Browsing by Author "Snyder, Gregory F."

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    HI versus Hα - comparing the kinematic tracers in modelling the initial conditions of the Mice
    (2018) Mortazavi, S. Alireza; Lotz, Jennifer M.; Barnes, Joshua E.; Privon, George C.; Snyder, Gregory F.
    We explore the effect of using different kinematic tracers (HI and Ha) on reconstructing the encounter parameters of the Mice major galaxy merger (NGC 4676A/B). We observed the Mice using the SparsePak Integral Field Unit (IFU) on the WIYN telescope, and compared the Ha velocity map with VLA H I observations. The relatively high spectral resolution of our data (R approximate to 5000) allows us to resolve more than one kinematic component in the emission lines of some fibres. We separate the H alpha-[N II] emission of the star-forming regions from shocks using their [NII]/H alpha line ratio and velocity dispersion. We show that the velocity of star-forming regions agree with that of the cold gas (H I), particularly, in the tidal tails of the system. We reconstruct the morphology and kinematics of these tidal tails utilizing an automated modelling method based on the IDENTIKIT software package. We quantify the goodness of fit and the uncertainties of the derived encounter parameters. Most of the initial conditions reconstructed using H alpha and HI are consistent with each other, and qualitatively agree with the results of previous works. For example, we find 210 +/-(50)(40) Myr, and 180 +/-(50)(40) Myr for the time since pericentre, when modelling H alpha and HI kinematics, respectively. This confirms that in some cases, H alpha kinematics can be used instead of HI kinematics for reconstructing the initial conditions of galaxy mergers, and our automated modelling method is applicable to some merging systems.
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    Investigating the Effect of Galaxy Interactions on the Enhancement of Active Galactic Nuclei at 0.5 < z < 3.0
    (2020) Shah, Ekta A.; Kartaltepe, Jeyhan S.; Magagnoli, Christina T.; Cox, Isabella G.; Wetherell, Caleb T.; Vanderhoof, Brittany N.; Calabro, Antonello; Chartab, Nima; Conselice, Christopher J.; Croton, Darren J.; Donley, Jennifer; de Groot, Laura; de la Vega, Alexander; Hathi, Nimish P.; Ilbert, Olivier; Inami, Hanae; Kocevski, Dale D.; Koekemoer, Anton M.; Lemaux, Brian C.; Mantha, Kameswara Bharadwaj; Marchesi, Stefano; Martig, Marie; Masters, Daniel C.; McGrath, Elizabeth J.; McIntosh, Daniel H.; Moreno, Jorge; Nayyeri, Hooshang; Pampliega, Belen Alcalde; Salvato, Mara; Snyder, Gregory F.; Straughn, Amber N.; Treister, Ezequiel; Weston, Madalyn E.
    Galaxy interactions and mergers are thought to play an important role in the evolution of galaxies. Studies in the nearby universe show a higher fraction of active galactic nuclei (AGNs) in interacting and merging galaxies than in their isolated counterparts, indicating that such interactions are important contributors to black hole growth. To investigate the evolution of this role at higher redshifts, we have compiled the largest known sample of major spectroscopic galaxy pairs (2381 with Delta V < 5000 km s(-1)) at 0.5 < z < 3.0 from observations in the COSMOS and CANDELS surveys. We identify X-ray and IR AGNs among this kinematic pair sample, a visually identified sample of mergers and interactions, and a mass-, redshift-, and environment-matched control sample for each in order to calculate AGN fractions and the level of AGN enhancement as a function of relative velocity, redshift, and X-ray luminosity. While we see a slight increase in AGN fraction with decreasing projected separation, overall, we find no significant enhancement relative to the control sample at any separation. In the closest projected separation bin (< 25 kpc, Delta V < 1000 km s(-1)), we find enhancements of a factor of 0.94(-0.16)(+0.21) and 1.00(-0.31)(+0.58) for X-ray and IR-selected AGNs, respectively. While we conclude that galaxy interactions do not significantly enhance AGN activity on average over 0.5 < z < 3.0 at these separations, given the errors and the small sample size at the closest projected separations, our results would be consistent with the presence of low-level AGN enhancement.