solving the mystery of weak emission line quasars at …seminari/pres/2013/shemmer2013.pdf ·...

Ohad ShemmerUniversity of North Texas

Collaborators: S.F. Anderson (U. Washington), W.N. Brandt (Penn State), A.M. Diamond-Stanic (UCSD), X. Fan (U. Arizona), P. Hall (York U.),

R. Lane (UNT), S. Lieber (UNT), P. Lira (U. Chile), B. Luo (Penn State), H. Netzer (Tel Aviv U.), R. Plotkin (U. Michigan), G.T. Richards (Drexel), D.P. Schneider (Penn State), M. Stein (UNT), M.A. Strauss (Princeton),

B. Trakhtenbrot (ETH), J. Wu (CfA)

University of Bologna, September 19, 2013

Solving the Mystery of Weak Emission Line Quasars at High Redshift


Outline

✴ Quasars and Active Galactic Nuclei (AGN)

✴ Weak Emission Line Quasars: History and Mystery

✴ Insights from Multiwavelength Observations

✴ Scenarios for Quenching Emission Lines in Quasars

✴ Summary, Open Questions, and Ongoing Work


Quasars

and

Active Galactic Nuclei (AGN)

Quasars and Active Galactic Nuclei (AGN)Most galaxies harbor supermassive (~106-1010 M⊙) black holes (BHs) in their centers.

Active galaxies

Quasi Stellar Object (QSO),or quasar (Quasi Stellar Radio Source).

3C 273

Ordinary (or `passive’) galaxies

Seyfert galaxy

Luminosity LuminosityNuclear Nuclear

AGN are powered by mass accretion onto their central supermassive BHs. L = !Mc2


Quasars and Active Galactic Nuclei (AGN)

Urry & Padovani 95

The inner light-year of an AGN:

a unified view of the central engine.



Typical quasar spectrum

Quasars and Active Galactic Nuclei (AGN)

Francis+91

Broad (1000 km s-1 < FWHM < 10000 km s-1) and narrow (FWHM < 1000 km s-1) emission lines superposed on a blue continuum.


Weak Emission Line Quasars (WLQs):

History and Mystery


About 100 SDSS sources at z = 2.2 - 5.9 with quasar-like continua but extremely weak or undetectable emission lines in their UV spectra. (Discovered mainly via surveys searching for BL Lacertae objects.)

Fan+99

Prototype: SDSS J153259.96-003944.1

Selected as a high-redshift

quasar candidate based on its

colors and lack of proper motion.

WLQs: History and Mystery

Equivalent Width (EW or Wλ)



EW ≡�

Fl(λ)− Fc(λ)Fc(λ)

dλ ∼ F (line)Fc(λ)

1

Diamond-Stanic+09

WLQs constitute >3 σ deviation

Distributions of broad emission line equivalent widths (EWs) in SDSS quasars at z>3

WLQs are defined as quasars having EW ≤ 15.4 Å for the Lyα+N V emission-line complex (EW ≤ 10 Å for C IV).




1000 1100 1200 1300 1400 1500 1600

Rest-Frame Wavelength [Å]

5

10

15

Ly!

C IV

5

10

15

5

10

15

5

10

15

10

20

30

2468

10

F" [

10-1

7 erg

s cm

-2 s

-1 Å

-1]

1000 1100 1200 1300 1400 1500 1600

2468

1

2

3

1234

1

2

3

2

4

6

8

SDSS J121221.56+534128.0 z=3.1

SDSS J114153.34+021924.3 z=3.5

SDSS J031712.23-075850.3 z=2.7

SDSS J092832.88+184824.4 z=3.8

SDSS J123132.37+013814.0 z=3.2

SDSS J123743.08+630144.9 z=3.4

SDSS J101204.04+531331.8 z=3.0 SDSS J130216.13+003032.1 z=4.5

SDSS J133422.63+475033.6 z=5.0

SDSS J133550.81+353315.8 z=5.9

SDSS J142103.83+343332.0 z=4.9

Shemmer+09

Lyα + N V



1100 1200 1300 1400 1500 1600 1700 1800Rest-Frame Wavelength [Å]

0

5

10

15

F! [

arbi

trar

y un

its]

Ly"

N V + Si II

S IV + O IV]

C IV

SDSS Quasar Template

Mean WLQ Spectrum

HST Spectrum of PHL 1811

Shemmer+09

Why are the UV emission lines in WLQs so weak or absent?



Are WLQs simply high-redshift BL Lacertae objects?

BL Lacs are blazars almost bereft of emission lines due to relativistically boosted continua. Found mostly at low redshifts; display rapid and large-amplitude variability as well as significant polarization.



0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Redshift

0

50

100

150

BL L

acs w

ith R

elia

ble

Reds

hifts

Redshift distribution of BL Lacs(Shemmer+09)



Insights

from

Multiwavelength Observations

Insights from Multiwavelength Observations


UV

- op

tica

l

✴ quasar luminosities (LBol~1047-1048 erg s-1).

✴ no broad absorption lines.

✴ no significant variability.

✴ no significant polarization.

✴ typical (blue) quasar continua.

✴ no detection of multiple images (not lensed).

Clues from the UV - optical band

WLQs show:


X-ra

y

✴ no sign of significant absorption.

✴ typical quasar power-law spectra.

X-ray clues:10

30.

01

Coun

ts s

1 keV

1

SDSS J123132.38+013814.0z=3.2

10.5 2 5

20

2

Observed Frame Energy (keV)

Shemmer+09

Shemmer+09

Joint fitting the X-ray spectra of

11 WLQs

(However, so far, results are tentative: based mostly on shallow Chandra observations.)

ΓNH


5

4

3

2

1

0

-1

log R

-2-1.5-1-0.5ox

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

ro

WLQ at z>2.2 (this work)WLQ at z>2.2 (S06)WLQ at z<1 (S06)BL Lac (DXRBS)BL Lac (EMSS)BL Lac (RGB)BL Lac (Slew)BL Lac (SDSS)

Radio weakness

X-ray weakness

Radio-Quiet AGNsPHL 1811

2QZ J215454.3-305654

PG 1407+265

rad

io -

opti

cal -

X-ra

y

If WLQs are the long-sought, high-redshift BL Lacs, then where is the ‘parent’ population of X-ray and radio bright weak-lined sources at high redshift?

Shemmer+09; Plotkin+10

(Optical - X-ray `color’)

(Opt

ical

- R

adio

`co

lor’)


typical quasars



Tracing the WLQ UV-to-mid-IR spectral energy distribution (SED) with Spitzer IRAC+MIPS 24µm photometry. Distinguishing a quasar SED from a BL Lac SED.


Rest-Frame Wavelength [μm]

νF ν

[10-1

4 er

g cm

-2 s

-1]

Diamond-Stanic+09; Lane+11

10

10 10

10

100

10 10

1

10

!F

! [

10

-14 e

rg c

m-2

s-1

]

1010

10

100

10

1

10

1010

10

0.1 110

100

0.1 1

Rest-Frame Wavelength [µm]

1

10

0.1 1

10

SDSS J004054.65-091526.8 SDSS J123743.08+630144.9 SDSS J135249.82-031354.3

SDSS J031712.23-075850.4 SDSS J130216.13+003032.1 SDSS J140300.22+432805.4

SDSS J085332.78+393148.8

SDSS J11415342.9+021924.3

SDSS J120715.46+595342.9

SDSS J121221.56+534128.0

SDSS J130332.42+621900.3

SDSS J133219.66+622716.0

SDSS J133422.63+475033.6

SDSS J13350.81+353315.8

SDSS J140850.92+020522.7

SDSS J144231.72+011055.3

SDSS J153259.96-003944.1

SDSS J154734.95+444652.5

10

10 10

10

100

10 10

1

10

!F

! [1

0-1

4 e

rg c

m-2

s-1

]

1010

10

100

10

1

10

1010

10

0.1 110

100

0.1 1

Rest-Frame Wavelength [µm]

1

10

0.1 1

10

SDSS J004054.65-091526.8 SDSS J123743.08+630144.9 SDSS J135249.82-031354.3

SDSS J031712.23-075850.4 SDSS J130216.13+003032.1 SDSS J140300.22+432805.4

SDSS J085332.78+393148.8

SDSS J11415342.9+021924.3

SDSS J120715.46+595342.9

SDSS J121221.56+534128.0

SDSS J130332.42+621900.3

SDSS J133219.66+622716.0

SDSS J133422.63+475033.6

SDSS J13350.81+353315.8

SDSS J140850.92+020522.7

SDSS J144231.72+011055.3

SDSS J153259.96-003944.1

SDSS J154734.95+444652.5

UV

- op

tica

l - m

id-IR



0.2

1

0.2

1

F [

Arb

itrar

y U

nits]

0.1 0.2 0.3 1 2 3 4 5Rest-Frame Wavelength [µm]

0.2

1

0.2

1a)

a)

b)

c)

d)

Lane+11

WLQs are unbeamed quasars with intrinsically weak UV emission lines. Can be selected only via spectroscopic surveys.

UV

- op

tica

l - m

id-IR

LBLPLBB

Ordinary quasar SED

Luminous quasar SED

z~6 quasar SED



Q: What mechanism can hinder the formation of broad emission lines in luminous quasars?

Q: Are the broad emission line regions in WLQs unusually gas deficient or subject to exotic ionization conditions?

Q: Do WLQs mark a brief evolutionary phase that all quasars go through?



What determines broad emission line strength in AGN?

✴ Ionizing continuum SED

✴ Broad emission line region properties

✴ Orientation (i.e., obscuration)

✴ AGN evolution or AGN “states”?

✴ ....


Scenarios for Quenching

Emission Lines in Quasars


Leighly+07

1100 1200 1300 1400 1500 1600 1700 1800Rest-Frame Wavelength [Å]

0

5

10

15

F! [

arbi

trar

y un

its]

Ly"

N V + Si II

S IV + O IV]

C IV


Mean WLQ Spectrum

HST Spectrum of PHL 1811

Shemmer+09

Are there low-redshift analogs to high-redshift WLQs?

Soft SED responsible for weak high-ionization emission lines in WLQs?

Extremely High Accretion Rates or Abnormal Broad Emission Line Regions?

Clues from low redshift

4000 4500 5000Rest-Frame Wavelength [Å]

5.5

6

6.5

F [a

rbitr

ary

units

]

H

H

Fe II

H

Fe II


PHL 1811WLQ ?

Rest-Frame Wavelength [Å]

Fe II

Fe II

PHL 1811

LEdd =4!GMmpc

"T

! 1.3 " 1038

!

M

M!

"

erg s"1

Bolometric luminosity of the Sun

L! = 3.83 ! 1033 erg s"1

Eddington Luminosity

The Sun’s Eddington ratio!

L

LEdd

"

sun

!L!

LEdd

" 3 # 10"5

Frad

Fgrav



The accretion rate - line strength relationship



0.01 0.1 1L / LEdd

10

100

EW(C

IV)

[Å]

Baskin & Laor (2004)Shemmer & Lieber, in prep.

Determining low ionization emission line EWs and L/LEdd in WLQs


Determine accretion rates from near-IR spectra of the Hβ region:

L/LEdd ∝ νLν(5100Å)0.5 FWHM(Hβ)-2

Gemini-North


1000 1100 1200 1300 1400 1500 1600Rest-Frame Wavelength [Å]

5

10

15

F ! [1

0-17 e

rg s

-1 c

m-2

Å-1

]

5

10

15

20SDSS J1141+0219

SDSS J1237+6301 Ly" + N V

C IV

Ly" + N V

C IV

4400 4600 4800 5000 5200 5400Rest-Frame Wavelength [Å]

1

2

F ! [1

0-17 e

rg s

-1 c

m-2

Å-1

]

H" [O III]

H" [O III]

1

2

3 SDSS J1141+0219

SDSS J1237+6301H"

[O III]

Shemmer+10

For two WLQs: typical quasar L/LEdd values and exceptionally weak Hβ lines.

z ~ 3.5

The accretion rate - line strength relationship



0.01 0.1 1L / LEdd

10

100

EW(C

IV)

[Å]

Baskin & Laor (2004)Shemmer & Lieber, in prep.WLQ

PHL 1811

The only two WLQs observed are clear outliers


XMM-Newton observations of WLQs: utilizing the hard-X-ray power-law photon index as an accretion-rate indicator (Stein+13, in prep.).

Cross-checking L/LEdd determinations

XMM-Newton

-1.5

-1.0

-0.5

0.0

log

(L /

L Edd)

L (5100Å) < 1046 ergs s-1

L (5100Å) > 1046 ergs s-1

BCESFITEXYMLE

1.5 2 2.5-1.0-0.50.00.51.0

log

(L /

L Edd)

BCES

log(L/LEdd) = (1.0 ± 0.3)! ! (2.5 ± 0.5)

Shemmer+08


XMM-Newton

Γ≅1.9


Orientation?

Wu+11

✴PHL 1811 analogs at high redshift - a subset of WLQs?

✴Thicker shielding gas in WLQs?

✴X-ray ‘normal’ WLQs observed at lower inclinations, and PHL 1811 analogs at high redshift are viewed at higher inclinations?


‘Cold’ Accretion Disk?

Laor & Davis+11

Disk SED peak frequency decreases as black-hole mass increases and black-hole spin decreases. Fewer energetic photons are available for ionizing the broad emission line region.


Summary, Open Questions,

and

Ongoing Work

Summary, Open Questions, and Ongoing Work


✴ WLQs are a remarkable new class of quasars. They may constitute a missing link in our understanding of emission-line formation and the accretion process in AGN.

✴ Should distinguish between (at least) two competing scenarios: extremely high L/LEdd or ‘anemic’ broad emission line region.

✴ The key to understanding the weakness of the UV lines lies in near-IR (rest-frame optical) and X-ray spectroscopy of many WLQs in conjunction with photoionization modeling.

✴ Ultimate goal: understanding the role that L, MBH, L/LEdd, the SED, and the broad emission line region physical properties play in determining the relative strengths of low- and high-ionization emission lines in all AGN.

solving the mystery of weak emission line quasars at …seminari/pres/2013/shemmer2013.pdf ·...

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