Studying Nearby Starbursts with HST

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. Star Clusters Interstellar Medium Detailed look at the starburst phenomenon Nearby Starburst Galaxies • 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 • Broad-band HST imaging • of 3 nearby starbursts • (F300W, F547M, F814W) • Constrain age and mass of each cluster M 83 NGC 3077 NGC 5253 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. If cluster colors can be measured accurately, their ages can be determined The two-color diagram What happens to a cluster as is ages? 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 extinctionincomplete sampling • Cluster populations are often highly crowdedmakes aperture photometry extremely difficult • Cluster sizes are variablemakes profile-fitting photometry extremely difficult • Galaxy backgrounds can be highly variablemakes any photometry more difficult Extreme Starbursts :: Lijiang Aug 2005

8. Aperture Photometry vs. Profile-Fitting Photometry: a hybrid approach The Challenge of Cluster Photometry 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. Extinction from Hα/Hβ NGC 3077 NGC 5253 Extreme Starbursts :: Lijiang Aug 2005

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

14. 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 0.2-1 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. 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