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

30 August 2010

Evolution of Galaxy Stellar Mass Functions, Mass Densities, and Mass to Light ratio from z~7 to z~4

Authors: Gonzalez, Labbé, Bouwens, Illingworth, Franx, Kriek
Link to article: arXiv:1008.3901v1

This paper address a very important question about the built-up and evolution of galaxies at high redshift, by deriving stellar masses from SED fitting for ~400 LBG observed with Hubble-WFC3/IR and Spitzer-IRAC in the GOODS South field. Using Bruzual & Charlot models with a Salpeter IMf, masses are obtained assuming a constant Star Formation History for galaxies. 

By fitting the Mass vs Luminosity relation at z~4 - with a slope that makes the M/L ratio increase with luminosity - and finding no clear evidence for evolution with redshift, this work use the UV Luminosity Functions of Bouwens et al. (2007-2010) and Monte-Carlo simulations to derive Mass Functions (MF) at z~4,5,6,7. The results show a significant difference with theoretical expectations from numerical simulations, and especially a much more flatter faint end slope. 

The last part of this paper show a comparison of the stellar mass growth computed by 2 different approaches: a quite large disagreement is found between the integration of the SFR density over time [SFRD ~ (1+z)^-6.3] compared with the integration of MF for the 4 bins of redshift [SMD ~ (1+z)^-2.8]. The authors propose that dust extinction overestimates, low duty cycle for SF or shortcomings in the modeling of faint galaxies may explain this noticeable difference.

27 August 2010

Predicted UV properties of very metal-poor starbursts

Authors:  Raiter, Schaerer, Fosbury
Link to article: arXiv:1008.2114

The properties of the rest-frame UV emission from low-metallicity starbursts are studyied in detail, with the aim of providing a basis for the interpretation of observations of high redshift galaxies in which zero or low-metallicity stars are forming.  A number of important effects are included, which were not accounted for in the earlier work of Schaerer (2002) on the emission properties of low-metallicity galaxies.  Among these are that the nebular line emission can be enhanced appreciably when particularly massive, hot stars are illuminating the gas within the galaxy.  The authors also pay particular attention to the impact that 2-photon emission can have on the equivalent widths of emission lines, especially Ly_alpha and He II 1640.  

20 August 2010

A relationship between AGN jet power and radio power

Authors: Cavagnolo, McNamara, Nulsen, Carilli, Jones & Birzan
Link to article: arxiv:1006.5699

The powerlaw scaling relation between jet power (derived from X-ray cavities) and radio power by Birzan et al. (2008) for clusters is extended to giant ellipticals. A powerlaw scaling is found over 6 orders of magnitude in jet power and it is found consistent with the relations of Willott et al. (1999) if the energy in non-radiating particles is about 100 times larger than in synchrotron-emitting electrons (ranging between tens to thousands). The scatter for the relation still is considerable - more than 1 dex wide for 68% confidence. The authors furthermore discuss the behaviour of poorly confined sources, which are not included in the fits.

13 August 2010

Accretion Disks in Active Galactic Nuclei: Gas Supply Driven by Star Formation

Authors: Wang, Yan, Gao, Hu, Li & Zhang
Link to article: arXiv:1007.4060

An analytic model of star formation and gas accretion in the inner ~1pc region surrounding a black hole powering an AGN is presented.  Turbulence generated by supernovae is taken to be responsible for the transport of angular momentum that allows gas to accrete onto the central black hole via a Shakura-Sunyaev accretion disk, which resides between the star forming region and the black hole.  In this model, the black hole accretion rate varies as the star formation rate to the power ~5/7.  The authors further discuss how this model can explain the observed metallicity-luminosity relation of AGN and the formation of nuclear star clusters.