553 research outputs found
Decomposition of AGN host galaxy images
We describe an algorithm to decompose deep images of Active Galactic Nuclei
into host galaxy and nuclear components. Currently supported are three galaxy
models: A de-Vaucouleurs spheroidal, an exponential disc, and a two-component
disc+bulge model. Key features of the method are: (semi-)analytic
representation of a possibly spatially variable point-spread function; full
two-dimensional convolution of the model galaxy using gradient-controlled
adaptive subpixelling; multiple iteration scheme. The code is computationally
efficient and versatile for a wide range of applications. The quantitative
performance is measured by analysing simulated imaging data. We also present
examples of the application of the method to small test samples of nearby
Seyfert 1 galaxies and quasars at redshifts z < 0.35.Comment: 12 pages, 15 figures, accepted for publication in MNRA
A Catalytic Spectrophotometric Method for the Analytical Determination of Trace Amounts of Mercury (II)
Abstract A catalytic method has been developed for the determination of microgram amounts of mercury (II) based on its catalytic effect on the rate of a ligand substitution reaction. The reaction studied involved the substitution of cyanide in hexacyanoferrate (II) by resacetophenone benzoic acid hydrazone (2', 4'-dihydroxy propiophenone benzoic acid hydrazone) and the reaction was monitored spectrophotometrically. Satisfactory results were obtained for the determination of mercury (II) in the range 0.1086-0.9774 µg/ml. The relative standard deviation was less than 2.1%. The method detection limit and limit of quantification was found to be 0.041 µg/ml and 0.083 µg/ml respectively (n=7). The correlation coefficient for the determination was found to be 0.9989. The effect of foreign ions on the determination was studied
The Discovery and Nature of Optical Transient CSS100217:102913+404220
We report on the discovery and observations of the extremely luminous optical
transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic
observations show this transient was coincident with a galaxy at redshift
z=0.147, and reached an apparent magnitude of V ~ 16.3. After correcting for
foreground Galactic extinction we determine the absolute magnitude to be M_V
=-22.7 approximately 45 days after maximum light. Based on our unfiltered
optical photometry the peak optical emission was L = 1.3 x 10^45 erg s^-1, and
over a period of 287 rest-frame days had an integrated bolometric luminosity of
1.2 x 10^52 erg. Analysis of the pre-outburst SDSS spectrum of the source shows
features consistent with a Narrow-line Seyfert1 (NLS1) galaxy. High-resolution
HST and Keck followup observations show the event occurred within 150pc of
nucleus of the galaxy, suggesting a possible link to the active nuclear region.
However, the rapid outburst along with photometric and spectroscopic evolution
are much more consistent with a luminous supernova. Line diagnostics suggest
that the host galaxy is undergoing significant star formation. We use extensive
follow-up of the event along with archival CSS and SDSS data to investigate the
three most likely sources of such an event; 1) an extremely luminous supernova;
2) the tidal disruption of a star by the massive nuclear black hole; 3)
variability of the central AGN. We find that CSS100217 was likely an extremely
luminous type IIn supernova that occurred within range of the narrow-line
region of an AGN. We discuss how similar events may have been missed in past
supernova surveys because of confusion with AGN activity.Comment: submitted to Ap
Spectrophotometry and structural analysis of 5 comets
We discuss the morphology and spectrophotometry of 5 comets visible in
August, 2001. We decompose comae into coma profiles and azimuthally
renormalized images, in which general and local features are quantitatively
comparable. Comet 19P/Borrelly showed a strong gas fan toward the solar
direction, but no detectable gas in the tail. Dust in its inner coma was
collimated toward the antisolar direction and the tail, with no dust in the
outer coma. The contribution of spatial variations structure was moderate,
about 35%. Comet 29P Schwassmann-Wachmann 1 was observed in outburst: we
detected ``spinning'' jet structures. A high level of dust production resulted
in an unusually high Af\rho=16600 cm. The spatial variations reached -77%, at
the minimum, due in part to a jet and a ring-like structure in 1 arcminute
distance from the nucleus. In comet C/2001 A2, we detected a strong
post-perihelion increase of dust and gas activity, in which the C_2 profile
became one magnitude brighter over a 3-day period. For comets C/2000 SV74 and
C/2000 WM1, we present detailed pre-perihelion spectrophotometry and
morphological information. Comet C/2000 SV74 showed high dust production
(Af\rho=1479 cm). Its coma suggests a steady-state outflow of material, while
the low contribution of spatial variations support high level activity. The
coma of C/2000 WM1 is dominated by solar effects, and CO+ forms the bulk of its
gas activity. Despite its large heliocentric distance, we observed a nice tail.Comment: 10 pages, 4 figures, accepted for publication in A&
Evolution and Impact of Bars over the Last Eight Billion Years: Early Results from GEMS
Bars drive the dynamical evolution of disk galaxies by redistributing mass
and angular momentum, and they are ubiquitous in present-day spirals. Early
studies of the Hubble Deep Field reported a dramatic decline in the rest-frame
optical bar fraction f_opt to below 5% at redshifts z>0.7, implying that disks
at these epochs are fundamentally different from present-day spirals. The GEMS
bar project, based on ~8300 galaxies with HST-based morphologies and accurate
redshifts over the range 0.2-1.1, aims at constraining the evolution and impact
of bars over the last 8 Gyr. We present early results indicating that f_opt
remains nearly constant at ~30% over the range z=0.2-1.1,corresponding to
lookback times of ~2.5-8 Gyr. The bars detected at z>0.6 are primarily strong
with ellipticities of 0.4-0.8. Remarkably, the bar fraction and range of bar
sizes observed at z>0.6 appear to be comparable to the values measured in the
local Universe for bars of corresponding strengths. Implications for bar
evolution models are discussed.Comment: Submitted June 25, 2004. 10 pages 5 figures. To appear in Penetrating
Bars through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes a New Note,
eds. D. Block, K. Freeman, R. Groess, I. Puerari, & E.K. Block (Dordrecht:
Kluwer), in pres
Particle Dark Matter Constraints from the Draco Dwarf Galaxy
It is widely thought that neutralinos, the lightest supersymmetric particles,
could comprise most of the dark matter. If so, then dark halos will emit radio
and gamma ray signals initiated by neutralino annihilation. A particularly
promising place to look for these indicators is at the center of the local
group dwarf spheroidal galaxy Draco, and recent measurements of the motion of
its stars have revealed it to be an even better target for dark matter
detection than previously thought. We compute limits on WIMP properties for
various models of Draco's dark matter halo. We find that if the halo is nearly
isothermal, as the new measurements indicate, then current gamma ray flux
limits prohibit much of the neutralino parameter space. If Draco has a moderate
magnetic field, then current radio limits can rule out more of it. These
results are appreciably stronger than other current constraints, and so
acquiring more detailed data on Draco's density profile becomes one of the most
promising avenues for identifying dark matter.Comment: 13 pages, 6 figure
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