Engineering topics

Richstone, D. O.

Publications and source records attributed to Richstone, D. O..

10 records

NASA NTRS2000

Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 From The Nuclear Stellar Dynamics

We analyze the nuclear stellar dynamics of the SBO galaxy NGC 1023, utilizing observational data both from the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and from the ground. The stellar kinematics measured from these long-slit spectra show rapid rotation (V equals approx. 70 km/s at a distance of O.1 deg = 4.9 pc from the nucleus) and increasing velocity dispersion toward the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar kinematics assuming an axisymmetric mass distribution with both two and three integrals of motion. Both modeling techniques point to the presence of a central dark compact mass (which presumably is a supermassive black hole) with confidence > 99%. The isotropic two-integral models yield a best-fitting black hole mass of (6.0 +/- 0.4) x 10(exp 7) solar masses and mass-to-light ratio (M/L(sub v)) of 5.38 +/- 0.08, and the goodness-of-fit (CHI(exp 2)) is insensitive to reasonable values for the galaxy's inclination. The three-integral models, which non-parametrically fit the observed line-of-sight velocity distribution as a function of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4) x 10(exp 7) solar masses and M/L(sub v) of 5.56 +/- 0.02 (internal errors), and the edge-on models are vastly superior fits over models at other inclinations. The internal dynamics in NGC 1023 as suggested by our best-fit three-integral model shows that the velocity distribution function at the nucleus is tangentially anisotropic, suggesting the presence of a nuclear stellar disk. The nuclear line of sight velocity distribution has enhanced wings at velocities >= 600 km/s from systemic, suggesting that perhaps we have detected a group of stars very close to the central dark mass.

Bower, G. A.↗

NASA NTRS1983

The evolution of clusters of galaxies. I - Very rich clusters

A multiple one-body Monte Carlo code is used to investigate the evolution of galaxies in a steady cluster potential under the influence of dynamical friction, two-body relaxation, tidal stripping, and galaxy mergers. The basic assumptions, estimated time scales, method and computer program, and effects of uncertainties in galaxy encounter physics are addressed. Numerical experiments in which the mass initially carried by galaxies and the mass function are varied are reported. It is shown that the formation of a very massive cluster galaxy depends critically on the number of galaxies, the initial division of cluster material between galaxies and a smooth intracluster medium, the mass spectrum of the galaxies, and chance. By the end of all simulations, less than half of the mass in the central regions of the cluster is bound to galaxies. It appears possible to produce any of the Bautz-Morgan classes from very similar initial conditions.

Richstone, D. O.↗

NASA NTRS1982

Character of prolate galaxies

It is still not known whether elliptical galaxies are oblate, prolate or triaxial. The prototype prolate galaxy NGC2685 has a rapid observed stellar rotation rate around the projected minor axis. It is shown that a steady figure, exactly prolate model can have no such rotation, and that a nearly prolate model fails by a factor of 7. The galaxy is suggested to be oblate with gas disk that is the wreck of a dwarf companion.

Richstone, D. O.↗

NASA NTRS1982

Galactic mass loss - A mild evolutionary correction to the angular size test

Galactic mass loss due to gas production by an evolving stellar population and removal due to supernovae or some other energy source can alter the size of a galaxy over a long time through the adiabatic invariants of the orbits. Numerical and analytic results show that if the mass profile changes homologously, the scale size of the galaxy does also. Under conventional assumptions about galaxy age and initial mass function, this bloating is smaller than the differences between open and flat cosmologies at z = 0.5. If, however, some elliptical galaxies maintain star formation until recent epochs and then lose a (correspondingly) larger fraction of their mass, the effect may be important. It may also be important in decreasing the size of cD galaxies as a result of gas accretion.

Richstone, D. O.↗

NASA NTRS1982

Scale-free models of galaxies. II - A complete survey of orbits

A complete set of orbits starting at over 400 distinct points spread out in the phase space of an oblate scale-free potential is investigated. Each orbit is followed for a time that corresponds to a Hubble time in a realistic galaxy potential suitable for an E5 or E6 galaxy. It is noted that none of the orbits in the survey is ergodic. All of the survey orbits are regular, visiting a region at least one dimension smaller than expected from the classical integrals of motion. Thus, for all practical purposes, they have an extra nonclassical isolating integral. Approximately 95% of the survey orbits are box orbits, the rest being pipes (formerly tubes). The survey exposes an ambiguity in the original classification scheme for orbits, which, it is noted, can be resolved on the basis of the topology of an orbit's surface of section. Nevertheless, the distinction between high order very convoluted pipes and boxes is probably artificial for practical purposes.

Richstone, D. O.↗

NASA NTRS1981

A new determination of the halo luminosity density of the galaxy

The distribution of tangential velocities for arbitrary halo velocity dispersions and rotation rates are explicitly computed, assuming a particular form of the halo velocity distribution function near the sun. It is found that for a specific model of the halo velocity dispersion tensor that Schmidt's (1975) estimate of the mass carried by halo stars of 0.25-0.70 solar masses should be revised by a factor of between 1.0 and 2.0, depending on the rotation rate of the halo. Although obtaining a mass density in all stars from the stellar density in that mass range is extremely uncertain, it is found, in agreement with earlier work, that even under rather extreme assumptions about the remnants the observed stars and expected remnants fail to provide the theoretically expected mass. Comparison of the luminosity to the theoretical mass yields a mass to light ratio consistent with that of rich clusters of galaxies.

Richstone, D. O.↗

NASA NTRS1977

The nebulosity near the quasar 3C 249.1

Spectroscopic observations made 2 arcsec away from 3C 249.1 with a cooled SIT camera spectrograph and with a multichannel spectrometer yield convincing evidence for the presence of fairly narrow emission lines of forbidden O II, forbidden O III, forbidden Ne III, and perhaps H-beta. The redshift of these emission lines, z = 0.3125, is, within the accuracy of the observations, the same as that of the broad emission lines in the quasar itself; this appears to rule out a gravitational-redshift interpretation for the quasar redshift. The main difficulty in making models for the extended emission-line region is that of understanding the strong forbidden O II lines. For this purpose, shell, cloud, and disk models are discussed, as is time-dependent ultraviolet illumination of the nebula. Simple models, in which the nebular is exposed to the unaltered extrapolated quasar continuum flux, fail to produce the observed line ratios.

Richstone, D. O.↗

NASA NTRS1975

Velocity dispersions in galaxies. IV - The nucleus of NGC 1068

A high-resolution spectrum of the Seyfert galaxy NGC 1068, obtained with an integrating television system, is compared with the spectrum of a KO III star (delta Tau) to derive the line-of-sight velocity dispersion of the stars in the galactic nucleus. An Fe I absorption line observed at 4059.7 A yields a velocity dispersion of 150 (plus or minus 50) km/sec. An upper limit for the nuclear mass is derived in terms of this velocity dispersion, an estimated nuclear radius of 136 pc, and a Hubble constant of 50 km/sec per Mpc. The results, 14 (+10, -8) by 10 to the 8th power solar masses, is shown to be consistent with a number of quasar models scaled down in luminosity to provide the energy source for a Seyfert nucleus. Strong H and K interstellar absorption lines superposed on the spectrum of NGC 1068 are analyzed.-

Richstone, D. O.↗

NASA NTRS1973

Absorption lines in the spectrum of the quasar Markarian 132.

Wavelengths and profiles of several absorption lines in the spectrum of the quasar Markarian 132, obtained with the aid of an integrating television sensor, are presented. An attempt is made to derive column densities and internal Doppler velocities by fitting theoretical Voigt profiles to the observed spectra. C IV lines show that the absorption must occur in at least two separate clouds with a relative velocity of 160 km/sec.

Morton, D. C.↗

NASA NTRS1972

Early-type stars and the mean-square electron density in the galactic disk.

An assessment is made of the total supply of ionizing photons from hot stars, within several hundred parsecs of the sun. The resulting photoionized H II regions probably contribute an average emission measure of the order of 5 pc per cm to the 6th power, through the galactic disk; this is smaller than other recent estimates.

Richstone, D. O.↗