Barbara Cunow

The Muenster Redshift Project. III. Observational Constraints on the Deceleration Parameter

The redshift-volume test for determining the deceleration parameter q0 is applied to 89,125 galaxies with redshifts z ? 0.2 (redshift errors ?z = 0.031) and magnitudes 14.0 ? rF ? 18.0 mag, obtained within the Muenster Redshift Project (MRSP). With samples of this size, cosmic curvature effects can be measured even at intermediate redshifts. Comparatively small z-values and red photometric magnitudes assure that biased object selection and galaxy evolution do not affect the measurements in uncontrolled ways. In the first step of our analysis, the redshift-volume test assumes a minimum model of passive galaxy evolution. For the cosmological constant ? = 0 and for the evolutionary models of Rocca-Volmerange & Guiderdoni, the total sample yields the deceleration parameter q0 = 0.10 with the 95% confidence limit, q0 < 0.75. In a second step, we evaluate?within the errors of the first step?whether our q0-value is over- or underestimated, using those observed evolutionary trends that appear to be nearly q0 independent. The trends indicate that our result q0 = 0.10 can be regarded as an upper limit. Effects of incompleteness, errors in the (K + E)-corrections due to extreme galaxy mixtures, as well as different models of population synthesis, large-scale clustering, galactic reddening, and gravitational lensing, are discussed. We conclude that the combination of MRSP redshift data, observed evolutionary trends in the galaxy luminosity functions, and passive galaxy aging suggests an open universe.

The Muenster Redshift Project

The Muenster Redshift Project is based on microdensitometer scans of pairs of direct and objective prism Schmidt plates, used for the determination of positions, magnitudes, morphological types, and low-dispersion redshifts of galaxies and quasars. From these data structural features and parameters which characterize the present universe are derived. The 0.9 million redshifts, reduced so far, permit us to take a first step towards very large-scale analysis.

INVESTIGATION OF AGE AND METALLICITY GRADIENTS AND DUST EXTINCTION IN DISC GALAXIES IN THE HUBBLE DEEP FIELD

Using HST data, disc scalelengths in the UV, optical and NIR wavelength regions are used to study age and metallicity gradients and dust extinction in disc galaxies of intermediate redshifts in the Hubble Deep Field North. The observed colour gradients are compared to model calculations of dusty disc galaxies. First results indicate that the age and metallicity gradients in the HDF galaxies differ from the age and metallicity gradients found in local spiral galaxies.

Star cluster analyses from multi-band photometry: the key advantage of SALT's U -band sensitivity

Conventionally, CMD analyses of nearby star clusters are based on observations in 2 passbands. They are plagued by considerable degeneracies between age, metallicity, distance (and extinction) that can largely be resolved by including additional passbands with U being most appropriate for young SCs and I or a NIR band for old globular clusters. For star clusters that cannot be resolved, integrated photometry in suitably selected passbands was shown to be as accurate as spectroscopy in independently revealing ages, metallicities, internal extinction, and photometric masses and their respective 1 sigma uncertainties, when analysed with a dedicated analysis tool for their Spectral Energy Distributions (SEDs) (cf. Anders et al. 2004a, b, de Grijs et al. 2003b). For external galaxies, rich star cluster populations can thus be efficiently analysed using deep exposures in 4 suitable filters. Again, the inclusion of the U-band significantly reduces the uncertainties in the cluster parameters. The age and metallicity distributions of star cluster systems yield valuable information about the formation history of their parent galaxies (Fritze - v. A. 2004). Here, we present our GALEV evolutionary synthesis models for star clusters of various metallicities (Anders, Fritze - v. A. 2003), recently extended to include the time evolution of CMDs, the dedicated SED Analysis Tool AnalySED we developed, show results on the basis of HST data, and present first data for a young star cluster system in the ongoing spiral-spiral merger NGC 1487 obtained with SALT during the SALTICAM Performance Verification Phase.

Investigation of Age and Metallicity Gradients in Spiral Galaxies

Optical and near-infrared disc scalelengths are used to investigate age and metal-licity gradients in the discs of spiral galaxies.The observed colour gradients are compared to model calculations, and the analysis indicates that the stars become younger and less metal-rich with increasing distance from the centre of the galaxy.

Investigation of Disc Scalelengths of Sb Galaxies

For a sample of 21 Sb galaxies, disc scalelengths rD in B and I are investigated in order to measure the dust content. The ratios rD (B)/rD (I) increase from 1.0 for face-on galaxies to 1.5 for edge-on galaxies. B and I images of model galaxies are calculated for a variety of geometries, optical depths and inclination angles. The best agreement between data and simulations is found for model galaxies for which the scalelength ro of the stellar disc is 12.5% larger in the B passband than in the I passband, and for which the scalelength of the dust disc is 50% larger than r0(I). This indicates that the observed scalelength ratios are produced by dust extinction as well as intrinsic colour gradients within the stellar disc. The central optical depth in B for face-on view for the best-fitting model is τ 0 B =0.

Internal Absorption in Spiral Galaxies Using Four Colours

The internal absorption in spiral galaxies is investigated statistically using data in the UV, optical and near-infrared wavelength regions. It is shown that a three-component model of the galaxy structure leads to absorption values which are consistent with values found from studies of individual galaxies using surface-brightness profiles and rotation curves.