Day 646

Sunday.

1401.6171
Star formation and substructure in galaxy clusters
Cohen, Hickox, Wegner, Einasto, Vennik

Investigate the relationship between SF and substructure in 107 nearby galaxy clusters from SDSS.  Past studies suggest that cluster mergers enhance cluster SF, while other find no such relationship.  The SF fraction in multi-component clusters (0.228pm0.007) is higher than that in single-component clusters (0.175pm0.016) for galaxies with M_r^0.1<-20.5.  In both single- and multi-component clusters, the fraction of SF galaxies increases with cluster centric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all cluster centric distances and local densities.  Comparing the SF fraction in individual clusters to several statistical measures of substructure, find weak, but in most cases significant at greater than 2 sigma, correlations between substructure and SF fraction.  These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.

1401.6175
The discovery of a radio halo in PLCK G147.3-16.6 at z=0.65
van Weeren et al

Discovery of radio halo signal (centrally-located, extended radio emission) in a binary merging cluster at z=0.65 for an integrated flux density of 7.3pm1.1 mJy at 610 MHz.  More could be discovered with GMRT.  [seems to be the highest z radio halo of cluster detected?]

1401.6180
Effects of the initial conditions on cosmological $N$-body simulations
L'Huillier, Park, Kim

Study the accuracy of N-body sims and their dependence on changes in the ICs and the simulation algorithms.  Test the influence of the ICs (the pre-initial configuration pre-IC), the order of the Lagrangian perturbation theory (LPT), and the initial redshift, on the statistics associated with the LSS of the universe such as the halo mass function, the density PS, and the maximal extent of the LSSs.  Find that glass or gird pre-IC give similar results at z<2; but the initial excess of power in the glass ICs yields a subtle difference in the PS and the mass function at high-z.  The LPT order used to generate the ICs of the simulations is found to play a crucial role.  First-order LPT (1LPT) simulations underestimate the number of massive haloes wrt second-order (2LPT) ones, typically by 2% at 1e14 Msun/h for an initial z of 23, and the small-scale power with an underestimation of 6% near the Nyquist frequency for z_ini=23.  Moreover, at higher z, the high-mass end of the mass function is significantly underestimated in 1LPT simulations.  On the other hand, when the LPT order is fixed, the starting z has a systematic impact on the low-mass end of the halo mass function.

1401.6378
Observations of the most massive deeply embedded star clusters in the Milky Way
Galván-Madrid, Liu

Summarize the comprehensive gas surveys of some of the most luminous, deeply embedded (optically obscured) star formation regions in the MW, which are the local cases of massive star clusters and/or associations in the making.  The approach emphasizes multi-scale, multi-resoluton imaging in dust and free-free continuum, as well as in molecular- and hydrogen recombination lines, to trace the multiple gas components from 0.1 pc (core scale) all the way up to the scales of the entires giant molecular cloud (GMC), or ~100 pc.  Highlight results in W49A, the most luminous Galactic SF region (L~1e7 Lsun), which appears to be forming a young massive cluster (or a binary star cluster) with M*>5e4 Msun that may remain bound after gas dispersal.  The surveyed sources share elements in common---the 10-100 pc scale GMCs are filamentary but have one or two central condensations (clumps) far denser than the surrounding filaments and that host the (forming) massive stars.

1401.6416
Orbital motion effects in astrometric microlensing
Sajadian

In microlensing events, the light centroid shift in the source trajectory (the astrometric trajectory) falls off much more slowly than the light amplification as the source distance from the lens position increases.  As a result, perturbations developed with time such as lens orbital motion can make considerable deviations in astrometric trajectories.  The rotation of the source trajectory due to lens orbital motion produces a more detectable astrometric deviation because the astrometric cross-section is much larger than the photometric one.  Among binary microlensing events with detectable astrometric trajectories, those with stellar-mass BHs have most likely detectable astrometric signatures of orbital motion.  Detecting lens orbital motion in their astrometric trajectories helps to discover further secondary components around the primary even without any photometric binary signatures as well as resolve close/wide degeneracy.  For these binary microlensing events, evaluate the efficiency of detecting orbital motion in astrometric trajectories and photometric light curves by performing MC simulation.  Conclude that astrometric efficiency is 87.3% whereas the photometric efficiency is 48.2%.