We investigated the intrinsic shape of the luminosity density of the triaxial galaxy NGC 661 by comparing its observed profiles of photometric parameters with the projected surface brightness of model galaxies. We examined NGC 661 which shows a small scale variation in the ellipticity profile at ∼ 0.3 re. We suggest complex form of density distributions which might explain it.

At 5 GHz, about 20 point sources were detected earlier by Glendenning & Kronberg (1986) in the central 800 pc of NGC 2146. Our observations with higher sensitivity and resolution made with MERLIN and the VLA confirms the detection of 18 sources, and resolves 7 of them (Fig.1). Additional 1.6-GHz MERLIN observations disclose 9 sources coincident in position with those detected at 5 GHz, which allows us to derive their spectral indices α51.6 (Sv ∼ να). Only 3 sources have indices (α < 0) consistent with synchrotron emission from supernova remnants or radio supernovae, while the others have very steep inverted spectra (α > 0).

In recent years it has become possible to use high resolution radio interferometry and other techniques to study the sub-kiloparsec scale circumnuclear gas in the centres of Active Galactic Nuclei. This gas presumably provides the fuel source for the AGN activity and also plays a role in obscuring the direct view of the central engine from certain directions. The status of high resolution observations of the ionised, atomic and molecular phases of this circumnuclear gas are briefly reviewed.

With the aim of probing HI gas in AGN we have searched different samples of radio sources for the 21cm atomic hydrogen line in absorption. Depending on the source morphology, we are able to probe gas that either belongs to the host galaxy ISM, or gas that is situated on scales < 1kpc which then may be connected with the AGN fueling. For the HI absorption detected in 3C216, we argue that such sub-kpc scale gas instead might be due to a jet-cloud interaction.

We present sensitive, high-resolution λ21-cm VLBA+VLA observations of the radio jet and nuclear HI absorption in NGC 4151. The 25-mas (1.6-pc) resolution continuum image reveals a highly collimated radio jet, underlying the discrete components seen previously with MERLIN and the VLA. Spatially and kinematically complex HI absorption is detected against the whole 3-pc extent of the continuum component predicted by Ulvestad et al. to contain the AGN. Instead, we suggest the component against which the absorption is detected is part of the eastern counterjet, ruling it out as the location for the AGN.

We have used VLBI HI absorption imaging to search for evidence for a circumnuclear atomic structure in five radio galaxies. Of these, we have found that two, (PKS 2322-123 and 1946+708), are very symmetric on parsec scales and exhibit strong evidence for a circumnuclear torus, confirming the prediction of the unified scheme. The two nearby extended radio galaxies NGC 5128 and NGC 315, on the other hand, have asymmetric core-jet morphologies on parsec scales, and their HI absorption profiles appear to arise from gas in the host galaxy which is not associated with the AGN at all. This is also consistent with the unified scheme of AGN. One remaining source, NGC 3894, also has symmetric jets, but has a very complicated HI structure which changes on parsec scales. This source requires further study.

We conducted an observation of weak HI and OH absorption features in the parsec-scale nuclear region of NGC 3079 using a global VLBI network; the VLBA, the VLA and the Green Bank 43-m telescope of NRAO. One mas corresponds to 0.076 pc in NGC 3079.

We present MERLIN observations of the atomic and molecular gas of IC 694 a member of the merger system Arp 299. The radio continuum of IC 694 is consistent with a disk of synchrotron emission powered by supernovae remnants. The atomic and molecular gas are located in a similarly orientated 250 pc large disk.

The phenomenon of chemically distinct galactic nuclei is quite new and hardly studied yet. During the last 10 years we search for chemically distinct nuclei in disk galaxies, and after our first work (Silchenko, Afanasiev, & Vlasyuk 1992) two dozens of those are already found. A question posed now is if the galaxies with chemically distinct nuclei have also distinct circumnuclear disks and if these disks can be identified with chemically distinct areas. An answer for the first part of the question is certainly ‘YES’; the second part is far less clear. The observations presented here are made during 1996-1998, mostly with the Multi-Pupil Field Spectrograph (MPFS) of the 6m telescope (Afanasiev et al. 1990). The MPFS allows to obtain a set of 96 to 240 spectra from an extended area; each spectrum corresponds to an element of 1.3 × 1.3 before mid-1998 and 1.0 ' 1.0 later. Seeings were 1.5 − 2.5. What do we mean when telling about chemically distinct nuclei? We recognize them by a sharp drop of metal absorption-line equivalent widths when passing from the point-like nuclei to the surrounding bulges. Figure 1 presents 4 examples of the radial profiles of the magnesium and iron absorption-line indices in the Lick system (Worthey et al. 1994). The data for M 31 are long-slit data from the 1m telescope of the Special Astrophysical Observatory; the cross-sections are taken in 5 various position angles (for details, Silchenko, Burenkov, & Vlasyuk 1998). The other data are azimuthally averaged measurements from the MPFS (for details, see Silchenko 1999a,b and Afanasiev & Silchenko 2000). All the profiles decrease prominently within the radius comparable to the spatial resolution; in the bulges they flatten off. The metallicity drops between the nuclei and the bulges by a factor of 2 to 10. The behaviours of the magnesium and iron indices can be similar or different. The most interesting feature is revealed by comparing the iron and magnesium profiles in NGC 1023 and NGC 7331: the magnesium peaks in the very center whereas the maxima of the iron index are at the R ≈ 1. We should treat this phenomenon as an evidence for a short-duration star formation burst in the center and a more prolongated one in its neighborhood.

A deep (∼ 70ks) Chandra ACIS pointing at the merging system NGC 4038/39 gives us an exceptional detailed view of its X-ray emission and demonstrates the capabilities of Chandra's sub-arcsecond resolution. We detect an extraordinarily luminous population of pointlike sources, that may suggest 10-100M⊙ Black Hole counterparts. We also detect a luminous hot ISM, with features ranging to large scale outflows to hot superbubbles.

We performed near infrared integral field spectroscopy of several star clusters and the nuclei of the prototypical merger NGC 4038/39 (“The Antennae”). Near infrared (NIR) images covered both galaxies. The collision of the two gas-rich spiral galaxies has triggered a starburst obvious from a large number of young star clusters. ISO data suggest that the most active star formation occurs in the region where the two galaxy disks overlap. A significant fraction of the total bolometric luminosity of the system is produced there. Since this region is heavily extincted in the optical, the investigation was made in the NIR. Using Brγ emission and CO absorption features as age indicators, we derive the ages and mass estimates of the star clusters from a comparison with stellar synthesis models. Extinction is calculated from the Brγ/Hα ratio. The young, bright star clusters have ages ranging from 4-12 Myrs, while the nuclear starbursts are much older (50-80 Myrs). The overlap region hosts most of the youngest star clusters below ∼8 Myrs, while the northwestern region is dominated by star clusters in the age range between 8 and 12 Myrs. Several regions, including the northern nucleus, show evidence for sequential star formation on small spatial scales (< 100pc).

We present high resolution Chandra X-ray imaging of two starburst galaxies, M82 and NGC 3256. The central x-ray source observed by ROSAT and ASCA in M82 is resolved into 3 or 4 sources. Most of these sources are variable, suggesting that the point sources are powered by accretion. The brightest of these central sources is ∼ 1041ergs s−1 in the high state, and is responsible for the variability observed by ROSAT and ASCA. Assuming this source radiates at the Eddington limit, the mass is ∼ 500M⊙. The diffuse hard (2-10 keV) emission in M82 is spatially coincident with diffuse radio emission and Pα. This is consistent with diffuse hard X-ray emission arising from hot thermal gas in the starburst region. Approximately 14 sources with LX > 1039ergs s−1 were detected in NGC 3256, including both nuclei. Two of these sources have LX > 1040ergs s−1. This observation suggests that “super Edington” sources may be preferentially associated with starburst galaxies (see also paper by Fabbiano in this volume)

Markarian 273 and Markarian 231 are ultra-luminous IR galaxies which show signs of merger activity. Their radio continuum and spectral line emission has been imaged on scales of tens of parsec using MERLIN. Mrk 273 and Mrk 231 are classed as Seyfert types 2 and 1 respectively. The distribution and velocity gradients shown by OH masers and HI absorption are consistent with material in a rotating disk or ring, with the axis at greater than 45° to the line of sight in Mrk 273, and at less than 45° to the line of sight in Mrk 231. We estimate the amount of mass enclosed and infer its distribution from irregularities in the maser morphologies and comparison with HI and radio continuum data.

We present results from integral field spectroscopy of the narrow line region of NGC 1068, carried out with the MPE 3D near infrared imaging spectrometer. A map and velocity field of the [Fe II] fine structure line at 1.64μm is presented. The kinematics of the [Fe II] emission, which arises in partially ionized zones, shows red shifted emission in the north eastern cone of the NLR, and blue shifted emission in the south west, reversed relative to high ionization species such as [Si vI] or [O III]. We propose a model geometry of the narrow line region which is consistent with existing data and explains the observed [Fe II] kinematics.

We present results from sub-arcsecond near infrared integral field spectroscopy and millimeter IRAM-interferometry of the interacting galaxy NGC 6240. Using stellar absorption features in the NIR we determined the stellar velocity field and dispersion in NGC 6240. The two NIR emission peaks show rapid rotation and indicate a prograde encounter of the two progenitor galaxies. From the velocity dispersion an excess mass between the two nuclei is detected. This mass can be attributed to a massive rotating disk of cold CO gas located between the nuclei.

We study the size distribution of massive young clusters (MYCs) and of the cavities around them. We discuss the existence of two cluster populations and we find evidences for molecular cloud confinement in the early stages of development.

Subarcsecond radio and infrared observations reveal a class of luminous, obscured, optically thick HII regions associated with extremely large young clusters in nearby starburst galaxies. VLA images show bright radio nebulae with ne ∼ 104 cm−3, densities characteristic of young Galactic compact HII regions. Excitation of the nebulae requires the presence of several thousand O stars within regions of 1-10 pc extent, corresponding to clusters containing 105–106 stars. The compact nebulae are also bright in the mid-infrared, and can for significant fractions of not only the total IR luminosity, but also the total bolometric luminosity, of the parent galaxies. The prototype for these “supernebulae” is the large, obscured cluster in the dwarf galaxy NGC 5253.

Why do the circumnuclear (inner 1-2 kpc) regions of some spirals develop starbursts, which are intense short-lived (t ≪ 1 Gyr) episodes of star formation characterized by a high star formation rate per unit mass of molecular gas (SFR/MH2), which I refer to as the star formation efficiency (SFE), while others with comparable gas content become non-starbursts? I address this question and other issues on circumnuclear evolution using high resolution (2” or 100-200 pc) CO (J=1>0) observations from the Owens Valley Radio Observatory, optical and NIR images, along with radio continuum (RC) and Brγ data. The sample galaxies are all nearby, moderately inclined, and include the brightest nearby starbursts comparable to M82 and control non-starbursts. Detailed results are in Jogee (1999) and Jogee, Kenney, & Scoville 2000 (in prep.)

A new sample of IRAS galaxies at high galactic latitudes has been built by optically identifying IRAS point sources.

In no more than about 100 cases, an apparently interacting system of galaxies is located near the IR source. The large majority are unambiguously identified with a single, relatively isolated galaxy. This confirms that, although galaxy interaction may trigger starburst activity, the IR luminosity in most objects is due to normal star formation in the disc.

Many evidences demonstrate that the Milky Way is a barred galaxy with the near end of the bar pointing in the first Galactic quadrant (e.g. Gerhard 1999 for a review), thus offering an exceptional chance to study the detailed three-dimensional structure and dynamics of a real bar. One of the best tracer of the Galactic bulge/bar are the red clump stars: they are very numerous, sufficiently bright to be detected throughout the bulge, and their absolute I-magnitude has an intrinsic dispersion of only 0.2 magnitude, with a mean value almost independent of colour and metallicity (Paczyński & Stanek 1998, Udalski 2000). Here we outline an ongoing project aiming to recover the 3D bulge stellar distribution as primarily traced by these stars, as in Stanek et al. (1997), but in a non-parametric way and from the VR database of the MACHO experiment within an almost fully observed ∼ 8° × 8° bulge area centred on (l, b) ≈ (4°, − 6°) (e.g. Alcock et al. 1997), soon complemented with I-band photometry.