Polarimetry as a clue toward the nature of

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Polarimetry as a clue toward the nature of
FeLoBAL quasars
Daniel Lawther, Dark Cosmology Centre, Uni. of
Copenhagen
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Polarimetry as a clue toward the nature of
FeLoBAL quasars
Structure of this talk - What are FeLoBAL
quasars? - Why are they important? - What do we
want to learn about them? - Can polarimetry aid
our understanding?
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Broad Absorption Line Quasars
C IV 1550 Å
Absorption troughs can reach line widths of a few
thousand km/s, can be detached from the BEL, and
are blueshifted. 10-40 of quasars have C IV BAL
- selection issues! Emission line properties
seem identical to non-BALs
F d?
Rest wavelength Å
Trump et al., AJ Supplement Series, 1651-18,
2006 July
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HiBALs vs. LoBALs
Mg II 2796 Å
HiBAL broad absorption in high-ionization lines
(e.g., C IV 1550Å) only. LoBAL also in low
ionization lines (e.g., Mg II 2796 Å). LoBALs
1 of optically-selected, 10 of IR-selected
quasars. (Boroson and Meyers 92)
F d?
Rest wavelength Å
Trump et al., AJ Supplement Series, 1651-18,
2006 July
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Iron LoBAL Quasars
Fe II
Mg II
Fe II
z0.865
z0.894
z2.11
2000 Å
2900 Å
Hall et al. 2002, ASP Conference Series Vol. 255
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Iron LoBAL Quasars
Fe II
Mg II
Fe II
z0.865
systemic velocity
z0.894
z2.11
2000 Å
2900 Å
Hall et al. 2002, ASP Conference Series Vol. 255
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Overlapping-trough FeLoBALs
1600 Å
3000 Å
2500 Å
4500 Å
Rest wavelength
Rest wavelength
Hall et al. 2002, ASP Conference Series Vol. 255
These objects are (obviously) heavily reddened.
Combined with a weak X-ray output, this makes
them easy to miss in surveys!
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Increasingly dusty BALs...
Reichard et al., AJ, 1262594-2607, 2003 December
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Why are FeLoBALs important?

• I don't know... yet. It depends on what causes
  them! Three possible scenarios have been
  suggested

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Why are FeLoBALs important?

• I don't know... yet. It depends on what causes
  them! Three possible scenarios have been
  suggested
• 1) (FeLo)BALs are an orientation effect - the
  underlying mechanism is present in all quasars

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BAL quasars an orientation effect?
Predictions BALs will always be seen at a
specific range of radio-axis PAs a suitable
mirror will reveal unabsorbed LOS.
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Why are FeLoBALs important?

• I don't know... yet. It depends on what causes
  them! Three possible scenarios have been
  suggested
• 1) (FeLo)BALs are an orientation effect - the
  underlying mechanism is present in all quasars
• 2) (FeLo)BALs are an early stage of quasar
  evolution

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BALs as an evolutionary phase
Absorbing cocoon
Acc. disk
- (FeLo)BALs as an intermediate step between
ULIRG and ordinary quasar? - Predictions BALs
will have a wide range of radio-axis PAs
spectropolarimetric signature of a shell
geometry?
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Why are FeLoBALs important?

• I don't know... yet. It depends on what causes
  them! Three possible scenarios have been
  suggested
• 1) (FeLo)BALs are an orientation effect - the
  underlying mechanism is present in all quasars
• 2) (FeLo)BALs are an early stage of quasar
  evolution
• 3) FeLoBALs are just weird - intrinsically
  different from normal quasars, irrespective of
  viewing angle and active lifetime.

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Why are FeLoBALs important?

• ...because they can constrain the unification
  model
• OR
• because they are a key piece of the quasar
  turn-on puzzle
• OR
• because they must somehow form in a different
  manner to ordinary quasars.

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BAL spectropolarimetry existing studies(Kill or
replace with plots!)

• LoBALs show decreasing polarised flux towards
  long wavelengths (Kartje 95)
• Polarisation not correlated with radio loudness
  (Green et al. 2008)
• Light at bottom of BAL troughs is highly
  polarized -gt scattered paths are less absorbed?
• BALs can show polarization with PA parallel to
  the radio axis(Brotherton et al. 2006), and with
  viewing angles close to the radio axis (Wang et
  al. 2007), indicating non-edge-on viewing angle.

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What do I want to know?

• What are the characteristics of FeLoBAL host
  galaxies (my thesis, IR SEDs, ...)

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What do I want to know?

• What are the characteristics of FeLoBAL host
  galaxies (my thesis, IR SEDs, ...)
• FeLoBAL inclination range (from radio axis, from
  polarimetry, from radio spectral index)

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What do I want to know?

• What are the characteristics of FeLoBAL host
  galaxies (my thesis, IR SEDs, ...)
• FeLoBAL inclination range (from radio axis, from
  polarimetry, from radio spectral index)
• How reliable are the inclination indicators if
  FeLoBALs are wierd?

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What do I want to know?

• What are the characteristics of FeLoBAL host
  galaxies (my thesis, IR SEDs, ...)
• FeLoBAL inclination range (from radio axis, from
  polarimetry, from radio spectral index)
• How reliable are the inclination indicators if
  FeLoBALs are wierd?
• Where are the LoBAL outflows?

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What do I want to know?

• What are the characteristics of FeLoBAL host
  galaxies (my thesis, IR SEDs, ...)
• FeLoBAL inclination range (from radio axis, from
  polarimetry, from radio spectral index)
• How reliable are the inclination indicators if
  FeLoBALs are wierd?
• Where are the LoBAL outflows?
• Where is the absorbing Fe II ?

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My MSc thesis FeLoBAL host galaxy studies using
HST imaging
Orientation scenario FeLoBALs should have host
galaxy properties statistically indistinguishable
from 'ordinary' quasar hosts. Evolutionary
scenario What causes quasar activity to start?
Major mergers are one possibility - in which
case, FeLoBAL hosts will display signs of recent
mergers. OddBALs Some subset of BALs are just
intrinsically different to other quasars. Host
galaxy signature unknown.
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FeLoBAL spectropolarimetry existing studies, Q
0059-2735
Lemy Hutsemekers, AA 356 L9-L12 (2000)
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FeLoBAL spectropolarimetry existing studies, Q
0059-2735
High P in BAL troughs
Lemy Hutsemekers, AA 356 L9-L12 (2000)
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FeLoBAL spectropolarimetry existing studies, Q
0059-2735
Similar P across continuum, FeII
Lemy Hutsemekers, AA 356 L9-L12 (2000)
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FeLoBAL spectropolarimetry existing studies, Q
0059-2735
Lemy Hutsemekers, AA 356 L9-L12 (2000)
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Existing studies, J 15563517
Flux
Polarization
BAL troughs
Brotherton et al. AJ 487L113-L116, 1997 Oct
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FeLoBAL spectropolarimetry a few suggestions
What is the sp.polarimetric signature of an
absorbing shell? - look at more FeLoBALs in
spectropolarimetry do we generally see polarized
BELs? Polarized light in BAL troughs? What do
overlapping-trough objects look like in
spectropolarimetry? Is there a lot of scattered
nuclear light in BAL troughs? (May be problematic
for my thesis!!!)