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 February 2012

The clustering of galaxies as a function of their photometrically-estimated atomic gas content

Authors: Li, C., et al.

The paper (link) introduces a new estimate for the mass of HI gas, based on a few photometric quantities: stellar mass, color, surface density, and color gradient. This mass estimate is then being applied to a large sample from SDSS, to study the clustering dependence on the HI fraction. The results are compared to recent SAMs from the Munich group, showing that the models disagree with the observations mostly at low stellar masses.

24 February 2012

The origin of disks and spheroids in simulated galaxies.

Sales et al. 2011 (MNRAS Submitted)

In this paper (link) the authors review the possible mechanisms to form disks in simulated galaxies and argue that the main mechanism responsible for disk formation is hot cooling gas. This is against previous works who found cold streams to be responsible for disk formation.

The effect of intergalactic helium on hydrogen reionisation: implications for the sources of ionising photons at z > 6

This paper (link) improves on existing reionisation simulations in two ways: by including helium in the radiative transfer simulations that are done in post-processing and by modeling the ionising emissivities in such a way that they are consistent with the observational constraints on the Thomson scattering optical depth and hydrogen photo-ionisation rate at z<6. The evolution of the volume fraction of ionised hydrogen is not significantly impacted by the inclusion of helium (and is in fact reproduced very well with a simple semi-analytic model), except for a small delay in reionisation when helium is included. The impact of helium on the temperature evolution is larger: at lower redshifts the volume averaged temperature of the IGM is higher. Comparing the simulation results with measurements of the IGM temperature shows that reionisation is mainly driven by sources with a soft spectrum. Contribution from mini-quasars or Pop III stars has to be small at redshifts 6 < z < 9. A significant number of ionising photons is produced by faint, low-mass galaxies.

MaGICC Disks: Matching Observed Galaxy Relationships Over a Wide Stellar Mass Range

In this paper (link) the authors demonstrate that using their feedback model (note this is just stellar feedback : supernovae + heating from massive stars) in cosmological zoom simulations results in galaxies that match observed relations between a wide range of properties. A key aspect of this result is that the simulations also reproduce the way these relations scale with stellar mass, suggesting that their feedback model has a realistic efficiency over 2 orders of magnitude in stellar mass. The authors claim that it is the amount of outflow they get in their models that allows them to get the correct mass dependence. They also show that this level of outflow is supported by OVI absorption line observations (which can indicate the radial extent of metal rich gas that has been ejected from a galaxy).

Growth of early SMBH and high redshift Eddington Ratio Distributions

This paper (link) uses a cosmological hydro simulation to explore the Edd. Ratios (ER) of the black holes that they seed in their simulation. A BH of mass 10^5 SM is seeded in haloes over 10^10 SM. They allow for Bondi-Hoyle Accretion with a modified parameter for the gas density close to the BH and compare it with Edd. Accretion to get the ERs. Various feedback effects are accounted for and they also plot the ER carefully so as to avoid any inherent trends. They find that the ER depends mostly on the the density of the gas being accreted.

They fit a universal log-normal distribution to the Edd. Ratio and compare it with observations. The Edd. Ratios they find are mostly < 1 implying sub-Eddnington accretion for the massive BH seeds in their work.