Neutral Gas Outflows and Inflows in Local AGN & High-z Lyman-alpha Emitters in COSMOS
Krug, Hannah Bowen
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This thesis is composed of two parts: (1) a search for neutral gas outflows and inflows in local active galactic nuclei (AGN) and ultraluminous infrared galaxies (ULIRGs), and (2) a deep and wide imaging search for high-redshift Lyman-alpha emitters (LAEs). In the first part, we utilize the R-C spectrograph on the Mayall 4m telescope at Kitt Peak National Observatory (KPNO) to look for Na I D absorption. Galactic outflows are thought to play a major role in galactic feedback and evolution, and previous studies of neutral gas have shown that galactic winds occur in most galaxies with high infrared (IR) luminosities. However, in composite systems where a starburst coexists with an active galactic nucleus (AGN), it is unclear whether the starburst or the AGN is driving the outflows. This thesis attempts to answer that question by looking at samples of Seyfert galaxies, Palomar-Green quasistellar objects (PG QSOs), and ULIRGs. We first describe the results from a search for Na I D outflows in 35 IR-faint Seyferts. We find that the outflow detection rates for IR-faint Seyferts are substantially lower than those of IR-luminous Seyferts. The outflow kinematics of Seyfert 2s resemble those of starburst galaxies, while the outflow velocities in Seyfert 1s are significantly larger. Taken together, these results suggest that the AGN does not play a significant role in driving the outflows in most Seyferts, except the high velocity outflows seen in Seyfert 1s. We also find high rates of detection of inflows in IR-faint Seyferts. We then perform the same analysis on a sample of 28 PG QSOs and 10 ULIRGs; this sample was taken from a survey of gas-rich mergers. When we combine our data with our Seyfert study results, as well as previous work, we note three important trends. We find that outflows in IR-luminous AGN and IR-luminous starbursts appear to be driven by fundamentally different processes, the AGN and star formation, respectively. We find the same distinction for outflows in AGN with optical spectral types of Type 1 (AGN) and Type 2 (star formation). We note fundamental differences between outflows in objects which have already undergone mergers versus those which have not. In the second part of this thesis, we search for z = 7.7 LAEs in the COSMOS field. These objects are useful probes of the epoch of reionization, as the Lya line should be attenuated by the intergalactic medium (IGM) at low to moderate neutral hydrogen fractions (xHI). We have utilized two ultra-narrowband filters on the NEWFIRM camera in order to isolate LAEs at z = 7.7. We find 5-sigma detections of four candidate LAEs in a survey volume of 2.8 x 10^4 Mpc^3. Using these results to construct a Lya luminosity function (LF) and comparing to previously established LFs at z = 5.7 and z = 6.5, we find no conclusive evidence for evolution of xHI over 5.7 < z < 7.7. Finally, we use a combination of imaging and spectroscopy to follow up those results, noting that, while imaging can rule out a candidate from being considered a high-redshift LAE, only spectroscopy can confirm that a target is indeed at z = 7.7. Imaging follow-up has essentially ruled out one candidate. We then perform spectroscopic follow-up with GNIRS on the Gemini-North telescope on our second brightest candidate. We fail to detect that candidate after 2.5 hours of integration; spectroscopic follow-up performed by collaborators on our two brightest candidates also yielded non-detections. We are thus left with only one viable z = 7.7 candidate. Such null results are consistent with other attempts detailed in the literature, implying that reionization is still ongoing.