Day 1045

Monday.


1601.07905
The eating habits of Milky Way mass halos: destroyed dwarf satellites and the metallicity distribution of accreted stars
Season, Mao, Wechsler

Study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of MW mass M_vir~1e12.1 Msun halos using a suite of 45 zoom-in, dissipation-less simulations. Empirical models are employed to relate (peak) sub halo mass to dwarf stellar mass, and use constraints from z=0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material.  The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M*~1e8-10 Msun.  Halos with more quiescent accretion histories tend to have lower mass progenitors (1e8-9 Msun), and lower overall accreted stellar masses.  Ultra-faint mass (M*<1e5 Msun) swarfs contribute a negligible amount (<<1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (~2-5%) of the very metal-poor stars with [Fe/H] < -2.  Dwarfs with masses 1e5 < M*/Msun < 1e8 provide a substantial amount of the very metal-poor stellar material (~40-80%), and even relatively metal-rich dwarfs with M*>1e8 Msun can contribute a considerable fraction (~20-60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails.  Finally, find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs.  Suggest that the MW could be a "transient fossils", a quiescent halo wit ha recent accretion event(s) that disguises the preceding formation history of the halo.


1601.07967
IDCS J1426.5+3508: weak lensing analysis of a massive galaxy cluster at $z=1.75$
Mo, Gonzalez, Jee, Massey, Rhodes, et al

Present a WL study of the galaxy cluster IDCS at z=1.75, which is the highest redshift SL cluster known and the most distant cluster for which a WL analysis has been undertaken.  Using F160W, F814W, and F606W observations with the HST, detect tangential shear at 2 sigma significance.  Fitting a NFW mass profile to the shear with a theoretical median mass-concentration relation, derive a mass M_200,crit = (2.3-1.4+2.1)e14 Msun.  This mass is consistent with previous mass estimates from the SZ effect, X-ray, and SL.  The cluster lies on the local SZ-WL mass scaling relation observed at low redshift, indicative of minimal evolution in this relation.


1601.08228
The void galaxy survey: star formation properties
Beygu, et al

Study the SF properties of 59 void galaxies as part of the Void Galaxy Survey (VGS).  Current SFRs are derived from Ha and recent SFRs from near-UV imaging.  In addition, IR 3.4/4.6/12/22 um WISE emission is used as SF and mass indicator.  IR and optical colors show that the VGS sample displays a wide range of dust and metallicity properties.  Combine these measurements with stellar and HI masses to measure the sSFRs (SFR/M*) and SF efficiencies (SFR/M_HI).  Compare the SF properties of the sample with galaxies in the more moderate density regions of the cosmic web, 'the field'.  Find that sSFRs of the VGS galaxies as a function of stellar and HI mass are similar to those of the galaxies in these field regions.  Their SFRa is slightly elevated than the galaxies in the field for  a given total HI mass.  In the global SF picture presented by Kennicutt-Schmidt, VGS galaxies fall into the region of low average SF and correspondingly low HI surface density.  Their mean SFRa/M_HI and SFRa/M* are of the order of 1e-9.9 yr^-1.  Conclude that while the large scale underdense environment must play some role in galaxy formation and growth through accretion, find that even with respect to other galaxies in the more mildly underdense regions, the increase in star formation rate is only marginal.