UV to Mid-IR SEDs of Low Redshift Quasars

1. 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

2. 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

3. 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).

4. 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

5. 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 ground-based HST

6. 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 III]15.56 µm, [O IV]25.89 µm, …… • Power-law between ~5-8 µm, and beyond

7. 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

8. 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

9. 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

10. Result 1 of 3: Spectral Energy Distributions (diversity) • 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. Normalized at 8 µm Normalized at 5600 Å

11. 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

12. Result 2 of 3: Evidence of Intrinsic Reddening

13. Result 2 of 3: Evidence of Intrinsic Reddening (Is it real?) • Correlation holds without the “outliers”.

14. 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.

15. 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.

16. Result 3 of 3: Eigenvector one (EV1) in Mid-IR (Boroson & Green 1992)

17. Result 3 of 3: Eigenvector one (EV1) in Mid-IR r=0.64, p=1.0% • Equivalent width of Silicates 10µm seems also to be a parameter of EV1. • Consistent with the picture of covering factor.

18. 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.