Biases in Physical Parameter Estimates of Lyman Break Galaxies from Broad-band Photometry

Details Biases in Physical Parameter Estimates of Lyman Break Galaxies from Broad-band Photometry Biases in Physical Parameter Estimates of Lyman Break Galaxies from Broad-band Photometry

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21334403l&link_type=abstract

American Astronomical Society, AAS Meeting #213, #344.03; Bulletin of the American Astronomical Society, Vol. 41, p.479

Physics

Scientific paper

We investigate the biases and uncertainties in estimates of physical parameters of high-redshift Lyman break galaxies (LBGs), such as stellar mass, mean stellar population age, and star formation rate (SFR), obtained from broad-band photometry.
These biases arise from the simplifying assumptions often used in fitting the spectral energy distributions (SEDs).
By combining LCDM hierarchical structure formation theory, semi-analytic treatments of baryonic physics, and stellar population synthesis models, we construct model galaxy catalogs from which we select LBGs at redshifts z 3.4, 4.0, and 5.0.
The broad-band photometric SEDs of these model LBGs are then analysed by fitting galaxy template SEDs derived from stellar population synthesis models with smoothly declining SFRs.
We compare the statistical properties of LBGs' physical parameters -- such as stellar mass, SFR, and stellar population age -- as derived from the best-fit galaxy templates with the intrinsic values from the semi-analytic model.
We find some trends in these distributions: first, when the redshift is known, SED-fitting methods reproduce the input distributions of LBGs' stellar masses relatively well, with a minor tendency to underestimate the masses overall.
Second, there are large systematic biases in the distributions of best-fit SFRs and mean ages, in the sense that single-component SED-fitting methods underestimate SFRs and overestimate ages.
We attribute these trends to the different star formation histories predicted by the semi-analytic models and assumed in the galaxy templates used in the SED-fitting procedure, and to the fact that light from the current generation of star formation can hide older generations of stars.
We also investigate the biases when we analyse galaxies' SEDs by fitting templates with more complex SFHs, showing that this only provides better constraints on the SED-derived physical parameters in galaxies with particular types of SFHs, since the behavior of the biases is dependent on galaxy's SFH.

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