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

Outline Weak Emission-Line Quasars (WLQs) The project & its results Instabilities and a hypothesis of quasar’s reactivation 6 September 20123rd NCAC Symposium2 Based on Nikolajuk M. & Walter R., 2012, MNRAS, 420, 2518

PG , z em = 0.94 (McDowell et al.1995) 36 September 20123rd NCAC Symposium Weak Emission-Line Quasars LineEW [ Å] Ly  + N V 8 ± 3 Si IV + O IV] 4.3 ± 2 C IV 4.6 ± 2 C III] + SiIII] 9.9 Mg II 23 H β < 40 H  126 WLQ QSO EW – rest-frame Equivalent Width

Quasars 4 Forster et al. (2001) QSOs; the Large Bright Quasar Survey Ly α+N V C IV H γ +[OlIII] Mg II HβHβ [O III] HδHδ [O II] Si IV +O IV] C III]+Al III] LineEW [ Å] Ly  56 ± 29 Si IV + O IV]13 ± 9 C IV 38 ± 19 C III]28 ± 15 Mg II39 ± 21 H H  62 ± 36 H  325 ± 234 Diamond-Stanic et al. (2009) QSOs SDSS DR5 EW(Ly  +N V) = 64 Å and 1σ region Å EW(C IV) = 42 Å and 1σ region Å

Weak Emission-Line Quasars Shemmer et al. (2009) 56 September 2012 mean WLQ mean QSO 10 high-z WLQs (z> 2.2) from SDSS. 3rd NCAC Symposium

mean QSO SDSS J September 20123rd NCAC Symposium Weak Emission-Line Quasars Shemmer et al.(2010) z em = 1.66 Hryniewicz et al.(2010) (See also his poster #6) z em = 3.55 z em = 3.49 MgII HH

76 September 20123rd NCAC Symposium QSOs from the Sloan Digital Sky Survey DR5 (Diamond-Stanic et al. 2009) EW(Ly  +N V) WLQ EW(Lyα+NV, λ1216) ≤ 15.4Å Definition of WLQs: Weak Emission-Line Quasars 33

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 α r (between 1.5GHz and 5GHz) of radio-detected WLQs are significant steeper than those of BL Lacs (i.e. α r,WLQ ≈ −0.5 vs. α r,BLLac ≈ +0.3). A few properties of WLQs 3rd NCAC Symposium86 September 2012 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)

The shape of spectra in Far-UV ̶ soft X ray region with the median value = −1.60 (Shemmer et al. 2006,2009) A few properties of WLQs 9 Just et al. (2007) for normal QSOs) 6 September 2012 The IR band their IR continua seem to be similar to normal quasars. The X-ray band the most WLQs are not X-ray weak. (Shemmer et al. 2009, Wu et al. 2012) (Diamond-Stanic et al. 2009, Lane et al. 2011)

Possible explanations of WLQ phenomena 3rd NCAC Symposium 1)The difference in the ionizing continuum: BELR shielding gas BELR a)b) 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). Leighly et al. (2007b)Wu et al. (2011)

Possible explanations of WLQ phenomena 6 September 20123rd NCAC Symposium11 2)Low covering factor of the BELR BELR McDowell et al. (1995), Shemmer et al. (2010) The BELR has a lower covering factor, intercepting smaller fraction of the (normal) continuum radiation. Weak emission-lines are produced.

12 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), L Bol /L Edd of WLQs from the catalogue or Diamond-Stanic et al.  ox of 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). 6 September 20123rd NCAC Symposium The project & results

136 September 20123rd NCAC Symposium Our results 1)L Bol /L Edd of WLQs span the same region as normal quasars from BQS. 2)The large errors (because of weakness of CIV) in some WLQs do not allow us to fit a correlation EW(CIV)-L Bol /L edd, however, we compare  2 /d.o.f. to statistically quantify the hypothesis about different relations in BLQ & WLQ.  2 /d.o.f (BQS excl. PG ) = 1.3  2 /d.o.f (WLQ)  )Super-Eddington luminosities are not required in WLQs. Log EW(CIV) vs. Log L bol /L Edd

146 September 20123rd NCAC Symposium Our results Log EW(CIV) vs. α ox  ox indices of WLQs span the same region as non-BAL & BAL QSOs. 4)A soft ionizing continuum is not the reason for weak emission-lines in WLQs.

156 September 20123rd NCAC Symposium Our results The reason for the weak lines in WLQs (Ferland 2004) Assuming and we can rewrite and we obtain the relationship:

166 September 20123rd NCAC Symposium 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 α ox are responsible for variation in EW(line). 5)The gas covering factor of the BELR in WLQs is at least 10 times smaller than for normal QSOs.

176 September 20123rd NCAC Symposium Our results L(line)/L(line) ratios in WLQs. (Ferland 2004) The relationship: radio-quiet normal QSOs WLQs 0.46 ± ± ± ± 0.21

6 September 20123rd NCAC Symposium18 We can find ~100 WLQs among ~ QSOs which are seen in the Sloan Digital Sky Survey (SDSS) => prob.= 100/ = 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). Instability. WLQ ̶ quasar’s reactivation years < t life as QSO < 10 8 years (Haiman & Hui 2001, Martini &Weinberg 2001)

Instability. WLQ ̶ quasar’s reactivation. 6 September 20123rd NCAC Symposium19 An accretion disk is well visible, but the BELR is underdeveloped. BH

6 September 20123rd NCAC Symposium20 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 BH BLR HIL LIL HIL Instability. WLQ ̶ quasar’s reactivation.

21 Active phase of AGNs under the ionization and the radiation pressure instabilities takes ~10 6 and ~10 4 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. 6 September 20123rd NCAC Symposium Instability. WLQ ̶ quasar’s reactivation.

Conclusion: 22 Nowadays we know about 100 radio-quiet quasars with the weak emission-lines (WLQs) Accretion rates have values as 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. 6 September 20123rd NCAC Symposium