The hierarchical fragmentation of a molecular cloud is modeled as a random process by the Monte Carlo method. The mass function of fragments for different values of initial magnetic field is derived.

Taking the FCRAO Extragalactic CO Survey as an example, the requirements are examined for a galaxy survey which can be used to study the global molecular gas content of normal galaxies as a function of their size and type. The FCRAO survey is applied to derive the CO luminosity function of galaxies, and to look at variations in LCO/LB and CO/HI with Hubble type.

We have examined the global properties of 250 galaxies and galaxy pairs observed as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey with respect to bar type and arm type, and we have compared the results with the global properties of the same galaxies as a function of morphological type. The bar types of the galaxies were taken from RC2, and the arm types for 48% of the sample were taken from Elmegreen and Elmegreen (1987). We find the following:

1) There is little dependence of the star formation efficiency, as measured by the global FIR luminosity to molecular gas mass ratio, on bar type. Similarly, we find no obvious correlation between the global ratio of molecular to atomic gas mass and the bar type.

2) Variations of up to a factor of 6 are seen in the mean star formation efficiency with arm type, where flocculent galaxies appear to have slightly higher global star formation efficiencies than spirals with clearly delineated arms. Variations in the mean molecular to atomic gas mass ratio of a factor of 5 are seen as a function of arm type, but there is no apparent trend from flocculent to grand design spirals.

3) The decrease of a factor of 20 in the molecular to atomic gas mass ratio observed as a function of morphological type (Young and Knezek 1989) is more pronounced than the same ratio as a function of bar or arm type.

We have observed CO J=1−0 emission in 300 galaxies at 45″ resolution as part of the FCRAO Extragalactic CO Survey. The target galaxies were selected on the basis of their optical and infrared properties, such that they are either brighter than 12th magnitude in the blue, or brighter than 10 Jy at 100 μm. This data set has been used to investigate the global ratio of molecular to atomic gas mass, the fraction of galaxy mass in neutral gas, and the yield of high mass stars per unit mass of molecular gas, all as a function of morphological type and environment.

We report observations of the 12CO and 13CO J=1—0 transitions in external galaxies. The 12CO/13CO intensity ratio tends to vary with the degree of interaction.

Intense star formation activity, in the absence of interactions, occurs nearly always in barred spiral systems, but many barred galaxies do not show especially enhanced activity. On the other hand bars provide an efficient mechanism of transport of gas from the disk into the active star forming circumnuclear region (Combes and Gerin, 1987). The type of activity in the circumnuclear regions would also depend on the characteristics of the bars (Arsenault, 1989). The dynamics of the gas inside the bars could also be related to outflows of gas into the halo detected in some barred galaxies with intense nuclear activity.

The ratio between the intensities of the various CO line transitions, with the additional information about the isotope abundance, should enable us to probe the optical depth in the molecular clouds in galaxies. There are, of course, problems in interpretation as a result of the unknown structure of the clouds, their distribution and temperature. These problems become particularly important since most of the present data are derived in the vicinity of nuclei of galaxies.

CO(J=1−0) line observations of the southern arm of the barred-spiral galaxy M83 were made with the 45-m telescope of the Nobeyama Radio Observatory with a 17″-beam. The CO emission is concentrated to the spiral arm, but it is much weaker than in the bar. The comparison between the CO flux and the far ultraviolet flux suggests the star forming efficiency is much lower in the bar than in the spiral arm.

We have mapped the southern galaxies NGC 613, 1313, 1433, 1566, 1672, and 2442 in the 12CO(1-0) line with the SEST telescope. The sample bases on galaxies observed previously in radio continuum at the Molonglo Observatory (Harnett, 1985).

We present our recent results of high spatial resolution(2″-6″) CO and 13CO(J=1−0) observations with the Nobeyama Millimeter Array(NMA). We observed the central (1-2 kpc) regions of nearby galaxies, IC342, Maffei2, and NGC6946 with 2″-4″ resolution (45-90 pc) in CO and 13CO, and the 3' region of M51 with 4″-6″ resolution (180-280 pc). We discuss the structures and kinematics of molecular gas in the central region of nearby late-type spiral galaxies, and in spiral arms, and discuss the trigger of star formation from viewpoints of galactic shock, gas fueling by bars.

We have mapped the southern edge-on spiral galaxy NGC 4945 in 12CO(1-0) and 12CO(2-1) with the SEST telescope. Additional 13CO spectra were also obtained. The intense nuclear CO emission is in agreement with the revised classification of this galaxy as an Sc object. NGC 4945 was for many years known to be a prototype of nuclear activity with detections of various molecular lines at cm-wavelengths, an OH kilomaser, a superluminous H2O maser, etc. (Whiteoak, 1986). A host of molecules (CN, CS, C2H, HCN, CH3OH, etc.) has recently been detected at mm-wavelengths in the nucleus of NGC 4945 (Henkel et al., 1990).

The spiral galaxy NGC 4258 is known for its anomalous Hα and nonthermal radio arms perpendicular to the normal spiral arms (van der Kruit et al., 1972). Several models have been proposed to explain this phenomenon and its origin is most probably to be sought in the past activity of the nucleus of NGC 4258. Most of the characteristics of the anomalous arms, such as the symmetry with respect to the center, or the properties of the emission lines (pure Hα line emission with no continuum, line ratio between Hα and [NII]) are reminiscent of the optical and radio jets currently observed in active galaxies.

Spiral arm properties varies widely from one galaxy to another. For this reason detailed observational studies of galaxies with different morphologies are critical for the understanding of the role, if any, of the spiral arms, in the formation of the complexes of HI clouds, molecular clouds and ultimately for the formation of the massive stars.

We report 55″ resolution images of the 15μm [CII] fine structure line from the spiral galaxies M83, M51, and NGC6946. We drive variations in the global star formation activity within and between these galaxies.

The pair of galaxies NGC 4038/39 (Arp, 244) has been observed at Hα wavelength with a scanning Pérot-Fabry interferometer and an IPCS at the Cassegrain focus of the 3.6 m ESO telescope. Hα profiles were thus obtained inside 256 × 256 pixels (0.91″ × 0.91″ each), providing 5741 velocity points with an accuracy better than 16 km s-1, covering the central part of the merging system. The velocity field exhibits severe distortions, not surprising because of the strong interaction. Comparison of our data with recent CO data (Stanford et al., 1990) inside NGC 4039 show a fairly good agreement. The grand design of the velocity field of NGC 4038 more clearly reminds of a classical rotating disk. A rough estimate of the masses of the galaxies indicates that they are both around 1010 M⊙ within a radius of 40″. Comparison with the most recent model of the antennae (Barnes, 1988) shows a strong discrepancy, the observed radial velocity range being half the expected value and the nuclei velocities differing by only 30 km s-1 instead of the expected 300 km s-1.

Extragalactic HII regions and their ionizing star clusters are the most prominent signposts of recent starbirth activity in galaxies. In this paper, we present optical measurements of nearby extragalactic HII regions with the aim of investigating possible relationships between the newborn ionizing clusters and their dynamical environment. Evidence for variations in the measured HII region properties (size, Hα luminosity, and Hα equivalent width) are presented as a function of galaxy type and of position within individual galaxies. These variations, in turn, are compared with the corresponding kinematic and dynamical variations. The apparent sensitivity of the ionizing activity to the dynamical environment suggests that the total masses and upper stellar mass limits of the ionizing clusters are somehow constrained by the ambient tidal stresses and shear flows within the galaxies. We speculate that regions of high tidal stress and kinematic shearing tend to suppress the formation and maintenance of giant molecular clouds, thereby hindering the creation of giant clusters and massive stars therein.

Far-UV (200 nm) fluxes of late-type, disk-dominated galaxies are used as tracers of their current star formation activity. After dust extinction corrections, the UV luminosity per unit area is compared to the gas surface density for a sample of 28 non resolved spiral galaxies and through the disk of Messier 51 at a resolution of 50″ (imposed by CO data). In both cases, the current star formation rate per unit area shows a very good correlation with the total (atomic and molecular) gas surface density; much weaker correlations are found when one gas phase alone is concerned.

Until recently, molecular spectroscopy of extragalactic sources was based on the observation of a few molecules, only. From 1971 to 1980, nine molecular species have been detected, most of these with telescopes operating at cm-wavelengths (see the review of Morris and Rickard, 1982). With the exception of the widely distributed CO, only very little data had been obtained. CO is a tracer of low density molecular gas. To detect gas at higher densities (n(H2)≥ 104 cm—3), to trace its distribution and kinematics, to determine temperatures and to study chemical properties, we set up a project with two main lines of research: (1) We attempted to enlarge the number of detected molecular species and (2) we tried to study some of these in more detail, in order to obtain astrophysically relevant results.

As part as of an extragalactic CH 9-cm ground-state emission survey of OH emitters (megamasers) and absorbers, we report the detections of the 3335 MHz main line in M82 and of the 3264 MHz satellite line in the luminous far infrared (FIR) galaxies NGC 3079 and NGC 5793, obtained with the Nançay radiotelescope.

We obtained 21cm HI aperture synthesis maps of the “exploding galaxy (Lynds and Sandage 1963)” M82 using the D-configuration of the VLA in order to trace the distribution and kinematics of the atomic gas in and around M82 with a high sensitivity. A field centered at M82 and four adjacent fields were observed and mosaiced together with a spectral resolution of 48.8 kHz (10.3 km s—1) and 62″ × 68″ beam (FWHM). The detection sensitivity corresponds to 2.7 × 1019 atoms cm—2. In addition, we also obtained a set of large field (26′ × 26′) deep exposure Standard (Harris) R-band optical images using the Tek 2048 CCD on No.1 0.9-m telescope at Kitt Peak, Arizona, to compare the observed HI features with optical images.