Day 392

Thursday.  Planck Day.

1303.4739
A way forward for Cosmic Shear: Monte-Carlo control loops
Refregier, Amara

Cosmic shear: may shed new light on DM, DE and modified gravity.  Potential great, but results from this technique have been hampered because the measurement of this weak effect is difficult and limited by systematics effects.  In particular, a demanding step is the measurement of the WL shear from wide field CCD images of galaxies.  Describe the origin of the problem [what are they?] and propose a way forward for cosmic shear.  Proposed approach is based on MC control loops and draws upon methods widely used in particle physics and engineering.  Describe the control loop scheme and show how it provides a calibration method based on fast image simulations tuned to reproduce the statistical properties of a specific cosmic shear dataset.  Through a series of iterative loops and diagnostic tests, the MC image simulations are made robust to perturbations on modeling input parameters and thus to systematic effects.  Discuss how this approach can make the problem tractable and unleash to full potential of cosmic shear for cosmology.  [It's a flow chart.]

1303.4809
Reconciling the GRB rate and star formation histories
Jiminez, Piran

Many indications that GRBs arise from the death of massive stars, the GRB rate does not follow the global cosmic SFR and, within their hosts, GRBs are more concentrated in regions of very high SF.  Give explanation.  Use VESPA database of SDSS DR7 spectra; explore a multi-parameter space in galaxy properties, like stellar mass, metallicity, dust etc. to find the sub-set of galaxies that reproduce the recently obtained GRB rate.  Find: only galaxies with present stellar masses <1e10 Msun and low metallicity reproduce the observed GRB rate; consistent with direct observations of GRB hosts and provides and independent confirmation of the nature of GRB hosts.  Compute correlation function and show that they are anti-biased with respect to the DM:  They are in filaments and voids.  Using recent observations of massive stars in local dwarfs, show how the fact that GRB hosts galaxies are dwarfs can explain the observation that GRBs are more concentrated in regions of high SFR than SNe.  Explain these results using new theoretical advances in the field of star formation.

1303.4919
Relaxation in N-body simulations of disk galaxies
Sellwood

Show, with N-body sims with two mass species of particles, subject to collisional relaxation at a higher rate than is widely assumed.  Relaxation affects the vertical thickness of the disk most strongly, and drives the velocity ellipsoid to a moderately flattened shape similar to that observed for disk stars in the solar neighborhood.  The velocity ellipsoid in simulations with small numbers of particles quickly approaches this shape, but shot noise also dominates the in-plane behavior.  Simulations with higher, but reachable, numbers of particles relax slowly enough to be considered collisionless, allowing the in-plane dispersions to rise due to spiral activity without heating the vertical motions.

1303.4963
Age and metallicity gradients in fossil ellipticals
Eigenthaler, Zeilinger

Fossil galaxy groups are speculated to be old and highly evolved systems of galaxies that formed early in the universe and had enough time to deplete their L* galaxies through successive mergers of member galaxies, building up one massive central elliptical, but retaining the group X-ray halo.  Considering that fossils are the remnants of mergers in ordinary groups, the merger history of the progenitor group is expected to be imprinted in the fossil central galaxy (FCG).  Present for the first time radial gradients of single-stellar population (SSP) ages and metallicities in shape of FCGs to constrain their formation scenario.  This sample comprises some of the most massive galaxies in the universe exhibiting an average central velocity dispersion of sigma=271 pm 28 km/s.  Metallicity gradients are throughout negative with comparatively flat slopes, while age gradients are found to be insignificant.  All FCGs lie on the fundamental plane, suggesting that they are virialised systems.  Find that gradient strengths and central metallicities are similar to those found in cluster ellipticals of similar mass.  The comparatively flat metallicity gradients wrt those predicted by monolithic collapse suggest that fossils are indeed the result of multiple major mergers.  Hence conclude that fossils are not 'failed groups' that formed with a top heavy LF.  The low scatter of gradient slopes suggest a similar merging history for all galaxies in the sample.

1303.4995
The exciting lives of giant molecular clouds
Dobbs, Pringle

Evolution of GMCs in galactic disk simulation.  Follow individual GMCs, including SF, from their formation to dispersal.  Evolution of GMCs is highly complex.  GMCs often form from a combination of smaller clouds and ambient ISM, and similarly disperse by splitting into a number of smaller clouds and ambient ISM.  However some clouds emerge as the result of the disruption of a more massive GMC, rather from the assembly of smaller clouds.  Likewise in some cases, clouds accrete onto more massive clouds rather than disperse.  Because of the difficulty of determining a precursor or successor of a giving GMC, determining GMC histories and lifetimes is highly non-trivial.  Using a definition relating to the continuous evolution of a cloud, obtain lifetimes typically of 4-25 Myr for 1e5 Msun GMCs, over which time the SF efficiency is about 1%.  Also relate the lifetime of GMCs to their crossing time.  Find that the crossing time is a reasonable measure of the actual lifetime of the cloud, although there is considerable scatter.  The scatter is found to be unavoidable because of the complex and varied shapes and dynamics of the clouds.  Study cloud dispersal in detail and find both stellar feedback and shear contribute to cloud dispersion.  Also demonstrate that GMCs do not behave as ridge clouds, rather massive spiral arm GMCs evolve into smaller clouds in inter-arm spurs.

1303.5048
A CMB lensing mass map and its correlation with the cosmic infrared background
Holder, Viero, Zahn, ... Carlstrom, ... et al

Use a temperature map of the CMB obtained using SPT at 150 GHz to construct a map of gravitational convergence to z~1100, revealing the fluctuations in the projected mass density.  This map shows individual features that are significant at the 4 sigma level, providing the first image of CMB lensing convergence.  Cross-correlate this map with Herschel/SPIRE maps covering 90 square degrees at wavelengths of 500, 350, and 250 microns.  Show that these submm maps are strongly correlated with the lensing convergence map, with detection significances in each of the 3 submm bands ranging from 6.7 to 8.8 sigma.  Fit the measurement of the cross power spectrum assuming a simple constant bias model and infer bias factors of b=1.3-1.8, with a statistical uncertainty of 15%, depending on the assumed model for the redshift distribution of the dusty galaxies that are contributing to the Herschel/SPIRE maps.


1303.5051
No preferred Axies in WMAP Cosmic microwave background data after subtraction of the Integrated Sachs-Wolfe effect
Rassat, Starck

As the title says.  Investigate impact of method used to account for masked regions, as well as the impact of the ISW effect.  Aim: to identify trends in CMB data from different years and with different masks treatment, including WMAP9.  Use the reconstructed ISW field from 2MASS and NVSS, effectively reconstructing the low-z ISW signal out to z~1.  Regions of missing data are accounted for using the sparse inpainting technique, which does not assume the underlying field is either Gaussian or isotropic, but allows for it to be.  Focus on 2 large-scale anomalies, the Axis of Evil statistic and even/odd mirror parity, both of which search for preferred axes in the Universe.  After sparse inpainting and subtraction of the ISW field, find that there is no longer any AoE or mirror parity anomaly in any of the WMAP renditions.  The low quadrupole, quadrupole/octupole alignment and octupole planarity anomalies also disappear after subtraction of the ISW effect, showing that there seems to be no reason to believe that there exists any statistical anomalies in the CMB after all.