Understanding Lyman-alpha Nebulae at Low Redshift I: The Sizes,
  Powering, and Kinematics of "Green Bean" Galaxies
  A new but rare sample of spatially extended emission line nebulae, nicknamed
"Green Beans", was discovered at z~0.3 thanks to strong [OIII] emission, and
subsequently shown to be local cousins of the Lyman-alpha (Lya) nebulae found
at high redshift. Here we use follow-up APO/DIS spectroscopy to better
understand how these low redshift Lya nebulae compare to other populations of
strong emission line sources. Our spectroscopic data show that low-z Lya
nebulae have AGN-like emission line ratios, relatively narrow line widths
(FWHM<1000 km s^{-1}), and emission line kinematics resembling those of Type 2
AGN at the same redshift, confirming that they are powered by Type 2 AGN with
typical ionizing continua. While low-z Lya nebulae are larger and less
concentrated than compact, star-forming Green Pea galaxies, we find that they
resemble typical Type 2 AGN in terms of r-band concentration and size. Based on
this pilot study, low-z Lya nebulae appear to be a subset of Type 2 AGN with
bluer optical continua and high [OIII] equivalent widths but with comparable
sizes and similar [OIII] kinematics. These characteristics may simply reflect
the fact that low-z Lya nebulae are drawn from the high luminosity end of the
Type 2 AGN distribution, with higher nuclear activity driving higher [OIII]
equivalent widths and more central star formation leading to bluer optical
continua. Deeper spectroscopic follow-up of the full sample will shed further
light on these issues and on the relationship between these low-z Lya nebulae
and the Lya nebula population at high redshift.
