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The X-ray properties of Spitzer-selected type-2 quasars

The X-ray properties of Spitzer-selected type-2 quasars. Mark Lacy (SSC), Nick Seymour, Anna Sajina, Lisa Storrie-Lombardi, Lee Armus (SSC) Andreea Petric (Columbia), Gabriela Canalizo (Riverside), Susan Ridgway (NOAO), Elinor Gates (Lick Obs). Surveys for dust-obscured AGN.

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The X-ray properties of Spitzer-selected type-2 quasars

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  1. The X-ray properties of Spitzer-selected type-2 quasars Mark Lacy (SSC), Nick Seymour, Anna Sajina, Lisa Storrie-Lombardi, Lee Armus (SSC) Andreea Petric (Columbia), Gabriela Canalizo (Riverside), Susan Ridgway (NOAO), Elinor Gates (Lick Obs)

  2. Surveys for dust-obscured AGN • Chandra surveys vs Spitzer surveys • Spitzer finds objects on basis of hot dust emission. • Finds preferentially high accretion-rate objects (“dirty accretors”). • Chandra misses the most heavily obscured objects, but can find low accretion rate objects that Spitzer misses (e.g. some LINERS/XBONGs/low-luminosity radio galaxies - the “clean” accretors).

  3. Spitzer selection of AGN • Use “wedge” in IRAC color-color plot to select objects with hot dust continua, or require red power-law in mid-IR. • At bright (24mu flux ~5mJy) levels, <z>~0.6, median (bolometric) luminosity about x10 QSO/Seyfert divide. • Optically, our IR-wedge selected AGN sample is 33% normal type-1, 44% type-2, 14% reddened type-1 and 9% low-ionization in the optical (Lacy et al. 2006).

  4. What about the X-ray? • Some of our type-2 quasars overlap 20-50ks XMM pointings. • Most fluxes from 2XMM. • About half the type-2s are detected. • All the detected type-2 objects have high hardness ratios where available.

  5. X-ray survey strategies • Areal density of bright AGN low ~ 6/deg^2 to ~5mJy at 24mu. • Shallow X-ray survey will find the ~1/3 unobscured objects. • Deep pointed observations (~30ks) required for the obscured objects. • Contrast with GOODS-type surveys - finds these objects, but only at z>>1.

  6. ADIOS (Richards et al) • Wide area (~200deg^2) survey in SDSS equatorial field • Field is repeated when northern fields are unavailable • Limit ~25 mag • Applying for Spitzer/IRAC time, principally for quasar survey.

  7. Summary • Making sense of the AGN population requires both Spitzer and Chandra. • Host galaxy absorption/extinction probably plays an important role at the highest columns, but more study of heavily absorbed objects required. • May have to abandon the “pyramid scheme” to study luminous heavily absorbed quasars at z<1 (and other rare objects).

  8. The Compton thick elephant… (with apologies to Banksy (and the elephant))

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