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.

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 µm 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.