Interstellar Medium

X-ray image of the center region of the Milky Way, obtained with Chandra

Astronomers at UMass are involved in studying nearly all phases of the interstellar medium (ISM) using observational techniques that span the electromagnetic spectrum from x-rays to radio. Numerous studies of the ISM in the Milky Way and in nearby galaxies are either underway are planned using space-based facilities (HST, Chandra, Spitzer, FUSE, XMM-Newton and Herschel) and ground-based facilities (FCRAO, VLA, GBT, Arecibo, and LMT). These facilities are used to map the both the continuum and spectral line emission from the gas and dust in these galaxies. Two areas where we have much activity is the study of the densest and coldest component of the ISM, molecular clouds, and the most rarefied and hottest component, the hot, ionized gas.

The molecular phase of the ISM is important as it is most directly connected to star formation in both the Milky Way and other galaxies. The UMass group is endeavoring to better understand the physical and dynamical properties of the molecular gas and put this phase in context wth the global cycling of gas in galaxies - which is essential to understand galactic evolution. It is well known that stars are formed in molecular cloud cores, but we now seek a better understanding of how this occurs. Observational programs to study the gravitational infall signature and outflow signature associated with the birth of stars are in progress. There is also an incredible chemical complexity and diversity in molecular clouds, and today we also seek to explain the nature of this chemistry and understand its implications. For decades we have made use of the Five College Radio Astronomy (FCRAO) 14-m telescope located on the Quabbin Reservoir in central Massachusetts for much of our observational studies, however soon the Large Millimeter Telescope (LMT) will be available and will provide greatly improved resolution and sensitivity for these studies.

High-energy activities in the ISM are manifested through the creation of a pervasive hot gas component. The presence of this rarefied interstellar component can profoundly affect the geometry and dynamics of the cooler phases of the ISM, the propagation of cosmic rays and UV/soft X-ray photons, the strength and topology of the magnetic field, the galactic disk-halo interaction, the distribution of metal abundances, and so forth. However, there is little agreement yet on such basic issues as how much hot gas there is, which thermal state the gas is typically in, how the gas is distributed relative to cooler phases, what fraction of supernova mechanical energy is deposited into the hot gas, and where the energy is transferred or dissipated. To address these issues, UMass astronomers have a multiwavelength programs in place to characterize the global hot gas component. We are using our Galactic center region as a unique laboratory to study detailed physical processes involved in heating, mass loading, and outflows of hot gas. We have obtained data or observing time from HST, FUSE, Chandra, and XMM-Newton to map hot gas and to study its interplay with other components in nearby galaxies. We will further examine the relationship of the global hot gas properties to the star formation rate, morphological type, and clustering environment of galaxies.

Gas in Taurus, a nearby molecular cloud, obtained by FCRAO.