Day 1016

Thursday.


1512.00452
Detecting the disruption of dark-matter haloes with stellar streams
Bovy

Narrow stellar streams in the MW halo are uniquely sensitive to DM sub haloes, but many of these may be tidally disrupted.  Calculate the interaction between stellar and DM streams using analytical and N-body calculations, showing that disrupting objects can be detected as low-concentration sub haloes.  Through this effect, the streaminess [?] of the halo can be constrained, as well as the orbit and present position of individual DM streams.  This will have profound implications for the formation of haloes and for direct and indict-detection DM searches.


1512.00453
NIHAO V: Too big doesn't fail -- reconciling the conflict between LCDM predictions and the circular velocities of nearby field galaxies
Dutton et al

Compare the half-light circular velocities, V_1/2, of dwarf galaxies in the Local Group to the predicted circular velocity curves of galaxies in the NIHAO suite of LCDM sims.  Use a subset of 34 sims in which the central galaxy has a stellar luminosity in the range 0.5e5<L_V<2e8 Lsun.  The NIHAO galaxy simulations reproduce the relation between stellar mass and halo mass from abundance matching, as well as the observed half-light size vs luminosity relation.  The corresponding dissipation less sims over-predict the V_1/2, recovering the problem known as too big to fail (TBTF).  By contrast, the NIHAO sims have expanded DM haloes, and provide an excellent match to the distribution of V_1/2 for galaxies with L_V>2e6 Lsun.  For lower luminosities the simulations predict very little halo response, and tend to over predict the observed circular velocities.  In the context of LCDM, this could signal the increased stochasticity of SF in haloes below Mhalo ~1e10 Msun, or the role of environmental effects.  Thus, haloes that are "too big to fail", do not fail LCDM, but haloes that are "too small to pass" (the galaxy formation threshold) provide a future test of LCDM.


1512.00454
Warm-hot baryons comprise 5-10 per cent of filaments in the cosmic webEckert, ... Kneib, Erben, Israel, Jullo, Klein, Massey, ... et al

Observations of the CMB indicate the baryons account for 5% of the universe's total energy content, in the local universe, the census of all observed barons falls short of this estimate by a factor of two.  Cosmological sims indicate that the missing baryons might not have condensed into virtualized haloes, but reside through the filaments of the cosmic web (where matter density is larger than average) as a low-density plasma at temperatures of 1e5-7 Kelvin, known as the WHIM (warm-hot intergalactic medium).  There have been previous claims of the detection of warm baryons along the LoS to distant blazers and of hot gas between interacting clusters.  These observations were, however, unable to trace the LS filamentary structure, or to estimate the total amount of warm baryons in a representative volume of the Universe.  Report X-ray observations of filamentary structures of gas at 1e7 K associated with the galaxy cluster A2744.  Previous observations of this cluster were unable to resolve and remove coincidental X-ray point sources.  After subtracting these, hot gas structures that are coherent over scales of 8 Mpc are revealed.  The filaments coincide with over-densities of galaxies and DM, with 5-10% of their mass in baryonic gas.  This gas has been heated up by the cluster's gravitational pull and is now feeding its core.  The findings strengthen evidence for a picture of the Universe in which a large fraction of the missing baryons reside in the filaments of the cosmic web.


1512.00492
Dealing with missing data: an inpainting application to the MICROSCOPE space mission
Berg, Pires, Bagni, Touboul, Métris

Missing data are a common problem in experimental and observational physics.  They can be caused by various sources, either an instrument's saturation, or a contamination from an external event, or a data loss.  In particular, they can have a disastrous effect when one is seeking to characterize a colored-noise-dominated signal in Fourier space, since they create a spectral leakage that can artificially increase the noise.  It is therefore important to either take them into account or to correct for them prior to e.g. a Least-Square fit of the signal to be characterized.  In this paper, present an application of the inpainting algorithm to mock MICROSCOPE data; inpainting is based on sparsity assumption, and has already been used in various astrophysical contexts; MICROSCOPE is a French Space Agency mission, whose launch is expected in 2016, that aims to test the Weak Equivalence Principle down to the 1e-15 level.  Then explore the inpainting dependence on the number of gaps and the total fraction of missing values.  Show that, in a worse-case scenario, after reconstructing missing values with inpainting, a Least-Square fit may allow measurements of 1.1e-15 Equivalence Principle violation signal, which is sufficiently close to the MICROSCOPE requirements to implement inpainting in the official MICROSCOPE data processing and analysis pipeline.  Together with the previously published KARMA method, inpainting will then allow independent characterization and cross-check and Equivalence Principle violation signal detection down to the 1e-15 level.