  The Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) grism
PEARS (Probing Evolution And Reionization Spectroscopically) survey provides a
large dataset of low-resolution spectra from thousands of galaxies in the GOODS
North and South fields. One important subset of objects in these data are
emission-line galaxies (ELGs), and we have investigated several different
methods aimed at systematically selecting these galaxies. Here we present a new
methodology and results of a search for these ELGs in the PEARS observations of
the Hubble Ultra Deep Field (HUDF) using a 2D detection method that utilizes
the observation that many emission lines originate from clumpy knots within
galaxies. This 2D line-finding method proves to be useful in detecting emission
lines from compact knots within galaxies that might not otherwise be detected
using more traditional 1D line-finding techniques. We find in total 96 emission
lines in the HUDF, originating from 81 distinct "knots'' within 63 individual
galaxies. We find in general that [OIII] emitters are the most common,
comprising 44% of the sample, and on average have high equivalent widths (70%
of [OIII] emitters having rest-frame EW>100A). There are 12 galaxies with
multiple emitting knots--with different knots exhibiting varying flux values,
suggesting that the differing star formation properties across a single galaxy
can in general be probed at redshifts z~0.2-0.4. The most prevalent
morphologies are large face-on spirals and clumpy interacting systems, many
being unique detections owing to the 2D method described here, thus
highlighting the strength of this technique.
