Big secret - the largest infrared telescope NASA operates isn't in Earth orbit, though the air is pretty thin up there. The 3-meter Infrared Telescope Facility was originally built to support the Voyager encounters of the giant planets, and is still 50% devoted to solar-system studies. If my experience in getting a project scheduled is any guide, this is the most exclusive telescope I've ever used. The IRTF takes advantage of the high and dry conditions at Mauna Kea, and they have now pushed its image quality far beyond the initial "light-bucket" specifications. I've used it in a project with Sam Pascarelle and Rogier Windhorst to observe our good friends in the 53W002 cluster at redshift z=2.4, employing the unique tunable narrowband filter in the NSFCAM imager to trace redshifted H-alpha emission. We went to all this trouble because, for galaxies at such high redshift, the well-understood visible part of the spectrum reaches us in the infrared, so these data can give us a more secure measurement of how rapidly these young galaxies form stars than we can get from the ultraviolet radiation now reaching us as visible light (which is what we used to find them from HST data in the first place). We also sneaked in some images of the nucleus of Comet Hale-Bopp and some of the overlapping galaxies for my dust project. Funny, these days the IRTF really looks like the runt of the mountaintop. Anyway, we've traced the H-alpha emission from objects at z=2.4, as shown here, for comparison with HST results on their (originally UV) Lyman-alpha emission. The comparison can trace how much dust had formed in such young galaxies, and together with HST NICMOS data, show what their chemistry and thus star-formation history had been. These pictures show a 75-arcsecond portion of the cluster first in the K band at 2.2 microns, and then in the narrow filter including redshifted H-alpha emission. The circled objects are known cluster members based on optical observations. The three bright ones, which have active nuclei, are much brighter than other object in the H-alpha image; more data are being added to check on fainter ones, and see whether there are members too strongly affected by internal dust to be obvious at shorter wavelengths. The east-west elongation of the southernmost one (53W002 itself) is real, showing the aligned ionized gas in the direction of the radio source, as also seen in HST and Kitt Peak data on its Lyman-alpha emission and HST NICMOS spectroscopy of its [O III] 5007-Angstrom line (which reaches us at 1.69 microns wavelength).

Broad-band K image	Narrow-band redshifted H-alpha

And a little more recent - the submillimeter-bright galaxy ELAIS N2 850.4 seen in Hα (at redshift z=2.4), from work with Ian Smail. This image helped show the role of a global wind in this luminous galaxy.

Last changes: 11/1999	  © 1999