Day 376

Tuesday.

1302.5699
Vindicating single-T modified blackbody fits to Herschel SEDs (Research Note)
Bianchi

The bulk of dust mass in a galaxy can be equivalently estimated from i) the full SED of dust emission that includes a distribution of dust grains and a range of interstellar radiation field intensities, ii) the emission in the wavelength range 100um <= lambda <= 500um, by fitting to the data a simpler single temperature modified BB.  Also show that the dust mass does not depend significantly on the choice of beta, if both the dust mass and the absorption cross section are derived with the same assumption of beta.

1302.5717
Diffractive microlensing: a new probe of the local universe

If the wavelength of the observation is comparable to the Schwarzschild radius of lensing object, diffraction leaves an observable imprint on the lensing signature.  SKA may have sufficient sensitivity to detect the typical sources, giant stars in the bulge.  The diffractive signatures in a lensing event break the degeneracies between the mass of the lens, its distance and proper motion.

1302.6015
Baryon acoustic oscillations with the cross-correlation of spectroscopic and photometric samples
Nishizawa, Oguri, Takada

BAO requires sufficiently dense sampling of LSS tracers with spec-z, which becomes expensive at z>1.  Present alternative route: use cross-correlation of sparse spectroscopic tracers with a much denser photometric sample, where the spa tracers an be quasars or bright, rare galaxies that are easier to access spectroscopically.  Show that measurements of the cross-correlation as a function of the transverse comoving separation rather than the angular separation avoid a smearing of the BAO feature without mixing the different scales at different redshifts in the projection (even for wide z slice of delta z~1).  The bias, scatter, and catastrophic redshift errors of the photometric sample affect only the overall normalization of the X-correlation which can be marginalized over when constraining the angular diameter distance.  As a specific example, forecast expected accuracy of BAO geometrical test via x-correlation of SDSS and BOSS (quasar spec) sample with a dense photometric galaxy sample that is assumed to have a full overlap with the SDSS/BOSS survey region. Show that this x-correlation BAO analysis allows measurement of angular diameter distances to a fraction accuracy of ~10% at each z bin over 1<z<3, if the photoz errors of the galaxies are better than 10-20%.

1302.6211
The connection between star formation and metallicity evolution in barred spiral galaxies
Martel, Kawata, Ellison

Chemodynamical sims of barred disc galaxies, to determine the physical processes responsible for the increase in the central gas-phase metallicity and the central SFR observed in SDSS [for the barred galaxies, I presume].  SDSS fiber size determines the integrated area for spectra (2kpc diameter); chemical evolution depends critically upon the relative size of the bar and the aperture, which evolves strongly with time.  At t~0.5 Gyr, the bar is longer than 2kpc aperture.  Stars and gas lose angular momentum and follow elongated orbits that cause intense mixing of gas between the central region and its surroundings.  In the next 1.5 Gyr, the orbits of the gas contract significantly until the entire gas bar is contained in the 2kpc aperture, resulting in a net flux of gas into the central region; in the meanwhile, the metallicity in the central region increases steadily, enrichment dominated by metal-rich gas that is flowing into the central region.  Main result: the observed enrichment in the centers of barred galaxies is not dominated by in-situ enrichment by stars formed in the centre.  Rather, SF occurs along the full length of the bar, much of which occurs initially outside the 2kpc aperture; about 50% of the metals that end up in the central region originate form this extended bar-long SF, but flow into the central region due to loss of angular momentum.  Conclude: there is no direct connection between central SFR and central metallicity.  The global SFR (along the bar) and the large-scale flow of enriched gas play a major roe in the central metallicity.