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Polycyclic Aromatic Hydrocarbon from the MagellanicClouds
Hony and Spitzer/SAGE-SPEC teamGalliano, Seok, Neelamkodan, Kemper, Madden, Indebetouw, Gordon,
Sandstrom
11 Aug 2017
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 1 / 20
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Overview
1 Introduction: Polycyclic Aromatic HydrocarbonsAstronomical PAH bandsMain interest (tracers, photo-electric heating)
2 This studyMain objectivesPresentation of regions
3 Results and discussionFeature mapsTrendsDifferences between SMC and LMCResolution matters
4 Conclusions
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 2 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Astronomical PAH bands
What are PAHs?
NGC 7027
3 4 5 6 8 10 12Wavelength [µm]
Family of strong, broad emission bands in the mid-IR
Main fingers at 3.3, 6.2, 7.7, 7.9, 8.6, 11.2 and 12.7 µm
Found in many types of ISM and CSM, including harsh conditions
Stable
From abundant elements
Identified with resonances inaromatic macro-molecules
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 3 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Astronomical PAH bands
What are PAHs?
NGC 7027
3 4 5 6 8 10 12Wavelength [µm]
Family of strong, broad emission bands in the mid-IR
Main fingers at 3.3, 6.2, 7.7, 7.9, 8.6, 11.2 and 12.7 µm
Found in many types of ISM and CSM, including harsh conditions
Stable
From abundant elements
Identified with resonances inaromatic macro-molecules
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 3 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Astronomical PAH bands
What are PAHs?
Family of strong, broad emission bands in the mid-IR
Main fingers at 3.3, 6.2, 7.7, 7.9, 8.6, 11.2 and 12.7 µm
Found in many types of ISM and CSM, including harsh conditions
In the context of star formation:PAH emission from the edges ofilluminated clouds
Puga+09
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 4 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Main interest (tracers, photo-electric heating)
Why are they interesting?
Astronomical:
Strength used as SFR indicator
Equivalent Width is used as AGN diagnostic
Black: low-metallicity starburstsRed: 12+(O/H) > 8.35Green: 8 < 12+(O/H) < 8.35Blue: 12+(O/H) < 8
Calzetti 2010
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 5 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Main interest (tracers, photo-electric heating)
Why are they interesting?
Astronomical:
Strength used as SFR indicator
Equivalent Width is used as AGN diagnostic
Black: low-metallicity starburstsRed: 12+(O/H) > 8.35Green: 8 < 12+(O/H) < 8.35Blue: 12+(O/H) < 8
Calzetti 2010
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 5 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Main interest (tracers, photo-electric heating)
Why are they interesting?
Astronomical:
Strength used as SFR indicator
Equivalent Width is used as AGN diagnostic
Physical influence:
Source of free electrons in the neutral gas: dominatethe gas heating via photo-electric effect (PE)
PE-efficiency depends on charge state(Bakes&Tielens 1994)
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 6 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Main interest (tracers, photo-electric heating)
Why are they interesting?
Astronomical:
Strength used as SFR indicator
Equivalent Width is used as AGN diagnostic
Physical influence:
Source of free electrons in the neutral gas: dominatethe gas heating via photo-electric effect (PE)
PE-efficiency depends on charge state(Bakes&Tielens 1994)
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 6 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Main interest (tracers, photo-electric heating)
Band ratio variations: varying charge state
Strong observed variations
CC (6-9 µm) vsCH (3.3 and 11.2 µm)
CC modes activated by chargemeasured by Spitzer/IRAC4
Charge-balance follows G0/ne
Possible spatial trendswith respect to the exciting stars
Understand ISM heating
Does IRAC4 measure wellfull PAH emission?
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 7 / 20
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Introduction: Polycyclic Aromatic Hydrocarbons Main interest (tracers, photo-electric heating)
Band ratio variations: resolved in MW clouds
Berne+12S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 8 / 20
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This study Main objectives
Objectives: PAH spectral diagnositics
Metalicities different from the MW
Smallest attainable beams
Largest coverage (environments; distance to stars, ...)
Spitzer/IRS spectral maps (LMC+SMC)
1/2 -1/5 solar metallicity
5−14µm (SL1,2,3)
∼4′′ resolution (∼1pc)
50-100 pc
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 9 / 20
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This study Main objectives
Objectives: PAH spectral diagnositics
Metalicities different from the MW
Smallest attainable beams
Largest coverage (environments; distance to stars, ...)
Spitzer/IRS spectral maps (LMC+SMC)
1/2 -1/5 solar metallicity
5−14µm (SL1,2,3)
∼4′′ resolution (∼1pc)
50-100 pc
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 9 / 20
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This study Main objectives
Objectives: PAH spectral diagnositics
Metalicities different from the MW
Smallest attainable beams
Largest coverage (environments; distance to stars, ...)
Spitzer/IRS spectral maps (LMC+SMC)
1/2 -1/5 solar metallicity
5−14µm (SL1,2,3)
∼4′′ resolution (∼1pc)
50-100 pc
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 9 / 20
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This study Presentation of regions
Large is still small
Inside yellow boxes full IFU from CUBISM (Smith+2007)
beam matched using Pereira-Santaella+2010
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 10 / 20
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This study Presentation of regions
Sometimes more favourable geometry
∼10 000 independent spectra
Fitted to obtain continuum, emission lines and feature strengths
Monte Carlo error analysis
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 11 / 20
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Results and discussion Feature maps
Feature maps: SMC N66
PAH/mid-IR continuum
Strongly correlate with ionised gas(here S IV in orange contours)
• PAHs destroyed in the ionised gas
• mid-IR boosted due to hot dust
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 12 / 20
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Results and discussion Feature maps
Feature maps: LMC N4
PAH strength ionisation
Some spatial dependence of ionisation state
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 13 / 20
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Results and discussion Feature maps
Feature maps: LMC N11B
No discernible spatialtrends
Clumpy ISM al-lows radiation topenetrate the clouds
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 14 / 20
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Results and discussion Trends
CC modes go together (ionisation dominates)
SMCLMC
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 15 / 20
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Results and discussion Trends
Ionisation “follows” the mid-IR continuum colour
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 16 / 20
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Results and discussion Differences between SMC and LMC
SMC is fainter
Probably related to metallicity
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 17 / 20
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Results and discussion Differences between SMC and LMC
SMC is fainter and less ionised
See also Sandstrom+09S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 18 / 20
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Results and discussion Resolution matters
Ionisation is correlated with PAH brightness
Low ionisation:
Generally faint
Near brighter,ionised l.o.s.
Removed by spatialaveraging
Median Σ7.7/11.2
3.3 → 5.31 → 8 pc linearresolution
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 19 / 20
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Conclusions
Take away points
Ionisation dominates/explains band-ratio variations
Both galaxies span entire range (×5) of ratios (ionisation degree)
SMC fainter in PAHs and exhibits more low ionisation
Little spatial patterns (clumpiness)
Radiation heating acts far (>50 pc) into the cold gas at thesemetalicities
Physical state of the cloud interfaces driven by clumpy ISM
Probably related to more translucent ISM at low-Z
S. Hony (Heidelberg University) LMC and SMC PAH diagnostics 11 Aug 2017 20 / 20