1606.08847
The Dragonfly Nearby Galaxies Survey. I. Substantial variation in the diffuse stellar haloes around spiral galaxies
Merritt, van Dokkum, Abraham, Zhang
Galaxies are through to grow through accretion; as less massive galaxies are disrupted and merge over time, their debris results in diffuse, clumpy stellar halos enveloping the central galaxy. Present a study of the variation in the stellar halos of galaxies, using data from the Dragonfly Nearby Galaxies Survey (DNGS). The survey consists of wide field, deep (mu_g>31 mag/arcsec^2) optical imagine of nearby galaxies using the Dragonfly Telephoto Array. The sample includes 8 spiral galaxies with stellar masses similar to that of the MW, inclinations of 16-90 degrees and distances between 7-18 Mpc. Construct stellar mass surface density profiles from the observed g-band surface brightness in combination with the g-r color as a function of radius, and compute the halo fractions from the excess stellar mass (relative to a disk+bulge fit) beyond 8 half-mass radii. Find a mean halo faction of 0.009±0.005 and a large RMS scatter of 1.10+0.9-0.26 dex. The peak-to-peak scatter is a factor of >100 -- while some galaxies feature strongly structured halos resembling that of M31, three of the 8 have halos that are completely undetected in the data. Conclude that spiral galaxies as a class exhibit a rich variety in stellar halo properties, implying that their assembly histories have been highly non-uniform. Find no convincing evidence for an environmental or stellar mass dependence of the halo fraction in the sample.
1606.08862
Constraining stochastic gravitational wave background from weak lens gin of CMB B-modes
Shaikh, et al
A stochastic GW background (SGWB) will affect the CMB anisotropies via WL. Unlike WL due to LSS which only deflects photon trajectories, a SGWB has an additional effect on rotating the polarization vector along the trajectory. Study the relative importance of these two effects, deflection and rotation, specifically in the context of E-mode to B-mode power transfer caused by WL due to SGWB. Using WL distortion of the CMB as a probe, derive constraints on the spectral energy density Omega_GW of the SGWB, sourced at different redshifts, without assuming any particular model for its origin. Present these bounds on Omega_GW for different power-law models characterizing the SGWB, indicating the threshold above which observable imprints of SGWB must be present in CMB.
1606.09091
Constraint on neutrino masses from the lensing dispersion of Type Ia supernovae
Hada, Futamase
Investigate how accurate the total mass of neutrinos is constrained from the magnitude dispersion of Type Ia SNe due to the effects of gravitational lensing. For this purpose, use the propagation equation of light bundles in a realistic inhomogeneous universe and propose a sample selection for SNe to avoid difficulties associated with small scale effects such as strong lensing or shear effects. With a fitting formula for the NL matter PS taking account of the effects of massive neutrino, find that in the model it is possible to obtain the upper limit Sigma m_nu~1.0 eV for future optical imaging surveys: WFIRST and LSST. Furthermore, discuss how far SNeIa need to be observed and to what extend the magnitude error must be reduced except for lensing in order to realize the current tightest limit Sigma M_nu < 0.2 eV.
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