosmic environments: voids, sheets, filaments and knots. As the cosmic web may influence the formation and evolution of dark matter haloes and the galaxies they host, we aim to study the effect of these cosmic environments on the average mass of galactic haloes. To this end we measure the galaxy-galaxy lensing profile of 91,195 galaxies, within 0.039 < z < 0.263, from the spectroscopic Galaxy And Mass Assembly (GAMA) survey, using ~100 square degrees of overlapping data from the Kilo-Degree Survey (KiDS). In each of the four cosmic environments we model the contributions from group centrals, satellites and neighbouring groups to the stacked galaxy-galaxy lensing profiles. After correcting the lens samples for differences in the stellar mass distribution, we find no dependence of the average halo mass of central galaxies on their cosmic environment. We do find a significant increase in the average contribution of neighbouring groups to the lensing profile in increasingly dense cosmic environments. We show, however, that the observed effect can be entirely attributed to the galaxy density at much smaller scales (within 4 Mpc/h), which is correlated with the density of the cosmic environments. Within our current uncertainties we find no direct dependence of galaxy halo mass on their cosmic environment.

astro-ph.GA↗

arXiv2015

Gravitational Lensing Analysis of the Kilo Degree Survey

The Kilo-Degree Survey (KiDS) is a multi-band imaging survey designed for cosmological studies from weak lensing and photometric redshifts. It uses the ESO VLT Survey Telescope with its wide-field camera OmegaCAM. KiDS images are taken in four filters similar to the SDSS ugri bands. The best-seeing time is reserved for deep r-band observations that reach a median 5-sigma limiting AB magnitude of 24.9 with a median seeing that is better than 0.7arcsec. Initial KiDS observations have concentrated on the GAMA regions near the celestial equator, where extensive, highly complete redshift catalogues are available. A total of 109 survey tiles, one square degree each, form the basis of the first set of lensing analyses, which focus on measurements of halo properties of GAMA galaxies. 9 galaxies per square arcminute enter the lensing analysis, for an effective inverse shear variance of 69 per square arcminute. Accounting for the shape measurement weight, the median redshift of the sources is 0.53. KiDS data processing follows two parallel tracks, one optimized for galaxy shape measurement (for weak lensing), and one for accurate matched-aperture photometry in four bands (for photometric redshifts). This technical paper describes how the lensing and photometric redshift catalogues have been produced (including an extensive description of the Gaussian Aperture and Photometry pipeline), summarizes the data quality, and presents extensive tests for systematic errors that might affect the lensing analyses. We also provide first demonstrations of the suitability of the data for cosmological measurements, and explain how the shear catalogues were blinded to prevent confirmation bias in the scientific analyses. The KiDS shear and photometric redshift catalogues, presented in this paper, are released to the community through http://kids.strw.leidenuniv.nl .

astro-ph.CO↗

arXiv2015

The masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data

We use the first 100 sq. deg. of overlap between the Kilo-Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey to determine the galaxy halo mass of ~10,000 spectroscopically-confirmed satellite galaxies in massive ($M > 10^{13}h^{-1}{\rm M}_\odot$) galaxy groups. Separating the sample as a function of projected distance to the group centre, we jointly model the satellites and their host groups with Navarro-Frenk-White (NFW) density profiles, fully accounting for the data covariance. The probed satellite galaxies in these groups have total masses $\log M_{\rm sub} /(h^{-1}{\rm M}_\odot) \approx 11.7 - 12.2$ consistent across group-centric distance within the errorbars. Given their typical stellar masses, $\log M_{\rm \star,sat}/(h^{-2}{\rm M}_\odot) \sim 10.5$, such total masses imply stellar mass fractions of $M_{\rm \star,sat} /M_{\rm sub} \approx 0.04 h^{-1}$ . The average subhalo hosting these satellite galaxies has a mass $M_{\rm sub} \sim 0.015M_{\rm host}$ independent of host halo mass, in broad agreement with the expectations of structure formation in a $Λ$CDM universe.

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arXiv2014

The HST/ACS Coma Cluster Survey. X. Nuclear star clusters in low-mass early-type galaxies: scaling relations

We present scaling relations between structural properties of nuclear star clusters and their host galaxies for a sample of early-type dwarf galaxies observed as part of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Coma Cluster Survey. We have analysed the light profiles of 200 early-type dwarf galaxies in the magnitude range $16.0 < m_{F814W} < 22.6 $ mag, corresponding to $-19.0 < M_{F814W} < -12.4 $ mag. Nuclear star clusters are detected in 80% of the galaxies, thus doubling the sample of HST-observed early-type dwarf galaxies with nuclear star clusters. \changed{We confirm that the} nuclear star cluster detection fraction decreases strongly toward faint magnitudes. The luminosities of nuclear star clusters do not scale linearly with host galaxy luminosity. A linear fit yields L$_{nuc} \sim $L$_{gal}^{0.57\pm0.05}$. The nuclear star cluster-host galaxy luminosity scaling relation for low-mass early-type dwarf galaxies is consistent with formation by globular cluster accretion. We find that at similar luminosities, galaxies with higher Sérsic indices have slightly more luminous nuclear star clusters. Rounder galaxies have on average more luminous clusters. Some of the nuclear star clusters are resolved, despite the distance of Coma. We argue that the relation between nuclear star cluster mass and size is consistent with both formation by globular cluster accretion and in situ formation. Our data are consistent with GC inspiraling being the dominant mechanism at low masses, although the observed trend with Sérsic index suggests that in situ star formation is an important second order effect.

astro-ph.GA↗

arXiv2014

The Atlas3D project - XXIV. The intrinsic shape distribution of early-type galaxies

We use the Atlas3D sample to perform a study of the intrinsic shapes of early-type galaxies, taking advantage of the available combined photometric and kinematic data. Based on our ellipticity measurements from the Sloan Digital Sky Survey Data Release 7, and additional imaging from the Isaac Newton Telescope, we first invert the shape distribution of fast and slow rotators under the assumption of axisymmetry. The so-obtained intrinsic shape distribution for the fast rotators can be described with a Gaussian with a mean flattening of q=0.25 and standard deviation sigma_q = 0.14, and an additional tail towards rounder shapes. The slow rotators are much rounder, and are well described with a Gaussian with mean q = 0.63 and sigma_q =0.09. We then checked that our results were consistent when applying a different and independent method to obtain intrinsic shape distributions, by fitting the observed ellipticity distributions directly using Gaussian parametrisations for the intrinsic axis ratios. Although both fast and slow rotators are identified as early-type galaxies in morphological studies, and in many previous shape studies are therefore grouped together, their shape distributions are significantly different, hinting at different formation scenarios. The intrinsic shape distribution of the fast rotators shows similarities with the spiral galaxy population. Including the observed kinematic misalignment in our intrinsic shape study shows that the fast rotators are predominantly axisymmetric, with only very little room for triaxiality. For the slow rotators though there are very strong indications that they are (mildly) triaxial.

astro-ph.GA↗

arXiv2014

The HST/ACS Coma Cluster Survey - VII. Structure and Assembly of Massive Galaxies in the Center of the Coma Cluster

We constrain the assembly history of galaxies in the projected central 0.5 Mpc of the Coma cluster by performing structural decomposition on 69 massive (M_star >= 10^9 M_sun) galaxies using high-resolution F814W images from the HST Treasury Survey of Coma. Each galaxy is modeled with up to three Sersic components having a free Sersic index n. After excluding the two cDs in the projected central 0.5 Mpc of Coma, 57% of the galactic stellar mass in the projected central 0.5 Mpc of Coma resides in classical bulges/ellipticals while 43% resides in cold disk-dominated structures. Most of the stellar mass in Coma may have been assembled through major (and possibly minor) mergers. Hubble types are assigned based on the decompositions, and we find a strong morphology-density relation; the ratio of (E+S0):spirals is (91.0%):9.0%. In agreement with earlier work, the size of outer disks in Coma S0s/spirals is smaller compared with lower-density environments captured with SDSS (Data Release 2). Among similar-mass clusters from a hierarchical semi-analytic model, no single cluster can simultaneously match all the global properties of the Coma cluster. The model strongly overpredicts the mass of cold gas and underpredicts the mean fraction of stellar mass locked in hot components over a wide range of galaxy masses. We suggest that these disagreements with the model result from missing cluster physics (e.g., ram-pressure stripping), and certain bulge assembly modes (e.g., mergers of clumps). Overall, our study of Coma underscores that galaxy evolution is not solely a function of stellar mass, but also of environment.

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arXiv2012

The ATLAS3D Project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

We explore the connection between the local escape velocity, V_esc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-of-the-art photometry in the literature with residuals of 0.04 mags. We utilise these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local V_esc derived from the surface brightness. We find that the local V_esc is tightly correlated with the Mgb and Fe5015 linestrengths and optical colours, and anti-correlated with the Hbeta linestrength. In the case of the Mgb and Colour - V_esc relations we find that the relation within individual galaxies follows the global relation between different galaxies. We intentionally ignored any uncertain contribution due to dark matter since we are seeking an empirical description of stellar population gradients in early-type galaxies that is ideal for quantitative comparison with model predictions. We identify a population of galaxies that occur only at low V_esc that exhibit negative gradients in the Mgb - and Colour -V_esc relations. These galaxies typically have young central stellar populations and contain significant amounts of molecular gas and dust. Combining these results with N-body simulations of binary mergers we use the Mgb-V_esc relation to constrain the possible number of dry mergers experienced by the local early-type galaxy population - a typical massive ETG can have experienced only ~1.5 major mergers before becoming a significant outlier in the Mgb-V_esc relation. [Abridged]

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arXiv2012

The HST/ACS Coma Cluster Survey. VIII. Barred Disk Galaxies in the Core of the Coma Cluster

(ABRIDGED) We use high resolution (~0.1") F814W ACS images from the HST ACS Treasury survey of the Coma cluster at z~0.02 to study bars in massive disk galaxies (S0s), and in dwarf galaxies in the Coma core. Our study helps constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. (1) We characterize the fraction and properties of bars in a sample of 32 bright (M_V <= -18, M_* > 10^9.5 M_sun) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. Measuring the S0 bar fraction must be handled carefully, as the results depend on the method used: the bar fraction for bright S0s in the Coma core is 50%+/-11%, 65%+/-11%, and 60%+/-11% for three methods of bar detection: strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (Coma core, A901/902, Virgo). We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation across environments spanning two orders of magnitude in galaxy number density (n~300-10,000 gal/Mpc^3). We speculate that the S0 bar fraction is not significantly enhanced in rich clusters because S0s in rich clusters are less prone to bar instabilities as they are dynamically hot and gas poor due to ram pressure stripping and accelerated star formation. In addition, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We analyze a sample of 333 faint (M_V > -18) dwarf galaxies in the Coma core. Using unsharp-masking, we find only 13 galaxies with bar and/or spiral structure. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies, or that any disks present are too hot to develop instabilities.

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arXiv2011

Astro-WISE for KiDS survey production and quality control

The Kilo Degree Survey (KiDS) is a 1500 square degree optical imaging survey with the recently commissioned OmegaCAM wide-field imager on the VLT Survey Telescope (VST). A suite of data products will be delivered to ESO and the community by the KiDS survey team. Spread over Europe, the KiDS team uses Astro-WISE to collaborate efficiently and pool hardware resources. In Astro-WISE the team shares, calibrates and archives all survey data. The data-centric architectural design realizes a dynamic 'live archive' in which new KiDS survey products of improved quality can be shared with the team and eventually the full astronomical community in a flexible and controllable manner

astro-ph.IM↗

arXiv2011

The HST/ACS Coma Cluster Survey IV. Intergalactic Globular Clusters and the Massive Globular Cluster System at the Core of the Coma Galaxy Cluster

Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster is one of the nearest truly massive galaxy clusters, and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R<520 kpc). We estimate that there are 47000+/-1600 (random) +4000/-5000 (systematic) IGCs out to this radius, and that they make up ~70% of the central GC system, making this the largest GC system in the nearby Universe. Even including the GC systems of other cluster galaxies, IGCs still make up ~30-45% of the GCs in the cluster core. Observational limits from previous studies of the intracluster light (ICL) suggest that the IGC population has a high specific frequency. If the IGC population has a specific frequency similar to high-S_N dwarf galaxies, then the ICL has a total stellar mass of ~10^12 M_sun within the cluster core. The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central (NGC4874+ICL) system. The color distribution of the IGC population is bimodal, with blue, metal-poor GCs outnumbering red, metal-rich GCs by a ratio of 4:1. The fraction of red IGCs (20%), and the red color of those GCs, implies that IGCs can originate from the halos of relatively massive, L* galaxies, and not solely from the disruption of dwarf galaxies. (Abridged)

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arXiv2010

The HST/ACS Coma Cluster Survey III. Structural Parameters of Galaxies using single-Sérsic Fits

We present a catalogue of structural parameters for 8814 galaxies in the 25 fields of the HST/ACS Coma Treasury Survey. Parameters from Sérsic fits to the two-dimensional surface brightness distributions are given for all galaxies from our published Coma photometric catalogue with mean effective surface brightness brighter than 26.0 mag/sq. arcsec and brighter than 24.5 mag (equivalent to absolute magnitude - 10.5), as given by the fits, all in F814W(AB). The sample comprises a mixture of Coma members and background objects; 424 galaxies have redshifts and of these 163 are confirmed members. The fits were carried out using both the Gim2D and Galfit codes. We provide the following parameters: Galaxy ID, RA, DEC, the total corrected automatic magnitude from the photometric catalogue, the total magnitude of the model (F814W_AB), the geometric mean effective radius Re, the mean surface brightness within the effective radius <μ>_e, the Sérsic index n, the ellipticity and the source position angle. The selection limits of the catalogue and the errors listed for the Sérsic parameters come from extensive simulations of the fitting process using synthetic galaxy models. The agreement between Gim2D and Galfit parameters is sensitive to details of the fitting procedure; for the settings employed here the agreement is excellent over the range of parameters covered in the catalogue. We define and present two goodness-of-fit indices which quantify the degree to which the image can be approximated by a Sérsic model with concentric, coaxial elliptical isophotes; such indices may be used to objectively select galaxies with more complex structures such as bulge-disk, bars or nuclear components. We make the catalog available in electronic format at Astro-WISE and MAST.

astro-ph.CO↗

arXiv2010

The HST/ACS Coma Cluster Survey. II. Data Description and Source Catalogs

The Coma cluster was the target of a HST-ACS Treasury program designed for deep imaging in the F475W and F814W passbands. Although our survey was interrupted by the ACS instrument failure in 2007, the partially completed survey still covers ~50% of the core high-density region in Coma. Observations were performed for 25 fields that extend over a wide range of cluster-centric radii (~1.75 Mpc) with a total coverage area of 274 arcmin^2. The majority of the fields are located near the core region of Coma (19/25 pointings) with six additional fields in the south-west region of the cluster. In this paper we present reprocessed images and SExtractor source catalogs for our survey fields, including a detailed description of the methodology used for object detection and photometry, the subtraction of bright galaxies to measure faint underlying objects, and the use of simulations to assess the photometric accuracy and completeness of our catalogs. We also use simulations to perform aperture corrections for the SExtractor Kron magnitudes based only on the measured source flux and half-light radius. We have performed photometry for ~73,000 unique objects; one-half of our detections are brighter than the 10-sigma point-source detection limit at F814W=25.8 mag (AB). The slight majority of objects (60%) are unresolved or only marginally resolved by ACS. We estimate that Coma members are 5-10% of all source detections, which consist of a large population of unresolved objects (primarily GCs but also UCDs) and a wide variety of extended galaxies from a cD galaxy to dwarf LSB galaxies. The red sequence of Coma member galaxies has a constant slope and dispersion across 9 magnitudes (-21<M_F814W<-13). The initial data release for the HST-ACS Coma Treasury program was made available to the public in 2008 August. The images and catalogs described in this study relate to our second data release.

astro-ph.GA↗

arXiv2010

Barred Galaxies in the Coma Cluster

We use ACS data from the HST Treasury survey of the Coma cluster (z~0.02) to study the properties of barred galaxies in the Coma core, the densest environment in the nearby Universe. This study provides a complementary data point for studies of barred galaxies as a function of redshift and environment. From ~470 cluster members brighter than M_I = -11 mag, we select a sample of 46 disk galaxies (S0--Im) based on visual classification. The sample is dominated by S0s for which we find an optical bar fraction of 47+/-11% through ellipse fitting and visual inspection. Among the bars in the core of the Coma cluster, we do not find any very large (a_bar > 2 kpc) bars. Comparison to other studies reveals that while the optical bar fraction for S0s shows only a modest variation across low-to-intermediate density environments (field to intermediate-density clusters), it can be higher by up to a factor of ~2 in the very high-density environment of the rich Coma cluster core.

astro-ph.CO↗

arXiv2008

FIRST "Winged" and X-shaped Radio Source Candidates: II. New Redshifts

We report optical spectroscopic observations of X-shaped radio sources with the Hobby-Eberly Telescope and Multiple-Mirror Telescope, focused on the sample of candidates from the FIRST survey presented in Paper I (Cheung 2007). A total of 27 redshifts were successfully obtained, 21 of which are new, including that of a newly identified candidate source of this type which is presented here. With these observations, the sample of candidates from Paper I is over 50% spectroscopically identified. Two new broad emission-lined X-shaped radio sources are revealed, while no emission lines were detected in about one third of the observed sources; a detailed study of the line properties is deferred to a future paper. Finally, to explore their relation to the Fanaroff-Riley division, the radio luminosities and host galaxy absolute magnitudes of a spectroscopically identified sample of 50 X-shaped radio galaxies are calculated to determine their placement in the Owen-Ledlow plane.

astro-ph↗

arXiv2008

The HST/ACS Coma Cluster Survey: I - Survey Objectives and Design

We describe the HST ACS Coma cluster Treasury survey, a deep two-passband imaging survey of one of the nearest rich clusters of galaxies, the Coma cluster (Abell 1656). The survey was designed to cover an area of 740 square arcmin in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of January 27th 2007 leaves the survey 28% complete, with 21 ACS pointings (230 square arcmin) complete, and partial data for a further 4 pointings (44 square arcmin). Predicted survey depth for 10 sigma detections for optimal photometry of point sources is g' = 27.6 in the F475W filter, and IC=26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g' = 27.55 and IC = 26.65. For extended sources, the predicted 10 sigma limits for a 1 square arcsecond region are g' = 25.8 mag/sq. arcsec and IC = 25.0 mag/sq. arcsec. We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultra compact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich cluster benchmark for various well known global scaling relations and explore new relations pertaining to the nuclear properties of galaxies.

astro-ph↗

arXiv2007

Astro-WISE: Chaining to the Universe

The recent explosion of recorded digital data and its processed derivatives threatens to overwhelm researchers when analysing their experimental data or when looking up data items in archives and file systems. While current hardware developments allow to acquire, process and store 100s of terabytes of data at the cost of a modern sports car, the software systems to handle these data are lagging behind. This general problem is recognized and addressed by various scientific communities, e.g., DATAGRID/EGEE federates compute and storage power over the high-energy physical community, while the astronomical community is building an Internet geared Virtual Observatory, connecting archival data. These large projects either focus on a specific distribution aspect or aim to connect many sub-communities and have a relatively long trajectory for setting standards and a common layer. Here, we report "first light" of a very different solution to the problem initiated by a smaller astronomical IT community. It provides the abstract "scientific information layer" which integrates distributed scientific analysis with distributed processing and federated archiving and publishing. By designing new abstractions and mixing in old ones, a Science Information System with fully scalable cornerstones has been achieved, transforming data systems into knowledge systems. This break-through is facilitated by the full end-to-end linking of all dependent data items, which allows full backward chaining from the observer/researcher to the experiment. Key is the notion that information is intrinsic in nature and thus is the data acquired by a scientific experiment. The new abstraction is that software systems guide the user to that intrinsic information by forcing full backward and forward chaining in the data modelling.

astro-ph↗

arXiv2006

The Secondary Standards programme for OmegaCAM at the VST

The OmegaCAM wide-field imager will start operations at the ESO VLT Survey Telescope at Paranal, Chile, in 2007. The photometric calibration of OmegaCAM data depends on standard star measurements that cover the complete 1 square degree FoV of OmegeaCAM. A catalog fullfilling this requirement for eight Landolt equatorial fields, denoted the OmegaCAM Secondary Standards Catalog, will be constructed from OmegaCAM observations during the first year of operations. Here we present the 'Preliminary Catalog' which will be used to bootstrap the construction of the OmegaCAM Secondary Standards Catalog. Thus the Preliminary Catalog will be used to assess the performance of OmegaCAM+VST early-on. The catalog is based on WFC data from the INT at La Palma.

astro-ph↗

arXiv2006

Gravity's Relentless Pull: An interactive, multimedia website about black holes for Education and Public Outreach

We have created a website, called "Black Holes: Gravity's Relentless Pull", which explains the physics and astronomy of black holes for a general audience. The site emphasizes user participation and is rich in animations and astronomical imagery. It won the top prize of the 2005 Pirelli INTERNETional Awards competition for the best communication of science and technology using the internet. This article provides a brief overview of the site. The site starts with an opening animation that introduces the basic concept of a black hole. The user is then invited to embark on a journey from a backyard view of the night sky to a personal encounter with a singularity. This journey proceeds through three modules, which allow the user to: find black holes in the night sky; travel to a black hole in an animated starship; and explore a black hole from up close. There are also five "experiments" that allow the user to: create a black hole; orbit around a black hole; weigh a black hole; drop a clock into a black hole; or fall into a black hole. The modules and experiments offer goal-based scenarios tailored for novices and children. The site also contains an encyclopedia of frequently asked questions and a detailed glossary that are targeted more at experts and adults. The overall result is a website where scientific knowledge, learning theory, and fun converge. Despite its focus on black holes, the site also teaches many other concepts of physics, astronomy and scientific thought. The site aims to instill an appreciation for learning and an interest in science, especially in the younger users. It can be used as an aid in teaching introductory astronomy at the undergraduate level.

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