Day 437

Wednesday.  Saturday.  A full week behind (again).

135.5037
Gravitational lensing shear by an exotic lens object with negative convergence or negative mass
Izumi, Hagiwara, Nakajima, Kitamura, Asada

Static and spherically-symmetric modified spacetime metric depends on the inverse distance to the power of positive n (n=1 for Schwarzschild metric, n=2 for Ellis wormhole) in the weak-field approximation, and it has been shown that demagnification of images could occur for n>1 lens models associated with exotic matter (and energy), though they cause the gravitational pull on light rays.  The paper considers gravitational lensing shear by the demagnifying lens models and other models such as negative-mass compact objects causing the gravitational repulsion on light rays.  It shows radial shear [duh], and this signature can be used to search or constrain exotic matter or energy with GL surveys.  Voids may produce radially elongated images too.

1305.5534
Augmented reality in astrophysics
Vogt, Shingles

Augmented reality: consists of merging live images with virtual layers of information.  Explore potential of Augmented Reality for astrophysical research with (1) Augmented Posters and (2) Augmented Articles.  Highlight the potential of Augmented reality to improve the communication of scientific results in the field of astrophysics.  Discuss possible future trends for Augmented  Reality applications in astrophysics, and explore the current limitations associated with the technology.

1305.5535
Ursa Major II - Reproducing the observed properties through tidal disruption
Smith et al

dSph Ursa Major II's morphology, spectroscopy of individual stars provide a number of new constraints on its properties.  With a velocity dispersion of ~6 km/s, and under the assumption that the galaxy is virialised, M/L ratio is ~2000.  Using N-body sims, demonstrate that the observed luminosity, ellipticity, irregular morphology, velocity gradient and the velocity dispersion an be well reproduced through processes associated with tidal mass loss, and in the absence of DM.  These results highlight the considerable uncertainty that exists in measurement of the DM content of Ursa Major II.  ...

1305.5538
Dwarf galaxy formation with H2-regulated star formation: II. gas-rich dark galaxies at redshift 2.5
Kuhlen, Madau, Krumholz

Cosmological hydro sim of dwarf galaxy formation at z>2.5 using physically motivated model for H2-regulated SF, using Enzo.  Peak resolution of 1.9 proper parsecs at z=2.5  Show that SF prescription regulated by the local H2 abundance leads to the suppression of SF in dwarf galaxy haloes with M_h<1e10 Msun and to a large population of gas-rich "dark galaxies" at z=2.5 with low SF efficiencies and gas depletion timescales of >20 Gyr.  The fraction of dark galaxies is 60% at M_h~1e10 Msun and increases rapidly with decreasing halo mass.  Dark galaxies form late and their gaseous disks never reach the surface densities >5700 Msun/pc^2 (Z/10e-3 Zsun)^-0.88, that are required to build a substantial molecular fraction.  Despite this large population of dark galaxies, show that our H2-regulated simulations is consistent with both the observed luminosity function of galaxies and the cosmological mass density of neutral gas at z>2.5.  Results provide a theoretical explanation for the recent detection in fluorescent Lya emission of gaseous systems at high z with little or no associated SF.  Further propose that H2-regulation may offer a fresh solution to a number of outstanding "dwarf galaxy problems" in LCDM: regulation leads galaxy formation to become effectively stochastic on mass scales of M_h~1e10 Msun, and thus these massive dwarfs are not "too big to fail".

1305.5541
Measuring the X-ray background in the reionization era with first generation 21 cm experiments
Christian, Loeb

The X-ray BG during the epoch of reionization if currently poorly constrained.  Demonstrate that it is possible to use first generation 21 cm experiments to calibrate it.  Using numerical simulation 21cmFAST, calculate the dependence of the 21 cm power spectrum on the X-ray background flux. Comparing the signal to the sensitivity of the MWA array, find that in the redshift interval z=8-14 the 21 cm signal is detectable based on the upper limit set by the present-day unresolved soft X-ray background.  Show that there is no degeneracy between the X-ray production efficiency and the LyA production efficiency and that the degeneracy with the ionization fraction of the IGM can be broken.

1305.5548
Modeling the phase-space distribution around massive haloes
Lam, Schmidt, Nishimichi, Takada

The comparison between dynamical mass and lensing mass provides a targeted test for a wide range of modified gravity models.  With numerical simulation, have shown the measurement of the LoS velocity dispersion around stacked massive clusters whose lensing masses are known allows for stringent constraints on modified gravity on scales of 2-15 Mpc/h.  Here, develop a semi-analytical approach based on the halo model to describe the phase-space distribution and the LoS velocity dispersion for different tracers.  The model distinguishes contributions from the halo pairwise velocity and the virial velocity within halos.  Discuss observational complications, in particular the contribution from Hubble flow, and show how model can incorporate these complications.  Then incorporate the effects of modified gravity (f(R) and braneworld models), and show that the model predictions are in excellent agreement with modified gravity simulations.  More broadly, the phase-space distribution provides a sensitive test of the understanding of hierarchical structure formation when confronted with observations via this model.

1305.5571
Void statistics and hierarchical scaling in the halo model
Fry, Colombi

Study scaling behaviour of statistics of voids in the context of halo model of NL large-scale structure.  THe halo model allows understanding of why the observed galaxy void probability obeys hierarchical scaling, even though the premise from which the scaling is derived is not satisfied.  Argue that the commonly observed negative binomial scaling is not fundamental, but merely the result of the specific values of bias and number density for typical galaxies.  The model implies quantitative relations between void statistics measured for two populations of galaxies, such as SDSS red and blue galaxies, and their number density and bias.

1305.5586
Testing accuracy and precision of existing photometry algorithms on moving targets
Sonnet, et al

Photometry of moving targets offer different challenges for astronomical photometry software: (i) to aperture photometry because BG object contamination varies from image to image, and (ii) to routines that build a PSF model from point sources in the image because trailed field stars do not perfectly represent the PSF of the untrailed target.  Present the results of testing several photometry algorithms (tphot, DAOPHOT< DoPHOT, APT, and multiple techniques within SExtractor and IRAF's PHOT) on data for a faint, slow-moving solar system object with a known light curve.  Find that the newly-developed tphot software most accurately and precisely reproduces the object's true light curve, with particular advantages in centroiding, exclusion of contaminants from the target's flux, and fitting flux in the wings of the PSF.

1305.5587
A sub-Mercury-sized exoplanet
Barclay, ... Marcy, et al

As the title says.  Moon-sized object.

1305.5612
Two-year monitoring of intra-day variability of quasar 1156+295 at 4.8 GHz
Liu et al

It's an intra-day variable (IDV) source; seem to follow an annual cycle; can be fitted with an anisotropic interstellar scintillation (ISS) model, suggesting that the significant part of the flux density is due to ISS. The source underwent a dramatic flare in 2008.  Study possible consequences of the flare, by comparing the changes in its variability characteristics with the evolution of the 43 GHz VLBA corse size of the source.

1305.5641
Photometric redshifts for quasars in multi band surveys
Brescia et al

Multi Layer Perceptron with Quasi Newton Algorithm (machine learning method) can be used to cope with regression and classification problems on complex and massive data sets.  Describe its application to the evaluation of photometric redshfits for quasars.  Can get dz/(1+zspec) of 0.004 with scatter of sigma=0.069 for zspec<=3.6.  Fraction of catastrophic outliers (deviation > 2sigma) is <3%, leading to sigma=0.035 after their removal.  Based on 4 different surveys (SDSS, GALEX, UKIDSS, and WISE).

1305.5720
The gravitational universe
Danzmann, for eLISA consortium

Formation of first seed BHs at z~20; BH mass and spin measurements, trace history of BH across all stages of galaxy evolution, constrain any deviation from Kerr metric of GR.  eLISA: the first ever mission to study the entire Universe with gravitational waves.  

1305.5791
Intrinsic galaxy shapes and alignments II: modelling the intrinsic alignment contamination of weak lensing surveys
Joachimi, Semboloni, Hlivert, Bett, Hartlap, Hoekstra, Schneider

Build analytic models for the distribution of galaxy shapes based on halo properties extracted from Millennium simulation, differentiating between early- and late-type galaxies as well as central galaxies and satellites.  The resulting ellipticity correlations are investigated for their physical properties and compared to a suite of current observations.  The best model is then used to predict the IA contamination of planned WL surveys.  Find that late-type galaxy models generally have weak IA correlations, marginally increasing towards smaller galaxy separation and higher redshift.  The signal for early-type models at fixed halo mass strongly increases by three orders of magnitude over two decades in galaxy separation, and by one order of magnitude from z=0 to 2.  The intrinsic alignment strength also depends strongly on halo mass, but not on galaxy luminosity at fixed mass, or galaxy number density in the environment.  Identify models that are in good agreement with all observational data, except that all models over-predict alignments of faint early-type galaxies.  The best model yields an IA contamination of a Euclid-ike survey between 0.5-10% at z>0.6 and on angular scales larger than a few arcminutes.  Cutting 20% of red FG galaxies using observer-frame colours can suppress this contamination by up to a factor of two.

1305.5830
Bias deconstructed: Unravelling the scale dependence of halo bias using real space measurements
Paranjape, Sefusatti, Chan, Desjacques, Monaco, Sheth

Scale dependence of halo bias using real space X-correlation measurements in N-body simulations and in Pinocchio.  Compare reconstruction of the linear bias with previous estimates from N-body simulations, which are obtained directly in Fourier space at learge scales, and find very good agreement.