1803.03266
Dark haloes around neutron stars and gravitational waves
Nelson, Reddy, Zhou
Find that a class of models of MeV-GeV DM in which DM interacts strongly can be constrained by the observation of gravitational waves from neutron star mergers. Trace amounts of dark matter, either produced during the SN or accreted later, can alter the structure of NSs and influence their tidal polarizability. Focus on models of DM interacting by the exchange of light vector gauge bosons that couple to a conserved dark charge. In these models, dark matter accumulated in NSs can extend to large radii and enhance their tidal polarizability. Gravitational waves detected from the first binary NS merger GW170817 places useful constraints on such not-so compact objects. Dark haloes, if present, also predict a greater variability of NS tidal polarizabilities than expected for ordinary NSs.
1809.01146
Modeling baryonic physics in future weak lensing surveys
Huang, Eifler, Mandelbaum, Dodelson
Modifications of the matter power spectrum due to baryonic physics are one of the major theoretical uncertainties in cosmological WL measurements. Developing robust mitigation schemes for this source of systematic uncertainty increases the robustness of cosmological constraints, and may increase their precision if they enable the use of information from smaller scales. Here, explore the performance of two mitigation schemes for baryonic effects in WL cosmic shear: the PCA method and the halo-model approach in HMcode. Construct mock tomographic shear power spectra from four hydrodynamical simulations, and run simulated likelihood analyses with CosmiLike assuming LSST-like survey statistics. With an angular scale cut of ell_max<2000, both methods successfully remove the biases in cosmo parameters due to the various baryonic physics scenarios, with the PCA method causing less degradation in the parameter constraints than HMcode. For a more aggressive ell_max=5000, the PCA method performs well for all but one baryonic physics scenario, requiring additional training simulations to account for the extreme baryonic physics scenario of Illustris; HMcode exhibits tensions in the 2D poster distributions of cosmoloigal parameters due to lack of freedom in describing the PS for k>10/h Mpc. Investigate variants of the PCA method and improve the bias mitigation through PCA by accounting for the noise properties in the data via Cholesky decomposition of the covariance matrix. The improved PCA method allows for retention of more statistical constraining power while effectively mitigating baryonic uncertainties even for a broad range of baryonic physics scenarios.
1809.01171
The causes of the red sequence, the blue cloud, the green valley and the green mountain
Eals, et al
The galaxies found in optical surveys fall in two distinct regions of a diagram of optical color versus absolute magnitude: the red sequence and the blue cloud with the green valley in between. Show that the galaxies found in a submillimetre survey have almost the opposite distribution in this diagram, forming a 'green mountain'. Show that these distinctive distributions follow naturally from a single, continuous, curved Galaxy Sequence in a diagram of specific star-formation rate versus stellar mass without there being the need for a separate star-forming galaxy MS and region of passive galaxies. The cause of the red sequence and the blue cloud is the geometric mapping between stellar mass/sSFR and absolute magnitude/colour, which distorts a continuous Galaxy Sequence in the diagram of intrinsic properties into a bimodal distribution in the diagram of observed properties. The cause of the green mountain is Malmquist bias in the submillimetre waveband, with submillimetre surveys tending to select galaxies on the curve of the Galaxy Sequence, which have the highest ratios of submillimetre-to-optical luminosity. Thiseffect, working in reverse, causes galaxies on the curve of the Galaxy Sequence to be underrepresented in optical samples, deepening the green valley. The green valley is therefore not evidence (1) for there being two distinct populations of galaxies, (2) for galaxies in this region evolving more quickly than galaxies in the blue cloud and the red sequence, (c) [3?] for rapid quenching processes in the galaxy population.
1809.01274
H0LiCOW - IX. Cosmographic analysis of the doubly imaged quasar SDSS 1206+4332 and a new measurement of the Hubble constant
Birrer, Treu, et al
Present a blind time-delay strong lensing (TDSL) cosmographic analysis of the doubly imaged quasar SDSS 1206+4332. Combine the relative time delay between the quasar images, HST imaging, the Keck stellar velocity dispersion of the lensing galaxy, and wide-field photometric and spectroscopic data of the field to constrain two angular diameter distance relations. The combined analysis is performed by forward modeling the individual data sets through a Bayesian hierarchical framework, and it is kept blind until the very end to prevent experimenter bias. After unblinding, the inferred distances imply a Hubble constant H0=68.8+5.4-5.1 km/s/Mpc, assuming a flat Lambda CDM cosmology with uniform prior on Omega_m in [0.05,0.5]. The precision of the cosmographic measurement with the doubly imaged quasar SDSS 1206+4332 is comparable with those of quadruply imaged quasars and opens the path to perform on selected doubles the same analysis as anticipated for quads. The analysis is based on a completely independent lensing code than the previous 3 H0LiCOW systems and the new measurement is fully consistent with those. Provide the analysis scripts paired with the publicly available software to facilitate independent analysis. The consistency between blind measurements with independent codes provides an important sanity check on lens modeling systematics. By combining the likelihoods of the 4 systems under the same prior, obtain H0=72.5+2.1-2.3 km/s/Mpc. This measurement is independent of the distance ladder and other cosmological probes.
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