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

Starburst-AGN connection? oObservations in mid-60s: “hot-spot” nuclei Sersic, Pastoriza, et al. oSuggestions for connection: mid-80s Heckman, Keel, Terlevich, et al. oDeeply embedded star formation = large extinction: near-, mid-, far-IR & radio oMid-IR, IRAS/ISO, radio interferometers oRecent and future: oHST/NICMOS oMid-IR new tools (ESO, Gemini..) oVLA, mm interferometers, ALMA

Backgrounds oRelation to black-hole feeding? oGas compression mechanisms? Bars, nuclear discs.. oSurvival in black-hole gravitational potential, tidal effects? oSurvival in AGN X/UV radiation field? Dust, PaH?

Embedded Star Clusters…Super Star Clusters…Galactic Clusters? oGlobular clusters (GC): fossils from our galaxy oEarly theories: collapse from primordial material oBut… HST revealed Super Star Clusters (SSC) in local starburst galaxies

Embedded Young Massive Star Clusters M82: Archetypal starburst galaxy

Embedded Young Massive Star Clusters oHST revealed Young Massive Star Clusters (YMC) in local starburst galaxies o100s to 1000s in some galaxies o0.5pc to 200pc, mass~10^6Msol oAge, few Myr to 10 Myr oAre they adolescent GC ?

Embedded Young Massive Star Clusters oOn the GC time scale oYMCs are very young oOn stellar formation time scale oYMCs are already evolved oComparison with star formation oFirst stages of YMCs expected to be embedded

ESC…SSC…GC? oWe expect the cluster to be embedded in oDense region of ionized gas (UDHII) oCocoon of heated dust oWe can observe oRadio cm emission oIR nebular lines oMIR continuum oPAH

Embedded Young Massive Star Clusters oNot yet identified in observations oGiant molecular clouds oSub-mm emission of cold gas oFuture: observations with ALMA

Related questions? Black-hole feeding Gas compression mechanisms Survival in strong gravitational potential Survival in hard radiation field? Search for star formation close to AGN

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

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

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

NGC1365, NGC1808, N-band* *TIMMI2 data

NGC1365, NGC1808, N-band *TIMMI2 data

MIR templates

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

Interpretation: Embedded Star Clusters oFew objects known oAntennae, NGC5253, SBS , IIZw40 o10 6 to 10 7 solar masses oRadio index  =-0.1 oRadio emission o  =-0.1 : thermal free-free emission from HII regions o  =-0.8 : non-thermal emission from SNR

Interpretation: Embedded Star Clusters o In NGC1365 and NGC1808 clusters? o negative cm indices: -0.4 to -0.9 o share of thermal and non-thermal emission Fν thermal  ionizing photon production rate Fv non-thermal  SN rate

Starburst99 model oModel from Leitherer et al. 1999* o10 6 solar masses oInstantaneous star formation oSalpeter IMF oWe use: oSupernova rate oIonizing photon production rate oTotal star luminosity *

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

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

NGC1365 o3-6 Myr o solar masses oAv=20-40 mag NGC1808 o3-5 Myr o solar masses oAv=20-40 mag Simple model confirms that these objects are likely to be young embedded clusters: proto-globular clusters??

ISAAC data o Imaging in K, L and M bands oSED of the objects o LR spectroscopy in K(2.2µm) and L(3.5 µm) oMeasure Br  (K) and Br  (L) oMeasure extinction: deredden line fluxes oDetect PAH oCompare with more complex models

NGC1365 K L NK L N

NGC1808 K L NK L N

Improved Modeling ? oGRASIL ocode for spectrophotometry of evolving stellar populations taking into account the effects of dust Silva & Granato 1998

Survival of Embedded Star Clusters oCluster lifetime dependence on mass and environmental effects (Gieles et al, Portegies et al 2002, Baumgardt & Makino 2003). oN-body simulations, Galactic center: D=34 pc, density~700 solar mass/pc 3 o10 5 solar mass cluster: < Myr o10 6 solar mass cluster: < Myr oEffect of molecular cloud interactions odecrease lifetime by a factor 5-10 ohence lifetimes less than 50 Myr

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

NGC1068, N band, deconvolved

NGC1068, [NeII]

NGC1068, comparison with Subaru

NGC1068, comparison with NACO/VLT

NGC1068, comparison with [OIII] HST

Survival of Embedded Star Clusters in strong X/UV field? oNLR clouds: high density oIonization cone: protected cloud back-side oDust emission oPaH emission oStar formation? oJet-induced gas compression oTransient micro-bar? oOnly minor flux contribution in NGC1068, but size consistent (~14 pc)

Concluding remarks oObservational side: high-resolution imaging & MIR-NIR spectroscopy, mm/cm interferometry oModeling side: oCodes DUSTY or GRASIL (radiation transfer) oN-body simulations for lifetime estimates oStatistical approaches oFrequency of e-clusters occurrence around AGN oAge sequence versus location?