Day 697

Friday.

1407.2610
The most distant stars in the Milky Way
Bochanski, Willman, et al

Two stars, selected as M giant candidates based on their IR and optical colors and lack of proper motion, located at 274pm74 kpc and 238pm64 kpc.  Spectroscopically confirmed as outer halo giants.  First MW stars discovered beyond 200 kpc.  Both moving away from the Galactic center at 52pm10 and 24pm10 km/s.  Possible origins: tidal stripping from a dwarf galaxy, ejection from the MW's disk, membership in an undetected dwarf galaxy.  These M giants, along with two inner halo giants that were also confirmed during the campaign, are the first to map largely unexplored regions of the MW's outer halo.

1407.2612
The vast polar structure of the Milky Way attains new members
Pawlowski, Kroupa

The satellite galaxies of the MW align with and preferentially orbit in a VPOS, which also contains globular clusters, stellar and gaseous streams.  Similar alignments discovered around several other host galaxies.  Test whether recently discovered objects in the MW halo, the satellite galaxy/globular cluster transition object Crater and three stellar streams, are part of VPOS.  Predict Crater's proper motion by assuming that it also orbits in the VPOS.  One of the 3 streams aligns eel with the VPOS.  It appears to lie in the exact same orbital plane as the Palomar 5 stream and share its distance, suggesting a direct connection between the two.  The stream also crosses close to the Fornax dwarf galaxy and its oriented approximately along the galaxy's direction of motion.  The two other streams cannot align closely with the VPOS because they were discovered in the direction of M31/M33 outside the satellite structure.  Two new members of VPOS.

1407.2614
The gentle growth of galaxies at high redshifts in over dense environments
Romano-Diaz et al

Explore prevailing modes of galaxy growth for z~6-14, comparing substantially over dense and normal regions of the universe, using high-resolution zoom-in cosmological simulations.  Such rare over dense regions have been projected to host high-z quasars.  Demonstrate that galaxies in such environments grow predominantly by a smooth accretion from cosmo filaments which dominates the mass input from major, intermediate and minor mergers.  Find that by z~6, the accumulated galaxy mass fraction from mergers falls short by a factor of 10 of the cumulative accretion mass for galaxies in the over dense regions, and by a factor of 5 in the normal environments.  Moreover, the rate of the stellar mass input from mergers also lies below that of an in-situ SF rate.  The fraction of stellar masses in galaxies contributed by mergers in over dense regions is ~12% and ~33% in the normal regions, at these redshifts.  The median SF rates for ~few 1e9 Msun galaxies agrees well with the recently estimated rates for z~7 galaxies from Spitzer's SURF-UP survey.  Finally, find that the main difference between the normal and over dense regions lies in the amplified growth of massive galaxies in massive DM haloes.  This leads to the formation of >=1e10 Msun galaxies due to the ~100-fold increase in mass during the above time period.  Such galaxies are basically absent in the normal regions at these redshifts.
1407.2648
Probing satellite quenching with galaxy clustering
Chamberlain, Dalal, Hearin, Ricker

Satellites within simulated massive clusters are significantly spatially correlated with each other, even when those satellites are not gravitationally bound to each other.  This correlation is produced by satellites that entered their hosts relatively recently, and is undetectable for satellites that have resided in their hosts for multiple dynamical timescales.  Therefore, a measurement of clustering statistics of cluster satellites may be used to determine the typical accretion redshifts of those satellites into their observed hosts.  Argue that such measurements may be used to determine the fraction of satellite galaxies that were quenched by their current hosts, thereby discriminating among models for quenching of SF in satellite galaxies.