Day 851

Wednesday.

1503.04813
Galaxy and mass assembly (GAMA) blended spectra catalog: strong galaxy-galaxy lens and occulting galaxy pair candidates
Holwerda, et al

Cases where light from two galaxies are significantly detected in a single GAMA fibre.  Galaxy pairs identified from their blended spectrum fall into two principal classes: they are either SL, a passive galaxy lensing an emission-line galaxy; or occulting galaxies, serendipitous overlaps of two galaxies, of any type.  Blended spectra can thus be used to reliably identify SLs for follow-up observations and occulting pairs, especially those that are a late-type partly obscuring an early-type galaxy which are of interest for the study of dust content of spiral and irregular galaxies.  The GAMA survey setup and its auto automated z determination were used to identify candidate blended galaxy spectra from the X-corr peaks.  Identify 280 blended spectra with a minimum velocity separation of 600 km/s, of which 104 are lens pair candidates, 71 emission-line-passive pairs, 78 are pairs of emission-line galaxies and 27 are pairs of galaxies with passive spectra.  Visually inspected the candidates in SDSS and KiDS images.  Many blended objects are elliptical with blue fuzz (Ef in the classification).  These latter "Ef" classifications are candidates for possible SLs, massive ellipticals with an emission-line galaxy in one or more lensed images.  The GAMA lens and occulting galaxy candidate samples are similar n size to those identified in the entire SDSS.  This blended spectrum sample stands as a testament of the power of this highly complete, second-largest spectroscopic survey in existence and offers the possibility to expand e.g., SL surveys.


1503.04814
NIHAO project II: halo shape, phase-spar density and velocity distribution of dark matter in galaxy formation simulations
Butsky et al

Show the effect of galaxy formation on the DM distribution across a wide range of halo masses.  Focus on how baryon physics changes the DM halo shape, the "pseudo phase-space density distribution" and the velocity distribution within the viral radius, R_vir and in the solar neighborhood.  Study is based on the NIHAO galaxy formation simulations, a large suite of cosmo zoom-in sims.  The galaxies reproduce key properties of observed galaxies, and hence offer unique insight into how baryons changes the DM morphology and kinematics.  When compared to DM only sims, the NIHAO halos have similar shapes at R_vir, but are substantially rounder inside ~0.1 R_vir.  In DM-only sims the inner halo has a minor-to-major axis ratio of c/a~0.5.  In hydro sims c/a increases with halo mass and integrated star formation efficiency, reaching ~0.8 at the MW mass, reconciling a long-standing conflict between observations and DM only sims.  The radial profile of the phase-space Q parameter is best fit with a single power law in DM-only sims, but shows a substantial flattening within ~0.1 R_vir, with hydro.  Finally, the global velocity distribution of DM is similar in both DM-only and hydro sims, but in the solar neighborhood, hydro galaxies deviate substantially from Maxwellian.  Instead, DM particles show a more symmetric distribution, roughly Gaussian, around the mean, which has implications for direct DM detection experiments.  The results show that the comparison of theoretical predictions with observational data can no longer rely on pure collisions isms, but must include the effects of visible matter.


1503.04835
Habitability of waterworlds: runaway greenhouses, atmospheric expansion and multiple climate states of pure water atmospheres
Goldblatt

There are 4 different stable climate states for pure water atmospheres, as might exist on so-called "water worlds".  Map these as a function of solar constant for planets ranging in size from Mars to 10 M_earth.  The states are : globally ice covered (Ts<245K), cold and damp (270-290K), hot and moist (350-550K) and very hot and dry (<900K).  No stable climate exists fro 290-350K or 550-900K.  The union of hot moist and cold damp climates describe the liquid water habitable zone, the width and location of which depends on planet mass.  At each solar constant, 2 or 3 different climate states are available.  This is a consequence of strong non-linearities in both thermal emission and the net absorption of sunlight.  Across the range of planet sizes, account for the atmospheres expanding to high altitudes as they warm.  The emitting and absorbing surfaces (optical depth of unity) move the high altitude, making their area larger than the planet surface, so more thermal radiation is emitted and more sunlight absorbed (the former dominates).  The atmospheres of small planets expand more due to weaker gravity: the effective runaway greenhouse threshold is about 35W/m^2 higher for Mars, 10 W/m^2 higher for Earth or Venus but only a few W/m^2 higher for a 10 Earth-mass planet.  There is an underlying (expansion neglected) trend of increasing runaway greenhouse threshold with planetary size (40W/m^2 higher for a 10 Earth mass planet than for Mars).  Summing these opposing trends means that Venus-size (or slightly smaller) planets are most susceptible to a runaway greenhouse.  The habitable zone for pure water atmospheres is very narrow, with an insolation range of 0.07 times the solar constant.  A wider habitable zone requires background gas and greenhouse gas; N2 and CO2 on Earth, which are biologically controlled.  Thus, habitability depends on inhabitance.