Day 597

Wednesday.

1402.5490
A large lunar impact blast on September 11th 2013
Madiedo et al

As the title says.  Equivalent of 15 tones of TNT.

1402.5963
A constrained trasport scheme for MHD on unstructured static and moving meshes
Mocz, Vogelsberger, Hernquist

B-fields play an important role in many astrophysical systems and a detailed understanding of their impact on the gas dynamics requires robust numerical simulations.  Present a new method to evolve the ideal MHD equations on unstructured static and moving meshes that preserves the B-field divergence-free constraint to machine precision.  The method overcomes the major problems of using a cleaning scheme on the B-fields instead, which is non-conserative, not fully Galilean invariant, does not eliminate divergence errors completely, and may produce incorrect jumps across shocks.  The new method is a generalization of the constrained transport (CT) algorithm used to enforce the divergence(B)=0 condition on fixed Cartesian grids.  Preserving this at the discretized level is necessary to maintain the orthogonality between the Lorenz force and B.  The possibility of performing CT on a moving mesh provides several advantage over static mesh methods due to the quasi-Lagrangian nature of the former (i.e., the mesh generating points move with the flow), such as making the simulation automatically adaptive and significantly reducing advection errors.  Method preserves B-fields and fluid quantities in pure advection exactly.

1402.5964
From haloes to galaxies - I: the dynamics of the gas regulator model and the implied cosmic sSFR-history
Peng, Maiolino

Explore the basic parameters that drive the evolution of the fundamental properties of SF galaxies within the gas regulator model, or bathtub-model.  Derive the general analytic form of the evolution of the key galaxy properties, i.e. gas mass, SFR, stellar mass, sSFR, gas fraction, gas phase metallicity and stellar metallicity, without assuming that galaxies live in the equilibrium state.  Find that the timescale required to reach equilibrium, tau_eq, which is determined by the product of SF efficiency and mass-loading factor, is the central parameter in the gas regulator model that is essentially in control of the evolution of all key galaxy properties.  The scatters in most of the key scaling relations are primarily governed by tau_eq.  Most strikingly, the predicted sSFR evolution is controlled solely by tau_eq (apart from the cosmic time).  Although the precise evolution of the sSFR depends on tau_eq, the sSFR history is largely insensitive to different values of tau_eq.  The difference between the minimum and maximum sSFR at any epoch is less than a factor of four.  The shape of the predicted sSFR history simply mimics that of the specific mass increase rate of the dark matter haloes (sMIR_DM) with the typical value of the sSFR around 2*sMIR_DM.  The predicted sSFR from the gas regulator model is in good agreement with typical SAMs, but both are fundamentally different from the observed sSFR history.  This clearly implies that some key process is missing in both typical SAMs and gas regulator model, and so hint at some possible culprit.  Emphasize the critical role of tau_eq in controlling the evolution of the galaxy population, especially for gas rich low mass galaxies that are very unlikely to live around the equilibrium state at any epoch; this has been largely ignored in many similar studies.

1402.5975
Detecting floating black holes as they traverse the gas disk of the Milky Way
Wang, Loeb

A population of intermediate-mass BHs is predicted to be freely floating n the MW halo, due to gravitational wave recoil, ejection from triple BH systems, or tidal stripping in the dwarf galaxies that merged to make the MW.  As these BHs traverse the MW disk, a bow shock forms, producing detectable radio synchrotron emission from accelerated electrons.  Calculate the synchrotron flux to be ~0.01-10 mJy at GHz frequency, detected by JVLA, and ~0.1-1 uJy in the IR, detectable by HST and JWST.  The discovery of the floating BH population will provide insights on the formation and merger history of the MW as well as on the evolution of massive BHs in the early Universe.

1402.5976
Spectral energy distributions of QSOs at z>5: common AGN-heated dust and occasionally strong star-formation
Leipski, … Rix, et al

Present SEDs of 69 QSOs at z>5.  The detection rate of the QSOs with Spitzer is very high, but drops towards the Herschel bands with 30% detected in PACS (MIR in rest-frame) and 15% in SPIRE (FIR in rest-frame).  Perform multi-component SED fits for Herschel-detected objects and confirm that to match the observed SEDs, a clumpy torus model needs to be complemented by a hot (~1300K) component and, in cases with prominent FIR emission, also by a cold (~50K) component.  In the FIR detected cases, the luminosity of the cold component is on the order of 1e13 Lsun which is likely heated by SF.  From the SED fits, also determine that the AGN dust-to-accretion disk luminosity ratio declines with UV/optical luminosity.  Emission from hot (~1300K) dust is common in the sample, showing that nuclear dust is ubiquitous in luminous QSOs out to z=6.  However, about 15% of the objects appear under-luminous in the NIR compared to their optical emission and seem to be deficient in (but not devoid of) hot dust.  Within the full sample, the QSOs detected with Herschel are found at the high luminosity end in L_UV/opt and L_NIR and show low EWs in Halpha and Lya.  In the distribution of H_alpha EWs, as determined from the Spitzer photometry, the high-z WSOs show little different to low z AGN.

1402.6101
Effects of center offset and noise on weak-lensing derived concentraion-mass relation of dark matter halos.
Du, Fan

From the halo catalog of the Millennium Sims, analyze WL density profiles for clusters.  c-M relation can be biased by the center offset, selection effect and shape noise from intrinsic ellipticities of BG galaxies.  Different methods for finding cluster center employed.  Find: for intermediate z clusters, the highest peak from the two-scale smoothing method applied to the reconstructed convergence field, first with a smoothing scale of 2 arcmin and then 0.5 arcmin, corresponds the best to the true center.  Assuming the parameterized NFW profile, fit the reduced tangential shear signals around different centers.  It is shown that for the ensemble median values, a center offset larger than one scale radius r_s can bias the derived mass and concentration significantly lower than the true values especially for low mass haloes.  However, the existence of noise can compensate the offset effect and reduce the systematic bias although the scatters of mass and concentration get considerably larger.  Statistically, the bias effect of center offset on the c-M relation is insignificant if an appropriate center finding method is adopted.  On the other hand, noise from intrinsic ellipticities can bias the c-M relation derived from a sample of WL analyzed clusters if a simple chisq fitting method is used.  To account for the scatters and covariance between c and M properly, apply a Bayesian method to improve the statistical analysis on the c-M relation.  It is show that this new method allows us to derive the c-M relation with significantly reduced biases.

1402.6212
Cosmology and astrophysics from related galaxy clusters II: cosmological constraints
Mantz, Allen, Morris, Rapetti, Applegate, Kelly, von der Linden, Schmidt

Present cosmo constraints from f_gas for massive, dynamically relaxed galaxy clusters.  40 such clusters from Chandra, some with WL data.  Incorporating a robust gravitational lensing calibration of the X-ray mass estimates, and restricting measurements to the most self-similar and accurately measured regions of clusters, significantly reduces systematic uncertainties compared to previous work.  Data constrain intrinsic scatter in f_gas: 7.4pm2.3% in a spherical shell at radii 0.8-1.2 r_2500, consistent with the expected variation in gas depletion and non-thermal pressure for relaxed clusters.  From the lowest-z data in the sample, obtain a constraint on a combination of the Hubble parameter and cosmic baryon fraction h^3/2 Omega_b/Omega_m = 0.089pm0.012, that is insensitive to the nature of DE.  Combined with standard priors on h and Omega_b h^2, this provides a tight constraint on the cosmic matter density, Omega_m=0.27pm0.04, which is similarly insensitive to DE.  Using the entire cluster sample, extending to z>1, obtain consistent results for Omega_m and interesting constraints on DE: Omega_Lambda = 0.65pm0.2 for non-flat LCDM models, and w=-0.98pm0.26 for flat constant-w models.  Results are both competitive and consistent with those from recent CMB, SNIa and BAO data.  Present constraints on models of evolving DE from the combination of f_gas data with these external data sets, and comment on the possibilities for improved f_gas constraints using current and next-generationg X-ray observatories and lensing data.