Searcharxiv⌕ Search

arXiv subjects

Klaus J. Fricke

Publications and source records attributed to Klaus J. Fricke.

13 recordsLinked to original sources
arXiv2003

Chemically consistent evolution of galaxies: II. Spectrophotometric evolution from zero to high redshift

We present a new generation of chemically consistent evolutionary synthesis models for galaxies of various spectral types from E through Sd. The models follow the chemical enrichment of the ISM and take into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary isochrones, spectra and yields. Our first set of closed-box 1-zone models does not include any spatial resolution or dynamics. For a Salpeter initial mass function (IMF) the star formation rate(SFR) and its time evolution are shown to successfully parameterise spectral galaxy types E, ..., Sd. We show how the stellar metallicity distribution in various galaxy types build up with time to yield after $\sim 12$ Gyr agreement with stellar metallicity distributions observed in our and other local galaxies. The models give integrated galaxy spectra over a wide wavelength range (90.9Å- 160$μ$m), which for ages of $\sim 12$ Gyr are in good agreement not only with observed broad band colours but also with template spectra for the respective galaxy types. Using filter functions for Johnson-Cousins, as well as for HST broad band filters in the optical and Bessel & Brett's NIR filter system, we calculate the luminosity and colour evolution of model galaxies over a Hubble time. Including a standard cosmological model and the attenuation by intergalactic hydrogen we present evolutionary and cosmological corrections as well as apparent luminosities in various filters over the redshift range from z $\sim 5$ to the present for our galaxy types and compare to earlier models using single (=solar) metallicity input physics only. We also present a first comparison of our cc models to HDF data.(Abridged abstract)

astro-ph↗
arXiv2002

Wavelength and Redshift Dependence of Bulge/Total Light Ratios in Galaxies

We present evolutionary synthesis models for both components and add their spectra in various proportions to obtain the full range of local galaxies' B-band bulge-to-total light ratios. Bulge star formation is assumed to occur on a short timescale of $10^9$ yr, disk star formation proceeds at a constant rate. Models are presented for three scenarios: bulges and disks of equal age, old bulges and delayed disk star formation, and old disks with subsequent bulge star formation. We quantitatively show that bulge-to-total ($=$ B/T) light ratios for local galaxies increase significantly from U through I-bands with the rate of increase slightly depending on the relative ages of the two components. Hence, simultaneous decomposition of galaxy profiles in several bands can give direct information about the relative ages of bulges and disks and help constrain galaxy formation scenarios. The redshift evolution of B/T-ratios in various bands U, B, V, I, H is calculated accounting both for cosmological and evolutionary corrections. I- and H-bands show the smoothest redshift evolution and, hence, are best suited for a first order comparison of galaxies over the redshift range from ${\rm z=0}$ to ${\rm z \gta 1}$ but still are shown to increasingly overestimate B/T ratios at higher redshifts. This is a robust result irrespective of the respective ages of the bulge and disk stellar components and implies that the scarcity of bulge-strong systems at ${\rm z \geq 0.8}$ reported for HDF and Hawaiian Deep Field galaxies is further enhanced.

astro-ph↗
arXiv2002

VLT spectroscopy of globular cluster in NGC 3115

We present results derived from VLT-FORS2 spectra of 17 globular clusters associated with the nearby lenticular galaxy NGC3115. Comparing line-strength indices to new stellar population models by Thomas et al. we determine ages, metallicities and element abundance ratios. Our data are also compared with the Lick/IDS observations of Milky Way and M31 globular clusters. Our best age estimates show that the observed clusters which sample the bimodal colour distribution of NGC3115 globular clusters are coeval within our observational errors (2-3 Gyr). Our best calibrated age/metallicity diagnostic diagram (Hbeta vs [MgFe]) indicates an absolute age of 11-12 Gyr consistent with the luminosity weighted age for the central part of NGC3115. We confirm with our accurate line-strength measurements that the (V-I) colour is a good metallicity indicator within the probed metallicity range (-1.5 < [Fe/H] < 0.0). The abundance ratios for globular clusters in NGC3115 give an inhomogeneous picture. We find a range from solar to super-solar ratios for both blue and red clusters. This is similar to the data for M31 while the Milky Way seems to harbour clusters which are mainly consistent with [alpha/Fe] =~ 0.3.

astro-ph↗
arXiv2002

Large Velocity Gradients in the Tidal Tails of the Interacting Galaxy AM 1353-272 ("The Dentist's Chair")

We present VLT observations of the interacting system AM 1353-272. Using the FORS2 instrument, we studied the kinematics of the ionized gas along its prominent tidal tails and discovered strikingly large velocity gradients associated with seven luminous tidal knots. These kinematical structures cannot be caused by streaming motion and most likely do not result from projection effects. More probably, instabilities in the tidal tails have lead to the formation of kinematically decoupled objects which could be the progenitors of self-gravitating Tidal Dwarf Galaxies.

astro-ph↗
arXiv2002

VLT spectroscopy of NGC3115 globular clusters

We present results derived from VLT-FORS2 spectra of 24 different globular clusters associated with the lenticular galaxy NGC3115. A subsample of 17 globular clusters have sufficiently high signal-to-noise to allow precision measurements of absorption line-strengths. Comparing these indices to new stellar population models by Thomas et al. we determine ages, metallicities and element abundance ratios. Our data are also compared with the Lick/IDS observations of Milky Way and M31 globular clusters. Unpublished higher order Balmer lines (HgammaA,F and HdeltaA,F) from the Lick/IDS observations are given in the Appendix. Our best age estimates show that the observed clusters which sample the bimodal colour distribution of NGC3115 are coeval within our observational errors (2-3 Gyr). Our best calibrated age/metallicity diagnostic diagram (Hbeta vs [MgFe]) indicates an absolute age of 11-12 Gyr. We confirm with our accurate line-strength measurements that the (V-I) colour is a good metallicity indicator within the probed metallicity range. The abundance ratios for globular clusters in NGC3115 give an inhomogeneous picture. We find a range from solar to super-solar ratios for both blue and red clusters. From our accurate recession velocities we detect, independent of metallicity, clear rotation in the sample of globular clusters. In order to explain the metallicity and abundance ratio pattern, particularly the range in abundance ratios for the metal rich globular clusters in NGC3115, we favour a formation picture with more than two distinct formation episodes.(Abridged)

astro-ph↗
arXiv1998

Environments of QSOs at intermediate redshifts

A preliminary analysis of fields around 20 mainly radio-quiet QSOs (RQQs) at intermediate redshift is summarized. We find overdensities of faint sources around 50% of our observed QSOs suggesting that they are located in groups or even clusters of galaxies.

astro-ph↗
arXiv1998

Chemically consistent evolution of galaxies: galaxy models compared to DLA systems

We have extended our chemical and cosmological galaxy evolution model to calculate the abundance evolution for altogether 16 different elements in spiral galaxies in a chemically consistent way which is a considerable step towards a more realistic galaxy modeling. Our models well reproduce observed average HII region abundances in all spiral types. All observed element abundances in DLA systems have been compiled. The conformity between observed and calculated abundances over the redshift range from z=4.5 through z=0.4 indicates that DLA galaxies may well evolve into the full range of present- day spiral galaxies from Sa through Sd. Comparison of our chemically consistent models with models using only solar metallicity input physics shows that differences in the redshift evolution are small for some elements but large for others. For those elements with large differences the chemically consistent models provide significant better agreement with observed DLA abundances. For typical spiral galaxies the star formation histories of our models clearly bridge the gap between high redshift DLA systems and the nearby spiral galaxy population. The slow redshift evolution of DLA abundances is understood in terms of the long star formation timescales in galactic and proto-galactic disks. Towards lower redshift z < 1.5 our models indicate that early type spirals drop out of the DLA samples as their gas content falls below ~50%. Implications for optical identification are discussed.

astro-ph↗
arXiv1997

The chemical evolution of galaxies causing damped Ly$α$ absorption

We have compiled all available data on chemical abundances in damped Lyman alpha absorption systems for comparison with results from our combined chemical and spectrophotometric galaxy evolution models. Preliminary results from chemically consistent calculations are in agreement with observations of damped Ly$α$ systems.

astro-ph↗
arXiv1996

Metallicity indicators across the spectrum of composite stellar populations

With a chemically consistent evolutionary synthesis approach we follow the enrichment of individual chemical elements in the ISM. We describe the time With a chemically consistent evolutionary synthesis approach we follow the enrichment of individual chemical elements in the ISM. We describe the time evolution of broad band colors U to K and metal indices (Fe5335, Fe5270, Mg2, Mgb), taking into account the increasing initial metallicities of successive generations of stars. Using specific star formation prescriptions for the different spectral types of galaxies, we show our model galaxy broad band colors, synthetic spectra, and ISM abundances are in agreement with observations of nearby samples and template galaxies of the respective spectral types. We compare our synthetic Mg2 indices with observations and study the time evolution of the stellar index [MgFe] for composite elliptical galaxy models and for simple stellar populations of various metallicities. We show how the luminosity weighted stellar metallicity indicators in different wavelength bands from U to K compare to each other for the various star formation histories and how they evolve in time. We analyse as a function of wavelength the luminosity contributions of stellar subpopulations with different metallicities in the various galaxy types. The relations between luminosity weighted stellar metallicity indicators in different passbands, stellar absorption indices and ISM abundances are shown to depend significantly on the star formation history and evolutionary stage.

astro-ph↗
arXiv1996

Implications for optical identifications of QSO absorption systems from galaxy evolution models

We have made an attempt to compile all currently available data on optically identified QSO absorber systems (Lindner et al. 1996) to establish the status quo of absorber galaxy data as a basis for the investigation of galaxy evolution. We present a first comparison with results from our galaxy evolutionary synthesis models to demonstrate the potential power of this kind of approach and to guide future observations to identify absorber galaxies.

astro-ph↗
arXiv1996

Optically identified QSO absorption systems and galaxy evolution

A comprehensive set of all available magnitudes, colors and redshifts for optically identified QSO absorbers is compiled from the literature. This results in a largely unbiased sample of galaxies at high redshifts, the size of the sample being reasonably large to allow for a first comparison with galaxy evolution models. We use our evolutionary spectral synthesis models describing various spectral types of galaxies with appropriate star formation histories. For a standard cosmology H0=50, Omega0=1, we find that all identified QSO absorbers up to a redshift about z=2 do fall within the evolving range of models which had been shown earlier to give good agreement with nearby galaxies of various spectral types. The most striking result is that all spectral types of galaxies from E through Sd seem to be present in this absorber candidate sample with the bulk of the objects being spirals of type Sa to Sc. We also show that such kind of high redshift galaxy sample should allow for significant restrictions of the cosmological parameters. While models with H0=50, Omega0=1 and any redshift of galaxy formation zform=5 ... 10 give reasonable agreement with observed luminosities and colors, present data seem to exclude the combination H0=50, Omega0=0.1. A low Omega0 together with a value of H0 > 50 might still be viable. Additional data, and in particular observations of absorbing galaxies in more than one passband, are required for further constraints. We realize that the present results depend on the adopted evolutionary models and on the input physics used which might be better constrained by future observations.

astro-ph↗