Day 744

Monday.

1409.3566
Tracing chemical evolution over the extent of the Milky Way's disk with APOGE red comp stars
Nidever, et al

Employ SDSS-III/APOGEE spectra survey to investigate the distribution of metallicity and alpha-element abundances of stars over a large part of the MW disk.  Use a sample of ~10k kinematically-unbiased red-clump stars with ~5% distance accuracy as tracers, the [alpha/Fe] vs [Fe/H] distribution of this sample exhibits a bimodality in [alpha/Fe] at intermediate metallicities, -0.9<[Fe/H]<-0.2, but at higher metallicities ([Fe/H]=+0.2) the two sequences smoothly merge.  Investigate the effects of the APOGEE selection function and volume filling fraction and find that these have lithe qualitative impact on the alpha-element abundance patterns.  The described abundance pattern is found throughout the range 5<R<11kpc and 0<|Z|<2 kpc across the Galaxy.  The [alpha/Fe] trend of the high-alpha sequence is surprisingly constant throughout the Galaxy, with little variation from region to region (~10%).  Using simple galactic chemical evolution models, derive an average SFE in the high-alpha sequence of ~4.5e-10 / yr, which is quite close to the nearly-constant value found in molecular-gas-dominated regions of nearby spirals.  This result suggests that the early evolution of the MW disk was characterized by stars that shared a similar SFH and were formed in a well-mixed, turbulent, and molecular-domiated ISM with a gas consumption timescale (1/SFE) of ~2 Gyr.  Finally, while the two alpha-element sequences in the inner Galaxy can be explained by a single chemical evolutionary track, this cannot hold in the outer Galaxy, requiring instead a mix of two or more population with distinct enrichment histories.
1409.3571
CFHTLenS: a weak lensing shear analysis of the 3D-matched-filter galaxy clusters
Ford, Van Waerbeke, ... etal

Present the cluster mass-richness scaling relation calibrated by WL analysis of >18k galaxy cluster candidates in CFHTLenS.  Detected using the 3D-Matched-Filter cluster-finder of Milkeraitis+, these cluster candidates span a wide range of masses, from the small group scale up to ~1e15 Msun, and 0.2<z<0.9.  The total significance of the shear measurement abounds to 54 sigma.  Compare cluster masses determined using WL shear and magnification, finding the measurements in individual richness binds to yield 1 sigma compatibility, but with magnification estimates biased low.  This first direct mass comparison yields important insights for improving the systematics handling of future lensing magnification work.  In addition, confirm analyses that suggest cluster miscentering has an important effect on the observed 3D-Matched-Filter halo profiles, and quantify this by fitting for projected cluster centered offsets, which are typically ~0.4 arcmin.  Bin the cluster candidates as a function of redshift, finding similar cluster masses and richness across the full range up to z~0.9.  Measure the 3D-MF mass-richness scaling relation M_200=M0(N_200/20)^beta.  Find a normalization M0~2.7e13 Msun, and a log slope of beta~1.4pm0.1, both of which are in 1 sigma agreement with results from the magnification analysis.  Find no evidence for a redshift-dependence of the normalization.  The CFHTLenS 3D-Matched-Filter cluster catalogue is now available.

1409.3697
A novel null test for the $\Lambda$CDM model with growth-rate data
Nesseris, Sapone

Present an alternative consistency check at the perturbative level for a homogeneous and isotropic Universe filled with a DE component.  This test makes use of the growth of matter perturbations data and it is able to not only test the homogeneous and isotropic Universe but also, within the framework of a Friedmann-Lemaitre-Robertson Walker Universe, if the DE component is able to cluster, if there is a tension in the data or if we are dealing with a modification of gravity.

1409.3708
Testing gravity theories using stars
Sakstein, Jain, Vikram

Modified gravity satisfies cosmic acceleration; to satisfy solar system test of gravity, a theory needs to include a screening mechanism that hides the modifications on small scales.  One popular and well-studied theory is chameleon gravity.  Our own galaxy is necessarily screened, but less dense dwarf galaxies may be unscreened and their constituent stars can exhibit novel features.  In particular, unscreened stars are brighter, hotter and more ephemeral than screens stars in our own galaxy.  They also pulsate with a shorter period.  In this essay, exploit these new features to constrain chameleon gravity to levels 3 orders of magnitude lower the previous measurements.  These constraints are currently the strongest in the literature.