The subject of cooling flows in clusters of galaxies remains a controversial one, primarily because many clusters which have large x-ray derived mass inflow rates do not show any optical manifestation of the inflow or of the final fate of the gas. However, a handful of cooling flow clusters do show extended blue continuum regions indicative of current star formation which may be caused by the cooling flows (Romanishin 1987, Romanishin and Hintzen 1988), while another group show spectral evidence of star formation (O'Connell and McNamara 1988). Most of the cluster galaxies which show evidence of star formation also show nuclear activity, in the form of radio emission.

A mechanism for fueling active galactic nuclei and nuclear starburst galaxies is suggested. It consists of two stages. First, a large-scale stellar bar sweeps the ISM into a gaseous disk of a few hundred pc radius. This disk may, under certain conditions, become dynamically unstable, induce radial flow, and feed viscosity-driven accretion flow around a black hole. It may lead to the formation of a black hole if none was present initially.

The first analysis of the Infrared Astronomical Satellite (IRAS) data revealed differences between barred and unbarred spirals. The study of Shapley-Ames galaxies, by De Jong et al (1984), revealed that barred spirals tend, on average, to be associated with “warmer” far infrared color temperatures and higher Lfir/Lblue ratios than unbarred spirals. In a related study Hawarden et al (1986) noted that barred and unbarred spirals could be partially segregated on the basis of the IRAS S25μm/S25μm flux ratio. Both sets of investigators attributed the differences, between barred and unbarred spirals, to a nuclear starburst in the barred types.

Jets emanating from AGN propagate first through an isothermal, but roughly power-law in density, galactic halo and then into a hotter, less dense, and uniform intergalactic medium (IGM) or intracluster medium (ICM). We use a three-dimensional boundary-following code (Mitteldorf & Wiita 1988), altered to allow for a two-phase external medium. We vary the beam power, P, the redshift, z, the radius of the galactic halo/IGM interface, Rh, the steepness of the power-law fall-off within the halo, n, and the temperature ratio of the IGM (or ICM) to the halo, Tr to estimate the average linear sizes of extragalactic radio galaxies (RGs). Good agreement is obtained with regard to the relationships between the overall linear size of such radio sources and both the total radio power (at fixed redshift) and the cosmological redshift (at fixed power). These numerical models tend to support recent analytical models (Gopal–Krishna & Wiita [GW] 1987, 1988).

Aiming at a physical interpretation of the cosmological evolution of radio galaxies, we extend to a high redshift our analytical model for the propagation of relativistic beams first through a hot gaseous halo of the parent elliptical galaxy and then through an even hotter, but less dense, diffuse IGM, after crossing a pressure-matched interface between the two media1–5. This model, verified by quasi-hydrodynamical numerical simulations5 has earlier explained: (1) the current mean size of classical double radio sources (D ∼350 kpc), (2) their steep linear-size evolution with redshift, z: D α (1+z)−3, (3). The correlation between size and radio luminosity (at fixed z): D α P0.3, (4) the number and <P> of giant radio galaxies, and (5) the break in the local radio luminosity function (LRLF), occurring near P ∼1024W.Hz−1 at 1 GHz (Ho = 50 kms−1 Mpc−1). Inputs to the model are observationally based average parameters of the halo1 {kTh∼1 keV, n(r) ∼10−2cm−3[1+(r/2kpc)2]−3/4}, IGM7 {kTIGM ∼18 keV (1+z)2, nIGM ∼7.10−7cm−3(1+z)3} and the beam4 {opening angle θ (radian) = 0.02 + 0.03 [29 - log P(t=0)]}. We assume a reasonable value of ∊ = 0.1 for the initial efficiency of conversion of the beam power, Lb (Watts) into (total) radio output Pt ∼1010. P(W.Hz−1). A gradual weakening of magnetic field within the expanding source raises the significance of inverse Compton losses against the Cosmic Microwave Background (CMB), leading to a reduced radio efficiency (RRE)3,2.

Electronographic plates have been obtained with the ESO 3,6 m telescope and the CFH telescope. One of the plates is reproduced figure 1. We have studied the regions surrounding the nucleus of 3C 120 (r<8″) and emitting in the continuum. The “jet” found by Wlérick et al. (1981) has been resolved into 3 condensations, A, B and D; another condensation C is located 7″ S-E of the nucleus; a filament F leaves the nucleus in the direction of condensation B. The 4 condensations have been measured in colours U B V and V′, this last band excluding the [OIII] emission lines. We have located each condensation with respect to the zones where gaz emission is observed and particularly two regions that we call E1 and E2. We have also located condensation A with respect to the radiojet and we have searched, in B and V colours, for polarization of this condensation. The results are the following:

1. 1. The 4 condensations are faint: 20,0<B<20,8, corresponding Jo the absolute magnitudes: −16,1 < Mg<−15, 3, using H = 60 km s−1 Mpc−1. Colours of condensations A, B and D are similar: U-B∼−0,20; B-V∼0,87; condensation C is less blue: U-B∼0,30; B-V∼0,90.

2. 2. The brightest condensation A is elongated nearby North-South, its southern part pointing toward S-E (Fig. 1). It is interesting to place A with respect to the radiojet (cf. Browne et al., 1982, Walker et al., 1987). The maximum of A is located 1″ North of the first knot of the jet but the southern part of A coincides with this knot. The maximum of the emission region E1 is located 1″ West of the maximum of A, but region overlaps a large part of A. Though no significant polarization has been found for A taken globally, we suggest that the flux of A consists of two parts: in the southern region of A, the flux could be synchrotron radiation corresponding to a spectral index radio-visible ∼0,7; the northern part of A would be a zone of star formation triggered by the impact of the jet on region E1; the situation is very similar to the one found with Minkowskis object (Van Breugel et al., 1985; Brodie et al., 1985), concerning the relative position of A and the jet, as well as the variation of polarization of this jet and its change of direction; on the other hand, A is not as blue as Minkowski's object and this is likely due to the fact that the number of young stars is smaller; the change of the polarization in a well localized part of the radio knot (Walker et al., 1987) suggests that the gazeous region E1 is flattened and that the jet crosses it obliquely.

3. 3. Condensations B and D form a chain with A and they are located in a region where no emission is observed; they are made probably of stars older than the one of condensation A.

4. 4. Brightness and colours of condensation C are similar to those of the nucleus of a spiral galaxy. We suggest that C is the residue of a galaxy captured by 3C 120; this agrees with the work of Heckman et al. (1986); these authors consider a galaxy merger as the origin of the activity of 3C 120 and, as they do not see any neighbouring galaxy, they state that the merger has nearly reached completion. The bright gazeous region E2 connects possibly C and the nucleus of 3C 120.

The peculiar nuclear region (Hummel et al., 1987) of the southern barred spiral NGC613 has been imaged with a CCD attached to the 90 cm CTIO reflector and integration time of one hour, using narrow band filters at Hα, Hβ, [OIII], [OII] and continua at 3765 Å(C[OII]), 5200 Å(CEβ) and 6476 Å(CHα), which allow to obtain pure line frames. Stone and Baldwin (1983) spectrophotometric standards have been observed for absolute calibration. The CHα (fig. 1) and CHβ (fig. 2) images show the well known 2 blobs structure, the SE of which is the nucleus. The ratio of both frames reveals an up to now unknown ring like structure (fig. 8) of 1400 × 2300 pc. The monochromatic color c(CHβ-CHα) reach 0.6 mag on the ring and 0.0 to 0.2 mag in its inner zone, where most of the gas emission is produced. The ratio Hα/Hβ (fig. 7) shows that the ring is practically absorption free, and that the dust is strongly concentrated in a zone of 400 pc, shifted 500 pc to the N of the nucleus, absorving up to 6 mag. in Hβ. Comparison with star monochromatic colors (O'Connell, 1973) lead to conclude that the ring colour is produced by red stars, with a mean spectral type G8 to K1, while in the central region it is A5 to F0. This ring is probably similar to that of HII regions observed in NGC 1097 (Osmer et al. 1974), but with the ionizing stars having evolved to RSG. The Hα pattern (fig. 3) presents only one maximum, displaced about 300 pc to the SE of the nucleus, being the weakest isophotes distorted to the W. The Hβ one (fig. 4) shows also one maximum, but the isodensities are elongated due to the extinction. The [OII] (fig. 6) shows a two blob like structure; and the [OIII], with the richest feature distribution, shows emission minima coincident with the [OII] blobs. The mean Hα/Hβ ratio is about 3.9, but mean extinction correction can be meaningless due to the distribution of dust. The ratios [OIII]/Hβ = 0.47 and [OII]/Hβ = 0.27, when compared with Stasińska's (1982) photoionization models, indicate higher than solar metallicity and Teff ≈ 40,000K for the ionizing source.

CCD slit spectra have been obtained at Lick Observatory of a sample of fourteen close interacting and irregular Seyfert galaxies. The spectra of the extranuclear emitting regions have been investigated and classified using the quantitative criteria recommended by Veilleux and Osterbrock to distinguish objects photoionized by thermal sources from objects photoionized by a “power law” continuum. From our data it results that four out of the twenty emitting regions identified are typical H II regions, while eight have spectra photoionized by a hard-photon spectrum. Seven regions show a twofold behavior which is interpreted in terms of a combination of photoionization, shock heating and scattering of light by dust.

The nucleus of the peculiar Sa galaxy IC 5135 has strong emission lines whose relative intensities resemble those of Seyfert 2 galaxies (Phillips, Charles, and Baldwin 1983). However, the galaxy exhibits relative line intensities such as [O III] λ5007/Hβ = 6.5 and He II λ4686/Hβ = 0.17 that are considerably smaller than typical Seyfert 2 values of 11 and 0.3, respectively (Koski 1978). New, high-resolution spectra (FWHM ≈ 2Å) obtained at Las Campanas Observatory reveal that the Hβ emission-line profile actually consists of a relatively strong, narrow component (FWHM ≈ 250 km s−1) superposed on a much weaker, broad base (FWHM ≈ 1000 km s−1; Fig. 1). A similar two-component profile is evident in [O I] λ6300, whose narrow core probably comes from circumnuclear H II regions that produce little [O III] and He II emission. The strong, high-order Balmer absorption lines are consistent with the presence of a young stellar population in the nucleus.

Most studies of active galaxies have concentrated on their unresolved nuclear regions because this is where their prodigous energy output originates. With the advent of CCDs, recent work has centered on determining how an AGN affects its host galaxy. To isolate the effect of an AGN on its host galaxy, a comparison between a set of galaxies containing active nuclei and a set of normal galaxies would be useful. In principle, if the active and normal galaxy samples are chosen properly, then any systematic differences found between the two samples in the line emission and/or continuum properties of the host galaxy can be attributed to nuclear activity.

Spectroscopic observations have shown that strong radio galaxies contain extra–nuclear gas which is rapidly rotating (Simkin 1979, Heckman et al. 1985). In addition, weak spiral-like structure has been observed in the inner regions of several strong radio galaxies classified as DE or E (Simkin and Michel 1986, Beichman et al. 1985, Hansen et al. 1987, Baum et al. 1988).

V and I CCD images for 13 Seyfert galaxies have been obtained at the Cassegrain focus of the JKT at the Roque de los Muchachos Observatory, Canary Islands. Integrated V and I magnitudes were obtained sampling the intensity of each galaxy in a circular area, up to a radial distance R at which the V surface brightness is 24 mag/sq arcsec. Mean luminosities MV = −21.89 and MI = −22.92 have been calculated adopting the galaxian radial velocities given by Adams (1977) and Ho = 55 kms−1 Mpc−1. By using elliptically averaged V and I luminosity profiles and the most outstanding morphological features from isophote maps we can distinguish two groups: 1) Galaxies with prominent bulge (Mk 50, Mk 124, Mk 348 and 3C227) where almost the entire profile is fitted by an r−1/4 law and no evidence for an exponential disk is found; some have a very diffuse external structure, like Mk 50 and Mk 348; and 2) Spiral galaxies (Mk 9, Mk 10, Mk 79, Mk 110, Mk 352, Mk 358 and Mk 618) showing spiral arms and exponential disks; most of them have also a prominent bar. Mk 42, whose luminosity profiles are strongly disturbed by a bright external ring, and NGC 985 a galaxy with a single arm, were both included in this group.

In earlier communications we have called attention to the existence of very tight spiral formations in the nuclei of some galaxies, particularly of the early type barred spirals, proposing a mechanism for their formation (Pişmiş and Moreno 1984). These kiloparsec-scale structures are loosely termed “rings” but their overall morphology suggests strongly that the image is a tightly wound double spiral usually delineated by knots of emitting material, “hot-spots”. A striking characteristic of these spirals is their very high luminosity compared to the outer regions of the galaxy. 26 galaxies with “nuclear” spirals are listed by Buta, thesis. A systematic search with short exposure high resolution imagery may reveal many more nuclear spirals. NGC 4736 (Sb) though not a barred spiral has a well defined inner spiral delineated by very luminous H II regions.

We have coadded the IRAS data on a sample of 188 multiple-nucleus and morphologically peculiar Markarian galaxies noted as “interacting” in the compilation of Mazzarella and Balzano (1986). We have increased the number of objects in this sample with 60μm and 100μm IRAS detections by a factor of two from what is available in the Point Source Catalog, allowing the determination of far-infrared (FIR) luminosities and colors for over 130 morphologically peculiar Markarian galaxies. The galaxies in this sample have diameters less than 2′, and thus were seen as point sources by IRAS. All far-infrared properties discussed here apply to the entire multiple-nucleus or peculiar system. These data provide a unique opportunity to study the far-infrared properties of mergers which have prior indications of starburst or Seyfert activity as evidenced by their ultraviolet excess.

Studies of the HEAO–1 A2 all–sky survey data have established that the level of anisotropy of the extragalactic X–ray background (XRB) is relatively low:

1. – The cell–to–cell XRB intensity variations can be entirely accounted for by Poisson fluctuations in the space distribution of known classes of sources; the 90% confidence upper limit to any additional contribution on a scale of 26 square degrees is 2.3% (Shafer and Fabian 1983).

2. – No significant correlations of XRB intensity fluctuations appear to be present; the formal 90% confidence upper limit on the amplitude of autocorrelations, relative to the mean background intensity, for an angular scale of 3° is Γ(3°) ≤ 1.9 × 10−2 (Persic et al. 1988).

I review the basic properties of low-luminosity active galactic nuclei (LLAGNs) — objects in which activity similar to, but intrinsically milder than, that in QSOs and luminous Seyferts is believed to be present. Until recently, most LLAGNs were first recognized as such and studied at optical wavelengths, but evidence for activity and valuable information concerning its nature are now also being obtained in many other spectral ranges. Low-ionization nuclear emission-line regions (LINERs) are the most common LLAGNs; in a large fraction of them the emission lines come from clouds of gas probably photoionized by a nonstellar continuum, rather than heated by shocks. It is also clear, however, that there could be substantial heterogeneity among LINERs, particularly those with extended emission; some may be produced by cooling flows, supernova-driven winds, and galaxy interactions or mergers. LLAGNs can easily be hidden from sight in a variety of ways, including obscuration by galactic or circumnuclear disks and dilution by bursts of star formation. Direct imaging, spectroscopy, and spectropolarimetry can be used to isolate the different components, especially with high spatial and/or spectral resolution. A surprising result is that Seyfert nuclei are sometimes found in dwarf and very late-type galaxies. The nearby Sd III-IV galaxy NGC 4395 contains the intrinsically faintest known Seyfert 1 nucleus, with a broad Ha luminosity only ∼ 0.1 that of M81. The idea that the apparent “activity” in some galaxies is a direct consequence of vigorous star formation has some strong supporting evidence, and should seriously be considered. As an example, I focus on the peculiar supernova 1987F, whose optical spectrum bears a striking resemblance to that of typical Seyfert 1 nuclei.

The nucleus of the nearby Sb galaxy M81 has been shown to exhibit many of the features prominent in luminous active galactic nuclei: a variable, compact VLBI radio source (Kellermann et al. 1976, Jones, Sramek and Terzian 1981), a central variable X-ray source (Elvis and van Speybroeck 1982, Fabbiano 1988), and broad wings of Balmer emission similar in extent to those typical to Seyfert 1 nuclei (Peimbert and Torres-Peimbert 1981, Shuder and Osterbrock 1981). The nucleus also shows a narrow-line spectrum in many ways typical of LINERs (Heckman 1980), now known to be representative of early-type spiral nuclei in general.

We present results from the study of six low activity galactic nuclei spectra with strong [NII] λλ6548 + 6584 emission lines in order to investigate if this characteristic is due to a peculiar chemical abundance. The selected galaxies NGC1358, NGC1386, NGC4941 and NGC6300 present Seyfert 2 (Sy2) activity, NGC3312 is a LINER and NGC7743 can be classified as intermediate between the two categories. All of them are nearby early type galaxies, whose nucleus present a prominent absorption spectrum with no direct evidence of a non-stellar continuum. Observations were made with the Tololo 1m telescope and 2DFRUTTI detector in the spectral region λλ3700 - 7000 A, with 5A (FWHM) resolution.

Two types of active nuclei have been observed in normal spiral galaxies in X-rays with the Einstein Observatory: low-activity AGN, and starburst regions. The prototype of the first kind is the nucleus of M81 (Elvis and Van Speybroeck 1982; Fabbiano 1988a), but similar nuclei might also be those of M33 and NGC 1313. Soft X-ray spectra of these nuclei suggest relatively steep soft X-ray components (Trinchieri, Fabbiano and Peres 1988; Fabbiano and Trinchieri 1987; Fabbiano 1988a), reminiscent of those observed in QSOs by Bechtold et al (1987) and Wilkes and Elvis (1987). In M81, in particular, this soft component might supply enough photons to explain the optical line spectrum. If this soft X-ray component originates from an accretion disk surrounding a central black hole, the mass of the latter is likely to be smaller than 104–5 solar masses.