Testing Models for the Quasar Big Blue Bump via Color-Color Diagrams

Details Testing Models for the Quasar Big Blue Bump via Color-Color Diagrams Testing Models for the Quasar Big Blue Bump via Color-Color Diagrams

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...454...77s&link_type=abstract

Astrophysical Journal v.454, p.77

Astronomy and Astrophysics

Astronomy

35

Accretion, Accretion Disks, Galaxies: Photometry, Galaxies: Quasars: General, Radiation Mechanisms: Thermal

Scientific paper

We discuss several models of quasar big blue bump emission in color-color and color-luminosity diagrams. We define several broad passbands: IR (0.8-1.6 μm), VIS (4000-8000 Å), UV (1000-2000 Å), UV1 (1400-2000 Å) and UV2 (1000-1400 Å), and SX (0.2-0.4 keV). The colors have been chosen to investigate characteristics of the big blue bump: (1) IR/VIS color represents the importance of the IR component and shows the contribution around ˜1 μm; (2) UV/VIS color shows the slope of the big blue bump (in a region where it dominates, a higher value means the bump gets steeper); (3) the combination of IR/VIS/UV colors shows the relative strength of the big blue bump and the IR component; (4) UV1/UV2 color is important as an indicator of a flattening of the spectrum in this region and the presence of the far-UV turnover, (5) UV/SX tests the relationship between the big blue bump and the soft X-ray component. All colors are needed to investigate the range of model parameters.
We describe the colors for several models: accretion disk models in Schwarzschild and Kerr geometries, single-temperature optically thin emission, combination of the main emission model and nonthermal power law or dust, and irradiation of the disk surface. We test models against the sample of 47 low-redshift quasars from Elvis et al. We find that (1) modified blackbody emission from an accretion disk in a Kerr geometry can successfully reproduce both the luminosities and colors of the quasars except for the soft X-ray emission; (2) no additional components (hot dust or power-law) are needed to fit the optical-UV colors when the irradiation of the surface of the disk is included in the model; (3) even modest (10%) irradiation of the surface of the disk modifies significantly the optical colors; (4) the simplest, single-temperature, free-free models need either an additional component or a range of temperatures to explain the observations.
Tables of predicted colors for each model family are provided on the AAS CD-ROM. A part of the tables is listed in the Appendix.

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