what do we know about the birth of super star clusters?
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What do we know about the birth of super star clusters?. Collaborators: Indraneil Biswas (UVa) Amy Reines (UVa) Rémy Indebetouw (UVa) Bill Vacca (NASA-Ames) Leslie Hunt (INAF) Barb Whitney (SSI) Chip Kobulicky (UWy) Kenny Wood (St.Andrews). - PowerPoint PPT PresentationTRANSCRIPT
What do we know about the birth of super star clusters?
Kelsey Johnson (UVa, NRAO)
Collaborators:Indraneil Biswas (UVa) Amy Reines (UVa)Rémy Indebetouw (UVa) Bill Vacca (NASA-Ames)Leslie Hunt (INAF) Barb Whitney (SSI)Chip Kobulicky (UWy) Kenny Wood (St.Andrews)
Why are Super Star Clusters Interesting?
• Plausibly proto-globular clusters
• Extreme mode of star formation
• Formation common in early universe
• Luminous “simple stellar populations” for probing galaxy evolution
• Impact on the ISM & IGM
How were these incredible clusters
formed?
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 cluster 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
Comparison of Radio SEDs(individual clusters)
24.5
25
25.5
26
26.5
27
9 9.5 10 10.5 11
log([ ])GHz
(log L
_[ / / ]erg s Hz
SBS 0335-052
He 2-10
NGC 5253
W49A
Johnson et al. in prep, Johnson & Kobulnicky 2003, Mezger et al. 1967, Turner et al. 1998, 2004
continuum of sources
Comparison of Radio SEDs(individual clusters)
24.5
25
25.5
26
26.5
27
9 9.5 10 10.5 11
log([ ])GHz
(log L
[ / / ])erg s Hz
SBS 0335-052
He 2-10
NGC 5253
W49A
Johnson et al. in prep, Johnson & Kobulnicky 2003, Mezger et al. 1967, Turner et al. 1998, 2004
• Radii of HII regions < a few pc
• Electron densities >104 - 106 cm-
3
Pressures > 108 kB
• Ionizing Luminosities > 1052-53 s-1
> 1000s O7-type stars
€
M*
Mcloud
≈ 0.5Mcloud
107 Msun
⎛
⎝ ⎜
⎞
⎠ ⎟
12 P
108 kBcm−3K
⎛
⎝ ⎜
⎞
⎠ ⎟
14
What can we learn from radio recombination lines?
(e.g. Mohan, Anantharamaiah, & Goss 2001)
• Densities: ne > 104 cm-3
• Radii: r ~ 2-10 pc
• Ionizing Flux: Nlyc > 1052
Nearly perfect agreement with simple models!
Example: prediction for H92 line
What do we (maybe?) know about their lifetimes?
*Caveat: The external pressure could be much higher
*Caveat: Star formation must be continuous over at least ~10 Myr
IC 4662 (2Mpc)
Linear Resolution ~ 10 pc
NLyc 20 - 2001049 s-1
Large OB associations
“Young” (<10 Myr) optically selected clusters and ultra-young
radio selected clusters are exclusive
Johnson, Indebetouw, & Pisano 2003
Different wavelengths probe different environments
Radio clusters also have an “infrared
excess”
Hot dust near the ionizing stars
Color scale: HST V-band
Contours: VLA X-band
Johnson, Indebetouw, Watson, & Kobulnicky 2004
(other examples in: Vanzi & Sauvage 2004, Cresci et al. 2005, Cabanac et al. 2005)
What can we learn from the near-infrared?
Haro 3
(See also: Hunt, Vanzi, & Thuan, 2001; Plante & Sauvage, 2002)
SBS 0335-052 ultra-low metallicity (Z 1/40 Z)
Color scale: HST NICMOS Pa
Contours: VLA + Pie Town X-band
Color scale: HST ACS F140LP
Contours: VLA + Pie Town X-band
Johnson & Hunt in prep.
NLyc 5,000 1049 s-1
5,000 O7* stars
What can we learn from the mid-infrared?
The radio sources alone account for at least 60% of the mid-IR flux from the entire galaxy
VLA 2 cm contour, Gemini 10m color
(Vacca, Johnson, & Conti 2002)
He 2-10
VLA 2 cm contour, HST V-band color
(Kobulnicky & Johnson 1999)
He2-10 He2-10
New Models: 3D Monte-Carlo Radiation Transfer
(à la Barb Whitney)
Fractal dust structure consistent with the actual ISM
Rin Rout
Fractal Structure
Cocoon Mass (SFE)
Ionizing source(s)
Dust Composition
% Clumpy Dust
Can we use infrared observations to probe the natal environment?
Johnson, Whitney, Indebetouw, & Wood submitted.
Geometric Sequence with Rin increasing
(pseudo-evolutionary sequence)
Near-IRJ, H, K
Spitzer IRAC3.6, (4.5+5.8), 8.0 m
Spitzer MIPS24, 70, 160 m
Example: 90% clumpy, Rout=50pc, SFE=10%
Rin = 5 pcRin = 10 pcRin = 20 pcRin = 30 pcRin = 45 pc
Johnson, Whitney, Indebetouw, & Wood submitted.
Geometric Sequence with Rin increasing
(pseudo-evolutionary sequence)
Near-IRJ, H, K
Spitzer IRAC3.6, (4.5+5.8), 8.0 m
Spitzer MIPS24, 70, 160 m
Example: 90% clumpy, Rout=50pc, SFE=10%
Rin = 5 pcRin = 10 pcRin = 20 pcRin = 30 pcRin = 45 pc
Dependence on Viewing Angle
Near-IRJ, H, K
Spitzer IRAC3.6, (4.5+5.8), 8.0 m
Spitzer MIPS24, 70, 160 m
Indebetouw, Whitney, Johnson, & Wood, ApJ 2006
QuickTime™ and aGIF decompressor
are needed to see this picture.
Variation with Clumpiness alone (averaged over all viewing
angles) Shape of the infrared SED can vary significantly with clumpy fraction
black = smoothred = 99% clumpy
[m]
F
[erg
/s/c
m2 ]
We need to be very careful in our interpretation of IR observations!
DDO 165
NGC1705
NGC1569
NGC7252: 8x107 M_sun
Weidner, Kroupa, & Larsen 2004
Is the formation of super star clusters special?
NGC1705
NGC1569
IC10 IZW18
Extracted from Neff & Ulvestad 2000Whitmore & Zhang 2002
• Linear resolution ~ 100pc• initial luminosity function compatible with a power-law
What is the initial cluster luminosity function?
> -0.1
Thermal radio sources in the Antennae
Resolution: radii ~4pc
HST I-band
Kobulnicky & Johnson 1999, Johnson et al. 2000, Johnson & Kobulnicky 2003, Biswas & Johnson submitted
> -0.1
Thermal radio sources in the He2-10
What is the initial cluster luminosity function?
It appears that in at least some extreme cases cluster formation does not follow a power-law
Probability < 10-
35 from power law
What is going on here?
1) Could be confusion, but this effect should be worse in the Antennae
2) Could be statistics, but similar numbers (12 in Antennae, 7 in He2-10)
3) Could be that for some reason low mass clusters aren’t radio sources, but we see these in other galaxies
4) Could be that dwarf galaxies can isolate a “mode” of star formation
Antennae He 2-10
Outstanding questions related to Massive Star Formation
Are there environmental differences between the formation of small associations and massive clusters?
e.g. Environmental requirements? Protostellar interactions?
How does the process of star formation vary between small associations and massive clusters?
e.g. Star formation efficiency?
What is the role of metallicity in super star cluster formation as it relates to globular cluster formation in the early universe?
e.g. Cooling, hardness of radiation field?
Looking toward the Future (IR - mm)
There is a lot of work to do!
106 M proto cluster at 10 Mpc
JWST
HERSCHELCARMA
ALMASPITZER
SOFIA
?