Day 563

Monday.

1312.1707
The MICE Grand Challenge Lightcone Simulation I: Dark matter clustering
Fosalba et al

MICE-GC: 7e10 DM partices in (3 Gpc/h)^3 comoving volume N-body simulation; 5 orders of magnitude in dynamic range.  Allows an accurate modeling of the growth of structure in the universe from the linear through the highly NL regime of gravitational clustering.  Validate the DM simulation outputs using 3D and 2D clustering statistics, and discuss mass-resolution effects in the NL regime by comparing to previous simulations and the latest numerical fits.  Show that the MICE-GC run allows for a measurement of the BAO feature with percent level accuracy and compare it to state-of-the-art theoretical models.  Also use sub-arcmin resolution pixelized 2D maps of the DM counts in the light cone to make tomographic analyses in real and redshift space.  Analysis shows the simulation reproduces the Kaiser effect on large scales, but find a significant suppression of power on NL scales relative to the real space clustering [due to z-space distortion or what?].  Complete validation by presenting an analysis of the 3pt correlation function in this and previous MICE simulations, finding further evidence for mass-resolution effects.  This is the first of a series of 3 papers in which the MICE-GC end-to-end simulation is presented, along with a wide (5000 sq deg) and deep (z<1.4) mock galaxy catalog constructed using a hybrid HOD and Halo Abundance Matching approach.  Accompanying these papers, make a first public release of MICE-GC light cone galaxy mock (MICECAT v1.0) through http://cosmohub.pic.es, to help develop and exploit new generation of astronomical surveys.

1312.1715
The Keplerian orbit of G2
Meyer et al

G2: the gaseous red emission-line object that is on a very eccentric orbit around the Galaxy's central BH, and predicted to come within 2400 Rs in early 2014.  Use laser guide star AO system on Keck I and II telescopes to obtain 3 epochs of spectroscopy and imaging at highest spatial resolution in near-IR.  Updated orbital solution from radial velocities + Br-Gamma line astrometry is consistent with earlier estimates.  Even ~6 months before pericenter passage there is no perceptible deviation from a Keplerian orbit.  Show that a proposed "tail" of G2 is likely not associated with it, but is rather an independent gas structure.  Also show that G2 does not seem to be unique, since several red emission-line objects can be found n the central arc second.  Taken together, seems more likely that G2 is ultimately stellar in nature, although there is clearly gas associated with it.

1312.1729
The flattening of the concentration-mass relation towards low halo masses and its implications for the annihilation signal boost
Sanchez-Conde, Prada

In standard CDM, there exists a tight connection between the properties of DM haloes, and their formation epochs.  Such relation can be expressed in terms of a single key parameter, namely the halo concentration.  In this work, examine the concentration-mass relation c(M), at present time over more than 20 orders of magnitude in halo mass (from Earth mass micro halos up to galaxy clusters).  Use the c(M) model proposed by Prada+ (2012) to test its predictions against results from N-body cosmo sims.  Despite little knowledge of halo concentrations below 1e8 Msun in simulations, the model works remarkable well; it is compatible with all the available data down to 1e6 Msun within 1 sigma.  Both simulation results and model show a clear flattening of the halo concentration-mass relation towards smaller masses that excludes the commonly used power-law c(M) models, and stands as a natural prediction for the CDM model.  Provide a parameterization for the c(M) relation that works accurately for all halo masses.  The flattening of the halo concentrations at low halo masses has decisive consequences e.g. for gamma-ray DM searches, as it implies more modest enhancements of the DM annihilation flux due to DM substructure than usually adopted in the literature, i.e. of ~1000 for galaxy clusters, and ~200 for MW-sized halos (e.g., Springel+2008, Gao+2012).  These values relied on such power-law c(M) extrapolations and those are clearly rejected.  Obtain much lower boosts, i.e., ~35 for galaxy clusters and ~15 for galaxies like MW.  These figures may have a critical impact on current and up-coming gamma-ray search strategies.  Finally provide a parameterization of the boost that can be safely used for dwarf- to cluster-size halos.

1312.1736
The Solar Neighborhood XXXII. The Hydrogen burning limit
Dieterich et al

Construct a HR diagram for the stellar/substellar boundary based on a sample of 63 objects ranging in spectral type from M6V to L4.  Report newly observed VRI photometry for all 63 objects and new trigonometric parallaxes for 37 objects.  The remaining 26 objects have trigonometric parallaxes from the literature.  Combine optical photometry and trigonometric parallaxes with 2MASS and WISE photometry and employ a novel SED fitting algorithm to determine effective temperatures, bolometric luminosities, and radii.  Uncertainties range from ~20K to ~150 K in temperature, ~0.01 to ~0.06 in log(L/Ls) and 3% to 10% in radius.  Check methodology by comparing calculated radii to radii directly measured via long baseline optical interferometry [did it work out OK?].  Find deviance for the local minimum in the radius-temperature and radius-luminosity trends that signals the end of the stellar MS and the start of the brown dwarf sequence at T~2075K, log(L/Ls)~-3.9, and (R/Rs)~0.086.  The existence of this local minimum is predicted by evolutionary models, but at temperatures ~400K cooler.  The minimum radius happens near the locus of 2MASS J0523-1403, an L2.5 dwarf with V-K=9.42.    Make qualitative arguments as to why the effects of the recent revision in solar abundances accounts for the discrepancy between the findings here and the evolutionary models.  Also report new color-absolute mag relations for optical and IR colors useful for estimating photometric distances.  Study the optical variability of all 63 targets and find an overall variability fraction of 36pm8% at a threshold of 15 milli-mags in the I band, in agreement with previous studies.  [tiny variability!  where does it come from?]

1312.1836
Discovery of the first B[e] supergiants in M 31
Kraus et al

B[e] supergiants (B[e]SGs) are transitional objects in the post-MS evolution of massive stars.  The small number of B[e]SGs known so far in the Galaxy and the Magellanic Clouds indicates that this evolutionary phase is short.  Nevertheless, the strong aspherical mass loss occurring during this phase, which leads to the formation of rings or disk-like structures, and the similarity to possible progenitors of SN1987A emphasize the importance of B[e]SGs for the dynamics of the ISM as well as stellar and galactic chemical evolution.  The number of objects and their mass loss behavior at different metallicities are essential ingredients for accurate predictions from stellar and galactic evolution calculations.  However, B[e]SGs are not easily identified, as they share many characteristics with luminous blue variables (LBVs) in their quiescent (hot) phase.  Present medium-resolution near-IR K-band spectra for four stars in M 31, which have been assigned a hot LBV (candidate) status.  Applying diagnostics that were recently developed to distinguish B[e]SGs from hot LBVs, classify two of the objects as bonafide LBVs; one of them currently in outburst.  In addition, firmly classify two stars as the first B[e]SGs in M 31 based on strong CO band emission detected in their spectra, and IR colors typical for this class of stars.

1312.1846
Multi-frequencey constraints on the non-thermal pressure in galaxy clusters
Colafrancesco et al

The origin of radio halos in galaxies clusters is still unknown and is the subject of debate both from the observational and theoretical point of view.  In particular the amount and the nature of non-thermal plasma and of the B-field energy density in clusters hosting radio halos is still unclear.  The aim of this paper is to derive an estimate of the pressure ratio X between the non-thermal and thermal plasma in radio halo clusters that have combined radio, X-ray and SZ effect observations.  From the simultaneous P-L_X and P-Y_SZ correlations [is P=plasma pressure?] for a sample of clusters observed with Planck, derive a correlation between Y_SZ and L_X that are used to derive a value for X.  This is possible since the Compton parameter Y_SZ is proportional to the total plasma pressure n the cluster (a sum of the thermal and non-thermal pressure) while the X-ray luminosity L_X is proportional only to the thermal pressure of the intracluster plasma.  Results indicate that the average (best fit) value of the pressure ratio in a self-similar cluster formation model is X=0.55 pm 0.05 in the case of an isothermal beta-model with beta=2/3 and a core radius r_c=0.3 R_500 holding on average for the cluster sample.  Also show that the theoretical prediction for the Y_SZ-L_X correlation in this model has a slope that is steeper than the best fit value for the available data.  The agreement with the data can be recovered if the pressure ratio X decreases with increasing X-ray luminosity as L_X^-0.96.  Conclude that the available data on radio halo clusters indicate a substantial amount of non-thermal pressure in cluster atmospheres whose value must decrease with increasing X-ray luminosity, or increasing cluster mass (temperature).

1312.1852
Parameterizing the local dark matter speed distribution: a detailed analysis
Kavanagh

A new parameterization of DM speed distribution f(v) proposed for use in the analysis of data from direct detection experiments.  This parameterization involves expressing the logarithm of the speed distribution as a polynomial in the speed v.  Present here a more detailed analysis of the properties of this parameterization.  Show that the method leads to statistically unbiased mass reconstructions and exact coverage of credible intervals [? verified using simulations?].  The method performs well over a wide range of DM masses, even when finite energy resolution and BGs are taken into account.  Also show how to select the appropriate number of basis functions for the parameterization.  Finally, look at how the speed distribution itself can be reconstructed, and how the method can be used to determine if the data are consistent with some test distribution.  In summary, show that this parameterization performs consistently well over a wide range of input parameters and over large numbers of statistical ensembles and can therefore reliably be used to reconstruct both the DM mass and speed distribution from direct detection data.

1312.1905
Molecules in the circumnuclear disk of the Galactic Center
Harada, et al

Within a few parsecs around the central BH Sgr A*, chemistry in the dense molecular cloud material of the circumnuclear disk (CND) can be affected by many energetic phenomena such as high UV-flux from the massive central star cluster, X-rays from Sgr A*, shock waves, and an enhanced CR flux.  Recently, spectroscopic surveys with the IRAM 30 m and the APEX 12 m telescopes of substantial parts of the 80-500 GHz frequency range were made toward selected positions in and near the CND.  These datasets contain lines from the molecules HCN, HCO+, HNC, CS, SO, SiO, CN, H2CO, HC3N, N2H+, H3O+ and others.  Conduct Large Velocity Gradient analyses to obtain column densities and total H densities, n, for each species in molecular clouds located in the SW lobe of CND.  The data for the above mentioned molecules indicate 1e5 cm^-3 < n<1e6 cm^-3, which shows that the CND is tidally unstable.  The derived chemical composition is compared with a chemical model calculated using the UCL_CHEM code that includes gas and grain reactions, and the effects of shock waves.  Models are run for varying shock velocities, CR ionization rates, and number densities.  The resulting chemical composition is fitted best to an extremely high value of CR ionization rage zeta~1e-14 s^-1, 3 orders of magnitude higher than the values in regular Galactic molecular clouds, if the pre-shock density is n=1e5 cm^-3.



1312.1916
All weather calibration of wide field optical and NIR surveys
Burke et al

Ground-based large-area surveys (e.g., DES, Pan-STARRS, and LSST) require calibration of broadband photometry that is stable in time and uniform over the sky to precisions of a per cent or better.  This performance will need to be achieved with data taken over the course of many years, and often in less than ideal conditions.  This paper describes a strategy to achieve precise internal calibration of imaging survey data taken in less than photometric conditions, and reports results of an observational study of the techniques needed to implement this strategy.  Find that images of celestial fields used in this case study with stellar densities of order one per arcmin-squared and taken through cloudless skies can be calibrated with relative precision of 0.5% (reproducibility).  Report measurements of spatial structure functions of cloud absorption observed over a range of atmospheric conditions, and find it possible to achieve photometric measurements that are reproducible to 1% in images that were taken through cloud layers that transmit as little as 25% of the incident optical flux (1.5 mag of extinction).  Find, however, that photometric precision below 1% is impeded by the thinnest detectable cloud layers.  Comment on implications of these results for the observing strategies of future surveys.  [what exactly is the strategy anyway?]

1312.1929
Simple expressions for second order density perturbations in standard cosmology
Uggla, Wainwright

Present 4 simple expressions for the relativistic first and second order fractional density perturbations for LCDM cosmologies in different gauges: Poisson, uniform curvature, total matter and synchronous gauges.  Use of a canonical set of quadratic differential expressions involving an arbitrary spatial function (comoving curvature perturbation) to describe the spatial dependence, which enables unifying, simplifying and extending previous seemingly disparate results.  The simple structure of the expressions makes the evolution of the density perturbations completely transparent and clearly displays the effect of the cosmological constant on the dynamics, namely that it stabilizes the perturbations.  Expect that the results will be useful in applications, e.g. studying the effects of primordial non-Gaussianity on the large scale structure of the universe.

1312.1947
Thermal escape from extrasolar giant planets
Koskinen et al

There are two distinct regimes f thermal escape from EGPs, and the transition between these regimes is relatively sharp.

1312.2002
Similarities and distinctions in cosmic-ray modulation during different phases of solar and magnetic activity cycles
Aslam, Badruddin

Study the solar-activity and solar-polarity dependence of galactic CR intensity (CRI) on the solar and heliospheric parameters playing a significant role in solar modulation.  … The relative CRI-response to changes in various parameters (solar activity by sunspot number (SSN), interplanetary plasma/field parameters, solar-wind velocity V, magnetic field B, tilt of the heliospheric current sheet (Lambda), neutron monitors [counts]).  Regression analysis to calculate and compare the CRI-response to changes in different solar/interplanetary parameters during (i) different phases of solar activity and (ii) similar activity phases but different polarity states.  Find that the CRI response is different during negative as compared to positive polarity states, not only with SSN and Lambda but also with B and V.  The relative CRI-response to changes in various parameters, in negative vs positive state, is solar-activity dependent (higher at low solar activity, and nearly equal in high solar-activity conditions).  Although results can be ascribed to preferential entry of charged particles via the equatorial/polar regions of the heliosphere as predicted by drift models, these results also suggest that we should look for any polarity-dependent response of solar wind and transport parameters in modulating CRI in the heliosphere.

1312.2006 [vote?]
Les Houches Lectures on physics beyond the standard model of cosmology
Khoury

Review various extensions of LCDM model, characterized by additional light degrees of freedom in the dark sector.  In order to reproduce the successful phenomenology of GR in the solar system, these fields must effectively decouple from matter on solar system/laboratory scales.  This is achieved through screening mechanisms, which rely on the interplay between self-interactions and coupling to matter to suppress deviations from standard gravity.  The manifestation of the new degrees of freedom depends sensitively on their environment, which in turn leads to striking experimental signatures.