1811.04083
Early dark energy can resolve the Hubble tension
Poulin, Smith, Karwal, Kamionkowski
Early dark energy (EDE) that behaves like cosmological constant at early times (z>~3000) and then decays away like radiation or faster at later times can solve the Hubble tension. In these models, the sound horizon at decoupling is reduced resulting in a larger value of the Hubble parameter H0 inferred from the CMB. Consider 2 physical models for this EDE, one involving an oscillating scalar field and another a slowly-rolling field. Perform a detailed calculation of the evolution of perturbations in these models. A MCMC search of the parameter space for the EDE parameters, in conjunction with the standard cosmological parameters, identifies regions in which H0 inferred from Planck CMB data agrees with the SH0ES local measurement. In these cosmologies, current BAO and SN data are described as successfully as in LCDM while the fit to Planck data is slightly improved. Future CMB and large-scale-structure surveys will further probe this scenario.
1811.04098
Systematically measuring Ultra Diffuse Galaxies (SMUDGes). I. Survey description and first results in the Coma galaxy cluster and environs
Zaritsky, et al
Present a homogeneous catalog of 275 large (effective radius >~5.3 arcsec) UDG candidates lying within an ~290 sq deg region surrounding the Coma cluster. The catalog results from the automated post processing of data from the Legacy Surveys, a 3-band imaging survey covering 14000 sq deg of the extragalactic sky. Describe a pipeline that identifies UDGs and provides their basic parameters. The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma cluster. Conclude that the majority of the detections are at roughly the distance of the Coma cluster, implying effective radii >=2.5 kpc, and that the sample contains a significant number of analogs of DF44, where the effective radius exceeds 4 kpc, both within the cluster and in the surrounding field. The g-z color of the UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories. A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but find both red and blue UDG candidates in the vicinity of the Coma cluster and a relative overabundance of blue UDG candidates in the lower density environments and the field. The eventual processing the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.
1811.04714
The stellar halo of isolated central galaxies in the Hyper Suprime-Cam imaging survey
Wang, et al
Study the faint stellar halo of isolated central galaxies, by stacking galaxy images in the HSC survey and accounting for the residual sky background sampled with random points. The surface brightness profiles in HSC r-band are measured up to 120 kpc from the galaxy center for a wide range of galaxy stellar mass (9.2<log_10(M*/Msun)<11.4), and down to a surface brightness of about 32.8 mag/arcsec^2, which an indication of signals to even large scales and fainter magnitudes. Failing to account for the outer stellar halo below the noise level of individual images will lead to underestimates of the total luminosity by <=20%. Splitting galaxies according to the concentration parameter of their light distributions, find that the surface brightness profiles of low concentration galaxies drop faster between 20 kpc and 100 kpc and are more extended beyond 100 kpc than those of high concentration galaxies. The profile of low concentration galaxies persist out to the average halo viral radius. Albeit the large galaxy-to-galaxy scatter, find a strong self-similarity of the stellar halo profiles. They show unified forms once the projected distance is scaled by the halo viral radius. The color of the stellar halo is redder in the center and bluer outside, with high concentration galaxies having redder and flatter color profiles. Such a color gradient persists to about 80 kpc for galaxies more massive than 1e10.2 Msun, whereas for galaxies with 9.2<log_10(M*/Msun)<10.2, the gradient is consistent with being flat between 10 and 30 kpc.
1811.04798
From globular clusters to the disc: the dual life of our Galaxy
Recio-Blanco
The halo and disc globular cluster population can be used as a tracer of the primordial epochs of the MW formation. In this work, literature data of globular clusters ages, chemical abundances, and structural parameters are studied, explicitly focussing on the origin of the known split in the age-metallicity relation of globular clusters. When the alpha-element abundances, which are less strongly affected by the internal light-element spread of globular clusters (Si, Ca), are considered, a very low observational scatter among metal-poor clusters is observed. A plateau at [SiCa/Fe]~0.35 dex, with a dispersion of only 0.05 dex is observed up to a metallicity of about -0.75 dex. Only a few metal-poor clusters in this metallicity interval present low [SiCa/Fe] abundances. Moreover, metal-rich globular clusters show a knee in the [alpha/Fe] versus [Fe/H] plane around [Fe/H] -0.75 dex. As a consequence, if a substantial fraction of galactic globular clusters has an external origin, they have to be mainly formed either in galaxies that are massive enough to ensure high levels of [alpha/Fe] element abundances even at intermediate metallicity, or in lower mass dwarf galaxies accreted by the MW in their early phases of formation. Finally, clusters in the metal-poor branch of the AMR present an anti-correlation of [SiCa/Fe] with the total cluster magnitude, while this is not the case for metal-rich branch clusters. In addition, this lack of faint high-alpha clusters in the young metal-poor population is in contrast with what is observed for old and more metal-poor clusters, possibly reflecting a higher heterogeneity of formation environments at lower metallicity, accretion of high-mass satellites, as a major contribution to the current MW globular cluster system both in the metal-poor and the metal-intermediate regime is compatible with the observations.
1811.04934
An HSC view of the CMASS galaxy sample. Halo mass as a function of stellar mass, size and S\'ersic index
Sonnenfeld, Wang, Bahcall
Aim: to determine the distribution of DM halo masses as a function of the stellar mass and the stellar mass profile, for massive galaxies in the BOSS CMASS sample. Methods: use grimy photometry from HSC to obtain Sersic fits and stellar masses of CMASS galaxies for which HSC weak lensing data is available, visually selected to have spheroidal morphology. Apply a cut in stellar mass, log(M*/Msun) > 11.0, selecting ~10k objects. Using a Bayesian hierarchical inference method, first investigate the distribution of Sersic index and size as a function of stellar mass. Then, making use of shear measurements from HSC, measure the distribution of halo mass as a function of stellar mass, size and Sersic index. Results: the data reveals a steep stellar mass-size relation R_e ~ M*^beta_R, with beta_R larger than unity, and positive correlation between Sersic index and stellar mass: n~M*^0.46. Halo mass scales approximately with the 1.7 power of the stellar mass. Do not find evidence for an additional dependence of halo mass on size of Sersic index at fixed stellar mass. Conclusions: the results disfavor galaxy evolution models that predict significant differences in the size growth efficiency of galaxies living in low and high mass haloes.
1811.04940
Weak lensing analysis of galaxy pairs using CS82 data
Gonzalez, et al
Analyze a sample of close galaxies pairs (relative projected separation <25/h kpc and relative radial velocities <350 km/s) using a WL analysis based on the CFHT Stripe 82 survey. Determine halo masses for the Total sample of pairs as well as for Interacting, Red and Higher luminosity pair subsamples with ~3 sigma confidence. The derived lensing signal for the total sample can be fitted either by a singular isothermal sphere with sigma_V=223±24 km/s for a NFW profile with R_200=0.30±0.03 h^{-1} Mpc. The pair total masses and total r band luminosities imply an average mass-to-light ratio of ~200 h Msun/Lsun. On the other hand, Red pairs which include a large fraction of elliptical galaxies, show a large mass-to-light ratio of ~345 h Msun/Lsun. Derived lensing masses were compared to a proxy of the dynamical mass, obtaining a good correlation. However, there is a large discrepancy between lensing masses and the dynamical mass estimates, which could be accounted by astrophysical processes such as dynamical friction, by the inclusion of unbound pairs, and by significant deviations of the density distribution from a SIS and NFW profiles in the inner regions. Also compared lensing masses with group mass estimates obtained from the Yang+ galaxy group catalog, finding a very good agreement with the sample of groups with 2 members. Red and Blue pairs show large differences between group and lensing masses, which is likely due to the single mass-to-light ratio adopted to compute the group masses.
1811.04942
Satellite galaxies in the Illustris-1 simulation: anisotropic locations around relatively isolated hosts
Brainerd, Yamamoto
Investigate the locations of luminous satellite galaxies in the z=0 slice of the hydro sim Illustris-1. As expected from previous studies, the satellites are distributed anisotropically in the plane of the sky, with a preference for being located near the major axes of their hosts. Due to misalignment of mass and light within the hosts, the degree of anisotropy is considerably less when the mean satellite location is measured with respect to the hosts' stellar surface mass density then when it is measured with respect to the hosts' DM surface mass density. When measured with respect to the hosts' dark matter surface mass density, the mean satellite location depends strongly on host stellar mass and luminosity, with the satellites of the faintest, least massive hosts showing the greatest anisotropy. This is caused by a strong correlation between the degree of anisotropy in the plane of the sky and host-satellite proximity in 3d. The satellites of the faintest, least massive hosts are dominated by objects that are close to their hosts in 3d, whereas the satellites of the brightness, most massive hosts are dominated by objects that are far from their hosts in 3d. When measured with respect to the hosts' stellar surface mass density, the mean satellite location is essentially independent of host stellar mass and luminosity. The satellite locations are, however, dependent upon the stellar masses of the satellites, with the most massive satellites having the most anisotropic distributions.
1811.05790
Prestige Bias on Time Allocation Committees?
Greaves
The TAC-serving boost in getting proposals accepted supports the hypothesis of a bias in operation. The magnitude of the effect is remarkable, and not readily explained in a fair scenario. Alternative models include TAC-members being mainly driven to proposed while serving, but this seems doubtful for applications to a highly-sought facility. Or, TAC-members could gain expertise at the meetings, and so start to apply more successfully (itself, perhaps "unequal access"), but N(TAC) fell back substantially afterwards, contrary to such a model.
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