1305.2413
Ultra-faint Ultravioldet galaxies at z~2 behind the lensing cluster Abell 1689: the luminosity function, dust extinction and star formation rate density
Alavi, et al
HST UV (F275W/F336W) imaging, used to identify z~2 SF galaxies via their Lyman break. Detect galaxies 100x fainter than previous surveys at this redshift. After removing multiple images, there are 58 galaxies between -19.5<M_UV<-13. Determine effective volume by calculating the intrinsic sensitivity of the observations as a function of source plane position (possible because Abell 1689 mass distribution is well constrained). Faint-end slope of LF is alpha=-1.56pm0.13, somewhat shallower than z>3. No turnover in the LF down to MUV=-13. Increasingly redder UV spectral slopes with L observed at higher redshifts, but with redder slopes at all L and average reddening of <E(B-V)>=0.15. Assume the stars in these galaxies are metal poor (0.2 Z_sun) compared to their brighter counterparts (Z_sun), resulting in bluer assumed intrinsic UV slopes and larger derived dust extinction. The total UV L density at z~2 is 4.3e26 erg/s/Hz/Mpc^3, 80% of which is emitted by galaxies in the L range of this sample. Determine the SFR density from UV-selected galaxies at z~2 (assuming constant dust extinction correction of 4.2 over all luminosities and a Kroupa IMF) of 0.147 M_sun/yr/Mpc^3, significantly higher than previous determinations because of the additional fainter galaxies and the larger dust correction factors.
1305.2418
Modified gravity-GADGET: a new code for cosmological hydrodynamical simulations of modified gravity models
Puchwein, Baldi, Springel
New code with modified gravity models presented (N-body & cosmo hydro sims). Employs multigrid-accelerated Newton-Gauss-Seidel relaxation solver on an adaptive mesh to efficiently solve for perturbations in the scalar degree of freedom of the modified gravity model. It is a new algorithm for P-Gadget3 code; can at the same time follow the baryonic physics included in P-Gadget3 (hydrodynamics, radiative cooling and star formation). Demonstrate that the code works reliably by comparison with analytical results of simple cases, and by comparing cosmo sims to results from the literature. Perform non-radiative and radiative cosmo hydro sims of f(R)-gravity model; also discuss the impact of AGN feedback on the matter PS, as well as degeneracies between the influence of baryonic processes and modifications of gravity.
1305.2420
Abell 2142 at large scales: an extreme case for sloshing?
Rossetti et al
Has multiple cold fronts, discovery of a new cold front at ~1 Mpc from the center. Residual images, thermodynamics and metal abundance maps are qualitatively in agreement with predictions from numerical simulations of the sloshing phenomenon, but at larger scales. Sloshing not confined to cores, but extends cluster-wide, extending well beyond the cooling region involving a large fraction of the ICM up to almost half of the virial radius. Absence of a cool core and a newly discovered giant radio halo in A2142, in spite of its relaxed X-ray morphology, suggest that large scale sloshing, or the intermediate merger which caused it, may trigger Mpc-scale radio emission and may lead to the disruption of the cluster cool core.
1305.2430
The structure of the Milky Way's hot gas halo
Miller, Bregman
Use LoS to 26 AGN, 1 LMC source and 2 galactic sources to find OVII Ka absorption to measure 1e6K gaseous halo around the MW. Beta model fit shows hot gas accounts for 10-50% of the missing baryons in the MW. Find Z>~0.2 Z_sun metallicity based on pulsar dispersion measure towards the LMC.
1305.2542
Magnetic fields of neutron stars
Reisenegger
NSs contain the strongest B-fields known in the Universe. Discuss briefly how these B-fields are inferred from observations, as well as the evidence for their time-evolution. Show: how these extremely strong fields are actually weak in terms of their effects on the stellar structure, as is also the case for magnetic stars on the upper MS and magnetic WDs, which have similar total magnetic fluxes. Propose a scenario in which a stable hydromagnetic equilibrium (containing a poloidal and toroidal field component) is established soon after the birth of the NS, aided by the strong compositional stratification of NS matter, and this state is slowly eroded by a non-ideal magneto-hydrodynamic processes such as beta decays and ambipolar diffusion in the core of the star and Hall drift and breaking of the solid in its crust. Over sufficiently long timescales, the fluid in the NS core will behave as if it were barotropic [i.e., density is only a function of pressure (and vice versa)], because, depending on temperature and magnetic field strength, beta decays will keep adjusting the composition to the chemical equilibrium state, or ambipolar diffusion will decouple the charged component from the neutrons. Therefore, the still open question regarding stable hydromagnetic equilibria in barotropic fluids will become relevant for the evolution, at least for "magnetar" fields, too strong to be stabilized by the solid crust.
1305.2619
Dark matter distributions around massive black holes: a general relativistic analysis
Sadeghian, Ferrer, Will
The CDM at the center of a galaxy will be redistributed by the presence of a massive BH. The redistribution may be determined using an approach pioneered by Gondolo and Silk: begin with a model distribution function for the DM, and "grow" the BH adiabatically, holding the adiabatic invariants of the motion constant. Unlike the approach of G&S, which adopted Newtonian theory together with ad hoc correction factors to mimic GR effects, carry out the calculation fully relativistically, using the exact Schwarzschild geometry of the BH. Find that the density of DM generically vanishes at r=2R_S, not 4R_S as found by G&S, where R_S is the Schwarzschild radius, and that the spike very close to the BH reaches significantly higher densities. Apply the relativistic adiabatic growth framework to obtain the final DM density for both cored and cusped initial distributions. Besides the implications of these results for indirect detection estimates, show that the gravitational effects of such a DM spike are significantly smaller than the relativistic effects of the BH, including frame dragging and quadrupolar effects, for stars orbiting close to the BH that might be candidates for testing the BH no-hair theorems.
1305.2628
An overview of the dwarf galaxy survey
Madden, et al
DGS is a 230h program of FIR and submm photometric and spectroscopic observations of Herschel which trace dust, gas and stars of a sample of 50 galaxies (selected with largest metallicity range achievable in the local universe) and span 4 orders of magnitude in SFR. Designed to get a handle on the physics of the ISM of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. Gas cooling in neutral and ionized phases also studied. Describe the sample selection and global properties of the galaxies, the observing strategy, as well as the vast ancillary database available to complement the Herschel observations. Full DGS survey's scientific potential described.
1305.3130
HERschel Observations of Edge-on Spirals (HEROES). I: Far-infrared morphology and dust mass determination
Verstappen et al
Edge-on spiral galaxies with prominent dust lanes provide us with an excellent opportunity to study the distribution and properties of the dust within them. HEROS set up to observe a sample of 7 large edge-on galaxies across various wavelengths for this investigation. Determine horizontal and vertical profiles from Herschel observations of the galaxies in the sample and describe the morphology. Modified BB fits to the global fluxes, measured using aperture photometry, result in dust temperatures and dust masses. The latter values are compared to these that are derived from radiative transfer models taken from the literature. On the whole, the Herschel flux measurements agree well with archival values. Find that the exponential horizontal dust distribution model often used in the literature generally provides a good description of the observed horizontal profiles. Three out of the 7 galaxies show signatures of extended vertical emission at 100 and 160 um at the 5 sigma level, but in two of these it is probably due to deviations from an exactly edge-on orientation. Only for NGC 4013, a galaxy in which vertically extended dust has already been detected in optical images, we can detect vertically extended dust, and the derived scale height agrees with the value estimated through radiative transfer modeling. Analysis hints at a correlation between the dust scale height and its degree of clumpiness, which we infer from the difference between the dust masses as calculated from modeling of optical data and from fitting the spectral energy distribution of Herschel datapoints.
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