Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt.........4r&link_type=abstract
PhD Thesis, INAOE, Mexico, 2002
Other
1
Scientific paper
The star formation rate (SFR) as a function of time is a common method used to discriminate between different galaxy formation models.
The SFR is measured by different tracers which depend on the distance to the object: the Hα luminosity is used up to redshift one; the forbidden line [OII]λ3727 is used on galaxies with redshifts between 0.4 and 1; the ultraviolet continuum and the far infrared luminosity are, in general, used for galaxies at redshifts higher than 2.
These tracers are based on the results of the synthetic population models which are very sensitive to differences in the initial mass function, metallicity or the stellar evolution models. Another uncertainty comes from the presence of dust in all galaxies with active star formation. Dust grains absorb part of the radiation emitted at optical and ultraviolet wavelengths producing a reddening of the observed object. To quantify the reddening effect is not straight forward due to the presence of stellar absorption lines. In order to have an unbiased history of the star formation rate I estimate the SFR in a group of nearby galaxies using four different estimators (\Ha, \OII, UV and FIR). I propose a new set of relations between the observed luminosities and the corresponding SFR by assuming that the SFR given by the FIR is absolute such that the SFR given by the \Ha, \OII\ and UV luminosities must be made equal to the value given by the FIR. As a result of this normalization I found a SFR history which, at redshift lower than one, follows: (1+z)4.5. In this redshift range there is a good agreement between the SFR given by optically selected samples and that given by FIR selected samples. At redshift higher than 1, and under the assumption that the SFR given by sub-mm selected samples comes from a galaxy population which has no optical counterpart, the SFR is almost constant up to redshift of about 4. At redshift higher than 4 optical and mm galaxy searches may not be sufficiently efficient. I investigated -- using 1-D chemo-hydrodynamical models -- the possibility of detecting the SZ signature of high redshift galaxies at an epoch when the dust emission is not yet dominant. The predicted SZ signature of individual galaxies is very weak. Nevertheless its detection may be possible with the new generation of mm telescopes (i.e. LMT/GTM, ALMA). I propose a differential camera (working simultaneously at 1 mm and 2 mm) mounted on a big collecting area telescope as the ideal instrument to detect the SZ signature. The large number of massive galaxies at high redshift, together with the fact that the SZ is independent of redshift, will produce an SZ ``background'' that if detected will put constraints on galaxy formation theories.
Finally I studied the SZ effect in a group of nearby elliptical galaxies where the presence of hot gas has been revealed by X-ray observations. I conclude that in these galaxies the SZ is weak but perhaps could be detected with the new generation of sensitive cameras and mm facilities. The star formation rate (SFR) as a function of time is a common method used to discriminate between different galaxy formation models.
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