R. Allen attended the meeting in South Africa on cold gas and dust in galaxies, and presented a review of the present state of knowledge of the molecular content of disk galaxies. He has concluded (Allen 1996) that there are presently no reliable tracers of the amount of H2 actually present in galaxy disks, and that significant amounts of cold molecular gas are likely to be present, especially in the inner disks of Sa-Sb galaxies.
Allen, Bohlin, and Knapen (Hertfordshire) continued their analysis of
the H I, H
, and UIT-UV data in M81. The morphology of these
tracers is being analysed in the framework of a PDR model; the UV produces
the H I by photodissociation. Up to now, such models have been applied to
small regions (
pc) of intense star formation in the Galaxy.
However, an attempt to model the spiral arm structures observed on larger
scales (
pc) in nearby galaxies has not been done. A plausible
model based on PDRS can indeed be constructed which explains both the
qualitative features of the morphology as well as the amounts of UV and
H I actually observed. A paper is in preparation.
Allen, Loinard, and Taylor (ST ScI/CSC) continued their program of searching for faint CO(1-0) emission in the outskirts of several nearby galaxies. Detections have been achieved so far in the outer parts of M51 and M61 using long integrations with the multi-beam system at FCRAO. This program will be continued in the coming year.
Together with Cuillandre (Toulouse), Lequeux (Paris), and Mellier (Paris), Allen has identified dust clouds in the far outer regions of M31, at and beyond the Holmberg radius of the galaxy. The identification was made by detecting the reddening of field galaxies viewed through the known H I clouds present there. If this dust has the Galactic reddening law, and if H I is the only component of the gaseous ISM present, then the dust to gas ratio is 0.5 of the value in the solar neighborhood. A scattered population of B-stars has also been identified in the same regions. A paper has been submitted (Cuillandre et al. 1996).
Allen has completed his work with Canzian on identifying the kinematic
signature of corotation in the spiral galaxy NGC 4321, and a paper has
been submitted (Canzian & Allen 1996). The result has been obtained
using the method of identifying galaxy-wide features in the velocity
field developed by Canzian; in this case the H
data were used.
N. Caon, in collaboration with D. Macchetto, W. Sparks and
M. Pastoriza (Instituto de Fisica, Porto Alegre, Brazil), has completed the
mapping of the distribution of the ionized, line-emitting gas in a sample of
73 elliptical and lenticular galaxies, as part of the ESO Key Project:
``Towards a physical classification of early-type galaxies.'' Morphology,
extension and total luminosity of the ionized gas were derived from narrow-band
H
+N II and broad-band images, finding that more than 70% of the sample
galaxies contain detectable amounts of warm gas.
These data were used to test the model in which the gas excitation and
ionization mechanism is conductive heating of the warm gas by hot electrons
associated with an X-ray emitting coronal halo; the H
luminosities
predicted by this model compare very well with the measured values. A strong
correlation was also found between the H
luminosity and the luminosity
in the B band inside the region occupied by the line-emitting gas, consistent
with the model in which post-AGB stars provide the UV ionizing photons and
account for the observed H
luminosities and equivalent widths in
early-type galaxies. It is likely that both conductive heating and UV photons
work together to excite and ionize the gas.
Long-slit spectra for 14 objects chosen among the ones with the most luminous and extended line-emitting regions were collected at the 3.6m telescope at ESO La Silla (Chile), in order to compare the gas and the stellar kinematics, and study the characteristics of the emission (equivalent widths, line ratios). Preliminary results for 6 objects show evidence for kinematic decoupling between gas and stars, suggesting an external origin (accretion) for the gas.
Maps of the dust distributions have also been obtained from multi-color imaging. They will be complemented with ISOCAM observations in the spectral region 5--17 micron(in 3 passbands), to map the warm dust and establish detailed comparisons with the features found in the optical images (knots and filaments of the line-emitting gas, dust lanes).
H. C. Ferguson continued his involvement in the Hopkins Ultraviolet
Telescope (HUT) project, analyzing data from the the Astro-2
mission of March 1995. Brown, Davidsen (JHU), and Ferguson constructed a grid
of stellar model atmospheres for stars in the temperature range 
K. Together with Dorman (GSFC), they applied this grid to
study the UV-emitting stellar population in elliptical galaxies. The results
favor high-metallicity, helium rich extreme-horizontal branch (EHB) stars as the
dominant contributor to the ubiquitous ``UV upturn'' in elliptical galaxies,
although metal-poor models cannot be completely excluded. Dixon (Berkeley),
Davidsen (JHU), and Ferguson used HUT observations of ``blank sky'' to
search for O VI emission from the Galactic halo. The 4
detection along
two lines of sight, is consistent with the expectation from self-photoionizing
Galactic fountain models. Dixon, Hurwitz (Berkeley), and Ferguson also used the
HUT data to search from O VI within clusters of galaxies, and the upper
limits provide interesting constraints on the amount of warm 
K gas that can be present at the center of cluster cooling flows.
L. Loinard (Grenoble & ST ScI) continued his project to map the CO(1-0)
emission in M31 using the FCRAO millimeter radio telescope. The atomic
and dust content are known quite well for M31 down to a scale of 
pc;
however, the only complete mapping of CO(1-0) in M31 has been done on the scale
of 1 kpc, and only a few isolated regions have been observed at better
resolution. The FCRAO radiotelescope provides a linear resolution of
about 150 pc on M31, which is useful for the comparison with other ISM tracers;
a project was therefore started last year to map the southern half of the
galaxy with the multi-beam receiver at FCRAO. Preliminary results of
the survey have been published by Loinard et al. (1996), and roughly
80% of the southern half of M31 has been mapped. Observing time has been
granted to finish the remaining 20%, and this is expected to be complete by
January 1997. Allen, Bohlin, and Loinard are using this CO(1-0) data together
with UIT UV data (at 150 nm) and existing 21 cm H I data in an attempt to
understand the morphology of these tracers in M31 in the framework of PDR
models.
K. Long, Charles (Oxford), Blair, and Gordon (LBNL) completed their
analysis of a 50 ks ROSAT PSPC observation of M33 in which they
identified 50 sources, many of which are associated with Pop I tracers in M33.
There are 10 sources which are positionally coincident with supernova remnants
identified in a companion optical/radio survey of M33 carried out by Gordon,
Kirshner (Harvard), Long, Duric (NM), Blair, and Smith (MI). From a spectral
analysis of the PSPC data, it is quite likely that a number of the other
sources in the X-ray survey are also supernova remnants. Long and Charles are
also continuing the effort to characterize X-ray source populations in
M33 as they analyze a large amount of HRI data on this object. As part of a
optical search for supernova remnants in nearby spirals, Blair and Long
completed their analysis of interference filter imagery of the Sculptor group
spirals NGC 300 and NGC 7793, identifying 28 SNRs in each galaxy. These are the
first large samples of SNRs to have been identified outside the Local Group.
The properties of these SNRs parallel the more extensive sample identified in
M33, although the dividing line between S II and H
ratios in the
Sculptor group spirals is less distinct, especially in N7793.
C. O'Dea, Stanghellini (IRA, Noto), Baum, and Charlot (IAP, Paris) analysed
optical images in the r and i filters of a sample of 40 GHz Peaked Spectrum
(GPS) Radio Galaxies. The GPS galaxies have absolute magnitudes in the Cousins
Rc band between -22 and 
, consistent with brightest cluster galaxies
and the hosts of other powerful radio sources. The GPS Hubble diagram and the
redshift distribution of r-i colors are consistent with both no-evolution
models and passive evolution models for elliptical galaxies. The GPS galaxies
are in good agreement with the Rc band Hubble diagram for 3CR galaxies at low
redshifts, 
. At higher redshifts, there is a suggestion that the GPS
galaxies are about 1 magnitude fainter than the 3CR galaxies. If real, this
may be due to 3CR galaxies having an extra component of blue light (the aligned
component?) which is not present in the GPS galaxies. We suggest that the
presence or lack of the blue light may be related to the presence or lack of a
powerful extended radio source.
B. Miller used H
imaging and nebular spectroscopy to investigate the
recent star formation histories of eight dwarf galaxies in the Sculptor
Group. Only two of the eight galaxies have current star formation, and
the oxygen abundances in their H II regions are 10--15% of solar. The
general star formation activity of the Sculptor Group dwarfs is less
than in dwarf galaxies in the Local Group or M81 Group. Since the mass
density in the Sculptor Group is less than in either the Local or M81
Groups, large-range gravitational interactions may play a role in
regulating star formation in dwarf galaxies. However, the O/H, M
relation seems to hold for all environments so galaxy mass appears to
be the primary factor governing a galaxy's chemical evolution.
Miller is working with Whitmore, Fall, and Schweizer (DTM) to find
globular clusters in galaxy merger remnants using the HST. They
have discovered a population of young, luminous clusters in NGC 3921.
The effective radii are all less than 5 pc (cf. Milky Way globulars have
R
pc) and the cluster luminosity function is described by a
power law with slope 
. They estimate that the number of globulars
has increased by about 40% during the merger and that the globular cluster
specific will increase from 0.7 to 1.8 over the next 5 Gyr and that NGC 3921
will look like a normal field elliptical. They will also continue their work
on new HST observations of the young merger remnants NGC 7252 and
NGC 4038/39 and of the old merger remnants NGC 1700 and NGC 3610. Their
goals are to see how cluster populations evolve with time and to use the
clusters to date the merger.
Miller, Whitmore, Ferguson, and Stiavelli are working on preliminary
analysis of a HST snapshot survey of dwarf elliptical (dE)
galaxies. The goals are to compare the globular cluster populations
of nucleated and non-nucleated dE's and to study the properties of the
nuclei. With twelve galaxies observed to date, their preliminary
finding is that nucleated dE's have higher globular cluster specific
frequencies, S
, than non-nucleated dE's. Also, both types seem to
have values of S
more like giant ellipticals than spirals or
irregulars. Finally, many of the nuclei are offset from the geometrical
centers of the galaxies.
Miller and Rubin (DTM) continue to obtain H
spectroscopy of Virgo
ellipticals and early-type spirals with kinematically distinct cores.
The kinematical information from the specta will be compared with HST
images of the cores of these galaxies in order to see the relationships
between the stars, dust, and gas.
K. Sahu continued his efforts in frequent, round-the-clock monitoring of the Galactic microlensing events through the PLANET (Probing Lensing Anomalies NETwork) collaboration. One of the prime objectives of this project is to look for extra-solar planetary systems, the signature of which would be a sharp extra peak on the microlensing light curve. The data can also be used to look for anomalies caused by other factors such as binary sources/lenses, extended sources, etc.
The PLANET collaboration, which started in 1995 through the initiatives of Sahu and Sackett (Kapteyn Lab, Groningen), has collaborative astronomers from Groningen, South Africa, and Australia. It uses a network of 1m-class telescopes situated at Chile, South Africa, and Australia to achive an almost continuous coverage in the monitoring program.
The data analysis of the 1995 pilot campaign has been completed and a binary event was detected. In 1996, a new 1-m telescope at Hobart, Australia, was added to the collaboration. S. Kane, a joint graduate student from ST ScI and Tasmania University (Australia), joined the project and participated in the observing from Hobart. PLANET has completed the 1996 campaign and the data analysis is now in progress.
Sahu is also conducting a program of spectroscopic study of the microlensed sources towards the Galactic bulge.
M. Stiavelli and collaborators continues to work on an HST snapshot survey of the bulge properties of a sample of 107 nearby spiral galaxies. The observations carried out so far indicate the widespread and unexpected presence of structures down to very small radii.
The study of the core properties of elliptical galaxies continued with two additional observing runs at the 2.5m Nordic Optical Telescope at La Palma (Moeller & Stiavelli in preparation). Multicolor images with subarcsec seeing conditions are now available for more than 100 objects.
The Near-IR properties of the jet and hotspot in M87 were studied using data obtained at the ESO 2.2m telescope with IRAC2 and at the 3.8m UKIRT telescope with IRCAM3. These very deep images show that the M87 radiolobe in the Near-IR has intermediate properties between the optical and the radio and allow for a more precise determination of the spectral break energy as a function of position along the jet and at the location of the hot spot (Stiavelli, Peletier, Carollo, 1996, MNRAS, in press).
A new project on the study of the evolution of the fundamental plane of elliptical galaxies with redshift was started. High quality data were obtained at the ESO 3.6m telescope and are being reduced (Stiavelli, Casertano, Moeller, in preparation).
A. Suchkov and a co-author, Marochnik, have published a monograph The Milky Way Galaxy. The book covers major issues of the structure and evolution of our Galaxy, including stellar populations, ISM, spiral structure, chemical and dynamical evolution, star formation and formation of the Galaxy.
B. Whitmore (1995a, 1995b) wrote two review articles summarizing recent HST observations of young star clusters in mergers and starbursting galaxies. These star clusters have the luminosities, colors, and spectra expected of proto-globular clusters. Hence, they may provide a natural explanation for why elliptical galaxies have a higher number of globular clusters per unit luminosity than spiral galaxies.
Schweizer (DTM), Miller (ST ScI/DTM), Whitmore and Fall completed a study
of the recent merger remnant NGC 3921, using HST observations. A search
for star clusters yielded 102 candidate globular clusters (GC) and 49 separate,
more extended stellar associations (A) brighter than 
mag. The color
indices of the GC's yield estimates of 250--750 Myr for the median age,
depending on the adopted metallicity (1.0--0.2 solar), and suggest a prolonged
formation period (several 100 Myr) roughly in agreement with the estimated
duration of the merger. Since from their colors most of these clusters appear
to be dozens of core crossing times old, they must be gravitationally bound.
Schweizer et al. estimate that the total number of GC's in NGC 3921 has
increased by 
40% during the merger, from about 
GC's before
to 
380 GC's after the merger.