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Astron. Astrophys. 328, L17-L20 (1997)

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5. Alignments along the minor axes of seyfert galaxies

As shown in Fig. 1 the minor axis of NGC4235 is well defined and the X-ray AGN's lie closely along it. This result has motivated a review of the previous cases of alignments across Seyferts. As Table 2 shows, in every case where the minor axis is well defined, the quasars are significantly aligned along it.


Table 2. Alignment angles of quasars from minor axis

a) NGC4258. The quasar with [FORMULA] is [FORMULA] from the position angle (p.a.) of the minor axis of the galaxy and the quasar with [FORMULA] is at [FORMULA] from the minor axis. Recently E.M. and G.R. Burbidge (1997) reviewed the evidence for ejection of gaseous and radio material along the minor axis of this Seyfert which has been renowned for ejection activity since 1961.

b) NGC2639. This Seyfert has a conspicuous pair of X-ray sources across it (Arp 1997a). As shown here in Fig. 4, E.M. Burbidge (1997) has determined the redshifts as [FORMULA] and.325 which reduces to insignificance the chance of accidental background configuration.

[FIGURE] Fig. 4. X-ray map of the region around NGC2639 (z =.011). Counts per ks are written above each quasar and redshifts measured by E.M. Burbidge written below.

Fig. 5 shows the inner [FORMULA] field around NGC2639 and in particular the 7 fainter X-ray sources coming out to the NE. As indicated they are exactly along the line of the NGC2639 minor axis. Four of these are identified with BSO's or blue compact galaxies (BCG's). They are almost certain to be quasars or quasar-like objects. They should be measured spectroscopically and their positions, accurate to a few seconds of arc, are given in Table 3.

[FIGURE] Fig. 5. Enlarged region around NGC2639 showing X-ray sources lying closely along the NE minor axis of the Seyfert. Intensities in cts/ks are labelled in the Fig. Positions and optical identifications are given in Table 3.


Table 3. X-ray sources NE of NGC2639 (Fig. 5)

Since these sources are closer to the ejecting galaxy we would have the natural interpretation that after the original ejection of the wide pair the position of the minor axes had rotated about [FORMULA] counterclockwise and was now ejecting the closer sources. (The northern quasar at [FORMULA] is about [FORMULA] smaller p.a. than a line directly across the nucleus to the [FORMULA] quasar. It may be gravitationally perturbed by an attracting object in its vicinity.) In general the quasars could be ejected out in narrow lines or cones and then rotation of the ejection axis or perturbations could then widen their distribution to an average of [FORMULA] as indicated in Table 2.

c) NGC4235. The strong X-ray source which is a quasar of [FORMULA] is only [FORMULA] from the well defined minor axis of the galaxy. In the other direction there is a BL Lac of [FORMULA] which lies only [FORMULA] from the minor axis direction. Note the similarity of redshift of the NGC4235 quasar to the two NGC2639 quasars. The redshift [FORMULA] is a major preferred redshift value for quasars in general and particularly those associated with low redshift galaxies (Arp et al. 1990).

d) NGC1097. The three cases just discuss have particularly conspicuous pairs and also well determined axis positions. More cases will accrue only slowly because this combination is not so frequently encountered. As an example we mention the active Seyfert NGC1097 which has about 40 quasars associated with it (Arp et al. 1984). But because NGC1097 is a barred spiral it is difficult to determine the position of its major axis. We have estimated a position which may be good to about [FORMULA]. As Table 3 shows, the four brightest and nearest quasars are then oriented within about [FORMULA] of the minor axis. Of course, this falls just between the long, luminous optical jets which emerge from the nucleus and must represent some form of ejection.

e) NGC3516. As this paper was being revised, word was received from Yaoquan Chu that he had measured the X-ray BSO candidates around the extremely active Seyfert NGC3516 (see Arp 1997a, Fig. 11). All were quasars and the redshifts turned out to have striking properties which are discussed by Chu et al. (1997). The importance for the discussion here, however, is that all six quasars (including the known BL Lac-type Sey 1) are aligned along the minor axis of NGC3516 to within [FORMULA]. This newest example has been added to the end of Table 2.

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998