Day 516

Thursday already.

1309.6274
Linear eclipse observations reveal anomalous thermal performance of Apollo reflectors
Murphy, McMillan, Johnson, Goodrow

Laser ranging measurements during the total lunar eclipse on 2010 Dec. 21 verify previously suspected thermal lensing [?] in the retroreflectors left on the lunar surface by the Apollo astronauts.  Signal levels during the eclipse far exceeded those historically seen at full moon [doesn't make sense?], and varied over an order of magnitude as the eclipse progressed.  These variations can be understood via a straightforward thermal scenario involving solar absorption by a ~50% covering of dust that has accumulated on the front surfaces of the reflectors.  The same mechanism can explain the long-term degradation of signal from the reflectors as well as the acute signal deficit observed near full moon.

1309.6314
Substructure in bulk velocities of Milky Way disk stars
Carlin et al

Find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the mid-plane as well as azimuthally.  These findings are based on LAMOST spectroscopic velocities for a sample of ~400k F-type stars, combined with proper motions from the PPMXL catalog for which corrections to the zero points [of what?  photometry?  astrometry?] based in part on spectroscopically discovered galaxies and QSOs from LAMOST have been derived.  In the region within 2kpc outside the Sun's radius and +/- 2kpc from the Galactic midplane, show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior.  Discuss this in the context of other recent findings, and conclude that likely seeing the signature of vertical disturbances to the disk due to an external perturbation.  

1309.6316
A spectroscopic sample of massive, evolved z~2 galaxies: implications for the evolution of the mass-size relation
Krogager et al

Deep NIR HST/WFC3 spectroscopy and imaging of 16 galaxies at z~2 in COSMOS, selected for the presence of 4000A break.  This sample significantly increases the number of spectroscopically confirmed evolved galaxies at this redshift with accurate structural measurements, and is the first representative sample of spectroscopically confirmed galaxies  at z~2.  By combining the grism observations with photometry in 30 bands, derive accurate constraints on their redshifts, stellar masses, ages, dust extinction and formation redshifts.  Fit the rest-frame optical [what band in rest frame?] surface brightness profiles, and show that these are well described by compact, high-n Sersic models.  Show that the slope and scatter of the z~2 mass-size relation of quiescent galaxies is consistent with the local relation, and confirm previous findings that the sizes for a given mass are smaller by a factor of 2 to 3.  Show that the observed evolution of the mass-size relation of quiescent galaxies between z=2 and 0 can be explained by quenching of increasingly larger SF galaxies, at a rate dictated by the increase in the number density of quiescent galaxies with decreasing redshift.  However, find that the scatter in the mass-size relation should increase in the quenching-driven scenario in contrast to what is seen in the data.  This suggests that merging is not needed to explain the evolution of the mean mass-size relation of massive galaxies, but may still be required to tighten its scatter, and explain the size growth of individual z=2 galaxies quiescent galaxies.  

1309.6317
The COS-Halos survey: rationale, design, and a census of circumgalactic neutral Hydrogen
Tumlinson et al

Design and methods of the COS-Haloes survey, a systematic investigation of the gaseous haloes of 44 0.15<z<0.35 galaxies using BG QSOs observed with HST/COS.  Survey yielded 39 spectra of z_em~0.5 QSOs with S/N~10-15 per resolution element.  The QSO sightlines pass within 150 physical kpc of the galaxies, which span early and late types over stellar mass log M*/Msun=9.5-11.5.  Find that the CGM exhibits strong HI, averaging 1 Ang in Lya EW out to 150 kpc, with 100% covering fraction for SF galaxies and 75% for passive.  Find good agreement in column densities between this survey and previous studies over similar range of impact parameter.  There is weak evidence for a difference between early- and late-type galaxies in the strength and distribution of HI.  Kinematics indicate that the detected material is bound to the host galaxy, such that >~90% of the detected column density is confined within pm 200 km/s of the galaxies.  This material generally exists well below the halo virial temperatures at T<~1e5 K.  Evaluate the number of possible origin scenarios for the detected material, and in the end favor a simple model in which the bulk of the detected HI arises in a bound, cool, low-density photoionized diffuse medium that is generic to all L* galaxies and may harbor a total gaseous mass comparable to galactic stellar masses.


1309.6321
Do we expect most AGN to live in disks?
Hopkins, Kocevski, Bundy

Observation indicate: a large fraction of the low to intermediate luminosity AGN population lives in disk-dominated hosts, while the more luminous quasars live in bulge-dominated hosts, in conflict with some previous model predictions.  Build and compare a semi-empirical model for AGN fueling which accounts for both merger and non-merger 'triggering.'  Show that the 'stochastic accretion' model - in which fueling in disk galaxies is essentially a random process arising whenever dense gas clouds reach the nucleus - provides a good match to the present observations at low/intermediate luminosities.  However, it falls short of the high-luminosity population.  Combine this with models for major merger-induced AGN fueling, which lead to rarer but more luminous events, and predict the resulting abundance of disk-dominated and bulge-dominated AGN host galaxies as a function of luminosity and redshift.  Compile and compare observational constraints from z~0-2.  The models and observations generically show a transition from disk to bulge dominance in hosts near the Seyfert-quasar transition, at all redshifts.  'Stochastic' fueling dominates AGN by number (dominant at low luminosity), and dominates BH growth below the knee in the present-day BH mass function (<1e7 Msun).  However it accounts for just ~10% of BH mass growth at >1e8 Msun.  In total, fueling in disky hosts accounts for ~30% of the total AGN luminosity density/BH mass density.  The combined model also accurately predicts the AGN luminosity function and clustering/bias as a function of luminosity and redshift; however, argue that these are not sensitive probes of BH fueling mechanisms.
1309.6322
A precision multi-band two-epoch photometric catalog of 44 million sources in the Northern sky from combination of the USNO-B and Sloan digital sky survey catalogs
Madsen, Gaensler

Present a new precision, multi-epoch photometric catalog that spans 60 years by combining the USNO-B and SDSS DR9 catalogs.  Recalibrate the photometry of the original USNO-B catalog and create a catalog with two epochs of photometry in up to 5 different bands for 43 million optical point sources that lie in the DR9 footprint of the northern sky.  The recalibrated objects span a magnitude range 14<m<20 and are accurate to ~0.1 mag.  Minimize the presence of spurious objects and those with inaccurate magnitudes by identifying and removing several sources of systematic errors in the two originating catalogs, with a focus on spurious objects that exhibit large apparent magnitude variations.  After accounting for these effects, find ~250k stars and quasars that show significant (>4 sigma) changes in brightness between the USNO-B and SDSS DR9 epochs.  Discuss the historical value of the catalog and its application to the study of long time-scale, large amplitude variable stars and quasars.

1309.6341
To stack or not to stack: spectral energy distribution properties of Lya-emitting galaxies at z=2.1
Vargas, Bish, Acquaviva, Gawiser, ... Koekemoer, Newman, et al

Build several stacked SEDs of 20 LAE galaxies at z=2.1.  Combine photometry to form average and median flux-stacked SEDs and postage stamp images to form average and median image-stacked SEDs.  Also introduce scaled flux stacks that eliminate the influence of variation in overall brightness.  Use SED fitting code SpeedyMC to constrain the physical properties of individual objects and stacks.  M* ranges from 2e7 to 8e9 Msun (median=3e8 Msun), ages ranging from 4 Myr to 500 Myr (median=100 Myr) and E(B-V) between 0.02 and 0.24 (median=0.12).  Do not observe strong correlations between Lya EW and stellar mass, age or E(B-V), implying that the Lya radiative transfer prevents Lya photons from resonantly scattering in dusty regions.  The SED parameters of the flux stacks match the average and median values of the individual objects, with the flux-scaled median SED performing best with reduced uncertainties.  Median image-stacked SEDs provide a poor representation of the median individual object, and none of the stacking methods captures the large dispersion of LAE properties.

1309.6435
Random time series in Astronomy
Vaughan

Time domain signals from: SNe, gamma-ray bursts, and other powerful explosions; see periodic phenomena (orbiting planets, pulsars, pulsations of stars) and aperiodic variations ('noise') from powerful systems like accreting BHs.  Review a few of the recent and future challenges in the burgeoning area of Time Domain Astrophysics, with particular attention to persistently variable sources, the recovery of reliable noise PS from sparsely sampled time series, higher-order properties of accreting BHs, and time delays and correlations in multivariate time series.

1309.6546
Is Voyager 1 inside an interstellar flux transfer event?
Schwadron, McComas

Plasma wave observations from Voyager 1 have recently shown large increases in plasma density, to about 0.1 /cm^3, consistent wit the density of the local interstellar medium.  However, corresponding magnetic field observations continue to show the spiral magnetic field direction observed throughout the inner helio-sheath.  These These apparently contradictory observations may be reconciled if Voyager 1 is inside an interstellar flux transfer event - similar to flux transfer events routinely seen at the Earth's magnetopause.  If this were the case, Voyager 1 remains inside the heliopause [no!!] and based on the Voyager 1 observations, can determine the polarity of the interstellar magnetic field for the first time.

1309.6624
Reconstructing primordial power spectrum using Planck and SDSS-III measurements
Wang, Zhao

Develop an accurate and efficient Bayesian method to reconstruct the primordial PS in a model-independent way, and apply to the latest cosmic microwave background measurement of Planck, and LSS observation of BOSS CMASS sample, combined with SNe (SNLS 3yr) and BAO measurements of SDSS-II, 6dF and WiggleZ.  Confirm that the scale-invariant primordial PS is strongly disfavored, and a model with suppressed power on horizon scales is supported by data.  Find that a modulation on scales 5e-4 <~k<~0.01/Mpc is mildly favored at 2 sigma level, whose origin needs further investigation.

1309.5388
Exploiting cross correlations and joint analyses
Rhodes et al

[Missed this Snowmass paper on Tuesday] Present a wide variety of ways in which information from multiple probes of DE may be combined to obtain additional information not accessible when they are considered separately.  Fundamentally, because all major probes are affected by the underlying distribution of matter in the regions studied, there exist covariances between them that can provide information on cosmology.  Combining multiple probes allows for more accurate (less contaminated by systematics) and more precise (since there is cosmological information encoded in cross-correlation statistics) measurements of DE.  The potential of cross-correlation methods is only beginning to be realized.  By bringing in information from other wavelengths, the capabilities of the existing probes of DE can be enhanced and systematic effects can be mitigated further.  Present a mixture of work in progress and suggestions for future scientific efforts.  Given the scope of future DE experiments, the greatest gains may only be realized with more coordination and cooperation between multiple project teams; recommend that this interchange should begin sooner, rather than later, to maximize scientific gains.