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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
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NASA NTRS1990

H I studies of the sculptor group galaxies

Results from large-scale mapping of the H I gas in the Sculptor group are presented. From this kinematic analysis, a mean global (M/L sub B) approx. equals 9 solar maximum/solar luminosity (at the last observed velocity point) is found for the individual galaxies. This is only a factor approx. 10 smaller than the (M/L sub B) dyn approx. equals 90 solar maximum/solar luminosity derived from a dynamical study of the whole group. The parameters derived from the mass models suggest that most of the unseen matter has to be concentrated around the luminous galaxies. Under the assumption that the Sculptor group is a virialized system and that all the mass is associated with the galaxies, an upper limit of approx. 40 kpc is derived for the size of the dark halos present in the five late-type spirals of the group.

Carignan, Claude↗
NASA NTRS1990

A classification of the galaxy groups

A statistical criterion has been proposed to reveal the random and physical clusterings among stars, galaxies and other objects. This criterion has been applied to the galaxy triples of the list by Karachentseva, Karaschentsev and Scherbanovsky, and the double galaxies of the list by Dahari where the primary components are the Seyfert galaxies. The confident physical, probable physical, probable optical and confident optical groups have been identified. The limit difference of radial velocities of components for the confident physical multiple galaxies has also been estimated.

Anosova, Joanna P.↗
NASA NTRS1991

UGC-A86 - A local group galaxy candidate

Deep CCD images were obtained for the object UGC-A86, an object identified on the Palomar Observatory Sky Survey, and listed in the Addendum of the UGC. Two objects are revealed at this location: perhaps a chance superposition in the sky of two galaxies at different distances or two interacting galaxies, or two components of the same galaxy. The brighter component is well resolved into stars, and a color-magnitude diagram has been obtained for it. Interpretation of the color-magnitude diagram is somewhat ambiguous, but it seems very likely that this galaxy is a dwarf member of the Local Group.

Saha, A.↗
NASA NTRS1993

A revised catalog of CfA galaxy groups in the Virgo/Great Attractor flow field

A new identification of groups and clusters in the CfAl Catalog of Huchra, et al. (1983) is presented, using a percolation algorithm to identify density enhancements. The procedure differs from that of the original Geller and Huchra (1983; GH) catalog in several important respects; galaxy distances are calculated from the Virgo-Great Attractor flow model of Faber and Burnstein (1988), the adopted distance linkage criteria is only approx. 1/4 as large as in the Geller and Huchra catalog, the sky link relation is taken from Nolthenius and White (1987), correction for interstellar extinction is included, and 'by-hand' adjustments to group memberships are made in the complex regions of Virgo/Coma I/Ursa Major and Coma/A1367 (to allow for varying group velocity dispersions and to trim unphysical 'spider arms'). Since flow model distances are poorly determined in these same regions, available distances from the IR Tully-Fisher planetary nebula luminosity function and surface brightness resolution methods are adopted if possible.

Nolthenius, Richard↗
NASA NTRS1990

RR Lyrae stars in local group galaxies. II - NGC 147

Deep CCD images of NGC 147 taken with the '4-shooter' on the Hale 5 m telescope have been processed to find and photometrically measure RR Lyrae stars. 36 variable stars have been found, of which 32 are surmised to be RR Lyrae stars. Finding charts, periods, and light curves are presented. The mean magnitude of the RR Lyraes is determined to be 25.25 mag. A distance modulus 23.92 is derived, based on the best currently available values of foreground extinction and mean absolute magnitudes of RR Lyrae stars. A wide range of periods is seen for the RR Lyrae stars, indicating a correspondingly wide range of metallicities for the stars in NGC 147. The distance modulus derived here places NGC 147 at a distance of 154 kpc from the center of M31, and in conjunction with the line sight velocities of these two galaxies, this implies a lower limit of 7.2 x 10 to the 11th solar masses for the mass of M31.

Saha, A.↗
NASA NTRS1990

RR Lyrae stars in local group galaxies. I - NGC 185

Deep CCD images of NGC 185 taken with the '4-shooter' on the Hale 5-m telescope have been processed to find and photometrically measure RR Lyrae stars. 176 variable stars have been found, of which 151 are surmised to be RR Lyrae stars. Finding charts, periods, and light curves are presented. The RR Lyrae stars in this galaxy have a very wide distribution of periods indicating a wide range of metallicity. The mean magnitudes of the RR Lyraes is determined to be 25.20 mag. A distance modulus of 23.79 is derived, based on the best currently available values of foreground extinction and mean absolute magnitudes of RR Lyrae stars.

Saha, A.↗
NASA NTRS1990

MCG 06-45-001 - Not a local group galaxy

Observations of (C-12)O and (C-13)O J = 1 to 0 for MCG 06-45-001 are examined. It is argued that two features of CO emission with velocities of 1 and 10 km/s indicate that the object is similar to the Galactic molecular clouds in the immediate vicinity, and not to a spiral galaxy as suggested previously. It is considered that CO emission cannot arise from a spiral galaxy at a distance of 2-5 Mpc and that the object is unlikely to be a nearby dwarf. The feature at 10 km/s is considered to arise from a molecular cloud associated with an H II region, which produces the observed IRAS flux.

Shore, Steven N.↗
NASA NTRS1992

RR Lyrae stars in Local Group galaxies. IV - IC 1613

Deep charge-coupled device images of a field in IC 1613 away from the star forming central regions were taken with the '4-shooter' on the Hale 5 m telescope, and processed to find photometrically measure variable stars. Fifteen RR Lyrae stars were found, and periods, light curves, and finding charts for them are presented. The mean magnitude of RR Lyrae stars in this galaxy is deduced to be 24.90 mag. Assuming the absolute g magnitude for RR Lyraes to be Mg = 0.73 mag, and using extinction Ag = 0.07 mag, a distance modulus of 24.10 +/- 0.27 mag is derived. The finding of RR Lyrae stars indicates the unambiguous presence of an old population. The distance modulus derived from them is smaller than that derived from the Cepheids by an amount which is dependent upon the RR Lyrae zero-point calibration adopted, and may be as large as 0.3 mag. The difference has the same sense and magnitude as the discrepancy in the LMC. The probable sources of the problem are discussed.

Saha, A.↗
NASA NTRS1993

A revised catalog of CfA1 galaxy groups in the Virgo/Great Attractor flow field

A new identification of groups and clusters in the CfA1 Catalog of Huchra et al. is presented, using a percolation algorithm to identify density enhancements. It is shown that in the resulting catalog, contamination by interlopers is significantly reduced. The Schechter luminosity function is redetermined, including the Malmquist bias.

Nolthenius, Richard↗
NASA NTRS1990

Isolated galaxies, pairs, and groups of galaxies

The authors searched for isolated galaxies, pairs and groups of galaxies in the CfA survey (Huchra et al. 1983). It was assumed that the distances to galaxies are given by R = V/H sub o, where H sub o = 100 km s(exp -1) Mpc(exp -1) and R greater than 6 Mpc. The searching procedure is close to those, applied to find superclusters of galaxies (Kalinkov and Kuneva 1985, 1986). A sphere with fixed radius r (asterisk) is described around each galaxy. The mean spatial density in the sphere is m. Let G (sup 1) be any galaxy and G (sup 2) be its nearest neighbor at a distance R sub 2. If R sub 2 exceeds the 95 percent quintile in the distribution of the distances of the second neighbors, then G (sup 1) is an isolated galaxy. Let the midpoint of G (sup 1) and G (sup 2) be O sub 2 and r sub 2=R sub 2/2. For the volume V sub 2, defined with the radius r sub 2, the density D sub 2 less than k mu, the galaxy G (sup 2) is a single one and the procedure for searching for pairs and groups, beginning with this object is over and we have to pass to another object. Here the authors present the groups - isolated and nonisolated - with n greater than 3, found in the CfA survey in the Northern galactic hemisphere. The parameters used are k = 10 and r (asterisk) = 5 Mpc. Table 1 contains: (1) the group number, (2) the galaxy, nearest to the multiplet center, (3) multiplicity n, (4) the brightest galaxy if it is not listed in (2); (5) and (6) are R.A. and Dec. (1950), (7) - mean distance D in Mpc. Further there are the mean density rho (8) of the multiplet (galaxies Mpc (exp -3), (9) the density rho (asterisk) for r (asterisk) = 5 Mpc and (10) the density rho sub g for the group with its nearest neighbor. The parenthesized digits for densities in the last three columns are powers of ten.

Kuneva, I.↗
NASA NTRS2003

An X-Ray Atlas of Groups of Galaxies

A search was conducted for a hot intragroup medium in 10(exp 9) low-redshift galaxy groups observed with the ROSAT PSPC. Evidence for diffuse, extended X-ray emission is found in at least 61 groups. Approximately one-third of these detections have not been previously reported in the literature. Most of the groups are detected out to less than half of the virial radius with ROSAT. Although some spiral-rich groups do contain an intragroup medium, diffuse emission is restricted to groups that contain at least one early-type galaxy.

Mulchaey, John S.↗
NASA NTRS1990

Observational properties of compact groups of galaxies

Compact groups are small, relatively isolated, systems of galaxies with projected separations comparable to the diameters of the galaxies themselves. Two well-known examples are Stephan's Quintet (Stephan, 1877) and Seyfert's Sextet (Seyfert 1948a,b). In groups such as these, the apparent space density of galaxies approaches 10(exp 6) Mpc(sub -3), denser even than the cores of rich clusters. The apparent unlikeliness of the chance occurrence of such tight groupings lead Ambartsumyan (1958, 1975) to conclude that compact groups must be physically dense systems. This view is supported by clear signs of galaxy interactions that are seen in many groups. Spectroscopic observations reveal that typical relative velocities of galaxies in the groups are comparable to their internal stellar velocities. This should be conducive to strong gravitational interactions - more so than in rich clusters, where galaxy velocities are typically much higher. This suggests that compact groups could be excellent laboratories in which to study galaxy interactions and their effects. Compact groups often contain one or more galaxies whose redshift differs greatly from those of the other group members. If these galaxies are at the same distance as the other members, either entire galaxies are being ejected at high velocities from these groups, or some new physical phenomena must be occurring. If their redshifts are cosmological, we must explain why so many discordant galaxies are found in compact groups. In recent years much progress has been made in addressing these questions. Here, the author discusses the current observational data on compact groups and their implications.

Hickson, Paul↗
NASA NTRS1993

Diffuse X-ray emission from the NGC 2300 group of galaxies - Implications for dark matter and galaxy evolution in small groups

The discovery of diffuse X-ray emission from the NGC 2300 group of galaxies using the ROSAT Position Sensitive Proportional Counter is reported. The gas distributions is roughly symmetric and extends to a radius of at least 0.2/h(50) Mpc. A Raymond-Smith hot plasma model provides an excellent fit the X-ray spectrum with a best-fit value temperature of 0.9 + -/15 or - 0.14 keV and abundance 0.06 + 0/.12 or - 0.05 solar. The assumption of gravitational confinement leads to a total mass of the group of 3.0 + 0.4 or - 0.5 x 10 exp 13 solar. Baryons can reasonably account for 4 percent of this mass, and errors could push this number not higher than 10-15 percent. This is one of the strongest pieces of evidence that dark matter dominates small groups such as this one. The intragroup medium in this system has the lowest metal abundance yet found in diffuse gas in a group or cluster.

Mulchaey, John S.↗
DOE OSTI2023

Investigating the large-scale environment of wide-angle tailed radio galaxies in the local Universe

We present a statistical analysis of the large-scale (up to two Mpc) environment of a homogeneous and complete sample, both in radio and optical selection, of wide-angle tailed radio galaxies (WATs) in the local Universe (i.e., with redshifts z ≲ 0.15). The analysis is carried out using the parameters obtained from cosmological neighbors within two Mpc of the target source. Results regarding the large-scale environments of the WATs are then compared with those of Fanaroff–Riley type I (FR Is) and type II (FR IIs) radio galaxies listed in two other homogeneous and complete catalogs and selected with the same criterion adopted for the WATs catalog. We obtain indication that at low redshift, WATs inhabit environments with a larger number of galaxies than those of FR Is and FR IIs. In the explored redshift range, the physical size of the galaxy group or cluster in which the WATs reside appears to be almost constant with respect to FR Is and FR IIs, being around one Mpc. From the distribution of the concentration parameter, defined as the ratio between the number of cosmological neighbors lying within 500 kpc and within one Mpc, we conclude that WATs tend to inhabit the central region of the group or cluster in which they reside, in agreement with the general paradigm that WATs are the brightest cluster or group galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗