Transcript Document

Starbursts
&
Super Star Clusters
J. Gallagher
U. Wisconsin-Madison
with L. J. Smith, M.
Westmoquette (UCL), R.
O’Connell (UVa), R. de
Grijs (U. Sheffield)
MODEST-6 Workshop- 29 August 2005
Super Star Clusters (SSCs):
Upper Mass Range for Young Compact Clusters-Densest Single Generation Stellar Systems-Endpoint of Star Formation Dissipational
Sequence
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Stellar mass >104 Msun
Half light radius R1/2 ≤ 5-7 pc
Within R1/2 N*(1 Msun) ~104 - 106 pc-3
Ages << globular clusters 0-few 100 Myr
Common in starbursts--sometimes tightly
packed in starburst “clumps”
Possible Starburst Scale-Intensity
ULIRGs
Intensity
high
M83
1012 L
N1275
M82
1010 L
Starbursts are not
simply scaled-up
NGC1569
versions of normal galactic
disks.
8
10 L
Orion
low
OB Assoc
Spiral arm
0.01
0.1
Starburst Scale (kpc)
Main SFR density
starburst contribution
from moderate mass
galactic starbursts:
1 “downsizing”.
Measuring Parameters
• Linear size R--high angular resolution, 0.1 arcsec or
better needed for D<10 Mpc; half light radius.
• Age tcl--spectral energy distributions; colors okay if
broad wavelength coverage; NIR alone difficult
• Luminosity Lcl()--photometry & extinction
correction; zone of radiative influence for ionization
and mechanical luminosities
• Chemical abundances Z*--stellar or HII spectra
• Dynamical mass--stellar velocity dispersion,
requires cool stars (tssc > 6-7 Myr)
• Stellar mass function--resolved cluster or Mdyn/L
with age & model from measured Lcl(, Z*, tcl, Mcl*)

(R)  0 R
3
R136 Radial Profile
Hunter et al. 1995
ApJ, 448, 179
Archetype:
30 Doradus:
small super star
cluster or “SSC”
Berstein & Novaki 1999, APOD
A = Double Cluster
B
De Marchi et al. 1997, ApJ, 479, L27
A
10
NGC 1569: Dwarf Starburst Galaxy
P. Anders, U. Goettingen; data HST: ESA/NASA
Composite spectra:
Mixture of ages--high mass
stars,
>30-40 Msun
present in SSCs;
RSGs in optical of cluster A
Cluster A
Cool star
Ho & Filippenko 1996, ApJ, 466, L83
WR*
Smith & Gallagher 2001, MNRAS, 326, 1027
NGC 1569 - NIR with WIYN 3.5-m Telescope;
Natural Seeing: SF Patterns: SSCs Embedded
in Young Star Clouds
NGC 1569--3
SSCs SSCs in ~10 Myr-10 induced shift in SF
Feedback
Amode?
Increased pressure of SSC A a dominant
B
factor?
SFR declines as dense ISM exhausted-and
ejected? GMC formation vs. destruction?
Is the formation of SSCs a statistical process as
the
stellar IMF appears to be:
More clusters= higher upper mass limit?
(Yes in Antennae--but are these compact SSCs?
(M82 ??)
OR
Is SSC formation in some cases a result of a
feedback enhanced mode of star formation?
(NGC1569?)
GC1569 SSCs NOT detected as luminous
X-ray sources: L(x) ≤ 2 x 1036 erg/s
Martin, Kobulnicky,
Heckman, 2002, ApJ,
574,663
M. Westmoquette (UCL), J. Gallagher (UW), L. J. Smith (UCL)
With NASA/ESA and WIYN Observatory/NSF
M82-nearby giant starburst
Stellar disk
M82: HST WFPC2 + WIYN
M82: 3.5-m WIYN Telescope I-band
M82 view from the
ground:
A VERY
disturbed
M82F
galaxy--
M82-SSCs
F&L
M82- clump
A
M82- clump B
J. Gallagher & L. J. Smith
bright starburst
clumps: dust and
superimposed
SSC “stars”
D=3.6 MPC 1
arcsec
≈19
pc
M82 SSCs & Starburst Clumps: V-band WFPC2
M82-A1 SSC: 106 M - r1/2~2-3 pc - t<10 Myr
>> L. Smith Talk for Details! <<
NGC 7673 starburstWFPC2
Homeier, Gallagher, Pasquali
~8 kpc
Clumping of compact young star clusters-a
step beyond super OB associations?
Characteristic of unstable gas-rich disks
subject to intense star formation?
Background galaxy
D=40 Mpc; MV=-20
Hubble Ultradeep Field: High-z clumpy & compact starbursts--a
key early star formation mode
Chandra X-ray contours: wind mass loading + thermaliza
Basic astronomy: Astrometry key to IDs,
especially as distance increases…
Chandra vs clusters in Antennae: Fabbiano et al. 2002, ApJ, 577, 710
1 arcsec= 73(D/15 Mpc) pc
Kaaret et al. 2004 MNRAS, 348, L28
M82-Chandra X-ray vs HST NIC IR:
X-Ray Shocked Winds & Binaries in SSCs?
Most SSCs not luminous
1 arcsecsources.
X-ray
Wind thermalization low
within clusters (clumpy
winds???)
BH binaries ejected
Implications for
intermediate mass BH
growth--nuclei vs. “field”
HST angular resolution essential to
measure sizes!
Age = 60  20 Myr
WHT spectroscopy: Gallagher & Smith 1999, MNRAS, 304, 540
430 pc
25 arcsec
M82-F
Smith & Gallagher 2001, MNRAS, 326, 1027
M82-F: WHT Echelle
Spectra & Mass: A
SSC?
SSCs haveDoomed
the mass
and size of
globular clusters.
 r( half mass )
2
M  7.5
Star formation at the high
G density
extreme of the interstellar gas
r( half
 3.3
pc
cloud
dissipation
sequence.
mass )
 of13
.4 km
/s
Roles
initial
conditions
&
environment in survival? SFE vs
6
M  1.2M
M sun
cl?10
Smith & Gallagher 2001, MNRAS, 326, 1027
L/M vs age of super star
clusters
3
2
1
0.1
M_min
M82-F
Appears to
lack low
mass stars!
BUT
mass
segregation
?
?
?
5 pc
“Using PSF-fitting photometry, we derive the cluster’s light-to-mass (L/M) ratio in both near-IR
and optical light and compare to population-synthesis models.
The ratios are inconsistent with a normal stellar initial mass function for the adopted age of
40–60Myr, suggesting a deficiency of low-mass stars within the volume sampled.King model
light profile fits to new Hubble Space Telescope ACS images ofM82-F, in combination with fits
to archival near-IR images, indicate mass segregation in the cluster. As a result, the virial
mass represents a lower limit on the mass of the cluster.”
McCrady, Graham, & Vacca 2005, ApJ, 621, 278
Mass
density
Low M/L in an older SSC--signature of impending
disruption? Why do GCs survive when mortality
rates seem high in nearby SSC systems?
Extra binding (DM???)--Special Formation
Galactic Conditions??
IMF
Tides
Age
ISM
Gallagher &
Grebel 2003,
IAU 217
Star
loss
Compl
exStar
Cluste
r
Ecolog
y:
Affects
Surviv
alRate
s!
Starburst field FUV spectra systematically “older” than SSCs
--> substantial cluster dissolution within ~10 Myr?
Chandar et al. 2005, ApJ, 628, 210
BUT Many M82 region B star clusters have
colors consistent with ages of near 1 gyr.
(also Parmentier, de Grijs & Gilmore 2003,
MNRAS, 342, 208) ->> Evidence of long lived
clusters and multiple bursts associated
with orbital period of M82.
de Grijs, O’Connell, Gallagher (2001)
M82 Starburst Clump B
~1000 Myr clusters
But where are the
2000 Myr clusters?
Cluster Dynamical Evolution: Mass
Segregation
t mass  t rh m * / m u*  0.1t rh
 70 ( M /10 )
5 1/2
Myr
Compact young star clusters may be unstable against
mass segregation. Primordial mass segregation
potentially amplified. IMF & survival complex
relationship.

M82-F as example.
Appears likely candidate for
disruption. Did low mass stars form in a more
extended region?
Summary
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SSCs are commonly produced in intense star forming events with
masses up to and beyond 106 Msun and R1/2 ~ 2-5 pc.
Densest stellar cluster--an extreme of star formation.
SSCs cluster to make “starburst clumps” where SSC-SSC interactions
are possible and which drive galactic winds.
SSCs contain a full range of intermediate-high mass stars.
Central stellar densities can exceed 105 stars/pc3.
Mass segregation may have a major influence on the observed
properties (low M/L ratios) and evolution (dissolution) of SSCs. PDMFs
thus are uncertain.
Statistics of SSCs suggest high early disruption rates in starbursts,
although in some cases significant numbers of clusters reach ~1 Gyr in
age.
SSCs do not appear to generally host strong X-ray sources, suggesting
that SNe II binaries are ejected.
M82--11.7 microns--compact star forming regions
Lipscy & Plavchan 2004, ApJ, 603, 82
NGC1569-photo ages: Anders et al. 2004, MNRAS, 347, 17
2002 A&A, 381, 825
Merlin: compact radio sources
SNRs in NGC1569: Triggered SF?
McCrady, Gilbert, & Graham 2003, ApJ, 596, 240
Cluster Dynamical Evolution:
Crossing Time
t cross  2 rh /(  3 ) ~ 1 Myr

1/
Cluster crossing times typically 1% or less
of galactic orbital periods and 10% or less
of massive star evolutionary time scales.

We are dealing with systems that
experience substantial dynamical
evolution: SSCs not durable?

Clusters & Dynamical Evolution: Two
Body Relaxation
Time scale for two-body relaxation to become important-a fundamental reference time in a star cluster:
t rh  700 ( M /10 )
5 1/ 2
C  (ln  /10 )
1
( rrh / 5 pc )
3/2
1
m * C Myr
1
But time scale varies with position and mass:
1
*
tr0   n m
3
2
*
Cluster cores evolve rapidly, especially if massive stars
Preferentially form near the cluster center.
O. Gerhard 2000, Massive
Stellar Clusters, p12
X-ray sources & clusters--diffuse hot gas backgrounds
Martin, Kobulnicky, Heckman
2002, ApJ, 574, 663
V(HII) ~ 100 km/s-Slow optical wind
M
8
2
S
U
P
E
R
W
I
N
D
!
A
C
H +[NII]
HST/WFPC2
Smith & Gallagher 2001, MNRAS, 326, 1027
Tosi et al WFPC2
Pasquali et al. WFPC2
Dwarf
starbursts:
NGC1705
Harris et al WFPC2
Nuclear
starbursts
: M83
Interactions: M82
Gallagher et al. WIYN
Major
mergers
:
NGC624
0
M82: Radio (Rodriguiz-Rico et al. 2004, ApJ, 616, 783) vs.
HST F160W NICMOS Image OR
Perils of 1 arcsec rms positions
+ SNR
x HII region