Telescopes / Instruments

 

We are currently using two telescopes at the Kitt Peak National Observatory near Tucson, Arizona to perform this survey: Steward Observatory's 2.3m Bok telescope and the WIYN 0.9m telescope. Both of these telescopes have wide-field optical imagers which have a square degree field of view (five times larger than the area of the full moon), consisting of a mosaic of CCDs containing a grand total of 64 million pixels. Such large fields of view are fundamental to efficiently cover our galaxy groups in a small number of pointings, as being so nearby, they are typically several degrees across on the sky.

IMG_3933 IMG_3941 IMG_3964
Steward Observatory's 2.3m (90") Bok telescope at the Kitt Peak National Observatory. The 90Prime imager on the 2.3m telescope with its square degree field of view is ideal for efficiently covering the nearby galaxy groups in the CHANGES survey.
The WIYN 0.9m observatory at Kitt Peak.
The WIYN 0.9m telescope with Mosaic1.1 optical imager attached, providing a full square degree field of view. The telescope was photographed while taking twilight sky flat images in the H-alpha filters, in the minutes prior to sunset.

Both instruments have a range of narrow-band H-alpha filters available which cover the full range of redshifts sampled by our group galaxies. While these galaxy groups are relatively nearby, being located within 80 Mpc, their recession velocities are of the order 1-5000 km/s, shifting the H-alpha emission line outside the standard narrow-band H-alpha filter used to probe star forming regions in our own Galaxy. Each of these narrow-band filters has a width of ~70nm allowing in just the light from H-alpha emission from galaxies within a specific range of recession velocities of width ~2000 km/s. For each galaxy or galaxy group we observe through one of these narrow-band filters, tuned to detect the H-alpha emission from galaxies having just the specific recession velocities placing them within the galaxy group.


The transmission functions of the H-alpha filters available for the Mosaic-1.1 imager on the WIYN 0.9m telescope. The wavelength in Angstroms is indicated along the bottom, while the corresponding recession velocity (in km/s) at which the H-alpha emission line is shifted to that wavelength is shown along the top. The greyscale filled curve indicates the standard H-alpha narrow band filter used to observe star forming regions in our own Galaxy, and extends only to cover galaxies out to 2000 km/s. The recession velocities of galaxies in the group associated with the galaxy NGC 5353 are shown as vertical colored lines (blue = late-type, red=early-type, green=unknown morphology). These have recession velocities in the range 2-3000km/s, beyond that covered by the standard H-alpha filter, but are well matched to the offset H-alpha+4 filter shown by the blue-filled transmission curve.

 
       

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