202 research outputs found
Fitting the Continuum Component of A Composite SDSS Quasar Spectrum Using CMA-ES
Fitting the continuum component of a quasar spectrum in UV/optical band is
challenging due to contamination of numerous emission lines. Traditional
fitting algorithms such as the least-square fitting and the Levenberg-Marquardt
algorithm (LMA) are fast but are sensitive to initial values of fitting
parameters. They cannot guarantee to find global optimum solutions when the
object functions have multiple minima. In this work, we attempt to fit a
typical quasar spectrum using the Covariance Matrix Adaptation Evolution
Strategy (CMA-ES). The spectrum is generated by composing a number of real
quasar spectra from the Sloan Digital Sky Survey (SDSS) quasar catalog data
release 3 (DR3) so it has a higher signal-to-noise ratio. The CMA-ES algorithm
is an evolutionary algorithm that is designed to find the global rather than
the local minima. The algorithm we implemented achieves an improved fitting
result than the LMA and unlike the LMA, it is independent of initial parameter
values. We are looking forward to implementing this algorithm to real quasar
spectra in UV/optical band.Comment: 23 pages, 8 figures, 5 table
The Effect of Variability on the Estimation of Quasar Black Hole Masses
We investigate the time-dependent variations of ultraviolet (UV) black hole
mass estimates of quasars in the Sloan Digital Sky Survey (SDSS). From SDSS
spectra of 615 high-redshift (1.69 < z < 4.75) quasars with spectra from two
epochs, we estimate black hole masses, using a single-epoch technique which
employs an additional, automated night-sky-line removal, and relies on UV
continuum luminosity and CIV (1549A) emission line dispersion. Mass estimates
show variations between epochs at about the 30% level for the sample as a
whole. We determine that, for our full sample, measurement error in the line
dispersion likely plays a larger role than the inherent variability, in terms
of contributing to variations in mass estimates between epochs. However, we use
the variations in quasars with r-band spectral signal-to-noise ratio greater
than 15 to estimate that the contribution to these variations from inherent
variability is roughly 20%. We conclude that these differences in black hole
mass estimates between epochs indicate variability is not a large contributer
to the current factor of two scatter between mass estimates derived from low-
and high-ionization emission lines.Comment: 76 pages, 15 figures, 2 (long) tables; Accepted for publication in
ApJ (November 10, 2007
Swift UVOT Observations of Core-Collapse SNe
We review recent UV observations of core-collapse supernovae (SNe) with the
Swift Ultra-violet/Optical Telescope (UVOT) during its first two years.
Rest-frame UV photometry is useful for differentiating SN types by exploiting
the UV-optical spectral shape and more subtle UV features. This is useful for
the real-time classification of local and high-redshift SNe using only
photometry. Two remarkable SNe Ib/c were observed with UVOT -- SN2006jc was a
UV bright SN Ib. Swift observations of GRB060218/SN2006aj began shortly after
the explosion and show a UV-bright peak followed by a UV-faint SN bump. UV
observations are also useful for constraining the temperature and ionization
structure of SNe IIP. Rest-frame UV observations of all types are important for
understanding the extinction, temperature, and bolometric luminosity of SNe and
to interpret the observations of high redshift SNe observed at optical
wavelengths.Comment: Figures are enlarged and colorized from print versio
Double-Damped Lyman Alpha Absorption: A Possible Large Neutral Hydrogen Gas Filament Near Redshift z=1
We report the discovery of two damped Ly-alpha absorption-line systems (DLAs)
near redshift z=1 along a single quasar sightline (Q1727+5302) with neutral
hydrogen column densities of N(HI) = (1.45\pm0.15)\times10^{21} and
(2.60\pm0.20)\times10^{21} atoms/cm2. Their sightline velocity difference of
13,000 km/s corresponds to a proper separation of 106h_{70}^{-1} Mpc if
interpreted as the Hubble flow (Omega_m=0.3, Omega_Lambda=0.7). The random
probability of such an occurrence is significantly less than 3%. With follow-up
spectroscopy, we find [Zn/H] = -0.58\pm0.15 (26.5% solar) and -1.32\pm0.28
(4.7% solar), respectively, and [Cr/H] = -1.26\pm0.15 (5.5% solar) and
-1.77\pm0.28 (1.7% solar), respectively, which is evidence for depletion onto
grains. Follow-up IR images show the two most likely DLA galaxy candidates to
have impact parameters of 22h_{70}^{-1} kpc and 32h_{70}^{-1} kpc if near z=1.
They are significantly underluminous relative to the galaxy population at z=1.
To investigate the possibility of additional high-N(HI) absorbers we have
searched the SDSS database for z>1 quasars within 30 arcmin of the original
sightline. Five were found, and two show strong MgII-FeII absorption near z=1,
consistent with classical DLA absorption approx 37% of the time, but almost
always N(HI) > 10^{19} atoms/cm2. Consequently, this rare configuration of four
high-N(HI) absorbers with a total sightline velocity extent of 30,600 km/s may
represent a large filament-like structure stretching over a proper distance of
241h_{70}^{-1} Mpc along our sightline, and a region in space capable of
harboring excessive amounts of neutral gas. Future studies of this region of
the sky are encouraged.Comment: ApJL, accepte
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