Clusters of galaxies are gravitationally bound configurations containing typically hundreds of galaxies in a region about 10 cm in size. They range from irregular clusters, with strong subclustering, no strong central concentration, and mainly spiral galaxies, to regular clusters, with smooth and centrally condensed galaxy distributions containing few spiral galaxies. Observations of these clus...

Recently, we conducted a Very Large Telescope (VLT) large program to search for forming clusters by looking for overdensities of Lyα emitters around high redshift radio galaxies. In total seven proto-clusters were discovered, including a protocluster around the radio galaxy MRC 0316–257 at z ∼ 3.13. This structure has an excess of Lyα emitters by a factor of 3 as compared to the field, and the ...

Observations of six luminous blue compact galaxies (BCGs) and two star forming companion galaxies were carried out with the CIGALE scanning Fabry-Perot interferometer attached to the ESO 3.6m telescope on La Silla. The observations were made in the Hα emission line which is prominent in BCGs. A velocity sampling of 5 km/s and a pixel size of 0.9 arcseconds were used. In this paper we present th...

We present radio and optical observations of the peculiar radio galaxy J1835+620, a member of a new sample of large angular size radio galaxies selected from the NRAO VLA Sky Survey. Its optical counterpart is in a group of at least three galaxies and shows strong, narrow emission lines which allow us to measure its redshift as z = 0.518. The derived cosmological distance places J1835+620 among...

I present near-infrared J (1.25μm), H (1.65μm), and K (2.2μm) imaging observations of 185 square arcminutes in 21 high galactic latitude fields. These observations reach limiting magnitudes of J ∼ 21 mag, H ∼ 20 mag and K ∼ 18.5 mag. The detection efficiency, photometric accuracy and selection biases as a function of integrated object brightness, size, and profile shape are quantified in detail...

In this paper we investigate the relation between the detailed isophotal shape of elliptical galaxies and the strength of the Hβ absorption in their spectra. We find that disky galaxies have higher Hβ indices. Stellar population synthesis models show that the Hβ line is a good age indicator, hence disky galaxies tend to have younger mean ages than boxy galaxies. We show that the observed trend ...

I present near-infrared J (1.25μm), H (1.65μm), and K (2.2μm) imaging observations of 185 square arcminutes in 21 high galactic latitude fields. These observations reach limiting magnitudes of J ∼ 21 mag, H ∼ 20 mag and K ∼ 18.5 mag. The detection efficiency, photometric accuracy and selection biases as a function of integrated object brightness, size, and profile shape are quantified in detail...

We give a summary of recent results on spatial and velocity biases in cosmological models. Progress in numerical techniques made it possible to simulate halos in large volumes with a such accuracy that halos survive in dense environments of groups and clusters of galaxies. Halos in simulations look like real galaxies, and, thus, can be used to study the biases – differences between galaxies and...

The severity of the mass discrepancy in spiral galaxies is strongly correlated with the central surface brightness of the disk. Progressively lower surface brightness galaxies have ever larger mass discrepancies. No other parameter (luminosity, size, velocity, morphology) is so well correlated with the magnitude of the mass deficit. The rotation curves of low surface brightness disks thus provi...

We present a table of redshifts for 2907 galaxies and stars in the 145 arcmin HST ACS GOODSNorth, making this the most spectroscopically complete redshift sample obtained to date in a field of this size. We also include the redshifts, where available, in a table containing just under 7000 galaxies from the ACS area with Ks,AB < 24.5 measured from a deep Ks image obtained with WIRCam on the CFHT...