Day 990

Friday.


1510.04270
Chandra Measurements of a complete sample of X-ray luminous galaxy clusters: the Luminosity-mass relation
Giles, et al

Statistically complete sample of 34 galaxy clusters in 0.15<z<0.3 observed with Chandra.  Present the mass-temperature calibration relation using hydrostatic mass estimates for the most relaxed clusters, and use this relation as a mass proxy for the full cluster sample.  Slope of the MT relation follows the self-similar expectation, and is consistent with previously published relations.  Investigate the LM relation for the cluster sample, utilising a method to fully account for selection bias.  Find that the difference in normalization of the LM relation with and without accounting for selection effects is ~2.  For a cluster of luminosity 1e45 erg/s, find that the mass estimated from the LM relation when we account for selection effects is ~40% higher compared to the sample LM relation (not accounting for selection effects.


1510.04287
Testing gravity with $E_G$: mapping theory onto observations
Leonard, Ferreira, Heymans

Present a complete derivation of the observationally motivated definition of the modified gravity statistic E_G.  Using this expression, investigate how variations to theory and survey parameters may introduce uncertainty in the GR prediction of E_G.  Forecast errors on E_G for measurements using 2 combinations of upcoming surveys, and find that theoretical uncertainties may dominate for a futuristic measurement.  Finally, compute predictions of E_G under modifications to GR in the quasi static regime, and comment on the pros and cons of using E_G to test gravity with future surveys.


1510.04307
Dissecting the multiphase circumgalactic medium around three massive lensing galaxies at z =0.4-0.7
Zahedi et al

Present multi-sightline absorption spectroscopy of the inner gaseous halo around 3 lensing galaxies at z=0.4-0.7.  Their spectral and photometric properties are characteristic of nearby passive elliptical galaxies with half-light radii of r_e=2.6-8 kpc and estimated total stellar masses of log M*/Ms=10.6-11.2.  The lensed QSO sight lines pass through the gaseous halo of the lensing galaxy at projected distances d=3-15 kpc or (1-2) r_e.  The absorption-line search reveals a diverse range of cool (T~1e4 K) halo gas properties among the 3 lensing galaxies.  Specifically, while the quadruple lens for HE0435-1223 shows no trace of associated Mg II or other ionic absorption features to very sensitive limit in all 4 sightlines,  strong MgII absorbers are found along both sightlines at the redshift of the double lens for HE0047-1756, and in one of the two sightlines at the redshift of the lens for HE1104-1805.  In addition to Mg II, associated FeII, MgI, and CaII absorption transitions are detected.  The absorbers are resolved into 8-15 individual components with a line-of-sight velocity spread of dv~300-600 km/s.  The large ionic column densities observed in a few of the components suggest a significant neutral gas fraction comparable to what is expected for Lyman limit or daped Lya absorbers.  The majority of the absorbing components exhibit a super solar Fe/Me ratio, whose pattern is remarkably uniform with a scatter of <0.1 dex across the full dv.  Given a predominantly old stellar population in these lensing galaxies, argue that the Fe-rich gas (which dominates the total absorption width) originates in the SNe Ia enriched inner regions at radius r~d.  The study demonstrates that combining spatially resolved gas kinematics and relative (Fe/Mg) abundance pattern provides a powerful tool to resolve the origin of chemically-enriched cool gas in massive halos.


1510.04388
Formation of ultra-compact blue dwarf galaxies and their evolution into nucleated dwarfs
Bekki

Propose that there is an evolutionary link between UCBDs (ultra-compact blue dwarfs) with active SF and nucleated dwarfs based on the results of numerical simulations of dwarf-dwarf merging.  Consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf-dwarf mergers.  Find that the remnants of dwarf-dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z~[0.2-1] Zsun).  Also find that the remnants of these mergers can have rather high mass-densities (1e4 Msun/pc^3) within the central 10 pc and small half-light radii (40-100 pc).  The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs.  SF can continue in nuclear gas disks (R<100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities.  These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after fading of young stars.  Discuss these results in the context of the origins of metal-rich ultra-compact dwarfs (UCDs) and SGNs.