Speaker
Stephanie Juneau
(CEA Saclay)
Description
Nebular line diagnostic diagrams probing the physical state of the ISM and/or the ionization sources in galaxies (star formation versus active galactic nuclei [AGN]) have been used extensively yet their behavior and interpretation at high redshifts are poorly understood. We present an empirical approach that takes into account both selection effects - due to emission line detection limit - and evolution of the galaxy population as a whole. Our approach is based on low-redshift analogs among >200,000 SDSS galaxies, and applied to galaxy samples out to z~2. As a result, we can not only predict the loci of higher-redshift galaxies on the traditional BPT and other diagnostic diagrams, we also gain a better understanding of the physical conditions of the interstellar gas in galaxies and the presence of AGN. Overall, this work supports evolution toward a lower electron density and ionization parameter with cosmic time, indicating a more diffuse geometry of the star-forming regions at the current epoch relative to early times, when galaxies would form their stars with a higher surface density, greatly affecting the ISM properties on galaxy-wide scales.
Author
Stephanie Juneau
(CEA Saclay)