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

On the link between associated MgII absorbers and star formation in quasar hosts

A few percent of quasars show strong associated MgII absorption, with velocities (v_off) lying within a few thousand km/s from the quasar systemic redshift. These associated absorption line systems (AALs) are usually interpreted as absorbers that are either intrinsic to the quasar and its host, or arising from external galaxies clustering around the quasar. Using composite spectra of ~1,800 MgII AAL quasars selected from SDSS DR7 at 0.4<~ z<~2, we show that quasars with AALs with v_off<1500 km/s have a prominent excess in [OII]3727 emission (detected at >7sigma) at rest to the quasar host, compared to unabsorbed quasars. We interpret this [OII] excess as due to enhanced star formation in the quasar host. Our results suggest that a significant fraction of AALs with v_off<1500 km/s are physically associated with the quasar and its host, and are most likely large-scale flows with typical velocities of a few hundred km/s. AAL quasars also have dust reddening lying between normal quasars and the so-called dust-reddened quasars. We suggest that the unique properties of AAL quasars can be explained if they are the transitional population from heavily dust-reddened quasar to normal quasars in the formation process of quasars and their hosts. This scenario predicts a larger fraction of young bulges, disturbed morphologies and interactions of AAL quasar hosts compared to normal quasars. The intrinsic link between associated absorbers and quasar hosts opens a new window to probe massive galaxy formation and galactic-scale feedback processes, and provides a crucial test of the evolutionary picture of quasars.Comment: ApJ in press; v2 matched to the accepted version; table data included in the source fil

Supermassive Black Hole Mass Estimates Using Sloan Digital Sky Survey Quasar Spectra at 0.7 < z < 2

We present MgII-based black hole mass estimates for 27,602 quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release Three. This estimation is possible due to the existence of an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. We regenerate this correlation by applying our measurement method to UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the Hbeta broad line region's radius. Our mass estimation method uses the line dispersion rather than the full width at half maximum of the low-ionization MgII emission line. We measure MgII line dispersions for quasars whose spectra have been reconstructed using the most significant eigenspectra produced through Principal Component Analysis. We have tested the reliability of using reconstructed spectra in black hole mass estimation using a Monte Carlo simulation and by comparing the results from original and reconstructed Data Release Three spectra. We show that using reconstructed spectra not only makes bias-free mass estimation possible for quasars with low spectroscopic signal-to-noise ratio, but also reduces the intrinsic scatter of the distribution of the black hole masses to lower than 0.15 dex.Comment: 38 Pages, 12 figures, 3 Tables, 1 hyperlink to catalogue data. Accepted for publication in ApJ

Improved redshifts for SDSS quasar spectra

A systematic investigation of the relationship between different redshift estimation schemes for more than 91000 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6) is presented. The publicly available SDSS quasar redshifts are shown to possess systematic biases of Dz/(1+z)>=0.002 (600km/s) over both small (dz~0.1) and large (dz~1) redshift intervals. Empirical relationships between redshifts based on i) CaII H & K host galaxy absorption, ii) quasar [OII] 3728, iii) [OIII] 4960,5008 emission, and iv) cross-correlation (with a master quasar template) that includes, at increasing quasar redshift, the prominent MgII 2799, CIII] 1908 and CIV 1549 emission lines, are established as a function of quasar redshift and luminosity. New redshifts in the resulting catalogue possess systematic biases a factor of ~20 lower compared to the SDSS redshift values; systematic effects are reduced to the level of Dz/(1+z)<10^-4 (30km/s) per unit redshift, or <2.5x10^-5 per unit absolute magnitude. Redshift errors, including components due both to internal reproducibility and the intrinsic quasar-to-quasar variation among the population, are available for all quasars in the catalogue. The improved redshifts and their associated errors have wide applicability in areas such as quasar absorption outflows, quasar clustering, quasar-galaxy clustering and proximity-effect determinations.Comment: Accepted to MNRAS. The QSO redshift catalogue and QSO template spectrum can be downloaded from ftp://ftp.ast.cam.ac.uk/pub/phewett/ until 1st May 201

Issues Involved in Faculty Implementation of Community Service-Learning in Teacher Education

This study examined how teacher education faculty from 21 institutions attempted to implement the curricular innovation of community service-learning. Faculty\u27s biggest successes were implementation of program/course changes, increased collaborations on campus or in the community, and perceived positive impact on pre-service teachers. Barriers to implementation included time, resistance, or inertia on the part of colleagues, limited finances, and other reform efforts and commitments that demanded immediate attention. The study highlights several key factors that contributed to faculty success: faculty ownership and involvement in decision making, site-specific professional development opportunities, resources to support faculty \u27s efforts, and written plans for implementation

Issues Involved in Faculty Implementation of Community Service-Learning in Teacher Education

This study examined how teacher education faculty from 21 institutions attempted to implement the curricular innovation of community service-learning. Faculty\u27s biggest successes were implementation of program/course changes, increased collaborations on campus or in the community, and perceived positive impact on pre-service teachers. Barriers to implementation included time, resistance, or inertia on the part of colleagues, limited finances, and other reform efforts and commitments that demanded immediate attention. The study highlights several key factors that contributed to faculty success: faculty ownership and involvement in decision making, site-specific professional development opportunities, resources to support faculty \u27s efforts, and written plans for implementation