1604.01424
A 2.4% Determination of the local value of the Hubble constant
Rises, et al
Use WFC3 on HST to reduce the uncertainty in the local value of H0 from 3.3% to 2.4%. Improvements come from observations of Cepheid variables in 10 new hosts of recent SNeIa, more than doubling the sample of SNeIa having a Cepheid-calibrated distance for a total of 18; these leverage with magnitude-redshift relation based on 300 SNeIa at z<0.15. All 18 hosts and the megamaser system NGC4258 were observed with WFC3, thus nullifying cross-instruemtn zero point errors. Other improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC4258, more Cepheids and a more robust distance to the LMC from late-type DEBs, HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for MW Cepheids. Consider 4 geometric distance calibrations of Cepheids: (i) megamasers in NGC4258, (ii) 8 DEBs in the LMC, (iii) 15 MW Cepheids with parallaxes, and (iv) 2 DEBs in M31. The H0 from each is 72.39±2.56, 71.93±2.70, 76.09±2.42, and 74.45±3.34 km/s/Mpc, respectively. The best estimate of 73.03±1.79 km/s/Mpc combines the anchors NGC4258, MW and LMC, and includes systematic errors for a final uncertainty of 2.4%. This value is 3.0 sigma higher than 67.3±0.7 km/s/Mpc predicted by LCDM with 3 neutrinos with a mass of 0.06 eV and the Planck data, but reduces to 1.9 sigma relative to the prediction of 69.3±0.7 km/s/Mpc with the combination of WMAP+ACT+SPT+BAO, suggesting systematic uncertainties in CMB measurements may play a role in the tension. If the conflict between Planck and the H0 is taken at face value, one plausible explanation could involve an additional source of dark radiation in the early Universe in the range of Delta N_eff=0.4-1. Anticipate signifiant improvements in H0 from upcoming parallax measurements.
1604.01769
Microlensing as a possible probe of event-horizon structure in quasars
Tomozeiu, Mohammed, Rabold, Saha, Wambsganss
In quasars which are lensed by galaxies, the point-like images sometimes show sharp and uncorrelated brightness variations (microlensing). These brightness changes are associated with the innermost region of the quasar passing through a complicated pattern of caustics produced by the stars in the lensing galaxy. In this paper, study whether the universal properties of optical caustics could enable extraction of shape information about the central engine of quasars. Present a toy model with a precent-shaped source crossing a fold caustic. The silhouette of a black hole over an accretion disk tends to produce roughly crescent sources. When a crescent-shaped source crosses a fold caustic, the resulting light curve is noticeably different form the case of a circular luminosity profile or Gaussian source. With good enough monitoring data, the crescent parameters, apart from one degeneracy, can be recovered.
1604.01788
The Carnegie-Chicago Hubble Program. I. A new approach to the distance ladder using only distance indicators of population II
Beaton, et al
An ongoing program to obtain a 3% measurement of H0 using alternative methods to the traditional Cepheid distance scale. Aim to establish a completely independent rout to H0 using RR Lyrae variables, the tip of the red giant branch (RGB), and SNeIa. This alternative distance ladder can be applied to galaxies of any Hubble Type, of any inclination, and, utilizing old stars in low density environments, is robust to the degenerate effects of metallicity and interstellar extinction. Given the relatively small number of SNeIa host galaxies with independently measured distances, these properties prove a great systematic advantage in the measurement of the Hubble constant via the distance ladder. Initially, the accuracy of the value of the Hubble constant will be set by the 5 Galactic RR Lyrae calibrators with HST Fine-Guidance Sensor parallaxes. With GAIA, bot the RR Lyrae zero point and TRGB method will be independently calibrated, the former with at least an order of magnitude more calibrators and the latter directly through parallax measurement of tip red giants. As the first end-to-end "distance ladder" completely independent of both Cepheid variables and the LMC, this path to H0 will allow for the high precision comparison at each rung of the traditional distance ladder that is necessary to understand tensions between this and other routs to H0.
1604.01923
Galaxy and mass assembly (GAMA): accurate panchromatic photometry from Optical priors using LAMBDAR
Wright, Robotham, et al
Present the Lambda Adaptive Multi-Band Deblending Algorithm in R (LAMBDAR), a novel code for calculating match aperture photometry across images that are neither pixel- nor PSF-matched, using prior aperture definitions derived from high res optical imaging. The development of this program is motivated by the desire for consistent photometry and uncertainties across large ranges of photometric imaging, for use in calculating spectral energy distributions. Describe the program, specifically key features required for robust determination of panchromatic photometry: propagation of aperture to images with arbitrary resolution, local background estimation, aperture normalization, uncertainty determination and propagation, and object deblending. Using simulated images, demonstrate that the program is able to recover accurate photometric measurements in both high-resolution, low-confusion, and low-resolution, high-confusion, regimes. Apply the program to the 21-band photometric dataset from GAMA Panchromatic Data Release (PDR: Driver+2016), which contains imaging spanning the far-UV to the far-IR. Compare photometry derived form LAMBDAR with that presented in Driver+2016, finding broad agreement between the datasets. Nonetheless, demonstrate that the photometry from LAMBDAR is superior to that form the GAMA PDR, as determined by a reduction in the outlier rate and intrinsic scatter of colors in the LABMDA dataset. Similarly find a decrease in the outlier rate of stellar masses and SFRs using LAMBDAR photometry. Finally, note an exceptional increase in the number of UV and mid-IR sources able to be constrained, which is accompanied by a significant increase in the mid-IR colour-colour parameter-space able to be explored.
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