An innovative tool for the construction of Evolutionary Synthesis models of Stellar Populations is presented. It is based on three independent matrices giving respectively 1) the fuel consumption during each evolutionary phase as a function of stellar mass, 2) the typical temperatures and gravities during such phases, and 3) colors and bolometric corrections as a function of gravity and temperature. The first matrix allows to calculate the relative contribution of each phase to the bolometric light of the population, thanks to the so-called Fuel Consumption Theorem (Renzini & Buzzoni 1986, in Spectral Evolution of Galaxies, ed. C. Chiosi and A. Renzini (Dordrecht:Reidel), p.195)). The other two matrices allow to distribute such contributions in the various passbands, and thus to compute the synthetic colors of the population as a function of age. The modular structure of the code allows to easily assess the impact on the synthetic spectral energy distribution of various model ingredients (e.g. uncertainties in the stellar evolutionary models, mixing length, temperature distribution of the horizontal branch (HB) stars, AGB mass loss, color-temperature transformations, etc.) Models have been computed with Y=0.27, Z=0.02 and for three choices of a double-slope IMF (s = 1 + x = 2.35, 3.5, 1.5 for M ≥ 0.6 M⊙ and s' = s − 2.5 for M < 0.6M⊙). Among the main results, it is found that: i) the appearence of an extended AGB has a strong impact on the integrated (V − K)0 color, which increases by ≃ 1.5 mag in Δt ≃ 400 Myr; ii) the inclusion of a blue-HB developing at ages around 10 Gyr produces a hook-shape in the (U − B)0 vs (B − V)0 locus described by aging stellar populations, in agreement with what observed for Magellanic Clouds Clusters.

We characterized isolated spiral galaxies as a reference for the properties of interacting ones: we selected all the spirals in CfA catalog with mB ≤ 13.0,δ ≥ 0, a≤ 4′ and 73° > i > 32°. The isolated ones were those having no companions in ΔD≤0.5Mpc and ΔV≤500 km/s and no satellites galaxies in their neighborhood (from Nilson catalog and Palomar charts). To select the isolated pairs of spirals we used Karachentsev's catalog applying similar conditions for mB , δ, a, i and the same isolation criteria. We used broad band CCD images (Johnson B,V e I), narrow band CCD images (Hα) and long slit spectra in Ha region. The BVI images analysis consisted on applying sharp-divided methods, obtaining simulated images (from bulge/disk decomposition and galaxy orientation in the sky) and Fourier analysis. From Hα images we determined total emission, size, distribution and flux of HII regions. We also obtained the rotation curves.

We use planetary nebulae observations (Hui et al. 1995) to build dynamical models of the dust-lane elliptical galaxy NGC 5128 (Centaurus A). The PN photometric and kinematical data extend out to 20 kpc (∼ 4r e) along the major axis and 10 kpc along the minor axis. Our models are built using a Quadratic Programming technique (Dejonghe 1989). The method produces fits to the data set, which consists of the photometry field (E2, well fitted by a r 1/4-law) together with the major- and minor- axis rotation curves and velocity dispersion profiles. Assuming the merger hypothesis for Cen A, we describe its kinematics in a spherical potential by two sub-systems, one rotating about the intrinsic short axis and the other about the intrinsic long axis of the galaxy.

Using ASCA, we have confirmed that the ISM of X-ray bright elliptical galaxies are surprisingly metal poor, as compared to the theoretical predictions. In fact the exact values of the derived metallicity depend considerably on the plasma emission codes. However, the overall metallicity cannot be larger than ∼ 1 solar. For low LX/LB galaxies, all the available plasma codes suggest abundances less than half a solar. The ASCA spectra may be compatible with somewhat higher metallicity if we assume there is an additional low-temperature component (e.g. kTe ∼ 0.3 keV). However, the derived abundance can not be over 1 solar. In particular, the Si abundance turns out to be < 1.5 solar, confirming the metal-poor nature of the ISM. These ASCA results are in severe contradiction with most of the SN Ia rate, particularly that of Tammann (1982). Considering further that a fairly long time (109–10yr) is needed for the stellar mass loss to accumulates into the ISM, it is suggested that the SN Ia rate has remained quite low throughout Hubble time.

Three-integral (3I) dynamical models for NGC 1600 were constructed as follows: (i) Lucy-inversion of CCD photometry and gravitational potential as in Binney, Davies, Illingworth (ApJ 361, 78, 1990), assuming axisymmetry. (ii) Third integral by perturbation theory as in Gerhard & Saha (MN 261, 311, 1991). (iii) Two- and three-integral distribution functions as in Dehnen & Gerhard (MN 261, 311, 1993), assuming various anisotropy patterns. The kinematic results from these models are presented in Fig. 1. The best-fitting 3I model (solid line, right panels) has outward-increasing radial anisotropy on the major axis and is nearly isotropic on the minor axis. The M/L of the various 3I-models varies only slightly around M/L=6.2.

We compare optical and infrared photometric and spectroscopic properties of high-redshift radio galaxies from the 3CR and B3 surveys. At a given redshift and a fixed restframe frequency, the two samples differ on average by an order of magnitude in radio power, thus providing a fair baseline in radio powerfor a range of redshifts. We present new optical and IR photometry and spectrosopy for a number of B3 sources. We combine these data with the existing corresponding information on B3 and 3CR sources, in order to explore different correlations of source properties with redshift, and among themselves. B3 sources follow the same trend as 3CR's in the K band Hubble diagram, although they do seem to be slightly fainter on average at a given redshift. This trend is slightly more prominent in the Gunn r band. This suggests that some fraction of the observed light in the r and K bands is contributed by an active nucleus, which also powers the radio lobes. The B3's also tend to have lower emission line luminosities than 3CR's at any given redshift, suggesting that there may be a correlation between line luminosity and radio power. Such a correlation is clearly seen and is followed by both samples. It suggests that the UV emission lines are largely powered by the active nucleus, ostensibly a hidden quasar, which is also responsible for the radio emission. We also examine the behavior of the optical and radio PA alignments for the combined B3+3CR data set. We find that high-power and high-redshift subsamples for both B3's and 3CR's show the alignments more prominently, but we still cannot tell which of these variables dominates this effect. This work was supported in part by the NSF PYI award AST-9157412, and the Bressler Foundation.

A study of 8 nearby spiral galaxies (NGC 2903, 3079, 3198, 3628, 4303, 4321, 4656 and 6946) is carried out using the radio continuum (RC) and far infrared (FIR) images at 1′ resolution. These images are used to study the radial gradients in the ratios of FIR to RC (Q60 and Q100), warm dust temperature (Td(60/100)) etc. The main results are illustrated with NGC 2903 as an example in Fig. 1, where azimuthally averaged quantities are plotted. Td(60/100) decreases away from the center (45–25 K), increasing again by ∼ 5 K in outer galaxies. Typically Q60 decreases by a factor of three away from the center in a given galaxy, but has an order of magnitude spread in the pixel values over all the galaxies. In contrast, Q100 shows flatter gradient, which is expected from the observed temperature gradient. 20 cm RC emission profile is also shown in Fig. 1. The RC and FIR profiles can be fitted by a combination of central gaussian and exponential disk components. In general RC and FIR have about the same fraction of exponential component with the exception of NGC 3628, in which the FIR is dominated by the gaussian while the RC is mostly disk component (see Fig. 2). In 5 of the remaining 7 galaxies, the exponential component contributes > 50% of the total. In general RC scale lengths are larger than the FIR.

We present our study of Arp 142, an interacting system which consists of irregular (NGC 2936) and spheroidal (NGC 2937) components. We discovered that NGC 2936 has very high internal motions, much higher than what is expected from the dynamics of interaction of such galaxies.

A population of primeval galaxies (PG's) should be detectable by directly imaging with two intermediate-band filters tuned to either side of the Lyman break (DeRobertis, M. M., and McCall, M. L. 1995, A.J., 109, 1947). In the figure below, the solid and short-dashed curves show the flux (left scale) as a function of redshift from a PG 0.7 Gyr old with a total stellar mass of as seen through filters with rest-frame passbands 890 ± 30 Å (‘β’) and 1010 ± 30 Å (‘ρ’), respectively, moved to redshift 5. The upper curves depict the colour β – ρ (right scale); the dotted line is for the 0.7 Gyr population, and the dot-dashed line is for a 7.5 Gyr model. A source can be identified as a PG if it can be clearly detected in the ρ filter and if it has a colour greater than +0.75 mag. Confusion with any old stellar systems at lower redshifts can be eliminated by supplementing observations with Gunn r and i. The colour condition selects Lyman break objects between redshifts 4.7 and 5.4, a range over an order of magnitude greater than is achievable through an emission line survey. The discriminatory power of the technique is not affected by internal dust.

We develop the idea (Harris & Pudritz 1994, ApJ, 429, 177) that, like currently forming star clusters and associations, globular clusters (mean mass ≃3×105 M ⊙) were born in the ‘cores’ of much larger (∼108 – 109 M ⊙) star-forming complexes which we call ‘supergiant molecular clouds,’ or SGMCs. The number N(m) of protoclusters at mass m is then determined by a steady-state balance between their growth by core-core collisions, and their self-destruction via the side effects of star formation. This mass spectrum is ultimately passed on to the globular cluster system (GCS) itself, by virtue of the very high star-formation efficiency required to produce a bound stellar cluster from a gaseous core.

As one of the richest nearby clusters, Coma is the ideal place to study the structure of galaxies as a function of environmental density, thus to constrain the theories of galaxy formation and evolution. For a magnitude limited sample of ≈ 40 E and S0 galaxies we want to obtain spectra with sufficient S/N and spatial resolution, that we can derive the rotation curves, the velocity dispersions profiles and the radial gradients of the line indices of Mg, Fe and Hβ. Following questions will be addressed:

1. • Are the radial velocity dispersion profiles and the rotation of galaxies in high density environments similar to those in low density environments? Data for galaxies in low density environment are available from Bender et al. (1994, MNRAS, 269, 785). Are the centrally measured velocity dispersions representative for the mean kinetic energy of the galaxy?

2. • Can the scatter in the Fundamental Plane (FP) - which tightly correlates the radii, surface brightnesses and (central) velocity dispersions (Djorgovski & Davis, 1987, ApJ, 313, 59; Dressier et al. 1987, ApJ, 313, 42) - for the Coma cluster be reduced if the mean kinetic energy is used instead of the central velocity dispersion? Can we derive stronger constraint on the variations in the M/L ratio than already implied by the FP?

3. • The radial gradients of the line indices can be used to test the hypothesis that the metallicity gradient depends on the so-called “escape velocity” of the stars introduced by Franx & Illingworth (1990, ApJ, 359, L41). Also we can check whether the age of the stellar population varies with radius. Ages and metallicities can be estimated from the data with the use of stellar population models (Worthey 1994, ApJS, 95, 105; Bruzual & Chariot 1993, ApJ, 405, 538).

4. • How does the radial variation of stellar populations and kinematics within the galaxies vary as a function of the clusters density profile?

The simultaneous UBVRI – observations of some Seyfert galaxies have been carried out at Crimean Astrophysical Observatory using the 1.25m telescope. Photometric errors are less than 0.01 mag. By analysis of the NGC 1275 light curves within one night we are discovered at least two types of variability: 1) The flares with the maximal amplitudes of 5 – 30 % in the U-band and durations of 15 – 30 minutes. 2) For the first time we have found rapid red flares. For instance, the red flare on the light curve 22-23.10.1992 lasted ∼ 65 minutes (see Figure. Vertical axes are in magnitudes). The amplitude in the filter I is ∼ 25 % (top panel). The light curve in the U-band is on the bottom panel. Fluxes in the U,B,V-bands were almost constant. One can see the flux decreasing in some filters before this flare. We conclude, that light curve of NGC 1275 nucleus could be represented by a superposition of rapid flares of different types.

We have obtained Hubble Space Telescope ultraviolet (UV; λc = 2320 Å) images of nine starburst galaxies using the FOC, with the aim of characterizing the anatomy of starbursts with ∼pc resolution at a wavelength where hot massive stars dominate the luminosity output. The images have been analysed in detail, and full results can be found in Meurer et al. (1995).

Surface photometry in I, J, K of the oval disk galaxy M 94 (NGC 4736) reveal a weak central stellar bar of 0.7 kpc semi-major axis length, comprising ≈ 14% of the total light within 20″. By stellar kinematics the existence of a small spheroidal bulge with v/à ≈ 0.8 was discovered. The ionized gas (Hα) in this region shows global and local deviations from the stellar kinematics. Model calculations of closed orbits for the cold gas in the combined potential of bar, disk, and bulge predict large non-circular motions in equilibrium flow. However, these do not fit the observed gas kinematics; obviously hydrodynamical forces play a role in the central region of M 94.

A new automated technique applied to APM scans of UKSTU photographic plates has been used to search for LSBGs in the Fornax cluster. 92 galaxies, almost all of which were classified by Ferguson (1989) as dwarf ellipticals, were found. Fields to the East and West of the cluster were found to have 46 and 13 LSBGs, respectively, as shown in the figure below (□ are LSBGs, ▲ are brighter galaxies).

The Revised Shapley-Ames Catalog (Sandage & Tamman, 1981) contains 335 spiral galaxies brighter than BT = 12. A subsample of these galaxies with δ ≥ –25° and total flux densities at 1.49 GHz (Condon, 1987) above 10 mJy were observed at λ2.8 cm using the 100-m radio telescope of the MPIfR Bonn. Depending on the expected flux density and extent of the source two observational methods were used: cross-scanning and mapping. In total, radio flux densities of 192 galaxies have been derived (Niklas et al., 1995). Additionally, a literature search was made in order to get flux densities at other frequencies.

A unified picture is presented of the formation of bar structures in disk galaxies of various morphological types. In order to discuss bar formation in the context of galactic disk formation, a simple analytic model is constructed of the growth of galactic disks by infall of primordial gas from haloes and subsequent star formation in the disks. It is monitored during the course of disk growth whether or not the condition for spontaneous bar formation (i.e., bar instability) is fulfilled for the stellar disk component.

We discuss the general classification of secular evolution in galaxies into terms of stellar dynamics. We present two-dimensional N-body simulations of a disk galaxy in which a central mass concentration is imposed after the formation of a strong bar. We show that the bar dissolves almost completely if the central mass concentration exceeds approximately 5% of the combined disk and bulge mass. This behavior can be understood in terms of previous work on single particle orbits (Hasan & Norman 1990, Hasan et al. 1993); the sustaining orbits aligned with the bar become stochastic as the Inner Lindblad resonance moves out past the minor axis of the bar. We present arguments that bar formation and subsequent thickening and dissolution will create a bulge-like stellar distribution from the central part of the disk. We discuss the predictions of such a model including the point that barred Scs with sufficient central mass concentrations should be building bulges now. We emphasize that bulges can come from a number of different mechanisms and we discuss the current evidence at both high and low redshift.

Infrared spectra of selected stellar absorption features (CO 2.29, 1.62 and Si 1.59 μm) of a sample of Seyferts and many calibrators (stellar clusters, normal galaxies and well known starbursters) are presented. For HII and Seyferts we also report Brγ measurements.

Recent observations of radio polarization from nearby galaxies show that the large-scale galactic magnetic field is aligned with spiral arms and bars and the magnetic field vectors in the interarm regions possess a spiral structure which has the same pitch angle as that in spiral arms. Our present project is going to address the following questions: What is the structure and evolution of the large-scale galactic magnetic field under the influence of spiral and bar structure in a galactic disk? To which extent could the resulting magnetic field account for the observed spiral pattern of magnetic field in nearby galaxies? The model is based on the particle-particle numerical scheme (SPH) involving two components: stars and molecular gas. The magnetic field is connected with the latter one. The magnetic field computations were performed first in two dimensions for 100 velocity fields: from 107 to 109 yrs. The resultant magnetic field is strongly affected by spiral arms, however at the given evolutionary stage its structure is different from the velocity field at the same time. The magnetic pitch angle distribution shows that the magnetic field “remembers” all the past velocity steps. The magnetic pitch angle distribution resulting after beam smoothing could quite well fit observations. The present model with fully 3D velocity field of interstellar gas should clear the problem if the magnetic field under the realistic velocity evolution of gas could explain the observed structure of large-scale magnetic field with constant pitch angle in the whole disk.