IAU Symposium Abstract S186-001T

Overview - Low-z Observations

F. Schweizer1
1 Carnegie Institution of Washington/DTM, Washington, D.C., USA < schweizer@dtm.ciw.edu >

Gravitational interactions and mergers are shaping and reshaping galaxies from our Local Group to the limits of the observable universe. Observations of interacting galaxies at low redshifts (z< 0.2) yield detailed information about some of the processes at work. Our Galaxy appears to be accreting the dwarf SgrI, including its globular clusters. There is tantalizing evidence that more massive accretions may help build bulges in disk galaxies. Major mergers of near-equal-mass spiral galaxies result in remnants that share many properties with ellipticals and thus are likely present-day protoellipticals. Gas plays a crucial role in these interactions. Because of its dissipative nature, it tends to get crunched into molecular form, turning into fuel for starbursts and active nuclei. Besides the evidence for ongoing interactions, signatures of past mergers in early-type galaxies abound: r^{1/4}-type light distributions; ripples and tails; counterrotating cores, disks, and even bulges; polar rings; young globular clusters; and aging starbursts. Clearly, galaxy formation is a prolonged process, and delayed transformations of galaxies occur to the present time. We remain challenged to understand the meaning of Hubble's morphological sequence, the existence of nearly pure disks, the merger rate, and the relative importance of various forms of interactions.