All Tables

Table 1: Characteristic luminosity L_* in units of $L_\odot$ at 12 ${\mu }$ m (Col. 3) and 24 ${\mu }$ m (Col. 4) of the z=0 luminosity functions used here, as a function of galaxy type (Col. 1). Column 2 gives the value of the parameter p₂, the rate defined by $\textit {SFR}_i(t)=M_{{\rm gas}}(t)/{p_2}$ . Galactic winds occur at an age of 3 Gyr in ellipticals of type E and ULIRG, and at 1 Gyr in ellipticals of type E2; there are no galactic winds in spirals. Infall time scale of ULIRGs is 100 Myr as for ellipticals of type E or E2; it regularly increases for spirals from 2.8 Gyr (Sa) to 8.0 Gyr (Im) (see text for details and references). The L_*(12 ${\mu }$ m) for the normal types (other than ULIRG) are derived from the L_*(B_J) of the observed optical luminosity functions from Heyl et al. (1997) and the $B_J-12~\mu$ m and $B_J-24~\mu$ m colours, in the AB magnitude system, are computed at $z\simeq 0$ with PÉGASE.3 (Cols. 5 and 6). The value of $L_{*}(12~\mu$ m) assigned to Sbc galaxies, the brightest emitters in this band, is that of the observed luminosity function measured with IRAS (Rush et al. 1993; Shupe et al. 1998); the same offset as for Sbc is then applied to all types. The last two columns show the adopted number density fraction by type: model 1 (normal galaxies only, Col. 7) uses the type distribution derived from the UV-optical-near IR faint counts (Fioc et al. 1999a) while model 2 (normal galaxies + ULIRGs, Col. 8) is built by replacing 1/3 of normal dust-poor ellipticals (9% of all galaxies) with ultra luminous elliptical galaxies (called ULIRGs). These last galaxies evolve as dusty ellipticals, they are $\simeq$ 2.5 to $\simeq$ 5 mag brighter than normal ellipticals (depending on wavelength), and are thus as luminous as spirals Sbc in the mid-IR at z=0. The number densities for the other galaxy types are identical in both models.