/[dA dln m] or = [l - exp - ]; for (m < m u ), with or = 0.8 (the asymptotic low-mass slope inferred from the mass distribution in young clusters at sub-stellar masses), Γ = 1.35 (the negative of the high-mass slope), m ch = 0.24 (producing a maximum at m max~ m ch), and m u = 120. For a disk age of 11 Gyr, the average value of the star formation rate per unit logarithmic mass interval at 1 MΘ at the solar circle is 620 kpc-2 Myr-1, and the ratio of the present to the mean SFR is b (t0 ) = 1.085, where t0 is the age of the disk.]]>
/ [dA dln m] o = [;l - exp - ] para (m < m u ), donde o = 0.8 (pendiente asintótica a masas bajas inferida de la distribución de masa en la región sub-estelar en asociaciones jóvenes), Γ= 1.35 (pendiente asintótica a masas altas), m ch = 0.24 (que produce un máximo a m max ~ m ch), y m u = 120. Para una edad del disco galáctico de 11 Gyr, el valor promedio de la tasa de formación estelar por unidad logarítmica de masa a 1 MΘ en el círculo solar es 620 kpc-2 Myr-1 y la razón entre la SFR presente y la SFR media es b (t0 ) = 1.085.]]>
Astrofísica
The stellar initial mass function and star formation in the galaxy
A. Parravano*, C.F. McKee**, D.J. Hollenbach**
* Universidad de Los Andes, Centro de Astrofísica Teórica, Mérida 5101a, Venezuela
** Physics Department and Astronomy Department University of California at Berkeley, Berkeley, CA 94720
*** NASA Ames Research Center, MS 245–3, Moffett Field, CA 94035
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Recibido el 13 de enero de 2004 Aceptado el 15 de marzo de 2004
Abstract
We use observational constraints on the galactic ionizing photon production, the surface mass distribution of field M dwarfs, and the mass distribution of brown dwarfs in clusters to produce an effective galactic initial mass function (IMF). We assume that the IMF can be expressed as the product of a smooth function of mass m (in units of MΘ),ψ (m), and a time dependent rate. We express the star formation rate per unit area per unit logarithmic mass interval as /[dA dln m] = [l – exp – ] for (m < mu ), with = 0.8 (the asymptotic low–mass slope inferred from the mass distribution in young clusters at sub–stellar masses), Γ = 1.35 (the negative of the high–mass slope), mch = 0.24 (producing a maximum at mmax~ mch), and mu= 120. For a disk age of 11 Gyr, the average value of the star formation rate per unit logarithmic mass interval at 1 MΘ at the solar circle is 620 kpc–2 Myr–1, and the ratio of the present to the mean SFR is b (t0 ) = 1.085, where t0 is the age of the disk.
Keywords: Stars: formation; stars: mass function; ISM: evolution.
Resumen
Se propone una función inicial de masa efectiva (FIME) para la Galaxia que satisface las siguientes restricciones observacionales: la producción de fotones ionizantes en la Galaxia, la distribución en masa de la densidad superficial de estrellas M y la distribución en masa de Enanas Marrones en asociaciones estelares jóvenes. Se supone que la FIME puede ser expresada como el producto de una función suave de la masa m (en unidades de MΘ), ψ (m) y una tasa dependiente del tiempo. Esta es: / [dA dln m] = [l – exp – ] para (m <mu ), donde = 0.8 (pendiente asintótica a masas bajas inferida de la distribución de masa en la región sub–estelar en asociaciones jóvenes), Γ= 1.35 (pendiente asintótica a masas altas), mch = 0.24 (que produce un máximo a mmax ~ mch), y mu= 120. Para una edad del disco galáctico de 11 Gyr, el valor promedio de la tasa de formación estelar por unidad logarítmica de masa a 1 MΘen el círculo solar es 620 kpc–2 Myr–1 y la razón entre la SFR presente y la SFR media es b (t0 ) = 1.085.
Descriptores: Formación estelar; función inicial de masa estelar.
We acknowledge support from the NASA Astrophysical Theory Program in RTOP 344–04–10–02, which funds The Center for Star Formation Studies, a consortium of researchers at NASA Ames, University of California at Berkeley, and University of California at Santa Cruz. AP was supported as a Senior Associate for part of this research by the National Research Council and by the Universidad de Los Andes by CDCHT project C–1098–01–05–B. The research of CFM is supported in part by NSF grant AST–0098365.
5. J.M. Scalo, The Stellar Initial Mass Function, proceedings of the 38th Herstmonceux Conference, ed. Gary Gilmore and Debbie Howell, ASP Conference Series, 142 (1998) 201 [ Links ]
6. J.M. Scalo, in proceedings for The Birth of Galaxies, Blois, France, June 1998, and astro–ph/9811341 [ Links ]
7. A. Parravano, D.J. Hollenbach, and C.F. McKee, Ap J 584 (2003) 797. [ Links ]
8. C.F. McKee and IP Williams, Ap J 476 (1997) 114. [ Links ]
9. A. A. Muench, E. A. Lada, and C. J. Lada, Ap J 533 (2000) 358. [ Links ]
/[dA dln m] 
or = 
[l - exp - 
]; for (m < m u ), with 
or = 0.8 (the asymptotic low-mass slope inferred from the mass distribution in young clusters at sub-stellar masses), Γ = 1.35 (the negative of the high-mass slope), m ch = 0.24 (producing a maximum at m max~ m ch), and m u = 120. For a disk age of 11 Gyr, the average value of the star formation rate per unit logarithmic mass interval at 1 MΘ at the solar circle is 
620 kpc-2 Myr-1, and the ratio of the present to the mean SFR is b (t0 ) = 1.085, where t0 is the age of the disk.]]>
/[dA dln m] 
= 
[l – exp – 
] for (m < mu ), with 
= 0.8 (the asymptotic low–mass slope inferred from the mass distribution in young clusters at sub–stellar masses), Γ = 1.35 (the negative of the high–mass slope), mch = 0.24 (producing a maximum at mmax~ mch), and mu = 120. For a disk age of 11 Gyr, the average value of the star formation rate per unit logarithmic mass interval at 1 MΘ at the solar circle is 
620 kpc–2 Myr–1, and the ratio of the present to the mean SFR is b (t0 ) = 1.085, where t0 is the age of the disk.