Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
in Local Group galaxies
Keith Smith
School of Chemistry,
The University of Nottingham
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Team
Martin Cordiner Nick Cox
NASA GSFC KU Leuven
Chris Evans Peter Sarre
UK ATC Nottingham
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Outline
• Diffuse Interstellar bands
– What they are
– Why they might be useful
• Extragalactic DIBs
– LMC & SMC
– M31
– M33
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
• Known since at least 1922
• “The longest standing unsolved problem in
all of spectroscopy” (Krelowski et al 1993)
Jenniskens & Désert 1994
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
• Broad optical absorption features
• Over 400 known
• Ubiquitous in the diffuse ISM
• Carriers are unidentified
• Possibly PAHs
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
• Most are
correlated
with E(B-V)
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
• Some work
better with
N(H I)
Herbig 1993
Figure from D Welty
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
Herbig 1993
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
• Fine structure gas phase molecules
Kerr et al 1996,1998
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Diffuse Interstellar Bands
Polarisation
less than
dust
Cox et al 2007
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Extragalactic DIBs
• Why extragalactic DIBs?
• Provide information on the carriers
– Different ISM conditions
– Disentangle information at other wavelengths
• Can be used as probes of ISM
– Use known correlations
– Measure E(B-V), N(H I), density, UV etc.
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Extragalactic DIBs
• DIBs in a z=0.5 DLA
• Handful of
cosmological
detections
York et al 2006
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Magellanic Clouds
Figure by D Welty (see also poster)
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
M31
•
Cordiner et al 2008a
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
M31
• FAR stronger than expected
Smith 2009
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
M33
•
Cordiner et al
2008b
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
M33
Cordiner et al 2008b
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
M33
• Keck DEIMOS
• 20/37 DIB detection
• 26/41 OB stars
Smith 2009
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
M31 again
• Gemini-N GMOS
• 31/34 OB stars
• 11/34 DIB
detections
W
Cordiner et al submitted E(B-V)
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
M31 again
Red 8µm
Green V
Blue UV field
○ DIB detections
× non-detections
Cordiner et al submitted
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Further Work
• WHT AF2 spectra of M33
– 34 OB stars
– E(B-V) = 0.0-0.8
– October 2009
• High resolution follow-up of the two
anomalously strong sightlines
• Improve statistics in LMC & SMC
Introduction Diffuse Bands LMC & SMC M31 M33 Summary Keith Smith 30.07.10
Summary
• Diffuse interstellar bands could be useful
• Detections in M31, M33, LMC, SMC, DLA
• Differ from MW relations
• Two sightlines with very strong DIBs