Friday, 30 May 2008

Radio jet duty cycles in nearby galaxies

from Shabala et al., arXiv:0805.4152

This figure shows the fractile distribution of radio source ages in four different stellar mass bins. There appears to be a strong trend whereby more massive galaxies host older radio sources, suggesting that the "on phase" of radio activity lasts longer for these galaxies. The on-time and the gas cooling rate show the same dependence on stellar mass, suggesting that the two are probably linked (i.e. the availability of fuel governs whether an AGN is on or off). Elsewhere in the paper the authors argue that higher-mass galaxies also exhibit more powerful and frequent radio jets. If true, this may be further evidence for a link between radio AGN and the shutdown of star formation.

Friday, 23 May 2008

Galaxy Size Problem at z=3: Simulated Galaxies Are Too Small

( by M.K. Ryan Joung (Princeton), Renyue Cen (Princeton), Greg Bryan (Columbia))

The authors run zoom simulations and find the simulated galaxies are too small to match the observations after corrections (blue line, bottom panel). I suspect that their feedback isn't strong enough to disrupt the inner star formation though.