Day 548

Tuesday.

1311.2910
Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars
Trujillo-Gomez, Klypin, Colin, Ceverino, Arraki, Primack

Disk galaxy sims at z=0 still form the bulk of their stars prematurely.  Investigate the process of stellar mass assembly in low-mass simulated galaxies, a dwarf and a typical spiral, focusing on the effects of radiation from young stellar clusters.  Employ a novel model of SF in which stars form deterministically with a small efficiency from SN explosions and stellar winds.  In galaxies with masses up to those of typical spirals, radiation efficiently suppresses SF by dispersing and heating high density gas, mostly in the central regions, preventing the formation of a massive bulge.  Once the galaxies reach this radiation-regulated growth regime, their global properties are robust to the specific choice of model parameters.  Only when radiative feedback is included do galaxies exhibit constant or even rising star formation histories, forming more tan 50% of their stars at z<1, an observed phenomenon that has so far eluded analytical and numerical models.  Low-mass galaxies with radiation pressure have a factor of ~100 reduction in the star formation rate at z=2, and a factor of ~10 at z=0.5.  Conclude that radiation feedback is the main mechanism that effectively decouples the growth of the galaxy from that of the DM halo.  Radiation does not affect the total baryon content of galaxies ,but instead maintains gas in a warm, low density phase where it cannot fuel star formation.  Find that the fraction of cold baryons within the simulated dwarf galaxy is 20-30%, in agreement with THINGS.  Unlike SN energy, radiation from massive stars reduces the central density of the DM halo of a galaxy with M*~1e8 Msun, in support of recent observations.

1311.2934
R144: a very massive binary likely ejected from R136 through a binary-binary encounter
Oh, Kroupa, Banerjee

R144: very massive, spectroscopic binary, appears isolated from the core of the massive young star cluster R136.  The dynamical ejection hypothesis as an origin for its location is claimed improbable by Sana+ due to its binary nature and high mass.  Demonstrate by means of direct N-body sims that a very massive binary system can be readily dynamically ejected from a R136-like cluster, through a close encounter with a very massive system.  One out of four N-body cluster models produces a dynamically ejected very massive binary system wit ha mass comparable to R144.  The system has a system mass of ~355 Msun [the binary system is this massive?] and is located at 36.8 pc from the center of its parent cluster, moving away from the cluster with a velocity of 57 km/s at 2 Myr as a result of a binary-binary interaction.  This implies that R144 could have been ejected from R136 through a strong encounter with another massive binary or single star.  In addition, discuss all massive binaries and single stars which are ejected dynamically from their parent cluster in the N-body models.

1311.2937
Constraining dark matter-baryon scattering with linear cosmology
Dvorkin, Bum, Kamionkowski

Derive constraints on elastic scattering between baryons and DM using Planck CMB data and Lya forest data from SDSS.  Elastic scattering allows baryons and DM to exchange momentum, affecting the dynamics of linear density perturbations in the early Universe.  Derive constraints to scattering cross sections of the form sigma propto v^n, allowing for a wide range of velocity dependencies with n between -4 and 2.  Improve and correct previous estimates where they exist, including velocity-independent cross section as well as DM millicharge and EM dipole moments.  Ly-a forest data dominates the constraints for n>-3, where the improvement over CMB data alone can be several orders of magnitude.  Dark matter-baryon scattering cannot affect the halo mass function on mass scales M>1e12 Msun.  Results imply, model-independently, that a baryon in the halo of a galaxy like MW does not scatter from DM particles during the age of the galaxy.

1311.2956
The evolution of the dust temperatures of galaxies in the SFR$-M_{\ast}$ plane up to $z$$\,\thicksim\,$$2$
Magnelli et al

Evolution of dust temperatures of galaxies in the SFR-M* plane up to z~2 using observations from Herschel.  From galaxies with reliably SFRs, M* and z estimates, grid the SFR-M* parameter space in several z ranges and estimate the many T_dust of each SFR-M*-z bin.  Dust temperatures are inferred using the stacked FIR flux densities of the bins.  At all z, T-dust increases with L_IR, sSFR==SFR/M*, and distances with respect to the MS (main sequence) of the SFR-M* plane (==log[sSFR(galaxy)/sSFR_MS(M*,z)]).  The T-dust-sSFR and t_dust-D_sSFR_MS correlations are statistically more significant than the T-dust-L_IR one.  While the slopes of these 3 correlations are z-independent, their normalization evolve from z=0 and z~2.  Convert these results into a recipe to derive T-dust from SFR, M* and z.  The existence of a strong T-dust-D_sSFR_MS correlation provides information on the dust and gas content of galaxies.  (i) The slope of the T-dust-D_sSFR_MS correlation can be explained by the increase of the SFE==SFR/Mgas with D_sSFR_MS as found locally by molecular gas studies.  (ii) At fixed D_sSFR_MS, the constant T-dust observed in galaxies probing large ranges in SFR and M* can be explained by an increase or decrease of the number of SF regions with comparable SFE enclosed in them.  (iii) At high redshift, the normalization towards hotter temperature of the T-dust-D_sSFR_MS correlation can be explained by the decrease of the metallicities of galaxies or by the increase of the SFE of MS galaxies [how about increasing CMB temp?].  All these results support the hypothesis that the conditions prevailing in the SF regions of MS and far-above-MS galaxies are different.

1311.3039
On the radius of habitable planets
Alibert

Drive a radius above which a planet is likely not habitable, based on the presence of a C-cycle as a necessary condition for long-term habitability.  Must fulfill two constraints: surface conditions compatible wit the existence of liquid water, and no ice layer at the bottom of a putative global ocean.  Above a given radius, these two constraints cannot be met.  Use 5-layer model (core, inner mantle, outer mantle, ocean, and atmosphere), for different masses and composition of the planets (Fe/Si ratio in particular).  Results show that for planets in the Super-Earth mass range (1-12 Mearth), the maximum that a planet, with a composition similar to that of the Earth, can have varies between 1.7 and 2.2 Rearth.  This radius is reduced when considering planets with higher Fe/Si ratios and taking radiation into account when computing the gas envelope structure.  These results can be used to infer, from radius and mass determinations using high-precision transit observations like those that will soon be performed by the CHaracterizing ExOPlanet Satellite (CHEOPS), which planets are likely not habitable, and therefore which ones should be considered as best targets for further habitability studies. 

1311.3101
Possible climates on terrestrial exoplanets
Forget, Leconte

To first order, climate primarily depends on 1) the atmospheric composition and the volatile inventory; 2) the incident stellar flux; 3) the tidal evolution of the planetary spin, which can notably lock a planet with a permanent night side.  [more content skipped]

1311.3246
Lithium abundance and surface magnetic fields: new constraints in magnetic models of M dwarfs
MacDonald, Mullan

Precise values of masses and radii, recently made available by eclipsing binary studies, makes modeling of M dwarfs worthwhile.  Measured radii consistently larger than standard stellar models.  Previously: magnetic fields inhibit the onset of convection according to physics-based prescription.  New constraints on the models of M dwarfs now provide measurements of Li abundance: key aspect of Li in terms of setting constraints on magnetic modeling is that Li burning starts at T=2.5 MK, and temperatures of just such magnitude are associated with the base of the convection zone: magnetic inhibition of convective onset can shift this base slightly closer to the surface, i.e. to slightly lower temperatures, thereby reducing the amount of Li depletion compared to a non-magnetic model.  In the present paper, consider how the magneto-convection models handle the new test of stellar structure provided by Li measurements.  Among the prime systems listed, find that plausible magnetic models work well for 2 systems but not for one (the fourth system on the list does not have enough info to warrant magnetic modeling).  For the one that doesn't fit, suggest that the observed Li may have been accreted from a circumstellar disk.  Find that the magneto-convection models of the 3 yield results which are consistent with the observed correlation between magnetic flux and X-ray luminosity.  

1311.3317
Velocity dispersions and dynamical masses of a large sample of quiescent galaxies at z>1: improved measures of the growth in mass and size
Belli, Newman, Ellis

Spectroscopy of 103 massive galaxies, 0.9<z<1.6; 56 are quiescent with high S/N absorption one spectra, gives robust stellar velocity dispersions for largest sample at z>1.  Effective radii from HST images; calculate dynamical masses and address key questions relating to the size growth of quiescent galaxies over 0<z<2.  Examine the relationship between stellar and dynamical masses at high z, finding that it closely follows that determined locally. Also confirm the utility of the locally-established empirical calibration which enables high-z velocity dispersions to be estimated photometrically, and determine its accuracy to be 35%.  To address recent suggestions that progenitor bias (continued arrival of recently-quenched larger galaxies) can largely explain the size evolution of quiescent galaxies, examine the growth at fixed velocity dispersion assuming this quantity is largely unaffected by the merger history.  Demonstrate that significant size and mass growth have clearly occurred in individual systems.  Parameterizing the relation between mass and size growth over 0<z<1.5 as R propto M^alpha, find alpha = 1.6pm0.3, in agreement with theoretical expectations from simulations of minor mergers.  Relaxing the assumption that the velocity dispersion is unchanging, examine growth assuming a constant ranking in galaxy velocity dispersion.  This approach is applicable only to the large-dispersion tail of the distribution, but yields a consistent growth rate of alpha=1.4pm0.2.  Both methods confirm that progenitor bias alone is insufficient to explain new observations and that quiescent galaxies have grown in both size and stellar mass over 0<z<1.6.  

1311.3372
Predictions for the detection of Earth and Mars Trojan asteroids by the Gaia satellite
Todd et al

Solar system objects down to V=20 mag observed, including Near-Eath Asteroids and objects at Solar elongations as low as 45 degrees, which are difficult to observe with ground-based telescopes.  Simulation show that Gaia will not detect the Earth trojan 2010 TK7, although it will detect any Earth Trojans with diameters larger than 600m.  Also find that Gaia will detect the currently known Mars Trojans and could discover more than 100 new Mars Trojans as small as 400m in diameter.  The results of the Gaia mission will tsp the predictions about the Mars Trojan asteroid population and lead to greater understanding about the evolution of the Solar System.

1311.3461
H0 revisited
Efstathiou

[short title!]  Reanalysis of Riess+2011 (R11) Cephid data using revised geometric maser distance to NGC 4258 of Humphreys+2013.  Explore different outlier rejection criteria designed to give a reduced chi-sq of unity and compare the results with the R11 rejection algorithm, which produces a reduced chi-squared that is substantially less than unity and, in some cases, seems to underestimate the errors on parameters.  Show the there are sub-luminous low metallicity Cepheids in the R11 sample that skew the global fits of the period-luinosity relation.  This has a small but non-negligible impact on the global fits using NGC 4258 as a distance scale anchor, but adds a poorly constrained source of systematic error when using the LMC as an anchor.  Also show that the MW Cepheid sample with accurate parallax measurements leads to a distance to NGC 4258 that is in tension with the maser distance.  Conclude that H0 based on NGC 4258 maser distance is H0=70.6 pm 3.3 km/s/Mpc, compatible within 1 sigma with the current determination from Planck for the base six-parameter LCDM cosmology.  If the H-band period-luminosity relation is assumed to be independent of metallicity and the three distance anchors are combined, Find H0=72.5pm2.5 km/s/Mpc, which differs by 1.9 sigma from the Planck values.  The differences between the Planck results and these estimates of H0 are not large enough to provide compelling evidence for new physics at this stage. 

1311.3467
A possible resolution of tension between {\it Planck} and Type Ia supernova observations
Li et al

Tension between Planck and SNIa can be alleviated if the light-curve fitting parameters are first calibrated with the help of the distance-duality relation in the distance estimation in SNe Ia observations with the angular diameter distance data of the galaxy clusters and then re-estimate the distances for the SNe Ia with the corrupted fitting parameters.  This was used to explore their cosmological implications in the context of the spatially flat cosmology.  Find a higher value for the matter density parameter, Omega_m, as compared to that from the original SNLS3, which is in agreement with Planck at 68.3% CL.  With absolute magnitude of SNe Ia determined first, obtain constraint on H0 with SNLS3 alone, also consistent with Planck.

1311.3662
Rotation of the cosmic microwave background polarization from weak gravitational lensing
Dai

When CMB photon travels from LSS through space-time metric perturbations, the polarization vector may rotate about its direction of propagation.  This gravitational rotation is distinct from, and occurs in addition to, the lensing deflection of the photon trajectory.  This rotation can be sourced by vector or tensor metric perturbations at linear order and is fully coherent with the curl deflection field.  It modifies the lensed CMB polarization power spectra as well as the temperature-polirzation cross-correlations.  Present complete results for WL of the full-sky CMB PS by general linear metric perturbations, taking into account both deflection of the photon trajectory and rotation of the polarization.  For the case of lensing by gravitational waves, show that the B modes induced by the rotation largely cancel those induced by the curl component of deflection.

1311.3666
Discovery of three z>6.5 quasars in the VISTA Kilo-degree Infrared Galaxy (VIKING) survey
Venemans et al

Optical surveys have to date discovered >60 quasars up to z~6.4, a limit set by the use of the z-band and CCD detectors.  Only z>6.4 quasar discovered at z=7.08, using NIR imaging. Report 3 new z>6.4 quasars in 332 sq deg of VIKING, thus extending the number from 1 to 4.  The newly discovered quasars have z=6.61, 6.75, and 6.89.  The absolute magnitudes are between -26.0 and -25.5, 0.6-1.1 mag fainter than the other z>6.4 quasar.  NIR spectroscopy revealed the MGII emission line in all three objects.  The quasars are powered by black holes with masses of ~(1-2)e9 Msun.  In the probed range 6.44<z<7.44, can set a lower limit on the space density of supermassive BHs of rho(M_BH>1e9 Msun)>1.1e-9 Mpc^-3.  The discovery of 3 quasars in the survey area is insistent with the z=6 quasar luminosity function when extrapolated to z~7.  Do not find evidence for a steeper decline in the space density of quasars with increasing redshift from z=6 to 7.  

1311.3670
The evolution of the dust and gas content in galaxies
Santini, … Genzel, et al

Herschel PACS and SPIRE observations on GOODSS, GOODSN and COSMOS to estimate the average Mdust of galaxies on a M*-SFR grid.  Study the scaling relations between Mdust, M* and SFR at z<=2.5.  No clear evolution of Mdust is observed at fixed SFR and M*.  Find a  tight correlation between SFR and Mdust, likely a consequence of the SK law.  The M*-Mdust correlation observed by previous works flattens or sometimes disappears when fixing the SFR.  Most if ti likely derives from the combination of the Mdust-SFR and M*-SFR correlations.  Investigate the gas content as inferred by converting Mdust by assuming that the dust/gas ratio scales linearly with the gas metallicity.  All galaxies in the sample follow, within uncertainties, the same SFR-Mgas relation (integrated S-K law), which broadly agrees with CO-based results for the bulk of the population, despite the completely different approaches.  The majority of galaxies at z~2 from stars with an efficiency (SFE==SFR/Mgas) ~5 times higher than at z~0.  It is not clear what fraction of such variation is an intrinsic redshift evolution and what fraction arises from selection effect.  The gas fraction (fgas) decreases with M* and increases with SFR, and does not evolve with z at fixed M* and SFR.  Explain these trends by introducing a universal relation between fgas, M* and SFR, non-evolving out to z~2.5.  Galaxies move across this relation as their gas content evolves in time.  Use the 3d fundamental fgas-M*-SFR relation and the z evolution of the Main Sequence to estimate the evolution of fgas in the average population of galaxies as a function of z and M*, and find evidence a downsizing scenario.