Day 1282

Monday.


1706.09899
The EAGLE simulations of galaxy formation: public release of particle data
The EAGLE team

This manual accompanies the release of the particle data for 24 simulations of the EAGLE suite of cosmo hydro sims of galaxy formation by the virgo consortium.  It describes how to download these snapshots and how to extract datasets from them, emphasizes the meaning of variables, and their units.  Provide examples for extracting the particle data in python.  This data release complements the earlier release of numerous integrated properties of the galaxies in EAGLE through an SQL relational database.  This database has been updated to include the additional simulations that are part of the present data release.  Scientists wanting to use EAGLE may find it useful to first investigate whether their analysis can be performed using the database, before accessing the particle data.  The particles in the snapshot files are indexed by a peano-hilbert key.  This allows for an eased extraction of simply connected spatial volumes, without needing to read the entire snapshot.  This makes it possible to analyse many aspects of galaxies using modest computing resources, even when using EAGLE sims with large numbers of particles.  A reading routine is provided to simplify this process.


1706.09906
Halo assembly bias and the tidal anisotropy of the local halo environment
Paranjape, Hahn, Sheth

Study the role of the local tidal environment in determining the assembly bias of DM haloes.  Previous results suggest that the anisotropy of a halo's environment (i.e., whether it lies in a filament orin a more isotropic region) can play a significant role in determining the eventual mass and the age of the halo.  Statistically isolate this effect using correlations between the large-scale and small-scale environments of simulated haloes at z=0 with masses between 1e11.6 < (m/(Msun/h)) < 1e14.9.  Probe the large scale environment using a novel alo-by-halo estimator of linear bias.  For the small-scale environment, identify a variable alpha_R that captures the tidal anisotropy in a region of radius R=4R_200b around the halo and correlates strongly with halo bias at fixed mass.  Segregating haloes by alpha_R reveals two distinct populations.  Haloes in highly isotropic local environments (alpha_R<~0.2) behave as expected form the simplest, spherically averaged analytical models of structure formation, showing a negative correlation between their concentration and large-scale bias at all masses.  In contrast, halos in anisotropic, filament-like environments (alpha_R>0.5) tend to show a positive correlation between bias and concentration at any mass.  The multi-scale analysis cleanly demonstrates how the overall assembly bias trend across halo mass emerges as an average over these different halo populations, and provides valuable insights towards building analytical models that correctly incorporate assembly bias.  Also discuss potential implications for the nature and detectability of galaxy assembly bias.


1706.09928
Instrumental response model and detrending for the Dark Energy Camera
Bernstein, et al

Describe the model for the mapping from sky brightness to the digital output of the DECam, and describe the algorithms adopted by the DES for inverting this model to obtain photometric measures of celestial objects from the raw camera output.  The calibration aims for fluxes that are uniform across the camera field of view and across the full angular and temporal span of the DES observations, approaching the accuracy limits set by shot noise for the full dynamic range of DES observations.  The DES pipeline incorporates several substantive advances over standard detrending techniques, including: principal-components-based sky and fringe subtraction; correction of the "brighter-fatter" nonlinearity; use of internal consistency in on-sky observations to disentangle the influences of quantum efficiency, pixel-size variations, and scattered light in the dome flats; and pixel-by-pixel characterization of instrument spectral response, through combination of internal-consistency constraints with auxiliary calibration data.  This article provides conceptual derivations of the detrending/calibration steps, and the procedures for obtaining the necessary calibration data.  Other publications will describe the implementation of these concepts for the DES operational pipeline, the detailed methods, and the validation that the techniques can bring DECam photometry and astrometry within ~2mmag and ~3 mas, respectively, of fundamental atmospheric and statistical limits.  The DES techniques should be broadly applicable to wide-field imagers.


1706.10281
Dark matter under the microscope: Constraining compact dark matter with caustic crossing events
Diego, Kaiser, Broadhurst, et al

A galaxy cluster acts as a cosmic telescope over BG galaxies but also as a cosmic microscope of the lens imperfections.  The diverging magnification of lensing caustics enhances the microlensing effect of substructure present within the lensing mass.  Fine-scale structure can be accessed as a moving background source brightens and disappears when crossing these caustics.  The recent recognition of a distant lensed star near the Einstein radius of the galaxy cluster MACSJ1149.5+2223 (Kelly+2017) allows the rare opportunity to reach sub solar mass microlensing through a super-critical column of cluster matter.  Here, compare these observations with high-resolution ray-tracing simulations that include stellar microlensing set by the observed intracluster starlight and also primordial BHs that may be responsible for the recently observed LIGO events.  explore different scenarios with microlenses from the intracluster medium and BHs, including primordial ones, and examine strategies to exploit these unique alignments.  Find that the best constraints on the fraction of compact DM in the small-mass regime can be obtained in regions of the cluster where the ICM plays a negligible role.  This new lensing phenomenon should be widespread and can be detected within modest-redshift lensed galaxies so that the luminosity distance is not prohibitive for detecting individual magnified stars.  Continuous HST monitoring of several such optimal arcs will be rewarded by an unprecedented mass spectrum of compact objects that can contribute to uncovering the nature of dark matter.


1706.10286
A comparison of cosmological parameters determined from CMB temperature power spectra form the South Pole Telescope and the Planck satellite
Aylor, Hou, Knox, Sstory, et al

The Planck CMB temperature data are best fit with a LCDM model that is in mine tension with constraints from other cosmological probes.  The SPT 2540 deg^2 SPT-SZ survey offers measurements on sub-degree angular scales (multipoles 650<ell<2500) with sufficient precision to use as an independent check of the Planck data.  Here, build on the recent joint analysis of the SPT-SZ and Planck data in Hou+2017 by comparing LCDM parameter estimates using the temperature power spectrum from both data sets in the SPT-SZ survey region.  Also restrict the multipole range used in parameter fitting to focus on modes measured well by both SPT and Planck, thereby greatly reducing sample variance as a driver of parameter differences and creating a stringent test for systematic errors.  Find no evidence of systematic errors from such tests.  When expanding the maximum multipole of SPT data used, see low-significance shifts in the angular scale of the sound horizon and the physical baryon and CDM densities, with a resulting trend to higher Hubble constant.  When SPT and Planck data are compared on the SPT-SZ sky patch to Planck full-sky data but keep the multipole range restricted, find differences in the parameters n_s and A_s e^-2tau.  Perform further checks, investigating instrumental effects and modeling assumptions, and find no evidence that the effects investigated are responsible for any of the parameter shifts.  Taken together, these tests reveal no evidence for systematic errors in SPT or Planck data in the overlapping sky coverage and multiple range and, at most, weak evidence for a breakdown of LCDM or systematic errors influencing either the Planck data outside the SPT-SZ survey area or the SPT data at ell>2000.