J-PLUS: Detecting and studying extragalactic globular clusters -- the
  case of NGC 1023
  Extragalactic globular clusters (GCs) are key objects for studying the
formation and evolution of galaxies. The arrival of wide-field surveys such as
the Javalambre Photometric Local Universe Survey (J-PLUS) offers new
possibilities for the study of GCs. Nevertheless, GCs are not detected a priori
by the data reduction pipeline of J-PLUS and, due to its pixel scale, the
standard techniques of GCs detection are challenged. To fill this gap, we
develop a semi-automatic pipeline to detect GCs in J-PLUS that can also be
adapted to similar surveys. As a case study, we use data from the S0 galaxy NGC
1023 and we also study the stellar population content of GC candidates in the
galaxy. To detect GCs, our methodology is based on Source Extractor and does
not require a previous filtering or modelling of the host galaxy. We study
colors and perform spectral energy distribution (SED) analysis on our final GC
candidate catalog to obtain stellar population parameters. In NGC 1023,
GCFinder identifies 523 GC candidates. We observe evidence of color bimodality
in a few broad-band colors but not on narrow-band colors. The SED analysis
reveals a clear metallicity bimodality and we observe that narrow-band filters
are very useful to constrain metallicities. We also identified a broad
age-metallicity relation as well as a wide metallicity distribution that are
evidence that NGC 1023 experienced accretion events in the past. It is the
first time this kind of study is performed with J-PLUS data. By detecting GC
candidates in wide-field images without modeling the light of the galaxy,
GCFinder becomes considerably faster, at a marginal loss of centrally-located
GC candidates of about 7 percent. As GCFinder is entirely based on Source
Extractor, it could be easily incorporated into automated software handling
wide-field surveys.
