Day 676

Wednesday.

1406.2314
Halo mass dependence of HI and OVI absorption: evidence for differential kinematics
Mathes et al

Study a sample of 14 galaxies (0.1<z<0.7) with HST/WFPC2 and COS or STIS quasar spectroscopy of Lya, Lyb, OVI1031, and OVI1037 absorption.  The galaxies, having 1.8<log(M/Msun)<12.2, lie within D=300 kpc of quasar sight lines, probing out to D/R_vir=3.  When the full range of galaxy virial masses and D/R_vir of the sample are examined, 40% of the HI absorbing clouds can be inferred to be escaping their host halo.  The fraction of bound clouds decreases as D/R_vir increases such that the escaping fraction is around 15% for D/R_vir<1, around 45% for 1<D/R_vir<2, and around 90% for 2<D/R_vir<3.  Adopting the median mass log(M/Msun)=11.5 to divide the sample into "higher" and "lower" mass galaxies, find mass dependence for the hot CGM kinematics.  To the survey limits, OVI absorption is found in only 40% of the HI clouds in and around lower mass haloes as compared to 85% around higher mass haloes.  For D/R<1, lower mass haloes have an escape fraction of 65%, whereas higher mass haloes have an escape fraction of 5%.  For 1<D/R_vir<2, the escape fractions are 55% and 35% for lower mass and higher mass haloes, respectively, for 2<D/R_vir<3, the escape fraction for lower mass haloes is around 90%.  Show that it is highly likely that the absorbing clouds reside within 4 virial radii of their host galaxies and that the kinematics are dominated by outflows.  Finding of "differential kinematics" is consistent with the scenario of "differential wind recycling" proposed by Oppenheimer+.  Discuss the implications for galaxy evolution, the stellar halo mass function, and the mass metallicity relationship of galaxies.

1406.2315
The discovery of seven extremely low surface brightness galaxies in the field of the nearby spiral galaxy M101
Merritt, van Dokkum, Abraham

Dwarf satellite galaxies are a key probe of DM and of galaxy formation on small scales and of the DM halo masses of their central galaxies.  They have very low surface brightness, which makes it difficult to identify and study them outside of the Local Group.  Used the Dragonfly Telephoto Array to search for dwarf galaxies in the field of the massive spiral galaxy M101.  Identify 7 large, LSB objects in this field, with effective radii of 10-30 arc seconds and central surface brightness of mu_g~25.5-27.5 mag/arcsec^2.  Given their large apparent sizes and low surface brightnesses, these objects would likely be missed by standard galaxy searches in deep fields.  Assuming the galaxies are dwarf satellites of M101, their absolute magnitudes are in the range `11.6<M_V<-9.3 and their effective radii are 350pc-1.3kpc.  Their radial surface brightness profiles are well fit by Sersic profiles with a very low Sersic index (n~0.3-0.7).  The properties of the sample are similar to those of well-studied dwarf galaxies in the LG, such as Sextans I and Phoenix.  Distance measurements are required to determine whether these galaxies are in fact associated with M101 or are in its foreground or BG.

1406.2320
Creating mock catalogues of stellar haloes from cosmological simulations
Lowing, ... Frenk, Cole et al

Present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmo sims and show how the catalogues can be used to test and interpret observational data.  Catalogues are constructed from a combination of methods.  A SAM is used to calculate the SFH in haloes in an H-body sim, and DM particles are tagged with this stellar mass.  The tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original N-body simulation is maintained.  A set of catalogues based on the Aquarius simulations of MW mass haloes have been created and made publicly available on a website.  Two example applications are discussed that demonstrate the power and flexibility of the mock catalogues.  Show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile.  Also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stelar populations, allow streams to be easily identified.

1406.2327
Late-stage galaxy mergers in COSMOS to z~1
Lackner, ... Capak, .. Ilbert, Koekemoer, Le Fevre, Scoville... et al

Develop an automated method to identify late-stage galaxy mergers before coalescence of the galactic cores.  ...  Correcting for incompleteness and contamination, the fractional merger rate increases strongly with (1+z)^3.8 pm 0.9, in agreement with earlier studies and with DM halo merger rates.  Separating the sample into SF and quiescent galaxies shows that the merger rate for SF galaxies increases strongly, (1+z)^4.5, while the merger rate for quiescent galaxies is consistent with no evolution (1+z)^1.1.  Limiting the sample to galaxies with spectroscopic redshifts from zCOSMOS, find that the SFRs and X-ray selected AGN activity in likely late-stage mergers are enhanced by factors of ~2 relative to a control sample.  Combining the sample with more widely separated paris, find that 8pm5% of SF and 20pm8% of AGN activity is triggered by close encounters (<143kpc) or mergers, once more suggesting that major mergers are not the only channels for SF and BH growth.