High resolution H-alpha imaging of the Northern Galactic Plane, and the
  IGAPS images database
  The INT Galactic Plane Survey (IGAPS) is the merger of the optical
photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton
Telescope (INT) obtained between 2003 and 2018. These capture the entire
northern Galactic plane within the Galactic coordinate range, -5<b<+5 deg. and
30<l<215 deg. From the beginning, the incorporation of narrowband H-alpha
imaging has been a unique and distinctive feature of this effort. Alongside a
focused discussion of the nature and application of the H-alpha data, we
present the IGAPS world-accessible database of images for all 5 survey filters,
i, r, g, U-RGO and narrowband H-alpha, observed on a pixel scale of 0.33 arcsec
and at an effective (median) angular resolution of 1.1 to 1.3 arcsec. The
background, noise, and sensitivity characteristics of the narrowband H-alpha
filter images are outlined. Typical noise levels in this band correspond to a
surface brightness at full one-arcsec resolution of around 2e-16
erg/cm2/s/arcsec2. Illustrative applications of the H-alpha data to planetary
nebulae and Herbig-Haro objects are outlined and, as part of a discussion of
mosaicking technique, we present a very large background-subtracted narrowband
mosaic of the supernova remnant, Simeis 147. Finally we lay out a method that
exploits the database via an automated selection of bright ionized diffuse
interstellar emission targets for the coming generation of wide-field
massive-multiplex spectrographs. Two examples of the diffuse H-alpha maps
output from this selection process are presented and compared with previously
published data.
