Global effects of interactions on galaxy evolution

Recent observations of the evolutionary properties of paired and interacting galaxies are reviewed, with special emphasis on their global emission properties and star formation rates. Data at several wavelengths provide strong confirmation of the hypothesis, proposed originally by Larson and Tinsley, that interactions trigger global bursts of star formation in galaxies. The nature and properties of the starbursts, and their overall role in galactic evolution are also discussed

Revisiting the Integrated Star Formation Law. I. Non-starbursting Galaxies

We use new and updated gas- and dust-corrected star formation rate (SFR) surface densities to revisit the integrated star formation law for local "quiescent" spiral, dwarf, and low surface brightness galaxies. Using UV-based SFRs with individual IR-based dust corrections, we find that "normal" spiral galaxies alone define a tight Σ_(H I + H2)–Σ_(SFR) relation described by an n = 1.41^(+0.07)_(-0.07) power law with a dispersion of 0.28^(+0.02)_(-0.02) (errors reflect fitting and statistical uncertainties). The SFR surface densities are only weakly correlated with H I surface densities alone, exhibiting a stronger and roughly linear correlation with H2 surface densities, similar to what is seen in spatially resolved measurements of disks. However, many dwarf galaxies lie below the star formation law defined by spirals, suggesting a low-density threshold in the integrated star formation law. We consider alternative scaling laws that better describe both spirals and dwarfs. Our improved measurement precision also allows us to determine that much of the scatter in the star formation law is intrinsic, and we search for correlations between this intrinsic scatter and secondary physical parameters. We find that dwarf galaxies exhibit second-order correlations with the total gas fraction, stellar mass surface density, and dynamical time, which may explain much of the scatter in the star formation law. Finally, we discuss various systematic uncertainties that should be kept in mind when interpreting any study of the star formation law, particularly the X(CO) conversion factor and the diameter chosen to define the star-forming disk in a galaxy