Day 763

Tuesday.

1410.2768
Origins of massive field stars in the galactic center: a spectroscopic study
Dong et al

A large number of evolved massive stars have been detected in the Galactic Center, outside the known star clusters; but their origins remain uncertain.  Present a spectroscopic study of eight such stars, based on new Gemini GNIRS and NIFS NIR observations.  This work has led to the discovery of a new O If+ star.  Compare the reddening-corrected J-K vs K diagram for the stars with the massive ones in the Arches cluster and use stellar evolutionary tracks to constrain their ages and masses. The radial velocities of both the stars and their nearby H II regions are also reported.  All of the stars are blue shifted relative to the Arches cluster by > 50 km/s.  Find that the source P35 has a velocity consistent with that of the surrounding molecular gas.  The velocity gradient of nearby ionized gas along the Gemini GNIRS long slit, relative to P35 and the adjacent -30-0 km/s molecular cloud, can best be explained by a pressure-driven flow model.  Thus, P35 most likely formed in situ.  3 more of the stars have radial velocities different from their adjacent molecular gas, indicating that they are interlopers.  The 4 stars closest to the Arches cluster have similar spectra, ages and masses to known cluster members, suggesting that they were likely ejected from the cluster via 3-body interactions.  Therefore, find that the relatively isolated stars partly formed in situ and partly were ejected from the known star clusters in the Galactic Center.

1410.2898
MC^2: Constraining the dark matter distribution of the violent merging galaxy cluster CIZA J2242.8+5301 by piercing through the Milky Way
Jee, ... Wittman, Hoekstra, ... et al

A merging system with a prominent (~2 Mpc long) radio relic, which together with the morphology of the X-ray emission provides strong evidence for a violent collision along the N-S axis.  Present constraints on the DM distribution of this unusual system using Subaru and CFHT imaging data.  Measuring a high S/N lensing signal from this cluster is potentially a challenging task because of its proximity to the MW plane (|b|~5 deg).  Overcome this challenge with careful observation planning and systematics control, which enables mapping the DM distribution of the cluster with high fidelity.  The resulting mass map shows that the mass distribution is highly elongated along the N-S merger axis inferred from the orientation of the radio relics.  Based on the mass reconstruction, identify 2 sub-clusters, which coincide with the cluster galaxy distributions.  Determine their masses using MCMC analysis by fitting 2 NFW haloes without fixing their centroids.  M200=11e14 Msun and 9.8e14 Msun, respectively, indicating a post-collision of 2 giant systems of nearly equal mass.  When the mass and galaxy centroids are compared in detail, detect ~1' (~190 kpc) offsets in both N and S sub-clusters.  Find that the galaxy luminosity-mass offset for the N clump is statistically signifiant at the 2 sigma level, whereas the detection is only marginal for the S sub-cluster in part because of a relatively large mass centroid error.  Conclude that it is yet premature to uniquely attribute the galaxy-mass misalignment to SIDM and discuss caveats.

1410.3266
Prospect for UV observations from the Moon
Safonova et al

Indian entry to the Google Lunar X PRIZE competition, "Team Indus" mission, expected to deliver ~30 kg of payloads to the Moon, with a rover as its primary payload.  Propose to mount a wide-field FUV (130-180 nm) imaging telescope as a payload on the Team Indus lander.  Fixed zenith pointing but with the option of a mechanism to allow observations of different attitudes.  Pointing towards intermediate ecliptic latitude (50 deg or above) ensures that the Sun is at least 40 deg off the line of sight at all times.  In this position, the telescope can cover higher galactic latitudes as well as parts of Galactic plane.  
1410.3282
How well can cold-dark-matter substructures account for the observed radio flux-ratio anomalies?
Xu, Sluse, Gao, Wang, Frenk, Mao, Schneider, Springel

Construct samples of generalized and specific lens potentials, to which add (rescaled) sub halo populations from the galaxy-scale Aquarius and the cluster-scale Phoenix simulation suites.  Further investigate the lensing effects from sub haloes of masses several orders of magnitude below the simulation resolution limit.  The resulting flux ratio distributions are compared to the currently best available sample of radio lenses.  The observed anomalies in 3 specific samples are more likely to be caused by propagation effects or oversimplified lens modeling, singes of which are already seen in the data.  Among the quadruple systems that have closely located image triplets/pairs, the anomalous flux ratios of MG0414+0534 can be reproduced by adding CDM sub haloes to its macroscopic lens potential, with a probability of 5-20%, for the 4 systems, these probabilities are only a few percent.  Hence find that CDM substructures are unlikely to be the whole reason for radio flux anomalies.  Discuss other possible effects that might also be at work.