elusive AGN Estelle PONS Mike WATSON University of Leicester UK Xray and Observational Astronomy XROA Group Estelle Pons The Xray Universe 2014 1 June 2014 Outline Introduction ID: 1012053
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1. New insights into optically elusive AGNEstelle PONS Mike WATSONUniversity of Leicester, UKX-ray and Observational Astronomy (XROA) GroupEstelle Pons - The X-ray Universe 20141June 2014
2. Outline IntroductionNarrow emission-line galaxy sampleSelectionClassificationX-ray & optical propertiesWhy X-ray Sy2 are optically misclassified as SFEstelle Pons - The X-ray Universe 20142June 2014
3. XMM-Newton and SDSS3XMM catalogue:∼ 370,000 unique X-ray sourcesSky coverage: 2%Flux limit: 10-15 erg.cm-2.s-1SDSS-DR9 spectroscopic sample:1,457,002 galaxies: 14.5 ≲ r ≲ 17.7 228,468 quasars GALSPEC products from the MPA-JHU group45% 3XMM sources lie in SDSS survey regionEstelle Pons - The X-ray Universe 20143GALSPEC (Kauffmann et al. 2003): improved spectral products - line fluxes corrected for Galactic reddening - stellar absorption lines subtracted - additional galaxy parameters derivedJune 2014 Introduction
4. NELG sampleSource selection5,000 sourcesEstelle Pons - The X-ray Universe 20144June 2014NELG sample:800 sources
5. NELG: X-ray vs. optical classificationOptical: BPT diagnostic diagram (Baldwin, Philips & Terlevich 1981)Based on narrow emission line ratiosSeparates SF galaxies and type 2 AGN by their excitation mechanismX-ray: LHX > 1042 erg.s-1Remove sources with X-ray powered by SFEstelle Pons - The X-ray Universe 20145June 2014BPT AGNBPTComposite objectsBPT SFX-ray AGN: 314 sources41 sources→ “elusive AGN”(13%)
6. X-ray & optical propertiesEmission-line widthEstelle Pons - The X-ray Universe 20146June 2014NLS1(59%)X-ray Seyfert 2(41%)FWHMBalmer = FWHMforbiddenNLS1“Broad” lines can extend down up to ∼ 500 km/sBPT-SF region (Castello-Mor et al. 2012)Permitted lines larger than forbidden lines (v2 = M∙G/R)Mean errors
7. X-ray spectral analysisFitting: absorbed PL + additional components (soft excess, Fe K line)Low number of counts → large errorsNLS1: unobscured + steeper photon indexX-ray Sy2: high HR2 → signs of absorptionJune 2014Estelle Pons - The X-ray Universe 20147ObscurationX-ray Sy2NLS1“Obscured”“Unobscured”Hardness Ratio (HR): X-ray spectral shape & absorption indicatorLow HR (HR2 < 0.4) → unabsorbed X-ray spectra NLS1: all have a low HR X-ray Sy2: obscured and unobscured HRMean errors
8. June 2014Estelle Pons - The X-ray Universe 20148NLS1: BH mass & Eddington ratioMBH ∝ (L5100Å)0.5∙FWHMHα2.06BH mass: virial equilibrium→ scaling relation (Xiao et al. 2011)→ NLS1: expected low mass BHTypical AGN: MBH ∼ 107 – 108 M☉→ Observed:MBH < 5∙106 M⊙
9. June 2014Estelle Pons - The X-ray Universe 20149NLS1: BH mass & Eddington ratioEddington ratio 𝜆: 𝜆 = Lbol / LEdd → 𝜆 ∝ LHX / MBH NLS1: expected high 𝜆 → Netzer et al. 2007: 𝜆 > 0.25 → Observed: 𝜆 ≳ 0.25𝜆 = 0.25
10. Why X-ray Sy2 are optically classified as SF?Compton-thick (CT) absorbersSpherical gas clouds surrounding the nuclei (Comastri et al. 2002, Civano et al. 2007) → ionizing photons could not create the NLRHost galaxy gas and dust along the line of sight hiding the NLR (Rigby et al. 2006) Mid-IR luminosity (Goulding et al. 2011) → no CT obscuration + Unobscured X-ray Sy2: truly unabsorbedJune 2014Estelle Pons - The X-ray Universe 2014101. Obscuration hypothesis
11. 2. Optical dilution hypothesisAGN intrinsic weakness in respect to the host galaxy4000Å break: Dn4000 60% are dominated by galaxy starlight + possible SF contributionJune 2014Estelle Pons - The X-ray Universe 201411Continuum dominated by the host galaxyContinuum dominated by the AGN
12. 3. Low accretion rates hypothesisIntrinsically weak optical emission compared to other AGNLow 𝜆 X-ray Sy2: 𝜆 < 0.05Unobscured X-ray Sy2: 𝜆 ≲ 0.01 True Sy2 June 2014Estelle Pons - The X-ray Universe 201412Typical AGN: 𝜆～0.1 – 1 →𝜆 ∝ LHX / MBHMBH ∝ LK,Bulge0.93
13. True Sy2True Sy2: No optical BL + no intrinsic absorptionNo BLR: Trump et al. 2011 → BLR disappear for 𝜆 < 10-2 June 2014Estelle Pons - The X-ray Universe 201413MBH ∝ L5100Å0.52 . FWHMB.Hα2.06LB.Hα ∝ L5100Å1.16NL fitted BL predicted BL measured/upper limit
14. Observations consistent with predictions → Δ ∼ 0Δ ∼ 2500 Large differences between the predicted and observed fluxes No BLJune 2014Estelle Pons - Lunchtime Talk14Δ = fBroadHα,predicted - fBroadHα,measured
15. ConclusionsX-ray NELGs: BPT diagram and X–ray AGN selection → 13% of the sources misclassified as BPT-SFNature of these “elusive AGN”:59%: NLS1s → contribution to the Balmer line flux from both the BLR and NLR41%: X-ray Sy2Misclassification: optical dilution by the host galaxy stralight + low accretion rates (optically underluminous)Unabsorbed Sy2: very low 𝜆 + lack BL → True Sy2Estelle Pons - The X-ray Universe 201415June 2014