Day 618

Monday.

1403.7203
The zCOSMOS redshift survey: evolution of the light in bulges and discs since z~0.8
Tasca, .. Le Fevre, Ilbert, Lilly, Koekemoer, … et al

Study the chronology of galactic bulge and disc formation by analyzing the relative contributions of these components to the B-band rest-frame luminosity density at different epochs.  Present the first estimate of the evolution of the fraction of rest-frame B-band light in galactic bulges and discs since z~0.8.  Perform a bulge-to-disc decomposition of HST/ACS images of 3266 galaxies in the zCOSMOS-bright survey with spectra z with the range 0.7<z<0.9.  Find that the fraction of B-band light in bulges is 26pm4 and 74pm4, respectively.  When compared with rest-frame B-band measurements of galaxies in the local Universe in the same mass range 1e9 Msun<M<1e11.5 Msun, find that the B-band light in discs decreases by ~30% from z~0.7-0.9 to z~0, while the light from the bulge increases by ~30% over the same period of time.  Interpret this evolution as the consequence of SF and mass assembly processes, as well as morphological transformation, which gradually shift stars formed at half the age of the Universe from SF late-type/irregular galaxies to earlier times and ultimately into spheroids.

1403.7205
Touching the void: a striking drop in stellar halo density beyond 50 kpc
Deason, Belokurov, Koposov, Rockosi

Use A-type stars selected from SDSS DR9 to measure the outer slope of the MW stellar halo density profile beyond 50 kpc.  A likelihood-based analysis is employed that models the ugr photometry distribution of blue horizontal branch (BHB) and blue straggler (BS) stars.  In the magnitude range, 18.5<g<20.5, these stellar populations span a heliocentric distance range of: 10 kpc< D_BS<75 kpc, 40 kpc < D_BHB < 100 kpc.  Contributions from contaminations, such as QSOs, and the effect of photometric uncertainties, are also included in the modeling procedure.  Find evidence for a very steep outer halo profile, with power-law index alpha ~ 6 beyond Galactocentric radii r=50 kpc, and even steeper slopes favored (alpha~6-10) at larger radii.  This result holds true when stars belonging to known over densities, such as the Sagittarius stream, are included or excluded.  Show that, by comparison to numerical simulations, stellar haloes with shallower slopes at large distances tend to have more recent accretion activity.  Thus, it is likely that the MW has undergone a relatively quiets accretion history over the past several Gyr.  Measurement of the outer stellar halo profile may have important implications for dynamical mass models of the MW, where the tracer density profile is strongly degenerate with total mass-estimates. 

1403.7235
What the "simple renormalization group" approach to dark matter clustering really was
McDonald

The past approach (McDonald 2007) to improving PT calculations of the DM PS, with a derivation based on the idea of renormalization group flow with time.  In spite of a questionable approximation made in deriving it, subsequent comparisons by several groups between the predictions of the resulting equation and the N-body simulations showed remarkable improvement relative the standard PT (SPT) at similar order.  In this note, show that the same final equation can be derived cleanly from the point of view not of flowing with time but with NL coupling strength, i.e., gradually dialing the coupling from the trivial value zero to the physical one.  This understanding makes it clear how to extend the approach to higher order and other statistics. While this is not necessarily the best approach among many, it may be interesting in that it contains a unique way of suppressing UV sensitivity.  In passing, remind the reader of references demonstrating that SPT works remarkably well without improvement (except near z=0, where, fortunately for SPT, there is very little volume in the Universe).

1403.7303
Did gamma ray burst induce Cambrian explosion?
Chen, Ruffini

Cambrian explosion of bio-diversity happened around 540 million years ago (Mya).  Suggest that a nearby GRB event ~500 parsecs away, which should occur about once per 5 Gy, might have triggered it.  Due to a relatively lower cross section and the conservation of photon number in Compton scattering, a substantial fraction of the GRB photons can reach the sea level and would induce DNA mutations in organisms protected by a shallow layer of water or soil, thus expediting the bio-diversification.  This possibility of inducing genetic mutations is unique among all candidate sources for major incidents in the history of bio-diversification.  A possible evidence would be the anomalous abundance of certain nuclear isotopes with long half-lives transmuted by the GRB photons in geological records from the Cambrian period.  Notation also imposes constraints on the evolution of exoplanet organisms and the migration of panspermia.

1403.7309
A new method for PSF correction using the ellipticity of re-smeared artificial images in weak gravitational lensing shear analysis
Okura, Futamase

Propose a new method for PSF correction in WL analysis using an artificial image wit the same ellipticity as the lensed image.  This avoids the systematic error associated with the approximation in PSF correction used in previous approaches.  Test the new method with simulated objects which have Gaussian or Sersic profiles smeared by Gaussian PSF, and confirm that there is no systematic error.

1403.7463
The wavelength dependence of high-redshift galaxy structure in the rest-frame ultraviolet
Bond, … Coe, Grogin, Gawiser, … et al

Present the rest-frame UV wavelength dependence of the Petrosian-like HLR (r_50) and the concentration parameter for a sample of 198 SF galaxies at 0.5<z<1.5.  Find a ~5% decrease in HLR from 1500A to 3000A, with HLR at 3000A ranging from 0.6 kpc to 6 kpc.  Also find a decrease in concentration of ~0.07 (1.9<C_3000<3.9).  The lack of strong relationship between HLR and wavelength is consistent with a model in which clumpy SF is distributed over length scales comparable to the galaxy's rest-frame optical light.  While the wavelength dependence of HLR is independent of size at all redshifts, concentration decreases more sharply in the FUV (~1500A) for large galaxies at z~1.  This decrease in concentration is caused by a flattening of the inner ~20% of the light profile in disk-like galaxies, indicating that the central regions have different UV colors than the rest of the galaxy.  Interpret this as a bulge component with older stellar populations and/or more dust.  The size-dependent decrease in concentration is less dramatic at z~2, suggesting that bulges are less dusty, younger, and/or less massive than the rest of the galaxy at higher redshifts.

1403.7520
The Gemini planet imager: first light
Macintosh, Graham, … et al

Combines a high-order AO system, a diffraction-suppressing coronagraph, and an integral field spectrograph with low spectral resolution but high spatial resolution; tuned for maximum sensitivity to faint planets near bright stars.  During first light observations, achieved an estimated H band Strehl ratio of 0.89 and 5-sigma contrast of 1e6 at 0.75 arc seconds and 1e5 at 0.35 arc seconds.  Observation of Beta Pictrois clearly detect the planet in a single 60-second exposure with minimal post-processing.  Beta Pictoris b is observed at a separation of 434pm6 milli-arcseconds and position angle 211.8 deg.  Fitting the Keplerian orbit of Beta Pic b using the new position together with previous astrometry gives a factor of 3 improvement in most parameters over previous solutions.  The planet orbits at a semi-major axis of 9AU near the 3:2 resonance with the previously-known 6 AU asteroidal belt and is aligned with the inner warped disk.  The observations give a 4% posterior probability of a transit of the planet in late 2017.