Emission-line galaxies from the pears Hubble ultra deep field: A 2D detection method and first results

The Hubble Space Telescope Advanced Camera for Surveys grism Probing Evolution And Reionization Spectroscopically (PEARS) 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 is 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 [O III] emitters are the most common, comprising 44% of the sample, and on average have high equivalent widths (70% of [O III] emitters having rest-frame EW > 100 angstrom). 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 less than or similar to 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.