3,966 research outputs found
The Spectral Energy Distribution of Normal, Starburst and Active Galaxies
We present the results of an extensive literature search of multiwavelength
data for a sample of 59 galaxies, consisting of 26 Starbursts, 15 Seyfert 2's,
5 LINER's, 6 normal spirals and 7 normal elliptical galaxies. The data include
soft X-ray fluxes, ultraviolet and optical spectra, near, mid/far infrared
photometry and radio measurements, selected to match as closely as possible the
IUE aperture (10" X 20"). The galaxies are separated into 6 groups with similar
characteristics, namely, Ellipticals, Spirals, LINER's, Seyfert 2's, Starbursts
of Low and High reddening, for which we create average spectral energy
distributions (SED). The individual groups SED's are normalized to the
7000\AA flux and compared, looking for similarities and differences
among them.The bolometric fluxes of different types of galaxies were calculated
integrating their SED's. These values are compared with individual waveband
flux densities, in order to determine the wavebands which contribute most to
the bolometric flux. Linear regressions were performed between the bolometric
and individual band fluxes for each kind of galaxy. These fits can be used in
the calculation of the bolometric flux for other objects of similar activity
type, but with reduced waveband information. We have also collected
multiwavelength data for 4 HII regions, a thermal supernova remnant, and a
non-thermal supernova remnant (SNR), which are compared with the Starburst
SED's.Comment: 29 pages, 13 postscript figures and 10 tables. To appear in The
Astronomical Journa
Starbursts and Star Clusters in the Ultraviolet
Hubble Space Telescope ultraviolet (UV) images of nine starburst galaxies
reveal them to be highly irregular, even after excluding compact sources
(clusters and resolved stars). Most (7/9) are found to have a similar intrinsic
effective surface brightnesses, suggesting that a negative feedback mechanism
is setting an upper limit to the star formation rate per unit area. All
starbursts in our sample contain UV bright star clusters indicating that
cluster formation is an important mode of star formation in starbursts. On
average about 20% of the UV luminosity comes from these clusters. The brightest
clusters, or super star clusters (SSC), are preferentially found at the very
heart of starbursts. The size of the nearest SSCs are consistent with those of
Galactic globular clusters. The luminosity function of SSCs is well represented
by a power law with a slope alpha ~ -2. There is a strong correlation between
the far infrared excess and the UV spectral slope. The correlation is well
modeled by a geometry where much of their dust is in a foreground screen near
to the starburst, but not by a geometry of well mixed stars and dust.Comment: 47 pages, text only, LaTeX with aaspp.sty (version 3.0), compressed
postscript figures available at
ftp://eta.pha.jhu.edu/RecentPublications/meurer
New Solutions of the Inflationary Flow Equations
The inflationary flow equations are a frequently used method of surveying the
space of inflationary models. In these applications the infinite hierarchy of
differential equations is truncated in a way which has been shown to be
equivalent to restricting the set of models considered to those characterized
by polynomial inflaton potentials. This paper explores a different method of
solving the flow equations, which does not truncate the hierarchy and in
consequence covers a much wider class of models while retaining the practical
usability of the standard approach.Comment: References added, and a couple of comment
Jet directions in Seyfert galaxies: B and I imaging data
We present the results of broad-band B and I imaging observations for a
sample of 88 Seyfert galaxies (29 Seyfert 1's and 59 Seyfert 2's), selected
from a mostly isotropic property, the flux at 60m. We also present the B
and I imaging results for an additional sample of 20 Seyfert galaxies (7
Seyfert 1's and 13 Seyfert 2's), selected from the literature and known to have
extended radio emission. The I band images are fitted with ellipses to
determine the position angle and ellipticity of the host galaxy major axis.
This information will be used in a future paper, combined with information from
radio observations, to study the orientation of radio jets relative to the
plane of their host galaxies (Kinney et al. 2000). Here we present surface
brightness profiles and magnitudes in the B and I bands, as well as mean
ellipticities and major axis position angles.Comment: To appear in The Astrophysical Journal Supplement Series, June 2000.
48 pages, 7 tables, 19 gif and 11 postscript figures. Better quality figures
can be obtained with the autho
Parallel J-W Monte Carlo Simulations of Thermal Phase Changes in Finite-size Systems
The thermodynamic properties of 59 TeF6 clusters that undergo
temperature-driven phase transitions have been calculated with a canonical
J-walking Monte Carlo technique. A parallel code for simulations has been
developed and optimized on SUN3500 and CRAY-T3E computers. The Lindemann
criterion shows that the clusters transform from liquid to solid and then from
one solid structure to another in the temperature region 60-130 K.Comment: 4 pages, 5 figures; presented at the conference on computational
physics, Aachen (2001) accepted for publication in Comp.Phys.Com
Numerical solutions of the three-dimensional magnetohydrodynamic alpha-model
We present direct numerical simulations and alpha-model simulations of four
familiar three-dimensional magnetohydrodynamic (MHD) turbulence effects:
selective decay, dynamic alignment, inverse cascade of magnetic helicity, and
the helical dynamo effect. The MHD alpha-model is shown to capture the
long-wavelength spectra in all these problems, allowing for a significant
reduction of computer time and memory at the same kinetic and magnetic Reynolds
numbers. In the helical dynamo, not only does the alpha-model correctly
reproduce the growth rate of magnetic energy during the kinematic regime, but
it also captures the nonlinear saturation level and the late generation of a
large scale magnetic field by the helical turbulence.Comment: 12 pages, 19 figure
Boundary Effective Field Theory and Trans-Planckian Perturbations: Astrophysical Implications
We contrast two approaches to calculating trans-Planckian corrections to the
inflationary perturbation spectrum: the New Physics Hypersurface [NPH] model,
in which modes are normalized when their physical wavelength first exceeds a
critical value, and the Boundary Effective Field Theory [BEFT] approach, where
the initial conditions for all modes are set at the same time, and modified by
higher dimensional operators enumerated via an effective field theory
calculation. We show that these two approaches -- as currently implemented --
lead to radically different expectations for the trans-Planckian corrections to
the CMB and emphasize that in the BEFT formalism we expect the perturbation
spectrum to be dominated by quantum gravity corrections for all scales shorter
than some critical value. Conversely, in the NPH case the quantum effects only
dominate the longest modes that are typically much larger than the present
horizon size. Furthermore, the onset of the breakdown in the standard
inflationary perturbation calculation predicted by the BEFT formalism is likely
to be associated with a feature in the perturbation spectrum, and we discuss
the observational signatures of this feature in both CMB and large scale
structure observations. Finally, we discuss possible modifications to both
calculational frameworks that would resolve the contradictions identified here.Comment: Reworded commentary, reference added (v2) References added (v3
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