The effect of dust on photometric redshift measurement: a self-consistent technique

A new method is developed for estimating photometric redshifts, using reali stic template SEDs, extending over four decades in wavelength (i.e. from 0. 05 mum to 1 mm). The template SEDs are constructed for four different spect ral types of galaxies (elliptical, spiral, irregular and starburst), satisf ying the following characteristics: a) they are normalised to produce the o bserved colours of galaxies at z similar to 0; b) incorporate the chemo-pho tometric spectral evolution of galaxies of different types, in agreement wi th the observations; c) allow treatment of dust contribution and its evolut ion with redshift, consistent with the spectral evolution models; d) includ e absorption and re-emission of radiation by dust and hence, realistic esti mates of the far-infrared radiation; e) include correction for inter-galact ic absorption by Lyman continuum and Lyman forest. Using these template SED s, the photometric redshifts are estimated to an accuracy of Deltaz = 0.11. The simultaneous and self-consistent modelling of both the photometric and chemical evolution of galaxies and the effect of dust, makes this technique particularly useful for high redshift galaxies. The effects on the estimat ed photometric redshifts, due to assumptions in the evolutionary population synthesis models, are investigated and discussed. Also, the degeneracy in the predicted photometric redshifts and spectral types are examined, using a simulated galaxy catalogue.