arXiv subjects

G. Schneider

Publications and source records attributed to G. Schneider.

58 records · Page 4Linked to original sources

arXiv1999

Photometric Redshifts and Morphologies of Galaxies in the NICMOS Parallel Fields

We present positions, magnitudes, sizes and morphological classifications for 111 galaxies discovered in the Hubble Space Telescope NICMOS Camera 1 and Camera 2 parallel fields. We combine the magnitudes measured in the JHK-analog filters with those from deep ground-based images in V and/or R to measure photometric redshifts for 71 objects using Bruzual-Charlot population synthesis models. We find that these objects fall in the range z ~ 0.0 - 2.7, with a mean redshift of 0.8 and a mean luminosity of 1.6 L*. The NICMOS images reveal many of the objects to be ordered spirals and ellipticals similar to those in the local universe. However, we find a higher fraction (~ 14%) of morphologically peculiar and/or interacting galaxies than is observed among local galaxies (~ 3% - 4%). This is consistent with the results from other deep HST images including the Hubble Deep Field and Hubble Medium Deep Survey Field that the fraction of peculiar and interacting galaxies increases with redshift. As the NICMOS images of the sample galaxies cover their rest-frame near infrared and optical emission, this result increases confidence that such changes in morphology are genuine, as opposed to an effect produced by viewing galaxies in the rest-frame ultraviolet. We also find that at least 26 of the sample galaxies appear to be members of (non-interacting) pairs or groups, based on their proximity to one another and photometric redshifts. This is consistent with the results of recent ground-based optical surveys covering larger areas, and with the detection of galaxy groups and filaments at redshifts higher than those covered by our sample.

astro-ph↗

arXiv1999

The Circumstellar Disk of HD 141569 Imaged with NICMOS

Coronagraphic imaging with the Near Infrared Camera and Multi Object Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'') radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected light image at 1.1 micron shows the disk oriented at a position angle of 356 +/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic scattering function of the dust in the disk makes the side inclined toward us, the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from the star and falls off to both larger and smaller radii. A region of depleted material, or a gap, in the disk is centered 250 AU from the star. The dynamical effect of one or more planets may be necessary to explain this morphology.

astro-ph↗

arXiv1998

A Candidate Substellar Companion to CoD -33 7795 (TWA 5)

We present the discovery of a candidate substellar object in a survey of young stars in the solar vicinity using the sensitivity and spatial resolution afforded by the NICMOS coronagraph on the Hubble Space Telescope. The H=12.1 mag object was discovered approximately 2 arcsec from the TW Hydrae Association member CoD -33 7795 (TWA 5), and the photometry implies a spectral type M8-M8.5, with a temperature of approximately 2600K. We estimate that the probability of a chance alignment with a background objectof this nature is < 2 X 10^(-5), and therefore postulate the object (TWA 5B) is physically associated at a projected separation of 100 AU. Given the likely youth of the primary (~ 10 Myr), current brown dwarf cooling models predict a mass of approximately 20 Jupiter masses for TWA 5B.

astro-ph↗

arXiv1998

NICMOS Imaging of the Nuclei of Arp 220

We report high resolution imaging of the ultraluminous infrared galaxy Arp 220 at 1.1, 1.6, and 2.22 microns with NICMOS on the HST. The diffraction-limited images at 0.1--0.2 arcsecond resolution clearly resolve both nuclei of the merging galaxy system and reveal for the first time a number of luminous star clusters in the circumnuclear envelope. The morphologies of both nuclei are strongly affected by dust obscuration, even at 2.2 microns : the primary nucleus (west) presents a crescent shape, concave to the south and the secondary (eastern) nucleus is bifurcated by a dust lane with the southern component being very reddened. In the western nucleus, the morphology of the 2.2 micron emission is most likely the result of obscuration by an opaque disk embedded within the nuclear star cluster. The morphology of the central starburst-cluster in the western nucleus is consistent with either a circumnuclear ring of star formation or a spherical cluster with the bottom half obscured by the embedded dust disk. Comparison of cm-wave radio continuum maps with the near-infrared images suggests that the radio nuclei lie in the dust disk on the west and near the highly reddened southern component of the eastern complex. The radio nuclei are separated by 0.98 arcseconds (corresponding to 364 pc at 77 Mpc) and the half-widths of the infrared nuclei are approximately 0.2-0.5 arcseconds. At least 8, unresolved infrared sources -- probably globular clusters -- are also seen in the circumnuclear envelope at radii 2-7 arcseconds . Their near-infrared colors do not significantly constrain their ages.

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