Day 812

Thursday.

1410.5423
Glow in the dark matter: observing galactic haloes with scattered light
Davis, Silk

Constrain upper limit on the DM-photon cross section using the Dragonfly instrument, by considering the observation of diffuse haloes of light around the disks of spiral galaxies.

1410.5631
Data driven discovery in astrophysics
Longo et al

Describe some of the recent examples of machine learning tool applications on big data.

1501.01306
Understanding the cosmic web
Cautun et al

At early times the cosmic is dominated by tenuous filaments and sheets, which, during subsequent evolution, merge together, such that the present day web is dominated by fewer, but much more massive, structures.  Also show that voids are more naturally described in terms of their boundaries and not their centers.  Illustrate this for void density profiles, which, when expressed as function of the distance from void boundary, show a universal profile in good qualitative agreement with the theoretical shell-crossing framework of expanding underdense regions.

1501.01398
Can we measure galaxy environments with photometric redshifts?
Lai, ... Merson, Baugh, et al

Quantify how the density measured with the nearest neighbor approach is affected by photo-z uncertainties by using the Durham mock catalogs, in which the 3D real-space environments and the properties of galaxies are exactly known.  Furthermore, present an optimization scheme in the choice of parameters used in the 2D projected measurement which yields the tightest correlation with respect to the 3D real-space environments.  By adopting the parameters in the density measurements, show that the correlation between the 2D projected optimized density and real-space density can still be revealed, and the color-density relation is also visible even for a photo-z uncertainty up to sigma[Delta_z/(1+z)] = 0.06.  Find that a deep (i~25) photometric z survey with sigma[Delta_z/(1+z)]=0.02 yields a comparable performance of density measurement to a shallower i~22.5 (24.1) spectroscopic sample with 40%(20%) sampling rate.  Finally, discuss the application of the local density measurements to the Pan-STARRS Medium Deep survey, one of the largest on-going deep imaging surveys.  Using data from ~5deg^2 of survey area, results show that it is possible to measure local density and to probe the color-density relation in the PS-MDS, confirming the simulation results.  The color-density relation, however, quickly degrades for data covering smaller areas.

1501.01487
Tests for the expansion of the Universe
Lopez-Corredoira

Review some independent cosmo tests of the expansion of the universe: CMB temperature vs z, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczy'nski test.  Some tests favor expansion and others favor a static Universe.  Almost all tests are susceptible to the evolution of galaxies and/or other effects.  Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, and evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.