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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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