Engineering topics

Huchra, J. P.

Publications and source records attributed to Huchra, J. P..

At least 37 records · Page 2

NASA NTRS1988

Linear clusters of galaxies - A194

New measurements for 160 redshifts and previous measurements for 108 other redshifts are presented for galaxies within 5 deg of A194. The galaxy distribution in A194 is shown to be inconsistent with a spherically symmetric King model. A mass-to-light ratio is derived using the virial theorem which is lower than the mean for the groups in the CfA redshift survey (Huchra and Geller, 1982; Geller, 1984). A nonparametric test for galaxy-cluster alignment and a Chi-squared test are used to search for alignment of galaxy major axes with the axis of A194. Evidence for neither luminosity segregation nor significant differences in the velocity or surface distributions of galaxies as a function of morphological type is found.

Chapman, G. N. F.↗

NASA NTRS1988

The dynamics of the Corona Borealis supercluster

The dynamics of the Corona Borealis (Cor Bor) supercluster was studied on a sample of 1555 galaxies in the vicinity of the six Abell clusters (A2061, A2065, A2067, A2079, A2089, and A2092) which comprise the supercluster. For all galaxies in this sample, photographic R photometry and accurate positional data are available. New R photometry and/or new redshifts were obtained for 97 galaxies, bringing the number of galaxies in this system for which the redshifts are available to 182. The central cluster R band luminosity, X-ray luminosity, and surface density were correlated with the cluster velocity dispersion and virial mass. The amount of matter in the supercluster, estimated to be about 8.2 x 10 to the 15th solar masses, is considered to be sufficient to bind the six Cor Bor clusters, which are contained within a volume of about 13 Mpc in radius. Dynamical time scales are comparable with the Hubble time, making it unlikely that the system is virialized.

Postman, M.↗

NASA NTRS1987

Linear clusters of galaxies - A999 and A1016

Redshifts have been measured for galaxies in two of the 'linear' clusters of the sample of Adams, Strom, and Strom (1980), including 44 redshifts in A999 and 40 in A1016. From the data, it is concluded that the galaxies in A999 are probably drawn from a spherically symmetric distribution, while those in A1016 probably are not. Both A999 and A1016 have mass-to-light ratios lower than typical of other clusters. The effect of anisotropy on the determination of cluster masses from the virial theorem is examined, and it is found that if the shortest axes of these clusters are close to the line of sight, the mass-to-light ratio may be underestimated by about 50 percent. No significant evidence is found for alignments of individual cluster members with the cluster axis in the convincing linear cluster A1016. There is similarly no evidence of segregation by luminosity morphological type in A1016.

Chapman, G. N. F.↗

NASA NTRS1987

A study of a flux-limited sample of IRAS galaxies

Redshift data and accurate four-color infrared photometry are presented for a complete IRAS sample of galaxies brighter than 2 Jy at 60 microns. A simple power law provides a good fit to the distribution for luminosities from 10 to the 10th to 10 to the 12th solar. There is no indication of an exponential dropoff in the luminosity function at high energies. A flattening of the luminosity function occurs at L less than 10 to the 20th solar. The highest luminosity galaxies typically are found in multiple, possibly interacting, systems and exhibit marginally narrower infrared spectral energy distributions than the isolated spirals which predominate at low luminosities. Infrared-bright galaxies come from a different population than the majority of optically bright galaxies. In particular, galaxies of low blue luminosity are not strong infrared emitters.

Smith, Beverly J.↗

NASA NTRS1987

A redshift survey of IRAS galaxies

Results are presented from a redshift survey of all 72 galaxies detected by IRAS in Band 3 at flux levels equal to or greater then 2 Jy. The luminosity function at the high luminosity end is proportional to L sup -2, however, a flattening was observed at the low luminosity end indicating that a single power law is not a good description of the entire luminosity function. Only three galaxies in the sample have emission line spectra indicative of AGN's, suggesting that, at least in nearby galaxies, unobscured nuclear activity is not a strong contributor to the far infrared flux. Comparisons between the selected IRAS galaxies and an optically complete sample taken from the CfA redshift survey show that they are more narrowly distributed than those optically selected, in the sence that the IRAS sample includes few galaxies of low absolute blue luminosity. It was also found that the space distributions of the two samples differ: the density enhancement or IRAS galaxies is only approx. 1/3 that of the optically selected galaxies in the core of the Coma cluster.

Smith, Beverly J.↗

NASA NTRS1986

Probes of large-scale structure in the Corona Borealis region

The present redshift survey of the Corona Borealis region encompasses redshifts, magnitudes and positions for 83 galaxies covering a 16.4 sq deg region; a complementary survey covers 39.2 sq deg, is complete to m(B)0 of 15.5, and encompasses 37 galaxies. The combined survey furnishes further support for the 'bubble-like' geometry revealed by the shallower CfA survey. The redshift distribution obtained is noted to be very similar to that in the neighboring Bootes region. The structure of voids and surfaces in the galaxy distribution is insensitive to luminosity for M(B)0 of less than about -17.4.

Postman, M.↗

NASA NTRS1986

Combined ultraviolet studies of astronomical sources

Topics addressed include: Cygnus Loop; P Cygni profiles in dwarf novae; YY Gem; nova shells; HZ Herculis; activity cycles in cluster giants; Alpha Ori; metal deficient giant stars; ultraviolet spectra of symbiotic stars detected by the Very Large Array; time variability in symbiotic stars; blue galaxies; and quasistellar objects with X-ray spectra.

Baliunas, S. L.↗

NASA NTRS1986

An X-ray and optical study of the cluster of galaxies Abell 754

X-ray and optical data for A754 are used to study the relative distribution of the luminous and dark matter in this dense, rich cluster of galaxies with X-ray luminosity comparable to that of the Coma Cluster. A quantitative statistical comparison is made of the galaxy positions with the total mass responsible for maintaining the X-ray emitting gas in hydrostatic equilibrium. A simple bimodal model which fits both the X-ray and optical data suggests that the galaxies are distributed consistently with the projected matter distribution within the region covered by the X-ray map (0.5-1 Mpc). The X-ray and optical estimates of the mass in the central region of the cluster are 2.9 x 10 to the 14th and 3.6 + or - 0.5 x 10 to the 14th solar masses, respectively.

Fabricant, D.↗

NASA NTRS1986

The cluster-cluster correlation function

The clustering properties of the Abell and Zwicky cluster catalogs are studied using the two-point angular and spatial correlation functions. The catalogs are divided into eight subsamples to determine the dependence of the correlation function on distance, richness, and the method of cluster identification. It is found that the Corona Borealis supercluster contributes significant power to the spatial correlation function to the Abell cluster sample with distance class of four or less. The distance-limited catalog of 152 Abell clusters, which is not greatly affected by a single system, has a spatial correlation function consistent with the power law Xi(r) = 300r exp -1.8. In both the distance class four or less and distance-limited samples the signal in the spatial correlation function is a power law detectable out to 60/h Mpc. The amplitude of Xi(r) for clusters of richness class two is about three times that for richness class one clusters. The two-point spatial correlation function is sensitive to the use of estimated redshifts.

Postman, M.↗

NASA NTRS1986

A slice of the universe

A preliminary discussion is presented of recent results obtained as part of the extension of the Center of Astrophysics redshift survey. Several features of the results are striking. The distribution of galaxies in the sample, which contains 1100 galaxies in a 6 deg x 117 deg strip going through the Coma cluster, looks like a slice through the suds in the kitchen sink. It appears that the galaxies are on the surfaces of bubble-like structures with diameters of 25-50/h-Mpc. The largest bubble in the survey has a diameter comparable with the most recent estimates of the diameter of the void in Bootes. This topology poses serious challenges for current models for the formation of large-scale structure. The best available model for generating these structures is the explosive galaxy formation theory of Ostriker and Cowie (1981).

De Lapparent, V.↗

NASA NTRS1985

The X-ray cluster Abell 744

X-ray and optical observations of the cluster of galaxies Abell 744 are presented. The X-ray flux (assuming H(0) = 100 km/s per Mpc) is about 9 x 10 to the 42nd erg/s. The X-ray source is extended, but shows no other structure. Photographic photometry (in Kron-Cousins R), calibrated by deep CCD frames, is presented for all galaxies brighter than 19th magnitude within 0.75 Mpc of the cluster center. The luminosity function is normal, and the isopleths show little evidence of substructure near the cluster center. The cluster has a dominant central galaxy, which is classified as a normal brightest-cluster elliptical on the basis of its luminosity profile. New redshifts were obtained for 26 galaxies in the vicinity of the cluster center; 20 appear to be cluster members. The spatial distribution of redshifts is peculiar; the dispersion within the 150 kpc core radius is much greater than outside. Abell 744 is similar to the nearby cluster Abell 1060.

Kurtz, M. J.↗

NASA NTRS1985

The magnitude-redshift relation for 561 Abell clusters

The Hubble diagram for the 561 Abell clusters with measured redshifts has been examined using Abell's (1958) corrected photo-red magnitudes for the tenth-ranked cluster member (m10). After correction for the Scott effect and K dimming, the data are in good agreement with a linear magnitude-redshift relation with a slope of 0.2 out to z = 0.1. New redshift data are also presented for 20 Abell clusters. Abell's m10 is suitable for redshift estimation for clusters with m10 of no more than 16.5. At fainter m10, the number of foreground galaxies expected within an Abell radius is large enough to make identification of the tenth-ranked galaxy difficult. Interlopers bias the estimated redshift toward low values at high redshift. Leir and van den Bergh's (1977) redshift estimates suffer from this same bias but to a smaller degree because of the use of multiple cluster parameters. Constraints on deviations of cluster velocities from the mean cosmological flow require greater photometric accuracy than is provided by Abell's m10 magnitudes.

Postman, M.↗

NASA NTRS1985

Combined ultraviolet studies of astronomical source

As part of its Ultraviolet Studies of Astronomical Sources the Smithsonian Astrophysical Observatory for the period 1 Feb. 1985 to 31 July 1985 observed the following: the Cygnus Loop; oxygen-rich supernova remnants in 1E0102-72; the Large Magellanic Cloud supernova remnants; P Cygni profiles in dwarf novae; soft X-ray photoionization of interstellar gas; spectral variations in AM Her stars; the mass of Feige 24; atmospheric inhomogeneities in Lambda Andromedae and FF Aquarii; photometric and spectroscopic observation of Capella; Alpha Orionis; metal deficient giant stars; M 67 giants; high-velocity winds from giant stars; accretion disk parameters in cataclysmic variables; chromospheric emission of late-type dwarfs in visual binaries; chromospheres and transient regions of stars in the Ursa Major group; and low-metallicity blue galaxies.

Dupress, A. K.↗

NASA NTRS1985

Combined ultraviolet studies of astronomical sources

Ultraviolet studies of various astronomical entities are reported. Among the specific phenomena examined were supernova remnants, dwarf novae, red giant stars, stellar winds, binary stars, and galaxies.

Dupree, A. K.↗

NASA NTRS1985

The Virgo cluster redshift survey

A complete (99 percent) velocity survey is presented of the 471 galaxies brighter than m(pg) = 15.5 that are within the 6-deg radius of the central region of the Virgo cluster. There are 602 galaxies with measured velocities in the 6-deg circle, of which about 362 have the velocities lower than 3000 km/s and are assumed to be cluster members. From the velocity data, the cluster luminosity function was derived, and the mean Virgo velocity (for the Hubble constant and Virgo infall calculations) was calculated. In addition, the velocity data were used to study internal dynamics of the Virgo cluster.

Huchra, J. P.↗

NASA NTRS1984

How to find galaxies at high redshift

The UV and optical spectra presented for the blue star-forming galaxies Mrk 357, Mrk 496, and Mrk 26 have sufficiently large redshifts to make Lyman-alpha observations possible. Weak Lyman-alpha emission is observed in Mrk 357 and Mrk 469, with a flux value comparable to that of H-beta, and no detectable Lyman-alpha emission is detected in the case of Mrk 26. All three objects exhibit strong UV continuum emission, which is characteristic of hot stars, and although little evidence of dust is found, the observational constraints on extinction and neutral hydrogen column densities allow substantial reductions of the Lyman-alpha flux by dust absorption in conjunction with large line optical depths. These results imply that primeval galaxy detection calls for attention to be given to redshifted continuum emission from massive galaxies.

Hartmann, L. W.↗

NASA NTRS1984

Seven poor clusters of galaxies

The measurement of 83 new redshifts from galaxies in the region of seven of the poor clusters of galaxies identified by Morgan et al (1975) and Albert et al (1977) has been followed by an estimation of cluster masses through the application of both the virial theorem and the projected mas method. For each system, these two estimates are consistent. For the two clusters with highest X-ray luminosities, the line-of-sight velocity dispersions are about 700 km/sec, while for the five other clusters, the dispersions are of the order of less than about 370 km/sec. The D or cD galaxy in each poor cluster is at the kinematic center of each system.

Beers, T. C.↗

NASA NTRS1984

A complete sample of quasars at B = 19.80

A quasar candidate spectroscopic UV-excess survey with B less than 19.80 has yielded 35 quasars in the 1.75 sq deg region studied. The X-ray data for the 35 quasars are used to show that quasars with B lower than 19.80 and z lower than 2.2 constitute 24 + 10, -8 percent of the observed X-ray background at 2 keV. This sample is combined with one containing 22 quasars with B values lower than 18.25, and it is noted that fits of evolution and luminosity functions are substantially similar to previous results, although the confidence limits for the model parameters are reduced by a factor of 2. Pure luminosity evolution models are found to produce very good fits to the observed N(less than B) data, and are used to estimate the overall contribution of quasars to the X-ray background.

Marshall, H. L.↗