1201.5891
Accretion geometry of the low-mass X-ray binary Aquila X-1 in the Soft and Hard states
Sakurai, Yamada, Torii, Noda, Nakazawa, Makishima
* Comptonization: change in radiation spectrum due to scattering by electrons. Relevant for high T, low density plasma, having large optical thickness in Thomson scattering.
NS low-mass X-ray binary Aquila X-1 observed 7 times in the decaying phase of an outburst. Constrain the flux-dependent accretion geometry; spectrum successfully explained by an optically-thick disk emission plus a Comptonized blackbody component. Characteristics of the hard state successfully explained by the same two continuum components but with rather different parameters including much stronger thermal Comptonization, of which the seed photon source was identified with BB emission from the NS surface [!]. As a result, the accretion flow in the hard state is inferred to take a form of an optically-thick and geometrically-thin disk down to a radius of 21pm4 km for the NS, and then in turn into an optically-thin nearly-spherical hot flow.
1201.5892
Subhaloes in self-interacting galactic dark matter haloes
Vogelsberger, Zavala, Loeb
Present N-body sim with a new class of self-interacting DM models which do not violate any astrophysical constraints. Take MW-like DM halo from Aquarius and re-simulate it for a few representative cases for this new model. Find: the main halo only develops a small core (~1 kpc) followed by a density profile identical to that of CDM outside that radius. Subhalo mass function nor the radial number density of subhaloes altered. Significant change in the inner density structure of subhaloes resulting in the formation of a large density core. So the inner circular veloctiy profiles of the most massive subhaloes differen significantly from te CM predictions. Demonstrate that they are compatible with the observational data of the brightest MW dSphs. No subhaloes that are more concentrated than that inferred from the kinematics of the MW dSphs. Conclude that these models offer anin teresting alternative to the CDM model that can reduce the recently reported tension between the brightest MW satellites and the dense subhalos found in CDM simulations.
1201.5899
Entropy production in collisionless systems. II. Arbitray phase-space occupation numbers
Barnes, Williams
* violent relaxation: the rapid evolution of a star cluster or galaxy that has formed in a configuration far from equilibrium. During violent relaxation, the orbits of individual stars change dramatically because of changes in the gravitational potential of the system. It is thought to play an important part in shaping elliptical galaxies during the first billion years of their evolution.
1201.5918
The effect of major mergers on age and metallicity across the fundamental plane
Porter, Somerville, Croton, Covington, Graves, Faber, Primack
Other's attempt to determine SFH of elliptical galaxies by tracking correlations between the stellar pop params (age, metallicity) and the structural parameters that enter the fundamental plane (size and velocity dispersion). These studies have found that velocity dispersion, rather than effective radius or dynamical mass, is the main predictor of the galaxy's stellar age and metallicity. Apply an analytic model that predicts the structural properties of remnants formed in major mergers to progenitor disk galaxies with properties taken from two different SAMs. Predict the effective radius, velocity dispersion, luminosity, age and metallicity of the merger remnants, enabling comparison to observations. Find tight correlation between age and velocity dispersion, find a stronger dependence of age and metallicity on effective radius than observations report. The correlations arise as a result of the dependence of gas fraction, age, and metallicity on the stellar mass in the progenitor disk galaxies. These dependences induce a rotation in the radius-velocity plane [??] between the correlations with effective radius and circular velocity .... The differences between this result and observations suggest that major mergers alone cannot produce the observed lack of correlation between effective radius and stellar population parameters. Simulations show subsequent minor mergers introduce scatter in the effective radius, while leaving the velocity dispersion essentially unchanged, could bring sims closer to observations.
1201.5926
Observational tests of inflation with a field derivative coupling to gravity
Tsujikawa
A field kinetic coupling with the EInstein tensor leads to a gravitationally enhanced friction during inflation, by which even steep potentials with theoretically natural model parameters can drive cosmic acceleration. In the presence of this non-minimal derivative coupling, we place observational constraints on a number of representative inflationary models such as chaotic inflation, inflation with exponential potentials, natural inflation, and hybrid inflation. Show that most of the models can be made compatible with the current observational data mainly due to the suppressed tensor-to-scalar ratio.
1201.5955
Constraining inflation with future galaxy redshift surveys
Huang, Verde, Vernizzi
Future galaxy surveys will bring a large number of Fourier modes of the distribution of the LSS of this Universe. These modes are complementary to those of the CMB and cam be used to set constraints on the models of the early universe, such as inflation. Using MCMC, compare power of CMB with that of combination of CMB and galaxy survey data, to constrain the power spectrum of primordial fluctuations generated during inflation. Combine Planck with Euclid as example, consider models of slow-roll inflation, show that the inclusion of LSS improves the constraints by halving the error bars on the scalar spectral index and its running. Attempt to reconstruct the inflationary single-field potential, a similar conclusion can be reached. Then study models with features in the power spectrum. Consider ringing features produced by a break in the potential and oscillations such as in axion monodromy. Adding LSS improves the constraints on features by more than a factor of two. In axion monodromy, show that there are oscillations with small amplitude and frequency in momentum space that are undetected by CMB alone but can be measured by including galaxy surveys in the analysis.
1201.6010
Planetary nebula kinematics in NGC 1316: a young Sombrero
McNeil-Moylan, Freeman, Arnaboldi, Gerahard
Present 796 PNe in NGC 1316, use PNe and existing kinematics to explore the rotation of this merger remnant and constrain dynamical models. The 2d velocity field indicates dynamically-important rotation that rises in the outer parts, possibly due to the outward transfer of angular momentum during the merger. The modeling indicates a high DM content, particularly in the outer parts, that is consistent with previous estimates from dynamical models, lensing and stellar population models. The exceptionally large sample of PNe velocities makes it possible to explore the kinematics of NGC 1316 in detail. Comparing the results to other early-type galaxies, NGC 1316 represents a transition phase from a major-merger event to a bulge-dominated galaxy.
1201.6031
Interstellar gas within ~10pc of Sgr A*
Ferriere
3d picture of interstellar gas out to about 10pc of the dynamical center of our Galaxy (Sgr A*). Compile different gaseous components identified near Sgr A*, and retain all information relating to their spatial configuration and/or physical state. 3d representation of interstellar gas describes component in terms of its precise location and morphology, and its thermodynamic properties. 5 basic components: (1) a central cavity with roughly equal amounts of warm ionized and atomic gases, (2) a ring of mainly molecular gas, (3) a SNe remnant filled with hot ionized gas, (4) a radio halo of warm ionized gas and relativistic particles, and (5) a belt of massive molecular clouds. While the halo gas fills 80% of the studied volume, the molecular components enclose 98% of the interstellar mass.
1201.6074
Star formation in the early universe: beyond the tip of the iceberg
Tanvir et al
HST imaging (late-time) of 6 Swift GRBs at 5<z<9.5. Data include very deep observations of the field of the most distant spectroscopically confirmed burst at z=8.2. Place limits on the luminosities of their host galaxies. One seemed to have excess flux (corresponding to a host galaxy), the others didn't. All hosts lie below L* at their respective redshifts, with SFR < 4 Msun/yr in all cases. Stacking the 5 fields with WFC3-IR data, conclude a mean SFR 90% confidence. Not yet possible to make stronger statements now, but studies hold great potential in the future.
1201.6108
The cosmic history of the spin of DM haloes within the LSS
Trowland, Lewis, Bland-Hawthorn
N-body sims to investigate the evolution of the orientation and magnitude of DM halo angular momentum within the LSS since z=3. Evolution of the alignment of halo spins with filaments and with each other, as well as the spin parameter, which is a measure of magnitude of angular momentum. Found: angular momentum vectors of DM haloes at high z have weak tendency to be orthogonal to filaments and high mass haloes have stronger orthogonal alignment than low mass haloes. Since z=1, the spins of low mass haloes have become weakly aligned parallel to filaments, whereas high mass haloes keep their orthogonal alignment. This recent parallel alignment of low mass casts doubt on tidal torque theory as the sole mechanism for the build up of angular momentum. Find a significant alignment of neighboring DM haloes only at very small separations, r<0.3 Mpc.h, which is driven by substructure. A correlation of the spin parameter with halo mass is confirmed at high z. [do they mean observationally?]
1201.6230
UV extinction towards a quiescent molecular cloud in the SMC
Apellaniz, Rubio
The mean UV extinction law for the SMC is taken as a template for low-metallicity galaxies, but the current derivation is based on only 5 stars. Should increase the number of targets, to assess dependence on parameters such as metallicity and SF activity. Obtain HST STIS slitless UV spectroscopy of 25"x25" FoV, combine with ground-based NIR and visible photometry of the stars in the field. Use CHORIZOS to derive the visible-NIR extinction values of each star. The unextinguished SEDs obtained in this way were then used to derive the UV extinction law for the 4 most extinguished stars. Results: extinction law vary significantly star-by-star.
1201.6245
Comparison of Fe and Ni opacity calculations for a better understanding of pulsating stellar envelopes
Gilles et al
* Rosseland mean value opacity: Use a temperature derivative of Planck distribution (normalized) as the weighting function, when defining the average opacity. The Rosseland opacity is derived in the diffusion approximation to the radiative transport equation; valid whenever the radiation field is isotropic over distances comparable to or less than a radiation mean free path, such as in local thermal equilibrium.
* Planck opacity: use Planck BB radation energy distribution as the weighting function.
Opacity: important ingredient of the evolution of stars. Opacity coefficient calculations complicated by the plasma containing partially ionized heavy ions that contribute to the opacity dominated by H and Ne. The astrophysical community has greatly benefited from the work of the contributions of Los Alamos, Livermore, and the Opacity Project, but unexplained differences up to 50% in the radiative forces and the Rosseland mean values for Fe have been noticed for conditions corresponding to stellar envelopes. Such uncertainty has a real impact on the understanding of pulsating stellar envelopes on the excitation of modes and on the identification of the mode frequencies. Temperature and density conditions equivalent to those found in stars can now be produced in laboratory experiments for various atomic species. Recently, spectra of Ni and Fe plasmas have been measured for temperatures between 15 and 40 eV and densities of ~3 mg/cm^3. Present the set of opacity calculations performed by 8 different groups for conditions relevant to the experiment and to astrophysical stellar envelope conditions.
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