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Bohm A.,Institute of Astro and Particle Physics | Ziegler B.L.,University of Vienna
Astrophysics and Space Science Proceedings | Year: 2011

We have constructed a data set of >250 field disk galaxies at redshifts 0:1 < z < 1:0 with Very Large Telescope (VLT) spectroscopy and Hubble Space Telescope imaging. This is one of the largest kinematical samples of distant disks to date. We use spatially resolved rotation curves to derive maximum rotation velocities and total masses; we also investigate disk sizes, bulge-to-disk ratios, stellar population properties etc. The stellar-to-total-mass ratios are constant over the probed cosmic epoch, which favors a hierarchical buildup of the dark matter halos the disks reside in. On the other hand, the mean stellar mass-to-light ratios evolve more strongly in the low-mass galaxies than in high-mass galaxies and the mean stellar ages are lower for low-mass galaxies than for high-mass galaxies. This points to an anti-hierarchical evolution of the stellar populations (aka " downsizing"). © Springer-Verlag Berlin Heidelberg 2011.

Bissaldi E.,Max Planck Institute for Extraterrestrial Physics | Bissaldi E.,Institute of Astro and Particle Physics
Nuovo Cimento della Societa Italiana di Fisica C | Year: 2011

In the first two years since the launch of the Fermi Observatory, the Gamma-ray Burst Monitor (GBM) has detected over 500 Gamma-Ray Bursts (GRBs), of which 18 were confidently detected by the Large Area Telescope (LAT) above 100 MeV. Besides GRBs, GBM has triggered on other transient sources, such as Soft Gamma Repeaters (SGRs), Terrestrial Gamma-ray Flashes (TGFs) and solar flares. Here we present the science highlights of the GBM observations. © Società Italiana di Fisica.

Ferreras I.,University College London | Bohm A.,Institute of Astro and Particle Physics | Ziegler B.,University of Vienna | Silk J.,University Pierre and Marie Curie
Monthly Notices of the Royal Astronomical Society | Year: 2013

We analyse the Tully-Fisher relation at moderate redshift from the point of view of the underlying stellar populations, by comparing optical and NIR photometry with a phenomenological model that combines population synthesis with a simple prescription for chemical enrichment. The sample comprises 108 late-type galaxies extracted from the FORS Deep Field and William Herschel Deep Field surveys at z ≲ 1 (median redshift z = 0.45). A correlation is found between stellar mass and the parameters that describe the star formation history, with massive galaxies forming their populations early (zFOR ~ 3), with star formation timescales, τ1 ~ 4 Gyr, although with very efficient chemical enrichment time-scales (τ2 ~ 1Gyr). In contrast, the stellar-to-dynamical mass ratio - which, in principle, would track the efficiency of feedback in the baryonic processes driving galaxy formation - does not appear to correlate with the model parameters. On the Tully-Fisher plane, no significant age segregation is found at fixed circular speed, whereas at fixed stellar-to-dynamical mass fraction, age splits the sample, with older galaxies having faster circular speeds at fixed Ms/Mdyn. Although our model does not introduce any prior constraint on dust reddening, we obtain a strong correlation between colour excess and stellar mass. © 2013 The Authors.

Tonini C.,Swinburne University of Technology | Tonini C.,University of Portsmouth | Maraston C.,University of Portsmouth | Ziegler B.,ESO | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We use the semi-analytic model GalICS to predict the Tully-Fisher relation in the B, I and K bands, and its evolution with redshift, up to z~ 1. We refined the determination of the disc galaxies rotation velocity, with a dynamical recipe for the rotation curve, rather than a simple conversion from the total mass to maximum velocity. The new recipe takes into account the disc shape factor, and the angular momentum transfer occurring during secular evolution leading to the formation of bulges. This produces model rotation velocities that are lower by ~30 kms-1 in case of Milky Way like objects, and ≤20-30 kms-1 for the majority of the spirals, amounting to an average effect of ~20-25 per cent. We implemented stellar population models with a complete treatment of the thermally pulsing asymptotic giant branch, which leads to a revision of the mass-to-light ratio in the near-IR. Due to this effect, K-band luminosities increase by ~0.5 at redshift z= 0 and by >1 at z= 3, while in the I band at the same redshifts the increase amounts to ~0.3 and ~0.5 mag. With these two new recipes in place, the comparison between the predicted Tully-Fisher relation with a series of data sets in the optical and near-infrared, at redshifts between 0 and 1, is used as a diagnostics of the assembly and evolution of spiral galaxies in the model. At redshifts 0.4 < z < 1.2 the match between the new model and data is remarkably good, especially for later-type spirals (Sb/Sc). At z= 0 the new model shows a net improvement in comparison with its original version of 2003, and in accordance with recent observations in the K band, the model Tully-Fisher also shows a morphological differentiation. However, in all bands the z= 0 model Tully-Fisher is too bright. We argue that this behaviour is caused by inadequate star formation histories in the model galaxies at low redshifts. The star formation rate declines too slowly, due to continuous gas infall that is not efficiently suppressed. An analysis of the model disc scalelengths, at odds with observations, hints to some missing physics in the modelling of disc formation inside dark matter haloes. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Lovisari L.,Institute of Astro and Particle Physics | Schindler S.,Institute of Astro and Particle Physics | Kapferer W.,Institute of Astro and Particle Physics
Acta Polytechnica | Year: 2011

The hot gas that fills the space between galaxies in clusters is rich in metals. Due to their large potential well, galaxy clusters accumulate metals over the whole history of the cluster, and retain important information on cluster formation and evolution. We derive detailed metallicity maps for a sample of 5 clusters, observed with XMM-Newton, to study the distribution of metals in the Intra-Cluster Medium (ICM). We show that even in relaxed clusters the distribution of metals shows many inhomogeneities with several maxima separated by low metallicity regions. We also found a deviation from the expected temperature-metallicity relation.

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