1. Polarimetry as a clue toward the nature of
FeLoBAL quasars
Daniel Lawther, Dark Cosmology Centre, Uni. of Copenhagen

2. 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?

3. 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 dλ
Rest wavelength [Å]
Trump et al., AJ Supplement Series, 165:1-18, 2006 July

4. HiBALs vs. LoBALs F dλ 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 dλ
Rest wavelength [Å]
Trump et al., AJ Supplement Series, 165:1-18, 2006 July

5. Iron LoBAL Quasars Fe II* Fe II* Mg II z=0.865 z=0.894 z=2.11 2000 Å
2900 Å
Hall et al. 2002, ASP Conference Series Vol. 255

6. Iron LoBAL Quasars Fe II* Fe II* Mg II z=0.865 z=0.894 z=2.11
~ systemic velocity
z=0.894
z=2.11
2000 Å
2900 Å
Hall et al. 2002, ASP Conference Series Vol. 255

7. Overlapping-trough FeLoBALs
2500 Å
Rest wavelength
4500 Å
1600 Å
Rest wavelength
3000 Å
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!

8. Increasingly dusty BALs...
Reichard et al., AJ, 126: , 2003 December

9. Why are FeLoBALs important?
I don't know... yet. It depends on what causes them! Three possible scenarios have been suggested:

10. 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

11. 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.

12. 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

13. 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?

14. 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.

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

16. 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 -> 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.

17. What do I want to know?
What are the characteristics of FeLoBAL host galaxies (my thesis, IR SEDs, ...)

18. 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)

19. 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?

20. 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?

21. 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 ?

22. 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.

23. FeLoBAL spectropolarimetry: existing studies, Q 0059-2735
Lemy + Hutsemekers, A&A 356 L9-L12 (2000)

24. FeLoBAL spectropolarimetry: existing studies, Q 0059-2735
High P% in BAL troughs
Lemy + Hutsemekers, A&A 356 L9-L12 (2000)

25. FeLoBAL spectropolarimetry: existing studies, Q 0059-2735
Similar P% across continuum, FeII
Lemy + Hutsemekers, A&A 356 L9-L12 (2000)

26. FeLoBAL spectropolarimetry: existing studies, Q 0059-2735
Lemy + Hutsemekers, A&A 356 L9-L12 (2000)

27. Existing studies, J 1556+3517 Flux Polarization % BAL troughs
Brotherton et al. AJ 487:L113-L116, 1997 Oct

28. 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!!!)