Emission-Line Galaxies from the PEARS Hubble Ultra Deep Field: A 2-D Detection Method and First Results

TL;DR

This paper introduces a novel 2D detection method for emission-line galaxies in the Hubble Ultra Deep Field, revealing numerous compact star-forming knots and demonstrating the technique's effectiveness over traditional methods.

Contribution

A new 2D line-finding approach for identifying emission-line galaxies that detects compact knots within galaxies, enhancing detection of faint and clumpy star-forming regions.

Findings

Detected 96 emission lines from 81 knots in 63 galaxies.

[OIII] emitters are the most common, with high equivalent widths.

Multiple emitting knots within single galaxies indicate varied star formation.

Abstract

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.