Day 655

Tuesday.

Nature
The different neighbors around Type-1 and Type-2 active galactic nuclei
Villaroel, Korn; Gaskell

Find strong differences in the color and AGN activity of the neighbors to type-1 and type-2 AGN, and in how the fraction of AGN residing in spiral hosts changes depending n the presence or not of a neighbor.  These finding suggest that an evolutionary link between the two major AGN types might exist.

1405.2338
The SLUGGS survey: exploring the metallicity gradients of nearby early-type galaxies to large radii
Pastorello et al

Stellar metallicity gradients in the outer regions of galaxies are a critical tool for disentangling the contributions of in-situ and ex-situ formed stars.  In the two-phase galaxy formation scenario, the initial gas collapse creates steep metallicity gradients, while the accretion of stars formed in satellites tends to flatten these gradients in the outskirts, particularly for massive galaxies.  Obtain radial stellar metallicity profiles for 22 nearby early-type galaxies.  From the Ca triplet lines in the NIR, measure the metallicity of the starlight up to 3 effective radii.  Find a relation between the outer metallicity gradient and galaxy mass, in the sense that lower mass systems show steeper metallicity gradients than more massive galaxies.  This result is consistent with a picture in which the ratio of ex-situ to in-situ formed stars is lower in less massive galaxies as a consequence of the smaller contribution by accretion.  In addition, infer a correlation between the strength of the Ca triplet feature in the NIR and the stellar IMF slope that is consistent with recent models in the literature.

1405.2340
Is the effect of the sun's gravitational potential on dark matter particles observable?
Bozorgnia, Schwetz

Gravitational focusing (GF) is negligible for low masses; in the region of DM masses below 40 GeV an annual modulation signal can be established with a future direct detection experiment. Hard to establish the presence of GF from data. In the high-mass region where GF is more important the significance of annual modulation itself is very low.

1405.2577
Dark matter heating and early core formation in dwarf galaxies
Madau, Shen, Governato

Results from LCDM sims of a group of isolated dwarf galaxies that has been shown to reproduce the observed stellar mass and cold gas content, resolved SFHs, and metallicities of dwarfs in the Local Volume.  Investigate the energetics and timetable of the cusp-core transformation.  SNe-driven gas outflows remove DM cusps and create kpc-size cores in all systems having a stellar mass above 1e6 Msun.  The "DM core mass removal efficiency" -- dark mass ejected per unit stellar mass -- ranges today from a few to a dozen, and increases with decreasing host mass.  Because dwarfs form the bulk of their stars prior to z~1 and the amount of work required for DM heating and core formation scales approximately as Mvir^5/3, the unbinding of the DM cusp starts early and the formation of cored profiles is not as energetically onerous as previously claimed.  DM particles in the cusp typically migrate to 2-3 core radii after absorbing a few percent of the energy released by SNe.  The present-day slopes of the inner DM mass profiles, Gamma=d log M/dlogR=2.5-3, of the simulated dwarfs are similar to those measured in the luminous Fornax and Sculptor dwarf spheroids.  None of the simulated galaxies has a circular velocity profile exceeding 20 km/s in the inner 1 kpc, implying that SN feedback is key to solve the "too-big-to-fail" problem for MW sub haloes.

1405.2666
An optical survey geometry of weak lensing survey: minimizing super-sample covariance
Takahashi, Soma, Takada, Kayo

The super-sample covariance (SSC) significantly degrade the statistical precision of WL PS measurement even for a wide-area survey.  Using the 1000 mock realizations of the log-normal model, which approximates the WL field for a Lambda-domianted CDM, study an optical survey geometry to minimize the impact of SSC continuation.  For a continuous survey geometry with a fixed survey area, a more elongated geometry such as a rectangular shape of 1:400 side-length ratio reduces the SSD effect and allows for a x2 improvement in the cumulative S/N of PS measurement up to l_max~ a few 1e3, compared to compact geometries such as squares or circles.  When we allow the survey geometry to be disconnected but with a fixed total area, assuming 1x1 sq. degrees patches as the fundamental building blocks of survey footprints, the best strategy is to locate the patches with ~15degrees separations.  This separation angel corresponds to the scale at which the 2pt correlation function as a negative minimum.  The best configuration allows for a factor 100 gain in the effective area coverage as well as a factor 2.5 improvement in the S/N at high multipoles, yielding a much wider coverage of multipoles than in the compact geometry.