1204.1338
SDSS J184037.78+642312.3: the first pulsating extremely low mass white dwarf
Hermes, et al
* White dwarf: a small star composed mostly of electron-degenerate matter. Its faint luminosity comes from the emission of stored thermal energy. Over 97% of stars in MW is expected to be a WD (they are not massive enough to be a neutron star--many low mass stars out there). H-burning star turns red and He-burning (C and O end-products); if cannot burn C due to low mass (1e9 K), then inert core of C and O accumulate, while the outer mass sheds into a PN. The remaining core is a WD, usually composed of C and O. If progenitor has 8<M/Msun<10.5, C burns but not Ne, and will form a O-Ne-Mg WD. Some He WD form apparently through mass loss in binary systems. SDSS found over 9k WDs. Mass distribution strongly peaked at 0.6 Msun, majority at 0.5 < M/Msun < 0.7. The extremes are 0.17 and 1.33. Interior of WD maintains a constant temperature of 1e7K due to high thermal conductivity but very low opacity. An outer shell of non-degenerate matter cools from 1e7K to 1e4K, and is roughly a BB. The center crystalizes in BCC (detected in astroseismological observations of pulsating WDs); the crystal fraction can be 32% to 90%. Atmosphere purified by gravity: The light elements (H or He) are usually 1000x more abundant than the other heavier elements.
Discovery of ELM WD: This DA (H-atmosphere) WD is by far the coolest and the lowest-mass pulsating WD, with Teff = 9100 K and log g = 6.22, which corrresponds to a mass ~0.17 Msun. This low-mass pulsating WD greatly extends the DAV (or ZZ Ceti) instability strip, effectively bridging the log g gap between WDs and main sequence stars. Detect high-amplitude variability in J1840 on timescales exceeding 4000 s, with a non-sinusoidal pulse shape. Observations also suggest that the variability is multi-periodic. The star is in a 4.6 hr binary with another compact object, most likely another WD. Future: probe the interior of a low-mass, (presumably) He-core WD using the tolls of astroseismology from time-series photometry.
1204.1339
Dark matter collisions with the human body
Freese, Savage
The dominant contribution is from scattering off of oxygen (hydrogen) nuclei for the spin-independnet (spin-dependent) interactions, assuming DM is a WIMP. In an average year, ~10 WIMPs (assuming 60 GeV WIMP) interaction in a 70 kg human body per year, for the maximum allowed interactions. Higher rates (1e5/yr, or 1/min) for 10-20 GeV WIMPs with large cross section.
1204.1341
Ligt echoes of transients and variables in the local universe
Rest, Sinnott, Welch
Astronomical light echoes: the time-dependent light scattered by dust in the vicinity of varying objects. Utility: mapping out 3d distribution of interstellar dust, spectroscopically-useful light echoes around centuries-old supernovae in the MW and LMC, view from multiple perspectives, obtain a spectroscopic time series of the outburst, establish accurate distances to the source event. Broader range of variable objects whose properties may be better understood from light echo observations. New light echo techniques not yet realized in practice.
1204.1344
The formation of the first cosmic structures and the physics of the z~20 universe
O'Leary, McQuinn
Cosmo simulations in LCDM of the formation of the first structures prior to astrophysical reheating and ionization (15<z<200). Self-consistently accounts for the impact of pressure on the rate of growth of modes, temperature fluctuations in the gas, and the dark matter-baryon supersonic velocity difference. Difficult to simulate accurately, as the Jeans length of the cold intergalactic gas must be resolved while also capturing a representative sample of the universe. Simulations support recent studies that find: DM-baryon velocity difference has a surprisingly large impact on the accretion of gas onto the first star-forming mini haloes (1e6 Msun). The halo gas is often significantly downwind of such halos and with lower densities, which delays the formation of the first stars in most locations in the universe. Also: dynamical friction plays an important role in the nonlinear evolution of the differential velocity, acting to erase the velocity difference quickly in overdense gas as well as sourcing as well as sourcing visually-apparent bow shocks and mach cones throughout the universe. Use both GADGET and Enzo to test the robustness of these conclusions. Find: particle coupling in GADGET between gas and DM can result in spurious growth that mimics nonlinear growth in the matter power spectrum. Companion paper estimates the impact of the DM-baryon velocity differential on redshifted 21cm radiation. The initial conditions generator CICsASS publicly available.
1204.1345
The impact of the supersonic baryon-dark matter velocity difference on the z~20 21cm background
McQuinn, O'Leary
Tseliakhovich and Hirata (2010) showed that during the cosmic Dark Ages the baryons were typically moving supersonically with respect to the DM with spatially variable Mach number. Such supersonic motion may source shocks that heat the universe, and may also suppress star formation in the first haloes. Even a small amount of coupling of the 21 cm signal to this motion has the potential to vastly enhance the 1cm brightness temperature fluctuations at 15<z<40, as well as to imprint acoustic oscillations in this signal. Present estimate for the size of this coupling, calibrate with a suite of simulations. Self-consistently account for gas pressure and DM-baryon relative velocity v_bc. Find: supersonic velocity difference dramatically suppresses structure formation at 10-100 comoving kpc scales; sources shocks throughout the universe, and impacts the accretion of gas onto the first star-forming mini haloes as large as 1e7 Msun; but find that v_bc-sourced temperature fluctuations can contribute only as much as 10% of the fluctuations in the 21cm signal . Find that v_bc could source an O(1) component in the power spectrum of the 21cm signal via the x-ray (but not UV) backgrounds produced once the first stars formed. If 1e6 Msun mini haloes reheated the universe via their X-ray backgrounds, find that the pre-reionization 21cm signal would be larger than previously anticipated and exhibit significant acoustic features. Show that structure formation shocks are unable to heat the universe sufficiently to erase a strong 21cm absorption trough at z~20 that is found in most models of the sky-averaged 21cm intensity.
1204.1346
Atmospheric dispersion effects in weak lensing measurements
Plazas, Bernstein
Wavelength dependence of atmospheric refraction causes elongation of finite-bandwidth images along the elevation vector, which produces spurious signals in WL shear measurements, unless calibrated and removed to high precision. Because astrometric solutions and PSF characteristics are typically calibrated from stellar images, differences between the reference star's spectra and the galaxies' spectra will leave residual errors in both the astrometric positions (Delta R) and in the second moment (width) of the wavelength-averaged PSF (Delta nu) for galaxies. Estimate the level of Delta V that will induce spurious weak lensing signals in PSF-corrected galaxy shapes that exceed the statistical errors of the DES and the LSST cosmic-shear experiments. Also estimate the Delta R signals that will produce unacceptable spurious distortions after stacking of exposures taken at different air masses and hour angles. Using standard galaxy and stellar spectral templates, calculate the resultant errors in the grid bands, and find that atmospheric dispersion differentials, left uncorrected, exceed the DES cosmic-shear requirements in the g and r bands, and exceed the stricter LSST requirements in i band. Find that a simple correction linear in galaxy color is accurate enough to recover the use of r band for DES and i band for LSST. More complex approaches to correction of the atmospheric dispersion signal will be needed to use the g band for DES cosmic-shear measurements or to use the g or r bands for LSST cosmic-shear measurements.
1204.1365
Fast generation of mock maps from realistic catalogs of astrophysical objects
De Domenico, Lyberis
Novel method to generate a mock on a spherical surface by using a real distribution. Resulting surrogate map mimics the clustering features of the real data, including the effects of non-uniform exposure, if any. The method is model-independent, preserving the angular correlation function as well as the angular power spectrum of the original data. Can be reliably adopted to mimic the angular clustering of objects distributed on a spherical surface, and it can be easily extended to include further information, as the spatial clustering of objects distributed inside a sphere. Applications to real data presented (2MRS).
1204.1368
Present-day descendants of z-3 Ly-{\alpha} emitting galaxies in the Millennium-II halo merger trees
Soler, Gawiser, Bond, Padilla, Francke
Created mock catalog of LAE at z=3.1 to study the properties of their descendants. Several models created by selecting the sub-haloes to match the number density and typical DM mass determined from observations of these galaxies. Use mass-based and age-based selection criteria to study their effects on descendant populations at z=2,1, and 0. For the best models, the z=0 descendants have median DM halo mass of 1e12.7 Msun, with wide scatter in mass (11.8 to 13.7). Found 55% of sub-halos were centrals with M-median=1e12 Msun, confirming that central descendants of z=3.1 LAEs have halo masses typical of L* type galaxies. The satellite sub-haoes reside in group/cluster environments with dark matter masses around 1e14 Msun. The median descendant mass is robust to various methods of age determination, but not well constrained, data limited.
1204.1371
The galactic center weather forecast
Moscibrodzka, Shiokawa, Gammie, Dolence
What happens when the gas clump near Sgr A* arrives at the SMBH around 2013? Increase in \dot{M} will cause Sgr A* to gain a persistent component in NIR luminosity (not just currently observed flares), X-ray and mid-IR also persists, In general the characteristic ring of emission due to the photon orbit becomes brighter, more extended, and easier to detect by the planned even horizon telescope submm VLBI experiment.
1204.1375
The viewing angles of broad absorption line versus unabsorbed quasars
DiPompeo, Brotherton, DeBreuck
Significant difference in the radio spectral index distributions of broad absorption line quasars and unabsorbed quasars, with and overabundance of BAL quasars with steeper radio spectra, suggesting that source orientation does play into the presence or absence of BAL features. Spectral difference are different enough to see the intrinsic variation in viewing angle (based on MC simulations). Orientation cannot be the only factor determining whether BAL features are present, but it does play a role.
1204.1399
Gas and metal distributions within simulated disk galaxies
Gibson, Court, Cunnama, Molla
Chemodynamical galactic archaeology efforts: (i) the spatio-teomparl infall rate of gas onto the disk (classical galactic chemical evolution models "inside-out" disk growth)--half in corona and half in cooler gas streams, gas enters the disk orthogonal to the system rather than in-plane; (ii) the radial age gradient predicted by spectrophometric [?] models of disk galaxies; recover age gradient troughs/inflections consistent with those observed, without recourse to radial migrations.
1204.1439
Stochastic gravitational wave background originating from halo mergers
Inagaki, Takahashi, Sugiyama
Construct a merger tree using either Press-Schechter or Sheth-Tormen with MC; from N-body sims of two-halo mergers, estimate the amount of gravitational wave emission induced by the individual merger process. Combine GW emission to the merger tree, and obtain GWB. Find Omega_GW~1r-19 for f~1e-17 to -16 Hz. Most of the contribution on the GWB comes from halos with masses below 1d15 Msun and mergers at low redshift, 0<z<0.8.
1204.1463
Mass of highly magnetized white dwarfs exceeding the Chandrasekhar limit: an analytical view
Kundu, Mukhopadhyay
WDs with very high surface B-fields observed; expect B-field in the core would be much higher (1e14 G). Analytically study the effect of high B-field on relativistic cold electron, and hence its effect on the stability and the mass-radius relation of a magnetic white dwarf. In strong B-felds the EoS of Fermi gas is modified and Landau quantization [?] comes into play. Number of Landau levels restricted to 1 or 2. Conditions in which transition from the 0th Landau to first Landau level occur studied; Effect of strong B-field on the star collapsing to a WD, and the mass-raidus relation of the resulting star. It is possible to have WDs with mass more thant the Chandrasekhar limit.
1204.1480
Non-Gaussianity from extragalactic point-sources
Lacasa
Population of compact extragalactic sources contribute to non-Gaussianity at CMB frequencies: Study using full-sky simulations. Clustering of IR sources enhances their non-Gaussianity by several orders of magnitude; their bispectrum peaks in the squeezed triangles. Find that radio sources yield an important positive bias to local fNL at low frequencies, but this bias is efficiently reduced by masking detectable sources IR sources produce a negative bias at high frequencies, not dimmed by the masking, since their clustering is dominated by faint sources.
1204.1497
The baryonic Tully-Fisher relation predicted by cold dark matter cosmogony
Desmond
Providing a theoretical basis for the TFR in the CDM paradigm is problematic: simple calculations suggest too low a slope and too high a scatter. This paper aims to develop a rigorous prediction for the relation in the context of CDM by accounting for all relevant TFR-independent effects observed in numerical simulations of DM haloes, including their expected scatter. Consistent treatment of these effects [which ones?] goes a large way towards reconciling the CDM prediction with the data; the normalization becomes almost perfect, although the slope remains somewhat low. Predicted scatter is too large, but may be reduced to near that of the data by accounting for observational selection effects.
1204.1504
Cosmological neutrino entropy changes due to flavor statistical mixing
Bernardini
Entropy changes due to localization and decoherence effects should modify the predictions for the cosmological neutrino background temperature . ...
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