Special topics
An astrophysical peek into Einstein's static Universe: No Dark Energy
Mitra
Show that the cosmological constant is zero, in order that the fluid pressure and acceleration are uniform and finite in Einstein's static universe (ESU). ... judging from his endnotes, this is a semi-crackpot paper.
1201.2940
The distribution of metals in hot DA white dwarfs
Dickinson, Barstow, Hubeny
* DA WDs: H absorption lines (H-dominated atmospheres), 80% of WDs. No metal or He I lines
* DB, DC, DO, DZ and cool DQ: He-dominated atmospheres, classification depends on effective temperature. DO: He II lines (45k-100k K), DB: He I lines, DC: featureless (below 12000 K)
* Z: metal lines, no H or He I lines
* Q: carbon lines present
* X: unclear or unclassifiable spectrum
* hot DQ: Small fraction (0.1%) have C dominated atmosphere.
Metal abundances in hot white dwarfs: stellar evolution important. Three DA WDs found to have aboundant, stratified photospheric nitrogen (narrow absorption line profiles of the FUV N V doublet, and lack of EUV continuum absorption. Other models say the 3 stars can be well described by homogeneous models. Re-analysis of the N absorption features presented, to test which models better represent the observed data and apply the results to the line profiles seen in another. Degeneracy seen in the modeling of the N absorption line profiles of 3, with low abundance, homogeneously distributed N models most likely being a better representation of the observed data. In the other one, no degeneracy seen, and the deep line profiles cannot be modeled satisfactorily.
1201.2941
Herschel observations of interstellar chloronium
Neufeld et al
* chloronium: the univalent H2Cl+ cation, derived from chlorane
Observed parachloronium (H2Cl+) toward 6 sources in the Galaxy with HIFI. Interstellar chloronium absorption in foreground molecular clouds along the bright submillimiter continuum source sight-lines, Sgr A and W31C. Found 35Cl and 37Cl isotopologues (absorption difference 1 GHz at 485GHz). Chloronium accounts for 4-12% of chlorine nuclei in the gass photodissociation region and the Orion South condensation. (Ortho-to-para ratios considered, probably has different absorption rates.) ... The chloronium abundances are typically at least a factor 10 larger than the predictions of steady-state theoretical models for the chemistry of interstellar molecules containing chlorine; a puzzle.
1201.2942
ALMA CO and VLT/SINFONI H2 observations of the Antennae overlap region: mass and energy dissipation
Herrera, Boulanger, Nesvabda, Falgarone
Analysis of super-giant molecular complexes (SGMCs) in the overlap region of the Antennae galaxy merger at angular resolutions of 0.9"/0.7" (ALMA/VLT). All but one SGMC have multiple velocity components offset from each other by up to 150 km/s. Kinematics of H2 and CO are well matched. Line ratios vary by up to a factor of 10 among SGMCs and different velocity components of the same SGMCs. A compact source with the highest H2/CO line ratio of near-IR H2 line emission, conincides with the steepest CO velocity gradient, 50pc in size, virial mass of ~2e7 Msun: prehaps a re-cluster cloud that has not yet formed significant numbers of massive stars. H2 emission is powered by shocks; Demonstrate how H2 and CO lines can be used as tracers of energy dissipation and gas mass, respectively. Variations in the H2/CO line ratio may indicate that the SGMCs are dissipating their turbulent kinetic energy at different rates. The compact source could represent a short (~1Myr) evolutionary stage in the early formation of super-star clusters.
1201.2943
Origin of the 12um Emission across galaxy populations from WISE and SDSS surveys
Donoso, Yan, Tsai, Eisenhardt, Stern, Assef, Leisawitz, Jarrett, Stanford
WISE (Wide-field Infrared survey Explorer) cross-match with SDSS spectra sources, 1e5 galaxies. Sample dominated (70%) by SF galaxies from the blue sequence, with total IR luminosities in the range 1e8-12 Lsun. Identify which stellar populations are responsible for most of the 12um emission, find that in SF galaxies, is produced by stellar populations younger than 0.6 Gyr. In contrast, in weak AGN, act as an extension of massive SF galaxies, connecting the SF and weak AGN sequences [?]. Suggests a picture where galaxies form stars normally until an AGN (possibly after a starburst episode) starts to gradually quench the SF activity. Find: 4.6-12 um color is a useful first-order indicator of SF activity in a galaxy.
1201.2944
Understanding Dual AGN activation in the nearby universe
Koss, Mushotzky, Treister, Veilleux, Vasudevan, Trippe
Fraction of dual AGN in 167 nearby (z<0.05), moderate luminosity, unltra hard X-ray selected AGN. Combine Chandra and Gemini observations, find AGN at <100kpc is 10% (16/167). Close dual AGN (<30kpc) tend to be more common among X-ray luminous systems; X-ray luminosity of both AGN increases strongly with decreasing galaxy separation (suggest merging event is key in powering both AGN). 50% are dual AGN (<15kpc), more likely to occur in major mergers, tend to avoid absorption line galaxies with elliptical morphologies. SDSS Seyferts much less likely than x-ray to be found in dual AGN (<30kpc) because of small number of companions, fiber collision limits, AGN better detected in xray, and higher fraction of dual AGN companions with increasing AGN luminosity. [i didn't get the last one]
1201.2945
SPIDER - VII. The entral dark matter content of bright early-type galaxies: benchmark correlations with mass, structural parameters and environment
Tortora, La Barbera, Napolitano, de Carvalho, Romanowsky
DM content of 4.5k (M*>1e10Msun), low z (<0.1) Early-type galaxies (ETGs) with ugrizYJHK photometry and spectroscopy of SDSS and UKIDSS. Results: (1) DM fractions increase systematically with K-band effective radius Re, Sersic index n, mass proxies (velocity dispersion, stellar and dynamical mass), and decrease with central stellar density. (2) All correlations involving DM fractions are caused by two fundamental ones: galaxy effective radius and central velocity dispersion, where the correlations are independent of each other. ETGs populate a central DM plan (total-to-stellar mass ratio, effective radius, and velocity dispersion) whose scatter is ~0.15 dex. (3) in general, a Chabrier IMF is favoured with respect to a bottom-heavier Salpeter IMF (4) The central DM content of ETGs does not depend significantly on the environment where galaxies reside, with group and field ETGs having similar DM trends.
1201.2954
The galaxy optical luminosity function from the AGN and galaxy evolution survey (AGES)
Cool, Eisenstein, Kochanek, Brown, Caldwell, Dey, Forman, Hickox, Jannuzi, Jones, Moustakas, Murray
Optical luminosity function for 0.05<z<0.75 in AGES spectroscopic survey, from 12k galaxies down to I=20.4. Results from low z consistent with SDSS, at high z, find strong evidence for evolution in the luminosity function, including differential evolution between blue and red galaxies. Find luminosity density evolves as (1+z)^0.54 pm 0.64 for red galaxies, and (1+z)1.64pm0.39 for blue galaxies.
1201.2957
A multi-wavelength study of low redshift cluster of galaxies II. Environmental impact on galaxy growth
Atlee, Martini
Cluster study of morphology and SFR correlations. SFR depends strongly on R/R200, independent of projected local density at fixed radius. SFR show no residual dependence on stellar mass. A decline in the fraction of SFGx toward the cluster contributes most, accompanied by a reduction in SFRs among SF galaxies near the cluster center. Consistent with ram pressure stripping as the mechanism to truncate SF in galaxy clusters. Galaxies near the cluster center are more massive than galaxies farther out, suggesting that cluster galaxies experience dynamical relaxation during their evolution [??].
1201.2988
Getting steeper: mass-density profile evolution in the SLACS+BELLS strong gravitational lens sample
Bolton, Brownstein, Kochanek, Shu, Schlegel, Eisenstein, Wake, Connolly, Maraston, Weaver
Evolution of the central mass-density profile of massive elliptical galaxies from the SLACS and BELLS SL samples over 0.1<z<0.6. Find significant trend towards steeper mass profiles at later cosmic times. Show that this detection cannot be explained by variations in the lensing measurement aperture with redshift. Suggests that major dry mergers involving off-axis trajectories play a significant role in the secular evolution of the average mass-density structure of massive galaxies over the past 6 Gyr.
* Asymptotic giant branch: region of the HR diagram populated by evolving low to medium-mass stars. Period of stellar evolution undertaken by all low to intermediate mass (0.6-10 Msun) stars late in their lives. Observationally appear as a red giant. Interior structure characterized by a central and intert core of C and O, a shell where He is undergoing fusion to form carbon (He burning), and another shell where H is undergoing fusion forming He (H burning), and a very large envelope of material of composition similar to normal stars. Named because the AGB track is nearly aligned with the red giant track (horizontal branch).
1201.3062
Reliability of NH3 as the temperature probe of cold cloud cores
Juvela, Harju, Ysard, Lunittila
The ammonia spectra are found to be a reliable tracer of the mass averaged gas temperature, but if the cores are optically very thick, the accuracy is not guaranteed.
1201.3149
On the origin of the Supergiant HI shell and Putative companion in NGC 6822
Cannon et al
* NGC 6822: a dIrr local group galaxy ("Bernard's galaxy")
Can't find any companion to this galaxy, so the most likely explanation os the extended HI structure is a warped disk inclined to the line of sight.
1201.3187
A robust determination of the size of quasar accretion disks using gravitational microlensing
Jiminez-Vicente, Mediavilla, Munoz, Kochanek
Use 27 image pairs of 19 lensed quasars to determine a maximm liklihood estimate of the accretion disk size of an average quasar of r_s=4.0 light days at rest frame=1736A for microlenses with a mean mass of 0.3 Msun. This is a factor of 5 greater than the predictions of the standard thin disk model. The individual size estimates for the 19 quasars in sample are also in excellent agreement with the joint maximum likelihood analysis.
1201.3193
Fluorine abundances in dwarf stars of the solar neighbourhood
Recio-Blanco, de Laverny, Worley, Santos, Melo, Israelian
* Wolf-Rayet stars: evolved, massive stars (>20 Msun) which are losing mass rapidly by means of a very strong stellar wind (1e-5 Msun/yr) with speeds up to 2000 km/s. Very hot, with surface temperatures of 25k to 50k K. Normal stage in the evolution of very massive stars, with strong, broad emission lines of (He and _7N) or (He, _6C and _8O). Due to the strong emission lines, they can be observed in nearby galaxies. About 300 WR stars known in Galaxy, 100 in LMC, 12 in SMC.
* the numbers in _6C indicate the proton numbers of the elements, and are my inclusions, not the paper's.
* S-process : believed to occur mostly in AGB stars: _13C+_4He -> _16O + n
_22Ne + _4 He -> _25 Mg + n
* R-process : believed to occur in explosive environments over a few seconds. Rapid neutron capture, responsible for approximately half of the neutron-rich atomic nuclei that are heavier than iron. Rapid neutron capture on seed nuclei, typically ^56Ni.
* S-process and R-process have different abundances.
Origin of F: SNe II, AGB nucleosynthesis, or core of WR stars. Made some measurements, found no correlation between _9F and _26Fe abundance. Most F enriched stars are also _39Y (yttrium) and _40Zr (zirconium) enriched, suggesting that AGB F nucleosynthesis is the dominant source of F production for the observed stars. But correlation between F/Fe and s-elements are weak. No correlation found in [F/Fe] and [alpha/Fe] ratio, so SNe II do not appear to be the main site of F production.
1201.3225
Radio imaging of the Subaru/XMM-Newton Deep Field - III. Evolution of the radio luminosity function beyond z=1
Simpson, Rawlings, ... et al
Present photoz for radio galaxies in the SXNDF survey sample, good agreement with SKA z distribution; find no correlation between K-band magnitude and radio flux, but show that sources with 1.4 GHz (radio) flux densities below 1mJy are fainter in the NIR than brighter radio sources at the same redshift; implications for incompleteness when K-z are used to estimate redshifts. Only radio-loud hosts have SED consistent with predominantly old stellar populations, although the fraction of objects displaying such properties is a decreasing function of radio luminosity. Calculate Radio luminosity function up to z=4; find that space density of radio sources increases with lookback time to z~2, with more rapid increase for more powerful sources. At same radio luminosity, loud and quiet sources evolve differently: quiet source display strong evolution to z~2, while loud sources below the break in radio luminosity functions evolve more modestly and show hints of a decline in their space density at z>1, with decline occuring later for lower luminosity objects. If the radio luminosities of these sources are a function of their BH spins, then slowly-rotating black holes must have plentiful fuel supply for longer, perhaps they have yet to encounter the major merger that will spin them up and use the remaining gas in a major burst of SF.
1201.3238
Science performance of Gaia, ESA's space-astrometry mission
de Bruijne
GAIA: ESA mission for astrometry after Hipparcos; 106 CCD detectors, survey entire sky, repeatedly observe the brightest 1e9 objects down to 20th magnitude over 5 years. Science data: absolute astrometry: broad-band photometry, low-resolution spectro-photometry. Spectra: R=11500 for the brightest 1.5e8 sources, down to 17th magnitude. L2 point, thermo-mechanical stability. Parallaxes measured to 10 uas presision for stars <12mag, 25 ums for <15 mag, and 300uas for <20. Photometric errors in the milli-mag range. Spectro data measures radial velocities with errors of 15 km/s at mag=17. Primary science goal: unravel kinematical, dynamical, and chemical structure and evolution of the MW. Other science: stellar physics, SS bodies, fundamental physics, and exo-planets. Currently in production and qualification phase. Launch in 2013; final catalogue in 2021. DPAC responsible for processing of the data.
1201.3329
MASSIV: Mass assembly survey with SINFONI in VVDS - II. kinematics and close environment classification
Epinat, .. Le Fevre, ... et al
Probe kinematcis of 50 galaxies with 0.9<z<1.6 from MASSIV sample with 4.5e9 < M/Msun < 1.7e11 and 6 Msun/yr < SFR < 300 Msun/yr. Significant fraction of galaxies (30%) experienceing merging or with close companions that may be gravitationally linked; place lower limit on the fraction of interacting galaxies. Find >44% of galaxies display order rotation, wherease 35% are non-rotating objects [!!]. Most are rotation dominated (e.g., Vmax/sigma > 1) systems. Non-rotating objects are mainly small objects (Re<4kpc). Find local velocity dispersion of ionized gas component decreases continuously from z~3 to z=0. The proportion of disks also seems to be increasing in SF galaxies. Number of interacting galaxies seem to be at a maximum at z~1.2. These results draw a picture in which cold accretion may still be efficient at z~1.2, but in which mergers may play a much more significant role at z~1.2 than at higher redshift. From dynamical point of view, the redshift range 1<z<2 therefore appears as a transition period in the galaxy mass assembly process.
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