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Astron. Astrophys. 338, 807-812 (1998)

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3. The sample of elliptical galaxies

The 21 elliptical galaxies listed in Table 1 have been extracted from the sample by GJ95, who evaluated their FIR luminosity and dust mass from FIR data. All the galaxies are classified as E both in RSA and in de Vaucouleurs et al. (1991) and have magnitudes [FORMULA]. I selected those galaxies which have been detected at both 60 and 100 µm by IRAS (Knapp et al. 1989). H0 = 50 Km s-1Mpc-1 is assumed throughout this paper.


Table 1. The selected sample of elliptical galaxies.
Column (2): total blue luminosities taken from GJ95. Columns (3), (4) and (5): computed values for FIR luminosities, flux ratio and dust color temperatures. The dust masses in Column (6) are taken from GJ95. The FIR dust mass in Column (7) is derived by averaging the results of formulae which are usually adopted, while the FIR dust mass in Column (8) is derived by adopting a temperature distribution model as described in Sect. 2. The uncertainties for the mass evaluations are shown in Fig. 1. N and I stand for NGC and IC respectively.

For each galaxy the FIR luminosity, the flux ratio, the dust temperature and the dust mass from FIR data (hereafter FIR dust mass) have been derived and listed in Table 1. The FIR fluxes by Knapp et al. (1989) have been corrected taking into account the contribution of hot circumstellar dust (GJ95) and have been used for the computation of: the FIR luminosity in the band 40-120 µm (Helou et al. 1985), the flux ratio and the dust color temperature (Henning et al. 1990). The uncertainties in the three quantities depend on the flux uncertainties, which are estimated to be in the range 10[FORMULA]-30[FORMULA] (Knapp et al. 1989). The chemical and physical properties of the dust grains play a critical rôle in the evaluation of the uncertainties on temperature and mass. On the other hand, the present paper is mainly addressed to the dependence of the dust mass on the choice of a particular temperature distribution, and I will not discuss the problem of the dust properties (which will be studied in a forthcoming paper). A spectral index [FORMULA] for the dust is used in all the computations. The FIR dust masses listed in Table 1 are evaluated from the FIR fluxes by means of the single temperature and the temperature distribution models respectively.

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998