Probing the Birth of Super Star Clusters
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Transcript of Probing the Birth of Super Star Clusters
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