Studying Nearby Starbursts with HST

Jason Harris (Steward Observatory)

Daniela Calzetti, Jay Gallagher, Denise A. Smith, & Christopher Conselice

QuickTime™ and aDV/DVCPRO - NTSC decompressor

are needed to see this picture.

Extreme Starbursts :: Lijiang Aug 2005

Nearby Starburst Galaxies

Extreme Starbursts :: Lijiang Aug 2005

• 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

Star Clusters

Interstellar Medium

Detailed look at the starburst phenomenon

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

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

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

What happens to a cluster as is ages?

The two-color diagram

Extreme Starbursts :: Lijiang Aug 2005

If cluster colors can be measured accurately,their ages can be determined

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

The Challenge of Cluster Photometry

Aperture Photometry vs. Profile-Fitting Photometry:a hybrid approach

Extreme Starbursts :: Lijiang Aug 2005

Neighbor-cleaned Aperture Photometry

QuickTime™ and aFLIC Animation decompressorare needed to see this picture.

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

From Photometry to Mass and Age

Starburst99populationsynthesis models(Leitherer et al. 1999)

Extreme Starbursts :: Lijiang Aug 2005

Cluster Mass & Age Distributions

Interstellar Medium

NGC 3077 NGC 5253M 83

Narrow-band HST imaging:[OIII], Hα, [SII]

Extreme Starbursts :: Lijiang Aug 2005

Hα Morphology

NGC 3077 NGC 5253M 83

Extreme Starbursts :: Lijiang Aug 2005

log( [SII] / Hα )

Ionization Diagnostics

log( [SII] / Hα )

log(

[OIII]

/ H

β )

log( [SII] / Hα )

NGC 3077

NGC 4214

M 83

NGC 5253

Extreme Starbursts :: Lijiang Aug 2005

Photoionization models by Kewley et al. (2001)

Mapping the “shock” ionization

Black pixels are “non-photoionization” regions

NGC 3077 NGC 5253M 83

Extreme Starbursts :: Lijiang Aug 2005

200 pc 430 pc 410 pc

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 starburstExtreme Starbursts :: Lijiang Aug 2005

•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

Summary

Extreme Starbursts :: Lijiang Aug 2005