Dust obscured radio-quiet quasars at high redshifts
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Transcript of Dust obscured radio-quiet quasars at high redshifts
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Dust obscured radio-quiet quasars at high redshifts
Mark Lacy, NAASC/NRAOAndreea Petric (SSC), Susan Ridgway
(CTIO), Tanya Urrutia (SSC), Anna Sajina (Haverford), Alejo Martinez-Sansigre
(Oxford/Portsmouth)
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The co-evolution of black holes and massive galaxies
• Models can reproduce observed relation if galaxy mergers trigger quasar activity, and subsequent AGN feedback stops star formation.
• But only about 1/3 quasar hosts show signs of mergers.– Different timescales?– Star formation quickly
suppressed in quasars?– Selection effects?
Tremaine et al 2002
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IR-selected quasars• We have used
Spitzer to select samples of quasars based on their mid-infrared dust continua.
Blue continuum
Red continuum
Continuum+PAH
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Spectroscopy• Follow up with optical/IR
spectroscopy.• Classify optical spectra
as: – type-1 (normal quasar)– type-2 (high-ionization
narrow lines only)– red type-1 (1R)– starburst/LINER
• Based on broad lines, BPT diagrams, [NeV] emission, high-ionization UV emission lines.
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Evolution of obscured quasars
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Host galaxies of dust obscured quasars
• Hosts out to z~1 easy to image with HST/ACS.
• All show some signs of interaction/merger.
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Stacking at 160mu• Stack all z>2 type-1s (17) and obscured
quasars (37). Type-1s have lower SFRs.• Mean luminosity ~LIRG/ULIRG transition
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SEDs• Two z>2 obscured
quasars detected with MAMBO (1.3mm), corresponding to HLIRG luminosities.
• z=4.27 object also detected in CO.
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Summary• A population of radio-quiet, luminous, dust
obscured quasars exists out to at least z~4, whose numbers exceed those of normal quasars.
• Tentative evidence that the true peak of luminous quasar activity occurred at higher redshifts than currently believed.
• Dust obscured quasars seem to show higher star formation rates than their unobscured counterparts.