We present high-resolution imaging of the BL Lac objects 1ES 0229+200 (z = 0.14), Markarian 421 (z = 0.031) and the prototype BL Lac (z = 0.069). Our goal is to study the properties of the host galaxies of this enigmatic sources and to compare them with their non-actice counterparts. The observations were carried out with the Nordical Optical Telescope (NOT) at La Palma under sub-arcsecond seeing conditions (FWHM < 0.″8). The surface brightness profiles of the host galaxies were analyzed as described in Bender and Möllenhoff (A&A, 177, 71 (1987)). After masking the disturbing field stars/galaxies isophotes were fitted by ellipses down to 20.5 mag/arccsec2 in Markarian 421, 23.5 mag/arcsec2 in BL Lac and 25.5 mag/arcsec2 in 1ES 0229+200. Additionally, we analyzed the surface brightness profile of the companion of Markarian 421.

The surface brightness profiles of the host galaxies were analyzed as described in Bender and Möllenhoff (A & A, 177, 71 (1987)). After masking the disturbing field stars/galaxies isophotes were fitted by ellipses down to 20.5 mag/arccsec2 in Markarian 421, 23.5 mag/arccsec2 in BL Lac and 25.5 mag/arccsec2 in 1ES 0229+200. Additionally, we analyzed the surface brightness profile of the companion of Markarian 421.

Despite of the great interest in accretion disks around supermassive black holes there are still numerous controversies about their structure and their physical properties. Therefore we have calculated the structure of such disks for a wide range of parameters. For the viscosity we use a standard α-description with the main component of the stress tensor trϕ proportional to the gas pressure. The disk structure depends sensitively on material properties such as opacities and specific heats. In our calculations we have used an equation of state and mean opacities taking into account a list of the most important ionization processes as well as the radiation contributions to thermodynamic quantities.

Using the 3.′2 Arecibo beam, we have mapped the HI envelopes of a sample of 70 irregular galaxies (Sdm, Sm, Im and BCD), including 45 from the Virgo Cluster Catalog, 14 Field galaxies at similar redshifts, and 11 Nearby dwarfs chosen to give a complete sample out to 6 Mpc, within the Arecibo declination range. To explore correlations among variables characterizing the size and dynamics of these galaxies, we have combined this sample with all other mappings (multiple single beams and synthesis array) of irregulars and of spiral galaxies spanning the same redshift range (out to about 20 Mpc) available in the literature. In all, there are 128 mapped dwarfs and 119 mapped spirals in this dataset. We obtain the following correlations: rH,max = (2.75 ± .15)r25(0.890±.034) where both HI and optical radii are in kpc; LB = (3.59±.80) × 106rgm(2.70±.11) where LB is in solar luminosities and rgm is the geometric mean of rH,max and r25; LB = (125±36) Vc(3.62±.19) where the rotation speed is in km s−1; MH = (9.3 ± 1.1) × 106rgm(1.977±.056) where the HI mass is in solar units; and LB = (1.9+2.7−1.1) × 10−3Mndyn(1.164±.043) where Mdyn = Vc2rgm/G.

The dwarf irregular galaxy Ho IX (DDO 66) is a satellite of the giant spiral M81. Triggered by an interaction with M81 (Hopp & Schulte-Ladbeck, 1987 AA 187, 5), Ho IX may have recently undergone a burst of star formation. On very deep Calar Alto 3.5m telescope R images, we detected a ring-like nebula in the northeastern part of Ho IX, which is situated near to the giant CO molecular cloud recently discussed by Henkel et al. (1993 AA 273, L15). The structure of the nebula resembles supernova remnants like CTB 80. No HI-features can be detected at its location, especially no hole. It shows a blue central point source (R=21.7). A Lucy deconvolution of the 0.9″ seeing images indicates further faint point sources, perhaps a small stellar cluster. An optical long slit spectrum of the nebula shows emission lines with ratios as in old supernova remnants while it excludes normal HII regions, planetary nebula, or the LMC X-1 type nebula. The position of the central object coincides with a bright and variable ROSAT point source which was already detected by the Einstein spacecraft. The X-ray spectrum is rather steep and shows strong intrinsic absorption. The nature of the X-ray source and its possible connection to the optical nebula is not yet understood. Miller (1995, ApJ 446, L75) who independetly found the nebula interpretated his spectra as a supershell surrounding an OB association. Our optical nebula line ratios severely deviates from Miller's. Our ratios as the X-ray spectrum point more to a SNR at the M81 distance, most probably belonging to Ho IX.

The 100m radiotelescope at Effelsberg has been used to observe two samples of elliptical galaxies in the 21cm line of neutral hydrogen. One sample is defined by the elliptical galaxies in the Revised-Shapely-Ames catalog (RSA) (Huchtmeier 1994, Astron.Astrophys 286, p.389); the other sample is defined by all elliptical galaxies with IRAS 100 μ fluxes ≥ 500mJy north of declination –310 (Huchtmeier, Sage, Henkel 1995 Astron.Astrophys. in press). Among the detected galaxies there are 23 (RSA) and 24 (IRAS) isolated elliptical galaxies free of confusion by nearby galaxies with similar radial velocities. Global properties of these two samples of elliptical galaxies are discussed: their HI-properties, optical and IR luminosities, their optical colors, their masses of dust and of molecular hydrogen.

The two-point angular correlation function, ω(θ), is constructed from a catalog of 13,000 objects in 24 fields distributed over an area of 2 degrees square and complete to a limit of R = 23.5. The amplitude and slope of our correlation function on arcminute scales are in broad agreement with recent CCD results in the literature and decreases with depth. No evidence is found for a flattening of the slope of the correlation function away from δ ∼ 0.8. Using the redshift distribution from the recent I-band selected Canada-France Redshift Survey, the observed ω(θ) implies a value of the clustering length r0 = 1.86 ± 0.42h−1 Mpc (q0 = 0.5) at z = 0.48. This is consistent with the clustering of optically selected local galaxies, if clustering has developed with epoch. Specifically, clustering evolution to a CfA-like sample (with r0 = 5.5h−1 Mpc) would require growth in clustering stronger than the type seen in CDM-like models. Evolution to a less clustered IRAS-like sample (with r0 = 4h−1 Mpc) would require evolution represented by stable clusters of fixed physical size. If there was no growth in clustering (i.e galaxies are fixed in comoving space) then a local sample that is very weakly clustered (with r0 = 3h−1 Mpc) would result. These possibilities are discussed in the context of our understanding of the nature of the faint galaxy population.

We have collected integrated light spectra of bulges of 28 spiral galaxies. Our data sample the Hubble sequence uniformly from S0 to Sd types, and cover a large range in magnitude, viz, about −16 to −22 mag in r-Gunn band. In short, disks do not contribute to more than 14% of the total integrated light in our spectra, and all galaxies are analyzed under the same conditions. More to read in a forthcoming paper.

Galaxy evolution is one of the key questions in current astronomy. Observations of strong and recent galaxy evolution conflict with previous ideas of orderly and early evolution of galaxies.

Changes in the anisotropy of the stars and changes in the galaxy potential due to dark matter manifest themselves differently in the observable line (velocity) profile shapes (VPs) of elliptical galaxies (Gerhard 1993, MNRAS 265, 213). In Fig. 1, this is illustrated for a set of realistic spherical models (Jeske et al. 1995, preprint).

We investigate the distribution of soft X-rays and their spectral characteristics for a sample of nearby nuclear starburst galaxies in order to probe their evolution. NGC 4569 is a bright early-type spiral in the Virgo cluster, one of the few blue-shifted galaxies outside the local group. It is gas-deficient in the outer spiral arms, the neutral hydrogen strongly concentrated in the inner region [1]. The bright nucleus, embedded in a normal stellar bulge, is probably the result of a recent star formation episode [4]. Based upon optical spectroscopy of its nucleus [5], the galaxy has been classified as a LINER. The results on NGC 2903 will be presented separately [2].

Galactic disks are heated by some gravitational scattering process. The velocity dispersion and scale height increases with the age of the stellar populations as can be observed directly in the solar neighbourhood. This evolutionary effect can also be derived from the vertical structure of spiral galaxies seen edge-on. We use a physical model of a selfgravitating disk composed of isothermal subpopulations with increasing age and velocity dispersion and an exponential dust distribution (Just et al. 1995). The emissivity of the stars is computed from the luminosities in the different bands of single age populations which are computed with the method of photometric evolutionary synthesis (Einsel et al. 1995).

It is shown that at present one can not exclude a possibility that rare, wide and deep absorption feature of Lα damped type could be formed in a rich gas medium of distant clusters of galaxies, not verialized yet. In future massive galaxies are likely to be formed in the central regions of these clusters. Nuclei of these galaxies become very active during a short time, i.e. they pass a stage of QSO. Narrower absorption lines of metals and/or 21 cm associated with Lα damped systems can be formed in the clouds belonging to separate galaxies of these clusters.

In the chemodynamical models of galaxies the energy input from massive stars into the ambient medium results in a self-regulation of the star formation rate (SFR). A thorough analytical and numerical study of this model shows that there is always a strong and negative feed-back, and the SFR becomes almost independent of the assumed stellar birth function (SBF). The time-scale to reach this equilibrium is much shorter than the gas consumption time-scale, hence the models evolve along this solution for most of the time. This mechanism provides a physical explanation for a quadratic dependence of the SFR on gas density. For more details cf. Köppen et al. (1995), A&A 296, 99 and in preparation.

From overlapping scans in the IRAS all-sky survey and additional pointed observations the deepest far infrared survey before ISO exists in the region around the North Ecliptic Pole (NEP) (Hacking P. and Houck J.R., ApJS 63 p. 311). This survey contains detections up to 10 and fluxes up to 100 times fainter than the IRAS survey. In the central square degree around the NEP we combine the far IR-survey with deep radio data at 151 MHz and 1.5 GHz (Visser, A.E. et al., A&AS 110 p. 419, Kollgaard, R.I. et al., ApJS 93 p. 145) and own observation at 2.2μm (K′) and 435nm (B). The error circle around the IRAS source was chosen to include the true source with 85% probability (1.4 sigma). For 29 of the 32 IRAS sources we found at least one possible counterpart. Ten of the objects have multiple (up to four) counterparts in K′. Four of the IRAS sources have counterparts in the 1.5 GHz survey. The higher accuracy of the radio position (∼ 1″) allowed an unambiguous identification of the K′ counterpart. None of the IRAS sources could be found in the 151 MHz survey. The broad band spectra of the three galaxies with measured radio flux exhibit maximum emission between the radio band and 100μm which corresponds to emission by cool dust (< 50 K). Contrary to the infrared luminosity functions at 12μm and 60μm which show power laws, the K′ luminosity function is bimodal. The brightest K′ objects are all point sources. Due to the small number statistics the power law indices of the luminosity functions can not be distinguished. We find a linear relationship between the K′ flux and the flux at 60μm and 12μm over at least one decade. The large deviations by individual sources make an identification of the correct counterpart through this relation impossible. The spectral energy distributions of unambiguously identified sources span only one decade in energy (vSv), i.e. they have flat energy distributions. This suggests an identification of K′ objects with flat energy distribution in case of multiple counterparts.

We explore several structural and dynamical effects on the projected velocity dispersion as possible causes of the fundamental plane (FP) tilt of elliptical galaxies (Ciotti, Lanzoni & Renzini, 1995). Specifically, we determine the size of the systematic trend along the FP in the orbital radial anisotropy, in the dark matter (DM) content and distribution relative to the bright matter, and in the shape of the light profile that would be needed to produce the tilt, under the assumption of a constant stellar mass to light ratio. Spherical, non rotating, two-components models are constructed, where the light profiles resemble the R1/4 law. For these we can exclude orbital anisotropy as the origin of the tilt, while a systematic increase in the DM content and/or concentration may formally produce it. Also a suitable variation of the light profile can produce the desired effect, and there may be some observational hints supporting this possibility. However, fine tuning is always required in order to reproduce the tilt, while preserving the tightness of the galaxies distribution about the FP.

The suggestion of Lee (1994, ApJ, 430, L113) that the age spread among galaxies is responsible for the systematic variation of ultraviolet (UV) upturn among the early-type systems is confirmed here with the detailed population synthesis models. Our models suggest that the far-UV spectra of these systems are composite of hot metal-poor horizontal-branch (HB) stars (and their post-HB progeny) and metal-rich post-asymptotic giant-branch (PAGB) stars. The systematic variation of UV upturn, however, depends on the contribution from hot metal-poor HB stars and their progeny, which in turn depends on the ages of oldest stellar populations in galaxies. Consequently, our models predict that the strength of absorption features, such as C IV and Si IV, is anticorrelated with the strength of UV upturn. This is consistent with the far-UV spectra for NGC1399 and M31 obtained by the Hopkins Ultraviolet Telescope aboard the Astro-1 space shuttle mission. We note that the opposite trend is expected in other's models that favor metal-rich solution for the UV upturn phenomenon without age spread among galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. With the assumption that the UV upturn phenomenon is solely due to the age variations among galaxies, we tentatively estimate the difference in age between the giant ellipticals and our Galaxy to be 4 billion years or more. This suggests that the best estimate for the lower limit of the age of the Universe is close to 20 Gyrs, which of course would be in conflict with the current estimate of the Ho together with the standard cosmological models with zero cosmological constant. The reader is referred to Park & Lee (1995, ApJL, in press) for details of this work.

The large-scale dynamics and evolution of disk galaxies is controlled by the angular-momentum transport provided by non-axisymmetric perturbances through their gravity torques. To continuously maintain such gravitational instabilities, the presence of the gas component and its dissipative character are essential.

We are investigating field galaxy evolution with the optical multiband survey of Osmer et al. (1995, in preparation; Hall et al. 1992, Bull. A.A.S., 24, 1136), which covers some 3000 sq. arcmin of sky with CCD photometry in six broad-band filters from 3000-10000Å, complete down to R∼23. The sample contains some 9000 cataloged galaxies, of which 7000 have data in at least three colors.

Near-infrared longslit spectra of NGC 253 obtained with IRSPEC at the ESO NTT are presented. By analysis of the 12CO 2.29μm bandhead we find that the stellar population in the central starburst region (r ∼ 150 pc) rotates more slowly than the gas, but has a velocity dispersion of 128 km/s, about twice the value found for emission lines from the gas in this region. This implies an about five times higher dynamical mass than previously derived (Rieke et al. 1980), removing the need to invoke a lower mass cutoff in the starburst initial mass function. The peak of near-infrared emission is displaced from the dynamical center.

The observed physical characteristics of galaxies are (at least partly) determined by the influence of the surroundings after the formation of the galaxies. The examination of the frequency of the occurence of active galaxies, i.e. Seyfert galaxies, in different galaxy systems compared to a sample of field galaxies gives possibly an insight into this problem.

The galaxy groups were taken from the CfA redshift survey, the list of them is published in Mahtessian (1992, Soob. Byurakan. Obs. 65).