Day 1142

Monday.

1608.05446

Precise clustering and density evolution of redMaPPer galaxy clusters versus MXXL simulation
Jimena, Broadhurst, et al

Construct a large, redshift complete sample of distant galaxy clusters by correlating SDSS DR12 redshifts with clusters identified with redMaPPer algorithm.  The spectroscopic completeness is 97% for ~7000 clusters within the redMaPPer selection limit, z<0.325, so that the cluster correlation functions are much more precise than earlier work and not suppressed by photometric redshifts.  Derive an accurate power-law mass-richness relation from the observed abundance with respect to the mass function from Millennium XXL (MXXL) sims, adjusted to the Planck weighted cosmology.  The number density of clusters is found to decline by 20% over the range 0.1<z<0.3, in good agreement with the evolution predicted by MXXL.  The projected 3d correlation function scales with richness, lambda, rising from r0=14Mpc/h at lambda~25, to r0=22Mpc/h at lambda~60, with a gradient that matches MXXL when applying the mass-richness relation, whereas the observed amplitude of the correlation function at <z>=0.24 exceeds the MXXL prediction by 20% at the ~2.5 sigma level.  This tension cannot be blamed on spurious, randomly located clusters as this would reduce the correlation amplitude.  Full consistency between the correlation function and the abundances is achievable for the pre-Planck values of sigma8=0.9, Omega_m=0.25, and h=0.73, matching the improved distance ladder estimate of the Hubble constant.



1608.06942
Geometric corroboration of the earliest lensed galaxy at z~10.8 from robust free-form modeling
Chan, Broadhurst, Lim, Diego, Zitrin, Coe, Ford

A multiply-lensed galaxy, MACS0647-JD, with a probably photometric redshift of z~10.7±0.5 is claimed to constitute one of the very earliest known galaxies, formed well before reionization was completed.  However, spectral evidence that MACS0647-JD lies at high redshift has proven invisible and so see any independent lensing used "geometric redshift" derived from the angles between the 3 lensed images of MACS0647-JD, using the free-form mass model (WSLAP+) for the lensing cluster MACSJ0647.7+7015 (at z=0.591).  The lens model uses the 9 sets of multiple images, including those of MACS0647-JD< identified by the CLASH survey towards this cluster.  Convincingly exclude the low redshift regime of z<3, for which convoluted critical curves are generated by the method, as the solution bends to accommodate the wide angles of MACS0647-JD for this low redshift.  Instead, a best fit to all sets of lensed galaxy positions and redshifts provides a geometric redshift of z~10.8±0.4 for MACS0647-JD, strongly supporting the higher photometric redshift solution.  Importantly, find a tight linear relation between the relative brightnesses of all 9 sets of multiply lensed images and their relative magnifications as predicted by the model.  This agreement provides a benchmark for the quality of the lens model, and establishes the robustness of the free-form lensing method for measuring model-independent geometric source distances and for deriving objective central cluster mass distributions.  After correcting for its magnification the luminosity of MACS0647-JD remains relatively high at M_UV=-19.4, which is within a factor of a few in flux of some surprisingly luminous z~10-11 candidates discovered recently in Hubble black field surveys.


1608.07345
Prospects for characterizing the atmosphere of Proxima Centauri b
Kreidberg, Loeb

The newly detected Earth-mass planet in the habitable zone of Proxima Centauri could potentially host life -- if it has an atmosphere that supports surface liquid water.  Show that thermal phase curve observations with JWST from 5-12 microns can be used to test the existence of such an atmosphere.  Predicts the thermal variation for the bare rock versus a planet with 35% heat redistribution to the nightside and show that a JWST phase curve measurement can distinguish between these cases at 5 sigma confidence.  Also consider the case of an Earth-like atmosphere, and find that the ozone 9.8 micron band could be detected with longer integration times (a few months).  Conclude that JWST observations have the potential to put the first constraints on the possibility of life around the nearest star to the Solar System.