THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1995 AND 1996

2. Scientific Results during 1995 and 1996

2.1. Highlights from Semesters 95A, 95B, 96A, and 96B

2.1.1. Galaxies and Quasars

M.J. Ward and collaborators have mapped several starburst galaxies in the emission lines of Brackett and molecular hydrogen, using the new and improved Fabry-Perot etalon (with IRCAM3). The spatial information that this instrument provides can be used to identify the dominant excitation processes occuring at different hot spots within the same galaxy, and to ascertain whether or not the star formation is coeval. The same instrument was used to investigate the starformation properties of the circumnuclear ring in the Seyfert galaxy NGC1068. The Br and molecular hydrogen line morphologies are very different, indicating the relative importance of star formation, shocks and fluorescence. (Some examples of the high sensitivity emission line maps are given in the Royal Observatories newsletter, Spectrum, (1994, vol. 4, pg. 22) and in papers currently in press in the Monthly Notices of the Royal Astronomical Society.)

T. Shanks and collaborators used IRCAM3 to obtain deep K and J imaging of high redshift X-ray-luminous galaxies, which showed that many of these objects have strong pointlike nuclei and several are apparently undergoing mergers. In one object, in which the lines seen at optical wavelengths are narrow, the observers used CGS4 to detect a broad H line. This discovery has implications both for unified theories of AGN and for the origin of the cosmic X-ray background - it suggests that obscured QSOs may account for a large fraction of the X-ray background over a wide range of energies.

A. Stockton and co-observers obtained a very deep CGS4 spectrum of Cygnus A in the K band, which sets a stringent limit on any broad component to the Pa line (a factor of 10 lower than the best previous limit) and confirmed the [S IX] line suspected in their short observation of the previous year. Many new lines are evident in the new spectrum.

A total of 40 elliptical galaxies in clusters were imaged at J and K by B. Mobasher. The data are leading to a significant reduction in the D- relation for ellipticals compared to the optical. The infrared relation is being used to zero-point a similar relation in the field and to study the streaming motion in the Great Attractor region.

J, H, and K band imaging polarimetry of NGC 1068 by J.H. Hough and colleagues, using the dual beam polarimeter provided by the University of Hertfordshire, directly revealed for the first time the obscuring torus in this classic Seyfert 2 nucleus. The existence of the torus is in agreement with predictions of the unified theory of Seyfert galaxies. The orientation of the torus is accurately determined, and its diameter is at least 200 pc. More details on this work are given in § 2.2.3.

J-band spectra of the H emission in a sample of 0.7<z<1.5 field galaxies with redshifts that put the H line in spectral gaps between OH lines were obtained by K. Glazebrook and F. Economou. One H line was detected in an (I22, K19) galaxy at exactly the wavelength predicted by the optical redshift. M. Pettini and co-workers used the same technique in the K band to search for [OIII] and H emission in known z=3 galaxies. They observed three high redshift galaxies during two clear nights and obtained clear detections of [OIII] emission in two of the three (see back cover). These are the first detections of this kind and will allow estimates of masses, star formation rates, and dust extinction in galaxies in the process of formation. The investigators noted in their report that CGS4 is the only instrument available anywhere with sufficient spectral resolution (with the 150 l/mm grating) to separate the OH sky lines and sufficient sensitivity to detect line emission from normal galaxies at cosmological distances.