starbursts & super star clusters j. gallagher u. wisconsin-madison with l. j. smith, m....
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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 • 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”
0.01 0.1 1
Starburst Scale (kpc)
Inte
nsit
y
low
high
NGC1569
M82M83
Possible Starburst Scale-Intensity
ULIRGs
OB Assoc
Spiral arm
Orion
1012 L
1010 L
108 L
N1275Starbursts
Main SFR density starburst contribution from moderate mass galactic starbursts:
“downsizing”.
Starbursts are not simply scaled-up versions of normal galactic disks.
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*)
Archetype: 30 Doradus:
small super star cluster or
“SSC”
Berstein & Novaki 1999, APOD
R136 R
ad
ial P
rofi
le
€
ρ(R) ≈ρ 0 R−3
Hunter et al. 1995ApJ, 448, 179
A
B
10
NGC 1569: Dwarf Starburst GalaxyP. Anders, U. Goettingen; data HST: ESA/NASA
De Marchi et al. 1997, ApJ, 479, L27
A = Double Cluster
WR*
Composite spectra:Mixture of ages--high
mass stars, >30-40 Msun
present in SSCs;RSGs in optical of
cluster A
Ho & Filippenko 1996, ApJ, 466, L83
Cool star
Cluster A
NGC 1569 - NIR with WIYN 3.5-m Telescope; Natural Seeing: SF Patterns: SSCs Embedded in Young Star Clouds
B
A
SSCs10
NGC 1569--3 SSCs in ~10 Myr--Feedback induced shift in SF
mode?Increased pressure of SSC A a dominant
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 ??)
ORIs SSC formation in some cases a result of
a feedback enhanced mode of star formation?(NGC1569?)
NGC1569 SSCs NOT detected as luminous X-ray sources: L(x) ≤ 2 x 1036 erg/s
Martin, Kobulnicky, Heckman, 2002, ApJ, 574,663
M. W
estm
oque
tte
(UC
L),
J. G
alla
gher
(U
W),
L. J
. Sm
ith
(UC
L)
Wit
h N
ASA
/ESA
and
WIY
N O
bse
rvat
ory/
NSF
M82: HST WFPC2 + WIYN
M82-nearby giant starburst
Stellar disk
J. Gallagher & L. J. Smith
M82F
M82: 3.5-m WIYN Telescope I-band
M82 view from the ground:
A VERY disturbed galaxy--
bright starburst
clumps: dust and
superimposed SSC “stars”
D=3.6 MPC 1 arcsec
≈19 pc
M82- clump A
M82-SSCs F &
L
M82- clump B
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! <<
Star
burs
t Clu
mp
A
~10 M
yr
Melo
et al
. 200
5, ApJ
NGC 7673 starburst-WFPC2
Homeier, Gallagher, Pasquali
Clumping of compact young star clusters-a step beyond super OB associations?
Characteristic of unstable gas-rich disks subject to intense star formation?
D=40 Mpc; MV=-20
Background galaxy
~8 kpc
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
M82-Chandra X-ray vs HST NIC IR: X-Ray Shocked Winds & Binaries in SSCs?
Kaa
ret
et a
l. 20
04 M
NR
AS,
348
, L28 1 arcsec
Most SSCs not luminous X-ray
sources.
Wind thermalization low within clusters (clumpy winds???)
BH binaries ejected
Implications for intermediate mass BH
growth--nuclei vs. “field”
Age = 60 20 Myr W
HT
sp
ectr
osco
py:
Gal
lagh
er &
Sm
ith
199
9, M
NR
AS
, 304
, 540
25 a
rcsec
HST angular resolution essential to measure sizes!
430 p
cM82-F
€
M = 7.5σ 2r(half mass)
Gr(half mass) = 3.3 pc
σ =13.4 km /s
M =1.2 ×106 Msun
Sm
ith
& G
alla
gher
200
1, M
NR
AS
, 326
, 102
7M82-F: WHT Echelle Spectra & Mass: A
Doomed SSC?SSCs have the mass and size of globular clusters.
Star formation at the high density extreme of the interstellar gas cloud dissipation sequence.
Roles of initial conditions & environment in survival? SFE
vs Mcl?
Smit
h &
Gal
lagh
er 2
001,
MN
RA
S, 3
26, 1
027 L/M vs age of super star
clusters Appears to lack low mass stars!
BUTmass
segregation?
32
1
0.1
M_min
M82-F
?
McCrady, Graham, & Vacca 2005, ApJ, 621, 278
“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.”
?
5 pc
lossStar
Tides
GalacticIMF
Age
Massdensity
ISM
Gallagher & Grebel 2003, IAU 217
ComplexSta
r Cluste
r Ecology:
AffectsSurvivalRates!
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 Conditions??
Chandar et al. 2005, ApJ, 628, 210
Starburst field FUV spectra systematically “older” than SSCs--> substantial cluster dissolution within ~10 Myr?
de Grijs, O’Connell, Gallagher (2001)
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.
Cluster Dynamical Evolution: Mass Segregation
€
tmass ∝ trhm * /mu* ≤ 0.1trh
≈70(M /105)1/ 2 MyrCompact young star clusters may be unstable
againstmass segregation. Primordial mass segregationpotentially 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
• 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.
Cluster Dynamical Evolution: Crossing Time
€
tcross = 2rh /(σ 3) ~1 Myr
∝ 1/ρ
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
€
trh ≈ 700(M /105)1/ 2(rrh /5 pc)3 / 2 m*−1C Myr
C = (lnΛ/10)−1 ≈1
Time scale for two-body relaxation to become important--a fundamental reference time in a star cluster:
But time scale varies with position and mass:
€
tr0 ∝σ 3n*−1m*
−2
Cluster cores evolve rapidly, especially if massive stars Preferentially form near the cluster center.
O. Gerhard 2000, Massive Stellar Clusters, p12
Martin, Kobulnicky, Heckman 2002, ApJ, 574, 663
V(HII) ~ 100 km/s--Slow optical wind
X-ray sources & clusters--diffuse hot gas backgrounds
Dwarf starbursts: NGC1705
Nuclear starbursts: M83
Interactions: M82
Major mergers: NGC6240
Tosi et al WFPC2
Harris et al WFPC2
Pasquali et al. WFPC2
Gallagher et al. WIYN