NGC 1365 is one of the most prominent barred galaxies in the sky - with its strong bar and its conspicious, symmetric spiral structure it is also one of the most beautiful (Figs. 1 and 3). To look at this galaxy through the eyepiece at the prime focus of the European Southern Observatory (ESO) 3.6-m telescope is truly a precious experience. The bar and the blue spiral arms are well outlined, the nucleus itself is very intense and is seen surrounded by bright star forming regions. NGC 1365 has been classified as of type SBb(s)I by Sandage and Tammann (1981) and could well serve as a prototype barred supergiant galaxy. Accordingly, it is today one of the most extensively observed barred galaxies.
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Figure 1. Photograph of NGC 1365 obtained in a two-hour exposure at the prime focus of the ESO 3.6-m telescope on a III a-J plate with GG 385 filter. North is up and East is to the left. |
NGC 1365 lies within the field of the Fornax cluster of galaxies about 1°.2 from the cluster center (Fig. 2). With a total apparent B magnitude of 10m.32, NGC 1365 is one of the brightest galaxies in the cluster field, and it stands out among the members also because of its differing structure. NGC 1365 has no obvious optical companion except for a weak fuzzy object 8'.5 to the NW of the nucleus (Laustsen et al. 1987 plate 5). One of the nearest of the galaxies in the cluster region is the Seyfert 2 galaxy NGC 1386. In the southwestern outskirts of the cluster we find the peculiar radio galaxy Fornax A.
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Figure 2. The Fornax cluster of galaxies. NGC 1365 is seen to the lower right. The dominating elliptical cD galaxy close to the cluster centre is NGC 1399. Courtesy ESO. |
NGC 1365 shows obvious nuclear activity. The nucleus itself presents an optical spectrum with broad permitted emission lines underlying more narrow components, characteristic for a Seyfert Type 1.5 nucleus, and it emits a hard X-ray continuum. It is surrounded by a number of continuum radio sources, one of which seems to be a jet emerging from the nucleus. This jet is projected along the axis of a double cone within which high excitation gas streams out of the nucleus and out of the galactic plane. The nucleus is also surrounded by luminous star forming regions that, as we shall see, are composed of a large number of compact superclusters, one of which may contain one of the yet unresolved cicumnuclear radio sources - possibly a radio supernova.
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Figure 3. `True'-colour image of NGC 1365 combined from three exposures with the FORS1 multi-mode instrument at the UT1 of the ESO VLT in the B (blue), V (green) and R (red) optical bands. Courtesy ESO. |
Because of its display of a wide variety of nuclear activity, its regular structure, absence of interacting companions, a very suitable orientation for kinematic studies and its moderate distance, NGC 1365 is an attractive object for detailed all-embracing studies giving a global picture of a prototype barred galaxy.