Sunday, 7am. Saw the new apartment yesterday, to buy the previous tenant's laundry machine (for nearly the full price). I'm looking forward to moving in. Went for a jog to the church, a walk with Pers, then raking some leaves with Aaron. Then some really salty curry udon, then the Anime Exhibition with Daniela, Jennifer and Helen. Made some dal, did laundry, and then was knocked out for the night. Must work hard today.
1108.4136
Sterile neutrinos with eV masses in cosmology--how disfavoured exacty?
Hamann, Hannestad, Raffelt, Wong
Investigate the effects of eV-mass sterile neutrinos (suggested by global interpretations of neutrino oscillation data) on cosmology. Sterile neutrinos can thermalize prior to neutrino decoupling, contributing relativistic energy density in the early universe. CMB+LSS+BBN appears to prefer extra relativistic degrees of freedom within LCDM, but a "fully thermalized massive sterile neutrinos in the 1-2 eV mass range" necessarily violates the HDM limit on the maximum neutrino mass. [what is the HDM limit?]
But extending the framework with modifications within the neutrino sector improves somewhat the consistency of sterile neutrinos with precision cosmological data. (1) simplest: admit more additional relativistic degrees of freedom, not necessarily fully thermalised [how does that work physically?], but introduces an additional 1.5 massless species. (2) allowing an addition for a w != 1 improves the fit (slightly better than LCDM).
Any model containing eV-mass sterile neutrinos will induce an upward shift in the CDM density inferred from precision cosmological data.
Increasing the radiation content in the early universe can be problematic for BBN. Standard BBN preferres roughly an extra relativistic degree of freedom (which are interpreted here as a thermalised 1-2 eV sterile neutrino species), additional fully thermalised massless species are strongly disfavoured. But this BBN constraint can be circumvented with the introduction of a nu_e chemical potential, which itself could have been created by active-sterile oscillations in the early universe.
Not trivial to accommodate a strongly mixed eV-mass sterile neutrino in cosmology. If sterile eV-mass neutrinos becomes stronger, must consider a fairly complex modification of the standard LCDM cosmology.
* they combined CosmoMC with BBN stuff.
1108.4247
Mass assembly of galaxies: smooth accretion versus mergers
L'Huillier, Combes, Semelin
Most mass accreted through smooth accretion (77%). In the more massive galaxies, mergers are more common. Assembly time for 50% of mass, both in DM and in baryons, is a decreasing function of mass, which is compatible with the observations of downsizing [what is downsizing?]. ...
1108.4314
Galaxy disks are submaximal
Bershady, Martinsson, Verheijen, Wwestfall, Anderson, Swaters
Measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars is related to the maximum rotation speed (Vmax) as sigma(z,R=0)~0.26 Vmax (consistent with edge-on disk galaxy measurements, and the mean stellar velocity ellipsoid axial ratio sigma(z)/sigma(R)=0.6). This relation implies these galaxy disks are submaximal [what does this word mean?]. Find: disks in sample contribute only 15% to 30% of the dynamical mass within 2.2 disk scale-lengths (hR), with percentages increasing systematically with luminosity, rotation speed and redder color. Even for the most massive, fast-rotating disks of the reddest color (rest frame, face-on color B-K~4 mag), the disk mass is ~50% at 2.2hR. Spiral disks in general should be submaximal. Implies that the stellar M/L ratio, and hence accounting of baryons in stars, should be lowered by at least a factor of 3.
* how does this compare with Reina's? She finds that ~50% of mass comes from baryons within the optical radius, assuming the DM halo profile is NFW.
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