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Register a new userNICMOS imaging search for damped Lya galaxies
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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 Lya absorption lines and 5 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, that 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 arcsec (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-fit deconvolved Sersic-law surface-brightness profile, and the ellipticity and orientation.
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We have selected 14 J-dropout Lyman Break Galaxy (LBG) candidates with J110 - H160 > 2.5 from the NICMOS Parallel Imaging Survey. This survey consists of 135 square arcminutes of imaging in 228 independent sight lines, reaching average 5 sigma sensitivities of J110 = 25.8 and H160 = 25.6 (AB). Distinguishing these candidates from dust reddened star forming galaxies at z ~ 2-3 is difficult, and will require longer wavelength observations. We consider the likelihood that any J-dropout LBGs exist in this survey, and find that if L*(z=9.5) is significantly brighter than L*(z=6) (a factor of four), then a few J-dropout LBGs are likely. A similar increase in luminosity has been suggested by Eyles et al. and Yan et al., but the magnitude of this increase is uncertain.
We have obtained near-infrared (1.6 micron) images of 11 powerful 3CR radio galaxies at redshifts 0.8 < z < 1.8 using NICMOS on board HST. The high angular resolution permits a detailed study of galaxy morphology in these systems at rest-frame optical wavelengths, where starlight dominates over the extended, aligned UV continuum. The NICMOS morphologies are mostly symmetric and are consistent with dynamically relaxed, elliptical host galaxies dominated by a red, mature stellar population. The aligned structures are sometimes faintly visible, and nuclear point sources may be present in a few cases which manifest the ``unveiled AGN that is obscured from view at optical wavelengths. Our observations are consistent with the hypothesis that the host galaxies of z ~ 1-2 radio galaxies are similar to modern-day gE galaxies. Their sizes are typical of gE galaxies but smaller than present-day cD and brightest cluster galaxies, and their surface brightnesses are higher, as expected given simple luminosity evolution.
HST is used to study the power sources and the interaction-induced tidal disturbances within the most luminous galaxies in the local universe -- the Ultra-Luminous IR Galaxies (ULIRGs) -- through the use of I-band images with WFPC2 and H-band images with NICMOS. Such images are probing for the first time the fine-scale structures in the strong collision-disturbed morphologies of these rare and exotic galaxies.
We present NICMOS imaging of broad band and molecular hydrogen emission in Seyfert galaxies. In 6 of 10 Seyferts we detect resolved or extended emission in the 1-0 S(1) 2.121 or 1-0 S(3) 1.9570 micron molecular hydrogen lines. We did not detect emission in the most distant galaxy or in the 2 Seyfert 1 galaxies in our sample because of the luminosity of the nuclear point sources. In NGC 5643, NGC 2110 and MKN 1066, molecular hydrogen emission is detected in the extended narrow line region on scales of a few hundred pc from the nucleus. Emission is coincident with [OIII] and H alpha+[NII] line emission. This emission is also near dust lanes observed in the visible to near-infrared color maps suggesting that a multiphase medium exists near the ionization cones and that the morphology of the line emission is dependent on the density of the ambient media. The high 1-0 S(1) or S(3) H2 to H alpha flux ratio suggests that shock excitation of molecular hydrogen (rather than UV fluorescence) is the dominant excitation process in these extended features. In NGC 2992 and NGC 3227 the molecular hydrogen emission is from 800 and 100 pc diameter `disks (respectively) which are not directly associated with [OIII] emission and are near high levels of extinction (AV > 10). In NGC 4945 the molecular hydrogen emission appears to be from the edge of a 100 pc superbubble. In these 3 galaxies the molecular gas could be excited by processes associated with local star formation. We confirm previous spectroscopic studies finding that no single mechanism is likely to be responsible for the molecular hydrogen excitation in Seyfert galaxies.
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