Dust and Metals in Distant Galaxies

Interstellar dust causes reddening and dimming of light from background objects. To analyze how different the dust in distant galaxies is compared to dust in nearby galaxies, we look at multiple background quasars and try to fit their spectra with various models for known galaxies that have differing dust grain populations combined with a quasar spectrum template. Through fitting these models, we found that dust in most of the foreground galaxies we analyzed is similar to the SMC bar, a relatively thin area selected from the Small Magellanic Cloud (SMC). However, we note that all the objects we studied did not experience much reddening as most of their E(B-V)< 0, and therefore there was little to no dust extinction occurring in those galaxies. On another note, atomic absorption lines arising in gas clouds in foreground galaxies situated along sightlines to quasars can help with understanding the chemical composition of the galaxies. However, the column densities of elements derived from absorption line spectra depend on the atomic data used for the spectroscopic analysis. Many past column density determinations were based on old values of oscillator strengths. We used updated oscillator strengths of the transitions of the dominant ions of various key elements to calculate the changes in the column densities of these elements. We find that in some cases the column density differences arising from the improvements in oscillator strengths can be significant, even >2 times the measurement uncertainties in the original published values of the column densities.