Improvement of Moderate Redshift Quasar Surveys Utilizing Infrared and Optical Data

1. Improvement of Moderate Redshift Quasar Surveys Utilizing Infrared and Optical Data Ashley Stewart, Shelly Bursick, Julia Kennefick University of Arkansas S.George Djorgovski, Eilat Glikman Caltech • Introduction: What is a Quasar? • Bright centers of active galaxies. • Have large observed redshifts. • Important to the study of evolution of galaxies. • Advantage: • The addition of near infrared imaging helps separate 2 < z < 3 quasars from stars. Results: Image 5: Graph of cross matched data with known QSO’s and Candidates for spectroscopy shown. Z = 3 Z = 2 Z = 4 Image 3: Optical color vs. optical color magnitudes of synthetic quasars showing quasar colors for redshifts 2 to 3 are the same as stars when using optical filters. Image 1: Hubble Space Telescope image of quasar PKS 2349.1 Detection Methods: • First quasars were discovered in the 1960’s using radio technology. • The most successful method of detection is using optical telescopes. • Optical surveys account for most known quasars but are incomplete. • The SDSS has found thousands of quasars, including 26 of the 30 most distant quasars ever seen. Z = 4 Z = 3 Image 6: Spectrograph of known SDSS QSO at redshift .263.3 Z = 2 • Conclusion: • Proposal for time at KPNO has been submitted to complete spectroscopy. • Follow up spectroscopy will determine if addition of infrared imaging to optical surveys improves quasar selection at 2<z<3. • Thereby, improving the accuracy of determinations of quasar space densities. Image 4: Infrared color vs. optical color of synthetic quasars showing quasar colors for redshifts 2 to 3 differ from stars. • Our project: • Cross matched infrared data from the 2-micron All Sky Survey (2MASS) with the optical data from the Sloan Digital Sky Survey (SDSS). • Computed colors. • Graphed in color-color space with a stellar locus and modeled quasar data. • Challenges with Optical Surveys: • Quasar activity is found to peak between redshifts 2<z<3. • Optical surveys can be up to 90% incomplete at these redshifts. • Incompleteness is due to quasars of redshift 2<z<3 similarity in color to stars. References: 1Nemiroff, Robert. "APOD: October 22, 1995 - A Quasar-Galaxy Collision?." Astronomy Picture of the Day. 22 Oct 1995. NASA. 7 Dec 2006 <http://antwrp.gsfc.nasa.gov/apod/ap951022.html> 2Richards, Gordon T.. "The Sloan Digital Sky Survey Quasar Survey: Quasar Luminosity Function from Data Release 3." The Astronomical Journal 131(2006): 2766-2787. 3http://cas.sdss.org/astrodr5/en/tools/chart/list.asp • Data analysis: • Selected candidates that diverged from the stellar locus and that were within the same color space as synthetic quasar data. • Determined if these candidates had undergone spectral analysis by checking SDSS. • Those without spectra will be considered for follow up spectroscopy. Acknowledgements: We would like to thank the NSF and the NVO for funding and we acknowledge the use of data from the Sloan Digital Sky Survey and the 2MASS survey. Image 2: Redshifts vs. volume of space showing that peak quasar activity occurs between 2.2 to 2.8.2