Members Of Local Group Research Articles

HI Observations of the Irregular Galaxy IC 10

IC 10 is seen optically as a patchy nebulosity, approximately 3 × 4 arcmin in size, possibly heavily obscured due to its low (−3°) Galactic latitude. De Vaucouleurs and Freeman (1972) have classified it as a Magellanic barred irregular. With a heliocentric radial velocity of −350 km/sec, its distance is uncertain, and various investigators have placed it as far away as 3, and as near as 1 Mpc (Bottinelli et al., 1972; Roberts, 1962). For the latter value, IC 10 would be a Local Group member.

IS LGS 2 A LOCAL GROUP GALAXY

ABSTRACT The Local Group membership of Local Group Suspect (LGS) 2 discovered near M31 by Kowal et al. (1978) is investigated. A limiting 103a-O + GG13 plate and a deep V plate of LGS 2 were obtained by the Hale 5-m and CFHT 3.6-m telescopes, respectively. The plates fail to reveal any concentrations of resolved images near the position of LGS 2 while resolving Andromeda III, thus indicating that LGS 2 is either a small galactic reflection nebula or a dwarf galaxy more distant than M31 and M33.

Photographs of dwarf irregular galaxies in the vicinity of the Local Group and the M81 group

view Abstract Citations (39) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photographs of dwarf irregular galaxies in the vicinity of the Local Group and the M81 group. Fisher, J. R. ; Tully, R. B. Abstract Photographs of ten partially resolved dwarf irregulars are presented: the possible Local Group members DDO 69 = Leo A, DDO 70 = Sextans B, DDO 75 = Sextans A, DDO 155 = GR8, DDO 187, DDO 210, and DDO 216 = Pegasus, and the probable M81 group members DDO 53, DDO 165, and VII Zw 403. Magnitudes of the brightest stars are estimated, the global characteristics of these small galaxies are compared, and properties of the more interesting systems are discussed. Publication: The Astronomical Journal Pub Date: January 1979 DOI: 10.1086/112388 Bibcode: 1979AJ.....84...62F Keywords: Astronomical Photography; Galactic Structure; Galaxies; Local Group (Astronomy); Photographic Plates; Star Distribution; Stellar Evolution; Stellar Magnitude; Astronomy; Dwarf Galaxies:Local Group full text sources ADS | data products SIMBAD (15) NED (13)

Tools for Community-Managed Impact Assessment

Abstract Community and interest groups have often worked to introduce new impact assessment considerations into planning decisions. Their views represent perspectives and experience that are unique. This article presents a range of social impact assessment techniques that are available and evaluates their usefulness to local groups. The use of such techniques by local groups can serve to enhance their role in both local and regional scale planning and can provide purposeful activity for volunteer lay groups. Twelve techniques are discussed, ranging from simple impact checklists to complex data-based approaches. Five techniques which are relatively simple to use, do not require extensive use of data, and provide new insight into social impacts of proposed projects are identified as most useful to local groups. One technique is a check list procedure; the remainder are discussion-structuring approaches, the most complex of which is Delphi. A project comparisons technique is outlined, which focuses on predicting impacts through use of information about previous, similar projects. Local group members can use this procedure to bring information and experience from outside the community to bear on local impact assessments.

Solar Motion with Respect to the Nearest Galaxies

AbstractSolutions for solar motion with respect to 12 classical members of the restricted Local Group and 9 additional proposed members of an extended Local Group, all within 2 Mpc, suggest that the Local Group – both restricted and extended – is expanding at a rate, H* = 47 ± 12 ou 57 ± 11 km s-1 Mpc-1, which is significantly lower than its free-space (asymptotic) value Ho ≃, 90 km s-1 Mpc-1, as required by the rotating-expanding model of the Local supercluster. The differential rotation effects predicted by the model are detectable in the velocity residuals with correct phase L*o = 87° and amplitude A* = 30 to 40 km s-1 Mpc-1 in the first-order expansion.V = H*r + V⊙ cos A + A* r sin 2(L-L*o) cos2BThe solar motion with respect to the velocity centroid of the Local Group is V⊙ = 340 ± 18 km s-1 toward the apex 1 = 105° ± 5°, b = -11° ± 3°. With the conventional values of the solar motion within the Galaxy the apex of the galactic center in the Local Group is at supergalactic coordinates L = 325° ± 11°, B = -12° ± 11° with a velocity VG = 140 + 25 km s-1.The residual velocity dispersion σ = 40 to 50 km s-1 implies a virial theorem mass VT ≃ 9 x 1011⊙ not significantly in excess of that which can be accounted for by the member galaxies and intergalactic gas clouds.

The Nature of the Remarkable Galaxy G. R.

view Abstract Citations (32) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Nature of the Remarkable Galaxy G. R. 8 Hodge, Paul W. Abstract The irregular galaxy G.R. 8 is found to be an extremely small galaxy, possibly close enough to be considered a Local Group member. Its mean dimension is on the order of only 100 pc. Photoelectric measurements show that it is considerably bluer than any other measured (non-quasi-stellar) galaxy, and that its color-magnitude diagram is like that of a very young, not very populous open cluster. Its luminosity function contains only one hundred stars in the top five magnitudes, and no H ii regions have been detected Its structure, as revealed by isophotes constructed from photoeJectric and photographic photometry, is like that of other irregular galaxies; an approximately exponential decrease of brightness characterizes the outer, unresolved portions. Publication: The Astrophysical Journal Pub Date: June 1967 DOI: 10.1086/149197 Bibcode: 1967ApJ...148..719H full text sources ADS | data products NED (5) SIMBAD (1)

Das Farben‐Durchmesser‐ und Farben‐Helligkeits‐Diagramm der Virgo‐Galaxien

Holmberg's photometric data of the Virgo cluster members are used to construct a color‐diameter and color‐magnitude diagram (figure 3). These diagrams show some characteristic features: 1. The late type spirals Sc — Sm are concentrated near a line — the Y‐branch — for which diameter and magnitude increase with increasing color index. 2. The early type spirals Sa — Sbc form the “X‐branch”, for which diameter and magnitude decrease for increasing color index. 3. Elliptical and lenticular galaxies show a large scatter in a small interval of colors. 4. The types Sa — Sbc are clearly separated in two groups (X and X́ in fig. 3).Only the X‐ and Y‐branch probably belong to the main Virgo cloud (the mean velocity being the same), whereas the X́‐galaxies indicate the presence of a more distant cloud (the velocity is about 400 to 500 km/s larger). The distribution of the galaxies on the sky further shows some peculiarities of the X́‐galaxies (fig. 4). They are accumulated in two sectors around the cluster center and perhaps indicate a cloud expanding from the center or from the radio galaxy Virgo A. Without this cloud the plot of the remaining spiral galaxies reveals a color‐diameter and color‐magnitude diagram of relative small dispersion about the mean curves (fig. 5). It is suggested that other clusters may also possess such pronounced diagrams offering favourable possibilities to derive distance, structure and evolution effects. For the Virgo cluster the distance modulus is derived by means of Holmberg's data for M 31 (X‐galaxy) and M 33 (Y‐galaxy) using the distances of Sandage for the Local Group members. From both the diameter and magnitude the same value results: 31.15 ± 0·08. With the mean velocity of the investigated galaxies the Hubble parameter becomes H = (88 ± 9) km/s/Mpc.

THE CLUSTERING OF GALAXIES

Inspecti of photographs obtained with wide-angle telescopes sho' that the distribution of galaxies over the sky is distinctly nt miform. The observed dumpiness of the distribution of ga ies is believed to be due to a tendency for galaxies to occur in sters. A cluster of galaxies is usually regarded as a distinct >e of aggregate of matter. It is the purpose of this paper to investigate some aspects of the validity of the concept of a cluster of galaxies as a distinct type of organization intermediate between an individual galaxy and the universe as a whole. In other words, is a cluster of galaxies an indivisible unit or can it be divided into subclusters or even smaller units ? Alternatively one may inquire if clusters of galaxies are the largest aggregates of matter or if they are themselves constituents of still larger organizations. In attempting to answer these questions we find it instructive to consider first the Group, which is presumably a rather typical example of a small cluster of galaxies. It is quite apparent that the members of this group are not distributed at random in space. The most striking example is the Andromeda Nebula with its two companions M 32 and NGC 205. A compact binary system is formed by the Magellanic Clouds. On a somewhat larger scale it is at once apparent that most of the members of the Local Group may be placed in two subgroups. One of these subgroups is formed by the Galaxy and the Magellanic Clouds. The other subgroup consists of NGC 147, NGC 185, NGC 205, M 31, M 32, M 33, and possibly NGC 404 and IC 10. The different orders of subclustering of the brightest Local Group members are shown schematically in Table I. It is well known that the surface distribution of galaxies in the region of the Virgo cluster is quite irregular. Some of this apparent irregularity may be due to a tendency toward subclustering within the Virgo cluster proper. More definite evidence of the existence of small-scale dumpiness in the Virgo cluster

The Clustering of Galaxies.

Inspecti of photographs obtained with wide-angle telescopes sho' that the distribution of galaxies over the sky is distinctly nt miform. The observed dumpiness of the distribution of ga ies is believed to be due to a tendency for galaxies to occur in sters. A cluster of galaxies is usually regarded as a distinct >e of aggregate of matter. It is the purpose of this paper to investigate some aspects of the validity of the concept of a cluster of galaxies as a distinct type of organization intermediate between an individual galaxy and the universe as a whole. In other words, is a cluster of galaxies an indivisible unit or can it be divided into subclusters or even smaller units ? Alternatively one may inquire if clusters of galaxies are the largest aggregates of matter or if they are themselves constituents of still larger organizations. In attempting to answer these questions we find it instructive to consider first the Group, which is presumably a rather typical example of a small cluster of galaxies. It is quite apparent that the members of this group are not distributed at random in space. The most striking example is the Andromeda Nebula with its two companions M 32 and NGC 205. A compact binary system is formed by the Magellanic Clouds. On a somewhat larger scale it is at once apparent that most of the members of the Local Group may be placed in two subgroups. One of these subgroups is formed by the Galaxy and the Magellanic Clouds. The other subgroup consists of NGC 147, NGC 185, NGC 205, M 31, M 32, M 33, and possibly NGC 404 and IC 10. The different orders of subclustering of the brightest Local Group members are shown schematically in Table I. It is well known that the surface distribution of galaxies in the region of the Virgo cluster is quite irregular. Some of this apparent irregularity may be due to a tendency toward subclustering within the Virgo cluster proper. More definite evidence of the existence of small-scale dumpiness in the Virgo cluster

The Extragalactic Distance Scale.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Extragalactic Distance Scale. van den Bergh, Sidney Abstract M m-M Name Type and class (DDO) (Sandage) M31 Sb I-Il 24.1 24.6 M33 Sc Il-Ill 24.9 24.5 LMC Ir/SBc iII-iV 18.6 19.2 SMC IrIV/IV-V 19.0 19.2 NGC 6822 Ir IV-V 25.0 24.1 Comparison of Sandage's distance moduli with the DDO distance moduli gives H 100+II~l7 (me) km/sec/Mpc. (The mean error takes into account the uncertainty in the correction for selection effects.) Two assumptions are involved in this determination of the Hubble constant. (1) The galactic absorption is given by ATi 0.24 cosec b (2) The distances of local group members are those given by Sandage, which are essentially based on the luminosity calibration of novae by T. Schmidt. Recent observations of globular clusters in M31 by Kron and Mayall and the revision of the absolute magnitudes of RR Lyrae stars by Eggen, Hoyle, and Sandage suggest that Sandage's distance moduli for members of the local group are possibly too large. If this is the case then the Hubble constant is probably slightly larger than 100 km/sec/Mpc. Publication: The Astronomical Journal Pub Date: March 1960 DOI: 10.1086/108189 Bibcode: 1960AJ.....65...57V full text sources ADS |