Eve Ostriker's Research

Eve Ostriker

My research focuses on the process of star formation, the dynamics of the interstellar medium, and the structure and evolution of disk galaxies. My expertise is theoretical, and my research uses large-scale numerical hydrodynamics and MHD simulations as well as analytic models. Codes developed in my research group are used for simulating astrophysical systems that are accessible primarily using millimeter radio arrays; processes we have studied range from dust settling in protostellar disks to the formation of giant molecular clouds (GMCs) and interarm spurs in spiral galaxies. I also work in close collaboration with faculty, postdocs, and students within the LMA in interpreting radio observations from astronomical systems. These studies focus on detailed analyses of structure and kinematics in comparison to self-consistent dynamical models.

ADS Listing for past 5 years

GMC and Spur Formation in Spiral Galaxies
The spiral arms in grand design galaxies -- including our own Milky Way -- initially grow in the underlying stellar disk, but the most dramatic consequences of spiral structure take place in the interstellar medium. Interstellar gas shocks as it enters spiral arms, raising both the volume density and the surface density often by more than an order of magnitude. These high post-shock densities enable self-gravitating enstabilities to develop. For very strong shocks, instabilities grow so rapidly that arms completely fragment into molecular clouds. For more moderate shock strengths, gas can begin to compress in the arm, but return to the interarm before collapse ensues. In the latter case, the overdense gas becomes sheared out into long trailing filaments in the interarms. These structures are observable as extinction "feathers" and in IR and molecular emission. Subsequent fragmentation into GMCs and stars leads to observable "spurs" marked by chains of HII regions. We initially discovered the spur formation process using local numerical models, and have expanded this research using global numerical simulations, optical/IR studies using HST and Spitzer data, and CARMA observations.

Turbulence in Molecular Clouds
Giant molecular clouds (GMCs) are the sites of essentially all star formation, and the dynamical processes in these systems therefore holds the key to defining the properties of the stars that form. The complex structure of GMCs is largely shaped by the collisions of cold molecular streams of gas, with the amounts and spatial distributions of high-density gas determined by the multi-scale dynamics of supersonic, magnetized turbulence. The clustering properties of stars, the stellar IMF, and the overall rate of star formation are all believed to derive from the the turbulent properties of GMCs, but the nature of these relationships are only now being discovered. An very active area of research involves using numerical simulations to model turbulent molecular clouds, and comparing the results of these models to observations of structure and kinematics observed in millimeter lines (from molecular gas) and continuum (from dust).

The work of my group was influential in establishing the importance of turbulence to GMC structure and evolution, and our current research continues to broaden and deepen understanding of both fundamental processes and observable consequences.

Kinematics of Spiral Arm Streaming
The flow of interstellar gas in spiral galaxies experiences large excursions from circular, constant-velocity orbits. In particular, gas is observed to "stream" along spiral arms, rather than flowing directly through them. This "streaming" is a consequence of large-scale shocks that develop when gas encounters the gravitational potential of the arm, which is created by stellar density waves that make up the arm "pattern". When gas is compressed in the arms, both radial and azimuthal velocity perturbations are induced. Based on spiral shock models, gas is predicted to have a local minium in the component of the velocity perpendicular to the arm where the gas density is highest, and a large postive gradient in the azimuthal velocity at the same location. By analyzing the two-dimensional CO and H alpha velocity fields in the grand design spiral galaxy M51 (the "Whirlpool"), these features have been clearly identified. Comparison of the recovered velocity field and CO intensity map with theory shows consistency with predictions based on angular momentum conservation, but indicates that the arm structure is dynamically evolving.

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