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K. Kuijken

Publications and source records attributed to K. Kuijken.

At least 145 records · Page 8Linked to original sources
arXiv2003

Large disk-like galaxies at high redshift

Using deep near-infrared imaging of the Hubble Deep Field South with ISAAC on the Very Large Telescope we find 6 large disk-like galaxies at redshifts z = 1.4-3.0. The galaxies, selected in K_s (2.2 micron), are regular and surprisingly large in the near-infrared (rest-frame optical), with face-on effective radii r_e = 0.65"-0.9" or 5.0-7.5 h_70^-1 kpc in a Lambda-CDM cosmology, comparable to the Milky Way. The surface brightness profiles are consistent with an exponential law over 2-3 effective radii. The WFPC2 morphologies in Hubble Space Telescope imaging (rest-frame UV) are irregular and show complex aggregates of star-forming regions ~2" (~15 h_70^-1 kpc) across, symmetrically distributed around the K_s-band centers. The spectral energy distributions show clear breaks in the rest-frame optical. The breaks are strongest in the central regions of the galaxies, and can be identified as the age-sensitive Balmer/4000 Angstrom break. The most straightforward interpretation is that these galaxies are large disk galaxies; deep NIR data are indispensable for this classification. The candidate disks constitute 50% of galaxies with L_V > 6 x 10^10 h_70^-2 L_sun at z = 1.4-3.0. This discovery was not expected on the basis of previously studied samples. In particular, the Hubble Deep Field North is deficient in large galaxies with the morphologies and profiles we report here.

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arXiv2002

Ultradeep Near-Infrared ISAAC Observations of the HDF-S: Observations, Reduction, Multicolor Catalog, and Photometric Redshifts

We present deep near-infrared (NIR) Js, H, and Ks-band ISAAC imaging of the WFPC2 field of the HDF-S. The 2.5'x 2.5' high Galactic latitude field was observed with the VLT under the best seeing conditions with integration times amounting to 33.6 hours in Js, 32.3 hours in H, and 35.6 hours in Ks. We reach total AB magnitudes for point sources of 26.8, 26.2, and 26.2 respectively (3 sigma), which make it the deepest ground-based NIR observations to date, and the deepest Ks-band data in any field. The effective seeing of the coadded images is ~0.45" in Js, ~0.48" in H, and ~0.46" in Ks. Using published WFPC2 optical data, we constructed a Ks-limited multicolor catalog containing 833 sources down to Ks,tot ~< 26 (AB), of which 624 have seven-band optical-to-NIR photometry. These data allow us to select normal galaxies from their rest-frame optical properties to high redshift (z ~< 4). The observations, data reduction and properties of the final images are discussed, and we address the detection and photometry procedures that were used in making the catalog. In addition, we present deep number counts, color distributions and photometric redshifts of the HDF-S galaxies. We find that our faint Ks-band number counts are flatter than published counts in other deep fields, which might reflect cosmic variations or different analysis techniques. Compared to the HDF-N, we find many galaxies with very red V-H colors at photometric redshifts 1.95 < z < 3.5. These galaxies are bright in Ks with infrared colors redder than Js-Ks > 2.3 (in Johnson magnitudes). Because they are extremely faint in the observed optical, they would be missed by ultraviolet-optical selection techniques, such as the U-dropout method.

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arXiv2002

Lensing by galaxies in CNOC2 fields

We have observed two blank fields of approximately 30 by 23 arcminutes using the William Herschel Telescope. The fields have been studied as part of the CNOC2 survey, and spectroscopic redshifts are available for 1125 galaxies in the two fields. We measured the lensing signal caused by large scale structure, and found that the result is consistent with current, more accurate measurements. We study the galaxy-galaxy lensing signal of three overlapping samples of lenses, and detect a significant signal in all cases. The estimates for the velocity dispersion of an L* galaxy agree well for the various samples. The best fit singular isothermal sphere model to the ensemble averaged tangential distortion around the galaxies with redshifts yields a velocity dispersion of σ_*=130^{+15}_{-17} km/s, in good agreement with other studies. We use a maximum likelihood analysis, where a parameterized mass model is compared to the data, to study the extent of galaxy dark matter halos. Making use of all available data, we find σ_*=111\pm12 km/s (68.3% confidence) for a truncated isothermal sphere model in which all galaxies have the same mass-to-light ratio. The value of the truncation parameter is not constrained that well, and we find s_*=260^{+124}_{-73} h^{-1} kpc (68.3% confidence The galaxy-galaxy lensing analysis allows us to estimate the average mass-to-light ratio of the field, which can be used to estimate Ω_m. The current result, however, depends strongly on the assumed scaling relation for s.

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arXiv2002

The Planetary Nebulae Spectrograph: the green light for Galaxy Kinematics

Planetary nebulae are now well established as probes of galaxy dynamics and as standard candles in distance determinations. Motivated by the need to improve the efficiency of planetary nebulae searches and the speed with which their radial velocities are determined, a dedicated instrument - the Planetary Nebulae Spectrograph or PN.S - has been designed and commissioned at the 4.2m William Herschel Telescope. The high optical efficiency of the spectrograph results in the detection of typically ~ 150 PN in galaxies at the distance of the Virgo cluster in one night of observations. In the same observation the radial velocities are obtained with an accuracy of ~ 20 km/s

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arXiv2002

Neutral Hydrogen and Optical Observations of Edge-on Galaxies: Hunting for Warps

We present 21-cm HI line and optical R-band observations for a sample of 26 edge-on galaxies. The HI observations were obtained with the Westerbork Synthesis Radio Telescope, and are part of the WHISP database (Westerbork HI Survey of Spiral and Irregular Galaxies). We present HI maps, optical images, and radial HI density profiles. We have also derived the rotation curves and studied the warping and lopsidedness of the HI disks. 20 out of the 26 galaxies of our sample are warped, confirming that warping of the HI disks is a very common phenomenon in disk galaxies. Indeed, we find that all galaxies that have an extended HI disk with respect to the optical are warped. The warping usually starts around the edge of the optical disk. The degree of warping varies considerably from galaxy to galaxy. Furthermore, many warps are asymmetric, as they show up in only one side of the disk or exhibit large differences in amplitude in the approaching and receding sides of the galaxy. These asymmetries are more pronounced in rich environments, which may indicate that tidal interactions are a source of warp asymmetry. A rich environment tends to produce larger warps as well. The presence of lopsidedness seems to be related to the presence of nearby companions.

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arXiv2000

Weak lensing study of low mass galaxy groups: implications for Omega_m

We report on the first measurement of the average mass and mass-to-light ratio of galaxy groups by analysing the weak lensing signal induced by these systems. The groups, which have velocity dispersions of 50-400 km/s, have been selected from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2). This survey allows the identification of a large number of groups with redshifts ranging from z=0.12-0.55, ideal for a weak lensing analysis of their mass distribution. For our analysis we use a sample of 50 groups which are selected on the basis of a careful dynamical analysis of group candidates. We detect a signal at the 99% confidence limit. The best fit singular isothermal sphere model yields an Einstein radius of 0.72+-0.29". This corresponds to a velocity dispersion of 274^{+48}_{-59} km/s (using photometric redshift distributions for the source galaxies), which is in good agreement with the dynamical estimate. Under the assumption that the light traces the mass, we find an average mass-to-light ratio of 191+-83 h Msun/Lsun in the restframe B band. Unlike dynamical estimates, this result is insensitive to problems associated with determining group membership. After correction of the observed mass-to-light ratio for luminosity evolution to z=0, we find 254+-110 h Msun/Lsun, lower than what is found for rich clusters. We use the observed mass-to-light ratio to estimate the matter density of the universe, for which we find Omega_m=0.19+-0.10 (Omega_Lambda=0), in good agreement with other recent estimates. For a closed universe, we obtain Omega_m=0.13+-0.07.

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arXiv2000

The Origins of Disk Heating

By making spectral absorption-line observations of disk galaxies at intermediate inclinations, we have been able to determine the amplitude of their constituent stars' random motions in three dimensions. This full measure of the shape of the velocity ellipsoid is a useful diagnostic for determining the "heating" mechanism responsible for creating the random motions. The analysis implies that the main heating process varies with galaxy type, with minor mergers dominating the heating in early-type disk galaxies, and spiral density waves the most important mechanism in late-type systems.

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arXiv2000

Weak Weak Lensing: How Accurately Can Small Shears be Measured?

Now that weak lensing signals on the order of a percent are actively being searched for (cosmic shear, galaxy-galaxy lensing, large radii in clusters...) it is important to investigate how accurately weak shears can be determined. Many systematic effects are present, and need to be understood. I show that the Kaiser et al. technique can leave residual systematic errors at the percent level (through imperfect PSF anisotropy correction), and present an alternative technique which is able to recover shears a factor of ten weaker.

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arXiv2000

Microlensing in M31 - The MEGA Survey's Prospects and Initial Results

January 2000 completes the first season of intensive, wide-field observations of microlensing and stellar variability in M31 by MEGA (Microlensing Exploration of the Galaxy and Andromeda) at the Isaac Newton 2.5m Telescope, the KPNO 4m, and the 1.3m and 2.5m telescopes of MDM Observatory. In preliminary analysis, we detect ~50000 variable objects, including some consistent with microlensing events. We present the level of sensitivity to be reached in our planned three-year program to test for the presence of a significant halo microlensing population in M31, as well as its spatial distribution and mass-function. We also discuss our application of image subtraction to these wide fields and HST WFPC2 Snapshot followup observations to confirm candidates identified from previous years' surveys. We present intermediate results from our smaller-field survey, on the MDM 1.3m and Vatican Advanced Technology 1.8m Telescope, from 1994-1998, wherein we have discovered 8 additional probable microlensing events, over about one-half the time base of the project, in addition to confirming three of our original 6 microlensing candidates from 1995.

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arXiv2000

Disc heating in NGC 2985

Various processes have been proposed to explain how galaxy discs acquire their thickness. A simple diagnostic for ascertaining this ``heating'' mechanism is provided by the ratio of the vertical to radial velocity dispersion components. In a previous paper we have developed a technique for measuring this ratio, and demonstrated its viability on the Sb system NGC 488. Here we present follow-up observations of the morphologically similar Sab galaxy NGC 2985, still only the second galaxy for which this ratio has been determined outside of the solar neighbourhood. The result is consistent with simple disc heating models which predict ratios of $σ_z / σ_R$ less than one

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arXiv2000

The Kinematics of the Planetary Nebula Population in M94

The planetary nebula populations of relatively nearby galaxies can be easily observed and provide both a distance estimate and a tool with which dynamical information can be obtained. Usually the requisite radial velocities are obtained by multi-object spectroscopy once the planetary nebulae have been located by direct imaging. Here we report on a technique for measuring planetary nebula kinematics using the double-beam ISIS spectrograph at the William Herschel Telescope in a novel slitless mode, which enables the detection and radial velocity measurements to be combined into a single step. The results on our first target, the Sab galaxy NGC 4736, allow the velocity dispersion of the stellar population in a disk galaxy to be traced out to four scale lengths for the first time and are consistent with a simple isothermal sheet model.

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arXiv2000

The Warp of the Galaxy and the Orientation of the LMC Orbit

After studying the orientation of a warp generated by a companion satellite, we show that the Galactic Warp would be oriented in a different way if the Magellanic Clouds were its cause. We have treated the problem analytically, and complemented it with numerical N-Body simulations.

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arXiv2000

Strong and weak lensing analysis of cluster Abell 2219 based on optical and near infrared data

We present a gravitational lensing study of the massive galaxy cluster A2219 (redshift 0.22). This investigation is based on multicolour images from U through H, which allows photometric redshifts to be estimated for the background sources. The redshifts provide useful extra information for the lensing models: we show how they can be used to identify a new multiple-image system (and rule out an old one), how this information can be used to anchor the mass model for the cluster, and how the redshifts can be used to construct optimal samples of background galaxies for a weak lensing analysis. Combining all results, we obtain the mass distribution in this cluster from the inner, strong lensing region, out to a radius of 1.5 Mpc. The mass profile is consistent with a singular isothermal model over this radius range. Parametric and non-parametric reconstructions of the mass distribution in the cluster are compared. The main features (elongation, sub-clumps, radial mass profile) are in good agreement.

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arXiv1999

Hubble Space Telescope weak lensing study of the z=0.83 cluster MS 1054-03

We have measured the weak gravitational lensing signal of MS 1054-03, a rich and X-ray luminous cluster of galaxies at a redshift of z=0.83, using a two-colour mosaic of deep WFPC2 images. The small corrections for the size of the PSF and the high number density of background galaxies obtained in these observations result in an accurate and well calibrated measurement of the lensing induced distortion. The strength of the lensing signal depends on the redshift distribution of the background galaxies. We used photometric redshift distributions from the Northern and Southern Hubble Deep Fields to relate the lensing signal to the mass. The predicted variations of the signal as a function of apparent source magnitude and colour agrees well with the observed lensing signal. We determine a mass of (1.2+-0.2)x10^15 Msun within an aperture of radius 1 Mpc. Under the assumption of an isothermal mass distribution, the corresponding velocity dispersion is 1311^{+83}_{-89} km/s. For the mass-to-light ratio we find 269+-37 Msun/Lsun. The errors in the mass and mass-to-light ratio include the contribution from the random intrinsic ellipticities of the source galaxies, but not the (systematic) error due to the uncertainty in the redshift distribution. However, the estimates for the mass and mass-to-light ratio of MS 1054-03 agree well with other estimators, suggesting that the mass calibration works well. The reconstruction of the projected mass surface density shows a complex mass distribution, consistent with the light distribution. The results indicate that MS 1054-03 is a young system. The timescale for relaxation is estimated to be at least 1 Gyr. Averaging the tangential shear around the cluster galaxies, we find that the velocity dispersion of an Lstar galaxy is 203+-33 km/s.

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arXiv1998

Weak lensing analysis of Cl 1358+62 using Hubble Space Telescope observations

We report on the detection of weak gravitational lensing of faint, distant background galaxies by Cl 1358+62, a cluster of galaxies at a redshift of z=0.33. The observations were made using the HST. The measured shear is consistent with a velocity dispersion of 780+-50 km/s. The weak lensing mass is slightly lower than dynamical estimates and agrees well with X-ray mass estimates. The mass distribution is elongated similar to the light. The axis ratio of 0.30+-0.15 and position angle of -21+-8 degrees were measured directly from the observed shear and agree very well with a previous strong lensing analysis. We estimate the mass-to-light ratio to be 90+-13 h50 M_sun/L_Vsun. The HST point spread function is highly anisotropic at the edges of the individual chips. This systematically perturbs the shapes of objects and we present a method for applying the appropriate correction.

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arXiv1998

Measuring Galaxy Potentials using Shell Kinematics

We show that the kinematics of the shells seen around some elliptical galaxies provide a new, independent means for measuring the gravitational potentials of elliptical galaxies out to large radii. A numerical simulation of a set of shells formed in the merger between an elliptical and a smaller galaxy reveals that the shells have a characteristic observable kinematic structure, with the maximum line-of-sight velocity increasing linearly as one moves inward from a shell edge. A simple analytic calculation shows that this structure provides a direct measure of the gradient of the gravitational potential at the shell radius. In order to extract this information from attainable data, we have also derived the complete distribution of line-of-sight velocities for material within a shell; comparing the observed spectra of a shell to a stellar template convolved with this distribution will enable us to measure the gradient of the potential at this radius. Repeating the analysis for a whole series of nested shells in a galaxy allows the complete form of the gravitational potential as a function of radius to be mapped out. The requisite observations lie within reach of the up-coming generation of large telescopes.

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arXiv1997

Warps and Secondary Infall

Secondary infall in galaxies could cause the angular momentum of the outer halo to change its orientation. The generation of warps due to this effect is studied using N-body simulations.

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