1306.6623
Photoevaporation of circumstellar disks revisited: the dust-free case
Tanaka, Nakamoto, Omukai
Photoevaporation by stellar ionizing radiation is believed to play an important role in the dispersal of disks around young stars. The rate in the Hollenback+ model is standard, but was derived by the 1+1D approximation of ionizing radiation transfer, which assumes that diffuse radiation propagates in a direction vertical to the disk. Revisit the photo evaporation of dust-free disks by solving the 2d axisymmetric radiative transfer for steady-state disks. Determine that direct stellar radiation is more important than the diffuse field at the disk surface. The radial density distribution at the ionization boundary is represented by the single power-law with an index -3/2 in contrast to the conventional double power-law. FOr this distribution, the photo evaporation rate from the entire disk can be written as a function of the ionizing photon emissivity, Phi_EUV, from the central star and the disk outer radius, r_d, as follows: Mdot_PE=5.4e-5 x (Phi_EUV/49 sec^-1)^1/2 x (r_d/1000 AU) Msun/yr. This new rate depends on the outer disk radius rather than on the gravitational radius as in the conventional model, caused by the enhanced contribution to the mass loss from the outer disk annuli. In addition, discuss its applications to present-day as well as primordial star formation.
1306.6626
Kuiper belt occultation predictions
Fraser, ... Bianco, ... et al
Present observations of 7 large Kuiper Belt Objects. Extract a point source catalog with ~0.01" precision; astrometry of target KBOs with 0.04-0.08" precision within that catalog. Developed a new technique to predict the future occurrence of stellar occultations by KBOs. The technique makes use of a maximum likelihood approach with determines the best-fit adjustment to cataloged orbital elements of an object. Using simulations of a theoretical object, discuss the merits and weaknesses of this technique compared to the commonly adopted ephemeris offset approach. Demonstrate that both method suffer from separate weaknesses, and thus, together provide a fair assessment of the true uncertainty in a particular prediction. Present occultation predictions made by both methods for the 7 tracked objects, with dates as late as 2015. Discuss observations of 3 separate close passages of Quaoar to field stars, which reveal the accuracy of the element adjustment approach, and which also demonstrate the necessity of considering the uncertainty in stellar position wen assessing potential occultations.
1306.6632
Bubble-induced star formation in dwarf irregular galaxies
Kawata et al
Simulate the evolution of an isolated dIrr in a fixed DM halo, similar in size to WLM, to study the SF and feedback mechanism. Use the new N-body/smoothed particle chemodynaics code GCD+, which adopts improved hydrodynamics, metal diffusion between the gas particles and new modelling of star formation and stellar wind and SNe feedback. Comparing the simulations with and without stellar feedback effects, demonstrate that the collisions of bubbles produced by strong feedback can induce SF in a more widely spread area. Also demonstrate that the metallicity in SF regions is kept low due to the mixing of the metal-rich bubbles and the metal-poor ISM. Simulations also suggest that the bubble-induced SF leads to many counter-rotating stars. The bubble-induced SF could be a dominant mechanism to maintain SF in dIrrs, which is different from larger spiral galaxies where the non-axisymmetric structures, such as spiral arms, are a main driver of SF.
1306.6635
Can supermassive black hole seeds form in galaxy mergers?
Ferrara, Haardt, Salvaterra
[Answer: No.] Been suggested that SMBHs at z=5-6 might form from super fast (Mdot>1e4 Msun/yr) accretion occurring in unstable, massive nuclear gas disks produced by mergers of MW-size galaxies. Such mechanism is claimed to work also for gas enriched to solar metallicity. These results are based on idealized polytropic equation of state assumption, essentially preventing the gas from cooling. Show that under more realistic conditions, the disk rapidly (<1 yr) cools, the accretion rate drops, and the central core can grow only to ~100 Msun. In addition, most of the disk becomes gravitationally unstable in about 100 yr, further quenching the accretion. Conclude that this scenario encounters a number of difficulties that possibly make it untenable.
1306.6642
The galaxy environment of a QSO at z~5.7
Bañados et al
High-z quasars are believed to reside in massive haloes in the early Universe and should therefore be located in fields with overdensites of galaxies, which are thought to evolve into galaxy clusters seen in the local Universe. However, despite many efforts, the relationship between galaxy overdensities and z~6 quasars is ambiguous, which can possibly be attributed to the difficulty of finding galaxies with accurate redshifts in the vicinity of z~6 quasars. So far, over density searches around z~6 quasars are based on studies of LBGs, which probe a redshift range of Delta z~1. This range is large enough to select galaxies which may not be physically related to the quasar. Here, use deep narrow- and broad-band imaging to study the environment of the z=5.72 quasar ULAS J0203+0012. The redshift range probed by our narrow band selection of LAEs in Delta z~0.1, significantly narrower than LBG searches. This is the first time that LAEs are searched for near a z~6 quasar, to provide clues on the environments of quasars at the end of the Epoch of Reionization. Find: no enhancement of LAEs in the surroundings of the ULAS quasar in comparison with blank fields. Explore different explanations and interpretations for this non-dentection of a galaxy overdensity, including that a) the strong ionization from the quasar may prevent galaxy formation in its immediate vicinity and that b) high-z quasars may not reside in the center of the most massive DM haloes. [Need a LAE survey to see clustering characteristics of high-z galaxies wrt quasar clustering!]
1306.6652
A new interpretation of the far-infrared - radio correlation and the expected breakdown at high redshift
Schleicher, Beck
Observations of galaxies up to z~2 show a tight correlation between FIR and radio continuum emission. Explain the FIR - radio continuum correlation by relating SF and B-field strength in terms of turbulent B-field amplification, where turbulence is injected by SNe explosions from massive stars. Calculate the expected amount of turbulence in galaxies based on their SFRs, and infer the expected B-field strength due to turbulent dynamo amplification. Estimate the timescales for CR energy losses via synchrotron emission, inverse Compton scattering, ionization and bremsstrahlung emission, probing up to which redshift strong synchrotron emission can be maintained. Find that the correlation between SFR and B-field strength in the local Universe can be understood as a result of turbulent B-field amplification. If the typical gas density in the ISM increases at high z, expect an increase of the B-field strength and the radio emission, as indicated by current observations. Such an increase would imply a modification of the FIR - radio correlation. Expect a breakdown when inverse Compton losses start dominating over synchrotron emission. For a given SF surface density, calculate the redshift where the breakdown occurs, yielding z ~ (Sigma_SFR/0.0045 M_sun /kpc^2/yr)^(1/(6-alpha/2)). In this relation, the parameter \alpha describes the evolution of the characteristic ISM density in galaxies as (1+z)^alpha. Both the possible raise of the radio emission at high z and the final breakdown of the FIR -- radio correlation at a critical z will be probed by the Square Kilometer Array and its pathfinders, while the typical ISM density in galaxies will be probed with ALMA.
1306.6660
How does non-linear dynamics affect the baryon acoustic oscillation?
Sugiyama, Spergel
Study the NL behavior of BAO in the PS and the correlation function by decomposing the DM perturbations into the short-and long-wavelength modes. The evolution of the DM fluctuations can be described as a global coordinate transformation caused by the long-wavelength displacement vector acting on short-wavelength modes undergoing NL growth. This description clarifies the relation between the existing modified perturbation theories: the regularized multi-point propagator method, the Lagrangian resummation theory, and the standard perturbation theory. The regularized multi-point propagator method and the Lagrangian resummation theory partially include the NL effects from the global coordinate transformation. This implies that these two models do not have more effective information on the NL evolution of DM PS than the standard perturbation theory, as the global coordinate transformation cancels due to the translation symmetry in the ensemble average. The representation in this paper clarifies the success of the standard perturbation theory at the 2-loop level corrections in describing the amplitude of the NL PS. Propose an extension of the standard 2-loop level perturbation theory model of the NL PS that more accurately models the NL evolution of the BAO than the standard perturbation theory. This extended model predicts the smoothing parameter of the BAO peak at z=0.35 as ~7.7 Mpc/h and describes the small NL shift in the peak position due to the galaxy random motions.
1306.6676
Nebular excitation in z~2 star-forming galaxies from the SINS and LUCI surveys: the influence of shocks and AGN
Newman, ... Genzel, etal
Based on high-res, spatially resolved data of 10 z~2 SF galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, probe the excitation properties of high-z galaxies and the impact of AGN, shocks and photoionization. Explore how these spatially-resolved line ratios can inform the interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the `composite' region of the z~0 [NII]/Ha versus [OIII]/Hb diagnostic (BPT) diagram, between SF galaxies and those with AGN. Based on resolved measurements, find that some of these galaxies likely host an AGN, while other appear to be affected by the presence of shocks possibly caused by an outflow or from enhanced ionization parameter as compared with HII regions in normal local SF galaxies. Find that the mass-excitaton (MEx) diagnostic, which separates purely SF and AGN hosting local galaxies in the [OIII]/Hb versus stellar mass plane, does not properly separate z~2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z~2 mass-metallicity relation (i.e. to the mass they would have at z~0 with the same metallicity), find better agreement between the MEx and BPT diagnostics. Finally, find that metallicity calibrations based on [NII]/Ha are more biased by shocks and AGN at high-z than the [OIII]/Hb/[NII]/Ha calibration.
1306.6692
Lensing simulation and power spectrum estimation for high resolution CMB polarization maps
Louis, N æss, Das, Dunkley, Sherwin
Present efficient algorithms for CMB lensing simulation and PS estimation for flat-sky CMB polarization maps. Build a pure B-mode estimator to remedy E to B leakage due to partial sky coverage. Show that the estimators are unbiased, and consistent with the projected errors. Demonstrate algorithm using simulated observations of small sky patches with realistic noise and weights for upcoming CMB polarization experiments.
1306.6721
HMFcalc: an online tool for calculating dark matter halo mass functions
Murray, Power, Robotham
The DM halo mass function (HMF) is a characteristic property of cosmological structure formation models, quantifying the number density of DM haloes per unit mass in the Universe. A key goal of current and planned large galaxy surveys is to measure the HMF and to use it to test theories of DM and DE. Present a new web application for calculating the HMF -- the frontend HMFcalc and the engine hmf. HMF calc has been designed to be flexible, efficient and easy to use, providing observational and theoretical astronomers alike with the means to explore standard functional forms of the HMF or to tailor their own Outline the theoretical background needed to compute the HMF, show how it has been implemented in hmf, and finally provide worked examples that illustrate HMFcalc's versatility as an analysis too.
1306.6766
Planck and the local Universe: quantifying the tension
Verde, Protopapas, Jiminez
Compare Planck with local measurements of H0; if neutrino mass degenerate, there is more tension between the two (odds of 1:50 to 1:150)
1306.6791
A fast and simple algorithm for detecting large scale structures
Pillastrini
Propose a gravitational potential method (GPM) as a supercluster finder, based on the analysis of the local gravitational potential distribution measured by fast and simple algorithm applied to a spatial distribution of mass tracers. Two step process: (1) measures the comoving local gravitational potential generated by neighboring mass tracers at the position of a test point-like mass tracer. The computation extend to all mass tracers of the sample provides a detailed map of the negative potential fluctuations. The most negative gravitation potential is provided by the highest mass density or, in other words, the deeper is a potential fluctuations in a certain regions of space and denser are the mass tracers in that regions. Therefore, from a smoothed potential distribution, the deepest potential well detects unambiguously a high concentration in the mass tracer distribution. (2) apply a density contrast criterion to that mass concentration, a central bound core may be identified and quantified in terms of memberships and total mass. Results/conclusions: agreement with other methodologies confirms GPM as a straightforward and powerful as well as fast cluster finder useful for analyzing large datasets.
1306.6870
On the complementarity of galaxy clustering with cosmic shear and flux magnification
Duncan, Joachimi, Heavens, Heymans, Hidebrandt
Motivate the use of galaxy clustering measurements using photo-z information, including a contribution from flux magnification, as a probe of cosmology. Present cosmological forecasts when clustering data along is used, and when clustering is combined with a cosmic shear analysis. Consider two types of clustering analysis: firstly, clustering with only redshift auto-correlations in tomographic redshift bins; secondly, using all available redshift bin correlations. Finally, consider how inferred cosmological parameters may be biased using each analysis when flux magnification is neglected. Results are presented for a Stage III ground-based survey, and a Stage IV space-based survey modelled with photometric redshift errors, and values for the slope of the luminosity function inferred from CFHTLenS catalogues. Find that combining clustering information with shear can improve constraints on cosmological parameters, giving an improvement to a DETF-like FoM by a factor of 1.33 when only auto-correlations in z are used for the clustering analysis, rising to 1.52 when cross-correlations in redshift are also included. The addition of gg lensing gives further improvement, with increases in FoM by a factor of 2.82 and 3.7 for each type of clustering analysis respectively. The presence of flux magnification in a clustering analysis does not significantly affect the precision of cosmological constraints when combined with cosmic shear and gg lensing . However if magnification is neglected, inferred cosmological parameter values are biased, with biases in some cosmological parameters larger than statistical errors.
1306.6883
pyro: A teaching code for computational astrophysical hydrodynamics
Zingale
pyro: a simple, freely -available code to aid students in learning the computational hydrodynamics methods widely used in astrophysics.
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