NICMOS imaging search for high-redshift damped Lyα galaxies |
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| Authors: | SJ Warren P Møller SM Fall P Jakobsen |
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| Institution: | 1Blackett Laboratory, Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BW;2European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany;3Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA;4Astrophysics Division, European Space Research and Technology Centre, 2200 AG Noordwijk, the Netherlands |
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| Abstract: | We are engaged in a programme of imaging with the STIS and NICMOS (NIC2) instruments aboard the Hubble Space Telescope ( HST ), to search for the galaxy counterparts of 18 high-redshift z >1.75 damped Ly α absorption lines and five Lyman-limit systems seen in the spectra of 16 target quasars. This paper presents the results of the imaging campaign with the NIC2 camera. We describe the steps followed in reducing the data and combining in mosaics, and the methods used for subtracting the image of the quasar in each field, and for constructing error frames that include the systematic errors associated with the PSF subtraction. To identify candidate counterparts, which are either compact or diffuse, we convolved the image and variance frames with circular top-hat filters of diameter 0.45 and 0.90 arcsec respectively, to create frames of summed S /N within the aperture. For each target quasar we provide catalogues listing positions and aperture magnitudes of all sources within a square of side 7.5 arcsec centred on the quasar, detected at S / N >6 . We find a total of 41 candidates, of which three have already been confirmed spectroscopically as the counterparts. We provide the aperture magnitude detection limits as a function of impact parameter, for both detection filters, for each field. The average detection limit for compact (diffuse) sources is H AB =25.0 (24.4) at an angular separation of 0.56 (0.79) arcsec from the quasar, improving to H AB =25.5 (24.8) at large angular separations. For the brighter sources we have measured the half-light radius and the n parameter of the best-fitting deconvolved Sersic-law surface brightness profile, and the ellipticity and orientation. |
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| Keywords: | galaxies: formation quasars: absorption lines quasars: general |
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