Showing papers by "G. Neugebauer published in 1996"

Visual and Near-Infrared Imaging of Ultraluminous Infrared Galaxies: The IRAS 2 Jy Sample

Abstract: New near-infrared and visual images at 2.2 μm and 6550 A are presented for 46 galaxies having infrared luminosities of L_(IR) > 8.5 x 10^(11) L_⊙, 60 μm flux densities greater than 1.94 Jy, and declinations greater than -35°. These galaxies make up a significant fraction of a complete, northern hemisphere sample of ultraluminous infrared galaxies. Visual and/or near-infrared imaging data now exist for 56 ultraluminous infrared galaxies out to nearly 50 000 km s^(-1). Of these 56 galaxies, 53 (95%) show evidence for current or past interactions. Among these systems, there are a large variety of visual morphologies, including strongly interacting pairs with apparent tidal tails, as well as single, distorted galaxies with close double nuclei. There are three galaxies which, to the limits of the imaging data, do not appear to have suffered a recent interaction or merger. Approximately 47% (25/53) of the interacting systems have double nuclei, with projected nuclear separations ranging from 0.3 to 48 kpc. Seven systems have nuclear separations larger than 10 kpc. If the 53 interacting galaxies are viewed as stages in the evolution of pairs of interacting spiral galaxies to a single, luminous AGN or starburst, the present imaging data can be used to estimate the lifetime of the bright infrared phase. Including only those sample galaxies with morphological evidence for interactions, we calculate a lower and an upper limit to the lifetime of the ultraluminous infrared phase of the sample as a whole to be 2 x 10^8 and 2 x 10^9 yr, respectively. Comparison of these dynamical estimates to models of the mergers of gas-rich galaxies and the rates at which fuel is exhausted by starbursts or AGN suggests the lifetime of the ultraluminous phase lies much closer to the smaller of these two values. Selecting galaxies based upon luminous infrared activity clearly biases the sample towards merging galaxies with small physical separations. However, the existence of pairs with large separations indicates that the ultraluminous phase may in some cases start early during the merger process. Alternatively, these systems may contain unresolved third nuclei responsible for triggering the ultraluminous activity. We briefly compare our results to recent models of merging spiral galaxies.

HST Observations of the Luminous IRAS Source FSC10214+4724: A gravitationally Lensed Infrared Quasar

Abstract: With a redshift of 2.3, the IRAS source FSC 10214+4724 is apparently one of the most luminous objects known in the universe. We present an image of FSC 10214+4724 at 0.8 μm obtained with the Hubble Space Telescope (HST) WFPC2 Planetary Camera. The source appears as an unresolved ( < 0”.06) arc 0”.7 long, with significant substructure along its length. The center of curvature of the arc is located near an elliptical galaxy 1”.18 to the north. An unresolved component 100 times fainter than the arc is clearly detected on the opposite side of this galaxy. The most straightforward interpretation is that FSC 10214+4724 is gravitationally lensed by the foreground elliptical galaxy, with the faint component a counterimage of the IRAS source. The brightness of the arc in the HST image is then magnified by ~ 100, and the intrinsic source diameter is -0”.01 (80 pc) at 0.25 μm rest wavelength. The bolometric luminosity is probably amplified by a smaller factor ( ~ 30) as a result of the larger extent expected for the source in the far-infrared. A detailed lensing model is presented that reproduces the observed morphology and relative flux of the arc and counterimage and correctly predicts the position angle of the lensing galaxy. The model also predicts reasonable values for the velocity dispersion, mass, and mass-to-light ratio of the lensing galaxy for a wide range of galaxy redshifts. A redshift for the lensing galaxy of ~ 0.9 is consistent with the measured surface brightness profile from the image, as well as with the galaxy's spectral energy distribution. The background lensed source has an intrinsic luminosity ~ 2 x 10^(13) L_⊙ and remains a highly luminous quasar with an extremely large ratio of infrared to optical/ultraviolet luminosity.

The First Diffraction-Limited Images from the W. M. Keck Telescope

Abstract: The first diffraction limited, 0.05s resolution, images on the W. M. Keck Telescope have been obtained at a wavelength of 2.2 micrometers. These images were part of an experiment to test the suitability of the Keck Telescope for speckle imaging. In order to conduct this test, it was necessary to modify the pixel scale of the Keck facility Near Infrared Camera (NIRC) to optimally sample the spatial frequencies made available by the Keck telescope. The design and implementation of the external reimaging optics, which convert the standard fl25 beam from the secondary mirror to fl182, are described here. Techniques for reducing speckle data with field rotation on an alt-az telescope are also described. Three binary stars were observed in this experiment with separations as small as 0.05s. With only 100 frames of data on each, a dynamic range of at least 3.5 mag was achieved in all cases. These observations imply that a companion as faint as 14.5 mag at 2.2 micrometers could be detected around an 11th magnitude point source.

1608+656: A gravitationally-lensed poststarburst radio galaxy

Abstract: The gravitational lens system 1608+656 displays four flat-spectrum, pointlike components that are the images of the unresolved core of a double-lobed radio source. The lensing mass is a galaxy at z = 0.630. New spectra of this system enable us to determine a conclusive redshift of 1.394 for the lensed object. The spectra show prominent high-order Balmer absorption lines and Mg II absorption. These lines, and the absence of [O II] emission, indicate that this is a poststarburst or E + A galaxy. It is unique among lensed objects in not being a quasar and among E + A galaxies in having the highest known redshift. Even allowing for lens magnification, the lensed object is a very luminous galaxy, with an absolute magnitude, M(r) = -22.8 mag. The deconvolved infrared image indicates that the galaxy may be slightly resolved. The radio luminosity density of the lobes is L_(1.4) = 5.78 × 10^(25) W Hz^(-1), which puts the source on the boundary between FR I and FR II radio galaxies. Together with the redshift for the lens and a satisfactory mass model, the determination of the lensed object redshift makes this system an excellent candidate for measuring H_0.

HST Observations of the Luminous IRAS Source FSC10214+4724: A Gravitationally Lensed Infrared Quasar

Abstract: With a redshift of 2.3, the IRAS source FSC 10214+4724 is apparently one of the most luminous objects known in the universe. We present an image of FSC 10214+4724 at 0.8 μm obtained with the Hubble Space Telescope (HST) WFPC2 Planetary Camera. The source appears as an unresolved ( < 0”.06) arc 0”.7 long, with significant substructure along its length. The center of curvature of the arc is located near an elliptical galaxy 1”.18 to the north. An unresolved component 100 times fainter than the arc is clearly detected on the opposite side of this galaxy. The most straightforward interpretation is that FSC 10214+4724 is gravitationally lensed by the foreground elliptical galaxy, with the faint component a counterimage of the IRAS source. The brightness of the arc in the HST image is then magnified by ~ 100, and the intrinsic source diameter is -0”.01 (80 pc) at 0.25 μm rest wavelength. The bolometric luminosity is probably amplified by a smaller factor ( ~ 30) as a result of the larger extent expected for the source in the far-infrared. A detailed lensing model is presented that reproduces the observed morphology and relative flux of the arc and counterimage and correctly predicts the position angle of the lensing galaxy. The model also predicts reasonable values for the velocity dispersion, mass, and mass-to-light ratio of the lensing galaxy for a wide range of galaxy redshifts. A redshift for the lensing galaxy of ~ 0.9 is consistent with the measured surface brightness profile from the image, as well as with the galaxy's spectral energy distribution. The background lensed source has an intrinsic luminosity ~ 2 x 10^(13) L_⊙ and remains a highly luminous quasar with an extremely large ratio of infrared to optical/ultraviolet luminosity.

Near Infrared Observations of IRAS 09104+4109

Abstract: Near infrared imaging and grism spectroscopy of the high luminosity infrared bright galaxy IRAS 09104+4109 have been obtained with the W. M. Keck Telescope. The imaging shows 6 “knots” of emission projected against the extended stellar envelope of the cD galaxy thought to be the source of the large far infrared luminosity. The luminosities of the knots are consistent with the bulges of galaxies accreting onto the central galaxy. In addition, there are 11 companion galaxies seen at radii of 40-150 kpc from the cD nucleus. These objects have colors in the range R—K~ 3.5±0.5 mag, J-H~0.9±0.2 mag H-K ~0.7±0.2 mag, which are consistent with galaxies at a redshift of 0.4. The companion galaxies have luminosities comparable to or less than the characteristic luminosity (L^*) of field galaxies. While the central cD galaxy is identified with the luminous infrared source, it appears to be a quiescent, radio-quiet galaxy, showing no evidence from its near infrared colors for a highly reddened nucleus as seen in other infrared luminous galaxies. The grism spectroscopy shows forbidden lines of low ionization stages of sulfer, iron, and oxygen, as well as hydrogen recombination lines and a strong line of neutral helium. A visual extinction of Av—2 mag is derived to the narrow line region surrounding the galaxy nucleus, based on the line ratios [S II]1.03 µm/0.407 µm and Pδ/Hβ. The near infrared spectrum is consistent with the optical classification of this system being a Seyfert 2 nucleus.