intrinsic absorption in quasars: bals & nals jonathan trump february 11, 2007
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Intrinsic Absorption in Quasars:
BALs & NALs
Jonathan TrumpFebruary 11, 2007
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Quasar Absorption Lines
• Intrinsic– Caused by material in the AGN engine itself
• Host– From gas in the host galaxy
• Intervening– From an intervening galaxy
This all has nothing to do with Type 2 AGN: we’re talking about absorption lines by diffuse gas, not global obscuration of the BLR by lots of dust!
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Why Should We Care?
• Dynamics– Mechanism for losing angular momentum?– Accretion disk as power source for winds– Effects on host?
• Composition– Densities– Abundances
• Unified Model– Evolution? Orientation?
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Broad Absorption Line Quasars
from Trump et al. 2006
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• Broad absorption– Typically >1000 km/s– Up to ~20,000 km/s
• Blueshifted from emission line– Typically few thousand km/s (~0.01c)– Up to ~60,000 km/s (0.2c)
• Outflowing gas “wind”– High velocity dispersion– High velocity
Broad Absorption Line Quasars
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The Zoo of BAL types
from Reichard et al. 2003
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• High-Ionization BALs– CIV 1550 Å, also SiIV, NV, Lyα– ~15% of quasars
• Low-Ionization BALs– MgII 2800 Å, also Al II, Al III– ~1-2% of quasars
• FeLoBALs– FeII or FeIII (widespread)– <0.1% of quasars
• Rarer objects: absorption in He, Balmer lines…
Broad Absorption Line Quasars
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FeLoBALs (they’re weird)
from Trump et al. 2006
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FeLoBALs (they’re weird)
For more about FeLoBALs, see Hall et al. 2002, ApJ, 141, 267
from Hall et al. 2007
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Characterizing BALs
• Balnicity Index (BI)– Weymann et al. 1991– Limits width, min/max blueshift, depth
• Absorption Index (AI)– Hall et al. 2002– Less limiting than BI, includes mini-BALs
• Characterization limited by S/N of spectra• BALQSOs are red, and LoBALs are redder• BALQSO fraction
– Underestimated by all surveys: fainter, redder, obscured in X-rays
• Typically saturated, but with partial coverage
km/s 25000
km/s 3000 901 Cdv.vf
km/s 25000
km/s 0'1 dvCvf
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What Causes BALs?
• Evolution– Young quasars in a dusty cocoon– Especially considered for LoBALs
• Orientation– Disk-driven wind in all quasars– Only visible in BALs because of orientation– Supporting evidence: Increased trough
velocity with luminosity (Trump et al. 2006)– See models by Murray & Chiang 1998, Proga
et al. 2000, etc.
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from Elvis 2000
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BALQSOs in Radio
• LBQS (Weymann et al. 1991): surprising lack of radio-loud BALQSOs
• SDSS (Reichard et al. 2003): same findings…– 10% of quasars are radio-loud, but only a few
percent of BALQSOs are radio-loud
• Supports orientation
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BALQSOs in X-rays
• From Brandt et al. 2000
• More UV absorption -> weaker in soft X-rays
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BALQSOs in X-rays
weaker X-rays -> harder spectrum
Absorbed in soft X-rays only
Gallagher et al. 2006
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BALQSOs in IR
• If BALQSOs are in a dusty cocoon, we’d expect stronger IR emission– Not the case!
• Spitzer survey of Gallagher et al. 2007 find similar properties to normal QSOs
• Occasionally, some narrow absorption in IR
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BALs from Orientation
Different absorption mechanisms originate at different scales from the central engine
from Gallagher & Everett 2007
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Narrow Absorption Lines
from Narayanan et al. 2004
from Wise et al. 2004
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Narrow Absorption Lines
• In >20% of all quasars (Wise et al. 2004), but hard to ID because of S/N & host/intervening lines
• Variability– Variable on the order of ~1 yr– Implies scales of <100 pc from the central
source– > Intrinsic!– Really, the only way to determine intrinsic
from host/intervening… but time-consuming
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BALs & NALs: In Summary
• BALs: big, broad, blueshifted absorption– High velocities & velocity dispersions require AGN
engine
• NALs: narrow, blueshifted absorption– High velocities & variability require AGN engine
• Typically weaker in X-rays, radio• Mid-IR “normal”• Probably caused by orientation
– Disk-driven winds– But LoBALs are tougher to explain…
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BALs from Orientation
from Gallagher & Everett 2007