Hα + [N II] observations of the H II regions in M81

Weipeng Lin, Xu Zhou, David Burstein, Rogier Windhorst, Jiansheng Chen, Wen Ping Chen, Zhaoji Jiang, Xu Kong, Jun Ma, Wei Hsin Sun, Hong Wu, Suijian Xue, Jin Zhu

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12 Scopus citations


In a first of a series of studies of the Hα + [N II] emission from nearby spiral galaxies, we present measurements of Hα + [N II] emission from H II regions in M81. Our method uses large-field CCD images and long-slit spectra and is part of the ongoing Beijing-Arizona-Taipei-Connecticut Sky Survey (the BATC survey). The CCD images are taken with the National Astronomical Observatories of China (NAOC) 0.6/0.9 m f/3 Schmidt telescope at the Xinglong Observing Station, using a multicolor filter set. Spectra of 10 of the brightest H II regions are obtained using the NAOC 2.16 m telescope with a Tek 1024 × 1024 CCD. The continua of the spectra are calibrated by flux-calibrated images taken from the Schmidt observations. We determine the continuum component of our Hα + [N II] image via interpolation from the more accurately measured backgrounds (M81 starlight) obtained from the two neighboring (in wavelength) BATC filter images. We use the calibrated fluxes of Hα + [N II] emission from the spectra to normalize this interpolated, continuum-subtracted Hα + [N II] image. We estimate the zero-point uncertainty of the measured Hα + [N II] emission flux to be ∼8%. A catalog of Hα + [N II] fluxes for 456 H II regions is provided, with those fluxes being on a more consistent linear scale than previously available. The logarithmically binned Hα + [N II] luminosity function of H II regions is found to have slope α = -0.70, consistent with previous results (which allowed α = -0.5 to -0.8). From the overall Hα + [N II] luminosity of the H II regions, the star formation rate of M81 is found to be ∼0.68 M yr-1, modulo uncertainty with extinction corrections.

Original languageEnglish (US)
Pages (from-to)1286-1294
Number of pages9
JournalAstronomical Journal
Issue number3 1773
StatePublished - Sep 2003


  • Galaxies: individual (M81)
  • Galaxies: photometry
  • H II regions

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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