Day 640

Sunday.

1311.0139
Probing a dark matter density spike at the Galactic Center
Lacroix, Boehm, Silk

DM profile at the inner galaxy is uncertain, but important if we want to determine the gamma-ray and radio fluxes from DM annihilations.  Use synchrotron emission to probe DM energy distribution in the inner galaxy.  First solve the problem of the CR diffusion on very small scales (<1e-3 pc) by using a Green's function approach, and use this technique to quantify the effect of a spiky profile (rho(r)~r^{-7/3}) on the morphology and intensity of the synchrotron emission expected from DM.  Illustrate results using 10 GeV and 800 GeV candidate weakly interacting DM particles annihilating directly into e+ e-.  The critical assumptions are that the DM is heavier than a few GeV and directly produces a reasonable amount of electrons and positrons in the galaxy.  Conclude that DM indirect detection techniques (including the Planck experiment) could be used to shed light on the DM halo profile on scales that lie beyond the capability of any current numerical simulations.

1401.5796
Chemodynamical evolution of the Milky Way disk II: variations with Galactic radius and height above the disk plane.
Minchev, Chiappini, Martig

Show that contamination by radial migration becomes more evident with increasing distance from the galactic center, because of the wider distribution of stellar birth radii for a given radial bin at z=0.  As a result, the scatter in the age-metllaicity relation increase significantly as a function of galactic radius.  Predict that the metallicity distributions of (unbiased) samples at different distances from the galactic center peak at approximately the same value, [Fe/H] ~ -0.15 dex, and have similar metal-poor tails extending to [Fe/H]~-1.3 dex.  In contrast, the metal-rich tail decreases with increasing radius.  Similarly, the [Mg/Fe] distribution always peaks at ~0.15 dex, but its low-end tail is lost as radius increases, while the high-end tails off at [Mg/Fe]~0.45 dex.  This metal-rich, [alpha/Fe]-poor tail results from stars migrating outwards, which are always close to the disk plane.  The reason for this is that migrators stay with cool kinematics, i.e., do not contribute to thick disk formation.  Demonstrate that during mergers stars migrating outwards arrive significantly colder than the in-situ population.  This has the important effect of working against disk flaring.  The radial metallicity and [Mg/Fe] gradients in the model show significant variations with height above the plane due to changes in the mixture of stellar ages.  An inversion in the radial metallicity gradient is found from negative to weakly positive and from positive to negative for the [Mg/Fe] gradient, with increasing distance from the disk plane.   ...

1401.5799
Where do galaxies end?
Shull

Galaxies: systems of stars and gas embedded in extended haloes of DM, formed by infall of smaller systems at earlier times.  True extend of a galaxy: virial radius (separation between collapsed structures in dynamical equilibrium and external infalling matter)?  Gravitational radius, gas accretion radius, "galactopause" )arising from outflows that stall at 100-200 kpc over a range of outflow parameters and confining gas pressures)?  Propose physical criteria to define bound structures, including a more realistic definition of R_vir (M*, M_h, z_a) for stellar mass M* and halo mass M_h, half of which formed at "assembly redshifts" z_a=0.7-1.3.  Estimate the extent of bound gas and DM around L* galaxies to be ~200 kpc.  The new virial radii, which mean R_vir~200 kpc, are 40-50% smaller than values estimated in HST/COS detections of H I and O VI absorbers around galaxies.  In the new formalism, the MW stellar mass, log M*=10.7pm0.1, would correspond to R_vir=153(+25-16) kpc for half-mass halo assembly at z_a=1.06pm0.03.  The frequency per unit redshift of low-redshift O VI absorption liens in QSO spectra suggests absorber sizes ~150 kpc when related to intervening 0.1 L* galaxies.  This formalism is intended to clarify semantic differences arising from observations of extended gas in galactic haloes, circumgalactic medium (CGM), and filaments of the IGM.  Astronomers should refer to bound gas in the galactic halo or GCM, and unbound gas as the CGM-IGM interface, on its way into the IGM.

1401.5800
CLASH-VLT: constraints on the Dark matter equation of state from accurate measurements of galaxy cluster mass profiles
Sartoris, … Borgani, Umetsu, Bartelmann, … Zitrin, … Broadhurst, Coe, … Melchior, et al

Constrain EoS from cluster galaxies (<<c, depends on gravitational potential only) with lensing (depends on gravitational potential plus the relativistic-pressure term that depends on cluster mass).  Data: kinematic and lensing mass profiles of MACS 1206.2-0847 at z=0.44 from CLASH.  Baryons contribute at most 15% to the total mass in clusters and their pressure is negligible, the EoS parameter describes the behavior of the DM fluid.  Measure w=0.00 pm0.15 (stat) pm0.08 (syst), averaged over the radial range 0.5 Mpc <r<r200.  

1401.5918
ESPRESSO: the next European exoplanet hunter
Pepe et al

ESPRESSO: Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations---the next VLT high resolution spectrograph.  Forseen to gain 2 magus with respect to its predecessor HARPS, and to improve the instrumental radial-velocity precision to reach the 10 cm/s level.  Operated with one or two Unit Telescopes (8.2m).  Main scientific drivers: search and characterization of rocky exoplanets in the habitable zone of quiet, nearby G to M-dwards and the analysis of the variability of fundamental physical constants.  Passed final design review in May 2013, entered the manufacturing phase, to be installed at Paranal Observatory in 2016; operation planned to start by the end of the same year.

1401.5945
A comet could not produce the carbon-14 spike in the 8the century
Usoskin, Kovaltsov

Increase in 14C ca. 775 AD recently found could be due to extreme solar energetic particle event [which would have produced auroras at low latitudes, which should have been recorded], or it could be due to a comet bringing additional 14C to Earth.  Calculate a realistic mass and size of such a comet to show that it would have been huge (~100 mms across and 1e14-15 ton of mass) and would have produced a disastrous impact on Earth.  Such an impact could not remain unnoticed in the geological records and chronicles.  The absence of an evidence for such a dramatic event makes this hypothesis invalid.

1401.6018
Intrinsic alignments in the cross-correlation of cosmic shear and CMB weak lensing
Hall, Taylor

Demonstrate that the IA of galaxies with LS tidal fields sources an extra contribution to the recently-detected cross-correlation of galaxy shear and weak lensing of the microwave background.  The extra term is the analogy of the 'GI' term in standard cosmic shear studies, and results in a reduction in the amplitude of the cross-correlation.  Compute the IA contribution in linear and NL theory, and show that it can be at roughly the 15% level for CFHT Stripe 82 z distribution, if the canonical amplitude of IA is assumed.  The new term can therefore potentially reconcile the apparently low value of the measured cross-correlation with standard LCDM.  Discuss various small-scale effects in the signal and the dependence on the source z distribution.  Discuss the exciting possibility of self-calibrating IA with a joint analysis of cosmic shear and WL of the microwave background.

1401.6137
The VIMOS public extragalactic redshift survey (VIPERS): a quiescent formation of massive red-sequence galaxies over the past 9 Gyr
Fritz et al

Evolution of CMR and LF at 0.4<z<1.3 from VIPERS using 45k galaxies with spectro-z down to i'_AB<22.5 over 10.32 deg2 in two fields.  … Regardless of the method of selecting ETGs, measure a consistent evolution of the red-sequence: find a moderate evolution of the RS intercept of Delta(U-V)=0.28 pm 0.14 mag, favoring exponentially declining SF histories with SF truncation at 1.7<z<2.3.  Together with the rise in the ETG number density by 0.64 dex since z=1, this suggests a rapid build-up of massive galaxies (M>1e11 Msun) and expeditious RS formation over a short period of ~1.5 Gyr starting before z=1.  This is supported by the detection of ongoing SF in ETGs at 0.9<z<1.0, in contrast with the quiescent red stellar populations of ETGs at 0.5<z<0.6.  There is an increase in the observed CMR scatter with redshift, two times larger than in galaxy clusters and at variance with theoretical models.  Discuss possible physical mechanisms that support the observed evolution of the red galaxy population.  Findings point out that the massive galaxies have experienced a sharp SF quenching at z~1 with only limited additional merging.  In contrast, less-massive galaxies experience a mix of SF truncation and minor mergers which build-up the low- and intermediate-mass end of the CMR.