Day 559

Friday.  And Saturday.  Sunday.

1312.0598
The impact of angular momentum on black hole accretion rates in simulations of galaxy formation
Rosas-Guevara, … Frenk, … et al

Feedback from AGN (energy liberated by gas accretion onto BHs) is a possible mechanism to explain the exponential cut-off at the massive end of the galaxy stellar mass function (SMF). SAMs of galaxy formation in which this form of feedback is assumed to suppress cooling in haloes where the gas cooling time is large compared to the dynamical time do indeed achieve a good match to the observed SMF.  Hydrosims of individual haloes in which gas is assumed to accrete onto the central BH at the Bondi rate have shown that a self-regulating regime is established in which the BH grows just enough to liberate an amount of energy comparable to the thermal energy of the halo.  However, this process is efficient at suppressing the growth not only of massive galaxies but also of galaxies like the MW, leading to disagreement with the observed SMF.  The Bondi accretion rate, however, is inappropriate when the accreting material has angular momentum.  Present an improved accretion model that takes into account the circularization and the subsequent viscous transport of in falling material and include it as a "sub grid" model in hydro sims of the evolution of haloes with a wide range of masses.  The resulting accretion rates are generally low in low mass (<1e11.5 Msun) halos, but show outbursts of Eddington-limited accretion during galaxy mergers.  During outbursts these objects strongly resemble quasars.  In higher mass haloes, gas accretion occurs continuously, typically at ~10% of the Eddington rate, which is conductive to the formation of radio jets.  The resulting dependence of the accretion behavior on halo mass induces a bread in the relation between galaxy stellar mass and halo mass in these simulations that matches observations.

1312.0602
GHOSTS I: a new faint very isolated dwarf galaxy at D = 12 +/- 2 Mpc
Monachesi, Bell, … et al

GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick disk, and Star clusters) HST/ACS survey found a new faint dwarf galaxy.  Member stars populate an approximately one mag range of its LF.  Using synthetic color-magnitude diagrams (CMDs) to compare with galaxy's CMD, find that the colors and magnitudes of GHOSTS I's individual stars are most consistent with being young He-burning and asymptotic giant branch stars at a distance of 12 pm 2 Mpc.  Morphologically, GHOSTS I appears to be actively forming stars, tentatively classify as dIrr galaxy; require larger magnitude range in its LF for a more secure classification.  Absolute magnitude is M_V=-9.85pm0.40, making it one of the least luminous dIrr galaxies known, and its metallicity is lower than [Fe/H] = -1.5 dex.  The HLR is 226 pm 38 pc and its ellipticity is 0.47 pm 0.07, similar to MW and M31 dwarf satellites at comparable luminosity.  There are no luminous massive galaxies or galaxy clusters within ~4 Mpc from GHOSTS I that could be considered as its host, making it a very isolated dwarf galaxy in the Local Universe.

1312.0607
The ages of young star clusters, massive blue stragglers and the upper mass limit of stars: analyzing age dependent stellar mass functions
Schneider, Izzard, … Langer, … et al

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems.  Show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters which can be used to infer their ages and to identify products of binary evolution.  Model the observed present day MF of the young Galactic Arches and Quintuplet star clusters using the rapid binary evolution code.  Find that shaping of the MF by stellar wind mass loss allows determination of the cluster ages to 3.5 pm 0.7 Myr and 4.8 pm 1.1 Myr, respectively [what were the previous estimates before?].  Exploiting the effects of binary mass exchange on the cluster mass function, find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars.  The resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of SF in these clusters.  Perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products.  Find that the most massive star is expected to be a binary product after 1.0 pm 0.7 Mpc in Arches and after 1.7 pm 1.0 Myr in Quintuplet.  Today, the most massive 9 pm 3 stars in Arches and 8pm3 in Quintuplet are expected to be such objects.  The findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 Msun limit and observations of four stars with initial masses of 165-320 Msun in R136 and SN 2007bi, which is thought to be a pair-instability SN from an initial 250 Msun star.  Using the stellar population of R136, revise the upper mass limit to values in the range 200-500 Msun.

1312.0608
Dissecting the gamma-ray background in search of dark matter
Cholis, Hooper, McDermott

Build and constrain a model for contributions to the extragalactic gamma-ray BG from astrophysical sources, including radio galaxies, SF galaxies, and blazers, using Fermi's catalog.  Combine with Fermi's measurement of the gamma-ray BG to derive constraints on the DM annihilation cross section, including contributions from both extragalactic and galactic halos and sub halos.  Competitive with Galactic Center and dSph galaxy constraints.  With 10 years of data, the improved constraints on the astrophysical source contributions will yield a sensitivity to DM annihilations that exceeds the strongest current constraints by a factor of ~5-10.

1312.0613
The habitable epoch of the early universe
Loeb

CMB had a T of 273-300K at 100<(1+z)<110, allowing early rocky planets (if any existed) to have liquid water chemistry on their surface and be habitable, irrespective of the distance from a star.  In standard LCDM, the first SF haloes within Hubble volume started collapsing at these redshifts, allowing the chemistry of life to possibly begin with the universe was 15 Myrs old.  The possibility of life starting when the average matter density was a million times bigger than it is today argues against the anthropic explanation for the low value of the cosmological constant.

1312.0615
On the evolution of the cosmic ionizing background
Fontanot, et al

Study the observed cosmic ionizing BG as a constraint on the sources responsible for the ionization of the Universe.  LF of LBGs at fixed Ly continuum photon escape fraction not able to reproduce the z evolution of this background; employ extrapolations of the high-z LFs to describe the contribution of LBGs to the ionizing photon rate, taking into account the smoothing of the baryonic perturbations, due to the BG itself, as well as a possible sharp increase of the escape fraction in dwarf galaxies.  Under the hypothesis of a dominant contribution of LBGs to cosmic reionization, results suggest that sources fainter than the current observational limits should be characterized by escape fractions of the order of ~0.1-0.3 (larger than the current estimates for bright galaxies) to account for a z>6 reionization and the measured evolution of cosmic ionizing background, at the same time.  The contribution to the background from quasars turns out to be relevant at z<3.  Overall, results support the case for dedicated observations of faint galaxies in the rest-frame UV, in order to better determine their physical properties.  Observed escape fractions outside proposed range bear relevant consequences on the nature of the astrophysical sources responsible for cosmic ionization and/or its buildup process.

1312.0936
The mass-radius relation between 60 exoplanets smaller than 4 Earth radii
Weiss, Marcy

Masses and radii of 60 exoplanets < 4 r_Earth with orbital periods shorter than 100 days.  Find nearly linear mass-raidus relation: M/M_E = 3.17 (R/R_E)^0.87, which is a shallower power-law index than in many previous mass-radius relations.  RMS mass is 3.9 M_E, reduced chi sq = 3.1, indicates diversity in planet compositions below 4 R_E.  The mass-raidus and mass-density relations reflect that planet density decreases as radius increases, indicating that larger exoplanets have a significant fraction of volatiles by volume (such as H/He envelopes).  Exoplanets have densities comparable to that of Earth at R=1.5 R_E, indicating likely rocky compositions among planets smaller than 1.5 R_E.  The scaling of the mass-radius relationship for exoplanets smaller than 1.5 R_E is not well-constrained but if SS terrestrial planets are included, find that relationship of M/M_E = 1.08 (R/R_E)^3.45 is a significant improvement of the nearly linear relationship.

1312.0943
Three gravitationally lensed supernovae behind CLASH galaxy clusters
Patel, .. Zitrin, Riess, .. Sako, .. Coe, Bartelmann, … et al

Observation of 3 gravitationally lensed SNe in CLASH, each detected in HST optical and IR images.  Two likely to be SNe Ia, the last a core-collapse SN.  The SNe Ia brighter in magnitude than expected by 1.0pm0.2 and 0.2pm0.2 mags.  Independent magnification estimate gives 0.83 and 0.28 increase in magnification.  The two SNe Ia provide a new test of the cluster lens model predictions: find that the magnification based on the SN Ia brightness and those predicted by the lens maps are consistent.  Results herald the promise of future observations of samples of cluster-lensed SNe Ia to help illuminate the DM distribution in clusters of galaxies, through the direct determination of absolute magnifications.

1312.0945
The mass-concentraion-redshift relation of cold dark matter haloes
Ludlow, Navarro, angulo, Boylan-Kolchin, Springel, Frenk, White

Show how assembly histories may be used to predict concentrations for haloes of all mass and at any redshift.  Link between concentration and the "collapse redshift" of a halo, as well as why concentration depends on mass and redshift solely through the dimensionless "peak height" mass parameter, $nu(M,z)=delta_crit(z)/sigma(M,z)$.  Combine these results with analytic mass accretion histories to extrapolate the c(M,z) relations to mass regimes difficult to reach through direct simulation.  Model predicts that, at given z, c(M) should deviate systematically from a simple power law at high masses, where concentrations approach a constant value, and at low masses, where concentrations are substantially lower than expected from extrapolating published empirical fits.  This correction may reduce the expected self-annihilation boost factor from substructure by about one order of magnitude.  The model also pre produces the c(M,z) dependence on cosmological parameters reported in earlier work, and thus provides a simple and robust account of the relation between cosmology and the mass-concentration-redshift relation of CDM haloes.

1312.1022
Are peculiar velocity surveys competitive as a cosmological probe?
Koda, Blake, … et al

Galaxy density and peculiar velocity relation improves constraints on the linear growth rate of cosmologicalLSS at low z, substantially reducing cosmic variance.  Present the results of Fisher matrix forecasts of correlated fields of galaxy density and velocity.  Peculiar velocity can improve the growth rate constraints by about a factor of two compared to density alone, if all information for k<0.2 h/Mpc can be used.  Future surveys can measure the growth rate f*sigma8 to 3% at z~0.025.  Although the velocity subsample is about an order of magnitude smaller than the redshift sample from the same survey, it improves the constraint by 40% compared to the same survey without velocity measurements.  Peculiar velocity surveys can also measure the growth rate as a function of wavenumber with 15-30 % uncertainties in bins with widths of 0.01 h/Mpc in the range 0.02 h/Mpc < k < 0.1 h/Mpc, which is a large improvement over galaxy density only.  Such measurements on very large scales can detect signatures of modified gravity or non-Gaussianity through scale-dependent growth rate or galaxy bias.  Use N-body simulations to improve the modeling of auto- and cross-PS of galaxy density and peculiar velocity by introducing a new z-space distortion term in the velocity, which has been neglected in previous studies.  The velocity PS has a damping in z space, which is larger than that naively expected from the similar effete in the galaxy power spectrum.

1312.1096
The M4 core project with HST --- I. Overview and first-epoch
Bedin et al

Observe core of M4, the nearest Galactic globular cluster, with HST and constrain the number of binaries with massive companions (BHs, NSs, or WDs) by measuring the "wobble" of the luminous (MS) companion around the center of mass of the pair, with an astrometric precision of ~50 micro-acrseconds.  The high spatial resolution and stable medium-band PSFs of WFC3/UVIS will make these measurements possible.  In this work describe (i) the motivation behind this study, (ii) observing strategy, (iii) the many other investigations enabled by this unique data set, and (iv) a preliminary reduction of the first-epoch data-set collected.

1312.1128
GLAMER part I:  A code for gravitational lensing simulations with adaptive mesh refinement
Metcalf, Petkova

Code for simulation of GL data.  AMR for choosing which rays to shoot based on the requirements of the source size, locate hand surface brightness distribution or to find critical curves/caustics.  A variety of source surface brightness models are implemented to represent galaxies and quasar emission regions.  The lensing mass can be represented by point masses (stars), smoothed immolation particles, analytic halo models, pixelized mass maps or any combinations of these.  The deflection and beam distortions (convergence and shear) are calculated by modified three algorithm when halos, point masses or particles are used and by FFT when has maps are used.  The combination of these methods allow for a very large dynamical range to be represented in a single simulation . Individual images of galaxies can be represented in a simulation that covers many square degrees.  For an individual strongly lensed quasar, sources sizes from the size of the quasar's host galaxy (~100 kpc) down th microlensing scales (1e-4 pc) can be probed in a self consistent simulation.  Descriptions of various tests of the code's accuracy are given.

1312.1170
Ray-tracing in pseudo-complex general relativity
Schönenbach et al

Ray-tracing methods applied to both standard GR and the pseudo-complex GR (pc-GR).  THe correction terms due to the investigated pc-GR model lead to weaker gravitational effects and slower orbital motions close to massive objets.  Thus, the accretion disk, surrounding a massive object, is brightened in pc-GR than in GR.  Iron K alpha emission line profiles are also calculated as those are good observable for regions of strong gravity.  Differences between the two theories are pointed out.

1312.1190
Astronomical redshifts and the expansion of space
Kaiser

Interpretation of redshift, "a pair of observers receding from each other in flat space-time where the effect is purely kinematic, is a subject of considerable debate.  It has been suggested that all redshifts are a relative velocity effect, raising the question of whether the wavelength always stretches in proportion to the emitter-receiver separation.  Here, show that for low z at least, Delta log (lambda/D) vanishes for a photon exchanged between any two freely-fralling observers in a spatially constant tidal field (D=space between the two), because such a field stretches wavelengths and the space between the observers identically.  But in general there is a non-kinematic, and essentially gravitational, component of the redshift that is given by a weighted average of the gradient of the tidal field along the photon path.  While the redshift can always be formally expressed using the Doppler formula, in situations where the gravitational redshift dominates, the 'relative velocity' is typically quite different from the rate of change of $D$ and it is misleading to think of the z as being a velocity or 'kinematic' effect.