Day 635

Tuesday.

1404.4870
Towards precision distances and 3d dust maps using broadband period-magnitude relations of RR Lyrae stars
Klein, Bloom

Determine the period-magnitude relations  of RR Lyrae stars in 13 photometric bandpasses from 0.4 to 12 um using time series observations of 134 stars.  The Bayesian formalism, extended from previous work to include the effects of LoS dust extinction, allows for the simultaneous inference of the posterior distribution of the mean absolute magnitude, slope of the period-magnitude power-law, and intrinsic scatter about a perfect power-law for each bandpass.  In addition, the distance modulus and LoS dust extinction to each RR Lyrae star in the calibration sample is determined, yielding a sample median fractional distance error of 0.66%.  The intrinsic scatter in all bands appears to be larger than the photometric errors, except in WISE W1 and W2 where the photometric error (sigma~0.05 mag) is to be comparable or larger that the intrinsic scatter.  Additional observations at these wavelengths could improve the inferred distances to these sources further.  As an application of the methodology, infer the distance to the RRc-type star RZCep at low Galactic latitude to be mu=8.0397pm0.0123 mag (405.4 pm 2.3 pc) with color excess E(B-V)=0.2461pm0.0089 mag.  This distance, equivalent to a parallax of 2467pm14 microarcsec, is consistent with the published HST parallax measurement but with an uncertainty that is 13 times smaller than the HST measurement.  If measurements (and methodology) hold up to scrutiny, the distances to these stars have been determined to an accuracy comparable to those expected with Gaia.  As RR Lyrae are one of the primary components of the cosmic distance ladder, the achievement of sub-1% distance errors within a formalism that accounts for dust extinction may be considered a strong buttressing of the path to eventual 1% uncertainties in Hubble's constant.

1404.4874
ense cores in galaxies out to z=2.5 in SDSS, UltraVISTA, and the five 3d-HST/DANDELS fields: number density, evolution, and the apparent need for efficient cooling at high redshift
van Dokkum, et al

Ask when the dense galactic cores of massive galaxies formed, and determine how galaxies gradually assembled around them.  Select galaxies that have a stellar mass 3e10 Msun inside r-1kpc out to z=2.5.  The number density of galaxies with dense cores appears to have decreased from z=2.5 to the present, probably at least in part due to stellar mass loss and the resulting adiabatic expansion.  Infer that dense cores were mostly formed at z>2.5, consistent with their largely quiescent stellar populations.  While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3from z=2.5 to 0 and their effective radii increase by a factor of 5-6.  As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z=2.5 to ~15% at z=0.  Because of their early formation, the contribution of dense cores to the total stellar mass budget of the Universe is a strong function of z.  The stars in cores with M(1kpc)>3e10Msun make up ~0.1% of the stellar mass density of the Universe today but 10%-20% at z=2, depending on their IMF.  The formation of these cores required the conversion of 1e11 Msun of gas into stars within 1 kpc, while preventing significant SF at larger radii.