Probing the Birth of Super Star Clusters

Kelsey JohnsonUniversity of Virginia

Hubble Symposium, 2005

Why study Why study massive star massive star

cluster cluster formation?formation?

Most stars form in clusters!

To understand star formation in general,

we need to understand the

“clustered” mode

Why study “Super Star Cluster” Why study “Super Star Cluster” formation?formation?

Spitzer image of 30Dor, NASA/JPL-Caltech/B.Brandl

• Formation (may) require extreme physical conditions

• They are plausibly the progenitors of globular clusters

• Formation mode was (probably) common in early universe

• They can have a tremendous impact on both ISM & IGM

“A cluster that is young enough to still contain

massive stars and has the possibility of evolving into a

globular cluster”

age ≤ 10 Million years

mass ≥ 104 - 105 M

radii ≤ a few parsecs

Super star clusters (SSCs):

A fossil inthe Milky

Way...

• > 10 billion years old

• a few parsecs in size

• ~ 104 - 106 stars

How were these incredible

objects formed?

Observational strategy:If we want to understand cluster formation, it’s not a bad idea to observe them while they are

forming.

HST image of the Antennae Galaxies B.Whitmore/NASA

Problem:Once clusters are fully visible in optical light,

their birth environments have been dramatically

altered

Can we learn from Galactic Star Forming Regions?

From Ultracompact HII Regions to Proto Globular Clusters

Key Questions:

How do the properties of star formation scale

between these regimes?

How do the properties depend on

environment?

Strategy: Look for sources with similar SEDs to Ultracompact HII regions

S

(cm)100 1

non-thermal

free-free

optically-thick free-free

Wood & Churchwell 1989

Compact, “inverted spectrum” sources

Very dense HII regions

• Radii of HII regions

• Electron densities Pressures

• Ionizing flux Stellar Masses

Model:

Henize 2-10 (9 Mpc, linear res ~ 20pc)

VLA 2 cm contour, Gemini 10m color-scale

(Vacca, Johnson, & Conti 2002)

Three brightest radio sources alone account for at least 60% of the mid-IR flux from the entire galaxy

VLA 2 cm contour, HST V-band color-scale

(Kobulnicky & Johnson 1999, Johnson & Kobulnicky 2003)

Haro 3 (13 Mpc, linear res ~ 20pc)

These radio clusters also have

an “infrared excess”

Hot dust near the ionizing stars

Color scale: HST V-band

Contours: VLA X-band

Johnson et al. 2004

Massive proto-cluster detected in mid-IR: Av > 15 - 30 AND similar embedded stellar mass

(Hunt, Vanzi, & Thuan, 2001; Plante & Sauvage, 2002)

SBS 0335-052 (53 Mpc, linear res ~ 25pc)

ultra-low metallicity (Z 1/40 Z)

NLyc 12,000 1049 s-

1 12,000 O7* stars Yikes!

Color scale: HST NICMOS Pa

Contours: VLA + Pie Town X-band

Color scale: HST ACS F140LP

Contours: VLA + Pie Town X-band

John

son &

Pla

nte

in p

rep.

3D Monte-Carlo Radiative Transfer

Johnson, Whitney, & Indebetouw in prep.

Near-IRJ, H, K

Spitzer IRAC3.6, (4.5+5.8), 8.0 m

Spitzer MIPS24, 70, 160 m

Modeling the Evolution of Super Star Clusters

Example: 90% clumpy, Rin = 5pc, Rout=50pc, SFE=10%

• Enables dust structure

• Enables multiple sources

3D Monte-Carlo Radiative Transfer: Super Star Clusters Geometric Sequence (pseudo evolution)

Johnson, Whitney, & Indebetouw, in prep

Model Evolution of SED

• SFE 10%, Rout=25pc

% Smooth

100%

90%

50%

10%

1%

Rin= 1pcRin= 3pcRin= 6pcRin= 9pcRin= 12pcRin= 15pcRin= 18pcRin= 21pcRin= 24pc

WARNING!WARNING!WARNING!WARNING!WARNING!WARNING!Assuming that dust cocoons are

smooth can lead to vastly misinterpreting Spitzer data. Proceed

with caution!

To Do List: • Directly measure densities, pressures, temperatures

(use IR forbidden lines, molecular lines, RRLs)

• Directly measure radii with high resolution (EVLA, SKA at some point)

• Determine how much ionizing radiation escapes (need bolometric luminosities,

clumpiness)

• Determine star formation efficiency (high resolution HI, CO, H2)

• Find out if the individual stars have individual cocoons? (dependence on the evolutionary

state?)

• Determine how clumpy the dust is (high-resolution imaging and SED

models)

• Determine the temperature profiles (high-resolution photometry and

SED models)

Looking toward the Future (IR - mm)

106 M proto cluster at 10 Mpc

Summary

• Super Star Clusters are an important mode of star formation (plausibly proto globular clusters!)

• We have a sample of natal clusters in a range of galactic environments, and we are learning about their formation

• Thermal IR SEDs can be significantly affected by clumping

• There is a lot to learn about these objects, and the new generation of telescopes will provide powerful diagnostics

• The future is extremely bright for this type of research