Day 858

Friday.


1503.07528
Hubble space telescope search for the transit of the Earth-mass exoplanet Alpha Centauri Bb
Demory, et al

HST observation of Alpha Centaur B in 2013 and 2014 for a total of 40 hours; precision of 115 ppm per 6-s exposure time in a highly-saturated regime.  Rule out the transiting nature of Alpha Cen Bb with the orbital parameters published in the literature at 96.6% CL.  Find in data a single transits-like event that could be associated to another Earth-size planet in the system, on a longer period orbit.  


1503.07533
A two-parameter matching scheme for massive galaxies and dark matter haloes
Kulier, Ostriker

Halo Abundance Matching has been used to construct a one-parameter mapping between galaxies and DM haloes by assuming that halo mass and galaxy luminosity (or stellar mass) are monotonically related.  While this approach has been reasonably successful, it is known that galaxies must be described by at least 2 parameters, as can be seen from the 2-parameter Fundamental Plane on which massive early-type galaxies lie.  In this paper, derive a connection between initial DM density perturbations in the early universe and present-day virtualized DM haloes by assuming simple spherical collapse combined with conservation of mass and energy.  Find that z=0 halo concentration, or alternatively the inner slope of the halo density profile alpha, is monotonically and positively correlated with the collapse z of the halo.  This is qualitatively similar to the findings of some previous works based on numerical simulations, with which the results are compared.  Then describe how the halo mass and concentration (or inner slope alpha) can be used as two halo parameters in combination with two parameters of early-type galaxies to create an improved abundance matching scheme.


1503.07596
The interstellar medium in galaxies seen a billion years after the Big Bang
Capak et al

Report measurements of the [CII] gas and dust emission in 9 typical (~1-4L*) SF galaxies ~1 Byrs after the big bang (z~5-6).  Find these galaxies have >12x less thermal emission compared with similar systems ~2 Byrs later, and enhanced [CII] emission relative to the far-IR continuum, confirming a strong evolution in the ISM properties in the early universe.  The gas is distributed over scales of 1-8 kpc, and shows diverse dynamics within the sample.  These results are consistent with early galaxies having significantly less dust than typical galaxies seen at z<3 and being comparable to local low-metallicity systems.


1503.07675
The non-gravitational interactions of dark matter in colliding galaxy clusters
Harvey, Massey, Kitching, Teylor, Tittley

Collisions between galaxy clusters provide a test of the non-gravitational forces acting on DM. Dark matter's lack of deceleration in the 'bullet cluster collision' constrained its self-interaction cross-section sigma_DM/m < 1.25 cm^2/g (68% CL) for long-ranged forces.  Using the Chandra and HST, now 72 collisions are observed, including both 'major' and 'minor' mergers.  Combining these measurements statistically, detect the existence of dark mass at 7.6 sigma significance.  The position of the dark mass has remained closely aligned within 5.8±8.2 kpc of associated stars: implying a self-interaction cross-section sigma_DM/m < 0.47 cm^2/g (95% CL) and disfavoring some proposed extensions to the standard model.


1503.07690
Counting voids to probe dark energy
Pisani, ... Hamaus, ... Hirata

Show that the number of observed voids in galaxy z surveys is a sensitive function of the equation of state of DE.  Using Fisher matrix formalism, find the error ellipses in the w0-wa plane when the EoS of DE is assumed to be of the form w_CPL(z)=w0+wa*z/(1+z).  Forces the number of voids to be observed with Euclid and WFIRST, taking in to account updated details of the surveys to reach accurate estimates of their power.  The theoretical model for the forecast of the number of voids is based on matches between abundances in simulations and the analytical prediction.  To take into account the uncertainties within the model, marginalize over its free parameters when calculating the Fisher matrices.  The addition of the void abundance constraints to the data from Planck, HST and SNe survey data noticeably tighten the w0-wa parameter space.  Thus quantify the improvement in the constraints due to the use of voids and demonstrate that the void abundance is a sensitive new probe for the DE EoS.