Extragalactic Research

FUNES continues the study of the kinematics of stars and gas in the central region of disk galaxies. This work has been done as part of his doctoral dissertation with BERTOLA (University of Padua), his superviser, and in collaboration with CORSINI (University of Padua), CAPPELLARI (University of Padua), PIZZELLA (University of Padua), VEGA BELTRAN (Instituto de Astrofisica de Canarias), and SARZI (University of Padua).

The researchers have studied the gas kinematics in the nuclear regions of a sample of 23 disk galaxies by obtaining high spatial resolution, long-slit spectra along their major axes in the H-alpha and O[III] 5007 spectral regions. The emission line spectra for 23 disk galaxies were obtained at the 3.6 m European Southern Observatory Telescope (La Silla, Chile), at the 2.5 m Isaac Newton Telescope (La Palma, Spain), and at the 4.5 m Multiple Mirror Telescope (Mt. Hopkins, Arizona, USA). In the circumnuclear regions, the gas kinematics has revealed a complex phenomenology. By comparing the gas velocity gradient and the velocity dispersion in the nuclear and outer regions, the researchers identified different types of bidimensional line shape in the position-velocity diagram. This kind of analysis allows one to identify galaxies that are characterized in their nucleus by the presence of a gaseous disk in Keplerian rotation. These objects are good candidates to harbor central massive black holes. For many of the galaxies in this sample, VBRI and H-alpha images were obtained at the Vatican Advanced Technology Telescope (VATT) on Mt. Graham in Arizona. In addition, a detailed study of the stellar and gaseous kinematics of Sa galaxies has shown an interesting phenomenon of bulge-disk orthogonal geometric and kinematical decoupling. This peculiarity suggests that the disk could be formed by accretion of material around the spheroidal component that we observe today. For the spheroidal components in S0 and Sa galaxies, R and I images were obtained also at the VATT for studying the intrinsic shape of bulges. The data have been reduced in Padua.

FUNES, in collaboration with RAFANELLI (University of Padua) and RICHTER (Astrophysikalisches Institut Potsdam), has started to investigate the relationship between gravitational interaction and galactic activity. The aim of this project is to identify signatures of interaction and/or merging in apparently isolated and morphologically undisturbed active galaxies. With this goal in mind, B, R, and H-alpha deep images of a spectroscopically selected sample of AGN were obtained at the VATT. The images were analyzed using an adaptive filtering technique designed to emphasize faint structures and knots and to reveal disturbed morphologies that can be interpreted as the effect of gravitational interaction. In addition, spectroscopic observations were carried out at the 1.52 m ESO telescope equipped with a slit spectrograph and at the Russian 6 m Special Astrophysical Observatory equipped with a Multi-Pupil-Fiber-Spectrograph. These observations show in some objects the presence of kinematical decoupling of gas and stars, a phenomenon interpreted as a signature of past interaction.

MOSS (Visiting Astronomer), working with WHITTLE (University of Virginia), has completed an objective-prism survey of H-alpha emission of an essentially complete magnitude-limited sample of galaxies of types Sa; he later conducted the same survey within 1.5 Abell radii of the centers of 8 low-redshift clusters (Abell 262, 347, 400, 426, 569, 779, 1367, and 1656). Some 320 galaxies were surveyed, of which 116 were detected in emission (39% of spirals; 75% of galaxies classified as peculiar). The emission survey distinguishes between "compact" and "diffuse" emissions, which are interpreted as circumnuclear starburst and normal disk emission, respectively. The circumnuclear emission is associated with a galactic bar or with a disturbed galaxy morphology, indicative of ongoing tidal interactions in the clusters (whether galaxy-galaxy, galaxy-group, or galaxy-cluster interactions).

It has been found that the frequency of tidally-induced starburst emission in spirals increases from regions of lower to higher galaxy surface density, and from clusters of lower to higher central galaxy space density. A similar trend is shown in the percentages of galaxies noted as disturbed and in the percentages of those classified as peculiar. Indeed, the fraction of spirals that are undergoing tidal distortion and/or tidally induced star formation in the richest cluster surveyed (Coma) appears comparable to the (large) fraction of spirals showing these effects in intermediate-redshift clusters. A very high fraction (70%) of galaxies classified as peculiar are found to have compact emission, typical of circumnuclear starburst emission. Although they are unlike spirals with such emission, these galaxies show no tendency to have tidal companions. It is considered that the galaxies classified as peculiar are likely to be ongoing mergers and represent a later stage of close double, interacting systems, many examples of which are found in the clusters with tidally induced star formation.

The H-alpha survey work has generated interest and is considered important because of the insight it may give into the evolution of cluster disk galaxies. Recent observations with the Hubble Space Telescope have shown the remarkable changes in cluster galaxy populations between intermediate redshifts (z ~ 0.5) and the present. At intermediate redshifts, a large fraction (up to 50%) of the cluster population are spirals, but these have been depleted by a factor of 2 by the present epoch and replaced with an S0 population. The discovery of enhanced tidally induced starburst emission in cluster spirals at low redshift suggests that tidal interactions may be the principal cause of this relatively recent morphological transformation of the cluster disk galaxy population. This picture accords well with the most recent theoretical modeling of clusters with a nonstatic potential undergoing collapse and infall, which predicts a high prevalence of galaxy tidal encounters.

MOSS and WHITTLE have also found that, for regions of comparable local galaxy surface density, the frequency of tidally induced starburst emission in spirals is greater in clusters of higher central galaxy space density. This implies that, for a given local density, morphological transformation of disk galaxies proceeds more rapidly in clusters of higher central galaxy density. This effect is considered to be due to subcluster merging and may provide an explanation for the anomalous lack of the correlation of galaxy type with surface density for irregular clusters at intermediate redshift.

MOSS, with ARAGON-SALAMANCA (University of Nottingham, UK) and BENNETT (Institute of Astronomy, Cambridge, UK), undertook U and B imaging of emission-line galaxies in several clusters, concentrating on Abell 1367 and Abell 1656, using the VATT2 CCD on the VATT. This observational program is designed to complement optical CCD H-alpha and continuum imaging that was previously obtained for these galaxies. The photometric and morphological information will be used together with detailed population synthesis models to help constrain timescales of star formation in the emission-line galaxies.

MOSS, KENNICUTT (Steward Observatory, University of Arizona), SAKAI (National Optical Astronomy Observatories, Tucson, Arizona), and WHITTLE (University of Virginia) have begun a deep survey of star formation in nearby galaxy clusters using the CCD Mosaic Imager on the 0.9 m telescope at Kitt Peak. The intent of the survey is to use the unique wide-field capability of the Mosaic Imager (8192 × 8192 pixels, giving a field ~1 degree square on the 0.9 m telescope) to derive a complete inventory of H-alpha derived star formation rates for galaxies in the clusters. To date, some ten fields in four clusters have been surveyed. The data will be used, together with the results of the objective prism H-alpha survey of clusters by MOSS and WHITTLE, to directly test and calibrate the incompleteness of prism-based luminosity functions. The aim of this work is to better understand incompleteness effects in determinations of the local star formation rate density. The Mosaic CCD data will also be used to further extend studies of environmental influences on star formation and the evolution of disk galaxies.

OMIZZOLO, with the assistance of CORBALLY, continues a series of observations with the 2.3 m telescope of Steward Observatory on Kitt Peak for low-resolution spectra of X-ray sources in order to identify quasars and obtain their redshift. These observations are part of a program to determine the luminosity function of low-redshift quasars and to study the influence of quasar environment on quasar evolution. For the latter purpose, imaging of the same objects has also been done at the VATT. The first of a series of articles detailing the results obtained thus far has been submitted for publication. This research is being conducted with CRISTIANI (University of Padua). Plans are also underway for a series of observations with the Telescopio Nazionale Galileo (Canary Islands).

As part of a continuing search for peculiar A-type stars, including lambda Boötis stars, in open clusters of all ages, CORBALLY and GRAY (Appalachian State University, Boone, North Carolina) have obtained classification spectra of nearly 70 late B, A, and early F-type stars in 11 young and intermediate-age open clusters, including NGC 1039, 6633, 7039, 7063, 7092, 7209, 7243, IC 1396, IC 4665, IC 4756, and Stock 2. The spectra were obtained with a resolution of 3.6 Å on the Dark Sky Observatory 0.8 m telescope of Appalachian State University and were classified on the MK System. Numerous classical Ap and Am stars were found among the 70 stars examined, along with a few emission-line stars.

CORBALLY, STRAIZYS, and LAUGALYS (ITPA, Vilnius, Lithuania) have derived the interstellar reddening law for 15 heavily reddened stars in the area that includes the North America and Pelican Nebulae and the dark cloud between them. Their method is based on photometry of these stars in the Vilnius seven-color system and on CORBALLY's MK spectral types. The mean reddening law in this area is very similar to the law for a much wider area in Cygnus derived earlier by other authors. It differs from the normal law by exhibiting somewhat stronger extinction in the violet and the near-ultraviolet spectral region, i.e., it shows a smaller "knee" in the blue part of the spectrum. CORBALLY has continued to obtain spectra with the Steward Observatory's 2.3 m telescope for heavily reddened stars in the Camelopardalis and Nova V1500 Cygni regions and for a list of photometrically peculiar stars, all selected by STRAIZYS.

Good photometric skies at the VATT in the spring enabled CORBALLY and GARRISON (David Dunlap Observatory, University of Toronto) to continue UBVRI observations of two calibration fields in the North Galactic Pole, where they are looking for G-dwarf star candidates. RUEGER (Diocese of Brooklyn) has been assisting in the processing of these observations.

ABT (National Optical Astronomical Observatories, Tucson, Arizona) and CORBALLY have finished their full report on the 285 candidate Trapezium systems that they have observed photometrically and spectroscopically in past years. They conclude that the maximum age of Trapezium systems, those groups of stars with relatively wide separations, is about 50 million years. They also find that Trapezium systems are large, with a median radius of 0.2 parsec and a maximum radius of 2.6 parsecs.

COYNE is working with THOMPSON (Steward Observatory, University of Arizona), Principal Investigator on the NICMOS instrument on the Hubble Space Telescope, in the analysis of polarimetric NICMOS data on bipolar nebulae and on disks around young stars. From the first set of data they expect to be able to establish the geometry of these nebulae; from the second set of data, they hope to obtain some indirect evidence of planet formation from the distribution of the scattering material in the disks.

BOYLE and PHILIP (Union College and Institute for Space Observations, Schenectady, New York) continued their work on the VATT, making CCD observations in the Stromvil photometric system of open clusters and globular clusters. They attended a workshop on the Stromvil system held in Vilnius, Lithuania, in October.

JANUSZ (summer visitor from Krakow, Poland) was instructed by BOYLE on how to use IRAF software programs to process CCD observations from VATT. He is continuing to process the data in Krakow.

DASGUPTA and SMRIGLIO (University of Rome) continued their collaboration with BOYLE and STRAIZYS and KAZLAUSKAS (Vilnius Observatory, Lithuania) concerning CCD observations from VATT as well as from the 1.52 m telescope of the Astronomical Observatory of Bologna, Italy. They are paying particular attention to improving the photometric calibration of the CCD observations in order to extract stellar magnitudes as accurately as possible. Such photometry results in the classification of the stars.

During the past two years, RETTIG (University of Notre Dame), TEGLER (Northern Arizona University), ROMANISHIN (University of Oklahoma), and CONSOLMAGNO have begun a program at the VATT to increase understanding of the Edgeworth-Kuiper Belt. This ring of small, frozen, distant objects orbiting beyond Neptune was predicted to exist more than forty years ago by Kuiper and Edgeworth, who believed it to be the source of short-period comets. But such objects were only first observed in 1995. Observations at the VATT, in collaboration with the University of Notre Dame, continued in 1999.

In 1998 TEGLER and ROMANISHIN reported that broadband colors of these faint objects are distributed into two groups: one set of objects appear to be neutrally colored, while another set are remarkably reddish, thought to indicate a surface rich in organic compounds. The ongoing VATT observations are designed to compare these colors with the colors of coma-free comets far from the Sun as well as with the colors of small irregular satellites of the outer planets. These satellites may have originally come from the Edgeworth-Kuiper Belt. Objects observed in 1999 included two newly discovered faint satellites of Uranus, Sycorax and Caliban; the coma-free comet P/Neujmin 1; the irregular moon Nereid orbiting Neptune; the irregular moon Phoebe orbiting Saturn; and all but one of the eight outer irregular moons of Jupiter.

Observing how the brightness of these objects varies with time yields information on both the spin rate (presumed to be the period of the fluctuation in brightness) and how asymmetric their shapes or colors are (as indicated by how much the brightness changes and if that brightness change is uniform over all colors.) Finally, the absolute measurement of the brightness itself can be translated (with appropriate assumptions about the object's intrinsic brightness, or albedo) into an estimate of the size of these objects.

A preliminary analysis of the data is already beginning to yield valuable results, which were reported at the annual American Astronomical Society's Division for Planetary Sciences meeting in October. Values for the irregular Uranian satellites Caliban (U1) and Sycorax (U2) are shown in the table below. There is excellent agreement between the colors from the 4 m telescope on Kitt Peak and the 1.8 m VATT for Sycorax; the V band photometry is in excellent agreement as well. Considering that the Kitt Peak telescope has 5 times the raw light-gathering power of the VATT, the fact that the two instruments give comparable results confirms both the superb location of the VATT and the remarkable quality of its optics.

Taking an average of the colors for Sycorax yielded a B-V value of 0.88 ± 0.02 and a V-R value of 0.42 ± 0.03. Interestingly, the B-V value compares well with the known B-V value of 0.867 for Pluto, and the combination of the two color indices is similar to the colors of the neutral class of Edgeworth-Kuiper Belt objects previously reported by TEGLER and ROMANISHIN. Based on the visual magnitudes and the known distance to the objects, and assuming an albedo of 0.04, a diameter of approximately 100 km was calculated for Caliban and approximately 190 km for Sycorax. Reduction of the other data continues.

Theoretical work on the rubble-pile nature of asteroids by CONSOLMAGNO and BRITT (University of Tennessee) was inspired by the meteorite density results obtained by these researchers and reported in previous annual reports.

A number of lines of evidence suggest that asteroids larger than a few hundred meters in diameter are not solid rocks but rather piles of rubble. Although recent radar observations of small, rapidly-spinning, near-Earth asteroids indicate that objects up to 100 m in diameter may be solid objects, none of the more than 500 larger objects observed so far have ever been observed to have spin rates so fast that they could not be held together by self-gravity alone. Images of asteroid Mathilde indicate that it has suffered extreme cratering events without having been destroyed, again an indication that it is not a rigid body but rather composed of fragments smaller than the resolution limit of the Mathilde imagery.

Using asteroid and meteorite densities (including new data for asteroids Eros and Eugenia first reported in 1999), BRITT and CONSOLMAGNO have calculated that a typical asteroid may be as much as 40% empty space. This raises the questions: At what size scale do these spaces occur? And is there evidence in the imagery of asteroids (or the small Martian moons Phobos and Deimos, which are thought to be captured asteroids) consistent with this degree of macroporosity?

A careful analysis of Phobos and Deimos imagery indicates that boulders of several tens of meters can be seen on their surface, but otherwise the surface appears to be covered with material that is smaller than the several-meter resolution of even the best images--anything from boulders down to a fine powder. Hundred-meter pieces are not visible on the surface of these asteroidal bodies. Indeed, a number of theoretical considerations suggest that the solid-rock components of asteroids may be at least partially sorted by size, with the larger pieces preferentially found in the center of the asteroids and smaller fragments more prevalent in the outer regions.

This rubble-pile model for asteroids has significance for understanding the current state of asteroidal bodies, including their response to continued impacts, and it also raises interesting questions about the origin of the asteroids themselves. Larger asteroids today are rubble piles, but were they ever solid rocks? Or is this porous structure characteristic of protoplanetary bodies even during the time of the accretion of the planets? Asteroid modeling to examine these questions continues.

The question of asteroid structure is related to a similar question concerning the meteorites that come from these asteroids: what processes lithified the meteorites?

Examination by CONSOLMAGNO, BLAND (British Museum of Natural History), and STRAIT (Alma College, Alma, Michigan) of the porosity of meteorite thin sections using a scanning electron microscope has shown that for many ordinary chondrites, the 10% porosity inferred for hand samples can be accounted for entirely by visible microcracks, a few microns wide but hundreds of microns in length, that run across grain boundaries. Such cracks must have been imposed after the formation of those boundaries and, hence, after the lithification of the rock itself. They are most probably due to impacts on the parent asteroid body. But this implies that the lithification process, in fact, completely closed the pore spaces between individual fragments of the meteorite. For terrestrial sandstones (the type of Earth rock whose physical structure best parallels the cumulate nature of meteorites), pressures of several hundred kilopascals are needed to effectively close out pore space. Such pressures are not found in any but the largest of the asteroids. Likewise, terrestrial sandstones are also lithified by the action of heat and water, which presumably are not present in the asteroids. Thus the mystery of what lithified the meteorites remains.

Brecciated meteorites, that is, meteorites that have been broken apart and relithified, presumably by impacts in the asteroid belt, may hold a key to the answer. A class of basaltic brecciated meteorites, known as Howardites, are now being studied by MOLIN (University of Padua) in consultation with CONSOLMAGNO. They are using samples from the Vatican meteorite collection to determine the peak temperatures experienced by pyroxenes in these meteorites at the boundaries between breccia fragments as a function of distance from the boundary. This should put limits both on the energy experienced during the lithification process and on the length of time over which that energy was deposited.

CORBALLY has studied the relationship between the "many worlds" concepts of Thomas Digges and of Giordano Bruno that came from each of their acquaintance with the Copernican system. The approach by Digges was mainly mathematical and experimental; that of Bruno was primarily philosophical. Yet, CORBALLY finds that the two approaches were complementary in providing the perspective of an infinite universe, a perspective that shaped the founding of modern astronomy.

COYNE and OMIZZOLO completed their book entitled Wanderers in the Universe: Astronomy and the Meaning of Life. OMIZZOLO gave a seminar in May on the themes of the book to the Department of Astronomy at the University of Padua, Italy.