1203.2607
A primordial star in the heart of the Lion
Caffau, et al
Study a metal poor star selected from SDSS spectra, reobserve at intermediate and high resolution; derive stellar parameters from photometry. Use 1D ATLAS models for spectra analysis, apply 3d and non-LTE corrections. [Fe/H]=-4.89 measured, one of the lowest known; absence of C and N enhancements indicates it has the lowest metallicity Z<7.4e-7 ever detected. No O measurement possible.
1203.2608
"Galaxy," Defined
Willman, Strader
Growing number of low luminosity and low surface brightness astronomical objects challenge notion of galaxies and star clusters; propose definition of galaxy that does not depend on CDM model of the universe. Galaxy: "gravitationally bound collection of stars whose properties cannot be explained by a combination of baryons and Newton's laws of gravity." Examine the classification of ultra-faint dwarfs, globular clusters, ultra-compact dwarfs, and tidal dwarfs. Kinematic studies an effective diagnostic over wide regime, but less useful for compact or very faint systems. Explore the utility of using the [Fe/H] spread as a diagnostic; public measurements for 16 MW dwarfs and 24 globular clusters to calculate spreads and uncertainties. Results: (i) no known, old star cluster with M_V>-10 has significant (>0.1 dex) spread in its Fe abundance; (ii) most known ultra-faint dwarfs can be unambiguously classified with a combination of kinematic and [Fe/H] observations; (iii) the observed [Fe/H] spreads in massive (>1e6 Msun) globular clusters do not necessarily imply that they are the stripped nuclei of dwarfs, nor a need for DM; and (iv) if UCD galaxies reside in dark matter haloes akin to those of UFDs of the same half-light radii, then they will show no clear dynamical signature of dark matter. Suggest several measurements that may assist the future classification of massive globular clusters, UCDs, and ultra-faint galaxies.
1203.2609
The source coins of submillimetre galaxies detected at 1.1mm
Scott, ..., Chapin, ... Halpern, ... Scott, Scoville, et al
Source counts of galaxies discovered at sub-mm and mm-wavelengths provide important information on the evolution of IR-bright galaxies. Combine data from 6 blank-field surveys at 1.1mm with AzTEC, totally 1.6 sq. deg in area with root-mean-square depths ranging from 0.4 to 1.7 mJy, and derive the strongest constraints to date on the 1.1mm source counts at flux densities S91100)=1-12mJy. Extend counts to ~20mJy from another AzTEC survey; see tentative evidence for enhancement relative to the exponential drop in the counts at S(1100)~13mJy and a smooth connection to the bright source counts at >20mJy measured at SPT; excess may be due to SL effects [!]. Compare counts to predictions from SAM and phenomenological models, and find: for most, the agreement is quite good at flux densities >4mJy, but find discrepancies at lower 1.1mm flux densities, and none of them are consistent with observed turnover in the normalized counts at S(1100)<2mJy. New results therefore may require modifications to existing evolutionary models for low luminosity galaxies. Alternatively, the discrepancy could arise from limited knowledge of the SED of faint galaxies in the local universe.
1203.2610
Numerical modeling of Auriga's Wheel -- a new ring galaxy
Smith, Lane, Conn, Fellhauer
Auriga's wheel: a bridge linking the ring of stars with neighboring elliptical galaxy; a recently discovered collisional ring galaxy. Use N-body/SPH modeling, study collisions between elliptical and late-type galaxy; near direct collision with some inclination in disk is found to reproduce the morphology ~50 Myr following the collision. Relatively low velocity (150 km/s) to form the bridge and match the separation. Best match model suggests total disk galaxy is ~5 times more massive than the elliptical. Find velocity of expansion of the ring is sensitive to the mass of the elliptical, while insensitive to the encounter velocity. Evolve into the future; mucleus moves further away in the direction of the stellar bridge; nucleus eventually merges with the elliptical galaxy ~100 Myr after present. Ring continues to expand for ~200 Myr before collapsing back. Low initial relative velocity of the two galaxies will eventually result in a complete merger.
1203.2611
Smooth(er) stellar mass maps in CANDELS: constraints on the longevity of clumps in high-redshift star-forming galaxies
Wuyts, .. Genzel, ... Bell, Deckel, Faber, ... Grogin, ... Koekemoer, Koo, ...Newman, et al
323 SF galaxies at 0.5<z<1.5 and 326 SF galaxies at 1.5<z<2.5 in the ERS and CANDELS-Deep regions of GOODS-South analyzed. Massive galaxies >1e10 Msun, have sSFR > 1/t_H. Model the 7-band optical ACS + NIR WFC3 SED of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints. Variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. Find: redder colors, older stellar ages, and increased dust extinction in nuclei of galaxies; big SF clumps less prominent or invisible on the inferred stellar mass distributions [?]. Off-center clumps contribute up to ~20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SF galaxies at z~1 and z~2, with the factional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Consistent with an inside-out disk growth scenario with a brief (100-200 Myr) episodic local enhancements in SF superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, if efficient on the orbital timescale.
1203.2612
An extremely primitive halo star
Caffau, et al
Lack of low-metallicity low-mass stars implies that low-mass stars (<0.8 Msun, those that survive to present day) cannot form at low Z, but here is a star found with Z=4.5e-5 Zsun, with a chemical pattern typical of classical extremely metal poor stars (no C, N, O). Li not detected, echo observed trend in Li depletion; implies stellar material must have experienced temperatures above 2e6 K in its history, a rather particular formation condition or internal mixing process for low Z, low mass stars.
1203.2613
Rapidly accreting supergiant protostars: embryos of supermassive black holes?
Hosokawa, Omukai, Yorke
Direct collapse of supermassive stars (SMSs) possible pathway for generating SMBH in early universe; could form via rapid mass accretion with Mdot~0.1-1 Msun/yr during the gravitational collapse of an atomic-cooling primordial gas cloud. Study how stars would evolve under such extreme rapid mass accretion, until 1000 Msun is reached. Calculate interior structure of accreting stars with primordial element abundances. For accretion rates higher than 0.01 Msun/yr, stellar evolution is qualitatively different from that expected at lower rates; high rate accretion exceeds radius of 100 Rsun, monotonically increase with stellar mass; R propto M*^0.5 in all cases; at 1000 Msun, radius at 7000 Rsun (~30 AU). Higher accretion rates shifts onset of H burning toward higher stellar masses; If accretion rate >0.1 Msun/yr, no significant H burning even after 1000 Msun accreted onto the protostar. Such "supergian" protostars have effective temperatures as low as Teff=5000K throughout evolution. Hardly emit ionizing photons. Do not create HII region or significantly heat surroundings; radiative feedback unable to hinder the growth of rapidly accreting stars to masses in excess of 1000 Msun if accretion rate is >0.01 Msun/yr.
1203.2614
Optimal mass configurations for lensing high-redshift galaxies
Wong, Ammons, Keeton, Zabludoff
Gravitational lensing properties of LoSs containing multiple cluster-scale halos, study motivated by their ability to lens very high-z (~10) sources into detectability. Control for the total mass along the LoS, isolate effects of distributing the mass among multiple halos and of varying the physical properties of the halos. Multiple-halo LoS can increase magnified source-plane region compared to the single cluster lens, and thus are generally better fields for detecting very high-z sources. Configurations that result in optimal lensing cross sections benefit from interactions between the lens potentials of the halos when they overlap somewhat on the sky, creating regions of high magnification in the source plane not present with the halos are considered individually. Effect of these interactions on the lensing cross section can be comparable to factor of ~3 changes in teetotal mass of the lens. Gain Gain in lensing cross section increases as the mass is split into more halos, provided that the lens potentials are projected close enough to interact with each other. A non-zero projected halo angular separation, equal halo mass ratio, and high projected halo concentration are the best mass configurations, whereas projected halo ellipticity, halo triviality, and the relative orientations of the halos are unimportant. Identified high-mass multiple-halo lines of sight in SDSS.
1203.2616
On combining galaxy clustering and weak lensing to unveil galaxy biasing via the halo model
Cacciato, Lahav, van den Bosch, Hoekstra, Dekel
Formulate the concept of NL and stochastic galaxy biasing in the framework of halo occupation statistics. Define galaxy bias function b_g(r_p) and galaxy-DM cross correlation function R_gm(r_p), where r_p is the projected distance. Use analytical halo model to predict how the scale dependence of b_g and R_gm over the range 0.1 Mpc/h < r_p < 30 Mpc/h, which depends on NL and stochasticity in HOD models. Quantify effect due to the presence of central galaxies, assumption of radial distribution of satellite galaxies, the richness of the halo, and the Poisson character of the probability to have a certain number of satellite galaxies in a halo of a certain mass. Overall, brighter galaxies reveal a stronger scale dependence, and out to a larger radius. In real-sapce, find that galaxy bias becomes scale independent, with R_g=1 for radii r>1-5Mpc/h, depending on luminosity; but is scale- dependent to much larger radii when using the projected quantities defined here. The projected bias functions have the advantage that they are more easily accessible observationally and their scale dependence carries are wealth of information regarding the properties of galaxy biasing. To observationally constrain the parameters of the HOD statistics and to unveil the origin of galaxy biasing, propose the use of the bias function Gamma_gm == b_g/R_gm. This function obtained via a combination of WL and galaxy clustering, and can be measured using existing and forthcoming imaging and spectroscopic galaxy surveys.
1203.2617
The importance of broad emission-line widths in single epoch black hole mass estimates
Assef, Frank, Grier, Kochanek, Denney, Peterson
Estimates of SMBHs in AGNs can be obtained efficiently only through single-epoch spectra, combining broad-emission-line widths and continuum luminosities; but the reliability of this method remain uncertain. Some study show that line widths contribute little information about the BH mass in these single-epoch estimates, and can be replaced by a constant value without significant loss of accuracy. Use a sample of nearby reverberation-mapped AGNs to show that this conclusion is not universally applicable. Use bulge luminosity to test how well the known M_BH-L_Bulge correlation is recovered when using randomly assigned line widths instead of the measured ones to estimate M_BH; find line widths provide significant information about M_BH, and that for this sample, the line width information is just as significant as that provided by the continuum luminosities. Discuss observational biases on the previous study; suggest the results can probably be explained as a bias of flux-limited, shallow quasar samples.
1203.2621
Evolution of galactic disks: multiple patterns, radial migration and disk outskirts
Minchev, Famaey, Quillen, Di Matteo, Combes, Vlajic, Erwin, Bland-Hawthorn
N-body Tree-SPH simulations: Disks initially truncated at three scale-lenths, can triple their radial extent, solely driven by secular evolution. Both type I and II observed disk surface-brightness profiles can be explained. Relate results to the strong angular momentum outward transfer, resulting from torques and radial migration associated with multiple patterns (central bars and spiral waves). Show that for stars ending up on cold orbits, the changes in angular momentum exhibit complex structure as a function of radius, unlike the expected effect of transient spirals alone. Evidence for NL coupling among m=1,2,3,4 density waves (m==patter multiplicity). Suggest: naturally occurring larger resonance widths at galactic radii beyond 4 scale-lengths may have profound consequences on the formation and location of breaks in disk density profiles, provided spirals are present at such large distances. Consdier effect of gas inflow and show that when in-plane smooth gas accretion of ~5 Msun/yr is included, the outer disks become more unstable, leading to a strong increase in the stellar velocity dispersion. This, in turn, causes the formation of a Type III profile in the old stellar population. Propose that observations of type II surface brightness profiles, combined with an up-turn in the stellar velocity dispersions beyond the disk break, could be a signature of ongoing gas-accretion. Suggest that disk outskirts comprised of stars migrated from the inner disk would have relatively large radial velocity diversions, and significant thickness when seen edge-on.
1203.2622
The optical cosmic epoch for precision cosmology
Loeb
THe statistical uncertainty in measuring the primordial density perturbations on a given comoving scale is dictated by the number of independent regions of that scale that are accessible to an observer. This number varies with cosmic time, and diminishes per Hubble volume in the distant maps in the distant past or future of the standard cosmological model. SHow that the best constraints on the initial power spectrum of linear density perturbations are accessible (e.g. through 21-cm intensity mapping) at z~10-50, and that the ability to constrain the cosmological initial conditions will deteriorate quickly in our cosmic future.
1203.2623
Young ages and other intriguing properties of massive compact galaxies in the local universe
Ferre-Mateu, Vazdekis, Trujillo, Sanchez-Blazquez, Ricciardelli, de la Rosa
Characterize kinematics, morphology, stellar populations and SFH of a sample of massive compact galaxies in nearby universe. Find: show elongated morphologies and are fast rotators. New high-quality long-slit spectra show that they have young mean luminosity-weighted ages and solar metallicities above [Z/H]>0. No significant stellar population gradients found. These objects had enormous star bursts which, in some cases, represent large fractions of their total stellar mass. These galaxies seem to be truly unique, as they do not follow the characteristic kinematical and stellar population patters of present-day massive ellipticals, spirals or dwarfs.
1203.2625
The S-star cluster at the center of the MW: on the nature of diffuse NIR emission in the inner tenth of a parsec
Sabha, et al
S-stars: a small cluster of high velocity stars surrounding Sgr A*. Constrain amount and nature of the stellar and DM mass associated with the cluster. Use NIR imaging for Ks luminosity function of cluster members, use diffuse BG emission and stellar number density counts; allows stellar light and mass contribution rom giant members. Use post-Newtonian N-body techniques to investigate the effect of stellar perturbations on the motion of S2, as means of detecting number and masses of the perturbers; find stellar mass derived from Ks luminosity is much smaller than the amount of mass present considering the uncertainties in the orbital motion of the star S2. Amount of light from fainter S-cluster members below the amount of residual light. If distribution of stars and stellar remnants is strongly peaked near Sgr A*, observed changes in the orbital elements of S2 can be used to constrain mass and numbers. Based on simulations of the cluster of high velocity stars, find at 2.2um close to confusion level or 8m class telescopes, blending will occur that last for typically 3 years before they dissolve due to proper motions [I assume they're talking about stellar appearances].
1203.2626
High-velocity clouds as streams of ionized and neutral gas in the halo of the MW
Lehner et al
High-velocity clouds (HVCs, ionized and neutral gas clouds at high galactic latitudes) may play an important role in the evolution of the MW; depends on their distances and total sky overing factor. Use 133 AGN sight-lines to HVC absorption, identify neutral, weakly ionized, or highly ionized HVCs over several decades in HI column densities. Sky covering factor is 68% for the entire Galactic sky (UV selected HVCs >90km/s); survey is complete. Predominantly ionized HVCs contain at least as much mass as the traditional HI HVCs, show that large HI HVC complese have generally ionized envelopes. Large regions of galactic sky covered with ionized high-velocity gas with little HI emission nearby. HVCs consistent with being decelerated or disrupted as they fall to the MW disk. HVCs with v>170 km/s largely associated with Magellatnic stream at b<0 deg, and its leading arm at b>0 deg. No evidence in the local group that any galaxy show a population of NVCs extending much farther away than 50 kpc from its host.
1203.2647
Strong biases in IR-selected gravitational lenses
Serjeant
Bright sub-mm selected galaxies found to be a rich source of SL lenses. But SL of extended sources leads to differential magnification. Use FG population of NFW plus deVauc density profile to quantify the effect of differential magnification on simulated FIR and sub-mm surveys. Emission line diagnostics are unaffected by magnification effects; C II and CO(J=1-0) fraction unaffected (used to infer densities and ionization parameters), but CO ladder significantly affected. FIR lensed galaxy surveys strongly select for high-z galaxies with caustics close to AGN, boosting apparent bolometric contribution of AGN Submm/mm surveys strongly select for caustics close to knots of star formation boosting the latter's bolometric fraction. Estimates of bolometric fractions from SED of SL IR galaxies are unreliable, unless a lens mass model is available to correct for differential magnification.
1203.2649
The optical gravitational lensing experiment. The catalog of stellar proper motions toward Magellanic clouds
Poleski
OGLE catalog.
1203.2656
Resolving the inner structure of QSO discs by fold caustic crossing events
Abolmasov, Shakura
As the title says.
1203.2681
Probing the inflation: small-scale power spectrum constraints from measurements of the CMB energy spectrum
Chuluba, Erickcek, Ben-Dayan
Spectral distortions of mu and y type depend on the shape and amplitude of the primordial power spectrum at k<1e4 Mpc^-1. Study constraints on the primordial power spectrum from COBE and forecasted for PIXIE. ...
1203.2695
Quantum corrections to gravity and their implications for cosmology and astrophysics
Fabris, et al
Quantum corrections may lead to surprisingly strong and interesting effects in astrophysics and cosmology: corrections to the Einstein-Hilbert action and to the cosmological constant. If quantum terms covariant and have sufficient magnitude, their functional form can be defined up to a single free parameter.
1203.2758
Constraining the dark energy equation of state with double source plane strong lenses
Collett, Auger, Belokurov, Marshall, Hall
Investigate possibility of constraining DE equation of state: measure ratio of Einstein radii in SL with two source planes. Quantity is independent of Hubble parameter; directly measures the growth of angular diameter distances as a function of redshift. Investigate prospects for a single double source plane system and for a forecast population of systems discovered by re-observing a population of single source lens already known. Find constraints comparable to current data sets (15% uncertainty on w) possible for a handful of systems. Method's degeneracy between Omega_m and w is almost orthogonal to CMB and BAO.
1203.2763
Magnetic fields of active galactic nuclei and quasars with polarized board H-alpha lines
Silant'ev, Gnedin, Buliga, Piotrovich, Natsvlishvili
No comments:
Post a Comment