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Star Formation around Active Galactic Nuclei: Lessons from the mid-IR

Star Formation around Active Galactic Nuclei: Lessons from the mid-IR. D. Alloin & E. Galliano. Embedded Young Massive Star Clusters. M82: Archetypal starburst galaxy. Embedded Young Massive Star Clusters. HST revealed Young Massive Star Clusters (YMC) in local starburst galaxies

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Star Formation around Active Galactic Nuclei: Lessons from the mid-IR

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  1. Star Formation around Active Galactic Nuclei: Lessons from the mid-IR D. Alloin & E. Galliano

  2. Embedded Young Massive Star Clusters M82: Archetypal starburst galaxy

  3. Embedded Young Massive Star Clusters • HST revealed Young Massive Star Clusters (YMC) in local starburst galaxies • 100s to 1000s in some galaxies • 0.5pc to 200pc, mass~10^6Msol • Age, few Myr to 10 Myr • Are they adolescent GC ?

  4. Embedded Young Massive Star Clusters • On the GC time scale • YMCs are very young • On stellar formation time scale • YMCs are already evolved • Comparison with star formation • First stages of YMCs expected to be embedded

  5. ESC…SSC…GC? • We expect the cluster to be embedded in • Dense region of ionized gas (UDHII) • Cocoon of heated dust • We can observe • Radio cm emission • IR nebular lines • MIR continuum • PAH

  6. Embedded Young Massive Star Clusters • Not yet identified in observations • Giant molecular clouds • Sub-mm emission of cold gas • Future: observations with ALMA

  7. NGC1365, NGC1808, visible From HST archive F814W F658N D=18.6Mpc, 1”=90pc D=10.9Mpc, 1”=53pc

  8. NGC1365, NGC1808, visible + radio D=18.6Mpc, 1”=90pc D=10.9Mpc, 1”=53pc Radio data: Forbes & Norris 1998 & Collison et al. 1994

  9. NGC1365, NGC1808, visible + radio =-0.75 F814W F658N 3.6cm 3.6cm =-0.4 =-0.4 =-0.3 =-0.5 =-0.6 D=18.6Mpc, 1”=90pc D=10.9Mpc, 1”=53pc Radio data: Forbes & Norris 1998 & Collison et al. 1994

  10. NGC1365, NGC1808, N-band* *TIMMI2 data

  11. NGC1365, NGC1808, N-band *TIMMI2 data

  12. MIR templates

  13. N-Band colors N_band colors Much redder than HII regions or PDR Deep silicate absorption Av of several 10s Strong [NeII] emission

  14. Interpretation:Embedded Star Clusters • Few objects known • Antennae, NGC5253, SBS0335-052, IIZw40 • 106 to 107 solar masses • Radio index =-0.1 • Radio emission • =-0.1 : thermal free-free emission from HII regions • =-0.8 : non-thermal emission from SNR

  15. Interpretation:Embedded Star Clusters • In NGC1365 and NGC1808 clusters? • negative cm indices: -0.4 to -0.9 • share of thermal and non-thermal emission Fν thermal  ionizing photon productionrate Fv non-thermal  SNrate

  16. Starburst99 model • Model from Leitherer et al. 1999* • 106 solar masses • Instantaneous star formation • Salpeter IMF • We use: • Supernova rate • Ionizing photon production rate • Total star luminosity * www.stsci.edu/science/starburst99

  17. Ionizing photon rate Thermal radio flux Star Luminosity BB flux Starburst99 model SN rate Non-thermal radio flux

  18. Weighing and dating the clusters? Cluster age Predicted cm flux Cluster mass Predicted 12.9µm F Av

  19. NGC1365 3-6 Myr 2 106 solar masses Av=20-40 mag NGC1808 3-5 Myr 0.3 106 solar masses Av=20-40 mag Weighing and dating the clusters? Simple model confirms that these objects are likely to be young embedded clusters: proto-globular clusters??

  20. ISAAC data • Imaging in K, L and M bands • SED of the objects • LR spectroscopy in K(2.2µm) and L(3.5 µm) • Measure Br (K) and Br (L) • Measure extinction: deredden line fluxes • Detect PAH • Compare with more complex models

  21. NGC1365 KLN

  22. KLN NGC1808

  23. Improved Modeling ? • GRASIL • code for spectrophotometry of evolving stellar populations taking into account the effects of dust Silva & Granato 1998

  24. Survival ofEmbedded Star Clusters • Cluster lifetime dependence on mass and environmental effects (Gieles et al, Portegies et al 2002, Baumgardt & Makino 2003). • N-body simulations, Galactic center: D=34 pc, density~700 solar mass/pc3 • 105 solar mass cluster: < 40-120 Myr • 106 solar mass cluster: < 180-500 Myr • Effect of molecular cloud interactions • decrease lifetime by a factor 5-10 • hence lifetimes less than 50 Myr

  25. NGC1068, N band, VISIR SV:knots identification & inner spiral

  26. NGC1068, N band, deconvolved

  27. NGC1068, [NeII]

  28. NGC1068, comparison with Subaru

  29. NGC1068, comparison with NACO/VLT

  30. NGC1068, comparison with [OIII] HST

  31. Survival of Embedded Star Clusters in strong X/UV field? • NLR clouds: high density • Ionization cone: protected cloud back-side • Dust emission • PaH emission • Star formation? • Jet-induced gas compression • Transient micro-bar? • Only minor flux contribution in NGC1068, but size consistent (~14 pc)

  32. Concluding remarks • Observational side: high-resolution imaging & MIR-NIR spectroscopy, mm/cm interferometry • Modeling side: • Codes DUSTY or GRASIL (radiation transfer) • N-body simulations for lifetime estimates • Statistical approaches • Frequency of e-clusters occurrence around AGN • Age sequence versus location?

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