Weak Emission Line Quasars:
Confronting New Challenges in Understanding
the Broad Emission Line Region
Ohad Shemmer
University of North Texas
The Inner Regions of Quasars, UT Austin, September 13, 2014
In Collaboration with:
S.F. Anderson (U. Washington)
R. Plotkin (U. Michigan)
W.N. Brandt (Penn State)
G.T. Richards (Drexel)
A.M. Diamond-Stanic (U. Wisconsin)
D.P. Schneider (Penn State)
X. Fan (U. Arizona)
M. Stein (UNT)
P. Hall (York U.)
M.A. Strauss (Princeton)
R. Lane (UNT)
B. Trakhtenbrot (ETH)
S. Lieber (UNT)
J. Wu (CfA)
P. Lira (U. Chile)
B. Luo (Penn State)
H. Netzer (Tel Aviv U.)
The Inner Regions of Quasars, UT Austin, September 13, 2014
Outline
✴ Weak emission line quasars (WLQs):
history and mystery
✴ Insights from multiwavelength observations
✴ What are WLQs telling us about the BELR
and SED?
✴ Summary of key questions
The Inner Regions of Quasars, UT Austin, September 13, 2014
Weak Emission Line Quasars (WLQs):
History and Mystery
The Inner Regions of Quasars, UT Austin, September 13, 2014
WLQs: History and Mystery
~100 SDSS sources, mainly at high redshift, with quasar-like continua but
extremely weak or undetectable emission lines in their UV spectra.
Prototype: SDSS J153259.96-003944.1
Selected as a high-redshift
quasar candidate based on its
colors and lack of proper motion.
Fan+99
Have we found the long-sought BL Lacs at high redshift?
The Inner Regions of Quasars, UT Austin, September 13, 2014
WLQs: History and Mystery
Distributions of broad emission line equivalent widths (EWs)
in SDSS quasars at z>3
Diamond-Stanic+09
WLQs constitute
>3σ deviation
WLQs were originally defined as quasars having EW ≤ 15.4 Å
for the Lyα+N V emission-line complex (EW ≤ 10 Å for C IV).
Q1: What determines the shape of the line EW distributions?
The Inner Regions of Quasars, UT Austin, September 13, 2014
WLQs: History and Mystery
Ly"
Shemmer+09
N V + Si II
F! [arbitrary units]
15
C IV
S IV + O IV]
SDSS Quasar Template
10
Mean WLQ Spectrum
5
HST Spectrum of PHL 1811
0
1100
1200
1300
1400
1500
1600
Rest-Frame Wavelength [Å]
1700
1800
Why are the UV emission lines in WLQs so weak or absent?
The Inner Regions of Quasars, UT Austin, September 13, 2014
WLQs: History and Mystery
Following Bev’s footsteps...
✴ Orientation?
✴ Obscuration?
✴ Polarization?
✴ Radio loudness?
...
✴ X-ray weakness?
The Inner Regions of Quasars, UT Austin, September 13, 2014
Insights
from
Multiwavelength Observations
The Inner Regions of Quasars, UT Austin, September 13, 2014
Insights from Multiwavelength Observations
Clues from the UV - optical band
UV - optical
(e.g., Diamond-Stanic+09):
✴ quasar luminosities (LBol ~1047-1048 erg s-1).
✴ typical (blue) quasar continua.
✴ no broad absorption lines.
✴ no significant variability.
✴ no significant polarization.
✴ no detection of multiple images (not lensed).
The Inner Regions of Quasars, UT Austin, September 13, 2014
Insights from Multiwavelength Observations
X-ray clues:
✴ no sign of significant absorption.
✴ typical quasar power-law spectra.
SDSS J123132.38+013814.0
z=3.2
0.01
0.5
Γ≅1.8
Shemmer+09
Joint fitting the
X-ray spectra of
11 WLQs
Γ
ï2 0 2 10ï3
r
Counts sï1 keVï1
X-ray
(However, so far, results are tentative: based
mostly on shallow Chandra observations.)
Shemmer+09
1
2
ObservedïFrame Energy (keV)
5
NH
The Inner Regions of Quasars, UT Austin, September 13, 2014
-0.8
5
4
-0.6
3
-0.4
2
-0.2
1
PG 1407+265
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)
0
0.2
-0.5
-1
log R
_ro (Optical - Radio `color’)
-1 Shemmer+09; Plotkin+10
Radio weakness
radio - optical - X-ray
Insights from Multiwavelength Observations
2QZ J215454.3-305654
0
typical quasars
Radio-Quiet AGNs
PHL 1811
X-ray weakness
_ox
-1.5
-1
-2
(Optical - X-ray `color’)
If WLQs are high-redshift BL Lacs, then where is the ‘parent’ population
of X-ray and radio bright weak-lined sources at such redshifts?
The Inner Regions of Quasars, UT Austin, September 13, 2014
Insights from Multiwavelength Observations
Diamond-Stanic+09; Lane+11
1
0.2
a) PL
0.2
Luminous-quasar SED
c)
0.1
Stacking SEDs of 18
WLQs using data from
SDSS+NIR+Spitzer
(Lane+11). WLQ SED is
consistent with an
ordinary-quasar SED.
z~6 quasar SED
1
0.2
BB
b)
1
0.2
LBL
Ordinary-quasar SED
1
hFh [Arbitrary Units]
UV - optical - mid-IR
a)
d)
0.2 0.3
1
2
3 4 5
Rest-Frame Wavelength [µm]
WLQs are unbeamed quasars. The UV emission lines are intrinsically
weak. Can be selected only via spectroscopic surveys.
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us
About the BELR and SED?
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Orientation? (see Niel Brandt’s talk for more details)
Wu+11
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
`Cold’ accretion disk?
Laor & Davis+11
Disk SED peak frequency
decreases as black-hole mass
increases. Fewer energetic
photons are available for
ionizing the BELR. Currently
investigating new HST UV
spectra of WLQs - searching
for a predicted continuum
drop below 1000Å (Plotkin et
al., in prep.).
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Extremely high accretion rates?
Clues from low redshift
Fh [arbitrary units]
SDSS Quasar Template
6.5
Ly"
Shemmer+09
N V + Si II
F! [arbitrary units]
15
C IV
H`
Ha
6
5.5
4000
Fe II
Fe II
4500
5000
Rest-Frame Wavelength [Å]
S IV + O IV]
SDSS Quasar Template
10
PHL 1811
WLQ ?
Mean WLQ Spectrum
5
HST Spectrum of PHL 1811
0
1100
1200
1300
1400
1500
1600
Rest-Frame Wavelength [Å]
1700
Are there low-redshift
analogs to high-redshift
WLQs?
PHL 1811
Leighly+07
1800
Fe II
Fe II
Rest-Frame Wavelength [Å]
Soft SED responsible for
weak high-ionization BELR
lines in WLQs?
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Determining low-ionization emission line EWs and Eddington ratios
[L/LEdd ∝ νLν(5100Å)0.5 FWHM(Hβ)-2]. Requires NIR spectroscopy.
Gemini-North
VLT
– 30 –
3
SiIV CIV
SDSS J1141+0219
z ~ 3.5
Hβ
[O III]
CIII]
MgII
Fλ [10
Fλ (Arbitrary Units)
Exceptionally weak Hβ lines
[O III]
SDSS J1237+6301
z ~ 3.5
-17
-1
-2
-1
erg s cm Å ]
2
Hβ
Hβ
[O III]
Hα
SDSS J0836
Shemmer+10
2
1
Hβ
PR
EL
IM
IN
AR
Y
z=1.749
SDSS J0945
z=1.683
Plotkin+14, in prep.
SDSS J1321
z=1.422
1
SDSS J1411
z=1.754
4400
4600
4800
5000
5200
Rest-Frame Wavelength [Å]
5400
1000
2000
3000
4000
Rest−frame Wavelength (Å)
5000
6000 7000
Fig. 1.— Full X-shoter spectra. The UVB, VIS, and NIR arms are shown in blue, orange, and red,
respectively.
Are the BELRs in WLQs unusually gas deficient
or subject to exotic ionization conditions?
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Extremely high accretion rates or anemic BELRs?
`Modified Baldwin Relation’
EW(C IV) [Å]
Excluding BAL quasars and RLQs
100
10
Baskin & Laor (2004)
1
0.01
0.1
1
L / LEdd
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Extremely high accretion rates or anemic BELRs?
`Modified Baldwin Relation’
EW(C IV) [Å]
Excluding BAL quasars and RLQs
100
10
Baskin & Laor (2004)
Shemmer & Lieber, in prep.
1
0.01
0.1
1
L / LEdd
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Extremely high accretion rates or anemic BELRs?
`Modified Baldwin Relation’
EW(C IV) [Å]
Excluding BAL quasars and RLQs
100
10
Baskin & Laor (2004)
Shemmer & Lieber, in prep.
WLQ
1
0.01
0.1
1
L / LEdd
Q2: Can we determine the Eddington ratio for all quasars?
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Extremely high accretion rates or anemic BELRs?
Γ≅1.9
log (L / LEdd)
0.0
Shemmer+08
-0.5
-1.0
46
-1
46
-1
iLi(5100Å) < 10 ergs s
iLi(5100Å) > 10 ergs s
XMM-Newton
XMM-Newton
6 log (L / LEdd)
-1.5
BCES
FITEXY
MLE
1.0
0.5
0.0
-0.5
-1.0
BCES
1.5
K
2
2.5
log(L/LEdd ) = (1.0 ± 0.3)Γ − (2.5 ± 0.5)
XMM-Newton observations of WLQs to cross-check L/LEdd determinations:
utilizing the hard-X-ray power-law photon index as an accretion-rate indicator
(Stein+14, in prep.).
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Extremely high accretion rates or anemic BELRs?
`Modified Baldwin Relation’
EW(C IV) [Å]
Excluding BAL quasars and RLQs
100
10
Baskin & Laor (2004)
Shemmer & Lieber, in prep.
WLQ
1
0.01
0.1
1
L / LEdd
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
Do WLQs mark a brief evolutionary phase that
all quasars go through (e.g., Hryniewicz+10)?
typical quasars
WLQs
20
N
WLQs constitute
a ≳4σ deviation.
10
0
-1.2
-1
-0.8 -0.6 -0.4 -0.2
0
0.2
0.4
0.6
0.8
log [EW(C IVobs) / EW(C IVpred)]
Q3: How long does it take the BELR to form?
The Inner Regions of Quasars, UT Austin, September 13, 2014
What are WLQs Telling Us About the BELR and SED?
On the To Do List:
✴
✴
✴
Obtain additional NIR and X-ray spectra of WLQs.
✴
Check the dependence of relative line strengths on C IV
blueshift.
✴
Ultimate goal: in conjunction with photoionization modeling,
understand the roles that L, MBH, L/LEdd, the SED, density,
and covering factor, play in determining the relative
strengths of the BELR lines.
Analyze available HST/STIS spectra of six WLQs.
Measure the relative strengths of low- and high-ionization
emission lines in WLQs and compare with ordinary quasars.
The Inner Regions of Quasars, UT Austin, September 13, 2014
Summary of Key Questions
The Inner Regions of Quasars, UT Austin, September 13, 2014
Summary of Key Questions
Q1: What determines the shape of the line EW distributions?
EW(C IV) [Å]
Q2: Can we determine the Eddington ratio for all quasars?
100
10
Baskin & Laor (2004)
Shemmer & Lieber, in prep.
WLQ
1
0.01
0.1
1
L / LEdd
Q3: How long does it take the BELR to form?
typical quasars
WLQs
N
20
10
0
-1.2
-1
-0.8 -0.6 -0.4 -0.2
0
0.2
0.4
0.6
0.8
log [EW(C IVobs) / EW(C IVpred)]
Feedback Welcome!
The Inner Regions of Quasars, UT Austin, September 13, 2014