The Interstellar Medium* Group @ STScI

The Interstellar Medium* Group at the Space Telescope Science Institute (STScI) is a collaboration between STScI research staff, associated external collaborators, and the students and postdocs with whom they work. We meet weekly, pool resources and expertise, and collaborate on research projects. We focus on interstellar, circumstellar, and circumgalactic media, mainly in nearby galaxies. But our interests are diverse and we often use stars and stellar populations in our analyses; hence the *. We hang out on the West 4th floor of the Rotunda.

Nearby Galaxies as Laboratories

The overall focus of the ISM*@ST group is the study of nearby galaxies (including the Milky Way) as laboratories for the physical processes of the ISM, star formation, stellar feedback, and galaxy evolution. We are broad in our approach: we use wavelengths from radio to ultraviolet, spectroscopy and imaging, bayesian inference and deep learning, targeted observations and archival studies. The following are some areas of specific scientific focus:

Lifecycle of Metals

We study the life-cycle of dust and metals in nearby galaxies, from the stars to the interstellar medium (ISM) via stellar winds, within the ISM between the dust and gas phases, and between the ISM and the circumgalactic medium (CGM) via galactic outflows. Components of this research path include:

  • Dust Production in asymptotic giant branch (AGB) stars and supernovae [DUSTiNGS]

  • Gas/Dust ratio variations within and between galaxies from multi-wavelength measurements: elemental depletions from ultraviolet spectroscopy; dust abundance from far-infrared, H I 21cm and CO rotational emission [METAL]

  • Galactic outflows and inflows from ultraviolet spectroscopy of stars and quasars [QuaStar]

  • The metallicity of stellar populations and the chemical enrichment of galaxies [LUVIT]

ISM Structure

We study the multi-dimensional structure of gas and dust in the nearby ISM using observational and statistical tools. Topics of interest include:

  • Properties and dynamics of the ISM with distinct temperature and density (i.e., "phases") from radio and mili-meter spectroscopy, plus synthetic observations of numerical simulations.

  • The ISM beyond 3D: connecting velocities traced by gas with 3D distances probed by dust [Kinetic Tomography] to measure flows of gas in and around spiral arms of the Milky Way and giant molecular clouds.

  • Characterizing the shapes and properties of multi-dimensional gas features probed with large-area surveys of the diffuse ISM (GALFA-HI).

  • Investigation of the impact of 3D ISM structure on photon radiative transfer [DIRTY]

Dust Properties

We investigate the size, shape, composition, and alignment of interstellar dust grains using a range of observations that are interpreted with a rich set of models.

A selection of the observations we pursue include:

  • ultraviolet through mid-infrared photometry and spectra of stars to measure extinction curves

  • ultraviolet and optical spectra of gas phase absorption lines to measure dust depletions

  • optical, infrared, and submillimeter surface brightness images to measure the thermal and non-thermal emission processes of dust

These observations are measured and interpreted with a range of models including:

  • the Bayesian Extinction And Stellar Tool [BEAST] that fits photometry of many sources to make dust column and average grain size maps

  • a dust grain fitting code (in development) that derives the distribution of grain sizes and compositions based on a range of observational constraints

  • the DustBFF code that fits infrared to submm dust emission to constrain dust surface densities, sizes, and compositions

  • the Dusty Evolved Star Kit (DESK), a tool for fitting grids of radiative transfer models to the spectral energy distributions of asymptotic giant branch stars

Star Formation & Stellar Populations

We study the different stages of star formation in the Milky Way and nearby galaxies, from molecular clouds, to young stellar objects (YSOs), to the UV emission from young massive stars. In particular, studying star formation in nearby galaxies allows us to study the effects of metallicity on the star formation process.

Our goals are to understand:

  • the properties of the molecular birth material

  • the rate of star-formation and the star formation history using a variety of tracers (e.g., YSOs, UV, FIR)

  • how the star formation rate and initial mass function (IMF) relate to the properties of parent molecular clouds.