Day 528

Monday.

1310.2938
Ancient light from young cosmic cities: physical and observational signatures of galaxy proto-clusters
Chiang, Overzier, Gebhardt

Perform systematic study of cluster formation utilizing cosmological simulations.  Use the Millennium Sims to track the evolution of DM and galaxies in 3k clusters from the earliest times to z=0.  Define an effective radius R_e for proto-clusters and characterize their growth in size and mass.  Show that the progenitor regions of galaxy clusters (M>1e14 Msun/h) can already be identified at least up to z~5, provided that the galaxy overdensities, delta_gal, are measured on a sufficiently large scale (Re~5-10 cMpc).  Present the overdensities in matter, DM haloes, and galaxies as functions of present-day cluster mass, redshift, bias and window size that can be used to interpret the structures found in real surveys.  Derive the probability that a structure having a delta_gal, defined by a set of observational selection criteria, is indeed a proto-cluster, and show how their z=0 masses can already be estimated log before virialization.  Galaxy overdensity profiles as a function of radius are presented.  Further show how their projected surface overdensities decrease as the uncertainties in redshift measurements increase.  Provide a table of proto-cluster candidates selected from the literature, and discuss their properties in the light of the simulations predictions.  This work provides the general framework that will allow us to extend the study of cluster formation out to much higher redshifts using the large number of proto-clusters that are expected to be discovered in, e.g., the upcoming HETDEX and HSC surveys.  

1310.2941
Galaxy Zoo: observing secular evolution through bars
Cheung et al

13k disk galaxies, 23.6pm0.4% bar fraction, with 1k barred galaxies having bar length measurements.  Characterize bars by the bar likelihood, the likelihood a bar is present in a given galaxy, and the bar length.  These two bar properties show correlations with the sSFR and the inner central structure of galaxies.  Comparing these observations to state-of-the-art simulations of bar evolution, which include live haloes and the effects of gas and star formation, reveals that these trends are consistent with the predicted effects of gas content and bulges on bar formation and evolution.  These results represent empirical evidence for secular evolution driven by bars in disk galaxies.  This work suggest that bars are critical evolutionary driver of their host galaxies in the local universe (z<1).  

1310.2951
The Matryoshka run: Eulerian refinement strategy to study statistics of turbulence in virialized cosmic structures
Miniati

Study the statistical properties of turbulence driven by structure formation in a massive merging galaxy cluster at redshift z=0.  Turbulence develops as the largest eddy turnover time is much shorter than the Hubble time independent of mass and redshift.  To achieve a sufficiently large dynamic range of spatial scales, employ a novel Eulerian refinement strategy where the cluster volume is refined with progressively finer uniform nested grids during gravitational collapse.  This provides an unprecedented resolution of 7.3 kpc/h across the virial volume.  The probability density function of various velocity derived quantities exhibit the same features characteristic of fully developed compressible turbulence as observed in dedicated periodic-box simulations.  Apply Hodge-Helmholtz decomposition to the velocity field and compute second and third order, longitudinal and transverse, structure functions for both solenoidal and compressional components, in the cluster core, virial region and beyond.  In general, the structure functions exhibit a well defined inertial range of turbulent cascade.  The injection scale is comparable to the virial radius but increases towards the outskirts.  In the inner Rvir/3, the spectral slope of the solenoidal component is close to Kolmogorov's but for the compressional component is substantially steeper and close to Burgers'.  In addition, the flow is mostly solenoidal and statistically rigorously consistent with fully developed, homogeneous and isotropic turbulence.  Small scale anisotropy appears due to numerical artifact.  Towards the virial region, however, the flow becomes increasingly compressional, the structure functions flatter and modest genuine anisotropy appears particularly close to the injection scale.