The case for OH suppression at near-infrared wavelengths

S. C. Ellis, J. Bland-Hawthorn

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Abstract

We calculate the advances in near-infrared (NIR) astronomy made possible through the use of fibre Bragg gratings to selectively remove hydroxyl emission lines from the night sky spectrum. Fibre Bragg gratings should remove OH lines at high resolution (R = 10 000), with high suppression (30 dB) whilst maintaining high throughput (≈90 per cent) between the lines. Devices presently under construction should remove 150 lines in each of the J and H bands, effectively making the night sky surface brightness ≈4 mag fainter. This background reduction is greater than the improvement adapative optics makes over natural seeing; photonic OH suppression is at least as important as adaptive optics for the future of cosmology. We present a model of the NIR sky spectrum, and show that the interline continuum is very faint (≈80 photons s-1 m-2 arcsec-2 μm-1 on the ecliptic plane). We show that OH suppression by high dispersion, that is, 'resolving out' the skylines, cannot obtain the required level of sensitivity to reach the interline continuum due to scattering of light. The OH lines must be suppressed prior to dispersion. We have simulated observations employing fibre Bragg gratings of first light objects, high-redshift galaxies and cool, low-mass stars. The simulations are of complete end-to-end systems from object to detector. The results demonstrate that fibre Bragg grating OH suppression will significantly advance our knowledge in many areas of astrophysics, and in particular will enable rest-frame ultraviolet observations of the Universe at the time of first light and reionization.

Original languageEnglish
Pages (from-to)47-64
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Volume386
Issue number1
DOIs
Publication statusPublished - 1 May 2008
Externally publishedYes

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Keywords

  • Atmospheric effects
  • Early Universe
  • Infrared: general
  • Instrumentation: miscellaneous

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