arXiv subjects

Stefan Noll

Publications and source records attributed to Stefan Noll.

25 records · Page 2Linked to original sources

arXiv2009

Frequency and properties of bars in cluster and field galaxies at intermediate redshifts

We present a study of large-scale bars in field and cluster environments out to redshifts of ~0.8 using a final sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. We characterize bars and their host galaxies and look for relations between the presence of a bar and the properties of the underlying disk. We investigate whether the fraction and properties of bars in clusters are different from their counterparts in the field. The total optical bar fraction in the redshift range z=0.4-0.8 (median z=0.60), averaged over the entire sample, is 25% (20% for strong bars). For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. We find that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher (~31%) than at larger distances (~18%). These findings however rely on a relatively small subsample and might be affected by small number statistics. In agreement with local studies, we find that disk-dominated galaxies have a higher optical bar fraction (~45%) than bulge-dominated galaxies (~15%). This result is based on Hubble types and effective radii and does not change with redshift. The latter finding implies that bar formation or dissolution is strongly connected to the emergence of the morphological structure of a disk and is typically accompanied by a transition in the Hubble type. (abridged)

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arXiv2008

The environments of starburst and post-starburst galaxies at z=0.4-0.8

Post-starburst (E+A or k+a) spectra, characterized by their exceptionally strong Balmer lines in absorption and the lack of emission lines, belong to galaxies in which the star formation activity ended abruptly sometime during the past Gyr. We perform a spectral analysis of galaxies in clusters, groups, poor groups and the field at z=0.4-0.8 based on the ESO Distant Cluster Survey. The incidence of k+a's at these redshifts depends strongly on environment. K+a's reside preferentially in clusters and, unexpectedly, in a subset of the sigma = 200-400 km/s groups, those that have a low fraction of [OII] emitters. In these environments, 20-30% of the recently star-forming galaxies have had their star formation activity recently truncated. In contrast, there are proportionally fewer k+a's in the field, the poor groups and groups with a high [OII] fraction. The incidence of k+a galaxies correlates with the cluster velocity dispersion: more massive clusters have higher proportions of k+a's. Spectra of dusty starburst candidates, with strong Balmer absorption and emission lines, present a very different environmental dependence from k+a's. They are numerous in all environments at z=0.4-0.8, but they are especially numerous in all types of groups, favoring the hypothesis of triggering by a merger. Our observations are consistent with previous suggestions that cluster k+a galaxies are observed in a transition phase as massive S0 and Sa galaxies, evolving from star-forming later types to passively evolving early-type galaxies. The correlation between k+a fraction and cluster sigma supports the hypothesis that k+a galaxies in clusters originate from processes related to the intracluster medium, while several possibilities are discussed for the origin of the k+a frequency in low-[OII] groups.(abr.)

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arXiv2008

The relation between star formation, morphology and local density in high redshift clusters and groups

We investigate how the [OII] properties and the morphologies of galaxies in clusters and groups at z=0.4-0.8 depend on projected local galaxy density, and compare with the field at similar redshifts and clusters at low-z. In both nearby and distant clusters, higher-density regions contain proportionally fewer star-forming galaxies, and the average [OII] equivalent width of star-forming galaxies is independent of local density. However, in distant clusters the average current star formation rate (SFR) in star-forming galaxies seems to peak at densities ~15-40 galaxies Mpc^{-2}. At odds with low-z results, at high-z the relation between star-forming fraction and local density varies from high- to low-mass clusters. Overall, our results suggest that at high-z the current star formation (SF) activity in star-forming galaxies does not depend strongly on global or local environment, though the possible SFR peak seems at odds with this conclusion. We find that the cluster SFR normalized by cluster mass anticorrelates with mass and correlates with the star-forming fraction. These trends can be understood given a) that the average star-forming galaxy forms about 1 Msun/yr in all clusters; b) that the total number of galaxies scales with cluster mass and c) the dependence of star-forming fraction on cluster mass. We present the morphology-density (MD) relation for our z=0.4-0.8 clusters, and uncover that the decline of the spiral fraction with density is entirely driven by galaxies of types Sc or later. For galaxies of a given Hubble type, we see no evidence that SF properties depend on local environment. In contrast with recent findings at low-z, in our distant clusters the SF-density relation and the MD-relation are equivalent, suggesting that neither of the two is more fundamental than the other.(abr.)

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arXiv2008

Spectroscopy of clusters in the ESO distant cluster survey (EDisCS).II. Redshifts, velocity dispersions, and substructure for clusters in the last 15 fields

AIMS. We present spectroscopic observations of galaxies in 15 survey fields as part of the ESO Distant Cluster Survey (EDisCS). We determine the redshifts and velocity dispersions of the galaxy clusters located in these fields, and we test for possible substructure in the clusters. METHODS. We obtained multi-object mask spectroscopy using the FORS2 instrument at the VLT. We reduced the data with particular attention to the sky subtraction. We implemented the method of Kelson for performing sky subtraction prior to any rebinning/interpolation of the data. From the measured galaxy redshifts, we determine cluster velocity dispersions using the biweight estimator and test for possible substructure in the clusters using the Dressler-Shectman test. RESULTS. The method of subtracting the sky prior to any rebinning/interpolation of the data delivers photon-noise-limited results, whereas the traditional method of subtracting the sky after the data have been rebinned/interpolated results in substantially larger noise for spectra from tilted slits. Redshifts for individual galaxies are presented and redshifts and velocity dispersions are presented for 21 galaxy clusters. For the 9 clusters with at least 20 spectroscopically confirmed members, we present the statistical significance of the presence of substructure obtained from the Dressler-Shectman test, and substructure is detected in two of the clusters. CONCLUSIONS. Together with data from our previous paper, spectroscopy and spectroscopic velocity dispersions are now available for 26 EDisCS clusters with redshifts in the range 0.40-0.96 and velocity dispersions in the range 166-1080 km/s.

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arXiv2006

The Evolution of Galaxy Dust Properties for 1<z<2.5

Fundamental properties of the extinction curve, like the slope in the rest-frame UV and the presence/absence of a broad absorption excess centred at 2175A (the UV bump), are investigated for a sample of 108 massive, star-forming galaxies at 1<z<2.5, selected from the FDF Spectroscopic Survey, the K20 survey, and the GDDS. These characteristics are constrained from a parametric description of the UV spectral energy distribution of a galaxy. It turns out that the sample galaxies host dust producing extinction curves with properties in between those of the Small and Large Magellanic Clouds (SMC and LMC, respectively). LMC-like extinction curves, which exhibit a UV bump, are mainly found among highly-reddened, UV-ultraluminous galaxies at z~2.4 and highly-reddened, near-IR-bright, star-forming galaxies at z~1.2. We discuss star-formation rates, total stellar masses, the morphology, and the chemical properties of our sample galaxies with respect to possible explanations for the different extinction curves.

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arXiv2003

The metal absorption systems of the QSO 0103-260 and the galaxy redshift distribution in the FORS Deep Field

Using the Uves echelle spectrograph at the ESO VLT, we observed the absorption line spectrum of the QSO 0103-260 in the Fors Deep Field. In addition to the expected Ly-alpha forest lines, we detected at least 16 metal absorption systems with highly different ionization levels in the observed spectral range. The redshifts of the metal absorption systems are strongly correlated with the redshift distribution of the high-z galaxies in the Fors Deep Field and with the strength (but not the number density) of the Ly-alpha forest lines. Both the metal systems and the galaxies show clustering at least up to the QSO emission line redshift of 3.365, but only few of these galaxy accumulations seem to form bound systems.

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arXiv2001

The Stellar Population of High Redshift Galaxies

Using the VLT we have obtained high quality spectra of about 70 high redshift (1- 4.6) galaxies within the FORS Deep Field (FDF). As expected most of them turn out to be (bright) starburst galaxies and the observed spectra agree with synthetic ones. The equivalent width of the CIV(1550) absorption line turns out to be a good indicator for the galaxies metallicity. Furthermore our high-z starburst galaxies show increasing metal content with decreasing redshift. Compared with local starburst galaxies they tend to be overliminous for their metallicity.

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