High-resolution H α imaging of the northern Galactic plane and the IGAPS image database

Greimel, R., et al.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. It captures the entire northern Galactic plane within the Galactic coordinate range |b|< 5° and 30° < ℓ < 215°. From the beginning, the incorporation of narrow-band Hα imaging has been a unique and distinctive feature of this effort. Alongside a focused discussion of the nature and application of the Hα data, we present the IGAPS world-accessible database of images for all five survey filters, i, r, g, URGO, and narrow-band Hα, observed on a pixel scale of 0.33 arcsec and at an effective (median) angular resolution of 1.1-1.3 arcsec. The background, noise, and sensitivity characteristics of the narrow-band Hα filter images are outlined. Typical noise levels in this band correspond to a surface brightness at full ∼1 arcsec resolution of around 2 × 10-16 erg cm-2 s-1 arcsec-2. Illustrative applications of the Hα data to planetary nebulae and Herbig-Haro objects are outlined and, as part of a discussion of the mosaicking technique, we present a very large background-subtracted narrow-band mosaic of the supernova remnant Simeis 147. Finally, we lay out a method that exploits the database via an automated selection of bright ionised diffuse interstellar emission targets for the coming generation of wide-field massive-multiplex spectrographs. Two examples of the diffuse Hα map output from this selection process are presented and compared with previously published data.RG benefitted from support via STFC grant ST/M001334/1 as a visitor to UCL. JED and MM acknowledge the support of research grants funded by the Science, Technology and Facilities Council of the UK (STFC, grants ST/M001008/1 and ST/J001333/1). MM was partially supported by the MINECO (Spanish Ministry of Economy) through grant ESP2016-80079-C2-1-R and RTI2018-095076-B-C21 (MINECO/FEDER, UE), and MDM-2014-0369 of ICCUB (Unidad de Excelencia ‘María de Maeztu’). AM acknowledges support from the State Research Agency (AEI) of the Spanish Ministry of Science, Innovation and Universities (MCIU) and the European Regional Development Fund (FEDER) under grant AYA2017-83383-P. PJG is partially supported by NRF-SARChI grant 111692 and acknowledges support from the Netherlands Organisation for Scientific Research (NWO), in contributing to the Isaac Newton Group of Telescopes and through grant 614.000.601. Aspects of the analysis presented have been carried out via TOPCAT and STILTS (Taylor 2006). This research has made use of both the SIMBAD database and the “Aladin sky atlas”, respectively operated and developed at CDS, Strasbourg, France. This research has also made use of the image manipulation software, MONTAGE. It is funded by the National Science Foundation under Grant Number ACI-1440620, and was previously funded by the National Aeronautics and Space Administration’s Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology