Galaxy interactions and the stimulation of nuclear activity

The author discusses the idea that interactions between galaxies can lead to enhanced galactic activity. He discusses whether, apart from the observational evidence, there is a strong theoretical or heuristic motivation for investigating galaxy interactions as stimulators of nuclear activity in galaxies. Galactic interactions as mechanisms for triggering nuclear starbursts are covered

Comparative Study of Photosynthesis Rates between Native Red Maple and Invasive Norway Maple in the Eastern Deciduous Forest

Invasive species, such as the Norway Maple, are often able to outcompete native species, such as the Red Maple by performing more efficiently in the environment compared to the native species. In this study, we examined if the Norway maple was able to outcompete the Red Maple in the Eastern Deciduous Forest because the Norway Maple had a higher rate of photosynthesis. The study found that the Norway Maple leaves had a slightly higher rate of carbon dioxide consumption than Red Maple leaves and that the Red Maple leaves had a higher rate of oxygen production compared to the Norway Maples. Since these differences were not statistically significant, the data suggested that the differences in the rate of photosynthesis between the two tree species is most likely very small. This suggests that the rate of photosynthesis is most likely not the advantage Norway Maples have over Red Maples that allows this invader to better compete for space in a forest

The Excess Far-Infrared Emission of AGN in the Local Universe

We have cross-correlated the Sloan Digital Sky Survey (SDSS) second data release spectroscopic galaxy sample with the IRAS faint-source catalogue (FSC). Optical emission line ratios are used to classify the galaxies with reliable IRAS 60 and 100 microns detections into AGN and normal star-forming galaxies. We then create subsamples of normal galaxies and AGN that are very closely matched in terms of key physical properties such as stellar mass, redshift, size, concentration and mean stellar age (as measured by absorption line indicators in the SDSS spectra). We then quantify whether there are systematic differences between the IR luminosities of the galaxies and the AGN in the matched subsamples. We find that the AGN exhibit a significant excess in far-IR emission relative to the star-forming galaxies in our sample. The excesses at 60 and 100 microns are 0.21 +/- 0.03 dex and 0.12 +/- 0.035 dex in log[L(60)/M*] and log[L(100)/M*], respectively. We then discuss whether the far-IR excess is produced by radiation from the active nucleus that is absorbed by dust or alternatively, by an extra population of young stars that is not detectable at optical wavelengths.Comment: 12 pages, 14 figures, accepted by MNRA