Day 638

Friday.

1003.1312 [that's weird]
Structure and dynamics of giant low surface brightness galaxies
Lelli, Fraternali, Sancisi

Ginat LSB galaxies are commonly thought to be massive, DM dominated systems.  However, this conclusion is based on highly uncertain rotation curves.  Present here a new study of two prototypical GLSB galaxies: Malin 1 and NGC 7589.  Reanalyze existing HI observations and derived new rotation curves, which were used to investigate the distributions of luminous and DM in these galaxies.  In contrast to previous findings, the rotation curves of both galaxies show a steep rise in the central parts, typical of high SB systems.  Mass decompositions with a DM halo show that baryons may dominate the dynamics of the inner regions.  Indeed, a "maximum disk" fit gives stellar M/L in the range of values typically find for HSB galaxies.  These results, together with other recent studies, suggest that GLSB galaxies are systems with a double structure: an inner HSB early-type spiral galaxy and an outer LSB disk.  Also tested the predictions of MOND: the rotation curve of NGC 7589 is reproduced well, whereas Malin 1 represents a challenging test for the theory.

1404.5959
A mass-dependenet density profile for DM haloes including the influence of galaxy formation
Di Cintio et al

Introduce a mass dependent density profile to describe the distribution of DM within galaxies, which takes into account the stellar-to-halo mass dependence of the response of DM to baryonic processes.  The study is based on the analysis of hydrosim galaxies from dwarf to MW mass, drawn from the MaGICC project, which have been shown to match a wide range of disk scaling relationships.  Find that the best fit parameters of a generic double power-law density profile vary in a systematic manner that depends on the stellar-to-halo mass ratio of each galaxy.  Thus, the quantity Mstar/Mhalo constrains the inner (gamma) and outer (beta) slopes of DM density, and the sharpness of transition between the slopes (alpha), reducing the number of free parameters of the model to two.  Due to the tight relation between stellar mass and halo mass, either of these quantities is sufficient to describe the DM halo profile including the effects of baryons.  The concentration of the haloes in the Hydrosims is consistent with N-body expectations up to MW mass galaxies, at which mass the haloes become twice as concentrated as compared to pure DM runs.  This mass dependent density profile can be directly applied to rotation curve data of observed galaxies and to semi analytic galaxy formation models as a significant improvement over the commonly used NFW profile.

1404.6014
Detection of the gravitational lens magnifying a type Ia supernova
Quimby, Oguri, et al

If a massive object warps space-time to form multiple images of a BG SNIa, a direct test of cosmic expansion is possible.  However, these lensing events must first be distinguished from other rare phenomena.  Report that a spectrum obtained of a SN (new type of super luminous SN or a normal SNIa magnified?) obtained after the SN faded away shows the presence of a FG galaxy -- the first found to strongly magnify a SNIa.  Discuss how more lensed SNIa may be found than previously predicted.