Cosmology

Abstract:

We present the detection of nuclear stellar discs in the low-luminosity elliptical galaxies, NGC 4458 and 4478, which are known to host a kinematically decoupled core. Using archival Hubble Space Telescope imaging, and available absorption line-strength index data based on ground-based spectroscopy, we investigate the photometric parameters and the properties of the stellar populations of these central structures. Their scalelength, h, and face-on central surface brightness, μ0c, fit on the μ0c-h relation for galaxy discs. For NGC 4458, these parameters are typical for nuclear discs, while the same quantities for NGC 4478 lie between those of nuclear discs and the discs of discy ellipticals. We present Lick/Image Dissector Scanner (IDS) absorption line-strength measurements of Hβ, Mg b and (Fe) along the major and minor axes of the galaxies. We model these data with simple stellar populations that account for the α/Fe overabundance. The counter-rotating central disc of NGC 4458 is found to have similar properties to the decoupled cores of bright ellipticals. This galaxy has been found to be uniformly old despite being counter-rotating. In contrast, the cold central disc of NGC 4478 is younger, richer in metals and less overabundant than the main body of the galaxy. This points to a prolonged star formation history, typical of an undisturbed disc-like, gas-rich (possibly pre-enriched) structure.

Abstract:

To examine the evolution of the early-type galaxy population in the rich cluster Abell 2390 at z=0.23 we have gained spectroscopic data of 51 elliptical and lenticular galaxies with MOSCA at the 3.5 m telescope on Calar Alto Observatory. This investigation spans both a broad range in luminosity (-19.3>M_B>-22.3) and uses a wide field of view of 10'x10', therefore the environmental dependence of different formation scenarios can be analysed in detail as a function of radius from the cluster centre. Here we present results on the surface brightness modelling of galaxies where morphological and structural information is available in the F814W filter aboard the Hubble Space Telescope (HST) and investigate for this subsample the evolution of the Fundamental Plane.

Abstract:

We introduce the NOAO Fundamental Plane Survey (NFPS), a wide-field imaging/spectroscopic study of rich, low-redshift galaxy clusters. The survey targets X-ray-selected clusters at 0.010 < z < 0.067, distributed over the whole sky, with imaging and spectroscopic observations obtained for 93 clusters. This data set will be used in investigations of galaxy properties in the cluster environment and of large-scale velocity fields through the fundamental plane. In this paper, we present details of the cluster sample construction and the strategies employed to select early-type galaxy samples for spectroscopy. Details of the spectroscopic observations are reported. From observations of 5479 red galaxies, we present redshift measurements for 5388 objects and internal velocity dispersions for 4131. The velocity dispersions have a median estimated error ∼7%. The NFPS has ∼15% overlap with previously published velocity dispersion data sets. Comparisons to these external catalogs are presented and indicate typical external errors of ∼8%.