Day 484

1308.1353
GLIMPSE: accurate 3d weak lensing reconstructions using sparsity
Leonard, Lanusse, Starck

Present GLIMPSE (Gravitational Lensing Inversionand MaPping with Sparse Estimators), a new algorithm to generate density reconstructions in 3d from photometric WL measurements. This is an extension of earlier work in 1d aimed at applying compressive sensing theory to the inversion of gravitational lensing measurements to recover 3d density maps.  Using the assumption that the density can be represented sparsely in the chosen bases - 2d transverse wavelets and 1d LoS Dirac functions - show that clusters of galaxies can be identified and accurately localized and characterized using this method.  Throughout, use simulated data consistent with the quality currently attainable in large surveys.  Present a thorough statistical analysis of the errors and biases in both the redshifts of detected structures and their amplitudes.  The GLIMPSE method is able to produce reconstructions at significantly higher resolution than the input data; in this paper, show reconstructions with 6x finer redshift resolution than the shear data [how is this possible? matched filters?].  Considering cluster simulations with 0.05<=z<=0.75 and 3e13 Msun/h <= Mvir <= 1e15 Msun/h, show that the redshift extent of detected peaks is typically 1-2 pixels, or Dz<~0.07, and that an unbiased estimator of the redshift of a detected cluster by considering many realizations of the noise can be recovered.  Also recover an accurate estimator of the mass, that is largely unbiased when the redshift is known, and whose bias is constrained to <~5% in the majority of simulations when the estimated redshift is taken to be the true redshift.  This shows a substantial improvement over earlier 3d inversion methods, which showed redshift smearing with a typical standard deviation of 0.2-0.3, a significant damping of the amplitude of the peaks detected, and a bias in the detected redshift.

1308.1380
Spectral synthesis of star-forming galaxies in the near-infrared
Martins et al

The NIR spectral regions is becoming a very useful wavelength range to detect and quantify the stellar population of galaxies [in the galaxy's rest frame, I suppose].  Models are developing to predict the contribution of TP-ABG stars, that should dominate the NIR spectra of populations 0.3 to 2 Gyr old.  When present in a given stellar population, these stars leave unique signatures that can be used to detect them unambiguously.  However, these models have to be tested in a homogeneous database of SF galaxies, to check if the results are consistent with what is found from different wavelength ranges.  In this work, perform SPS on nuclear and extended regions of 23 SF galaxies to understand how the SF tracers in the NIR can be used in practice.  SPS shows that for the galaxies with strong emission in the NIR, there is an important fraction of young/intermediate population contributing to the spectra, which is probably the ionization source in these galaxies.  Galaxies that had no emission lines measured in the NIR were found to have older average ages and less contribution of young populations.  Although the SPS method proved to be effective to find the young ionizing population in these galaxies, no clear correlation between these results and the NIR spectral indexes were found.  Thus, in practice, the use of these indices is still very limited due to observational limitations.

1308.1399
The properties of warm dark matter haloes
Lovell, Frenk, Eke, Jenkins, Gao, Theuns

DM particle candidates, such as the sterile neutrino, behave as warm dark matter (WDM).  For particle masses of order a keV, free streaming produces a cutoff in the linear fluctuation PS at a scale corresponding to dwarf galaxies.  Investigate the abundance and structure of WDM haloes and subhaloes on these scales using high resolution cosmo N-body sims of galactic haloes of mass similar to the MW's.  On scales larger than the free-streaming cutoff, the initial conditions have the same PS and phases as one of the DCM haloes previously simulate by Springel et al as part of the Virgo consortium Aquarius project.  Simulated 4 haloes with WDM particle masses in the range 1.4-2.3 keV and, for one case, carried out further simulations at varying resolution.  N-body simulations in which the PS cutoff is resolved are known to undergo artificial fragmentation in filaments producing spurious clumps which, for small masses <1e7Msun here) outnumber genuine haloes.  Have developed a robust algorithm to identify these spurious objects and remove them from halo catalogues.  Find that the WDM subhalo MF is suppressed by well over an order magnitude relative to the CDM case for masses <1e9 Msun.  Requiring that there should be at least as many subhaloes as there are observed satellites in the MW leads to a conservative lower limit to the (thermal equivalent) WDM particle mass of ~1.5 keV.  WDM haloes and subhaloes have very cuspy density distributions that are well described by NFW or Einasto profiles.  Their central densities are lower for lower WDM particle masses and none of the models we have considered suffer from the "too big to fail" problem recently highlighted by Boylan-Kolchin et al.

1308.1401
Signatures of first stars in galaxy surveys: multi-tracer analysis of the supersonic relative velocity effect and the constraints from the BOSS power spectrum measurements
Yoo, Seljak

Study the effect of the supersonic relative velocity between DM and baryons on large-scale galaxy clustering and derive the constraint on the relative velocity bias parameter from the BOSS PS measurements.  Recent work has shown that the relative velocity effect may have a dramatic impact on the SF at high z, if first stars are formed in minihalos around z~20, or if the effect propagates through secondary effects to stars formed at later redshifts.  The relative velocity effect has particularly strong signatures in the large scale clustering of these sources, including the BAO position.  Assuming that a small fraction of stars n low-redshift massive galaxies retain the memory of the primordial relative velocity effect, galaxy clustering measurements can be used to constrain the signatures of the first stars.  Luminous red galaxies contain some of the oldest stars in the Universe and are ideally suited to search for this effect.  Using the BOSS PS measurements from SDSS DR9, in combination with Planck, derive the upper limit on the fraction of the stars sensitive to relative velocity effect f_star<3.3% at the 95% CL in the CMASS galaxy sample.  If additional galaxy sample not sensitive to the effect is available in a given survey, a joint multi-tracer analysis can be applied to construct a sample-variance cancelling combination, providing a model-independent way to verify the presence of the relative velocity effect in the galaxy PS on large scales.  Such a multi-tracer analysis in future galaxy surveys can greatly improve the current constraint, achieving a 0.1% level in f_star.

1308.1404
Cosmic bandits: exploration versus exploitation in CMB B-mode experiments
Kovetz, Kamionkowski

To detect the B-mode in CMB, a signature of inflationary gravitational waves (IGWs), in the absence of FGs and lensing, is a prolonged integration over a single patch of sky over a few square degrees.  In practice, FGs abound, and the sensitivity to B-modes can be improved considerably by finding the region of sky cleanest of FGs.  The best strategy to detect B-modes thus involves a tradeoff between exploration (to find lower-FG patches) and exploitation (through prolonged integration).  This problem is akin to the multi-armed bandit (MAB) problem in probability theory, wherein a bandit faced a series of slot machines with unknown winning odds and must develop a strategy to maximize his/her winnings with some finite number of pulls.  While the optimal MAB strategy remains to be determined, a number of algorithms have been developed in an effort to maximize the winnings.  Formulate the search for IGW B modes in the presence of spatially-varying FGs as an MAB problem and develop adaptive survey strategies to optimize the sensitivity to IGW B modes.  Demonstrate, using realistic FG models and taking lensing-induced B modes into account, that adaptive experiments can substantially improve the upper bound on the tensor-to-scalar ratio (by 2-3x in single frequency experiments, and possibly even more).  Similar techniques can be applied to other surveys, including 21-cm measurements of signatures of the epoch of reionization, searches for a stochastic primordial gravitational wave background, deep-field imaging by the James Webb Space Telescope or various radio interferometers, and transient follow-up searches.