Stellar Population Gradients in ULIRGs: Implications for Gas Inflow Timescales

摘要: Using longslit, optical spectra of Ultraluminous Infrared Galaxies (ULIRGs), we measure the evolution in star-formation intensity during galactic mergers. In individual galaxies, resolve kpc scales allowing comparison nucleus, inner disk, and outer disk. We find that strength Hbeta absorption line increases with projected distance from center merger, typically reaching about 9 Angstrom around 10 kpc. At these radii, star formation must have rapidly decreased 300-400 Myr ago; only stellar populations deficient stars more massive than Type A produce such strong Balmer absorption. contrast, history central consistent continuous formation. Our measurements indicate gas depletion occurs disk inwards major This result is merger-induced inflow empirically constrains timescale. Numerical simulations accurately calculate total amount infalling but often assume timescale for infall. These new are therefore to modeling AGN activity.