1. Studying Nearby Starbursts with HST
Jason Harris (Steward Observatory)
Daniela Calzetti, Jay Gallagher, Denise A. Smith, & Christopher Conselice
Extreme Starbursts :: Lijiang Aug 2005

2. Nearby Starburst Galaxies
Detailed look at the starburst phenomenon
Star Clusters
Interstellar Medium
Age and Mass estimates
Star formation history; duration and duty cycle
Role of interactions
Cluster IMF; specific frequency; dissolution
Ionization and mechanical heating
Feedback and chemical enrichment
Outflows and infall
Extreme Starbursts :: Lijiang Aug 2005

3. Cluster Populations in Starburst Galaxies
M 83
NGC 3077
NGC 5253
Broad-band HST imaging
of 3 nearby starbursts
(F300W, F547M, F814W)
Constrain age and mass of each cluster
Extreme Starbursts :: Lijiang Aug 2005

4. What happens to a cluster as is ages?
Extreme Starbursts :: Lijiang Aug 2005

5. What happens to a cluster as is ages?
Extreme Starbursts :: Lijiang Aug 2005

6. What happens to a cluster as is ages?
The two-color diagram
If cluster colors can be measured accurately,
their ages can be determined
Extreme Starbursts :: Lijiang Aug 2005

7. The Challenge of Cluster Photometry
Star/cluster classification requires exquisite angular resolution, even for nearby starbursts
Starburst galaxies typically suffer heavy extinction incomplete sampling
Cluster populations are often highly crowded makes aperture photometry extremely difficult
Cluster sizes are variable makes profile-fitting photometry extremely difficult
Galaxy backgrounds can be highly variable makes any photometry more difficult
Extreme Starbursts :: Lijiang Aug 2005

8. The Challenge of Cluster Photometry
Aperture Photometry vs. Profile-Fitting Photometry:
a hybrid approach
Extreme Starbursts :: Lijiang Aug 2005

9. Neighbor-cleaned Aperture Photometry
Identify groups of non-crowding objects;
remove all other objects for
“clean” aperture photometry
Extreme Starbursts :: Lijiang Aug 2005

10. Extreme Starbursts :: Lijiang Aug 2005
Extinction from Hα/Hβ
NGC 3077
NGC 5253
Extreme Starbursts :: Lijiang Aug 2005

11. Extreme Starbursts :: Lijiang Aug 2005
From Photometry to
Mass and Age
Starburst99
population
synthesis models
(Leitherer et al. 1999)
Extreme Starbursts :: Lijiang Aug 2005

12. Cluster Mass & Age Distributions
Extreme Starbursts :: Lijiang Aug 2005

13. Narrow-band HST imaging:
Interstellar Medium
M 83
NGC 3077
NGC 5253
Narrow-band HST imaging:
[OIII], Hα, [SII]
Extreme Starbursts :: Lijiang Aug 2005

14. Extreme Starbursts :: Lijiang Aug 2005
Hα Morphology
M 83
NGC 3077
NGC 5253
Extreme Starbursts :: Lijiang Aug 2005

15. Ionization Diagnostics
log( [SII] / Hα )
M 83
NGC 3077
log( [OIII] / Hβ )
NGC 4214
NGC 5253
log( [SII] / Hα )
log( [SII] / Hα )
Photoionization models by Kewley et al. (2001)
Extreme Starbursts :: Lijiang Aug 2005

16. Mapping the “shock” ionization
200 pc
430 pc
410 pc
M 83
NGC 3077
NGC 5253
Black pixels are “non-photoionization” regions
Extreme Starbursts :: Lijiang Aug 2005

17. Results & Implications
• Non-photoionized (shocked?) Hα emission accounts for
~ 3%-4% of total emission, ~15%-25% by area.
• Starbursts in dwarfs deposit 70%-100% of mechanical energy in surrounding ISM (within kpc); may result in
propagating star formation
• Amount of “shocked” gas in dwarfs implies SF duration
>> 30 Myr (consistent with cluster/diffuse stellar ages)
• The starburst in the giant spiral M 83 deposits ~35%-75% of its mechanical energy in the ISM. The shocks are localized
in ‘bubbles’ (no extended shells): confined starburst
Extreme Starbursts :: Lijiang Aug 2005

18. Extreme Starbursts :: Lijiang Aug 2005
Summary
Study star-formation processes in nearby starburst galaxies
Broad-band imaging:
clusters formed on timescale of few x 107 yr
in NGC 5253, no clusters older than 20 Myr...efficient destruction?
very few “Super” star clusters
Narrow-band imaging:
non-photoionization accounts for only a few percent of Hα luminosity
most mechanical energy output from SNe deposited in ISM
non-photoionized regions in M 83 imply confined starburst
Extreme Starbursts :: Lijiang Aug 2005