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H. Rottgering

Publications and source records attributed to H. Rottgering.

44 records · Page 3Linked to original sources
arXiv2003

Detection of strong clustering of red K-selected galaxies at 2<z_phot<4 in the Hubble Deep Field South

The clustering properties of faint K<24 galaxies are measured in ultradeep J, H and K near-IR images of the Hubble Deep Field South (HDF-S), obtained with ISAAC at the VLT. A relatively large clustering amplitude is found up to K=24, at a level comparable to the measurements at K~19. The redshift distribution of K<24 galaxies extends to z_phot~4-5, and ~40% of the galaxies are at z_phot>2.At the highest redshifts, 2 1.7 reach r_0~8 h^-1 Mpc comoving. This is a factor of 3--4 higher than the correlation length of LBGs with similar number densities, down to V_606<27, and is also larger than the correlation length of galaxies with blue J-K<1.7 colors. Hence at z about 3 a color-density relation is observed which is similar to that observed locally. Fluctuations in the amplitude of clustering due to cosmic variance may affect our estimates derived from the small HDF-S field, but these are unlikely to change our main conclusions. The galaxies with red J-K>1.7 colors at 2<z_phot<4 are likely older and more massive galaxies, on average, than LBGs. They were presumably formed in the highest density perturbations at early epochs. Semi-analytical hierarchical models do predict the existence of strongly clustered populations at z~3, but with at least a factor of 10 lower number density than the one measured. The overall properties of this strongly clustered population consistently suggest that they are the progenitors, or building blocks, of local massive early-type galaxies and z~1 EROs, close to their major epochs of formation.

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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

BRIGHT lights, BIG city: Massive galaxies, giant Ly-a nebulae, and proto--clusters

High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super--massive black holes and proto--clusters. We report on deep narrow--band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-alpha nebulae centered on the galaxies and to search for over--dense regions around them. We discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.

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arXiv2001

The Spatial Clustering of Distant, z~1, Early-Type Galaxies

We examine the spatial clustering of extremely red objects (EROs) found in a relatively large survey of 700 arcmin^2, containing 400 galaxies with R-Ks>5 to Ks=19.2. A comoving correlation length r_0=12\pm3 /h Mpc is derived, under the assumption that the selection function is described by a passively evolving early-type galaxy population, with an effective redshift of z~1.2. This correlation length is very similar to that of local L* elliptical galaxies implying, at face value, no significant clustering evolution in comoving coordinates of early-type galaxies to the limiting depth of our sample, z~1.5. A rapidly evolving clustering bias can be designed to reproduce a null result; however, our data do not show the corresponding strong reduction in the average population density expected for consistency with underlying growth of the mass-function. We discuss our data in the context of recent ideas regarding bias evolution. The uncertainty we quote on r_0 accounts for the spikey redshift distribution expected along relatively narrow sightlines, which we quantify with detailed simulations. This is an improvement over the standard use of Limber's equation which, because of its implicit assumption of a smooth selection function, underestimates the true noise by a factor of ~ 3 for the parameters of our survey. We propose a general recipe for the analysis of angular clustering, suggesting that any measurement of the angular clustering amplitude, A, has an intrinsic additional uncertainty of σ_A/A=\sqrt{AC}, where AC is the appropriate integral constraint.

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arXiv2001

Deep VLT spectroscopy of high redshift radio galaxy MRC 2104-242: Evidence for a metallicity gradient

In this contribution we will present deep VLT spectroscopy observations of the giant emission line halo around the z=2.49 radio galaxy MRC 2104-242. The morphology of the halo is dominated by two spatially resolved regions. Lya is extended by >12" along the radio axis, C IV and He II are extended by ~8". The overall spectrum is typical for that of high redshift radio galaxies. Interestingly, N V is present in the spectrum of the region associated with the center of the galaxy hosting the radio source, the northern region, while absent in the southern region. Using a simple photoionization model, the difference in N V can be explained due to a metallicity gradient within the halo. This is consistent with a scenario in which the halo is formed by a massive cooling flow or originates from the debris of the merging of two or more galaxies. However, also other mechanisms such as jet-cloud interactions or starburst-winds could be important.

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arXiv2001

Deep VLT spectroscopy of the z=2.49 Radio Galaxy MRC 2104-242: Evidence for a metallicity gradient in its extended emission line region

We present spectroscopic observations of the rest-frame UV line emission around radio galaxy MRC 2104-242 at z=2.49, obtained with FORS1 on VLT Antu. The morphology of the halo is dominated by two spatially resolved regions. Lya is extended by >12 arcsec along the radio axis, CIV and HeII are extended by ~8 arcsec. The overall spectrum is typical for that of high redshift radio galaxies. The most striking spatial variation is that NV is present in the spectrum of the region associated with the center of the galaxy hosting the radio source, the northern region, while absent in the southern region. Assuming that the gas is photoionized by a hidden quasar, the difference in NV emission can be explained by a metallicity gradient within the halo. This is consistent with a scenario in which the gas is associated with a massive cooling flow or originates from the debris of the merging of two or more galaxies.

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arXiv2000

ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum Radio Galaxies

We present results from observations obtained with ISOPHOT, on board the ISO satellite, of a representative sample of seventeen CSS/GPS radio galaxies and of a control sample of sixteen extended radio galaxies spanning similar ranges in redshift (0.2 <= z <= 0.8) and radio luminosity (P_2.7 GHz >= 10^26 W/Hz). The observations have been performed at lambda = 60, 90, 174 and 200 microns. Seven of the CSS/GPS sources have detections >= 3 sigma at one or more wavelengths, one of which is detected at >= 5 sigma. By co-adding the data we have obtained average flux densities at the four wavelengths. We found no evidence that the FIR luminosities of the CSS/GPS sources are significantly different from those of the extended objects and therefore there is not any support for CSS/GPS sources being objects "frustrated" by an abnormally dense ambient medium. The two samples were then combined, providing FIR information on a new sample of radio galaxies at intermediate redshifts. We compare this information with what previously known from IRAS and discuss the average properties of radio galaxies in the redshift range 0.2 - 0.8. The FIR emission cannot be accounted for by extrapolation of the synchrotron radio spectrum and we attribute it to thermal dust emission. The average FIR luminosity is >= 6*10^11 L_sun. Over the observed frequency range the infrared spectrum can be described by a power law with spectral index alpha >~1.0 +/- 0.2. Assuming the emission to be due to dust, a range of temperatures is required, from >=80 K to \~25 K. The dust masses required to explain the FIR emission range from 5*10^5 M_sun for the hotter component up to 2*10^8 M_sun for the colder one. (abridged)

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