THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
2000

2. Scientific Highlights from 2000

2000 was a highly productive year for UKIRT and its visiting observers. The telescope was used in a wide variety of different programme styles: (i) interacting with other surveys - providing sensitive and high-resolution infrared data for combination with surveys at other wavelengths, and the rapid followup of key objects from the new optical/infrared sky surveys; (ii) carrying out and following up entirely UKIRT-based imaging and spectroscopic programmes; (iii) continuing to provide some of the most sensitive spectroscopy in the world in both the near (JHK) and thermal (L-M) infrared. Semester 00B produced a greater number of science ``firsts'' than any semester since the installation of UFTI in 1998.

Figure 1: UFTI imaging of two of the brightest SCUBA sources from the recent 8 mJy survey (Lutz et al. 2001, A&A 378, 70). The left panels show 3030 arcsec images centred on the interferometric position of the SCUBA source Lockman 850.1. The upper left panel is a 4 hour K-band image reaching K22. The lower left panel is a deep I-band image taken at the WHT, reaching I27. The circles have a diameter of 7 arcsec. While no optical counterpart is visible in the I-band exposure, the UFTI image shows a clear detection of the infrared counterpart to the SCUBA source, which is seen to be a multi-component object, the brightest peak of which coincides to sub-arcsec accuracy with the centroid of the dust emission. The two right-hand panels show comparable data for the 8 mJy SCUBA source ELAISN 2850.2. Once again while the I-band imaging (to I26) has failed to reveal the counterpart of the SCUBA source, the UFTI imaging has revealed a complex, red source with the brightest red clump coincident with the dust emission.

The combination of imaging data with those from other facilities proved fruitful. Crawford and collaborators carried out early follow-up of new Chandra X-ray sources. Smail and collaborators' cluster-lens imaging survey combined UFTI data with Hubble Space Telescope (HST) and Canada-France-Hawaii Telescope data. Brinchmann and Ellis obtained excellent data on mass assembly rates in HST field galaxies, taking full advantage of some superb seeing. UFTI on UKIRT is also proving to be an invaluable tool for identifying the counterparts of the sub-mm sources uncovered by surveys with the SCUBA camera on the James Clerk Maxwell Telescope. The followup of SCUBA detections of early-forming ellipticals (Dunlop and collaborators) is of particular interest; as demonstrated in Figure 1, the optical/infrared counterparts of many SCUBA sources are extremely faint and red, with complex, highly-clumped morphologies. For the detection of such objects not only is the K-band sensitivity offered by UFTI important, but also the excellent image quality assists in the detection of unresolved (or barely resolved) peaks of emission. Moreover, the relatively wide field-of-view of UFTI is required for performing accurate astrometry on the SCUBA fields.

2.2. Galactic

An ongoing highlight for UKIRT, since the initial discoveries of significant numbers of brown dwarf candidates in the 2 Micron All Sky Survey (2MASS) and Sloan Digital Sky Survey (SDSS), has been the confirmation and spectroscopic follow-up of these objects. In 2000, the spectral sequence of molecular absorption in L and T dwarfs was completed on the basis of CGS4 spectra (Leggett and collaborators), see Figure 2. Later in the year, the same group achieved the first accurate measurement of the thermal infrared flux from a T dwarf, demonstrating that these objects are fainter than expected at these wavelengths, possibly due to the (unexpected) presence of carbon monoxide.

Figure 2: The L to T dwarf spectral sequence; the top spectrum is for an L dwarf, the three central spectra early T dwarfs, the lower spectrum from a later T-type. T dwarfs are defined by the presence of absorption features due to CH₄ in both the H- and K-band regions; these bands strengthen while the K-band CO absorption weakens (Leggett et al. 2000 ApJ 536, L35).

This year UKIRT was also used to detect new objects both in the foreground of, and embedded in, molecular cloud complexes (Lucas and Roche; Jameson and collaborators). Lucas and Roche's Orion planetars, which brought UKIRT considerable publicity last year, were confirmed through a follow-up programme of CGS4 spectroscopy. Once again these objects were of considerable public interest, with good media coverage internationally, gaining excellent exposure on both the BBC and MSNBC web sites.

In the field of transient phenomena, Fassia and collaborators detected a late-epoch Supernova in the L and M bands - the first time this has been done so long (two years) after the initial event.

In studies of the interstellar medium, McCall and collaborators confirmed the presence of the key molecule H₃⁺ in diffuse interstellar clouds in the line-of-sight to HD183143, through CGS4 spectroscopy. This poses a serious challenge to models of H₃⁺ formation, which require very specialized conditions for the production of the molecule in the abundance seen.