Understanding Star Formation and AGN Activity at Z~2-3

Book excerpt: There is compelling evidence that the growth of supermassive black holes and the stellar populations of their host galaxies are intricately linked. At the same time, the exact relationship between the buildup of stellar mass and the growth of supermassive black holes is still not well understood. At z ~ 2, both star-formation and Active Galactic Nuclei (AGN) activity in the universe were at peak levels, and this epoch is ideal for exploring the coevolution of stars and supermassive black holes. This dissertation examines high-redshift galaxies, looking at the particular properties of star-forming galaxies, the stellar populations of AGNs and the relationship between black hole and star-formation activity at z ~ 2 - 3. I have used the magnification afforded by gravitational lensing of z ~ 2 star-forming galaxies to measure important physical properties of the stars and gas in these galaxies. Using near-IR spectroscopy, I have calculated the metallicities, ionization parameters, star-formation rates, and dynamical masses for two galaxies which help to explain the differences between local- and high-redshift star-forming galaxies. The third and fourth chapters of this work cover the analysis of a sample of z ~ 2 - 3 AGNs drawn from the UV-selected Lyman Break Galaxy (LBG) survey. I present a rest-frame UV composite spectrum for this sample of AGNs. This spectrum shows many emission and absorption features, such as HI Lyman-alpha, NV1240, NIV]1483,1486, CIV1548,1550, HeII1640, and CIII]1907,1909. Redshifted SiIV1394 absorption provides evidence for outflowing high-ionization gas in these objects at speeds of 10^3 km/s. Finally, by using optical, near-IR, and mid-IR photometry, which covers the rest-frame UV to near-IR portions of the galaxies spectral energy distributions, I have modeled the SEDs of the AGNs that comprise this sample. I have developed a unique dual-component modeling approach that allows me to correct for the presence of an AGN. Based on these results, I have explored the relationship in the host galaxy between AGN activity, maturity of the stellar population, and regulation of star formation.