In this paper we present new chemo-spectro-photometric models of elliptical galaxies in which infall of primordial gas is allowed to occur .
They aim to simulate the collapse of a galaxy made of two components , i.e .
luminous material and dark matter .
The mass of the dark component is assumed to be constant in time , whereas that of the luminous material is supposed to accrete at a suitable rate .
They also include the effect of galactic winds powered by supernova explosions and stellar winds from massive , early-type stars .
The models are constrained to match a number of properties of elliptical galaxies , i.e .
the slope and mean colours of the colour-magnitude relation ( CMR ) , V versus ( V–K ) , the UV excess as measured by the colour ( 1550–V ) together with the overall shape of the integrated spectral energy distribution ( ISED ) in the ultraviolet , the relation between the { Mg _ { 2 } } index and ( 1550–V ) , the mass to blue luminosity ratio { M / L _ { B } } as a function of the { B } luminosity , and finally the broad-band colours ( U–B ) , ( B–V ) , ( V–I ) , ( V–K ) , etc .
The CMR is interpreted as a mass-metallicity sequence of old , nearly coeval objects , whose mean age is 15 Gyr .
Assuming the law of star formation to be proportional to { M _ { g } ^ { k } ( t ) } with k = 1 , the rate of star formation as function of time starts small , grows to a maximum , and then declines thus easily avoiding the excess of metal-poor stars found by BCF with the closed-box scheme ( the analog of the G-Dwarf Problem in the solar vicinity ) .
Owing to their stellar content , infall models can easily reproduce all the basic data of the galaxies under examination .
As far as the UV excess is concerned , the same sources proposed by BCF are found to hold also with the infall scheme .
H-HB and AGB manqué stars of high metallicity play the dominant role , and provide a robust explanation of the correlation between the ( 1550–V ) colour and the luminosity , mass and metallicity of the galaxies .
Furthermore , these models confirm the potential of the ( 1550–V ) colour as an age indicator in cosmology as already suggested by BCF .
In the rest frame of a massive and metal-rich elliptical galaxy , this colour suffers from one major variation : at the onset of the so-called H-HB and AGB-manqué stars ( age about 5.6 Gyr ) .
This transition occurs at reasonably small red-shifts and therefore could be detected with the present-day instrumentation .