Vera C. Rubin’s research while affiliated with Carnegie Institute and other places

The discovery of SO galaxies with polar rings makes it possible to directly measure the gravitational potential of a galaxy in three dimensions. Schweizer, Whitmore and Rubin (1983) find a spherical potential in the case of A0136-0801. We have observed three more polar ring galaxies using the 4 meter telescope at CTIO. The following table summarizes the results for these three systems as well as A0136-0801, and figure 1 shows an example of the data.

Systematic rotational properties of field spiral galaxies are presented, as a function of Hubble type and of luminosity. Within a Hubble type, radius, nuclear velocity gradient, rotation velocity, mass, and mass density increase with luminosity, while m /L is constant. At fixed luminosity, V(max), mass, density, and m /L decrease from Sa through Sc. These variations are so systematic that it is possible to display them on a single diagram.

Modern detectors permit astronomers to examine galaxies at very low light levels, at very high velocity resolution, and for nearby objects, at very high spatial resolution. Such observations will lead to phenomenon not previously detected, and offer new insights into the phenomena we presently lump under the heading of “activity.”

“The stellar milky way, in the region of which, according to Argelander's admirable observations, the brightest stars of the firmament appear to be congregated, is almost at right angles with another milky way, composed of nebulae… the milky way composed of nebulae does not belong to our starry stratum, but surrounds it at great distance without being physically connected with it, passing almost in the form of a large cross through the dense nebulae of Virgo, especially the northern wing, through Coma Berenicis, Ursa Major, Andromeda's girdle, and Pisces Boreales”. These words, published 140 years ago by Alexander von Humboldt (1849), outline the program which brings us all to Hungary for this conference.

Thirty years ago, observational cosmology consisted of the search for two numbers: H o , the rate of expansion of the universe at the position of the Galaxy; and q o , the deceleration parameter. Twenty years ago, the discovery of the relic radiation from the Big Bang produced another number, 3 o K. But it is the past decade which has seen the enormous development in both observational and theoretical cosmology. The universe is known to be immeasurably richer and more varied than we had thought. There is growing acceptance of a universe in which most of the matter is not luminous. Nature has played a trick on astronomers, for we thought we were studying the universe. We now know that we were studying only the small fraction of it that is luminous. I suspect that this talk this evening is the first IAU Discourse devoted to something that astronomers cannot see at any wavelength: Dark Matter in the Universe.

We have examined star formation in two very luminous (M_V=-22 to -23) Sc-type spiral galaxies, NGC 801 and UGC 2885, using ultra-deep Halpha images. We combine these with UBV and 2MASS JHK images and HI maps to explore the star formation characteristics of disk galaxies at high luminosity. Halpha traces star formation in these galaxies to 4-6 disk scale lengths, but the lack of detection of Halpha further out is likely due to loss of Lyman continuum photons. Considering gravitational instabilities alone, we find that the gas and stars in the outer regions are marginally stable in an average sense, but considering dissipative gas and radial and azimuthal forcing, the outer regions are marginally unstable to form spiral arms. Star formation is taking place in spiral arms, which are regions of locally higher gas densities. Furthermore, we have traced smooth exponential stellar disks over 3-orders of magnitude and 4-6 disk scale lengths, in spite of a highly variable gravitational instability parameter. Thus, gravitational instability thresholds do not seem relevant to the stellar disk. One possibility for creating an exponential disk is that the molecular cloud densities and star formation rates have exponential profiles and this forces the stellar disk to build up such a profile. Another possibility is that the stellar disk is continuously adjusted to an exponential shape regardless of the star formation profile, for example through global dynamical process that scatter stars. However, such scattering processes are only known to operate in spiral systems, in which case they cannot explain the same dilemma of smooth exponential disks observed in dwarf irregular galaxies.

We present a photometric study of two galaxies, NGC 801 and UGC 2885, two of the most luminous spiral galaxies in the nearby universe, taking specific interest in the star formation in the outer disks of these galaxies. Our objectives were to find the star formation rate in the outer disks (r>r25) of these two galaxies and to compare our findings to the gas and established models. We used data in the UBV and JHK bands to trace older stars, very deep images in Hα to trace recent star formation, and HI maps to reveal the atomic gas. We converted the Hα fluxes to star formation rates as a function of radius, taking into account expected changes in metallicity and reddening with radius. We find that star formation in the outer disks is occurring at a significant rate, even where the gas density is too low to support star formation from gravitational instabilities. We also compare to the empirical star formation law of Bigiel et al. (2010) for lower luminosity spirals.

My life has been an interesting voyage. I became an astronomer because I could not imagine living on Earth and not trying to understand how the Universe works. My scientific career has revolved around observing the motions of stars within galaxies and the motions of galaxies within the Universe. In 1965, if you were very lucky and interested in using telescopes, you could walk into a research laboratory that was building instruments that reduced exposure times by a factor of 10 and end up making remarkable discoveries. Women generally required more luck and perseverance than men did. It helped to have supportive parents and a supportive husband.

DDO 125 may contain little or no dark matter, according to some radio observations of the neutral hydrogen gas in the disk. However, no dark matter could be the result of assuming a maximum stellar disk but, we can find out about the real stellar disk from kinematics of the stars. If a turnover in the rotation of the stars is detected and the rotation of the stars is flat after the turnover point, then dark matter would be needed to explain the stellar rotation curve of DDO 125. If there is, in fact, no turnover point and the stars and the gas follow each other kinematically, then there may be little or no dark matter detectable in this system. This could indicate a different evolutionary history. There are recent studies that show stars and gas do not move in the same way, thus, it could be quite possible that the stars and the gas of DDO 125 do not follow each other. Therefore, we propose to use the KPNO 4-m+Echelle as a 3 arcmin longslit spectrograph to obtain the stellar kinematics of DDO 125. We will use a cross-correlation function to determine heliocentric radial velocities and velocity dispersions as a function of radius for the stellar disk of DDO 125 and compare these to the gas kinematics determined from newly acquired 21 cm VLA HI data.

Charlotte Moore Sitterly was a scientist in an era when it was rare for a woman to have the opportunity to devote her life to forefront science. Following her graduation from Swarthmore College in 1920, she accepted a position at Princeton University as an assistant to Henry Norris Russell. In 1925 she started a study of the solar spectrum. She could then not know that she would devote much of her scientific career to gathering basic atomic data that are invaluable to the scientific community, even today. In 1931 she obtained a Ph.D. degree at the University of California, Berkeley, and returned to Princeton as a staff member of the Princeton University Observatory. In 1945 Moore moved to the National Bureau of Standards (NBS), to supervise preparation of the widely-used tables of atomic energy levels. Following the successful launching (1946) of a V2 rocket to obtain the ultraviolet spectrum of the Sun, she started working also with Richard Tousey and his group at the Naval Research Laboratory (NRL). Ultimately, they extended the solar spectrum down to 2200 angstroms. She continued her affiliations with both the NBS and the NRL until her death in 1990. Charlotte Moore was a rare scientist who devoted her career to obtaining accurate numbers, thus enabling the scientific community to open her tables and know that the data are reliable.