Day 1209

Wednesday.  Thursday.  Friday.  Monday.

1701.08120
Cooperative photometric redshift estimation
Cavuoti et al

In the modern galaxy surveys photometric redshifts play a role in a broad range of studies, from gravitational lensing and DM distribution to galaxy evolution.  Using a dataset of about 25,000 galaxies from KiDS-DR2, obtain photo-zs with 5 different methods (i) random forest, (ii) multi layer perception with quasi newton algorithm, (iii) multi layer perception with an optimization network based on the Levenberg-Marquardt learning rule, (iv) the Bayesian Photometric redshift model (BPZ) and (v) a classical SED template fitting procedure (Le Phare).  Show how SED fitting techniques could provide useful information on the galaxy spectral type which can be used to improve the capability of machine learning methods constraining systematic errors and reduce the occurrence of catastrophic outliers.  Use such classification to train specialized regression estimators, by demonstrating that such hybrid approach, involving SED fitting and machine learning in a single collaborative framework, is capable to improve the overall prediction accuracy of photometric redshifts.

Day 1208

Thursday.  Friday.  Monday.  Tuesday.

1701.06066
Environmental dependence of the galaxy stellar mass function in the Dark Energy Survey Science Verification Data
Etherington et al

Measurements of the galaxy stellar mass function are crucial to understand the formation of galaxies in the Universe.  In a hierarchical clustering paradigm it is plausible that there is a connection between the properties of galaxies and their environments.  Evidence for environmental trends has been established in the local universe.  DES provides large photometric datasets that enable further investigation of the assembly of mass.  In this study, use ~3.2 million galaxies from the SPT-East field in the DES SV dataset.  From grizY photometry, derive galaxy stellar masses and absolute magnitudes, and determine the errors on these properties using MC sims using the full photo-z probability distributions.  Compute galaxy environments using a fixed conical aperture for a range of scales.  Construct galaxy environment probability distribution functions and investigate the dependence of the environment errors on the aperture parameters.  Compute the environment components of the galaxy stellar mass function for the redshift range 0.15<z<1.05.  For z<0.75 find that the fraction of massive galaxies is larger in high density environment than in low density environments.  Show that the low density and high density components converge with increasing redshift up to z~1.0 where the shapes of the mass function components are indistinguishable.  The study shows how high density structures build up around massive galaxies through cosmic time.

Day 1207

Monday.  Tuesday.  Wednesday.

1701.03792
ot so lumpy after all: modeling the depletion of dark matter subhaloes by Milky Way-like galaxies
Garrison-Kimmel, Wetzel, et al

Explore the effects of baryons on subhalo populations in LCDM using cosmo zoom-in baryonic sims of MW-mass haloes from the Latte sim suite, part of FIRE.  Compare sims of the same 2 haloes run using (1) DM-only (2) full baryonic physics, and (3) DM with an embedded disk potential grown to match the FIRE sim.  Relative to baryonic sims, DMO sims contain ~2x as many subhaloes within 100 kpc of halo center; this excess is >5x within 25 kpc.  At z=0, the baryonic sims are completely devoid of sub haloes down to 3e6 Msun within 15 kpc of the MW-mass galaxy.  Despite the complexities of baryonic physics, the simple addition of an embedded central disk potential to DMO sims reproduces this subhalo depletion, including trends with radius, remarkably well.  Thus, the additional tidal field from the central galaxy is the primary cause of subhalo depletion. Subhalos on radial orbits that pass close to the central galaxy are preferentially destroyed, causing the surviving subhalo population to have tangentially biased orbits compared to DMO predictions.  The method of embedding a disk potential in DMO sims provides a fast and accurate alternative to full baryonic sims, thus enabling suites of cosmo sims that can provide accurate and statistical predictions of substructure populations.

Day 1206

Wednesday.  Thursday.  Friday.

1701.02307
Intrinsic alignment of redMaPPer clusters: cluster shape - matter density correlation
van Uitert, Joachimi

Measure the alignment of the shapes of galaxy clusters, as traced by their satellite distributions, with the matter density field using the public redMaPPer catalogue based on SDSS-DR8, which contains 26111 clusters up to z~0.6.  The clusters are split into nine redshift and richness samples; in each of them a positive alignment is detected, showing that clusters point towards density peaks.  Interpret the measurements within the tidal alignment paradigm, allowing for a richness and redshift dependence.  The IA amplitude at the pivot redshift z=0.3 and pivot richness lambda=30 is A_IA^gen = 12.6±1.5.  Obtain tentative evidence that the signal increases towards higher richness and lower redshift.  The measurements agree well with results of maxBCG clusters and with DM-only sims.  Comparing the results to IA measurement of luminosities red galaxies, find that the IA amplitude of galaxy cluster forms a smooth extension towards higher mass.  This suggests that these systems share a common alignment mechanism, which can be exploited to improve the physical understanding of IA.


1701.02739
Fast weak lensing simulations with halo model
Giocoli, et al

Full ray-tracing maps of GL, constructed from N-body sims, represent a fundamental tool to interpret present and future WL data.  However the limitation of computational resources and storage capabilities severely restrict the number of realisations that can be performed in order to accurately sample both the cosmic shear models and covariance matrices.  In this paper, present a halo model formalism for WL that allows to alleviate these issues by producing WL mocks at a reduced computational cost.  The model as input the halo population within a desired light-cone and the linear power spectrum of the underlined cosmo model.  Examine the contribution given by the presence of substructures within haloes to the cosmic shear power spectrum and quantify it to the percent level.  The method allows to reconstruct high-resolution convergence maps, for any desired source redshifts, of light-cones that realistically trace the matter density distribution in the universe, account for masked area and sample selections.  Compare the analysis on the same large scale structures constructed using ray-tracing techniques and find very good agreements both in the linear and non-linear regimes up to few percent levels.  The accuracy and speed of the method demonstrate the potential of the halo model for WL statistics and the possibility to generate a large sample of convergence maps for different cosmological models as needed for the analysis of large galaxy redshift surveys.


1701.02743
ZOMG II: does the halo assembly history influence central galaxies and gas accretion?
Romano-Diaz, et al

The growth-rate and the internal dynamics of galaxy-sized DM haloes depend on their location within the cosmic web.  Haloes that sit at the nodes grow in mass till the present time and are dominated by radial orbits.  Using zoom hydrodynamical sims including SF and feedback, study how gas accretes onto these different classes of objects that, for simplicity, dub 'accreting' and 'stalled' haloes.  Find that all haloes get a fresh supply of newly accreted gas in their inner regions, although this slowly decreases with time, in particular of the stalled haloes.  The inflow of new gas is always higher than (but comparable with) that of recycled material.  Overall, the cold-gas fraction increases (decreases) with time for the accreting (stalled) haloes. In all cases, a stellar disc and a bulge form at at the centre of the simulated haloes.  The total stellar mass is in excellent agreement with expectations based on the abundance-matching technique.  Many properties of the central galaxies do not seem to correlate with the large-scale environment in which the haloes reside.  However, there are two notable exceptions that characterize stalled haloes with respect to their accreting counterparts: i) the galaxy disc contains much older stellar populations; ii) its vertical scale-height is larger by a factor of two or more.  This thickening is likely due to the heating of the long-lived discs by mergers and close flybys.


1701.02954
Searching for galaxy clusters in the Kilo-Degree Survey
Radovich, et al

Present the tools used to search for galaxy clusters in KiDS, and the first results.  The cluster detection is based on an implementation of the optimal filtering technique that enables to identify clusters as over-densities in the distribution of galaxies using their positions on the sky, magnitudes, and photometric redshifts.  The contamination and completeness of the cluster catalog are derived using mock catalogs based on the data themselves.  The optimal signal to noise threshold for the cluster detection is obtained by randomizing the galaxy positions and selecting the value that produces a contamination of less than 20%.  Starting from a subset of clusters detected with high significance at low redshifts, shift them to higher redshifts to estimate the completeness as a function of redshift: the average completeness is ~85%.  An estimate of the mass of the clusters is derived using the richness as a proxy.  Obtained 1858 candidate clusters with 0<z_c<0.7 and mass 13.5<log(M500/Msun)<15 in an area of 114 eq. degrees (KiDS ESO-DR2).  A comparison with publicly available SDSS-based cluster catalogs shows that 50% of the clusters are matched (77% in the case of the redMaPPer catalog).  Also cross-matched the cluster catalog with the Abell clusters, and clusters found by XMM and in the Planck-SZ survey; however, only a small number of them lie inside the KiDS area currently available.

Day 1205

Tuesday.  Wednesday.  Thursday.  Friday.  Monday.  Tuesday.

1701.02151
Microlensng constraints on $10^{-10}M_¥odot$-scale primordial black holes from high-cadence observation of M31 with Hyper Suprime-Cam
Niikura, Takada, et al

Use HSC to conduct a high-cadence (2-min sampling) 7-hour long observation of Andromeda (M31) to search for the microlensing magnification of stars in M31 due to intervening primordial BHs (PBHs) in the halo regions of the MW and M31.  The combination of an aperture of 8.2m, a field-of-view of 1.5 degree diameter, and excellent image quality yields an ideal dataset for the microlensing search.  If PBHs in the mass range M_PBH=1e-13,qe-6 Msun make up a dominant contribution to DM, the microlensing optical depth for a single star in M31 is tau~1e-4--1e-7, owing to the enormous volume and large mass content between M31 and the Earth.  The HSC observation allows us to monitor more than tens of millions of stars in M31 and in this scenario we should find many microlensing events.  To test this hypothesis, extensively use and image subtraction method to efficiently identify candidate variable objects, and then monitor the light curve of each candidate with the high cadence data.  Although a number of real variable stars such as eclipse/contact binaries and stellar flares are successfully identified, find only one possible candidate of PBH microlensing whose genuite nature is yet to be confirmed.  Then use this result to derive the most stringent upper bounds on the abundance of PBHs in the mass range.  When combined with other observational constraints, the constraint rules out almost all the mass scales for the PBH DM scenario where all PBHs share a single mass scale.  

Day 1204

Friday.  Christmas. Monday.  Wednesday.  Friday.  New Years. Monday.

1612.09582
Perspective on MOND emergence from Verlinde's "emergent gravity" and its recent test by weak lensing
Milgrom, Sanders

Highlight phenomenological aspects of Verlinde's recent proposal to account for the mass anomalies in galactic systems without dark matter -- in particular in their relation to MOND.  Welcome addition to the MOND lore as it is, this approach have reproduced, so far, only a small fraction of MOND phenomenology, and is still rather tentative, both in its theoretical foundations and in its phenomenology.  What Verlinde has extracted from the approach, so far, is a formula -- of rather limited applicability, and with no road to generalization in sight -- for the effective gravitational field of a spherical, isolated, static baryonic system.  This formula cannot be used to calculate the gravitational field of disk galaxies, with their rich MOND phenomenology.  Notably, it cannot predict their rotation curves, except asymptotically.  It does not apply to the few-, or many-body problem; so, it cannot give, e.g., the two-body force between two galaxies, or be used to conduct N-body calculation of galaxy formation, evolution, and interactions.  The formula cannot be applied to the internal dynamics of a system embedded in an external field, where MOND predicts important consequences, etc.  Monday is backed by full-fledged, Lagrangian theories that can be, and are, routinely applied to all the above phenomena, and more.  Verlinde's formula, as it now stands, strongly conflicts with solar-system constraints, and cannot fully account for the mass anomalies in the cores of galaxy clusters (a standing conundrum in MOND).  The recent weak-lensing test of the formula is, in fact, testing a cornerstone prediction of mOND, one that the formula does reproduce, and which hs been tested before in the very same way.