Day 1008

Monday.  Tuesday.


1511.04075
Cluster-void degeneracy breaking: dark energy, Planck and the largest cluster & Void
Sahlin, Zubeldía, Silk

Combining galaxy cluster and void abundances breaks the degeneracy between mean matter density Omega_m and power spectrum normalization sigma8.  In a first for voids, constrain Omega_m=0.21±0.10 and sigma_8=0.95±0.21 for a flat LCDM universe, using extreme-value statistics on the claimed largest cluster and void.  The Planck-consistent results detect DE with two objects, independently of other DE probes.  Cluster void studies also offer complementarity in scale, density, and non-linearity - of particular interest for testing modified-gravity models.


1511.04086
Ubiquitous time variability of integrated stellar populations
Conroy, van Dokkum, Choi

Long period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution.  They have periods of up to ~1000d and amplitudes that can exceed a factor of three in the I-band flux.  These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population.  The overall number of long period variables in a population is directly related to their lifetime, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing.  The time variability of these stars has not been previously taken into account when molding the spectral energy distributions of galaxies.  Construct time-dependent stellar population models that include the effects of long period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87.  The pixel light curves display a variety of behaviors, including linearly rising and falling curves, semi-periodic curves, and sudden increases or decreases in the flux level.  The observed variation of 0.1-1% is very well matched to the predictions of the models.  The data provide a strong and novel constraint on the properties of variable stars in an old and metal-rich stellar population, and infer that the lifetime of long period variables in M87 is shorted by approximately 30% compared to predictions from the latest stellar evolution models.


1511.04090
Inverted initial conditions: exploring the growth of cosmic structure and voids
Pontzen, Slosar, Roth, Peiris

Introduce and explore "paired" cosmo sims.  A pair consists of an A and B simulation with initial conditions related by the inversion delta_A(x,t_i)=-delta_B(x,t_i) (under densities substituted for over densities and vice versa).  Argue that the technique is valuable for improving the understanding of cosmic structure formation.  The A and B fields are by definition equally likely draws from LCDM ICs, and in the linear regime evolve identically up to the overall sign.  As NL evolution takes hold, a region that collapses to form a halo in simulation A will tend to expand to create a void in simulation B.  Applications include (i) contrasting the growth of A-haloes and B-voids to test excursion-set theories of structure formation; (ii) cross-correlating the density field of the A and B universes as a novel test for perturbation theory,; and (iii) canceling error terms by averaging PS between the two boxes.  Generalizations of the method to more elaborate field transformations are suggested.


1511.04093
The story of supernova 'Refsdal' told by MUSE
Grillo, .. Suyu, ... Treu, et al

SN at z=1.489; DDT program at VLT gives 117 secure redshifts, 68 galaxy cluster members, and 18 multiple images belonging to 7 BG, lensed sources between 1.230 and 3.703.  Select a sample of 300 (164 spec and 136 photo-z) cluster members, within ~500 kpc from BCG, and a set of 88 reliable multiple images associated to 10 different background source galaxies and 18 distinct knots in the spiral galaxy hosting SN 'Refsdal'.  Exploit this information to build 6 detailed SL models, the best of which reproduces the observed positions of the multiple images with a rms offset of only 0.26".  Use these models to quantify the statistical and systematic errors on the predicted values of magnification and time delay of the next emerging image of SN 'Refsdal'.  Find that its peak luminosity should be approximately 20% fainter that the dimmest (S4) of the previously detected images but above the detection limit of the planned HST/WFC3 follow-up and should occur between March and June 2016.  Present the 2d reconstruction of the cluster mass density distribution and of the SN 'Refsdal' host galaxy surface brightness distribution.  Outline the roadmap towards even better strong lensing models with a synergetic MUSE and HST effort.


1511.04095
Bulge formation via mergers in cosmological simulations
Brooks, Christensen

[Review article for "Galactic Bulges"] Galaxy mergers have long been assumed to produce classical bulges in disk galaxies.  Under this bulge-formation model, though, the high rates of mergers in CDM galaxy formation theory predict many more classical bulges than are observed. Furthermore, simulations of galaxy formation continue to generally produce too massive of bulges.  Feedback offers a promising avenue for reducing merger-driven bulge growth by maintaining high gas fractions in galaxies and ejecting low-angular momentum gas driven to the centers of galaxies. After reviewing the results of relevant research that has been published to date, use cosmo sims to explore the ability of feedback to reduce or even prevent  bulge growth during mergers.  In dwarf galaxies, mergers actually reduce the central concentration of galaxies as the induced burst of SF drives out low angular momentum material.  This results shows the potential for feedback to reduce central mass growth.  However, also demonstrate that it is very difficult for current stellar feedback models to reproduce the small bulges observed in more massive disk galaxies like the MW.  Argue that feedback models need to be improved, or an additional source of feedback such as AGN is necessary to generate the required outflows.  


1511.04391
Measuring Baryon Acoustic Oscillations from the clustering of voids
Liang, ... Kitaura, et al

Investigate the necessary methodology to optimally measure the BAO signal ,from voids based on galaxy redshift catalogues.  To this end, study the dependence of the BAO signal on the population of voids classified by their sizes.  Find for the first time the characteristic features of the correlation function of voids including the first robust detection of BAOs in mock galaxy catalogues.  These show an anti-correlation around the scale corresponding to the smallest size of voids in the sample (the void exclusion effect), and dips at both sides of the BAO peak, which can be used to determine the significance of the BAO signal without any prior model.  Furthermore, the analysis demonstrates that there is a scale dependent bias for different populations of voids depending on the radius, with the peculiar property that the void population with the largest BAO significance corresponds to tracers with approximately zero bias on the largest scales.  Further investigate the methodology on an additional set of1000 realistic mock galaxy catalogues reproducing BOSS CMASS DR11 data, to control the impact of sky mask and radial selection function.  The solution is based on generating voids from randoms including the same survey geometry and completeness, and a post-rpcoessing cleaning procedure in the holes and at the boundaries of the survey.  The methodology and optimal selection of void populations validated in this work have been used to perform the first BAO detection from voids in observations, presented in a companion paper.


1511.04405
Signatures of the primordial universe from its emptiness
Kit aura, et al

Propose to measure BAOs from the minima of the density field.  based on two sets of accurate mock halo catalogues with and without BAOs in the seed ICs, demonstrate that the BAO signal cannot be obtained from the clustering of classical disjoint voids, but is clearly detected from overlapping voids.  The latter represent an estimate of all throughs of the density field.  Compute them from the empty circumsphere centers constrained by tetrahedra of galaxies using Delaunay triangulation.  The theoretical models based on an  unprecedented large set of detained simulated void catalogues are remarkably well confirmed by observational data. Use the largest recently publicly available sample of LRGs from BOSS DR11 to unveil for the first time a >3sigma BAO detection from voids in observations.  Since voids are nearly isotropically expanding regions, their center represent the most quiets places in the Universe, keeping in memory the cosmos origin, and providing a new promising window in the analysis of the cosmo LSS from galaxy survey.