NGC is a small spiral galaxy located in the same constellation, about 82 million light-years from Earth. These galaxies are quite close to each other in space, but they have very different histories. NGC has led an uneventful life, but NGC has engulfed several other galaxies in its violent history and shows the battle scars. Several clues in the structure of NGC reveal that its past was turbulent. NGC is situated south of the celestial equator and, as such, it is more easily visible from the southern emisphere.
For more information about photometry in astronomy, check the photometric system article on Wikipedia. The surface brightess reported below is an indication of the brightness per unit of angular area of NGC The area of sky represented in the image is 0.
Celestial coordinates for the J equinox of NGC are provided in the following table:. The simplified sky charts below show the position of NGC in the sky. These suggest that it may have already swallowed a dust-rich spiral galaxy about three billion years ago. Also seen around the galaxy are very faint tidal tails — wisps and shells of stars that have been torn from their original locations and flung into intergalactic space.
These features are produced by complex gravitational effects on the orbits of stars when another galaxy comes too close. All of these signs point to a violent past during which NGC annexed other galaxies and suggest that the disruptive behavior is continuing.
NGC seems to be relatively unperturbed and has a clear spiral structure. But its larger neighbour bears the scars of several past violent events when it has swallowed other galaxies. It also bears the name Fornax A, reflecting the fact that it is the brightest source of radio emission in the constellation — and in fact the fourth brightest radio source in the entire sky [2]. Withthese corrections, the XLF is well reproduced by a single-unbroken-powerlaw with a slope of The hot ISM hastemperatures in the 0.
Theseproperties suggest that the ISM may be subject to partial winds. Companions of Bright Barred Shapley-Ames Galaxies Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented.
Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology crooked arms , andgalaxies with normal disk morphology; the list includes all Hubbletypes.
The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC , NGC , and NGC , and one is astarburst galaxy, M Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
We detect H I within theprimary beam 30' half-power beamwidth in four of the five systems. However, in only one case is this gas associated with the targetedelliptical galaxy. In the other cases the H I is associated with anearby gas-rich disk or dwarf galaxy. The one H I detection is for NGC, where we tentatively detect an H I cloud lying between 20 and 40kpc southwest of the galaxy center.
Its origin is unclear. Our targeted systems all reside in groups or clusters, and itseems likely that tidal H I is shorter lived in these environments thansuggested by studies of more isolated merger remnants.
In contrast, wehave included systems hosting active galactic nuclei AGN in thecatalogue. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies PGC. We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity LB and the square of linear diameter D These local galaxy images represent a much fairerstatistical baseline than the galaxy atlas images presented by Frei etal.
Both analyses suggest that over two-thirds ofstrongly barred luminous local spirals i. Under the same conditions, most weaklybarred spirals classified SAB in the Third Reference Catalogue wouldbe classified as regular spirals.
The corresponding visibility of spiralstructure is assessed visually, by comparing luminosity classificationsfor the artificially redshifted sample with the corresponding luminosityclassifications from the Revised Shapley-Ames Catalog. Otherassociated parameters, such as integrated photometry and half-lightradii, are tabulated.
We findthat UV galaxy morphologies are usually significantly different fromvisible band morphologies as a consequence of spatially inhomogeneousstellar populations. Differences are quite pronounced for systems in themiddle range of Hubble types, Sa through Sc, but less so for ellipticalsor late-type disks. Normal ellipticals and large spiral bulges arefainter and more compact in the UV.
The far-UV light in these cases isprobably produced by extreme horizontal branch stars and theirdescendants in the dominant, low-mass, metal-rich population. The coolstars in the large bulges of Sa and Sb spirals fade in the UV while hotOB stars in their disks brighten, such that their Hubble classificationsbecome significantly later. In the far-UV, early-type spirals oftenappear as peculiar, ringlike systems.
In some spiral disks, UV-brightstructures closely outline the spiral pattern; in others, the disks canbe much more fragmented and chaotic than at optical wavelengths. A numberof systems have unusual UV-bright structures in their inner disks,including rings, compact knots, and starburst nuclei, which could easilydominate the UV light in high-redshift analogs. A significant butvariable fraction of the far-UV light in spiral disks is diffuse ratherthan closely concentrated to star-forming regions.
Dust in normal spiraldisks does not control UV morphologies, even in some highly inclineddisk systems. The heaviest extinction is apparently confined to thinlayers and the immediate vicinity of young H II complexes; the UV lightemerges from thicker star distributions, regions evacuated of dust byphotodestruction or winds, or by virtue of strong dust clumpiness.
Onlyin cases where the dust layers are disturbed does dust appear to be amajor factor in UV morphology. The UV-bright plume of M82 indicates thatdust scattering of UV photons can be important in some cases. In acompanion paper, we discuss far-UV data from the Astro-2 mission andoptical comparisons for another 35 galaxies, emphasizing face-onspirals. This behavior is consistent with that of higher redshiftsamples observed by Sullivan et al.
Although the galaxies in our sample show modest levels of attenuation with median values of 0. The innerstarburst ring and bisymmetric knots at intermediate radius, inparticular, argue for bar-mediated resonances as the primary drivers ofevolution in M94 at the present epoch.
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