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

Grist: Grid-based Data Mining for Astronomy

The Grist project is developing a grid-technology based system as a research environment for astronomy with massive and complex datasets. This knowledge extraction system will consist of a library of distributed grid services controlled by a work ow system, compliant with standards emerging from the grid computing, web services, and virtual observatory communities. This new technology is being used to find high redshift quasars, study peculiar variable objects, search for transients in real time, and fit SDSS QSO spectra to measure black hole masses. Grist services are also a component of the "hyperatlas" project to serve high-resolution multi-wavelength imagery over the Internet. In support of these science and outreach objectives, the Grist framework will provide the enabling fabric to tie together distributed grid services in the areas of data access, federation, mining, subsetting, source extraction, image mosaicking, statistics, and visualization

QSOs and Absorption Line Systems Surrounding the Hubble Deep Field

We have imaged a 45x45 sq. arcmin. area centered on the Hubble Deep Field (HDF) in UBVRI passbands, down to respective limiting magnitudes of approximately 21.5, 22.5, 22.2, 22.2, and 21.2. The principal goals of the survey are to identify QSOs and to map structure traced by luminous galaxies and QSO absorption line systems in a wide volume containing the HDF. We have selected QSO candidates from color space, and identified 4 QSOs and 2 narrow emission-line galaxies (NELGs) which have not previously been discovered, bringing the total number of known QSOs in the area to 19. The bright z=1.305 QSO only 12 arcmin. away from the HDF raises the northern HDF to nearly the same status as the HDF-S, which was selected to be proximate to a bright QSO. About half of the QSO candidates remain for spectroscopic verification. Absorption line spectroscopy has been obtained for 3 bright QSOs in the field, using the Keck 10m, ARC 3.5m, and MDM 2.4m telescopes. Five heavy-element absorption line systems have been identified, 4 of which overlap the well-explored redshift range covered by deep galaxy redshift surveys towards the HDF. The two absorbers at z=0.5565 and z=0.5621 occur at the same redshift as the second most populated redshift peak in the galaxy distribution, but each is more than 7Mpc/h (comoving, Omega_M=1, Omega_L=0) away from the HDF line of sight in the transverse dimension. This supports more indirect evidence that the galaxy redshift peaks are contained within large sheet-like structures which traverse the HDF, and may be precursors to large-scale ``pancake'' structures seen in the present-day galaxy distribution.Comment: 36 pages, including 9 figures and 8 tables. Accepted for publication in the Astronomical Journa

Spectral Decomposition of Broad-Line AGNs and Host Galaxies

Using an eigenspectrum decomposition technique, we separate the host galaxy from the broad line active galactic nucleus (AGN) in a set of 4666 spectra from the Sloan Digital Sky Survey (SDSS), from redshifts near zero up to about 0.75. The decomposition technique uses separate sets of galaxy and quasar eigenspectra to efficiently and reliably separate the AGN and host spectroscopic components. The technique accurately reproduces the host galaxy spectrum, its contributing fraction, and its classification. We show how the accuracy of the decomposition depends upon S/N, host galaxy fraction, and the galaxy class. Based on the eigencoefficients, the sample of SDSS broad-line AGN host galaxies spans a wide range of spectral types, but the distribution differs significantly from inactive galaxies. In particular, post-starburst activity appears to be much more common among AGN host galaxies. The luminosities of the hosts are much higher than expected for normal early-type galaxies, and their colors become increasingly bluer than early-type galaxies with increasing host luminosity. Most of the AGNs with detected hosts are emitting at between 1% and 10% of their estimated Eddington luminosities, but the sensitivity of the technique usually does not extend to the Eddington limit. There are mild correlations among the AGN and host galaxy eigencoefficients, possibly indicating a link between recent star formation and the onset of AGN activity. The catalog of spectral reconstruction parameters is available as an electronic table.Comment: 18 pages; accepted for publication in A