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

• 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).

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).

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.

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.

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.

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).

The Compton thick elephant…

(with apologies to Banksy (and the elephant))