ISO/NASA AGN key project, the far-infrared/X-ray spectral energy distributions of QSOs: characteristics of the ISO data

Eric Hooper ¹, Belinda Wilkes ¹, Kim McLeod ², Martin Elvis ¹, Chris Impey ³, Carol Lonsdale ⁴, Matt Malkan ⁵, & Jonathon McDowell ¹

¹ SAO

² Wellesley

³ Arizona

⁴ IPAC

⁵ UCLA

A substantial fraction of the bolometric luminosity of many quasars is emitted in the infrared (Elvis et al. 1994, ApJS, 95, 1). While IRAS provided an enormous boon in this waveband, the limiting flux of the sky survey was too large to detect quasars other than the most luminous or relatively nearby ones. The characteristics and evolution of the infrared spectral energy distribution (SED) remain poorly understood for much of the wide range of quasar subclasses. Observations with ISO are expanding the range of quasars which have mid and far infrared data. ISO's advantages over IRAS include better spatial resolution, more bandpasses, and pointed observations which provide deeper flux limits than the IRAS sky survey. Two major ISO observing programs have obtained broad-band photometry for large samples of quasars: a European Core program which focused primarily on low-redshift, mostly radio-loud quasars; and a complementary US Key Project (PI Wilkes) to examine quasars spanning a wide range of redshifts and SEDs, e.g., X-ray and IR-loud, plus those with unusual continuum shapes.

Our sample consists of 72 quasars observed with the ISOPHOT instrument in the following bands: 5, 7, 12, 25, 60, 100, 135, and 200 . Ninety percent of the quasars in the sample have redshifts less than 1, while the remaining 10% lie in the range 2 < z < 4.7. More than half of the sample consists of luminous X-ray sources, 25% are strong UV emitters, and smaller subgroups contain strong infrared sources, X-ray-quiet objects, red quasars, and BALs.

The majority of the targets, 53, were observed in chopped mode. We also have raster map data for 37 quasars, including 18 from the chopped group. Initial batch processing of the chopped data revealed that the fluxes for the brighter objects are generally consistent with IRAS values, particularly at the two shorter wavelength bands. However, some systematic difference with IRAS at 60 and 100 , plus suprisingly broad histograms of the ISO fluxes at these wavelengths, indicate that a deeper investigation is needed. We are exploring a variety of techniques for determining the source flux and detection probability, uncertainties, systematic flux errors, and sky brightness variations. At the ISO conference we will present a comprehensive overview of the sample using the most current analysis procedures and discuss any areas where future improvements are likely to be forthcoming. The large number of objects, wide wavelength coverage, and overlap between chopped and raster observing modes makes this sample a useful testbed for comparing observation and reduction techniques and checking the ISO flux calibrations against those from other infrared satellites.