Spectroscopic Study of the HST/ACS PEARS Emission-Line Galaxies
  We present spectroscopy of 76 emission-line galaxies (ELGs) in CDF-S taken
with the LDSS3 spectrograph on Magellan Telescope. These galaxies are selected
to have emission lines with ACS grism data in the Hubble Space Telescope
Probing Evolution and Reionization Spectroscopically (PEARS) grism Survey. The
ACS grism spectra cover the wavelength range 6000-9700 \AA\ and most PEARS
grism redshifts are based on a single emission line + photometric redshifts
from broad-band colors; the Magellan spectra cover a wavelength range from 4000
{\AA} to 9000 {\AA}, and provide a check on redshifts derived from PEARS data.
We find an accuracy of $\sigma_z$ = 0.006 for the ACS grism redshifts with only
one catastrophic outlier. We probe for AGN in our sample via several different
methods. In total we find 7 AGNs and AGN candidates out of 76 galaxies. Two
AGNs are identified from the X-ray full-band luminosity, $L_{X-ray,FB}>10^{43}$
erg$\;$s$^{-1}$, the line widths and the power-law continuum spectra. Two
unobscured faint AGN candidates are identified from the X-ray full-band
luminosity $L_{X-ray,FB}\sim10^{41}$ erg$\;$s$^{-1}$, the hardness ratio and
the column density, and the emission-line and X-ray derived SFRs. Two
candidates are classified based on the line ratio of [NII]\lambda6584/H$\alpha$
versus [OIII]$\lambda$5007/H$\beta$ (BPT diagram), which are between the
empirical and theoretical demarcation curves, i.e, the transition region from
star-forming galaxies to AGNs. One AGN candidate is identified from the
high-ionization emission line HeII{\AA}4686.
