A Comparison Of Galaxy Counts From Recent Surveys

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A Comparison Of Galaxy Counts From Recent Surveys

• T. Dolch (JHU), H.C. Ferguson (STScI)

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Correcting For Missing Light

• We adopt a simple, purely empirical, bivariate
  size-magnitude relation

Number-magnitude relation
Size-magnitude relation
Both mean size and width vary with magnitude
We construct a two-dimensional probability
distribution from this model, convolve it with
the observational transfer function, and
determine the best fit via maximum likelihood. We
fit GOODS and the UDF separately. The transfer
function is a smooth approximation to the scatter
and incompleteness of the surveys determined from
simulations where artificial galaxies were
inserted into the images and measured using
Sextractor (Ferguson et al. 2004).
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Data and Model Probability Distributions
Illustration using the GOODS z band. The white
square shows the region used for the fits.
Roughly 28000 galaxies are used in the fit.
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Number-magnitude and magnitude-size relations
Galaxy Counts Blue points are the GOODS z-band
data. The green line is the best-fit model after
application of the transfer function. The red
line is the input model with no observational
selection or measurement biases. Dotted lines
show the boundaries of the region used for the
fitting.
Galaxy Sizes in different intervals of apparent
magnitude (Sextractor MAG_AUTO).