Day 296

Wednesday.

1209.2114
Catch me if you can: is there a runaway-mass black hole in the Orion Nebula cluster?
Subr, Kroupa, Baumgardt

Dynamical evolution of Orion nebula cluster: fraction of residual gas probably expelled when ONC formed---probably was small previously.  Assume few-body relaxation played an important role during initial phase of evolution of ONC.  3-body interactions among OB stars led to their ejection from cluster; formation of a massive object via runaway physical stellar collisions also were likely.  Resulting depletion of high mass end of stellar mass function fit the observational data.  Speculate that runaway-mass star may have collapsed directly into a massive black hole (>100Msun), explaining the large velocity dispersion of the four Trapeziium stars in the ONC core.  BH likely to be a member of a binary system (70% probability), in which case it can be detected due to accretion of stellar winds from the secondary star, or through a measurement of motion of the secondary whose velocity would be > 10 km/s along the whole orbit.

1209.2116
Stellar kinamatics of the Andromeda II dwarf spheroidal galaxy
Ho, Geha, et al

Based on 531 red giant branch stars (spectroscopy).  Out to 1.1 kpc; mean systemic velocity of -192 km/s and dispersion of sigma_v = 8 km/s.  Almost no rotation along major axis, but along minor axis it's 9km/s (max).  Kinematical major axis misaligned by 67 deg with isophotal major axis.  Only known dwarf galaxy to show minor axis rotation.

1209.2118
Moving mesh cosmology: properties of neutral hydrogen in absorption
Bird, Vogelsberger, Sijacki, Zaldarriaga, Springel, Hernquist

AREPO (moving-mesh code) is better than GADGET (smooth-particle hydrodynamics) code with matching neutral hydrogen predictions with observation in the abundance of DLAs (high density systems).  The code difference : different methods for solving the Euler equations (but same gravity solvers and baryonic physics implementations).  But for describing low column density gas probed by Lyman-alpha forest, the codes only differ by a few percent, within observational error.

1209.2123
Escape fraction of ionizing radiation from starburst galaxies at high redshifts
Ferrara, Loeb

Data indicates: cosmic UV emissivity decreased with decreasing redshift near the end of reionization.  Since no evidence for very massive early stars, this could signal a decline with time in the mass-averaged escape fraction of ionizing radiation from galaxies <f_esc> at z>6.    Calculate the evolution if ionization fronts in DM haloes with host gas in hydro equilibrium at its cooling temperature floor (T~1e4K for atomic H).  Find high escape fraction only for the lowest mass haloes (M<1e8.7 Msun at z=9), provided their SF efficiency > 1e-3.  Since low-mass galaxy population depleted by radiative feedback, find that <f_esc> decreases with time during reionization.

* similar to another abstract a few days ago... maybe they got scooped?

1209.2125
THe significance of the integrated Sachs-Wolfe effect revisited
Giannantonio, Crittenden, Nichol, Ross

It's now at 4.4 sigma.  (compilation of data)

1209.2132
X-ray bright active galactic nuclei in massive galaxy clusters I: number counts and spatial distribution
Ehlert, Allen, Brandt, Xue, Luo, von der Linden, Mantz, Morris

X-ray point source in 43 massive clusters: catalog of 4210 rigorously selected x-ray point sources in 4.2 sq deg.  Reveals clear excess of sources compared to deep blank-field surveys---excess likely due to AGN associated with clusters.  Excess sources concentrated within the virial radii of clusters, largest excess near the center.  Radial profile a power law, with beta ~ -0.5.  Indication of increase in fraction of galaxies hosting X-ray AGN with increasing clustercentric radius: 5x to 10x higher near the virial radius than in the central regions.  Trend similar to observed SF in cluster member galaxies.

1209.2140
Golden gravitational lensing systems from the Sloan lens ACS survey. II. SDSS J1430+4105: a precise inner total mass profile from lensing alone
Eichner, Seitz, Bauer

Measured the inner mass profile from lensing alone, mass to light ratio measured, found to be more Salpeter like, etc.

1209.2143
On dark peaks and missing mass: a weak lensing mass reconstruction of the merging cluster system Abell 520
Clowe, Markevitch, Bradac, Gonzalez, Chung, Massey, Zaritsky

DM self-interaction cross section limit at 1 cm^2/g from difference between gas and DM center of mass in merging halo systems.  Abell 520 a possible exception.  Use HST mosaic images and Magellan image set to run WL analysis, show good agreement with previous works, with one difference: do not detect the previously claimed "dark core" that contains excess mass with no significant galaxy overdensity at the location of the X-ray plasma (which was causing derivation of larger cross section).    Find that the mass distribution of A520 is in good agreement with the luminosity distribution of the cluster galaxies.

1209.2152
The UV colours and dust attenuation of Lyman-break galaxies
Gonzalez-Perez, Lacey, Baugh, Frenk, Wilkins

Strong dependence of UV colors on dust properties---difficulty of using the UV continuum slope as a tracer of dust attenuation without any further knowledge of the dust characteristics and distribution in high-z galaxies.

1209.2173
Stochastic bias from non-Gaussian initial conditions
Baumann, Ferraro, Green, Smith

Show: stochastic form of scale-dependent halo bias arises in multi-source inflationary models, where multiple fields determine the initial curvature perturbation.  Study: curvaton models, quasi-single field inflation.  Present general forumla for both stochastic and non-stocahstic parts of the halo-bias in terms of the N-point cumulants.  At lowest order ,the stochasticity arises if the collapsed limit of the four-point function is boosted relative to the square of the 3-pt function in the squeezed limit.  Derive from barrier crossing formalism, and from peak-background split method.  

1209.2175
On the equivalence of barrier crossing, peak-background split, and local biasing
Ferraro, Smith, Green, Baumann

Show mathematical equivalence of barrier crossing formalism and peak-background split.

1209.2215
A suppressed contribution of low mass galaxies to reionization due to supernova feedback
Wyithe, Loeb

Describe a simple model for the SFR density function at high z based on the extended Press-Schechter formalism.  Postulate: a starburst following each merger, lasting for t_SF and converting at most f_star of galactic gas into stars.  Include simple prescription for SNe feedback that suppresses SF in low mass galaxies.  Constraining t_SF and f_star: find t_SF~1e7 years, comparable to MS lifetimes of SNe progenitors, indicating that high-z starbursts are quenched once SNe feedback had time to develop.  High z galaxies convert ~10% of their mass into galaxies with SFRs above ~1 Msun / year, but a smaller fraction for lower luminosity galaxies.  Best fit model successfully predicts the observed relation between SFR and stellar mass at z>4, while the deduced relation between stellar mass and halo mass is also consistent with data on the dwarf satellites of the MW.  Find: SNe feedback lowers the efficiency of SF in the lowest mass galaxies and makes their contribution to reionization small.  Result: photo-ionization feedback on low-mass galaxy formation does not significantly affect the reionization history.  Using SAM for the reionization history, infer that approximately half of the ionizing photons needed to complete reionization have already been observed in star-forming galaxies.

1209.2228
Euclid mission: building of a reference survey
Amiaux, Scaramella, Mellier, ... et al

Billions of galaxies over 15000 sq deg: drives scientific potential, duration and mass of the space craft.  Construction of a reference survey derives from the high level science requirements for a wide and deep survey.  The definition of a main sequence of observations and the associated calibrations were indeed a major achievement of the definition phase.  Demonstrated feasibility of covering the requested area in less than 6 years, while taking into account the overheads of space segment observing and maneuvering sequence.  The reference mission will be used for sizing the spacecraft consumables needed for primary science.  It will also set the framework for optimizing the time on the sky to fulfill the primary science and maximize the Euclid legacy.

1209.2233
Astrophiscs conducted by the Lunar university network for astrophysics research (LUNAR) and the center for lunar origins (CLOE)
Burns, Lazio, Bottke

Moon as a platform from and on which to conduct astrophysical measurements.  Illustrate how the Moon can be used as a platform to advance important goals in astrophysics.  

1209.2240
Can galactic chemical evolution explain the oxygen isotopic variations in the Solar system?
Lugaro, Liffman, Ireland, Maddison

Fractionation of oxygen isotopic compositions (3-isotope composition):  CO self-sheilding produced 16O-rich CO and 16O-poor H2O, where the H2O subsequently combined with interstellar dust to form relatively 16O-poor solids within the Solar nebula.  Another model for creating the different reservoirs of 16O-rich gas and 16O-poor solids suggests that these reservoirs were produced by Galactic chemical evolution (GCE) if the Solar System dust component was somewhat younger than the gas component and both components were lying on the line of slope one in the O 3-isotope plot.  [?]  GCE is not the cause of mass-independent fractionation of the O isotopes in SS; it is in contradiction with observations of the 18O/17O ratios in nearby molecular clouds and young stellar objects.  Very unlikely for GCE to produce a line of slope one, when considering the effect of incomplete mixing of stellar ejecta in the ISM.  Furthermore, the assumption that the Solar System dust was younger than the gas requires unusual timescales or the existence of an important stardust component that is not theoretically expected to occur nor has been identified to date.

1209.2243
Black holes in the early universe
Volonteri, Bellovary

This review:  report on basic questions regarding the cosmological significance of massive black holes.  What mechanisms of BH formation?  How massive were the seeds?  When and where did they form?  How is their growth linked to that of their host galaxy?  

1209.2249
Determining neutron star masses with weak microlensing
Tian, Mao

Determine mass of NS using distortion in background galaxy.

1209.2250
Counts of high-redshift GRBs as probe of primordial non-Gaussianities
Maio, Salvaterra, Moscardini, Ciardi

Use N-body, hydro, chemistry simulations of different cosmological volumes with various Gaussian and NG models, relate the cosmic SFR density with the corresponding GRB rate.  Assuming this correlation, find that positive local non-G (f_nl) might boost significantly the GRB rate at high z (z>>6).  GRBs can constrain f_nl!  But data is currently poor.  Distinguish contribution to GRB rate from PopIII vs metal-enriched PopII and I: conclude that the latter is a more solid tracer of the underlying matter distribution, while the former is strongly dominated by feedback mechanisms from the first, massive short-lived stars, rather than by possible non-Gaussian fluctuations, independent of PopIII IMF.

1209.2272
New observaions of the gas cloud G2 in the Galactic Center
Gillessen, Genzel, et al

As the title says.  The observations are impressive!

1209.2292
Characterizing the maganetic field in the intracluster medium
Nakwacki, et al

Turbulent motion during structure formation (such as energetic events and random motions of the hot ICM in galaxy clusters).  Radio diffuser emission probes the presence of B-fields and relativistic particles in the ICM.  Present results from numerical simulations of B-field turbulence in MHD and k(inetic)MHD frameworks.  See next paper for more content.