Monday. Quite productive yesterday (although I only finished half of what I wanted to do). Had dinner with Philippe as a thank-you for helping me out with moving the bed and signing the contract for the flat. Hope to use up some of the Bonn City Gutscheine (vouchers) for various things, like concerts, etc.
1110.4631
The X-ray properties of high-z FRI candicates in the COSMOS field
Tundo, Tozzi, Chiaberge
* okay, what the heck is a FRI?
* FRI: "Fanaroff-Riley I radio galaxies" (Fanaroff & Riley 1974) -- connection with elliptical massive galaxies in cluster at 1<z<2--can be used for cluster searches. Radio sources were divided into two classes by F&R, originally made based on the morphology of the large-scale radio emission, determined by distance between the brightest points in the radio emission. Class I: brightest towards the center (jets with plume, no hotspots at plume ends, low luminosity); Class II: brightest at the edges (dual jets with lobes and hotspots at the ends, high luminosity). Morphology turns out to reflect the method of energy transport in the radio source. FRIIs appear to transport energy efficiently to the ends of the lobs, while FRI beams are inefficient --the radiate a significant amount of their energy away as they travel. FRI/FRII division depends on host-galaxy environment: the I/II transition appears at higher luminosities in more massive galaxies. FRII jets remain relativisitc (>0.5c) till the end of the jet (hence the hotspot)--energy distribution consistent with this picture. FRI jets lose energy while they travel.
Report X-ray analysis of high-redshift (1<z<2) FRI sources, study nuclear properties by means of unresolved X-ray emission to constraint the presence of clusters surrounding the FRI sources. Among 19 FRI cancidates, 6 have an X-ray unresolved counterpart (plus 2 more, although not in the C-COSMOS catalog). Some of them have significant intrinsic absorption (N_H~1e22 cm^-2) and high X-ray luminosities wrt local FRIs. Stacking the non-detected sources, find evidence for unresolved soft X-ray emission and no detected hard emission (suggests unabsorbed spectrum). X-ray properties vary significantly from source to source among FRI candidates. Stacking all FRI candidates rules out presence of virialized haloes with temperature larger than 2-3 keV; upper limit on the average extended emission is still consistent with the prsence of ~1-2 keV hot gas.
1110.4634
Accretion onto BHs from large scalaes regulated by radiative feedback. II. Growht Rate and Duty Cycle
Park, Ricotti
Radiation-regulated accretion onto BHs from galactic scales: focus on effects of radiation pressure and angular momentum of gas on the periodic and short-lived luminosity bursts, found when the thermal pressure of the inoized sphere around the BH regulates the accretion rate. Simulations focus on intermediate-mass BH, but derive general scaling relationships. Find: once the ambient gas density exceeds a critical value n~5e6 cm^-3 / M_100Msun, the period of oscillations decreases rapidly [I guess the gas moves in faster at low density] and the duty cycle increases from 6% to 50% [more gas, AGN is turned on longer, less on-off oscillation, makes sense]. But maximum and mean accretion rates become Eddington-limited only if n> n_edd n_cr / T_4, where T_4 is the ambient gas temperature in units of 1e4K. In sub-Eddington regime, mean accretion rate onto BH is about 1% T4^2.5 of the BOndi rate (proportional to the thermal pressure of the ambient medium). Period of oscillation coincides with depletion time scale of the gas. n<n_cr depletion from pressure gradient; n>~ n_cr accretion onto the BH becomes the dominant gas depletion mechanism, explains the rapid decrease of the oscillation period and increasing duty cycle. Angular momentum of the accreting gas produces a time delay between the accretion rate near the sonic point and the luminosity output; something about alpha-model, that does not affect significantly the accretion rate and period of oscillations.
1110.4635
Optimized detection of shear peaks in weak lensing maps
Marian, Smith, Hilbert, Schneider
New method to extract cosmological constraints from WL peak counts ('hierarchical algorithm'). Combine information from WL maps sequentially smoothed with different-sized filters from largest to smallest, thus increasing the cosmological sensitivity of the resulting peak function. Compare cosmological constraints resulting from the peak abundance measured this way, with those using a filter of fixed size (standard WL peak studies). Use ray-tracing through N-body to get WL maps, as well as FIsher matrix formalism. Inclusion of low-S/N (~3) peaks yields [presumably with the multi-filter approach] constraints better than x2 single-sized filtering. For a large survey like Euclid or LSST combined with Planck CMB, the results for the hierarchical methods are: Delta n=0.0033, Delta Omega_m=0.0018, Delta sigma_8=0.0025, Delta w=0.0081. Forecast is conservative, since no knowledge of redshifts of the lenses assumed (single broad bin for source). If only peaks with S/N >=6 are considered, then there is little difference between the results of the two methods. Also examine the statistical properties of the hierarchical peak function: its covariance matrix has off-diagonal terms even for the highest-S/N bins, which are therefore not well described by a Poisson distribution.
* use more filter types, of different scales.
1110.4636
The Structure of the interstellar medium of star-forming galaxies
Hopkins, Quartaert, Murray
Present numerical methods for including stellar feedback in galaxy-scale simulations. Include: Heating by SNe (I & II), gas recycling and shock-heating from O-star & AGB winds, HII photoionization, and radiation pressure from stellar photons. Take energetics and time-dependence from stellar evolution models. Implement in simulations with pc-scale resolution, modeling galaxies from SMC-like dwarfs and MW analogues, to massive z~2 starburst disks. With feedback, ISM reaches a multi-phase steady state where GMCs continuously form, disperse, and re-form (unlike the case where there is none, in which gas cools and collapses without limit). Results: (1) SF galaxies self-regulate at Toomre Q~1. Most of volume is in diffuse host gas, with most of the mass in dense GMC complexes. The phase structure and gas mass at high densities are much more sensitive probes of stellar feedback physics then integrated quantities. (2) Different feedback mechanisms act on different scales: radiation & HII pressure are critical to prevent runaway collapse of dense gas in GMCs. SNe and stellar winds dominate the dynamics of volume-filling hot gas, primarily vents out the disk. (3) The galaxy-averaged SFR is determined by feedback. For a given feedback efficiency, restricting star formation to molecular gas or modifying the cooling function has little effect; but changing the feedback mechanisms directly translates to shifts off the Kennicutt-Schmidt relation. (4) self-gravity leads to marginally-bound GMCs with an M^-2 mass function with a cutoff at the Jeans mass; they live a few dynamical times before being disrupted by stellar feedback and turn ~1-10% of their mass into stars (increasing from dwarfs through starburst galaxies). Low-mass GMCs are preferentially unbound.
* Toomre Q parameter: instability criterion for differentially rotating disks.
* why not AGNs?
1110.4638
Stellar feedback in galaxies and the origin of galaxy-scale winds
Hopkins, Quataert, Murray
Feedback from massive stars: play a critical role in driving galactic super-winds that enrich the IGM and shape the galaxy mass function and mass-metallicity relation. Show that these feedback mechanisms drive galactic winds with outflow rates as high as x10-20 the galaxy SFR. The mass-loading efficiency (wind mass loss rate divided by SFR) scals inversely with circular velocity, consistent with momentum-conservation expectations. Study contributions of each feedback mechanism to galactic winds in a range of galaxy models, from SMC-like dwarfs & MW-analogues to z~2 clumpy disks. In massive, gals-rich systems (local starbursts and high-z galaxies), radiation pressure dominates wind generation. For NW-like spirals and dwarf galaxies the gas densities are much lower, and shock-heated gas from SNe and stellar winds dominates production of large-scale outflows. In all models, winds have multi-phase structure that depends on interactions between multiple feedback mechanisms operating on different spatial & time scales: any single mechanism fails to reproduce the winds observed. Provide functions for wind mass-loading and velocities as a function of galaxy properties, for use in cosmological simulations and semi-analytic models. These differ from typically-adopted formulae with explicit dependence on gas surface density that can be very important in both low-density dwarf galaxies and high-density gas-rich galaxies.
Astronomy colloquium (Oct 28, 11:00)
The multiphase extraplanar medium in spiral galaxies.
George Heald
Extraplanar region in spiral galaxies: interface between star-forming disk and the environment. Structure and kinematics of the baryonic material in this interface region are vital clues to the relative importance of various processes, such as cold gas accretions and galactic fountains, in determining the history of galaxies [why? the external environment thing?]. Strength and morphology of the magnetic fields in these regions may also be crucial to understanding the connection to the intergalactic medium. Describe results from two surveys : HALOGAS survey, and WSRT-SINGS survey. HALOGAS: first systematic investigation of cold gas accretion in nearby spiral galaxies; deep (120 hrs) WSRT observations of 22 edge-on galaxies; reveals presence of kinematically lagging extraplanar gas, and counterparts to the MW's high velocity clouds. WSRT-SINGS survey: polarimetric data for a partially overlapping galaxy sample; has lead to a common model of the magnetic field morphology in spiral galaxies. Conclude talk by describing directions for future work in both areas, possibly followed up by LOFAR and Square Kilometre Array.
Special Colloquium (Oct 26, 11:00)
New methods and tools for specifying the MW's magnetic field structure, and some implications for very high energy CR propagation
Phil Kronberg
MW's magnetic field structure recently measured: grand design around the sun (~1.5kpc), and a halo+disk magnetic field model. Define environment for HE CR propagation, to understand their energy-dependent anisotropies.
Special Colloquium (Oct 25, 14:00)
Mopra and the central molecular zone / Astronomy in Antarctica
Michael Burton
(1) Observe CMZ with Mopra, survey of CMZ with 18 molecular lines.
(2) Overview of Astronomy in Antarctica (neutrino, CMB, optical/IR/mm), and the cold, clear, dry and stable conditions of the high pleateau.
Master colloquium (Oct 25, 11:00)
Relativistic propagation effects in binary pulsars and the next generation of radio telescopes
Masooma Ali
Binary pulsar a powerful tool for testing gravity theories. Accurate measurement and analysis of ToAs (times of arrival) of pulses using timing models. Must understand limitations of timing models (due to better HW coming soon), based on the rst post-Newtonian approximation for the Shapiro propagation delay. Compare with analytic calculations and data simulations. Quantify at what level of timing precision will it be mandatory to introduce higher order corrections to model the observed ToAs. Conclusions for the most relativistic systems known at present (the Double Pulsar) and different configurations of pulsar binaries that may be discovered in the future.
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