arXiv subjects

Bodo L. Ziegler

Publications and source records attributed to Bodo L. Ziegler.

31 records · Page 2Linked to original sources

arXiv2004

The Evolution of Field Spiral Galaxies over the Past 8 Gyr

We have performed a large observing campaign of intermediate-redshift disk galaxies including spectroscopy with the FORS instruments of the VLT and imaging with the Advanced Camera for Surveys onboard the HST. Our data set comprises 113 late-type galaxies in the redshift range 0.1 2mag in rest-frame B. This evolution would be at variance with the predictions from numerical simulations. On the other hand, the disks of the distant galaxies are, for a given Vmax, slightly smaller than those of their local counterparts, as expected for a hierarchical structure growth. Hence, the discrepancy between the observations and theoretical predictions would be limited to the properties of the stellar populations. A possible explanation could be the suppression of star formation in low-mass disks which is not yet properly implemented in models of galaxy evolution. (abridged)

astro-ph↗

arXiv2004

Disk galaxy evolution up to redshift z=1

We have performed intermediate-resolution VLT/FORS spectroscopy and HST/ACS imaging of 129 field spiral galaxies within the FORS Deep Field. The galaxies cover the redshift range 0.1 < z < 1.0 and comprise all types from Sa to Sdm/Im. Spatially resolved rotation curves were extracted and fitted with synthetic velocity fields that take into account all geometric (e.g., inclination and misalignment) and observational effects (in particular, blurring due to optical beam smearing and seeing). Using these fits, the maximum rotation velocity Vmax could be determined for 73 objects. The Tully-Fisher relation of this sample at a mean look-back time of ~5Gyr shows a luminosity evolution which amounts to ~2mag in rest-frame B for low-mass spirals (Vmax~100km/s) but is negligible for high-mass spirals (Vmax~300km/s). This confirms our previous analysis which was limited to ground-based imaging. The observed overluminosity of low-mass galaxies is at variance with predictions from simulations. On the other hand, at given Vmax, we find slightly smaller disk sizes towards higher redshifts, in compliance with the CDM hierarchical model. The observed mass-dependent luminosity evolution might therefore point towards the need for a more realistic modelling of the stellar (i.e. baryonic) component in N-body codes.

astro-ph↗

arXiv2004

Quantitative interpretation of the rotation curves of spiral galaxies at redshifts z~0.7 and z~1

We present decompositions of the rotation curves of three spiral galaxies at redshifts z~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.

astro-ph↗

arXiv2004

A Detailed View of the Fundamental Plane of Early-Type Galaxies in Clusters at z~0.2

We present a spectroscopic sample of 48 early-type galaxies in the rich cluster Abell 2218 and 50 galaxies in Abell 2390. Since both samples are very similar, we combine them and investigate a total number of 98 early-type galaxies at z~0.2. A subsample of 34 galaxies with HST structural properties is used to construct the Fundamental Plane. Elliptical and S0 galaxies show a zeropoint offset of m_r~0.43 mag with respect to the local Coma FP. Both sub-samples, ellipticals and lenticulars, exhibit a similar, mild evolution and small scatter. The moderate amount of luminosity evolution is consistent with stellar population models of passive evolution, if z_f>=2 is assumed.

astro-ph↗

arXiv2004

Evolutionary Status of Early-Type Galaxies in Distant Poor Clusters

We introduce our project that investigates the kinematic properties of early-type galaxies in 6 distant poor clusters at z~0.25. This study represents a continuation of our efforts to understand galaxy evolution in low-density environments. Higher-resolution MOSCA spectra have been obtained at the Calar Alto 3.5-m telescope with which we can measure absorption line strengths and velocity dispersions. In conjunction with our HST/F702W images of all the clusters, we are able to construct the Fundamental Plane of ellipticals and S0 galaxies in poor clusters at a look-back time of ~3 Gyrs. For galaxies outside the HST field, we concentrate our analysis on the Mg-sigma and Faber-Jackson relations. With the line strength diagrams age/metallicity distributions can be derived in densities between the field and rich cluster environments. Comparing with our rich clusters at the same cosmic epochs, the dependence of galaxy formation models on the local environment can be tested more quantitatively.

astro-ph↗

arXiv2004

Chemical and mass evolution of galaxies

An introduction is given to projects investigating galaxy evolution quantitatively by spectroscopic observations of very distant galaxies that have weak apparent brightnesses and small sizes as it is feasible with 10m-class telescopes like SALT. Such methods encompass scaling relations like the Tully-Fisher and Fundamental Plane relations that can be utilized to determine the luminosity evolution and mass assembly of galaxies. The stellar populations can be analyzed with respect to age, metallicity, and chemical enrichment by measureing absorption line strengths. Possible effects on galaxy evolution of the environment in rich clusters of galaxies compared to the field are also addressed. For each method, recent applications are presented like the evolution of the TFR determined with 77 field spirals up to z=1, a study of the internal kinematics of distant cluster spirals and a comparison of the stellar populations of ellipticals in the field and in rich clusters at z=0.4.

astro-ph↗

arXiv2003

The Evolutionary Status of Early-type Galaxies in Abell 2390

We explore the evolution of the early-type galaxy population in the rich cluster Abell 2390 at z=0.23. For this purpose, we have obtained spectroscopic data of 51 elliptical and lenticular galaxies with MOSCA at the 3.5 m telescope on Calar Alto Observatory. As our investigation spans both a broad range in luminosity (-22.3<M_B<-19.3) and a wide field of view (10'x10'), the environmental dependence of different formation scenarios can be analysed in detail as a function of radius from the cluster center. In this paper, we present first results on the Faber-Jackson relation and, for a subsample of 14 galaxies with morphological and structural parameters from HST, we also investigate the evolution of the Kormendy relation and the Fundamental Plane. We find a mild luminosity evolution of the early-type galaxies in Abell 2390: our objects are on average brighter by m_B~0.4 mag.

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

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↗

arXiv2000

Evolution of Early-type Galaxies in Clusters

(Abriged) This is a short review on the evolution of elliptical and lenticular/S0 galaxies in the dense environment of rich clusters for look-back times of more than half the age of the Universe. In addition, new data are presented for the cluster Abell 2218. Scaling relations like the Fundamental Plane provide strong evidence that luminous ellipticals evolve purely passively up to redshifts of z=0.8 implying that no significant new stellar population was created during that time. This picture is supported by tight Mg-sigma and colour-magnitude relations at various redshifts and age/metallicity diagnostic diagrams. On the other hand, there is a strong decline in the frequency of S0 galaxies with redshift, while a significant proportion of the galaxies have disturbed morphologies and signs of ongoing interaction/merging. Numerous post-starburst galaxies are found as well as passive spiral galaxies. This raises the question whether the spiral galaxies falling into the cluster from the surrounding field could be transformed into S0 galaxies. A possible scenario would be that the intracluster medium first deprives the spirals of all their gas leading to the end of star formation. The subsequent evolution within the tidal field of the cluster could then turn the spirals into S0 galaxies over the ages. The study of a great number of early-type galaxies per cluster including sub-L* galaxies reveals, however, that this picture needs some finetuning since the relations mentioned above have a larger spread than those based on the observation of just a few luminous galaxies. First results are presented for 48 early-type galaxies in the cluster Abell 2218 at a redshift of z=0.18.

astro-ph↗

arXiv1997

M32-like galaxies: still very rare -- M32 analogues do not exist in the Leo group

New observations of galaxies in the direction of the Leo group, which were classified as being candidates for M32-like dwarf galaxies by Ferguson & Sandage (1990), show that these galaxies are normal elliptical galaxies at redshifts between z=0.02 and z=0.06. This result adds further evidence that the faint end of the luminosity function of elliptical galaxies falls off very steep and that objects like M32 are extremely rare.

astro-ph↗

arXiv1997

The Mgb-sigma Relation of Elliptical Galaxies at z=0.37

We derive absorption indices of ellipticals in clusters at z=0.37 from medium-resolution spectroscopy together with kinematical parameters. These galaxies exhibit a relationship between the Mgb linestrength and their internal velocity dispersion similar to local dynamically hot galaxies. But for any given sigma, Mgb of the distant ellipticals is significantly lower than the mean value of the nearby sample. The difference of Mgb between the two samples is small and can be fully attributed to the younger age of the distant stellar populations in accordance with the passive evolution model. The low reduction of Mgb at a look-back time of about 5 Gyrs requires that the bulk of the stars in cluster ellipticals have formed at very high redshifts of z_f>2. For the most massive galaxies, where the reduction is even lower, z_f probably exceeds 4. Unlike most methods to measure the evolution of ellipticals using luminosities, surface brightnesses or colours, the Mgb linestrength does not depend on corrections for extinction and cosmic expansion (K-correction) and only very little on the slope of the initial mass function. The combination of a kinematical parameter with a stellar population indicator allows us to study the evolution of very similar objects. In addition, the good mass estimate provided by sigma means that the selection criteria for the galaxy sample as a whole are well controlled. (abriged)

astro-ph↗

arXiv1997

The Mg-sigma Relation of Elliptical Galaxies at Various Redshifts

The correlation between the Mg absorption index and the velocity dispersion (sigma) of local elliptical galaxies is very tight. Because the Mg absorption depends on both metallicity and age of the underlying stellar population the observed Mg-sigma relation constrains the possible variation in metallicity and age for a given velocity dispersion. For a time interval with no change in metallicity any variation of the Mg index is caused only by the aging of the stars. We have measured the Mg absorption and velocity dispersion of ellipticals in three clusters at a redshift of z=0.37 and established their Mg-sigma relation. For any given sigma, the measured Mg absorption is weaker than the mean value for local ellipticals. Since the evolution of bright cluster ellipticals between z=0.4 and today is most probably only `passive' this reduction in Mg can be attributed solely to the younger age of the stellar population. The small weakening of the Mg absorption of the distant galaxies compared to the local values implies that most of the stars in cluster ellipticals must have formed at high redshifts (z_f > 2...4). The Mg-sigma test is a very robust method to investigate the evolution of elliptical galaxies and has several advantages over traditional methods using luminosities. A remaining problem is the aperture correction necessary to calibrate observations of galaxies at different distances. Here, we show that our general conclusions about the epoch of formation still hold when aperture corrections are calculated assuming a dependence of the radial gradient of sigma on the galaxy's effective radius rather than assuming no dependence as was done in all previous studies.

astro-ph↗