High-redshift obscured quasars

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High-redshift obscured quasars

• Alejo Martínez-Sansigre, Steve Rawlings
• and (many) others

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Discrepancies

• In radio-loud samples, find type-2 to type-1
  ratio11 (e.g. Willott et al. 2000).
• From hard X-ray background expect 3-41 (e.g.
  Comastri et al. 1995), although not clear at
  quasar luminosities (e.g. Ueda et al. 2003 also
  see review by R. Maiolino).
• Deep X-ray surveys find 11 for quasars (e.g.
  Zheng et al. 2004) but latest results disagree
  (Dwelly Page, 2006 Wang et al. 2006)
• Compton thick quasars? (e.g. Alexander et al.
  2005).
• Another type of obscuration not related to the
  torus? (Fabian 1999)

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Selecting high-z obscured quasars
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Selection Criteria

• S 24 µm gt 300 µJy Selects warm dust typical
  both of type-1s and type-2s (around break in LF)
• S 3.6 µm 45 µ Jy rejects type-1s and low-z
  type-2s (z phot lt 1.4)
• 350 µ Jy S 1.4 Ghz 2 mJy selects
  radio-intermediate quasars, to minimise
  contamination from ULIRGs

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The Quasar Fraction
Martinez-Sansigre et al., 2005, Nat
Using all obscured quasars
Using narrow line quasars only
q Unobscured / Total
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Possible Scheme?
Unified Scheme
Unobscured Obscured
Martinez-Sansigre et al., 2006a, MNRAS
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Radio Spectral Indices
FLAT SPECTRUM Type-2s jet is face on
Martinez-Sansigre et al., 2006b, MNRAS
Convention S? ? -a
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Similar sample in SXDF Compton-thick
z phot 1.90
z spec 2.08
Av 35
log Nh 24.5
Martinez-Sansigre et al., 2006c, MNRAS, subm.
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Summary

• Mid-IR radio reveals z 2 obscured quasars
• 50-80 of quasars obscured
• 50 of obscured quasars have blank optical
  spectra
• Some of these have the radio jet pointing at us
• They are Compton-thick.
• Thank You!

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Compton-thick!
Martinez-Sansigre et al., 2006c, MNRAS, subm.
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SXDF sample

• Multiwavelength, including X-rays
• Smaller area, so lower radio flux but more ULIRG
  contaminants
• Few z_spec (so far)
• SED fitting with a 3-component model (5 params)
• Use bayesian evidence to select between models
• Keep only objects with high probability of quasar
  over ULIRG (evid quasar 100x evid ULIRG)

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Results of xFLS Sample of 21

• 50 of candidates yield spectroscopic redshifts
  1.7lt z lt 4.2 plus one z1 contaminant
• 50 blank, but two confirmed at z2 with
  Spitzer-IRS (Host obscured)?
• Obscured to unobscured ratio is 11 to 31
• Some flat-spectrum obscured quasars host
  obscured?
• Can't check X-ray properties.

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SXDF results

• 2/12 detected in X-rays (50-100 ks XMM exp)
• These two have estimatd logNh 24.5 (cm-2)
• 10/12 undetected. Have same z, Lbol, and Avs
• Presumably logNh gt 24.5
• gas-to-dust ratios are Nh 1022-1023 x Av or
  more