UCLA

This thesis presents Adaptive Optics (AO) imaging and spectroscopic measurements of infrared excess sources in the Galactic Center to determine if they are similar to G2, the first example of a spatially-resolved object interacting with the supermassive black hole at the center of the Galaxy, Sgr A$^{*}$. Our goal is to understand the debated nature of these infrared excess sources and to understand their relationship with the supermassive black hole. Our objects have been monitored with AO from he past decade (2004 - 2015) and are within the inner 1\farcs75 of the supermassive black hole.

We initially focus on one source, G1, which gets comparably close to the supermassive black hole compared to G2 ($a_{min}\sim200-300$ AU) and lies on a very eccentric orbit ($e_{G1} = 0.99$). While G2 has been tracked before and during periapse passage ($T_{0} \sim$ 2014.2), G1 has been followed since soon after emerging from periapse ($T_{0} \sim$ 2001.3). Our observations of G1 double the previously reported observational time baseline, which improves its orbital parameter determinations. G1's orbital trajectory appears to be in the same plane as that of G2, but with a significantly different argument of periapse ($\Delta\omega$ = 21$\pm$4 degrees). This suggests that G1 is an independent object and not part of a gas stream containing G2 as has been proposed. Furthermore, we show for the first time that: (1) G1 is extended in the early epochs (those closest to periapse) along the direction of orbital motion and (2) G1 becomes significantly smaller over time, changing from 450 AU in 2004 to less than 170 AU in 2009 and thereafter. Based on these observations, G1 appears to be the second example of an object tidally interacting with a supermassive black hole. G1's continued survival 14 years after periapse, along with its compactness in epochs further from the time of periapse, suggests that this source is stellar in nature and may be consistent with a black-hole driven stellar binary merger induced by the Kozai mechanism.

We then observationally characterize several other infrared excess sources to see whether or not they share similar properties. We find another source, G3, has nearly identical observation properties to G1 and G2 but lies further away from Sgr A${*}$. G3 does not lie on the same orbital plane to G1 or G2 at all, suggesting that these objects do not necessarily all come from the same region. G3 does not lie on a highly eccentric orbit at all ($e\sim0.4$) and its periapse passage distance is significantly further away than G1 or G2 ($a_{min}\sim5000$ AU). Several other sources also exhibit Br-$\gamma$ emission, but also do not lie on the same orbital plane as G1 or G2.

G3 and other infrared excess sources supports the hypothesis that there is a population of objects that share similar observational qualities to G1 and G2 -- high infrared luminosities, cold dust temperatures, and Br-$\gamma$ emission line features. These new objects might therefore exist as a new population of sources in the Galactic center, and might not necessarily have the same physical manifestation.