This is the astro-ph blog of the Theoretical Modelling of Cosmic Structures group (TMoX) at the Max-Planck-Institute for Extraterrestrial Physics. We are an independent Max-Planck Research Group focusing on the various aspects in the formation and evolution of galaxies. Part of our focus is on the formation and evolution of early-type galaxies, super-massive black holes, the formation of the first structures in the universe and the enrichment history of the Universe. We are theoreticians using analytic modelling as well as numerical simulations in our work.

The CosmologyCake blog is dedicated to the discussion of research papers and current developments. We will regularly post interesting papers and comment on them. Feel free to leave your comments as well. We encourage authors of discussed papers to post replies if they wish to. Our aim is to provide a platform to discuss recent astro-ph papers within a wider audience. Please feel free to send papers you would like to be discussed to us at

27 September 2010

Transformations in the Fall: The Birth of the Early-Type Galaxies

The authors discuss in their paper (Feldmann et al. 2010; arXiv:1008.3386a recent high resolution cosmological hydro simulation of the formation of a galaxy group environment. The remarkable feature of their simulation is to be able to resolve the detailed formation history of individual group members with high mass resolution (SPH particle mass = 1E6 M_sun). Their main conclusion is that elliptical galaxies form by major mergers before the assembly of the group, and that gas cooling and associated star formation is strongly suppressed via ram-pressure stripping once galaxies enter the group environment.

17 September 2010

On the star formation rates in molecular clouds

Authors: C. Lada, M. Lombardo, J. Alveshttp;

The authors study the correlations between SFR and cloud mass in a sample of 8 molecular cloud complexes (11 clouds). They find that only the mass in the cores of the cloud is tightly linked to the SFR.
Total cloud mass and SFR do not correlate well, with variations which are considerable (more than one order of magnitude in scatter). Instead, the correlation between high-density mass (which is roughly 10 per cent the total one for almost all the objects in the sample) and SFR is linear and quite tight (with a scatter of about 2-3).
The only concern is the following: if the correlation between high-density mass and SFR is so tight, and if the high-density mass is roughly 10 per cent the total one, why is the correlation between total mass and SFR so bad?...

10 September 2010

Galaxy and Mass Assembly (GAMA): Dust obscuration in galaxies and their recent star formation histories

Authors: D. B. Wijesinghe, A. M. Hopkins et al.
Link to article: arXiv:1009.0616v1

Star formation rates derived through pan-spectral analysis of a sample of ~ 30.000 galaxies drawn from the Galaxy and Mass Assembly (GAMA) survey. In order to get the SFR in different bands (by means of linear scaling factors derived from population synthesis models), dust obscuration corrections are applied to the Hα, [OII] and UV luminosities by using a range of extinction laws drawn from the literature. 
The results of this study clearly show that the fine-tuned Fischera & Dopita (2005) obscuration curve (Rv = 4.5) give the best agreement when comparing the different corrected SFR indicators. One interesting finding of the paper is that the 2200 Å feature present in the obscuration curves of the Milky way, has to be removed in order to obtain complete consistency between all SFR indicators suggesting that this feature may not be common in the average integrated attenuation of galaxy emission.
The last part of this paper attempt to give constraints on the star formation history of local Universe galaxies by comparing the corrected data with the predictions of evolutionary synthesis models. The evolutionary paths are computed by assuming an exponentially decaying SFR and give the best fit to the data by using a Baldry & Glazebrook (2003) IMF with a characteristic SFR decay of 90 Myrs, which correspond to stellar population ages of the galaxies ranging from 200 to 500 Myrs.