Tuesday. Exhausted this morning, don't know why. Talking to Lance and Massimo about shape measurements was fun and informal, looking forward to it again today. Massimo looks like Uros from the front (it turns out that Massimo's from Trieste, a few km to Uros' home town. Their head shape is similar), and Martin from the back (hair and skin color---I guess I identify European people by their coloring). It's totally confusing, I felt like I was walking with Martin and talking to Uros.
1206.4999
Chemical abundances of metal-poor RR Lyrae stars in the Magellanic Clouds
Haschke et al
Spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the LMC and SMC [why?]. 6 RR Lyrae stars in LMC, 3 in SMC, chosen for lowest photometric metallicities: find as low as [Fe/H]_spec=-2.7. Photometric metallicities systematically too high (for metal poor stars, compare to spectroscopic). Trend is reversed for even more metal-poor stars. (<-2.8 dex). Determined abundance ratios for 10 chemical elements. Good [alpha/Fe] agreement with MW halo. Plausible that LMC-type galaxies contributed early chemically to MC halo, claimed in cosmological model.
1206.5000
CANDELS: the progenitors of compact quiescent galaxies at z~2
Barro,.. Koo, .. Bell, .. Dekel, ... Grogin, et al
CANDELS: HST imaging with multi-wavelength photometry to track the evolution of structure and activity of massive galaxies at z=1.4-3. Identify compact, SF galaxies (cSFGs) that are likely progenitors of compact, quiescent, massive galaxies (cQGs) at z=1.5-3 (based on number densities, masses, sizes and SF rates). At high z (>2) most sSFGs have sSFR half that of typical massive SFGs at the same epoch, and host X-ray luminous AGN 30 times more frequently; suggest cSFGs are formed by gas-rich processes (mergers or disk-instabilities) that induce a compact starburst and feed and AGN, which quench the SF on timescales of few 1e8 yr. cSFGs continuously being formed at z=2-3 and fade to cQGs by z=1.5. After this epoch, cSFGs are rare, truncating the formation of new cQGs. Meanwhile, existing cQGs at z=1 continue to enlarge to match local QGs in size, while less-gas-rich mergers and other secular mechanisms shepherd (larger) SFGs as later arrivals to the red sequence. In summary, propose tow evolutionary scenarios of QG formation: an early (z>2), fast-formaiton path of rapidly-quenched cSFGs that evolve into cQGs that later enlarge within the quiescent phase, and a slow, late-arrival (z<2) path for SFGs to form QGs without passing through a compact state.
(*) 1206.5002
stellar wind mass retention in star clusters: implications for subsequent episodes of star formation
Naiman, Ramirez-Ruz, Lin
Hydro-sims to explore a wide range of stellar cluster masses, compactness ,metallicities and stellar age combinations to determine the ideal conditions for gas retention. Find: up to 6.4% of the mass of the star cluster can be made up of retained stellar wind gas at the time of SF is triggered. Multiple episodes of SF can take place during the lifetime of a star cluster for >1 Gyr. Faroable SF time interval coincides with AGB phase. Gas retention is hampered by pulsar outflows or accretion onto compact objects.
1206.5003
Colliding planetary and stellar winds: charge exchange and transit spectroscopy in neutral Hydrogen
Tremblin, Chiang
When transiting, hot Jupiters absorb about 10% of the light in the wings of the stellar Lyman-alpha emission line; the absorption occurs at wavelengths Doppler-shifted from line center by pm100 km/s, much larger than the speeds with which partially neutral, 7000K H escapes from hot Jupiter atmospheres. Absorption arises from 1e6K H from the host stellar wind, made momentarily neutral by charge exchange with planetary H I. 2d Hydro-sim of collision, augmented by a chemistry module to compute the amount of hot H I produced by charge exchange. Contact discontinuity is KH unstable, about 20% are in equilibrium. Simulations show enough hot H I generated to reproduce the transit observations, and amount of absorption converges with both spatial resolution and time. Provide physical scaling relations that describe how absorption varies with stellar and planetary wind properties.
(*) 1206.5004
How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction?
Hilz, Naab, Ostriker
Observational evidence for inside-out growth of giant elliptical galaxies since z>2-3; many of the 1e11 Msun systems at high z have small sizes (1kpc) and surface brightness profiles with low Sersic indices n. The most likely descendants at z=0 have, on average, grown by a factor of two in mass and a factor of four in size, with n>5. Two assumptions can explain the evolution: compact ellipticals predominantly grow by collision less minor 'dry' mergers, and they are embedded in massive DM haloes which support the stripping of merging satellite stars at large radii. Run simulations with and without DM halos of spheroidal galaxy mergers. Only a few minor mergers (~3-5 with mass-ratios of 1:5) of galaxies embedded in massive DM halos can result in the observed concurrent inside-out growth and the rapid evolution in profile shapes. Apart from negative stellar metallicity gradients and positive age gradients, such a minor merger scenario also predicts significantly lower DM fractions for z~2 compact quiescent galaxies and their rare present day analogues. [Why? How?]
1206.5006
A general class of Lagrangian smoothed particle hydrodynamics methods and implications for fluid mixing problems
Hopkins
Smooth-particle hydrodynamics (SPH): intended to resolve certain difficulties in the treatment of fluid mixing instabilities. Show how a class of alternative SPH equations of motion (EOM) can be derived self-consistently from a discrete particle Lagrangian (guaranteeing manifest conservation of energy, entropy, momentum and angular momentum) in a manner which tremendously improves treatment of these instabilities and contact discontinuities. Derive a general EOM for any choice of volume element (particle 'weights') and method of determining smoothing lengths, specify this to a 'pressure-entropy formulation' which resolves problems in the traditional treatment of fluid interfaces. Implement in a new version of GADGET code, show that it works well, and conserves physical quantities. No additional computational expense.
(*) 1206.5007
Detecting the rise and fall of the first stars by their impact on cosmic reionization
Ahn, Illiev, Shapiro, Mellema, Koda, Mao
The first stars forming in mini haloes of 1e5-8 Msun at z~40: their contribution have been ignored for cosmic reionization so far. Show reionization began much earlier with mini halo sources than without, and was greatly extended, which boosts the intergalactic electron-scattering optical depth and the large-angle polarization fluctuations of the CMB significantly (although within WMAP uncertainties). Should be readily detectable by Planck.
(*) 1206.5010
Precise abundance analysis of the outer halo globular cluster M 75
Kacharov, Koch
M75 has high metallicity and shows signs of at least two generation of stars, formed on a short timescale. Discuss r-and s-process element abundances in the context of the earliest cluster enrichment phases.
1206.5016
Supernovae and their host galaxies. I. the SDSS DR8 database and statistics
Hakobyan et al
Creation of a large database: of host galaxies, for 3800 SNe in 3600 host galaxies from SDSS DR8, check host galaxy statistics on apparent mags, diameters, axial ratios, position angles, morphology from g-band image.
1206.5020
Galaxy zoo: quantifying morphological indicators of galaxy interaction
Casteels et al
Study morphological signatures of interaction between similar-mass galaxy pairs in SDSS. Find: observable features correlate with projected pair separation: disturbance, tidal tails (obvious); but spiral arms and bars as well. Robustly quantified using a control sample. Find: presence of spiral features enhanced at scales < 70 kpc/h, probably due to both increased SF and the formation of tidal tails. Bar decreases in paris with separations < 30 kpc/h, suggesting that bars are suppressed by close interactions between galaxies of similar mass. Morphological indicators of physical interactions provide a way of significantly refining standard estimates for the frequent of close pair interactions, based on velocity offset and projected separation. Presence of loosely wound spiral arms is found to be a particularly reliable signal of an interaction, for projected pair separations up to ~100 kpc/h. Use this indicator to demonstrate method of constraining the fraction of low-redshift galaxies in truly interacting pairs with M*>1e9.5 Msun and mass ratio <4 to be between 0.4-2.7 %.
1206.5022
Toward a unified AGN structure
Kazanas, Fukumura, Behar, Contopoulos, Shrader
Present a unified model for the structure and appearance of accretion powered sources across their entire luminosity range from galactic X-ray binaries to luminous quasars, with emphasis on AGN and their phenomenology. Notion of MHD winds launched from the accretion disks that power these objects is central. AGN phenomenology in 3 parameters: the wind mass flux in units of Eddington value, the observer's inclination angle, and the logarithmic slope between the O/UV and X-ray fluxes. The correlations of two parameters implied by this model appear to extend to and consistent with the characteristics of galactic X-ray sources, suggesting the presence of a truly unified underlying structure for accretion powered sources.
(*) 1206.5032
Gravity theories, transverse Doppler and gravitational redshifts in galaxy clusters
Zhao, Peacock, Li
Testing alternative gravity theories using gravitational redshifts in clusters; but the redshift signal cannot directly distinguish between the Einsteinian and f(R) gravity theories, because the mass of the cluster dark halo must be treated as an unknown fitting parameter, whose value must vary according to the theory adopted, otherwise the system would be in equilibrium in one gravity theory and out of equilibrium in another.
1206.5034
Cosmological post-Newtonian approximation compared with perturbation theory
Noh, Hwang
Correspondences with 1PN equations are available only in certain gauge conditions in the perturbation theory. Perturbed velocity and gravitational potential in the zero-shear gauge coincide with Newtonian equations which is valid even to 1PN order (and perturbed velocity in the comoving gauge); equations of perturbed density in the zero-shear gauge and the uniform-expansion gauge coincide to 1 PN order. Other correspondences available.
1206.5035
Detecting candidate cosmic bubble collisions with optimal filters
McEwen, Feeney, Johnson, Peiris
Review an optimal-filter-based algorithm for detecting candidate sources of unknown and differing size embedded in a stochastic BG, and its application to detecting candidate cosmic bubble collision signatures in WMAP7. 8 new candidate bubble collision signatures detected for follow-up analysis.
(*) 1206.5044
The Earth's figure axis determined from the polar motion data
Kubo
Polar motion data analyzed to obtain accurate position of the figure axis referred to the Earth-fixed frame [?] (variation of figure axis is the basic object to which the geophysical events are linked). Relation between the rotational and the figure axes is derived. The obtained figure axis exhibits stable annual and semi-annual variations while it has no component with the period of the Chandler wobble. Besides this general feature, it shows different patterns from year to year as well as small irregularities with shorter periods, most of which are considered to be significant but not attributed to the observational errors. Further, a simple model is introduced for the cause of the seasonal variation of the figure axis. The model explains both the variation of the figure axis obtained above and that of the rotational speed which is so far known. [?]
1206.5053
Why do compact active galactic nuclei at high redshift scintillate less?
Koay et al
Interstellar Scintillation at radio wavelengths:
Partially linked to the steepening of source spectral indices with redshift, caused either by selection biases or AGN evolution.
1206.5056
Cosmic acceleration from causal backreaction with recursive nonlinearities
Bochner
Revisit the causal back reaction paradigm, in which the need for DE is eliminated via the generation of an apparent cosmic acceleration from the causal flow of inhomogeneity information coming in towards each observer from distant structure-forming regions. ...
1206.5058
The Swift short gamma-ray burst rate density: prospects for detecting binary neutron star mergers by aLIGO
Coward et al
Present: 30% of sGRBs have accurate redshifts, highly biased by the limited sensitivity of Swift to detect sGRBs. Calculate a realistic sGRB rate density out to z=0.5. detection rate limits of 1-180 per Yr by aLIGO and Virgo coincidence search. Consistent with extrapolations.
1206.5091
Accurate classification of 29 objects detected in the 39 months Palermo Swift/BAT hard X-ray catalogue
Parisi et al
Optical spectroscopy for 29 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/BAT and listed in the Palermo catalogue. 28 sources AGN (7 type 1, 21 type 2), remaining object a galactic cataclysmic variable.
1206.5097
The role of star formation for the galactic dynamo
Elstner, Gressel
B-field amplification by fast dynamo is seen in local box simulations of SN-driven ISM turbulence. Derive scaling laws of the turbulent transport coefficients in dependence of the SN rate, density and rotation. Present dynamo models for different rotation curves and radial density distributions.
1206.5133
Searching for X-ray emission from AGB stars
Ramstedt Montez, Kastner, Vlemmings
Inconclusive. B-fields measured around AGB stars of all chemical types using maser polarization observations. If present, a large-scale B field would lead to X-ray emission.
1206.5207
Titan's transport-driven methane cycle
Mitchell
The strength of Titan's methane cycle, as measured by precipitation and evaporation, is key to interpreting fluvial erosion and other indicators of the surface-atmosphere exchange of liquids. But the mechanisms behind the occurrence of large cloud outbursts and precipitation on Titan have been disputed. Insolation only 1% (0.04W/m^2), not strong enough to be responsible for driving atmospheric convection. In contrast, climate simulations that allow atmospheric motion indicate a robust methane cycle with substantial cloud formation and/or precipitation. Argue that the top-of-atmosphere radiative imbalance is diagnostic of horizontal heat transport by Titan's atmosphere, and this constrains the strength of the methane cycle. This is calculated to be 0.5-1 W/m^2 at equatorial region; implies 2-3 MW of latitudinal heat transport by the atmosphere. ...
[Mon **/44] Jun 25
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