Spatially resolved quantitative spectroscopy of comets

Because of their temporal and spatial variations, modern ground-based studies of comets within approximately 4 A.U. of the sun are observationally demanding tasks. Over the years, researchers have attempted resolved spectroscopy of comets covering a wide range of intrinsic luminosity. Recently this group has developed spectral and direct-imaging procedures to detect weak ion tails submerged into the comae of even fairly faint comets. Although the last year was devoid of any really bright comet, re-analysis of older dust and gas production data of the 1986 P/Halley apparition has been almost completed. The main changes are that the nucleus does make a significant contribution to continuum light, and that the gravity effect in the dust escape velocity is somewhat larger than previously assumed. On the direct observational side, spectral studies of the 1987's Comet Bradfield show it to be qualitatively carbon-rich, at least in the outer coma ratio of CO(+) and CO2(+), compared the H2O(+) with respect to Halley at similar heliocentric distances

Spatially resolved quantitative spectroscopy of comets

The chemical composition of cometary nuclei and the velocity field of the ejected daughter species were investigated through conventional, high-resolution spectroscopy and indirectly by imaging the dissociation radicals in the outflowing cometary comae. Gas production rates and comae symmetries were studied, and coma outflow mechanisms were modeled

Keck Observations of the Most Distant Galaxy: 8C1435+63 at z=4.25

We report on Keck observations and confirm the redshift of the most distant galaxy known: 8C1435+63 at z=4.25. The spectrum shows a strong Ly$\alpha$ line, a Ly$\alpha$ forest continuum break and a continuum break at $\lambda_{rest}=912$\AA. The Ly$\alpha$ emission is spatially extended and roughly aligned with the radio source. The galaxy shows a double structure in the $I$-band ($\lambda_{rest}\approx$1500\AA) which is aligned with the radio axis; the two $I$-band components spatially coincide with the nuclear and southern radio components. Some fraction of the $I$ band emission could be due to a nonthermal process such as inverse compton scattering. In the $K$-band ($\lambda_{rest}\approx$4200\AA), which may be dominated by starlight, the galaxy has a very low surface brightness, diffuse morphology. The $K$ morphology shows little relationship to the radio source structure, although the major axis of the $K$ emission is elongated roughly in the direction of the radio source axis. The galaxian continuum is very red ($I-K>4$) and if the $K$ continuum is due to starlight, implies a formation redshift of $z_f > 5$. We speculate that this galaxy may be the progenitor of a present day cD galaxy.Comment: 4 pages + 4 figures; uuencoded tar compressed PostScript files; figures and tables included. To appear in 1 Jan 1995 issue of The Astrophysical Journal, Letters. Please direct requests/questions/comments to [email protected]

Spectroscopy of extremely distant radio galaxies

In this Letter we report the firm identification of two faint radio galaxies, 3C 13 and 3C 256, and a spectroscopic survey of 13 faint 3CR galaxies. The emission-line redshifts now extend up to z = 1.82 (3C 256), and we here present a list and a preliminary spectrum summary of the character of 11 new radio galaxies with z > 0. 77. About half of these luminous galaxies show low ionization emission-line spectra. Their strong [O II] lines can have luminosities up to 9 x 10^(43) ergs s^(-1) ; the emitted UV spectra have a much "softer" ionizing radiation field than those of QSOs and Seyfert nuclei. The spectra are of the narrow-line variety, with FWHM ≤ 1000 km s^(-1). The strong [O II] emission is often much extended and inclined, showing a considerable velocity amplitude. The most extreme cases are 3C 324 and 3C 267 (both with z > 1.0), but the phenomenon is moderately frequent. These are the most distant (non-QSO) galaxies known, and we can now extend the cosmological and galaxy evolution tests into previously unprobed territory

The Radio Galaxy 3C265 Contains a Hidden Quasar Nucleus

We report the discovery of broad MgII emission from the high redshift radio galaxy 3C265 (z=0.81). We detect the broad line in the nuclear spectrum and in the spatially extended galaxian component, both near the nucleus and in the spectrum of an off-nuclear knot located 31 kpc south east of the nucleus of the galaxy. These data provide strong support for the simplest form of the unification hypothesis, that radio galaxies are quasars whose optical radiation is directed in the plane of the sky rather than into our line of sight. These data also strongly support the scattering model for the alignment of the UV continuum emission with the radio axis. In 3C265, if the axis of the anisotropically emitted UV continuum radiation is identified with the major axis of the radio source, then the observed rest frame UV continuum emission implies that the opening angle of the radiation cone is large (half angle approximately 45 degrees). We also derive a mass estimate of 8x10^{10} Msun for the central region of 3C265 from its rotation curve. The implied mass-to-light ratio is low (M/L is roughly 2), and suggests that a significant fraction of the rest frame UV continuum emission from this galaxy is dominated by reprocessed radiation from the buried AGN. Finally, we detect the CaII\lambda3933 K line in absorption in the integrated spectrum of 3C265. This provides direct spectroscopic evidence for the existence of stars in a high redshift radio galaxy.Comment: 26 pages (including figures) in gzip-ed uuencoded compressed postscript format. Accepted for publication in ApJ, March 1, 1996 issu

Surface photometry of comet P/Encke

We have developed a scheme to clean cometary digital images from offending background-star trails, and applied this technique to a pair of deep Kitt Peak 4-m plates of comet P/Encke, taken in October 1980. Simultaneous and subsequent digital spectra have been obtained at Lick Observatory. The non-polluted coma images show a strong asymmetric sunward-oriented fan/jet, and an extended and rounder (mostly gaseous) main coma, out to ~ 10^5 km radius. The stellar-trail point-spread function has a narrow width (σ7~0.6 arcsec), so that spatial resolution better than ~300 km is achieved at the comet. The photometric gradient near the nucleus is very steep, strongly suggesting an icy-grain component which evaporates quickly (at radii ⩽ 500 km) in the sunlight. Further from the nucleus, the profile becomes shallower, bluer, and more gas dominated. The effect of solar radiation pressure on C_2, CN, and other molecules is probably responsible for the rounding of the outer, faint isophotes. The source of the molecules is likely to be larger than the nucleus itself, and a substantial fraction may originate in the jet. The technique described here may also be applicable in surface photometry of galaxies, in cases where the heavy image pollution by foreground stars is present

The Status of the Hubble Diagram In 1986

We present visual and near-infrared Hubble diagrams for first- ranked cluster galaxies, and moderate-flux and high-flux radio galaxies. The photometric improvements and the extension of the diagrams to large redshifts (up to z ≃ 1.8) for both 3CR and “1 Jy” class radio galaxies are highlighted. The absolute luminosities of these three types of “standard candles”, where their redshifts overlap, agree adequately. The near-IR (2μm) Hubble diagrams may be used to determine the global deceleration parameter, q_O, and the current data favor q_O ~ +0.2 to +0.3. The sensitivity to evolutionary changes in the giant galaxies is quite modest at these long wavelengths. On the other hand, the visual regime (BV R) shows a dramatic dependence on differential evolution effects, which dominate over the cosmological model differences. Most radio galaxies apparently have had active star formation, with a continually declining rate, but a few are quite faint and red; they may have had a relatively passive evolution