Low covering factor of the BLR in weak emission-line quasars Marek Nikołajuk Faculty of Physics Univ. of Białystok, Poland 3rd NCAC Symposium: „Accretion.

Low covering factor of the BLR in weak emission-line

quasars

Marek NikołajukFaculty 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

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Outline

• Weak Emission-Line Quasars (WLQs)• The project & its results• Instabilities and a hypothesis of quasar’s

reactivation

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Based on Nikolajuk M. & Walter R., 2012, MNRAS, 420, 2518

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PG 1407+265, zem = 0.94 (McDowell et al.1995)

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Weak Emission-Line Quasars

Line EW [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

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QuasarsForster et al. (2001) - 993 QSOs;

the Large Bright Quasar SurveyLy α+N V

C IV

Hγ+

[OlI

II]

Mg II

Hβ[O III]

Hδ[O II]

Si

IV +

O I

V]

C II

I]+

Al I

II] Line EW [Å]

Ly 56 ± 29

Si IV + O IV] 13 ± 9

C IV 38 ± 19

C III] 28 ± 15

Mg II 39 ± 21

H 62 ± 36

H 325 ± 234

Diamond-Stanic et al. (2009) - 3058 QSOs SDSS DR5

EW(Ly +N V) = 64 Å and 1σ region 39-102 Å EW(C IV) = 42 Å and 1σ region 26-67 Å

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Weak Emission-Line Quasars

Shemmer et al. (2009)

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mean WLQ

mean QSO

10 high-z WLQs (z> 2.2) from SDSS.

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mean QSO

SDSS J094533

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Weak Emission-Line Quasars

Shemmer et al.(2010)

zem = 1.66

Hryniewicz et al.(2010)(See also his poster #6)

zem = 3.55

zem = 3.49

MgII

H

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90611 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

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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).

A few properties of WLQs

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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.

)2500A(/)5GHz(R ff

f

(Diamond-Stanic et al. 2009; Plotkin et al. 2010a,2010b)

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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

2.08to1.37fromWLQ, ox ]log[)]2500()keV2([log

2500A2keV LLox

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)

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Possible explanations of WLQ phenomena

1) The difference in the ionizing continuum:

BELR

shie

ldin

g g

as

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)

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Possible explanations of WLQ phenomena

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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.

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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/LEdd 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).

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The project & results

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Our results

1) LBol/LEdd of WLQs span the same regionas 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)-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) = 1.32/d.o.f (WLQ) 1000

3) Super-Eddington luminosities are not required in WLQs.

Log EW(CIV) vs. Log Lbol/LEdd

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Our resultsLog EW(CIV) vs. αox

]log[)]2500()keV2([log

2500A2keV LLox

ox indices of WLQs span the same regionas non-BAL & BAL QSOs.

4) A soft ionizing continuum is not the reason for weak emission-lines in WLQs.

oxF

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Our resultsThe reason for the weak lines in WLQs

0.38384log EW(line)log ox

4 )line(EW(line) ionizingcontinuum LLL

(Ferland 2004)

Assuming and we can rewrite

and we obtain the relationship:

)keV2(ionizing LL )500A2(continuum LL

continuumionizing loglog)]2500()keV2([log3838.0 LLLLox

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Our resultsThe reason for the weak lines in WLQs

0.38384log EW(line)log ox

The gas covering factor (Ω/4π) is almost constant in normal QSOs and the changes of αox 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.

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Our results

L(line)/L(line) ratios in WLQs.

4 )line( ionizing LL

(Ferland 2004)

The relationship:

radio-quiet normal QSOs

WLQs

0.46 ± 0.14 0.59 ± 0.42

3.36 ± 1.47 0.44 ± 0.21

)Ly(

)CIV(

L

L

)MgII(

)CIV(

L

L

QSOsin)MgII()CIV(WLQin)MgII(

)CIV(

QSOsin)Ly()CIV(WLQin)Ly(

)CIV(

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We can find ~100 WLQs among ~100 000 QSOs which are seen in the Sloan Digital Sky Survey (SDSS) => prob.= 100/100000 = 10-3

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.

107 years < tlife as QSO < 108 years (Haiman & Hui 2001,

Martini &Weinberg 2001)

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Instability.WLQ ̶ quasar’s reactivation.

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An accretion disk is well visible, but the BELR is underdeveloped.

BH

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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

LILLIL

HIL

Instability.WLQ ̶ quasar’s reactivation.

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• Active phase of AGNs under the ionization and the radiation pressure instabilities 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.

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Instability.WLQ ̶ quasar’s reactivation.

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Conclusion:• 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.

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