Low covering factor of the BLR in weak emission-line quasars

1. Low covering factor of the BLR in weak emission-line quasars Marek Nikołajuk Faculty of PhysicsUniv. of Białystok, Poland 3rd NCAC Symposium: „Accretion flow instabilities”, Warsaw, 6 September 2012 In collaboration with Roland Walter from ISDC, Univ. of Geneva

2. Outline Based on Nikolajuk M. & Walter R., 2012, MNRAS, 420, 2518 Weak Emission-Line Quasars (WLQs) The project & its results Instabilities and a hypothesis of quasar’s reactivation 3rd NCAC Symposium

3. WeakEmission-LineQuasars PG 1407+265, zem = 0.94 (McDowell et al.1995) EW – rest-frameEquivalentWidth WLQ QSO 3rd NCAC Symposium

4. Quasars Forster et al. (2001) - 993 QSOs; the Large Bright Quasar Survey Ly α+N V Si IV +O IV] C IV C III]+Al III] Mg II Hγ+[OlIII] [O III] [O II] Hβ Hδ Diamond-Stanic et al. (2009) - 3058 QSOsSDSS DR5 EW(Ly+N V) = 64 Å and 1σ region 39-102 Å EW(C IV) = 42 Å and 1σ region 26-67 Å

5. WeakEmission-LineQuasars 10 high-z WLQs (z> 2.2) from SDSS. mean QSO mean WLQ Shemmer et al. (2009) 3rd NCAC Symposium

6. WeakEmission-LineQuasars zem = 1.66 H mean QSO zem = 3.55 MgII SDSS J094533 zem = 3.49 Hryniewicz et al.(2010) (Seealso his poster #6) 3rd NCAC Symposium Shemmer et al.(2010)

7. WeakEmission-LineQuasars 90611 QSOsfromthe Sloan Digital SkySurvey DR5 (Diamond-Stanic et al. 2009) EW(Ly+N V) Definition of WLQs: EW(Lyα+NV,λ1216) ≤ 15.4Å WLQ 3 3rd NCAC Symposium

8. A few properties of WLQs • The radio band • radio-quite or radio-intermediate • (i.e. 50% (35/70) of WLQs in Diamond-Stanic et al. sample has the radio parameter below 15 and only 7% (5/70) has R > 100). • the radio spectral slopes αr (between 1.5GHz and 5GHz) of radio-detected WLQs are significant steeper than those of BL Lacs (i.e. αr,WLQ≈ −0.5 vs. αr,BLLac≈ +0.3). • The optical/UV band • the continuum luminosities for WLQs and normal quasars show no statistically significant difference. The median values of the photon index α = −0.54 (for normal QSOs) and α = − 0.52 (for WLQs ; ). • Generally, WLQs show (very) weak linear polarization. They are within the range for optically selected quasars without a synchrotron component. (Diamond-Stanic et al. 2009; Plotkin et al. 2010a,2010b) 3rd NCAC Symposium

9. A fewproperties of WLQs • The IR band • their IR continua seem to be similar to normal quasars. (Diamond-Stanic et al. 2009, Lane et al. 2011) • TheX-ray band • the most WLQsare not X-rayweak. (Shemmer et al. 2009, Wu et al. 2012) • Theshape of spectra inFar-UV̶ soft X ray region • withthe median value = −1.60 • (Shemmer et al. 2006,2009) Just et al. (2007) for normalQSOs)

10. Possibleexplanations of WLQ phenomena Thedifferenceintheionizing continuum: A softer far-UV/X-ray spectrum in an AGN reduces ionization and photoelectric heating in the broad emission-line region (BELR). The EWs of emission-lines are reduced (e.g. Netzer et al. 1992, Korista et al. 1998, Leighly et al. 2007a). a) b) shielding gas BELR BELR Leighly et al. (2007b) Wu et al. (2011) 3rd NCAC Symposium

11. Possible explanations of WLQ phenomena Lowcoveringfactor of the BELR The BELR has a lower covering factor, intercepting smaller fraction of the (normal) continuum radiation. Weak emission-lines are produced. BELR McDowell et al. (1995), Shemmer et al. (2010) 3rd NCAC Symposium

12. The project & results Selection process: • The optical/UV spectra of 81 high-z (z < 2.2) WLQs were taken from SDSS DR7 quasar catalogue (Shen et al. 2011) under selection process of Diamond-Stanic et al. (2009). We add 2 intermediate-z (z=1.89, 1.67) WLQs retrieved serendipitously by Hryniewicz et al. (2010) and us in the SDSS quasar catalogue. • EW(CIV), LBol/LEddof WLQs from the catalogue or Diamond-Stanic et al. • oxof WLQs from Shemmer et al. (2006,2009) • We compare those WLQs’ properties with 254 radio-quiet quasars from the Bright Quasar Survey and the Chandra Multiwavelength Project (Boroson & Green 1992, Baskin & Laor 2004, Shang et al. 2007,Green et al.2009). 3rd NCAC Symposium

13. Our results Log EW(CIV) vs. Log Lbol/LEdd LBol/LEdd of WLQs span the same regionas normal quasars from BQS. The large errors (because of weakness of CIV) in some WLQs do not allow us to fit a correlation EW(CIV)-LBol/Ledd , however, we compare 2/d.o.f. to statistically quantify the hypothesis about different relations in BLQ & WLQ.2/d.o.f (BQS excl. PG0043+039) = 1.32/d.o.f (WLQ)  1000 Super-Eddington luminosities are not required in WLQs. 3rd NCAC Symposium

14. Ourresults Log EW(CIV) vs. αox oxindices of WLQsspanthe same regionas non-BAL & BAL QSOs. A soft ionizing continuum is not the reason for weak emission-lines in WLQs. 3rd NCAC Symposium

15. Ourresults The reason for the weak lines in WLQs (Ferland 2004) Assuming and we can rewrite and we obtain the relationship: 3rd NCAC Symposium

16. Our results The reason for the weak lines in WLQs The gas covering factor (Ω/4π) is almost constant in normal QSOs and the changes of αox are responsible for variation in EW(line). The gas covering factor of the BELR in WLQs is at least 10 times smaller than for normal QSOs. 3rd NCAC Symposium

17. Ourresults Therelationship: (Ferland 2004) L(line)/L(line) ratiosinWLQs. 3rd NCAC Symposium

18. Instability.WLQ ̶ quasar’sreactivation. We can find ~100 WLQs among ~100 000 QSOs which are seen in the Sloan Digital Sky Survey (SDSS) => prob.= 100/100000 = 10-3 107years < tlife asQSO < 108years(Haiman & Hui 2001, Martini &Weinberg 2001) • The relatively frequent occurrence of WLQs may suggest that a quasar’s active phase has an intermittent character. • The whole active phase consists of several sub-phases, each starting with a slow development of the BLR region. • (Hryniewicz et al. 2010). 3rd NCAC Symposium

19. Instability.WLQ ̶ quasar’sreactivation. An accretion disk is well visible, but the BELR is underdeveloped. BH 3rd NCAC Symposium

20. Instability.WLQ ̶ quasar’s reactivation. A disc wind is freshly launched. LILs (e.g. MgII) are observed (LIL’s region is formed close to the disk surface) HILs (e.g. CIV) are not observed (the wind has yet not formed the HIL’s region) => this stage of ‘true WLQ’ lasts about a few thousand years HIL HIL BLR LIL LIL BH 3rd NCAC Symposium

21. Instability.WLQ ̶ quasar’s reactivation. • Active phase of AGNs under the ionization and the radiation pressureinstabilities takes ~106 and ~104 years, respectively. • (Czerny 2006, Janiuk & Czerny 2011) • Relatively high number of WLQs among all QSOs points out to the radiation pressure instability (?) as a source of WLQ’s phenomena. 3rd NCAC Symposium

22. Conclusion: • Nowadays we know about 100 radio-quiet quasars with the weak emission-lines (WLQs) • Accretion rates have valuesas normal quasars. • The relationship between the rest-frame EW for C IV and the Eddington ratio observed in WLQs has different normalization than for QSOs. This shift disagrees with the super-Eddington hypothesis. • The weakness of emission-lines in some WLQs is likely caused by a low covering factor of the BELR rather than by a very soft ionizing continuum. • WLQs may be manifestation of the radiation pressure instability and duty cycle activity of QSOs. 3rd NCAC Symposium