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The low-mass part of the IMF From solar neighborhood to galactic implications

The low-mass part of the IMF From solar neighborhood to galactic implications. Mass-magnitude relations The Luminosity Function  The Mass Function The Substellar regime The galactic implication : M/L ratio. Gilles CHABRIER C.R.A.L., ENS-Lyon. Mass-Magnitude relationships.

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The low-mass part of the IMF From solar neighborhood to galactic implications

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  1. The low-mass part of the IMFFrom solar neighborhood to galactic implications Mass-magnitude relations The Luminosity Function  The Mass Function The Substellar regime The galactic implication : M/L ratio GillesCHABRIER C.R.A.L., ENS-Lyon

  2. Mass-Magnitude relationships Mmagnitude ; mmass dN/dm = (dN/dM)(dm/dM)-1 MFLFm-M Constraints from M-dwarf binaries: m-MV, m-MK, m-MJ, m-MH down to 0.1 Msun(Delfosse et al. ‘00; Segransan et al. ‘03)

  3. The Galactic Disk Luminosity Function • Hipparcos data (MV<11) + nearby (< 5pc) sample (Dahn et al. ‘86) • Hipparcos + revised nearby sample (< 5 to 14 pc) (Reid et al. ‘02)  V complete to MV=16 • Local sample in IR bands (Henry & McCarthy ‘90)  Kcomplete to MK=10 Metallicity dispersion :[M/H] = 0 ± 0.2 Age dispersion :0.8  m  0.15 on MS for 5108 1010yr 

  4. Chabrier, review PASP 2003, 115, 763

  5. Chabrier, ApJ 2003, 586, L133

  6. The Brown Dwarf Domain The first stars • BDs discovered down to a few Mjup • Need probability distributions for : - age: P(t) = (D)-1t b(t´)dt´ (SFR) - mass: P(m) = m p(m´)dm´ (IMF) - spatial dist’n: P(r)= r r´2n(r´)dr´ (Chabrier ‘02, ‘03)

  7. The Mass-to-Light ratio Death of the stars : the supernovae • Dynamical arguments (TF relation) + CDM hierarchical simulations of spiral discs  M/L ≈ 1/2  Salpeter ~ 70% galactic mass in objects m<1 Msun • Metal fraction (O-yield) better reproduced if massive stars IMF between Salpeter and Scalo (Portinari, Sommer-Larsen, Tantalo, ‘03)

  8. CONCLUSIONS IMF reasonably well determined from 1Msun to a few Mjup Consistent with star+BD counts and galactic M/L ratio Determination of galactic baryonic (stars + BDs) budget consistent with: power-law for m>1 Msun (≈ <MJeans>) + lognormal for m<1 Msun Theoretical fundation :star formation triggered by dissipation of large scale turbulence + further frag’n (Padoan & Nordlund) Hint for increasing characteristic mass w/ increasing z (decreasing Z)

  9. Chabrier,PASP ‘03

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