Day 478

Wednesday.


1307.7136
The long lives of giant clumps and the birth of outflows in gas-rich galaxies at high redshift
Bournaud, ... Dekel, ... Teyssier, et al

SF disk galaxies at high z are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood.  The main question: whether the clumps disrupt within their dynamical timescale (<50Myr), like molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (~300 Myr) in which case they can migrate inward and help build the central bulge.  Present 3.5-7pc resolution AMR simulations of high-z disks including photo-ionization, radiation pressure, and SNe feedback.  Modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles.  Find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their SFR, with velocities largely sufficient to escape galaxy.  The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (<=200Myr), as observed.  The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can re-accrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses.  Our simulations produce gaseous outflows with velocities, densities and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of high-z galaxies, without rapid dispersion and reformation of clumps.

1307.7147
A theory of grain clustering in turbulence: the origin and nature of large density fluctuations
Hopkins

Propose a theory for density fluctuations of aerodynamic grains embedded in a turbulent, gravitating gas disk.  The theory combines calculations for the average behavior of grains encountering a single turbulent eddy, with a hierarchical description of the eddy velocity statistics.  Show that this makes analytic predictions for a wide range of quantities, including: the distribution of volume-average grain densities, the PS and correlation functions of grain density fluctuations, and the maximum volume density of grains reached.  For each, predict how these scales as a function of grain stopping/friction time (t_stop), spatial scale, grain-to-gas mass ratio, strength of the turbulence (alpha), and detailed disk properties (orbital frequency, sound speed).  Test these against numerical simulations and find good agreement over a huge [is he allowed to say "huge"?  :D] parameter space.  Results from 'turbulent concentration' simulations and laboratory experiments are also predicted as a special case.  Predict that vortices on a wide range of scales act to disperse and concentrate grains hierarchically (even if the gas is incompressible).  For small grains this is most efficient in eddies with turnover time comparable to the stopping time.  But for large grains, shear and gravity are important and lead to a broad range of eddy scales driving fluctuations, with most power on the largest scales.  The grain density distribution is driven to a log-Poisson shape, with fluctuations for large grains up to >1000 times the mean density.  Predict much smaller grains will also experience large fluctuations, but on small scales (not resolved in most simulations).  Provide simple analytic expressions for the important predictions, and discuss implications for planetesimal formation, grain growth, and the structure of turbulence.

1307.7157
The generalized scaling relations for X-ray galaxy clusters: the most powerful mass proxy
Ettori

Discuss application to observational data of generalized scaling relations (gSR).  Extend the formalism of gSR in the self-similar model for X-ray galaxy clusters, showing that for a generic relation M_tot~L^a M_g^b T^c, where L, M_g and T are the gas luminosity, mass and temperature, respectively, the values of the slopes lay in the plane 4*a + 3*b + 2*c = 3.  Using published dataset, show that some projections of the gSR are the most efficient relations, holding among observed physical X-ray quantities, to recover the cluster mass.  This conclusion is based on the evidence that they provide the lowest chi^2, the lowest total scatter and the lowest intrinsic scatter among the studied scaling laws on both galaxy group and cluster mass scales.  By the application of the gSR, the intrinsic scatter is reduced in all the cases down to a relative error on M_tot below 16 %.  The best-fit relations are: M_tot~M_g^a T^{1.5-1.5a}, with a~0.4 and M_to L^a T^{1.5-2a}, with a~0.15.  As a byproduct of this study, provide the estimates of the gravitating mass at Delta=500 for 120 objects, 114 of which are unique entries.  The typical relative error in the mass provided from the gSR only (i.e., not propagating any uncertainty associated with the observed quantities) ranges between 3-5% on cluster scale and is about 10% for galaxy groups.  With respect to the hydrostatic values used to calibrate the gSR, the masses are recovered with deviations in the order of 10% due to the different mix of relaxed/disturbed objects present in the considered samples.  In the extreme case of a gSR calibrated with relaxed systems, the hydrostatic mass in disturbed objects is over-estimated by about 20%.

1307.7707
The densest galaxy
Strader, ... Conroy, et al

Ultra-compact dwarf around the Virgo elliptical galaxy NGC 4649 (M60), termed M60-UCD1.  With a dynamical mass of 2e8 Msun but a half-light radius of only ~24 pc, This UCD is more massive than any ultra-compact dwarfs of comparable size, and is arguably the densest galaxy known in the local universe.  Has a 2-component structure well-fit by a sum of Sersic functions, with an elliptical, compact inner component (n~3.3, r_h=14pc) and a round, exponential, extended (r_h=49pc) outer component.  Chandra data reveal a variable central X-ray source with L_X~1e38 erg/s that could be an active galactic nucleus associated with a massive BH or a low-mass X-ray binary.  Analysis of optical spectroscopy shows the object to be old (~>10 Gyr) and of solar metallicity, with elevated [Mg/Fe] and strongly enhanced [N/Fe] that indicates light element self-enrichment; such self-enrichment may be generically present in dense stellar systems.  The velocity dispersion (~70 km/s) and resulting dynamical M/L_V=4.9pm0.7 are consistent with expectations for an old, metal-rich stellar population with a Kroupa IMF.  The presence of a massive BH or a mild increase in low-mass stars or stellar remnants is therefore also consistent with this M/L_V.  The stellar density of the galaxy is so high that no dynamical signature of DM is expected.  However, the properties of this UCD suggest an origin in the tidal stripping of a nucleated galaxy with M_B~-18 to -19.

1307.7715
nu-LCDM: neutrinos reconcile Planck with the local universe
Wyman, Rudd, Vanderveld, Hu

Two-part tension with 6-parameter flat LCDM: (1) the Planck satellite suggests a higher normalization of matter perturbations than local measurements of galaxy clusters.  (2) the expansion rate of the Universe today, H_0, derived from local distance-redshift measurements is significantly higher than that inferred using the acoustic scale in galaxy surveys and the Planck data as a standard ruler.  The adidtion of a sterile neutrino species changes the acoustic scale and brings the two into agreement; adding mass to the active neutrinos or to a sterile neutrino can suppress the growth of structure, bringing the cluster data into concordance as well.  For the fiducial dataset combination, with statistical errors for clusters, a model with a massive sterile neutrino shows 3.5 sigma evidence for a non-zero mass and an even stronger rejection of the minimal model.  A model with massive active neutrinos and a massless sterile neutrino is similarly preferred.  An eV-scale sterile neutrino mass --- suggested by short baseline and reactor anomalies --- is well within the allowed range.

1307.7735
The tenth data release of the Sloan digital sky survey: first spectroscopic data from the SDSS-III Apache point observatory galactic evolution experiment
Ahn, et al

SDSS DR10 released.  APOGEE, BOSS spectra included.  APOGEE is NIR R~22,500 300-fiber spectrograph covering 1.514-1.696 microns; studies the chemical abundances and radial velocities of 100k red giant star candidates in the bulge, bar, disk and halo of MW.  DR10 includes 178k spectra of 57,454 stars, each typically observed 3 or more times, from APOGEE.  Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included.  DR10 also doubles the number of BOSS spectra over DR9.  DR10 includes a total of 1.5M BOSS spectra (927k galaxy spectra, 182k quasar spectra, and 159k stellar spectra), selected over 6373 square degrees.

1307.8062
Optimising spectroscopic and photometric galaxy surveys: same-sky benefits for dark energy and modified gravity
Kirk, Lahav, Bridle, Jouvel, Abdalla, Frieman

Combine (i) WL with photo-z, and (ii) galaxy clustering and RSD with spectroscopic redshifts.  Combining surveys greatly improves their power to measure both DE and modified gravity.  An independent, non-overlapping combination sees a DE FoM >4x larger than that produced by either survey alone.  The synergies between the surveys are strongest for MG, where their constraints are orthogonal, producing a non-overlapping joint FoM nearly 2 orders of magnitude larger than either alone.  Projected angular PS formalism makes it easy to model the cross-correlation observable when the surveys overlap on the sky, producing a joint data vector and full covariance matrix.  Calculate a same-sky improvement factor, from the inclusion of these cross-correaltions, relative to non-overlapping surveys.  Find nearly a factor of 4 for DE and more than a factor of 2 for MG.  THe exact forecast FoM and same-sky benefits can be radically affected by a range of forecasts assumption, which is explored methodically in a sensitivity analysis.  Show that fiducial assumptions produce robust results which give a good average picture of the science return from combining photometric and spectroscopic surveys.