13,962 research outputs found
Radiative Transfer and Radiative driving of Outflows in AGN and Starbursts
To facilitate the study of black hole fueling, star formation, and feedback
in galaxies, we outline a method for treating the radial forces on interstellar
gas due to absorption of photons by dust grains. The method gives the correct
behavior in all of the relevant limits (dominated by the central point source;
dominated by the distributed isotropic source; optically thin; optically thick
to UV/optical; optically thick to IR) and reasonably interpolates between the
limits when necessary. The method is explicitly energy conserving so that
UV/optical photons that are absorbed are not lost, but are rather redistributed
to the IR where they may scatter out of the galaxy. We implement the radiative
transfer algorithm in a two-dimensional hydrodynamical code designed to study
feedback processes in the context of early-type galaxies. We find that the
dynamics and final state of simulations are measurably but only moderately
affected by radiative forces on dust, even when assumptions about the
dust-to-gas ratio are varied from zero to a value appropriate for the Milky
Way. In simulations with high gas densities designed to mimic ULIRGs with a
star formation rate of several hundred solar masses per year, dust makes a more
substantial contribution to the dynamics and outcome of the simulation. We find
that, despite the large opacity of dust to UV radiation, the momentum input to
the flow from radiation very rarely exceeds L/c due to two factors: the low
opacity of dust to the re-radiated IR and the tendency for dust to be destroyed
by sputtering in hot gas environments. We also develop a simplification of our
radiative transfer algorithm that respects the essential physics but is much
easier to implement and requires a fraction of the computational cost.Comment: 25 pages, 17 figures, submitted to MNRA
Recommended from our members
Chelydra serpentina
Number of Pages: 4Integrative BiologyGeological Science
Anisotropy of the Microwave Sky at 90 GHz: Results from Python II
We report on additional observations of degree scale anisotropy at 90~GHz
from the Amundsen-Scott South Pole Station in Antarctica. Observations during
the first season with the Python instrument yielded a statistically significant
sky signal; in this paper we report the confirmation of that signal with data
taken in the second year, and on results from an interleaving set of fields.Comment: 10 pages, plus 2 figures. Postscript and uufiles versions available
via anonymous ftp at ftp://astro.uchicago.edu/pub/astro/ruhl/pyI
Simulating multiple merger pathways to the central kinematics of early-type galaxies
Two-dimensional integral field surveys such as ATLAS^3D are producing rich
observational data sets yielding insights into galaxy formation. These new
kinematic observations have highlighted the need to understand the evolutionary
mechanisms leading to a spectrum of fast-rotators and slow-rotators in
early-type galaxies. We address the formation of slow and fast rotators through
a series of controlled, comprehensive hydrodynamical simulations sampling
idealized galaxy merger scenarios constructed from model spiral galaxies.
Idealized and controlled simulations of this sort complement the more
'realistic' cosmological simulations by isolating and analyzing the effects of
specific parameters, as we do in this paper. We recreate minor and major binary
mergers, binary merger trees with multiple progenitors, and multiple sequential
mergers. Within each of these categories of formation history, we correlate
progenitor gas fraction, mass ratio, orbital pericenter, orbital ellipticity,
and spin with remnant kinematic properties. We create kinematic profiles of
these 95 simulations comparable to ATLAS^3D data. By constructing remnant
profiles of the projected specific angular momentum (lambda_R = /
, triaxiality, and measuring the incidences of kinematic
twists and kinematically decoupled cores, we distinguish between varying
formation scenarios. We find that binary mergers nearly always form fast
rotators. Slow rotators can be formed from zero initial angular momentum
configurations and gas-poor mergers, but are not as round as the ATLAS^3D
galaxies. Remnants of binary merger trees are triaxial slow rotators.
Sequential mergers form round slow rotators that most resemble the ATLAS^3D
rotators.Comment: MNRAS, in press, 12 pages, 15 figure
Time relaxation of interacting single--molecule magnets
We study the relaxation of interacting single--molecule magnets (SMMs) in
both spatially ordered and disordered systems. The tunneling window is assumed
to be, as in Fe8, much narrower than the dipolar field spread. We show that
relaxation in disordered systems differs qualitatively from relaxation in fully
occupied cubic and Fe_8 lattices. We also study how line shapes that develop in
''hole--digging'' experiments evolve with time t in these fully occupied
lattices. We show (1) that the dipolar field h scales as t^p in these hole line
shapes and show (2) how p varies with lattice structure. Line shapes are not,
in general, Lorentzian. More specifically, in the lower portion of the hole,
they behave as (h/t^p)^{(1/p)-1} if h is outside the tunnel window. This is in
agreement with experiment and with our own Monte Carlo results.Comment: 21 LaTeX pages, 6 eps figures. Submitted to PRB on 15 June 2005.
Accepted on 13 August 200
Suspensions of supracolloidal magnetic polymers: self-assembly properties from computer simulations
We study self-assembly in suspensions of supracolloidal polymer-like
structures made of crosslinked magnetic particles. Inspired by self-assembly
motifs observed for dipolar hard spheres, we focus on four different topologies
of the polymer-like structures: linear chains, rings, Y-shaped and X-shaped
polymers. We show how the presence of the crosslinkers, the number of beads in
the polymer and the magnetic interparticle interaction affect the structure of
the suspension. It turns out that for the same set of parameters, the rings are
the least active in assembling larger structures, whereas the system of Y- and
especially X-like magnetic polymers tend to form very large loose aggregates
Comparison of CAD for Rectangular Microstrip Antennas
Calculations of several cases for rectangular microstrip antennas using more accurate cavity model have been compared with the conventional cavity calculations, expressions generated by curve fitting to full wave solutions and published experimental values for a variety of different substrate thickness and patch sizes with width to length ratio of 1.5 and with r = 10.8 and r = 2.33
Radius Dependent Luminosity Evolution of Blue Galaxies in GOODS-N
We examine the radius-luminosity (R-L) relation for blue galaxies in the Team
Keck Redshift Survey (TKRS) of GOODS-N. We compare with a volume-limited, Sloan
Digital Sky Survey sample and find that the R-L relation has evolved to lower
surface brightness since z=1. Based on the detection limits of GOODS this can
not be explained by incompleteness in low surface-brightness galaxies. Number
density arguments rule out a pure radius evolution. It can be explained by a
radius dependent decline in B-band luminosity with time. Assuming a linear
shift in M_B with z, we use a maximum likelihood method to quantify the
evolution. Under these assumptions, large (R_{1/2} > 5 kpc), and intermediate
sized (3 < R_{1/2} < 5 kpc) galaxies, have experienced Delta M_B =1.53
(-0.10,+0.13) and 1.65 (-0.18, +0.08) magnitudes of dimming since z=1. A simple
exponential decline in star formation with an e-folding time of 3 Gyr can
result in this amount of dimming. Meanwhile, small galaxies, or some subset
thereof, have experienced more evolution, 2.55 (+/- 0.38) magnitudes. This
factor of ten decline in luminosity can be explained by sub-samples of
starbursting dwarf systems that fade rapidly, coupled with a decline in burst
strength or frequency. Samples of bursting, luminous, blue, compact galaxies at
intermediate redshifts have been identified by various previous studies. If
there has been some growth in galaxy size with time, these measurements are
upper limits on luminosity fading.Comment: 34 Total pages, 15 Written pages, 19 pages of Data Table, 13 Figures,
accepted for publication in Ap
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