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1707.01904
Individual stellar halos of massive galaxies measured to 100 kpc at $0.3<z<0.5$ using Hyper Suprime-Cam
Huang, Leauthaud, et al
Massive galaxies display extended light profiles that can reach several hundreds of kilo parsecs. These stellar halos provide a fossil record of galaxy assembly histories. Using data that is both wide (~100 sq deg) and deep (i>28.5 mag/arcsec^1 in i-band), present a systematic study of stellar haloes of a sample of more than 3000 galaxies at 0.3<z<0.5 with log M*/Msun>11.4. The study is based on high-quality (0.6 arcsec seeing) imaging data from HSC SSP, which enables us to individually estimate surface mass density profiles to 100 kpc without stacking. As in previous work, find that more massive galaxies exhibit more extended outer profiles. When this expended light is not properly accounted for as a result of shallow imaging or inadequate profile modeling, the derived stellar mass function can be significantly underestimated at the highest masses. Across the sample, the ellipticity of outer light profiles increases substantially as larger radii is probed. Show for the first time that these ellipticity gradients steepen dramatically as a function of galaxy mass, but detect no mass-dependence in outer color gradients. The results support the two-phase formation scenario for massive galaxies in which outer envelopes are built up at late times from a series of merging events. Provide surface mass density profiles in a convenient tabulated format to facilitate comparisons with predictions from numerical simulations of galaxy formation.
1707.01907
Constraints on the mass-richness relation from the abundance and weak lensing of SDSS clusters
Murata, et al
Develop a method for constraining the scaling relation of optical richness (lambda) with halo masses (M) for a sample of galaxy clusters based on a forward modeling approach for the Planck cosmology, where the probability distribution of optical richness for a given mass is modeled: P(ln lambda | M). To model the abundance and the stacked lensing profiles, employ the halo emulator that outputs the halo mass function and the stacked lensing profile for an arbitrary set of halo mass and redshift, calibrated based on a suite of high-resolution N-body simulations. By applying the method to 8,312 SDSS redMaPPer clusters with 20<=lambda<=100 and 0.10<=z_lambda<=0.33, show that the log-normal distribution model for P(ln lambda | M), with four free parameters, well reproduces the measured abundances and lensing profiles simultaneously. The constraints are characterized by the mean relation, <ln lambda>(M)=A+Bln(M/Mpivot), with A=3.21 and B=1.00 for the pivot mass scale Mpivot=3e14 Msun/h, and the scatter sigma_{ln_lambda|M} = sigma_0 + q ln(M/Mpivot) with sigma_0=0.45 and q=-0.17. However, find that a large scatter for the low richness bins, especially 20<=lambda<~30, is required in order for the model to reproduce the measurements by the contributions from low-mass haloes for the Planck cosmology. Without such a large scatter, the model prediction for the lensing profiles tends to overestimate the measured amplitudes. This might imply a possible contamination for low-richness clusters due to the projection effects. Such a low-mass halo contribution is significantly reduced when applying the method to the sample of 30<=lambda<=100.
1707.01908
Microlensing makes lensed quasar time delays significantly time variable
Tie, Kochanek
The time delays of gravitationally lensed quasars are generally believed to be unique numbers whose measurement is limited only by the quality of the light curves and the models for the contaminating contribution of gravitational microlensing to the light curves. This belief is incorrect -- gravitational microlensing also produces changes in the actual time delays on the ~day(s) light-crossing time scale of the emission region. This is due to a combination of the inclination of the disk relative to the line of sight and the differential magnification of the temperature fluctuations producing the variability. Demonstrate this both mathematically and with direct calculations using microlensing magnification patterns. Measuring these delay fluctuations can provide a physical scale for microlensing observations, removing the need for priors on either the microlens masses or the component velocities. That time delays in lensed quasars are themselves time variable likely explains why repeated delay measurements of individual lensed quasars appear to vary by more than their estimated uncertainties. This effect is also an important new systematic problem for attempts to use time delays in lensed quasars for cosmology or to detect substructures (satellites) in lens galaxies.
1707.02160
TOPCAT: Desktop exploration of tabular data for astronomy and beyond
Taylor
TOPCAT, the Tool for OPerations on Catalogues And Tables, is an interactive desktop application for retrieval, analysis and manipulation of tabular data, offering a powerful and flexible range of interactive visualization options amongst other features. Its visualization capabilities focus on enabling interactive exploration of large static local tables - millions of rows and hundreds of columns can easily be handled on a standard desktop or laptop machine, and various options are provided for meaningful graphical representation of such large datasets. TOPCAT has been developed in the context of astronomy, but many of its features are equally applicable to other domains. The software, which is free and open source, is written in Java, and the underlying high-performance visualization library is suitable for re-use in other applications.
1707.02259
Exploring cosmic origins with CORE: gravitational lensing of the CMB
Challinor, et al
Lensing of the CMB is now a well-developed probe of LS clustering over a broad range of redshifts. By exploiting the non-Gaussian imprints of lensing in the polarization of the CMB, the CORE mission can produce a clean map of the lensing deflections over nearly the full-sky. The number of high-S/N modes in this map will exceed current CMB lensing maps by a factor of 40, and the measurement will be sample-variance limited on all scales where linear theory is valid. Here, summarize this mission product and discuss the science that it will enable. For example, the summed mass of neutrinos will be determined to an accuracy of 17 meV combining CORE lensing and CMB two-point information with contemporaneous BAO measurements, 3 times smaller than the minimum total mass allowed by neutrino oscillations. In the search for B-mode polarization from primordial gravitational waves with CORE, lens-induced B-modes will dominate over instrument noise, limiting constraints on the gravitational wave power spectrum amplitude. With lensing reconstructed by CORE, one can "delens" the observed polarization internally, reducing the lensing B-mode power by 60%. This improves to 70% by combing lensing and CIB measurements from CORE, reducing the error on the gravitational wave amplitude by 2.5 compared to no delensing (in the null hypothesis). Lensing measurements from CORE will allow calibration of the halos masses of the 40,000 galaxy clusters that it will find, with constraints dominated by the clean polarization-based estimators. CORE can accurately remove Galactic emission from CMB maps with its 19 frequency channels. Present initial findings that show that residual Galactic foreground contamination will not be a significant source of bias for lensing power spectrum measurements with CORE.
1707.02863
The impact of redshift on galaxy morphometric classification: case studies for SDSS, DES, LSST and HST with Morfometryka
de Albernaz Ferreira, Ferrari
Carried a detailed analysis on the impact ofcosmo redshift in the non-parametric approach to automated galaxy morphology classification. Artifically redshifted each galaxy from the EFIGI 4458 sample (re-centered at z~0) simulating SDSS, DES, LSST, and HST instruments setups over the range 0<z<1.5. Then traced how the morphometry is degraded in each z using Morfometryka. In the process, re-sampled all catalog to several resolutions and to a diverse SNR range, allowing us to understand the impact of image sampling and noise on the measurements separately. Summarize by exploring the impact of these effects on the capacity to perform automated galaxy supervised morphological classification by investigating the degradation of the classifier's metrics as a function of redshift for each instrument. The overall conclusion is that a reliable classification can be made for z<0.2 with SDSS, z<0.5 with DES, z<0.8 for LSST and for at least z<1.5 with HST.
1707.03169
Morpho-z: improving photometric redshifts with galaxy morphology
Soo, Moraes, Joachimi, Hartley, Lahav, et al
Conduct a comprehensive study of the effects of incorporating galaxy morphology information in photometric redshift estimation. Using machine learning methods, assess the changes in the scatter and catastrophic outlier fraction of photometric redshifts when galaxy size, ellipticity, Service index and surface brightness are included in training on galaxy samples from the SDSS and the CFHT Stripe-82 survey (CS82). Show that by adding galaxy morphological parameters to full ugriz photometry, only mild improvements are obtained, while the gains are substantial in cases where fewer passbands are available. For instance, the combination of grz photometry and morphological parameters almost fully recovers the metrics of 5-band photo-zs. Demonstrate that with morphology, it is possible to determine useful redshift distribution N(z) of galaxy samples without any color information. Also find that the inclusion of quasar redshifts and associated object sizes in training improves the quality of photometric redshift catalogues, compensating for the lack of a good star-galaxy separator. Further show that morphological information can mitigate biases and scatter due to bad photometry. As an application, derive both point estimates and posterior distributions of redshifts for the official CS82 catalogue, training on morphology and SDSS Stripe-82 ugriz bands when available. The redshifts yield a 68th percentile error of 0.058(1+z), and a catastrophic outlier fraction of 5.2 per cent. Further include a deep extension trained on morphology and single i-band CS82 photometry.
1707.03358
Small-scale structure and the Lyman-$\alpha$ forest baryon acoustic oscillation feature
Hirata
The BAO feature in the Ly-a forest is one of the key probes of the cosmic expansion rate at z~2.5, well before DE is believed to have become dynamically significant. A key advantage of the BAO as a standard ruler is that it is a sharp feature and hence is more robust against broadband systematic effects than other cosmo probes. However, if the Ly-a forest transmission is sensitive to the initial streaming velocity of the baryons relative to the dark matter, then the BAO peak position can be shifted. Investigate this sensitivity using a suite of hydro sims of small regions of the IGM with a range of box sizes and physics assumptions; each sim starts from initial conditions at the kinematic decoupling era (z~1059), undergoes a discrete change from neutral gas to ionized gas thermal evolution at reionization (z~8), and is finally processed into a Ly-a forest transmitted flux cube. Streaming velocities suppress small-scale structure, leading to less violent relaxation after reionization. The changes in the gas distribution and temperature-density relation at low z are more subtle, due to the convergent temperature evolution in the ionized phase. The change in the BAO scale is estimated to be of the order of 0.12% at z=2.5; some of the major uncertainties and avenues for future improvement are discussed. The predicted streaming velocity shift would be a subdominant but not negligible effect (of order 0.26 sigma) for the upcoming DESI Ly-a forest survey, and exceeds the cosmic variance floor. It is hoped that this study will motivate additional theoretical work on the magnitude of the BAO shift, both in the Ly-a forest and in other tracers of LSS.
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