Near Infrared Observations of the Highest Redshift Radio Galaxy, 4C41.17, with the W. M. Keck Telescope

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Session 76 -- Keck
Oral presentation, Thursday, 2:30-4:00, Dwinelle 155 Room

[76.03] Near Infrared Observations of the Highest Redshift Radio Galaxy, 4C41.17, with the W. M. Keck Telescope

J. R. Graham (UC Berkeley), K. Matthews , B. T. Soifer (Caltech), J. E. Nelson (UC Berkeley), W. Harrison (CARA), G. Jernigan (UC Berkeley), S. Lin, G. Neugebauer (Caltech), G. Smith (CARA), C. Ziomkowski (Caltech)

The near infrared camera on the W. M. Keck telescope has been used to image the distant radio galaxy 4C41.17 at Z = 3.8. The camera uses a state-of-the-art 256x256 InSb array from SBRC to provide a significant field (38''x38'') while well sampling (0.15"/pixel) stellar images.

A 1000 s integration with a K (2.0 - 2.3$\mu m$) filter achieves a 1 $\sigma$ limiting magnitude of 24.5 in a 1.''2 diameter beam. The image size is seeing limited with FWHM of 0.''7. galaxy appears as a thin arc of emission extending over $\simeq$ 6'' or 26 $kpc$ ($H_0 = 75 km\;s^{-1} \;Mpc^{-1}$, $q_0 = 0.5$). Preliminary astrometry shows that the radio peak B3 is associated with the brightest K peak, while B1 is coincident with a weaker K peak. The galaxy K magnitude is fainter than previously reported. Since the 2.0 - 2.3 $\mu m$ filter excludes redshifted [O~III] we conclude that line emission makes a substantial contribution to the flux measured in a standard K filter. There is a marked concentration of faint (K$\simeq21$ mag.) red objects in the vicinity of 4C41.17 which are not detected in previous optical or infrared images. At least five such objects are located within a radius of 8'' (35 $kpc$). If these are at the same distance of 4C41.17 then they each have $M_B \simeq -21.8$. The small projected distance between 4C41.17 and its faint companions suggests that these objects will not survive as distinct galaxies in a cluster, but will merge to form a single galaxy.

The W. M. Keck Observatory is a partnership between the University of California and the California Institute of Technology, made possible by the generous gift of the W. M. Keck Foundation and support of its president, Howard Keck. We are most grateful for their visionary endowment that has made possible the first of the next generation of telescopes. It is a pleasure to also thank all of the many devoted people whose unflagging efforts have made possible the success of the W. M. Keck Observatory.

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