arXiv subjects

B. L. Ziegler

Publications and source records attributed to B. L. Ziegler.

At least 37 records · Page 2Linked to original sources

arXiv2007

2D velocity fields of simulated interacting disc galaxies

We investigate distortions in the velocity fields of disc galaxies and their use to reveal the dynamical state of interacting galaxies at different redshift. For that purpose, we model disc galaxies in combined N-body/hydrodynamic simulations. 2D velocity fields of the gas are extracted from these simulations which we place at different redshifts from z=0 to z=1 to investigate resolution effects on the properties of the velocity field. To quantify the structure of the velocity field we also perform a kinemetry analysis. If the galaxy is undisturbed we find that the rotation curve extracted from the 2D field agrees well with long-slit rotation curves. This is not true for interacting systems, as the kinematic axis is not well defined and does in general not coincide with the photometric axis of the system. For large (Milky way type) galaxies we find that distortions are still visible at intermediate redshifts but partly smeared out. Thus a careful analysis of the velocity field is necessary before using it for a Tully-Fisher study. For small galaxies (disc scale length ~2 kpc) even strong distortions are not visible in the velocity field at z~0.5 with currently available angular resolution. Therefore we conclude that current distant Tully-Fisher studies cannot give reliable results for low-mass systems. Additionally to these studies we confirm the power of near-infrared integral field spectrometers in combination with adaptive optics (such as SINFONI) to study velocity fields of galaxies at high redshift (z~2).

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arXiv2006

Internal kinematics of modelled interacting disc galaxies

We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly rising or falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curves to show that the appearance of these distortions strongly depends on the viewing angle. We also find in this way that the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results are consistent with previous theoretical and observational studies. As an illustration of our results, we compare our simulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find remarkable similarities.

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arXiv2005

Downsizing Scaling Relations

Faber-Jackson and Tully-Fisher scaling relations for elliptical and spiral galaxy samples up to z=1 provide evidence for a differential behaviour of galaxy evolution with mass. In compliance with the downsizing scenario, the stellar populations of less massive galaxies display a stronger evolution than the more massive ones. For spirals, this may be attributed to a suppressed star formation efficiency in small dark matter halos. For ellipticals, star formation must have been negligible at least during the past ~4Gyr in all environments.

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arXiv2005

Internal kinematics of isolated modelled disk galaxies

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 investigate systematic effects on the shape of RCs both by observational constraints and internal properties of the galaxies. We mainly focus on effects that occur in measurements of intermediate and high redshift galaxies. We find that RC parameters are affected by the observational setup, like slit misalignment or the spatial resolution and 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 find that V_c is usually lower than typical characteristic velocities derived from RCs. V_max alone is in general not a robust estimator for the virial mass.

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arXiv2004

Kinematic and chemical evolution of early-type galaxies

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~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~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 0.3-0.5mag for both samples. We compare measured Lick absorption line strengths (Hdelta, Hgamma, Hbeta, Mg_b, & Fe5335) with evolutionary stellar population models to derive light-averaged ages, metallicities and the element abundance ratios Mg/Fe. We find that all these three stellar parameters of the distant galaxies obey a scaling with velocity dispersion (mass) which is very well consistent with the one 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 ~5Gyr. The calculated luminosity evolution of a simple stellar population model for the derived galaxy ages and lookback times is in most cases very consistent with the mild brightening measured by the scaling relations.

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arXiv2004

The star formation history of intermediate redshift late-type galaxies

We combine the latest observations of disk galaxy photometry and rotation curves at moderate redshift from the FORS Deep Field (FDF) with simple models of chemical enrichment. Our method describes the buildup 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 which best reproduce the photometric observations in the observed redshift range (0.5<z<1). We find the star formation efficiency to correlate well with vMAX so that massive disks are more efficient in the formation of stars and have a smaller spread in stellar ages. This trend presents a break at around vMAX 140km/s. 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. No clear trend is seen between galaxy mass and infall timescale or gas outflows. The model presented in this paper suggests massive disks have formation histories resembling those of early-type galaxies, with highly efficient and short-lived bursts, in contrast with low-mass disks, which have a more extended star formation history. 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 disks.

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arXiv2004

Internal kinematics of spiral galaxies in distant clusters. Part II. Observations and data analysis

We have conducted an observing campaign with FORS at the ESO-VLT 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 MOS-spectra have been obtained for seven galaxy clusters at 0.3 2 hours we reach an S/N>5 in the emission lines appropriate for the deduction of the galaxies' internal rotation velocities from [OII], Hbeta, or [OIII] 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 as well as tables with photometric, spectral, and structural parameters of individual galaxies are presented.

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arXiv2004

Internal kinematics of spiral galaxies in distant rich galaxy clusters

We present our project on galaxy evolution in the environment of distant rich clusters aiming at disentangling the importance of specific interaction and galaxy transformation processes from the hierarchical evolution of field galaxies. Spatially resolved MOS spectra were gained with VLT/FORS to analyze the internal kinematics of disk galaxies. First results are shown for the clusters MS 1008.1-1224 (z=0.30), Cl 0303+1706 (z=0.42), and Cl 0413-6559 (z=0.51). Out of 35 late type cluster members, 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 peculiar kinematics. 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 with corresponding redshifts. The same is true for seven non-cluster galaxies observed in the cluster fields. The TF-cluster spirals do not show any significant luminosity evolution as might be expected from certain clusterspecific phenomena. Contrary to that, the disturbed kinematics of the non--TF cluster spirals indicate ongoing or recent interaction processes.

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arXiv2004

The Tully-Fisher relation at intermediate redshift

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<z<1.0. The galaxies were selected upon apparent brightness (R<23) and encompass all late spectrophotometric types from Sa to Sdm/Im. Spatially resolved rotation curves have been extracted for 77 galaxies and fitted with synthetic velocity fields taking into account all observational effects from inclination and slit misalignment to seeing and slit width. We also compared different shapes for the intrinsic rotation curve. To gain robust values of V_max, our analysis is focussed on galaxies with rotation curves which extend well into the region of constant rotation velocity at large radii. If the slope of the local Tully-Fisher relation (TFR) is held fixed, we find evidence for a mass-dependent luminosity evolution which is as large as up to 2 mag for the lowest-mass galaxies, but is small or even negligible for the highest-mass systems in our sample. In effect, the TFR slope is shallower at z~0.5 in comparison to the local sample. We argue for a mass-dependent evolution of the mass-to-light ratio. An additional population of blue, low-mass spirals does not seem a very appealing explanation. The flatter tilt we find for the distant TFR is in contradiction to the predictions of recent semi-analytic simulations.

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arXiv2004

The FORS Deep Field Spectroscopic Survey

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 the 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 Ly alpha 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.

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arXiv2003

Exploring the Selection of Galaxy Clusters and Groups: An Optical Survey for X-ray Dark Clusters

Data from a new, wide field, coincident optical and X-ray survey, the X-ray Dark Cluster Survey (XDCS) are presented. This survey comprises simultaneous and independent searches for clusters of galaxies in the optical and X-ray passbands. Optical cluster detection algorithms implemented on the data are detailed. Two distinct optically selected catalogues are constructed, one based on I-band overdensity, the other on overdensities of colour-selected galaxies. The superior accuracy of the colour-selection technique over that of the single passband method is demonstrated, via internal consistency checks and comparison with external spectroscopic redshift information. This is compared with an X-ray selected cluster catalogue. In terms of gross numbers, the survey yields 185 I-band selected, 290 colour selected and 15 X-ray selected systems, residing in ~11deg^2 of optical + X-ray imaging. The relationship between optical richness/ luminosity and X-ray luminosity is examined, by measuring X-ray luminosities at the positions of our 290 colour-selected systems. Power law correlations between the optical richness/ luminosity versus X-ray luminosity are fitted, both exhibiting approximately 0.2 dex of intrinsic scatter. Interesting outliers in these correlations are discussed in greater detail. Spectroscopic follow up of a subsample of X-ray underluminous systems confirms their reality.

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arXiv2003

Internal kinematics of spiral galaxies in distant clusters Part I

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 MOS spectroscopy with FORS at the VLT. First results are presented for the clusters MS1008.1-1224 (z=0.30), Cl0303+1706 (z=0.42), and Cl0413-6559 (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), or too strong geometric distortions (9) or too low S/N (4 galaxies) 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 seven galaxies observed in the cluster fields that turned out not to be members. The mass-to-light ratios of the 13 TF cluster spirals cover the same range as the distant field population indicating that their stellar populations were not dramatically changed by possible clusterspecific interaction phenomena. The cluster members with distorted kinematics may be subject to interaction processes but it is impossible to determine whether these processes also lead to changes in the overall luminosity of their stellar populations.

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arXiv2003

Early-type Galaxies in the Cluster Abell 2390 at z=0.23

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.

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arXiv2003

Internal Kinematics of Spiral Galaxies in Distant Clusters

We present first results from our project to examine the internal kinematics of disk galaxies in 7 rich clusters with 0.3<=z<0.6. Spatially resolved MOS spectra have been obtained with FORS at the VLT. We concentrate here on the clusters MS1008.1-1224 at z=0.30 and Cl0413-6559 (F1557.19TC) at z=0.51. Out of 22 cluster members, 12 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 intrinsically peculiar kinematics. The 12 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 with corresponding redshifts. The same is true for 6 galaxies observed in the cluster fields that turned out not to be members. In particular, these cluster spirals do not show any significant luminosity evolution as might be expected from certain clusterspecific phenomena. Contrary to that, the other half of the cluster sample with disturbed kinematics also shows a higher degree of structural assymetries on average indicating ongoing or recent interaction processes.

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arXiv2002

Globular Clusters in Compact Groups

We have studied globular cluster systems (GCSs) around elliptical galaxies in Hickson compact groups using multi-band deep, high quality images from Keck, VLT and CFHT. Analyzing the luminosity functions, specific frequencies, color and spatial distributions, we could determine the properties of the GCSs of those galaxies and trace their star formation histories. We have found poor populations, concentrated toward the center of the galaxies, with bimodal color distributions. The study of GCSs around galaxies in small groups are a blank on the globular cluster literature.

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arXiv2002

Scaling Relations of Field Spirals at intermediate Redshift

In the last few years, galaxies at redshifts up to z~1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10m-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<z<1.0. We find evidence for a B-band luminosity increase of up to 2mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical simulations based on the hierarchical merging scenario.

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arXiv2002

Galaxy Properties in Low X-Ray Luminosity Clusters at z=0.25

We present the first spectroscopic survey of intrinsically low Lx clusters at z>>0, with HST WFPC2 imaging and ground-based spectroscopy. We study 172 confirmed cluster members in a sample of ten clusters at z=0.23-0.3, with Lx<4.E43 h^{-2} ergs/s. The core of each cluster is imaged with WFPC2 in the F702W filter, and the spectroscopic sample is statistically complete to Mr-19.0+5log(h), within an 11' field. The clusters are dynamically well-separated from the surrounding field and the velocity dispersions range from ~350-850 km/s. Emission line galaxies in these clusters are relatively rare, comprising only 22 +/- 4% of the sample. There is no evidence that these emission-line galaxies are dynamically distinct from the majority of the cluster population, though our sample is too small to rule out the ~30% difference that has been observed in more massive clusters. We find eleven galaxies, comprising 6% of the cluster members, which are disk-dominated but show no sign of emission in their spectrum. Most of these are relatively isolated, spiral galaxies with smooth disks. We find no cluster members with a starburst or post-starburst spectrum. The striking similarity between the spectral and morphological properties of galaxies in these clusters and those of galaxies in more massive systems at similar redshifts implies that the physical processes responsible for truncating star formation in galaxies are not restricted to the rare, rich cluster environment, but are viable in much more common environments. In particular, we conclude that ram pressure stripping or cluster-induced starbursts cannot be solely responsible for the low star formation rates in these systems.

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arXiv2001

The evolution of the Tully-Fisher relation of spiral galaxies

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 R=23. Spatially resolved rotation curves were derived from spectra obtained with FORS2 at the VLT. High-mass galaxies with v_max>=150 km/s show little evolution, whereas the least massive systems in our sample are brighter by about 1-2 mag compared to their local counterparts. For the entire distant sample, the TFR slope is flatter than for local field galaxies (-5.77+-0.45 versus -7.92+-0.18). Thus, we find evidence for 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 z>=0.2. 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.

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