Day 201

Tuesday.  Packed for tomorrow.  Today is a busy day.


1202.2354
Frame-dragging effects on magnetic fields near a rotating black hole
Karas, Kopacek, Kunneriath


* ergosphere: region located outside a rotating BH.  "ergon" (Greek) == "work" (English).  It is theoretically possible to extract Energy and mass from the BH in this region.  The radius of the ergosphere at equator corresponds to Schwarzschild radius of non-rotating BH and with minimum radius at poles (down to 1/2 of Schwarzschild radius for maximally rotating BH).  Within the ergosphere, spacetime is dragged along in the direction of the rotation of the BH at a speed greater than the local speed of light in relation to the rest of the universe ("frame-dragging"). 


Proceeding, "the central kpc in galactic nuclei":  Discuss role of GR frame dragging acting on B-field lines near a rotating Kerr BH.  Near the ergosphere the magnetic structure becomes strongly influenced and magnetic null points can develop.  Consider aligned B-fields as well as fields inclined with respect to the rotation axis, and the 2 cases are shown to behave in profoundly different ways.  Construct surfaces of equal values of local E and B intensities, which have not yet been discussed in the full generality of a boosted rotation BH.


1202.2355
Regularizing made-to-measure particle models of galaxies
Morganti, Gerhard


Made-to-measure methods: powerful tools to build galaxy models reproducing observational data; work by adapting the particle weights in an N-body system until the target observables are well matched.  Introduce MPR (moving prior regularization) method for such particles, based on determining from the particles a distribution of priors in phase space, which are updated in parallel with the weight adaptation.  Allows construction of smooth models from noisy data without erasing global phase-space gradients.  Compared t the std weight entropy regularization, biases in the anisotropy structure removed, local fluctuations in the intrinsic distribution function reduced.  Investigate uncertainties in the inferred dynamical structure increase with less complete and noisier kinematic data, ...  Apply MPR technique to two intermediate luminosity elliptical galaxies NGC 4697 and 3379, obtaining smoother dynamical models in luminous and DM potentials.


1202.2356
The properties of dynamically ejected runaway and hyper-runaway stars
Perets, Subr


Runaway stars: have large peculiar velocities.  Two mechanisms for ejection, both involving binarity or higher multiplicity.  (1) Binary SNe scenario: velocity gained when massive companion explodes.  (2) From gravitational interactions between stars and binaries in dense, compact clusters or cluster cores.  Study the ejection scenario.  Use N-body sims of massive clusters, with analytic arguments, in order to characterize the expected ejection velocity distribution of runaway stars.  Find the ejection velocity distribution of the fastest runaways (~80km/s) depends on the binary distribution of the cluster; distribution of lower velocity runaways appears independent of the binaries properties.  Velocity distribution foloow a simple power law: Gamma(v)~v^-8/3 for high v, and v^-3/2 for the low v.  Calculate total expected ejection rates, explore mass function and their binarity.    Binarity [?] of runaways is a decreasing function of their ejection velocity, with no binaries expected to be ejected with v>150 km/sAlso find that hyper-runaways with velocities of hundreds of km/s can be dynamically ejected from stellar clusters, but only at very low rates, which cannot account for a significant fraction of the observed population of hyper-velocity stars in the Galacitc halo.


* There was a recent paper about hyper-velocity stars coming from tidal stripping of a large globular cluster in the MW...


1202.2357
Shallow DM cusps in galaxy clusters
Laporte, White, Naab, Ruszkowski, Springel


Study the evolution of the stellar and DM components in a galaxy cluster of 1e15 Msun from z=3 to present, using high-res N-body sims.  At z=3, the dominant progenitor haloes were populated with spherical model galaxies [?] with and without accounting for adiabatic contraction.  Apply weighting scheme that changes the relative amount of dark and stellar material assigned to each simulation particle in order to produce luminous properties which agree better with abundance matching arguments and observed bulge sizes at z=3; permits study of the effect of initial compactness on the evolution of the mass-size relation.  Find that for more compact initial stellar distributions the size of the final BCG grows with mass according to r propto M^2, whereas for more extended initial distributions, r propto M.    Results show that collisionless mergers in a cosmo context can reduce the strengh of inner DM cusps with changes in log slope of 0.3 to 0.5 at fixed radius.  Shallow cusps wuch as those found recently in several strong lensing clusters thus do not necessarily conflict with CDM, but may rather reflect on the initial structure of the progenitor galaxies, which was shaped at high z by their formation process.


1202.2360
Insight into the formation of the MW through cold halo substructure.  III. Statistical chemical tagging in the smooth halo
Schlaufman, Rockosi, Lee, Beers, Prieto, Rashkov, Madau, Bizyaev


Find: relative contribution of satellite galaxies accreted at high z to the stellar population of the MW's smooth halo increases with distance, becoming observable relative to the classical smooth halo about 15 kpc from the Galactic center.  In particular, determine LoS-averaged [Fe/H] and [alpha/Fe] in the metal-poor MS turnoff (MPMSTO) population along every SEGUE spectroscopic LoS.  For LoS which there are no detection of cold halo substructure elements, compile the largest spectro sample of stars in the smooth component of the halo ever observed in situ beyond 10kpc.  Find significant spatial autocorrelation in the [Fe/H] in the MPMSTO population in the distant half of sample beyond about 15 kpc from the Galactic center.  Inside of 15kpc however, find no significant spatial autocorrealtion in [Fe/H].  At the same time, perform SEGUE-like observations of N-body sims of NW analog formation.  Find: while haloes formed entirely by accreted satellite galaxies provide a poor match to observations of the halo within 15 kpc of the Galactic center, it is observed that spatial autocorrelation in [Fe/H] in the simulations at larger distances.  This observation is an example of statistical chemical tagging and indicates that spatial autocorrelation in metallicity is a generic feature of stellar haloes formed from accreted satellite galaxies.


1202.2411
Joint analysis of X-ray and SZ observations of galaxy clusters using an analytic model of the ICM
Haslter, .. .Carlstrom, ... Mantz, ... et al


Joint analysis of X-ray and SZ effect data using analytic model that describes the gas properties of galaxy clusters.  The join analysis allows measurement of the cluster gas mass fraction profile and Hubble constant independent of cosmo parameters. [HOW???]  Weak cosmo priors are used to calculate the overdensity radius within which the gas mass fractions are reported.  Such an analysis can provide direct constraints on the evolution of the cluster gas mass fraction with z.  Validate the model and joint analysis on high S/N data from the Chandra X-ray observatory and the SZ array for two clusters, A2631 and A2204.


1202.2623
HST survey of the Perseus Cluster - IV: Compact stellar systems in the Perseus Cluster core and Ultra Compact Dwarf formation in SF filaments
Penny, Forbes, Conselice


Suggest: star-forming filaments are formation site for some UCDs; tidal disruption of dwarf galaxies is another formation channel for UCD formation in the core of Perseus as tidal disruption is ongoing in this region, as evidenced by shells around NGC 1275; also, UCDs may siimply be massive GCs based on strong similarities in the colour trends of the two populations.


1202.2644
The maximal runaway temperature of Earth-like planets
Shaviv, Shaviv, Wehrse


Generalize the problem of semi-gray model to cases in which a non-negligible fraction of the stellar radiation falls on the long-wavelength range, and/or that the planetary long-wavelength emission penetrates into the transparent short wavelength domain of the absorption.  Apply the most general assumptions and independently of any particular properties of an absorber, show that greenhouse effect saturates and any Earth-like planet has maximal temperature which depends on the type and distance to its main-sequence star, its albedo and the primary atmospheric components which determine the cutoff frequency below which the atmosphere is optically thick.  Two primary mechanisms are responsible for the saturation of the runaway greenhouse effect, depending on the value of the wavelength above which the atmosphere becomes optically thick.  Unless this wavelength is small and resides in the optical region, saturation is achieved by radiating the thermal flux of the planet through the short wavelength tail of the thermal distribution.  This has the observational implication, the radiation from such a planet should be skewed towards the NIR.  Otherwise, saturation takes place by radiating through windows in the FIR.


1202.2713
[Fe II] as a tracer of SNe Rate in near-by Starburst galaxies
Rosenberg, van der Werf, Israel


Found: a strong linear and morphological correlation exists between SNe and [FeII]_{1.26}.  Relation valid for normal SF galaxies, but breaks down for extreme ultra luminous galaxies.  Conclude that [Fe II] emission can be generally used to derive accurate SNe rates.


1202.2716
DM density profiles of the haloes embedding early-type galaxies: characterizing halo contraction and DM annihilation strength
Chae, Kravtsov, Frieman, Bernardi


Devise a anew procedure of determining DM distribution in haloes.  First make a self-consistent bivariate statistical match of stellar mass and velocity dispersion with halo mass.  Then selecting early-type galaxy-halo systems, perform Jeans dynamical modeling with the aid of observed statistical properties of stellar mass profiles and velocity dispersion profiles.  DM density profiles derived using SDSS galaxies and haloes from up-to-date cosmological dissipationless simulations deviate significantly from the dissipationless profile of NFW or Einasto in terms of inner density slope and/or concentration.  From these DM profiles find that DM density is enhanced in the inner region of most early-type galactic haloes providing an independent dynamical evidence for halo contraction.  The main characteristics of halo contraction are: (1) the mean DM density within the effective radius has increased by a factor from ~1 for clusters with M_vir > 1e15 Msun to ~4-5 for galaxies with M_vir < 1e12 Msun, and (2) the enhancement is more frequently realized by steepened density slope than increased concentration compared with the fiducial NFW profile.  Based on these results, predict that haloes of nearby elliptical and lenticular galaxies can be promising targets for gamma-ray emission from DM annihilation.


1202.2735
Discovery & Depth
Kulkarni


The best bets for the next 10 years in astronomy:  Extra-solar planets, Astrometry, and Transients!  In one word: "Discoveries."  Skr*w Dark Energy (a.k.a., "Depth"), not going to get anywhere there.


1202.2847
Parity violation of primordial B fields in the CMB bispectrum
Shiraishi


Find: helical PMFs (primordial magnetic fields) produce characteristic signals, which disappear in parity-conserving cases, such as the intensity*3 bispectra arising from Sum^3_{n=1} l_n = odd.  ....