Sidebar- Radio Galaxies and UGC 6697

Radio galaxies are among the most intriguing objects in the universe. They are often distinguished by a pair of huge diffuse lobes that pour forth radio waves. The lobes are often associated with a central, compact solar-system-sized radio source. Some think that black holes power the energy at the source of radio galaxies. The source is linked to the lobes via jets which spew material that travels at near light speeds.

UGC (Uppsala General Catalogue of Galaxies ) 6697 is a radio source associated with an irregular galaxy Zwicky 97087 in the Abell 1367 Coma Berenices supercluster. The Coma supercluster is a huge cluster of densely-packed (~10,000 in number) galaxies mostly of the lenticular, dust-free, 'SO' type and elliptical type, crowded at the supercluster core. UGC 6697 is an usual object in a number of respects and has been extensively studied in all wavelengths in the last 15 years, especially by G. Gavazzi at the Istituto di Fisica Cosmica, Milan, Italy and his colleagues.


The Abell 1367 Coma Berenices supercluster.
(Click on the picture for an expanded view. 18kB.)

From what I gathered from my cursory readings of this object, UGC 6697 is an unusual radio source, whose associated galaxy Zwicky 97087 (and several companion galaxies) seems to be plowing through the Coma supercluster to the supercluster's center, with gas and dust being stripped in the process and streaming out behind it. This very energetic object emits radiation at almost all wavelengths including X-ray wavelengths. It is also the site of very active star formation and its material isn't rotating around it's central core in a typical fashion.

Here are some details of the unusual features of this UGC 6697 radio source:

  1. Radio asymmetries. In the radio wavelengths, the object has a marked asymmetry, which resembles a head-tail source, that, in turn, reflects an intrinsic asymmetry of the parent galaxy Zwicky 97087 (Gavazzi et al., 1984). The Very Large Array Radio telescope H I emission maps confirm that the atomic gas in the cluster (Zwicky 97073, 97079, and 97087) is displaced from its optical centers (Dickey, J.M. and Gavazzi, G., 1991). The researchers take this as evidence that Zwicky 97087 and its neighbors are entering the dense medium of the cluster core for the first time.

  2. Optical asymmetries. The optical morphology of the associated galaxy cluster (Zwicky 97073, 97079, and 97087) is also disturbed. The galaxies are systematically brighter at the side with the sharp radio gradient, and fainter on the opposite side. The parent galaxy Zwicky 97087 also shows a sequence of faint diffuse knots trailing to the northwest behind the bright disk (total extension ~= 60 kpc) with associated radio emission (G. Gavazzi and W. Jaffe, 1985).

  3. Peculiar Rotation Curve of associated galaxy Zwicky 97087 (Gavazzi et al., 1984). The 'rotation curve' is a scientific expression for the circular velocity of a test mass as a function of its position in the galactic disk. This information is important for constructing models of the galaxy's mass distribution, and as a means of interpreting observation data. (Bowers and Demming, 1984.)

  4. High star formation rate. Optical and radio data from this galaxy, as well as some statistical surveys show that it has a much higher than average star formation rate than the other galaxies in the Coma Berenices supercluster (G. Gavazzi and W. Jaffe, 1985). Some have concluded that its enhanced current star formation might occur due to molecular gas collapse stimulated by the ram-pressure mechanism. The 'ram-pressure' mechanism is a mechanism for stripping gas from galaxies in rich clusters. The galaxies' relative motion through the cluster medium is analogous to the wind knocking the hat off of a rapidly pedaling cyclist. (which may explain the "swept-back" look of head-tail radio sources (Shu, F. 1982)).

  5. CO molecular gas distribution is normal for Zwicky 97087. No asymmetries were found (Boselli et al., 1994). If an asymmetry were found, that would be the signature of a tidal interaction, either between the local galaxies or with the Coma Berenices cluster as a whole. An explanation for this distribution and the asymmetries found elsewhere is that ram-pressure is exerted by the hot intergalactic gas. This would explain not only the peculiar atomic gas and star formation distributions, but also the orientation of the radio tails.

  6. UGC 6697 has an associated X-ray source (Fruscione and Gavazzi, 1990).

References

(1)
Boselli, A.; Gavazzi, G; Combes, F.; Lequeux, J.; Casoli, F. (1994). Astronomy and Astrophysics 285, 69-78.

(2)
Bowers, R.L. Deeming, Terry (1984). Astrophysics II: Interstellar Matter and Galaxies, Jones and Bartlett Publ., pp. 542-543.

(3)
Dickey, J.M. and Gavazzi, G. (1991). Astrophysical Journal 373, 347-353.

(4)
Fruscione, A. and Gavazzi, G. (1990). Astronomy and Astrophysics 230, 293.

(5)
G. Gavazzi; Tarenghi, M.; Jaffe, W.; Bokensberg, A.; Butcher, H. (1984). Astronomy and Astrophysics 137, 235-244.

(6)
G. Gavazzi and W. Jaffe, (1985). Astrophysical Journal 294, L89-L92.

(7)
Shu, Frank (1982). The Physical Universe, University Science Books, p. 347.

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Last Modified by Amara Graps on 8 November 1997.
© Copyright Amara Graps, 1996-1997.
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