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 tmoxgroup@googlemail.com.

8 November 2010

The first galaxies: assembly of disks and prospects for direct detection

Authors: A. Pawlik, M. Milosavljevic and V. Bromm
Link to the paper: arXiv:1011.0438

The authors study the formation of a galaxy embedded in a 109 solar masses halo at redshift z=10. Galaxies of this mass should be possible to observe with the James Webb Space Telescope (JWST).

The authors do not include star formation and feedback, but concentrate on the formation history of the galaxy in the presence of primordial and molecular cooling. The first result is that the galaxy for a gas disk with and without the inclusion of molecular cooling. Indeed, molecular cooling seems to act only on the thickness and fragmentation of the disk, but not on its assembly and gas content. This is one of the first simulations showing that such a halo can host a disk.

The second result is that a simple modeling of the star formation history of the galaxy gives estimates of its detectability with JWST. The authors predict that JWST could distinguish between normal and top-heavy IMF in the starburts case, and between starburst and continuous star formation. Their model can be rescaled to different values of parameters like, e.g., the escape fraction of photons.

5 November 2010

Jet-powered molecular hydrogen emission from radio galaxies

Authors: P. Ogle et al.
Link to the paper: arXiv:1009.4533

The authors examine a sample of 55 radio galaxies with z < 0.22 and find 31% percent of those to exhibit particularly strong mid-IR emission from warm H2 (T = 100 - 1500 K, with masses in this phase typically around some 108, up to 2 x 1010 solar masses), putting them in a newly (re)defined class of "molecular hydrogen emission galaxies" (MOHEGs). They argue that the jets in these sources may interact with the cold H2 in these galaxies and shock-heat it, resulting in the observed emission. They find that X-rays originating from the AGN are incapable of powering the H2 emission, but that cosmic rays may still be an alternative explanation if a cosmic ray pressure 25 times higher than thermal pressure is deemed to be reasonable.

The radio MOHEGs show only low to moderate star formation rates (< 3 solar masses per year) and much less 7.7 ┬Ám PAH emission then normal star forming galaxies with respect to the mid-IR continuum (a factor of 10 - 100 lower). The H2 luminosity does not show much correlation with radio power, but several sources in clusters with X-ray cavities indicate that the ratio between H2 luminosity and kinetic jet power may lie around 10-4 to some 10-3. Most (14 of 17) radio MOHEGs belong to close galaxy pairs, groups or cluster and the authors conjecture that this environment or past gas-rich mergers may deliver large quantities of gas to the galaxies.

The authors conclude that jet-driven outflows may be responsible for the emission, although the details are yet very unclear. The jet powers, however, would more than sufficient for this.