Starbursts Super Star Clusters J Gallagher U WisconsinMadison
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 R 1/2 ≤ 5 -7 pc Within R 1/2 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 high b r ta Intensity S ULIRGs s st ur M 83 1012 L M 82 N 1275 1010 L Starbursts are not simply scaled-up NGC 1569 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 136 Radial Profile Hunter et al. 1995 Ap. J, 448, 179 Archetype: 30 Doradus: small super star cluster or “SSC” Berstein & Novaki 1999, APOD
A = Double Cluster B De Marchi et al. 1997, Ap. J, 479, L 27 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 Cool star Ho & Filippenko 1996, Ap. J, 466, L 83 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 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? (M 82 ? ? ) OR Is SSC formation in some cases a result of a feedback enhanced mode of star formation? (NGC 1569? )
GC 1569 SSCs NOT detected as luminous X-ray sources: L(x) ≤ 2 x 1036 erg/s Martin, Kobulnicky, Heckman, 2002, Ap. J, 574, 663
M. Westmoquette (UCL), J. Gallagher (UW), L. J. Smith (UCL) With NASA/ESA and WIYN Observatory/NSF M 82 -nearby giant starburst Stellar disk M 82: HST WFPC 2 + WIYN
M 82: 3. 5 -m WIYN Telescope I-band M 82 view from the ground: A VERY disturbed M 82 F galaxy-- M 82 -SSCs F&L M 82 - clump A M 82 - clump B J. Gallagher & L. J. Smith bright starburst clumps: dust and superimposed SSC “stars” D=3. 6 MPC 1 arcsec ≈19 pc
M 82 SSCs & Starburst Clumps: V-band WFPC 2 M 82 -A 1 SSC: 106 M - r 1/2~2 -3 pc - t<10 Myr >> L. Smith Talk for Details! << A p , M elo e l. a t 5 00 J p A um l C r t s My r u 0 b r ~1 a t 2 S
NGC 7673 starburst. WFPC 2 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, Ap. J, 577, 710 1 arcsec= 73(D/15 Mpc) pc
Kaaret et al. 2004 MNRAS, 348, L 28 M 82 -Chandra X-ray vs HST NIC IR: X-Ray Shocked Winds & Binaries in SSCs? Most SSCs not luminous X 1 arcsec -ray sources. 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 M 82 -F
Smith & Gallagher 2001, MNRAS, 326, 1027 M 82 -F: WHT Echelle Spectra & Mass: A SSC? SSCs have. Doomed 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?
Smith & Gallagher 2001, MNRAS, 326, 1027 L/M vs age of super star clusters 3 2 1 0. 1 M_min M 82 -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– 60 Myr, suggesting a deficiency of low-mass stars within the volume sampled. King model light profile fits to new Hubble Space Telescope ACS images of. M 82 -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. ” Mc. Crady, Graham, & Vacca 2005, Ap. J, 621, 278
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? ? Gallagher & Grebel 2003, IAU 217 Compl ex. Star Cluster Ecolog y: Affects Surviv al. Rate s!
Starburst field FUV spectra systematically “older” than SSCs --> substantial cluster dissolution within ~10 Myr? Chandar et al. 2005, Ap. J, 628, 210
BUT Many M 82 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 M 82. de Grijs, O’Connell, Gallagher (2001)
M 82 Starburst Clump B ~1000 Myr clusters But where are the 2000 Myr clusters?
Cluster Dynamical Evolution: Mass Segregation Compact young star clusters may be unstable against mass segregation. Primordial mass segregation potentially amplified. IMF & survival complex relationship. M 82 -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 R 1/2 ~ 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/pc 3. 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.
M 82 --11. 7 microns--compact star forming regions Lipscy & Plavchan 2004, Ap. J, 603, 82
NGC 1569 -photo ages: Anders et al. 2004, MNRAS, 347, 17
2002 A&A, 381, 825 Merlin: compact radio sources SNRs in NGC 1569: Triggered SF?
Mc. Crady, Gilbert, & Graham 2003, Ap. J, 596, 240
Cluster Dynamical Evolution: Crossing Time 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: But time scale varies with position and mass: Cluster cores evolve rapidly, especially if massive stars Preferentially form near the cluster center. O. Gerhard 2000, Massive Stellar Clusters, p 12
X-ray sources & clusters--diffuse hot gas backgrounds Martin, Kobulnicky, Heckman 2002, Ap. J, 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/WFPC 2
Smith & Gallagher 2001, MNRAS, 326, 1027
Tosi et al WFPC 2 Pasquali et al. WFPC 2 Dwarf starbursts: NGC 1705 Harris et al WFPC 2 Nuclear starbursts : M 83 Major mergers: NGC 624 0 Interactions: M 82 Gallagher et al. WIYN
M 82: Radio (Rodriguiz-Rico et al. 2004, Ap. J, 616, 783) vs. HST F 160 W NICMOS Image OR Perils of 1 arcsec rms positions + SNR x HII region
- Slides: 41