Day 714

Sunday (Friday).

1407.8178
Velocity anti-correlation of diametrically opposed galaxy satellites in the low redshift universe
Ibata, Ibata, Famaey, Lewis

[covered in Day 708 as Nature paper]

1407.8181
X-ray bright active galactic nuclei in massive galaxy clusters III: New insights into the triggering mechanisms of cluster AGN
Ehlert, Allen, ... Mantz ... von der Linden, et al

Find evidence for evolution in the cluster AGN population beyond the expected evolution of field AGN.  Analysis show that overall number density of cluster AGN scales with the cluster mass as ~M500^-1.2 [less likely to find AGN for more massive clusters].  No evidence for overall number density depending on the cluster redshift in a manner different than field AGN, nor there is any evidence that the spatial distribution of cluster AGN (given in units of the cluster overdensity radius r500) strongly depends on the cluster mass or redshift.  The M^-1.2 scaling relation is consistent with theoretical predictions of the galaxy merger rate in clusters, which is expected to scale with the cluster velocity dispersion sigma as ~sigma^-3 or ~M^-1.  This consistency suggests that AGN in clusters may be predominantly triggered by galaxy mergers, a result that is further corroborated by visual inspection of Hubble images for 23 spectroscopically confirmed cluster member AGN in the sample.  A merger-driven scenario for the triggering of X-ray AGN is not strongly favored by studies of field galaxies, however, suggesting that different mechanisms may be primarily responsible for the triggering of cluster and field X-ray AGN.

1407.8184
Are scalar and tensor deviations related in modified gravity?
Linder

Modified gravity theories on cosmic scales have 3 key deviations from GR.  They can cause cosmic acceleration without a physical, highly negative pressure fluid, can cause a gravitational slip between the two metric potentials, and can cause gravitational waves to propagate differently, e.g., with a speed different from the speed of light.  Examine whether the deviations in the metric potentials as observable through modified Poisson equations for scalar density perturbations are related to or independent from deviations in the tensor gravitational waves.  Show analytically that they are independent instantaneously in covariant Galileon gravity -- e.g. at some time one of them can have the general relativity value while the other deviates -- through related globally -- if one deviates over a finite period, the other at some point shows a deviation.  Present expressions for the early time and late time de Sitter limits, and numerically illustrate their full evolution.  This in(ter)dependence of the scalar and sensor deviations highlights complementarity between cosmic structure surveys and future gravitational wave measurements.

1407.8279
A new method of CCD dark current correction via ext rating the dark information from scientific images
Ma, Shang, Hu, Liu, Wang, Wei

As the title says.  [Their observations did not allow them to obtain dark frames.  Method description not in abstract.  Uses image pairs to estimate the spatial variation in the dark current.]