Wednesday.
1512.03057
Exploring the SDSS Photometric galaxies with clustering redshifts
Rahman, Mendez, Ménard, Scranton, Schmidt, Morrison, Budavári
Apply clustering-based z inference to all extended source from SDSS photometric catalogue, down to r=22. Map the relationships between colors and redshift, without assumption of the sources' spectral energy distributions (SED). Identify and late SF, quiescent galaxies, and AGN, as well as color changes due to spectral features, such as the 4000 A break, redshirting through specific filters. The mapping is globally in good agreement with color-reshift tracks computed with SED templates, but reveals informative differences, such as the need for a lower fraction of M-type stars in certain templates. Compare the clustering-redshift estimates to photometric z and find those two independent estimators to be in good agreement at each limiting magnuide considered. Finally, present the global clustering-redshift distribution of Sloan extended sources, showing objects up to z~0.8. While the overall shape agrees with that inferred from photometric redshifts, the clustering redshift technique results in a smoother distribution, with no indication of structure in redshift space suggested by the photo-z estimates (likely artifacts imprinted by their spectra training set). Also infer a higher fraction of high-z objects. The mapping between the 4 observed colors and redshift can be used to estimate the z probability distribution function of individual galaxies. This work is an initial step towards producing a general mapping between redshift and all available observables in the photometric space, including brightness, size, concentration, and ellipticity.
1512.03814
The XXL Survey. XIII. Baryon content of the bright cluster sample
Eckert, et al
Traditionally, galaxy clusters have been expected to retain all the material accreted since their formation epoch. For this reason, their matter content should be representative of the Universe as a whole, and thus their baryon fraction should be close to the Universal baryon fraction. Make use of the sample of the 100 brightest galaxy clusters discovered in the XXL survey to investigate the fraction of baryons in the form of hot gas and stars in the cluster population. Measure the gas masses of the detected haloes and use a mass--temperature relation directly calibrated using WL measurements for a subset of XXL clusters to estimate the halo mass. Find that the WL calibrated gas fraction of XXL-100-GC clusters is substantially lower than was found n previous studies using hydrostatic masses. The best-fit relation between gas fraction and mass reads f_gas,500 = 0.055±0.007(M_500/1e14 Msun)^0.21±0.11. The baryon budget of galaxy clusters therefore falls short of the Universal baryon fraction by about a factor of two at r_500. The measurements require a hydrostatic bias 1-b=M_X/M_WL=0.72±0.08 to match the gas fraction obtained using lensing and hydrostatic equilibrium. Comparing the gas fraction measurements with the expectations from numerical simulations, the results favor an extreme feedback scheme in which a significant fraction of the baryons are expelled from the cores of halos. This model is, however, in contrast with the thermodynamical properties of observed haloes, which might suggest that WL masses are over estimated. Note that the mass bias 1-b=0.58 as required to reconcile Planck CMB and cluster counts should translate into an even lower baryon fraction, which poses a major challenge to the current understanding of galaxy clusters.
1512.04535
Cross-correlation of gravitational lensing from DES science verification data with SPT and Planck lensing
Kirk, et al
Measure the cross-correlation between WL of galaxy images and of the CMB. The effects of gravitational lensing on different sources will be correlated if the ending is caused by the same mass fluctuations. Use galaxy shape measurements from DES SV (139 deg sq) and overlapping CMB lensing from SPT and Planck. The DES source galaxies have a median redshift of z_med~0.7, while the CMB lensing kernel is broad and peaks at z~2. The resulting cross-correlationis maximally sensitive to mass fluctuations at z~0.44. Assuming the Planck 2015 best-fit cosmology, the amplitude of the DESXSPT cross-power is found to be A=0.88±0.30 and that from DESXPlanck to be A=0.86±0.39, where A=1 corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of 2.9sigma and 2.2sigma respectively. Demonstrate that the results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photometric z uncertainty and CMB lensing systematics. Significant IA of galaxy shapes would increase the X-corr signal inferred from the data; calculate a value of A=1.08±0.36 for DESXSPT when correcting the observations with a simple IA model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation, given the size of the statistical uncertainties and the significant impact of systematic errors, particularly IAs. Provide forecasts for the expected S/N of the combination of the 5-year DES survey and SPT-3G.
1512.04654
Deja Vu all over again: The reappearance of supernova Refsdal
Kelly, et al
In HST imaging taken on 10 Nov 2014, 4 images of SN 'Refsdal' (z=1.49) appeared in an Einstein-cross--like configuration (images S1-S4) around an early-type galaxy in the cluster MACS J1149.5+2223 (z=0.54). The gravitational potential of the cluster creates 3 full images of the SF host galaxy of the SN. Almost all lens models of the cluster have predicted that the SN should reappear within approximately one year in a second host-galaxy image, offset by ~8" from the previous images. In HST observations taken on 11 Dec 2015, find a new source that is interpreted as a new image of SN Refsdal. This marks the first time the appearance of a SN a a particular time and location in the sky was successfully predicted in advance! Use these data and the light curve from the first 4 observed images of SN Refsdal to place constraints on the relative time delay and magnification of the new image (SX), compare to images S1-S4. This enables, for the first time, to test lens model predictions of both magnifications and time delays for a lensed SN. Find that the timing and brightness of the new image are consistent with the blind predictions of a fraction of the models. The reappearance illustrate the discriminatory power of this blind test and its utility to uncover sources of systematic uncertainty in the lens models. From planned HST photometry, expect to reach precision of 1-2% on the relative time delay between S1-S4 and SX.
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