Day 470

Monday.

1307.5065
Semi-analytic galaxy formation in f(R)-gravity cosmologies
Fontanot, Puchwein, Springel, Bianchi

The f(R)-gravity models imply the existence of a 'fifth-force', which is however locally suppressed, preserving the successes of GR on solar system scales.  Employ high-res numerical sims of f(R)-gravity models coupled with SAM for galaxy formation to obtain detailed predictions for the evolution of galaxy properties.  Show that DM haloes in f(R)-gravity models are characterized by a modified virial scaling with respect to the LCDM scenario, reflecting a higher DM velocity dispersion at a given mass.  This effect is taken into account in the SAM by an appropriate modification of the mass-temperature relation.  Find that the statistical properties predicted for galaxies (such as the stellar mass function and the cosmic SFR) in f(R)-gravity show generally only very small differences relative to LCDM, smaller than the dispersion between the results of different SAM models, which can be viewed as a measure of their systematic uncertainty.  Also demonstrate that galaxy bias is nto able to disentangle between f(R)-gravity and the standard cosmological scenario.  However, f(R)-gravity imprints modifications in the linear growth rate of cosmic structures at large scale, which can be recovered from the statistical properties of large galaxy samples.

1307.5066
Giga-z: a 100,000 object superconducting spectrophotometer for LSST follow-up
Marsden, Mazin, O'Brien, Hirata

Simulate the performance of a new type of instrument: SuperMOS (Superconducting Multi-Object spectrograph), that uses Microwave Kinetic Inductance Detectors (MKIDs).  MKIDs, a new detector technology, feature good QE in the UVOIR, can count individual photons with microsecond timing accuracy and, like X-ray calorimeters, determine their energy to several percent.  The performance of Giga-z, a SuperMOS designed for wide field imaging follow-up observations, is evaluated using simulated observations of the COSMOS mock catalog with an array of 100,000 R_{423 nm} = E/Delta E = 30 MKID pixels.  Compare results against a simultaneous simulation of LSST observations.  In 3 years on a dedicated 4m-class telescope, Giga-z could observe ~2 billion galaxies, yielding a low resolution SED spanning 350-1350 nm for each; 1000x the number measured with any currently proposed LSST spectroscopic follow-up, at a fraction of the cost and time.  Giga-z would provide redshifts for galaxies up t o z~6 with magnitudes m_i < 25, with accuracy sigma_{Delta z/(1+z)}=0.03 for the whole sample, and 0.007 for a select subset.  Also find catastrophic failure rates and biases that are consistently lower than for LSST. The added constraint on DE parameters for WL+CMB by Giga-z using the FoMSWG default model is equivalent to multiplying the LSST Fisher matrix by a factor of alpha=1.27 (w_p), 1.53 (w_a), or 1.98 (Delta gamma).  This is equivalent to multiplying both the LSST coverage area and the training sets by alpha, and reducing all systematics by a factor of 1/sqrt(alpha), advantages that are robust to even more extreme models of IA.

1307.5067
Moving objects in the Hubble Ultra Deep Field
Kilic, Giannias, von Hippel

Compare 2004 UDF to the 128-orbit 2012 UDF; find 12 sources brighter than I=27 mag that display >3 sigma proper motions.  Do not find any proper motion objects fainter than this magnitude limit.  Combining optical and NIR photometry, model the SED of each point source using stellar templates and WD models.  For I<27 mag, identify 23 stars with K0-M6 spectral types and two faint blue objects that are clearly old-thick disk white dwarfs.  Measure a thick disk [of the MW, I presume] WD space density of 0.1-1.7 e-3 per cubic parsec from these two objects.  There are no halo WDs in the UDF down to I=27 mag.  Combining the HDF N, S, and the UDF data, do not see any evidence for DM in the form of faint halo WDs, and the observed population of WDs can be explained with the standard Galactic models.

1307.5083
Cosmic variance of the spectral index from mode coupling
Bramante, Kumar, Nelson, Shandera

Demonstrate that local, scale-dependent non-Gaussianity can generate cosmic variance uncertainty in the observed spectral index of primordial curvature perturbations.  In a universe much larger than the current Hubble volume, locally unobservable long wavelength modes can induce a scale-dependence in the PS of typical subvolumes, so that the observed spectral index varies at a cosmologically significant level (Delta ns ~ O(0.04)).  Similarly, show that the observed bispectrum can have an induced scale dependence that varies about the global shape.  If tensor modes are coupled to long wavelength modes of a second field, the locally observed tensor power and spectral index can also vary.  All of these effects, which can be introduced in models where the observed non-G is consistent with bounds from the Planck satellite, loosen the constraints that observations place on the parameters of theories of inflation with mode coupling.  Suggest observational constraints that future measurements could aim for to close this window of cosmic variance uncertainty.