Probing the Birth of Super Star Clusters Kelsey Johnson University of Virginia Hubble Symposium, 2005

Why study massive star cluster formation? Most stars form in clusters! To understand star formation in general, we need to understand the “clustered” mode

Why study “Super Star Cluster” 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 ≥ M  radii ≤ a few parsecs Super star clusters (SSCs):

A fossil in the Milky Way... > 10 billion years old a few parsecs in size ~ 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) 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 10  m 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: A v > AND similar embedded stellar mass (Hunt, Vanzi, & Thuan, 2001; Plante & Sauvage, 2002) SBS (53 Mpc, linear res ~ 25pc) ultra-low metallicity (Z  1/40 Z  ) N Lyc  12,000  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 Johnson & Plante in prep.

3D Monte-Carlo Radiative Transfer Johnson, Whitney, & Indebetouw in prep. Near-IR J, H, K Spitzer IRAC 3.6, ( ), 8.0  m Spitzer MIPS 24, 70, 160  m Modeling the Evolution of Super Star Clusters Example: 90% clumpy, R in = 5pc, R out =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%, R out =25pc % Smooth 100% 90% 50% 10% 1% R in = 1pcR in = 3pcR in = 6pcR in = 9pcR in = 12pcR in = 15pcR in = 18pcR in = 21pcR in = 24pc

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, H 2 ) 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) 10 6 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