Superb Observations with OHS (CISCO)
July 6, 2000
On May 24th and 25th of this year, OHS (CISCO) at the Nasmyth focus of Subaru Telescope observed the distant radio galaxy 4C+40.36 located about 10 billion light years from Earth. 4C+40.36 is a strong emitter of radio waves. It also produces strong emission due to hydrogen, helium, oxygen and neon gases. This galaxy is known to be very distant because the wavelengths of its gaseous emission lines are greatly shifted towards longer wavelengths. This redshift (z = 2.27) places the galaxy's strong hydrogen (H-alpha) emission line nearly exactly at the wavelength of the 2.15 um filter used to create the red information in this pseudo-color image, making the galaxy appear unusually red. Note the faint companion galaxy on the right side of 4C+40.36, seen for the first time in these observations.
The following figure shows spectroscopic observations of 4C+40.36. In the uppermost spectrum (a) obtained using just CISCO, emission lines due to the galaxy are completely overpowered by the normal night sky OH airglow emission lines. In the middle spectrum (b) obtained using OHS in combination with CISCO, the night sky emission lines are greatly suppressed and the emission lines from galaxy 4C+40.36 are now just visible along the center of the spectrum. The bottom panel (c) shows the same spectrum as the middle one except that the night sky lines have been subtracted out using a computer to leave just the underlying spectrum of 4C+40.36. Without the use of OHS, the galaxy would have been lost in the glare of the OH emission lines.