The Fundamental Plane (FP) is one of the most important universal relations in early type galaxies because it contains valuable information about the formative and evolutionary process of galaxies (Djorgovski & Davis 1987, Dressler et al. 1987). The commonly used form of the scaling relation in the FP is described as Re = σAIB, where Re, σ, and I are effective radius, central velocity dispersion, and mean surface brightness of elliptical galaxies, respectively. The exponents A, B are considered to be 1.56 ± 0.07 and −0.94 ± 0.09 in the FP derived by K band photometry, respectively, and these values deviate significantly from the values A = 2.0 and B = −1.0 expected from virial theorem (Pahre et al. 1995; Djorgovski, Pahre, & de Carvalho 1996). This apparent deviation requires that the ratio of dynamical mass (M) to luminosity of elliptical galaxies (L) depends on M as M/L ∝ Mα (α = 0.12 ± 0.03 for K band). Possible interpretations for the required dependence of M/L on M are generally considered to be divided into the following two. One is that the required dependence of M/L on M results from the fact that the mean stellar age and metalicity of elliptical galaxies depend systematically on M. The other is that the required dependence reflects the M dependence of structural and kinematical properties of elliptical galaxies (“nonhomology”). Although we should not neglect the importance of stellar populations in generating the M dependence of the M/L (Renzini & Ciotti 1993), we here consider that the origin of the required M dependence of M/L is closely associated with the structural and kinematical properties dependent on M or L in elliptical galaxies.

Absorption line velocity profiles (vps) contain important information on the anisotropy and mass distribution of elliptical galaxies (e.g., Gerhard 1993, Merritt 1993). Here we briefly present results of an extensive analysis of the E0 galaxy NGC 6703 (Gerhard et al. 1997). This work is part of an observational and theoretical program aimed at understanding the orbit structure and dark matter content of ellipticals at intermediate radii (a preliminary account is given in Saglia et al. 1997).

We present broad band photometry (B and R) of the classic shell galaxy NGC 474. Preliminary results indicate that the shells have a similar colour to and follow the same trend of colour with radius as the underlying galaxy.

Boxy/peanut-shaped bulge galaxies constitute at least 20-30% of all spirals. Distribution functions and numerical simulations studies have shown that the slow decay of the orbit of a companion into a larger spiral can lead to the formation of a boxy/peanut bulge. However, the bar-buckling instability now appears a more likely process. Thin bars either do not form or, as shown by N-body simulations, buckle and settle with an increased thickness, appearing boxy or peanut-shaped when seen edge-on. This project aims to determine the dynamical state of a sample of 30 edge-on spirals, 3/4 of which have boxy/peanut-shaped bulges, half having close-by companions.

It is well known that, under favorable conditions, tidal interactions between a spiral galaxy and a more compact elliptical leads to the formation of embedded rings in the disk (e.g. Chatterjee 1979, Bull. Astron. Soc. India, 7, 32); in addition there are also nuclear rings whcih do not seem to have a tidal origin (e.g. Buta 1986, ApJ, 306, 768). The two types of rings occur in different regions of the spirals, which can be explained on the basis of the tidal hypothesis by extending the previous research work of Chatterjee (1984, Ap&SS, 106, 309). In this context, using the same theory, we study many normal on-axis collisions (as rings are best formed for this orientation) between a disk galaxy, modeled as an exponential disk with a polytropic n = 0,3,4, bulge (mass being equally distributed amongst the polytropic indices), and a compact spherical intruder, modeled with a polytropic n = 2, 3, 4, distribution (mass being equally distributed amongst the polytropic indices). The internal energy changes suffered by the disk, have a direct bearing on the sharpness of the rings, and are directly obtained from the relationship, for the fractional change in internal energy of the disk, as fE = γβ, where β is a function of the galactic models and the collision parameter γ = G(σs/V2) ∝ σs/V2 (where σs is the projected velocity of collision). We find that sharp rings form for fE ≥ 0.5; beyond this value of fE the intensity contrast of the rings diminish. However, fairly sharp rings (from an observational point of view) form for fE ≥ 1/3, which corresponds to 7 ≥ 0.01; which corresponds to a density maximum near a region ~ (1/3)R (R being the radius of the disk galaxy), so that rings of tidal origin are not expected to be prominent at a distance interior to ~ 1/3 of the radius of the disk galaxy. They are not expected to form interior to ~ 1/10 of the radius of the disk.

The kinetic description of gravitating systems has acquired vital importance in the context of trends in galaxy formation and evolution as evidenced by the existence of the virial and fundamental planes. The fundamental plane deviates for brighter and fainter ellipticals; until the brightest cluster members (BCMs), whose structures have been most modified by interactions, seem to occupy a fundamental plane with a different slope as compared to normal ellipticals. Extending the work of Magalinsky (1972, AZh, 49, 1017; Sov. Astron.-AJ, 16, 830), the Vlasov equation is applied to study small perturbations (considered as protogalaxies) of the exact solution corresponding to a spatially homogeneous medium in expansion. It is found that a perturbation attains a saturated size whose scale length, as a function of a reduced parameter of evolution (in terms of the characteristic frequency of dispersion of momenta, τ), R(τ) ∝ K.E./P.E. ∝ (K.E.)2/σ ∝ (δV)2/Proj.density ∝ σ2/I, which has the parametric form of the virial plane. The subsequent evolution is characterized principally by the variation of the energy due to the gravitational interactions between stars (considered as mass points), given by the potential energy such that the harmonic mean separation scale (between stars) characterizes this evolution. In this stage of the evolution the harmonic scale separation has the parametric form, 〈r−1〉 ∝ (K.E.)1/2, and 〈r−1〉 ∝ (P-E.) such that 〈r−1〉 ∝ (K.E.)1/2/(P.E.) ∝ σ/I. Notice that this is the parametric form of the fundamental plane of evolved ellipticals since the harmonic scale separation determines a physically significant scale.

Recent analysis of extended rotation curves of late-type spirals have confirmed that these objects have detectable amounts of dark matter (DM) already in the optical region, with dark-to-luminous mass ratio scaling inversely with luminosity. Since currently available rotation curves of early-type spirals are often fragmentary and not extended enough, the question remains open as to whether dark halos are unequivocally present in Sa galaxies. To address this point we have observed a sample of 7 SA's measuring major axis velocities and velocity dispersion for both stars and ionized gas. Here we present results for two objects, NGC 2179 and NGC 2775. We have constructed detailed dynamical models which, for each galaxy, explain the observed kinematics for both stellar and gaseous component and which are consistent with observed photometry. The best fit model for NGC 2179 involves an oblate isotropic rotator bulge, a thin exponential disk with the same mass-to-light ratio, and a pseudo-isothermal DM halo. The mass-to-light ratio in the inner galaxy was found to be M/LR = 4.5 (M/LR)⊙ reaching M/LR = 7.5 (M/LR)⊙ at the optical radius (Ropt). For NGC 2775 the best fit model involves an oblate isotropic rotator bulge and a thin exponential disk, with M/Lr = 3.5 (M/Lr)⊙, and M/Lr = 4.7 (M/Lr)⊙ respectively. No DM halo was needed to explain the data extending to 0.7 Ropt. In the inner regions the gas rotates as fast as stars but with negligible velocity dispersion. This rules out the case where the gas kinematics is dominated by random motion, and leads us to speculate we are seeing gas rotating on a non-equatorial plane, resulting from a past external acquisition, possibly from the companion galaxy NGC 2777.

We report on new observations of the globular cluster systems (GCSs) of two galaxies: M86 (NGC 4406) in Virgo and NGC 4696, the central giant elliptical (gE) in the Centaurus cluster. Previous observations in M86 showed no evidence for bimodality, but using only (V - I) for small cluster samples. The NGC 4696 GCS is unstudied. We used the integrated Washington (C - T1) color. This metallicity index is more than twice as sensitive to [Fe/H] as (V - I). In M86 we have about 1100 good GC candidates, and about 650 in NGC 4696, with mean internal metallicity errors ~ 0.15 dex. Both of these GCSs are found to have bimodal metallicity distributions (MDs). Our data strengthen previous results that MDs for the GCSs of gEs are widespread. The evidence for 2 separate populations in these galaxies is corroborated by examining the surface density distributions: the metal-rich clusters are more centrally concentrated than their metal-poor counterparts. The overall radial metallicity gradient present in the M86 GCS is due to the varying radial mix of the 2 populations. The existence of 2 GC populations signifies that there were 2 distinct epochs or events of cluster formation in a gE. The simple collapse model of gE formation is ruled out.

We report on an ongoing study of the optical–near-IR colors of globular clusters (GCs) in E galaxies. The motivation is that (i) HST images give the necessary resolution to discriminate against foreground stars and background galaxies, while the photometry goes very deep; (ii) Near-IR observations reach only the brightest clusters, but provide a much larger color baseline which is very useful to e.g., identify intermediate-age clusters such as those found in the LMC and in NGC 5128 (cf. Minniti et al. 1996, ApJ, 467, 221), and to measure more accurate metallicities, particularly at the metal-rich extreme of the metallicity distribution.

We present new optical imagery and ROSAT HRI X-ray imagery of the elliptical galaxy NGC 5846. A filamentary dust lane is detected in its central region, with a morphology strikingly similar to that observed for the optical nebulosity and the X-ray emission (cf. Fig. 1). A physical connection between the different phases of the interstellar medium therefore seems likely. The energy deposited from the hot gas into heating of the dust grains is consistent with the temperature distribution of the X-ray-emitting gas, which is found to be lowest in the dusty regions. The optical extinction of the dust is consistent with the Galactic extinction curve. We argue that the dust as well as the optical nebulosity are products of an interaction with a small, gas-rich galaxy, not remnants of a cooling flow. A full account of this work is currently in press in Astronomy and Astrophysics, and a preprint is available through http://www.stsci.edu/science/preprints/prep1191/prep1191.html.

There are known to be several giant elliptical galaxies with high globular cluster specific frequencies, which possess about three or more times the normal number of globular clusters for their luminosity. The origin of high specific frequency globular cluster systems is not yet known.

We examine a model of galaxy formation where the bulge is formed at very early stages and this burst of star formation leads to a galactic wind which interacts with a huge surrounding gaseous envelope.

We investigate the nature of stellar populations of major galaxy mergers between late-type spirals considerably abundant in interstellar medium by performing numerical simulations designed to solve both the dynamical and chemical evolution in a self-consistent manner. We particularly consider that the star formation history of galaxy mergers is a crucial determinant for the nature of stellar populations of merger remnants, and therefore investigate how the difference in star formation history between galaxy mergers affects the chemical evolution of galaxy mergers.

IC 4889 is an apparently normal E5 elliptical (Jedrzejewsky 1987, MNRAS, 226, 747) with an extended ionized gas emission (Macchetto et al. 1996, A&AS, 120, 463). We performed long-slit spectroscopic observations along different position angles: 0°, 10°, 90° and 135°.

The onset of gaseous inflows and central activity in interacting galaxies is driven largely by induced bars in the host galaxies. The stability of galaxies against growing bar modes is a direct function of their structural properties — galaxies with central bulges or low disk surface densities are more stable against central starbursts than are bulgeless or disk-dominated systems. Low surface brightness galaxies prove less prone to bar formation and central starbursts than do normal high surface brightness galaxies. This stability of LSB disks also resolves many of the dynamical pitfalls encountered when attempting to link poststarburst “E+A” galaxies to interactions involving normal high surface brightness galaxy progenitors.

We present a numerical simulation of two merging equal-mass, gas-rich disk galaxies. Special emphasis is given to an accurate treatment of the interstellar medium physics and star formation with its feedback. We will explain how the negative feedback from young stars restricts the bulk of the star formation during the merger-induced starburst to the nucleus.

The results of the FCRAO Extragalactic CO Survey are used to examine the trends regarding the molecular gas distribution, the star formation efficiency, and the global gas surface densities (HI and H2) in galaxies as a function of environment. Relative to a sample of isolated Sbc-Scd galaxies, the strongly interacting galaxies have more compact gas distributions, a higher mean value for the global star formation efficiency, and a larger fraction of gas in molecular form. Not only is the molecular gas redistributed during interactions, but evidence is presented for an enhanced conversion of atomic to molecular gas as well.

The power output in luminous infrared galaxies (LIGs, LIR ≳ 1011L⊙, H0 = 75 kms−1 Mpc−1) can approach the bolometric luminosity of quasars and can be provided by either starbursts or dust-enshouded QSOs, or both. Most LIGs appear to comprise of mergers of gas-rich galaxies. So, intense bursts of star formation apparently result from interaction and merging of galaxies, but the exact physical processes involved in collecting the large amount of gas involved and in initiating the starbursts are not well understood.

Arp 299 is an IR-luminous (LIR ≈ 8 × 1011L⊙) merger system of two galaxies, IC 694 and NGC 3690, at a distance of 40 Mpc. Its proximity and richness in molecular gas make it suitable for studying the effects of gravitational interactions and starburst activity on molecular cloud distributions, dynamics, and physical conditions. Previous low resolution observations (10 - 30″) indicated that the CO/13CO 1-0 intensity ratio is unusually high, > 20, suggesting an unusual population of molecular clouds (Aalto et al. 1991; Casoli et al. 1992).

We propose a physical mechanism for the triggering of starbursts in interacting spiral galaxies by shock compression of the pre-existing disk giant molecular clouds (GMCs). We show that as a disk GMC tumbles into the central region of a galaxy following a galactic tidal encounter, it undergoes a radiative shock compression by the pre-existing high pressure of the central molecular intercloud medium. The shocked outer shell of a GMC becomes gravitationally unstable, which results in a burst of star formation in the initially stable GMC. In the case of colliding galaxies with physical overlap such as Arp 244, the cloud compression is shown to occur due to the hot, high-pressure remnant gas resulting from the collisions of atomic hydrogen gas clouds from the two galaxies. The resulting values of infrared luminosity agree with observations. The main mode of triggered star formation is via clusters of stars, thus we can naturally explain the formation of young, luminous star clusters observed in starburst galaxies.