5,300 research outputs found
Probing Cool and Warm Infrared Galaxies using Photometric and Structural Measures
We have analyzed a sample of nearby cool and warm infrared (IR) galaxies
using photometric and structural parameters. The set of measures include
far-infrared color (), total IR
luminosity (), radio surface brightness as well as radio,
near-infrared, and optical sizes. In a given luminosity range cool and warm
galaxies are considered as those sources that are found approximately below and above the mean color in the far-infrared
diagram. We find that galaxy radio surface brightness is well correlated with
color whereas size is less well correlated with color. Our analysis indicates
that IR galaxies that are dominated by cool dust are large, massive spirals
that are not strongly interacting or merging and presumably the ones with the
least active star formation. Dust in these cool objects is less centrally
concentrated than in the more typical luminous and ultra-luminous IR galaxies
that are dominated by warm dust. Our study also shows that low luminosity early
type unbarred and transitional spirals are responsible for the large scatter in
the diagram. Among highly luminous galaxies, late type unbarred
spirals are predominately warm, and early type unbarred and barred are
systematically cooler. We highlight the significance of diagram
in terms of local and high redshifts sub-millimeter galaxies.Comment: Accepted for publication in ApJ, 2006, 23 pages, 3 postscript
figures, 1 table. The table can be obtained on request from the author
X-ray Signatures of an Ionized Reprocessor in the Seyfert galaxy Ton S 180
We discuss the hard X-ray properties of the Seyfert galaxy Ton S 180, based
upon the analysis of ASCA data. We find the X-ray flux varied by a factor ~2 on
a time scale of a few thousand seconds. The source showed significantly higher
amplitude of variability in the 0.5-2 keV band than in the 2-10 keV band. The
continuum is adequately parameterized as a Gamma ~ 2.5 power-law across the
0.6--10 keV band . We confirm the recent discovery of an emission line of high
equivalent width, due to Fe K-shell emission from highly-ionized material.
These ASCA data show the Fe line profile to be broad and asymmetric and
tentatively suggest it is stronger during the X-ray flares, consistent with an
origin from the inner parts of an accretion disk. The X-ray spectrum is complex
below 2 keV, possibly due to emission from a blend of soft X-ray lines, which
would support the existence of an ionized reprocessor, most likely due to a
relatively high accretion rate in this source.Comment: 24 pages, 8 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journa
An Atlas of Warm AGN and Starbursts from the IRAS Deep Fields
We present 180 AGN candidates based on color selection from the IRAS
slow-scan deep observations, with color criteria broadened from the initial
Point-Source Catalog samples to include similar objects with redshifts up to
z=1 and allowing for two-band detections. Spectroscopic identifications have
been obtained for 80 (44%); some additional ones are secure based on radio
detections or optical morphology, although yet unobserved spectroscopically.
These spectroscopic identifications include 13 Sy 1 galaxies, 17 Sy 2 Seyferts,
29 starbursts, 7 LINER systems, and 13 emission-line galaxies so heavily
reddened as to remain of ambiguous classification. The optical magnitudes range
from R=12.0-20.5; counts suggest that incompleteness is important fainter than
R=15.5. Redshifts extend to z=0.51, with a significant part of the sample at
z>0.2. The sample includes slightly more AGN than star-forming systems among
those where the spectra contain enough diagnostic feature to make the
distinction. The active nuclei include several broad-line objects with strong
Fe II emission, and composite objects with the absorption-line signatures of
fading starbursts. These AGN with warm far-IR colors have little overlap with
the "red AGN" identified with 2MASS; only a single Sy 1 was detected by 2MASS
with J-K > 2. Some reliable IRAS detections have either very faint optical
counterparts or only absorption-line galaxies, potentially being deeply
obscured AGN. The IRAS detections include a newly identified symbiotic star,
and several possible examples of the "Vega phenomenon", including dwarfs as
cool as type K. Appendices detail these candidate stars, and the
optical-identification content of a particularly deep set of high-latitude IRAS
scans (probing the limits of optical identification from IRAS data alone).Comment: ApJ Suppl, in press. Figures converted to JPEG/GIF for better
compression; PDF with full-resolution figures available before publication at
http://www.astr.ua.edu/keel/aoagn.pd
Plasma Dynamics
Contains research objectives and summary of research.U.S. Atomic Energy Commission (Contract AT(11-1)-3070)National Science Foundation (Grant GK-37979X)National Science Foundation (Grant GK-28282X1
Recommended from our members
A Health Systems Approach to Integrated Community Case Management of Childhood Illness: Methods and Tools
Integrated community case management (iCCM) of childhood illness is an increasingly popular strategy to expand life-saving health services to underserved communities. However, community health approaches vary widely across countries and do not always distribute resources evenly across local health systems. We present a harmonized framework, developed through interagency consultation and review, which supports the design of CCM by using a systems approach. To verify that the framework produces results, we also suggest a list of complementary indicators, including nine global metrics, and a menu of 39 country-specific measures. When used by program managers and evaluators, we propose that the framework and indicators can facilitate the design, implementation, and evaluation of community case management
Applied Plasma Research
Contains research objectives and reports on three research projects.National Science Foundation (Grant GK-2581)Joint Services Electronics Program under Contract DA 28-043-AMC-02536(E
The Spectral Energy Distribution and Emission-Line properties of the NLS1 Galaxy Arakelian 564
We present the intrinsic spectral energy distribution (SED) of the NLS1
Arakelian 564, constructed with contemporaneous data obtained during a
multi-wavelength, multi-satellite observing campaign in 2000 and 2001. We
compare it with that of the NLS1 Ton S180 and with those obtained for BLS1s to
infer how the relative accretion rates vary among the Sy1 population. Although
the peak of the SED is not well constrained, most of the energy is emitted in
the 10-100 eV regime, constituting roughly half of the emitted energy in the
optical/X-ray ranges. This is consistent with a primary spectral component
peaking in the extreme UV/soft X-ray band, and disk-corona models, hence high
accretion rates. Indeed, we estimate that \dot{m}~1. We examine the emission
lines in its spectrum, and we constrain the physical properties of the
line-emitting gas through photoionization modeling. The line-emitting gas is
characterized by log n~11 and log U~0, and is stratified around log U~0. Our
estimate of the radius of the H\beta-emitting region ~10 \pm 2 lt-days is
consistent with the radius-luminosity relationships found for Sy1 galaxies. We
also find evidence for super-solar metallicity in this NLS1. We show that the
emission lines are not good diagnostics for the underlying SEDs and that the
absorption line studies offer a far more powerful tool to determine the
ionizing continuum of AGNs, especially if comparing the lower- and
higher-ionization lines.Comment: 15 pages, 10 figures; accepted for publication in The Astrophysical
Journal, LaTeX emulateapj.st
Plasmas and Controlled Nuclear Fusion
Contains reports on ten research projects split into three sections.National Science Foundation (Grant GK-2581
Spitzer view on the evolution of star-forming galaxies from z=0 to z~3
We use a 24 micron selected sample containing more than 8,000 sources to
study the evolution of star-forming galaxies in the redshift range from z=0 to
z~3. We obtain photometric redshifts for most of the sources in our survey
using a method based on empirically-built templates spanning from ultraviolet
to mid-infrared wavelengths. The accuracy of these redshifts is better than 10%
for 80% of the sample. The derived redshift distribution of the sources
detected by our survey peaks at around z=0.6-1.0 (the location of the peak
being affected by cosmic variance), and decays monotonically from z~1 to z~3.
We have fitted infrared luminosity functions in several redshift bins in the
range 0<z<~3. Our results constrain the density and/or luminosity evolution of
infrared-bright star-forming galaxies. The typical infrared luminosity (L*)
decreases by an order of magnitude from z~2 to the present. The cosmic star
formation rate (SFR) density goes as (1+z)^{4.0\pm0.2} from z=0 to z=0.8. From
z=0.8 to z~1.2, the SFR density continues rising with a smaller slope. At
1.2<z<3, the cosmic SFR density remains roughly constant. The SFR density is
dominated at low redshift (z<0.5) by galaxies which are not very luminous in
the infrared (L_TIR<1.e11 L_sun, where L_TIR is the total infrared luminosity,
integrated from 8 to 1000 micron). The contribution from luminous and
ultraluminous infrared galaxies (L_TIR>1.e11 L_sun) to the total SFR density
increases steadily from z~0 up to z~2.5, forming at least half of the
newly-born stars by z~1.5. Ultraluminous infrared galaxies (L_TIR>1.e12 L_sun)
play a rapidly increasing role for z>~1.3.Comment: 28 pages, 17 figures, accepted for publication in Ap
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