Day 562

Friday.  Saturday.  Sunday, one week behind.

1312.1699
Mergers as triggers for nuclear activity: A near-IR study of the close environment of AGN in the VISTA-VIDEO survey
Karouzos, Jarvis, Bonfield

AGN triggered by major or minor galaxy mergers, or through secular processes like cooling gas accretion and/or formation of bars?  Investigate the close environment of active galaxies selected in the X-ray, the radio, and the mid-IR.  Utilize DR1 of near-IR VISTA Deep Extragalactic Observations (VIDEO) survey of XMM-LSS field.  Use 2 measures of environment density: counts within a given aperture and a finite redshift slice (pseudo-3D density) and closet neighbor density measures Sigma_2 and Sigma_5.  Select both AGN and control samples, matching them in redshift and apparent Ks-band magnitude.  Find that AGN are found in a range of environments, with a subset of the AGN samples residing in over-dense environments.  Seyfert-like X-ray AGN and flat-spectrum radio-AGN are found to inhabit significantly over-dense environments compared to their control sample.  The relation between over-densities and AGN luminosity does not however reveal any positive correlation.  

1312.1700
The pressure of the star forming ISM in cosmological simulations
Munshi, et al

Examine the pressure of SF ISM of MW-sized disk galaxies using fully cosmological SPH+N-body, high resolution simulations.  These simulations include explicit treatment of metal-line cooling in addition to dust and self-sheilding, H2 based SF.  The 4 simulated haloes have masses ranging from a few times 1e10 to nearly 1e12 Msun.  Using a kinematic decomposition of these galaxies into present-day bulge and disk components, find that the typical pressure of the SF ISM in the present-day bulge is higher than that in the present-day disk by an order of magnitude [because SF has ceased in the bulge?].  Also find that pressure of the SF ISM at high z is on average higher than ISM pressures at low z [more SF at higher z, usually z~2-3; the universe should have 3-4x higher density around here!].  This explains why the bulge forms at higher pressures: the disk assembles at lower redshift, when the ISM is lower pressure and the bulge forms at high z, when the ISM is at higher pressure.  If ISM pressure and IMF variation are tied together as suggested in studies like Conroy 2012, these results could indicate a time-dependent IMF in MW-like systems, as well as a different IMF in the bulge and the disk.