Browsing by Author "Bohm, A."

Using a sample of 57 VLT FORS spectra in the redshift range 1.37 < z < 3.40 (selected mainly from the FORS Deep Field survey) and a comparison sample with 36 IUE spectra of local (z approximate to 0) starburst galaxies we derive C and Si equivalent width values and estimate metallicities of starburst galaxies as a function of redshift. Assuming that a calibration of the C equivalent widths in terms of the metallicity based on the local sample of starburst galaxies is applicable to high-z objects, we find a significant increase of the average metallicities from about 0.16 Z(.) at the cosmic epoch corresponding to z approximate to 3.2 to about 0.42 Z(.) at z approximate to 2.3. A significant further increase in metallicity during later epochs cannot be detected in our data. Compared to the local starburst galaxies our high-redshift objects tend to be overluminous for a fixed metallicity. Our observational results are in good agreement with published observational data by other authors and with theoretical predictions of the cosmic chemical evolution.

We present a systematic investigation of rotation curves (RCs) of fully hydrodynamically simulated galaxies, including cooling, star formation with associated feedback, and galactic winds. Applying two commonly used fitting formulae to characterize the RCs, we investigated systematic e. ects on the shape of RCs by both the observational constraints and internal properties of the galaxies. We mainly focused on e. ects that occur in measurements of intermediate and high redshift galaxies. We found that RC parameters are affected by the observational setup, like slit misalignment or the spatial resolution and that they also depend on the evolution of a galaxy. Therefore, a direct comparison of quantities derived from measured RCs with predictions of semi-analytic models is difficult. The virial velocity V(c), which is usually calculated and used by semi-analytic models, can differ significantly from fit parameters like V(max) or V(opt) inferred from RCs. We found that V(c) is usually lower than typical characteristic velocities derived from RCs. Vmax alone is in general not a robust estimator of the virial mass.

We introduce our project on galaxy evolution in the environment of rich clusters, aiming at disentangling the importance of specific interaction and galaxy transformation processes from the hierarchical evolution of galaxies in the field. Emphasis is laid on the examination of the internal kinematics of disk galaxies through spatially resolved multiobject spectroscopy with FORS at the Very Large Telescope. First results are presented for the clusters MS 1008.1 - 1224 (z = 0.30), Cl 0303 + 1706 (z = 0.42), and Cl 0413 = 6559 (F1557.19TC; z = 0.51). Out of 30 cluster members with emission lines, 13 galaxies exhibit a rotation curve of the universal form rising in the inner region and passing over into a flat part. The other members have either intrinsically peculiar kinematics (4), too strong geometric distortions (9), or a too low signal-to-noise ratio (4) for a reliable classification of their velocity profiles. The 13 cluster galaxies for which a maximum rotation velocity could be derived are distributed in the Tully-Fisher diagram very similar to field galaxies from the FORS Deep Field that have corresponding redshifts and do not show any significant luminosity evolution with respect to local samples. The same is true for the seven galaxies observed in the cluster fields that turned out not to be members. The mass-to-light ratios of the 13 Tully-Fisher cluster spiral galaxies cover the same range as the distant field population, indicating that their stellar populations were not dramatically changed by possible cluster-specific interaction phenomena. The cluster members with distorted kinematics may be subject to interaction processes, but it is impossible to determine whether or not these processes also lead to changes in the overall luminosity of their stellar populations.

We have conducted an observing campaign with the FORS instruments at the ESO-Very Large Telescope to explore the kinematical properties of spiral galaxies in distant galaxy clusters. Our main goal is to analyse transformation - and interaction processes of disk galaxies within the special environment of clusters as compared to the hierarchical evolution of galaxies in the field. Spatially resolved multi object spectra have been obtained for seven galaxy clusters at 0.3 < z < 0.6 to measure rotation velocities of cluster members. For three of the clusters, Cl 0303+17, Cl 0413-65, and MS 1008-12, for which we presented results including a Tully-Fisher-diagram in Ziegler et al. (2003), we describe here in detail the sample selection, observations, data reduction, and data analysis. Each of them was observed with two setups of the standard MOS-unit of FORS. With typical exposure times of >2 h we reach an S/N > 5 in the emission lines appropriate for the deduction of the galaxies' internal rotation velocities from [OII], H(beta), or [OIII] emission line profiles. Preselection of targets was done on the basis of available redshifts as well as from photometric and morphological information gathered from own observations, archive data, and from the literature. Emphasis was laid on the definition of suitable setups to avoid the typical restrictions of the standard MOS unit for this kind of observations. In total we assembled spectra of 116 objects of which 50 turned out to be cluster members. Position velocity diagrams, finding charts for each setup as well as tables with photometric, spectral, and structural parameters of individual galaxies are presented.

We investigate in detail 13 early-type field galaxies with 0.2 < z < 0.7 drawn from the FORS Deep Field. Since the majority ( 9 galaxies) is at z approximate to 0.4, we compare the field galaxies to 22 members of three rich clusters with z = 0.37 to explore possible variations caused by environmental effects. We exploit VLT/FORS spectra ( R approximate to 1200) and HST/ACS imaging to determine internal kinematics, structures and stellar population parameters. From the Faber-Jackson and Fundamental Plane scaling relations we deduce a modest luminosity evolution in the B-band of 0.3 - 0.5 mag for both samples. We compare measured Lick absorption line strengths (H delta, H gamma, H beta, Mg-b, and Fe 5335) with evolutionary stellar population models to derive light-averaged ages, metallicities and the element abundance ratios Mg/Fe. We find that these three stellar parameters of the distant galaxies obey a scaling with velocity dispersion ( mass) which is consistent with that of local nearby galaxies. In particular, the distribution of Mg/Fe ratios of local galaxies is matched by the distant ones, and their derived mean offset in age corresponds to the average lookback time. This indicates that there was little chemical enrichment and no significant star formation within the last similar to 5 Gyr. The calculated luminosity evolution of a simple stellar population model for the derived galaxy ages and lookback times is in most cases consistent with the mild brightening measured by the scaling relations.

We present decompositions of the rotation curves of three spiral galaxies at redshifts z similar to 0.7 and 1 into contributions by their bulges, disks, and dark halos, respectively. In order to set constraints on the degeneracy of the decompositions we interpret the morphology of the spiral structures quantitatively in the framework of density wave theory. Galaxy models constrained in such a way show that the distant galaxies, which are much younger than nearby galaxies, have very likely "maximum disks", i.e. are dominated in their inner parts by baryonic matter. We argue that current theories of the cosmogony of galaxies must allow for these types of galaxies.

In the last few years, galaxies at redshifts up to zsimilar to1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10 m-class telescopes. With kinematic and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation (TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at redshifts 0.1

We use the very deep and homogeneous I-band selected dataset of the FORS Deep Field (FDF) to trace the evolution of the luminosity function over the redshift range 0.5 < z < 5.0. We show that the FDF I-band selection down to I-AB = 26.8 misses of the order of 10% of the galaxies that would be detected in a K-band selected survey with magnitude limit K-AB = 26.3 (like FIRES). Photometric redshifts for 5558 galaxies are estimated based on the photometry in 9 filters (U, B, Gunn g, R, 1, SDSS z, J, K and a special filter centered at 834 nm). A comparison with 362 spectroscopic redshifts shows that the achieved accuracy of the photometric redshifts is Deltaz/(z(spec) + 1) less than or equal to 0.03 with only similar to1% outliers. This allows us to derive luminosity functions with a reliability similar to spectroscopic surveys. In addition, the luminosity functions can be traced to objects of lower luminosity which generally are not accessible to spectroscopy. We investigate the evolution of the luminosity functions evaluated in the restframe UV (1500 Angstrom and 2800 Angstrom), u', B, and g' bands. Comparison with results from the literature shows the reliability of the derived luminosity functions. Out to redshifts of z similar to 2.5 the data are consistent with a slope of the luminosity function approximately constant with redshift, at a value of -1.07 +/- 0.04 in the UV (1500 Angstrom, 2800 Angstrom) as well as u', and -1.25 +/- 0.03 in the blue (g', B). We do not see evidence for a very steep slope (alpha less than or equal to -1.6) in the UV at similar to 3.0 and similar to 4.0 favoured by other authors. There may be a tendency for the faint-end slope to become shallower with increasing redshift but the effect is marginal. We find a brightening of M and a decrease of phi with redshift for all analyzed wavelengths. The effect is systematic and much stronger than what can be expected to be caused by cosmic variance seen in the FDF. The evolution of M and phi from z = 0 to z = 5 is well described by the simple approximations M (z) = M-0( ) + a ln (1 + z) and phi (z) = phi(0)( ) (1 + z)(b) for M and phi . The evolution is very pronounced at shorter wavelengths (a = -2.19, and b = -1.76 for 1500 Angstrom rest wavelength) and decreases systematically with increasing wavelength, but is also clearly visible at the longest wavelength investigated here (a = -1.08, and b = -1.29 for g'). Finally we show a comparison with semi-analytical galaxy formation models.

We present the B-band Tully-Fisher relation (TFR) of 60 late-type galaxies with redshifts 0.1-1. The galaxies were selected from the FORS Deep Field with a limiting magnitude of. Spatially resolved rotation curves R p 23 were derived from spectra obtained with FORS2 at the Very Large Telescope. High-mass galaxies with v(max) greater than or similar to 150 km s(-1) show little evolution, whereas the least massive systems in our sample are brighter by similar to1-2 mag compared with their local counterparts. For the entire distant sample, the TFR slope is flatter than for local field galaxies (-5.77+/-0.45 vs. -7.92+/-0.18). Thus, we find evidence for the evolution of the slope of the TFR with redshift on the 3 sigma level. This is still true when we subdivide the sample into three redshift bins. We speculate that the flatter tilt of our sample is caused by the evolution of luminosities and an additional population of blue galaxies at zgreater than or similar to0.2. The mass dependence of the TFR evolution also leads to variations for different galaxy types in magnitude-limited samples, suggesting that selection effects can account for the discrepant results of previous TFR studies on the luminosity evolution of late-type galaxies.

We present a catalogue and atlas of low-resolution spectra of a well defined sample of 341 objects in the FORS Deep Field. All spectra were obtained with the FORS instruments at the ESO VLT with essentially the same spectroscopic set-up. The observed extragalactic objects cover the redshift range 0.1 to 5.0. 98 objects are starburst galaxies and QSOs at z > 2. Using this data set we investigated the evolution of the characteristic spectral properties of bright starburst galaxies and their mutual relations as a function of redshift. Significant evolutionary effects were found for redshifts 2 < z < 4. Most conspicuous are the increase of the average C IV absorption strength, of the dust reddening, and of the intrinsic UV luminosity, and the decrease of the average Lyalpha emission strength with decreasing redshift. In part the observed evolutionary effects can be attributed to an increase of the metallicity of the galaxies with cosmic age. Moreover, the increase of the total star-formation rates and the stronger obscuration of the starburst cores by dusty gas clouds suggest the occurrence of more massive starbursts at later cosmic epochs.

The FORS Deep Field project is a multi-colour, multi-object spectroscopic investigation of a similar to7' x 7' region near the south galactic pole based mostly on observations carried out with the FORS instruments attached to the VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this study is to improve our understanding of the formation and evolution of galaxies in the young Universe. In this paper the field selection, the photometric observations, and the data reduction are described. The source detection and photometry of objects in the FORS Deep Field is discussed in detail. A combined B and 1 selected UBgRIJKs photometric catalog of 8753 objects in the FDF is presented and its properties are briefly discussed. The formal 50% completeness limits for point sources, derived from the co-added images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R, I, J and Ks (Vega-system), respectively. A comparison of the number counts in the FORS Deep Field to those derived in other deep field surveys shows very good agreement.

We combine the latest observations of disc galaxy photometry and rotation curves at moderate redshift from the FORS Deep Field (FDF) with simple models of chemical enrichment. Our method describes the build-up of the stellar component through infall of gas and allows for gas and metal outflows. In this framework, we keep a minimum number of constraints and we search a large volume of parameter space, looking for the models that best reproduce the photometric observations in the observed redshift range (0.5 < z < 1). We find that star formation efficiency correlates well with v(max), so that massive discs are more efficient in the formation of stars and have a smaller spread in stellar ages. This trend presents a break at around v(max) similar to 140 km s(-1). Galaxies on either side of this threshold have significantly different age distributions. This break has been already suggested by several authors in connection with the contribution from either gravitational instabilities or supernova-driven turbulence to star formation. The gas infall time-scale and gas outflows also present a correlation with galaxy mass, so that massive discs have shorter infall time-scales and smaller outflow fractions. The model presented in this paper suggests that massive discs have formation histories resembling those of early-type galaxies, with highly efficient and short-lived bursts, in contrast with low-mass discs, which have a more extended star formation history. The ages correlate well with galaxy mass or luminosity, and the predicted gas-phase metallicities are consistent with the observations of local and moderate-redshift galaxies. One option to explain the observed shallow slope of the Tully-Fisher relation at intermediate redshift could be small episodes of star formation in low-mass discs.

Using the Very Large Telescope in Multi Object Spectroscopy mode, we have observed a sample of 113 field spiral galaxies in the FORS Deep Field (FDF) with redshifts in the range 0.1