Statistical properties of multi-epoch spectral variability of SDSS stripe 82 quasars
- Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)
- Department of Physics and Information Science, Yamaguchi University, Yamaguchi, Yamaguchi 753-8512 (Japan)
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 252-5210 (Japan)
- Center of Astro Engineering and Department of Electrical Engineering, Pontificia Universidad Catolica de Chile, Av. Vicuña Mackenna 4860, Santiago (Chile)
We investigate the UV-optical (longward of Lyα 1216 Å) spectral variability of nearly 9000 quasars (0 < z < 4) using multi-epoch photometric data within the SDSS Stripe 82 region. The regression slope in the flux-flux space of a quasar light curve directly measures the color of the flux difference spectrum, then the spectral shape of the flux difference spectra can be derived by taking a careful look at the redshift dependence of the regression slopes. First, we confirm that the observed quasar spectrum becomes bluer when the quasar becomes brighter. We infer the spectral index of the composite difference spectrum as α{sub ν}{sup dif}∼+1/3 (in the form of f{sub ν}∝ν{sup α{sub ν}}), which is significantly bluer than that of the composite spectrum α{sub ν}{sup com}∼−0.5. We also show that the continuum variability cannot be explained by accretion disk models with varying mass accretion rates. Second, we examine the effects of broad emission line variability on the color-redshift space. The variability of the 'Small Blue Bump' is extensively discussed. We show that the low-ionization lines of Mg II and Fe II are less variable compared to Balmer emission lines and high-ionization lines, and the Balmer continuum is the dominant variable source around ∼3000 Å. These results are compared with previous studies, and the physical mechanisms of the variability of the continuum and emission lines are discussed.
- OSTI ID:
- 22351348
- Journal Information:
- Astrophysical Journal, Vol. 783, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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