UV to Mid-IR SEDs of Low Redshift Quasars

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UV to Mid-IR SEDs of Low Redshift Quasars
Zhaohui Shang(Tianjin Normal University/Universit
y of Wyoming) Michael Brotherton, Danny
Dale(University of Wyoming) Dean Hines(Space
Science Institute)
Xian Oct. 20, 2006
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Quasar Spectral Energy Distributions (SED)

• Significant energy output over wide frequency
  range
• Big blue bump (UV bump) strongest energy
  output
• Infrared bump energy output comparable to UV
  bump
• Important in determining the bolometric
  luminosity of quasars (AGNs)

• Quasar SED (Elvis et al. 1994)
• Infrared broad band photometry

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Recent Results from Spitzer (broad band IRAC)

• 259 SDSS quasars (Richards et al. 2006,
  astro-ph/0601558)
• Overall SEDs consistent with the mean SEDs of
  Elvis et al. 1994
• SED diversity leads to large uncertainty in
  determining bolometric luminosity if assuming
  mean SED, e.g., LBol9?L?(5100Å).

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Recent Results from Spitzer (broad band IRAC,
MIPS)

• 13 high-redshift (zgt4.5) quasars (Hines et al.
  2006, ApJ, 641, L85)
• Consistent with SEDs of low-redshift quasars
  (Elvis et al. 1994)

• Our project
• Mid-IR SED from spectra (Spitzer IRS)
• Study emission features
• Add best data from other bands (e.g., X-ray)
• Improve bolometric correction

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Sample and Data (UV-optical)

• Sample 1 22 PG quasars (Laor et al. 1994, Shang
  et al. 2003)
• Sample 2 17 AGNs from FUSE UV-bright sample
  (Kriss 2000, Shang et al. 2005)
• Z lt 0.5
• Quasi-simultaneous UV-optical spectra to reduce
  uncertainty from variability
• Rest wavelength coverage 1000 8000 Å, (some 900
  9000 Å)

FUSE
ground-based
HST
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Sample and Data (Infrared)

• Sample 1 22 PG quasars (Laor et al. 1994, Shang
  et al. 2003)
• Sample 2 17 AGNs from FUSE UV-bright sample
  (Kriss 2000, Shang et al. 2005)
• Spitzer IRS mid-IR spectra (rest frame 5-35 µm)
  
• MIPS far-IR (24, 70, 160 µm) photometry (not
  used)

• Available mid-IR spectra UV-optical
• Total 15 objects (6 radio-loud, 9 radio-quiet)
• Silicates features at 10 and 18 µm(Siebenmorgen
  et al. 2005, Sturm et al. 2005, Hao et al. 2005,
  Weedman et al. 2005)
• Emission lines Ne III15.56 µm, O IV25.89 µm,
  
• Power-law between 5-8 µm, and beyond

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Results 1 of 3 Spectral Energy Distributions

• Our sub-sample of 15 objects
• Composite spectrum (UV optical mid-IR)
• Normalized at 5600 Å
• Clear Silicates features around 10 and 18 µm

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Results 1 of 3 Spectral Energy Distributions

• Our sub-sample of 15 objects
• Composite spectrum (UV optical mid-IR)
• Normalized at 5600 Å
• Clear Silicates features around 10 and 18 µm

• Near-IR composite spectrum (Glikman et al. 2006)
• 27 AGNs (zlt0.4)
• 1 micron inflexion

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Result 1 of 3 Spectral Energy Distributions

• Our sub-sample of 15 objects
• Composite spectrum (UV optical mid-IR)
• Normalized at 5600 Å
• Clear Silicates features around 10 and 18 µm

• Near-IR composite spectrum (Glikman et al. 2006)
• 27 AGNs (zlt0.4)
• 1 micron inflexion

• Compared to the mean SEDs of Elvis et al. 1994
• Normalized to UV-optical
• Overall similar patterns
• More details with emission features

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Result 1 of 3 Spectral Energy Distributions
(diversity)

• Individual mid-IR spectral are different.
• Contribute differently to the bolometric
  luminosity(LMIR8 to 30 of LBol, assuming
  LBol9?L?(5100Å)

• Bolometric luminosity estimate must take into
  account the diversity of the (mid-) infrared
  spectra.
• Mid-IR spectra can help to improve the bolometric
  correction.

Normalized at 8 µm
Normalized at 5600 Å
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Result 1 of 3 Spectral Energy Distributions
(radio-loud/quiet)
Normalized at 8 µm
Normalized at 5600 Å
Small difference between radio-loud and
radio-quiet
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Result 2 of 3 Evidence of Intrinsic Reddening
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Result 2 of 3 Evidence of Intrinsic Reddening
(Is it real?)

• Correlation holds without the outliers.

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Result 2 of 3 Evidence of Intrinsic Reddening
(is it real?)

• Correlation holds without the outliers

• Correlation is NOT caused by a correlation
  between spectral slope and the UV luminosity.
• Show direct evidence of intrinsic dust reddening.
• All quasars have intrinsic reddening (our sample
  is blue).
• Mid-IR UV-optical info could lead to good
  estimate of intrinsic reddening.

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Result 3 of 3 Eigenvector one (EV1) in Mid-IR

• Our sub-sample of 15 objects
• Composite spectrum (UV optical mid-IR)
• Normalized at 5600 Å
• Clear Silicates features around 10 and 18 µm

(Boroson Green 1992)

• Strong anti-correlation between OIII and FeII
  emissions
• Involve many other UV-optical, soft X-ray
  parameters.
• May related to covering factor.
• May be driven by Eddington Accretion ratio L/LEdd.

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Result 3 of 3 Eigenvector one (EV1) in Mid-IR
(Boroson Green 1992)
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Result 3 of 3 Eigenvector one (EV1) in Mid-IR
r0.64, p1.0

• Equivalent width of Silicates 10µm seems also to
  be a parameter of EV1.
• Consistent with the picture of covering factor.

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Summary

• We constructed the UV-optical and mid-IR
  composite spectra of low-redshift broad-line
  (type I) quasars from a sub-sample.
• Unlike borad-band SEDs, the composites show
  detailed mid-IR features.
• Mid-IR spectra needs to be considered in
  estimating a better bolometric luminosity.
• All quasars seem to have intrinsic dust
  reddening.
• Mid-IR and UV-optical information may be used to
  estimate the intrinsic reddening.
• Silicates 10µm feature is a parameter in the
  Eigenvector 1 relationships.
• This agrees with the UV-optical results.