UV to Mid-IR SEDs of Low Redshift Quasars

Zhaohui Shang(Tianjin Normal University/University of Wyoming)

Michael Brotherton, Danny Dale(University of Wyoming)

Dean Hines(Space Science Institute)

Xi’an Oct. 20, 2006

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

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., LBol=9λLλ(5100Å).

Recent Results from Spitzer (broad band – IRAC, MIPS)

• 13 high-redshift (z>4.5) 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

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 < 0.5• Quasi-simultaneous UV-optical spectra to reduce uncertainty from

variability• Rest wavelength coverage 1000 – 8000 Å, (some 900 – 9000 Å)

FUSE HST ground-based

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-opticalTotal 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 III]15.56 µm, [O IV]25.89 µm, ……

• Power-law between ~5-8 µm, and beyond

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

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 (z<0.4)• 1 micron inflexion

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 (z<0.4)• 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

Result 1 of 3: Spectral Energy Distributions (diversity)

Normalized at 5600 Å

Normalized at 8 µm

• Individual mid-IR spectral are different.

• Contribute differently to the bolometric luminosity(LMIR~8% to 30% of LBol, assuming LBol=9λLλ(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.

Result 1 of 3: Spectral Energy Distributions (radio-loud/quiet)

Normalized at 5600 Å Normalized at 8 µm

Small difference between radio-loud and radio-quiet

Result 2 of 3: Evidence of Intrinsic Reddening

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

• Correlation holds without the “outliers”.

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.

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.

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

(Boroson & Green 1992)

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

• Equivalent width of Silicates 10µm seems also to be a parameter of EV1.

• Consistent with the picture of covering factor.

r=0.64, p=1.0%

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.