Day 700

Wednesday.

1407.1906
Building unbiased estimators from non-Gaussian likelihoods with application to shear estimation
Madhavacheril, McDonald, Sehgal, Slosar

Develop a general framework for generating estimators of a given quantity which are unbiased to a given order in the difference between the true value of the underlying quantity and the fiducial position in theory space around which the likelihood is expanded.  Apply this formalism to reserve the optimal quadratic estimator and show how the replacement of the second derivative matrix with the Fisher matrix is generic way of creating an unbiased estimator (if one does not modify the initial guess at the weight matrix C^{-1} iteratively based estimates from the data, which generally creates a bias).  Next, apply the approach to estimation of shear lensing, closely following the work of B+A (2014).  The first order estimator reduces to their estimator in the limit of zero shear, but it also naturally allows for the case of non-constant shear and the easy calculation of correlation functions of power spectra using standard methods.  Both the first order estimator and B+A's estimator exhibit a bias which is quadratic in true shear.  The third-order estimator is, at least in the realism of the toy problem of B+A, unbiased to 0.1% in relative shear errors (Delta g)/g for shears up to |g|=0.2.

1407.2584
The Primordial Inflation Polarization Explorer (PIPER)
Lazear, ... Bennett, ... et al

PIPER is a balloon-borne CMB polarimeter designed to search for evidence of inflation by measuring the large-angluar scale CMB polarization signal.  BICEP2 recently reported a detection of B-mode plower corresponding to the tensor-t-scalar ratio r=0.2 on ~2 degree scales.  If the BICEP2 signal is caused by inflationary gravitational waves (IGWs), then there should be a corresponding increase in B-mode power on angular scales larger than 18 degrees.  PIPER is currently the only suborbital instrument capable of fulling testing and extending the BICEP2 results by measuring the B-mode PS on angular calls theta=~0.6deg to 90 deg, covering both the deionization bump and recombination peak, with sensitivity to measure the tensor-to-scalar ratio down to r=0.007, and four frequency bands to distinguish foregrounds.  PIPER will accomplish this by mapping 85% of the sky in 4 frequency bands over a series of 8 conventional balloon flights from the northern and southern hemispheres.  The instrument has background-limited sensitivity provided by fully cryogenic (1.5K) optics focusing the sky signal onto four 32x40 pixel arrays of time-domain multiplexed Transition-Edge Sensor (TES) bolometers belt ad 140 mK.  Polarization sensitivity and systematic control are provided by front-end Variable-delay Polarization Modulators (VPMs), which rapidly modulate only the polarized sky signal at 3 Hz and allow PIPER to instantaneously measure the full Stokes vector (I,Q,U,V) for each pointing.  Describe the PIPER instrument and progress towards its first flight.

1407.2600
Dark Sky Simulations: Early data release
Skillmann, ... Wechsler, Holz, ... et al

The Dark Sky Simulations are an ongoing series of cosmological N-body simulations designed to provide a quantitative and accessible model of the evolution of the large-scale universe.  Such models are essential, since we lack a sufficiently accurate analytic model of NL gravitational clustering.  Made public the simulation of 1e12 (10240^3) particles in (8Gpc/h)^3, performed with 2HOT (purely tree-based adaptive N-body method), running on 200k processors, with data analysis by yt [?].  Provide an overview of the derived halo catalogs, mass function, PS and light cone data.  Show self-consistency in the mass function and mass PS at the 1% level over a range of more than 1000 in particle mass.  Present a novel method to distribute and access very large datasets, based on an abstraction of the WWW as a file system, remote memory-mapped file access semantics, and a space-filling curve index.  This method has been implemented for the data release, and provides a means to not only query stored results such as halo catalogs, but also to design and deploy new analysis techniques on large distributed datasets.

1407.2906
Pre-flight integration and characterization of the SPIDER balloon-borne telescope
Rahlin, et al

Present the results of integration and characterization of the SPIDER instrument after the 2013 pre-flight campaign.  SPIDER is a balloon-borne polarimeter designed to probe the primordial gravitational wave signal in the degree-scale B-mode polarization of the CMB.  With six independent telescopes housing over 2000 detectors in the 94 GHz and 150 GHz frequency bands, SPIDER will map 7.5% of the sky with a depth of 11 to 14 muK*arcmin at each frequency, which is a factor of ~5 improvement over Planck.  Discuss the integration of the pointing, cryogenic, electronics, and power subsystems, as well as pre-flight characterization of the detectors and optical systems.  SPIDER is well prepared for a December 2014 flight from Antarctica, and is expected to be limited by astrophysical FG emission, and not instrumental sensitivity, over the survey region.

1407.3787
A 52 hours VLT/FORS2 spectrum of a bright z~7 HUDF galaxy: no Ly-alpha emission
Vanzella et al

52hr integration over the past 5 years of the z~7 candidate in HUDF show no emission line or continuum over the whole wavelength range, up to 10100A.  Combine upper limits with SED modeling to refine redshift estimate to z=6.82pm0.1 (1 sigma); SED modeling also indicates dust-corrected SFR of ~20 Msun/yr.  A plausible interpretation is that it is moderately evolved and contains sufficient gas and dust to attenuate the Lya emission, before it reaches the IGM.  The redshift confirmation or even the best z~7 candidates is very hard to achieve (unless the Lya or unusually strong rest-UV nebular emission lines are present) with the current generation of 8-10m class telescopes.  Show that both JWST and E-ELT will be necessary to make decisive progresses.  Currently, the increased redshift accuracy obtained with this kind of analysis makes ALMA an interesting option for the redshift confirmation.

1407.3795
Globular clusters and dark satellite galaxies through the stream velocity
Naoz, Narayan

The formation of purely baryonic globular clusters with no gravitationally bound DM is still a theoretical challenge.  Show that these objects might form naturally whenever there is a relative stream velocity between baryons and DM.  The stream velocity causes a phase shift between linear modes of baryonic and DM perturbations, which translates to a spatial offset between the two components when the collapse.  For a 2 (3) sigma density fluctuations, baryonic clumps with masses in the range 1e5 to 2.5e6 Msun (1e5 to 4e6 Msun) collapse outside the virial radii of their counterpart DM haloes.  These objects could survive as long-lived DM-free objects and might conceivably become globular clusters.  In addition, their DM counterparts, which were deprived of gas, might become dark satellite galaxies.

1407.3955
Dark matter fraction in lens galaxies: new estimates from microlensing
Jiménez-Vicente, Mediavilla, Kochanik, Muñoz

A joint estimate of the stellar/DM mass fraction in lens galaxies and the average size of the accretion disk of lensed quasars from microlensing measurements of 27 quasar image pairs seen though 19 lens galaxies.  The maximum likelihood estimate for the fraction of the surface mass density in the form of stars is alpha=0.2pm0.1 near the Einstein radius of the lenses (~1-2 effective radii).  The estimate for the average accretion disk size is r_s=6.0 sqrt(M/0.3Msun) light-days.  The fraction of mass in stars at these radii is significantly larger than previous estimates from microlensing studies assuming quasars were point-like.  The corresponding local DM fraction of 80 is in good agreement with other estimates based on strong lensing or kinematics.  The size of the accretion disk inferred in the present study is slightly larger than previous estimates.

1407.4025
Joint astrometric solution of Hipparcos and Gaia: a recipe for the Hundred Thousand Proper Motions project
Michalik, Lindegren, Hobbs, Lammers

First Gaia data expected in 2016; 100k stars in common with Hipparcos.  24 yr difference between the two will allow accurate proper motions.  Predict proper motion accuracies between 14 and 145 muas/yr, depending on stellar magnitude and amount of Gaia available.  Improvement of proper motion expected with later and more accurate Gaia data.