The circumgalactic medium (CGM), loosely defined as the region between a galaxy disk and its virial radius, has long been of interest to astronomers and astrophysicists because it acts as an interface between galaxies and their surroundings. Studying it, therefore, gives us hints of how gas flows between galaxies and the intergalactic medium (IGM), fueling star formation for instance. This thesis addresses some of the current and future observation, analysis and instrumentation challenges that should be tackled for a better understanding of the CGM.
Chapter 1 is an overview of science related to the CGM and of instruments that our lab works on: the Circumgalactic Hydrogen-Alpha Spectrograph (CHaS) and the Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall). It sets the ground for a better understanding of the science discussed in subsequent chapters. CHaS is an IFU spectrograph installed on a 2.4 m telescope at the MDM Observatory in Arizona (Melso et al. 2022). It has high sensitivity and high spectral resolution, and it collects individual spectra from points across our targets using a microlens array, allowing us to make detailed spectral maps of observed astronomical objects. FIREBall is a balloon-born UV multi-object spectrograph, allowing us to look at yet another emission line prominent in the CGM. In this thesis, we will focus on what a future FIREBall detector might look like.
Chapters 2 and 3 present data collected with CHaS in November 2021 from two very distinct objects: NGC 6946 (the Fireworks galaxy) and M76 (the Little Dumbbell nebula). Both chapters address how we process spectral data from CHaS images and the subsequent making of velocity maps. Using CHaS images, we tackle anomalous gas motion and formations in both targets. We compared the data presented in both chapters to previous literature, showing that CHaS velocity maps were more detailed and complimented previous findings.
NGC 6946 is known for being a prolific star forming galaxy and also for having holes in its HI distribution, which have historically been attributed to the expansion and bursting of gas bubbles. In Chapter 2, we find that the motion around these holes is indeed consistent with expanding bubbles and galactic fountains on their edges, with velocities in the -20 km/s to 20 km/s range, consistent with what Boomsma et al. (2008) found, going up to +/-60 km/s, similar to the velocities found by Efremov et al. (2002). We also found that Long et al. (2019)'s supernova remnants candidates catalog had a clear position correlation with the boundaries of different holes in the Boomsma et al. (2008) HI hole catalog, suggesting that these holes might indeed be related to gas bubbles resulting from supernova explosions.
The Little Dumbbell nebula, on the other hand, show its own set of anomalies. M76 is a butterfly planetary nebula with a central torus and two polar lobes. We find that these lobes are not completely symmetric. In fact, the wester lobe is more rounded and the eastern one is more stretched and fragmented. From our velocity maps, we propose a couple of explanations for how the ISM might interact with the nebula both in the core star's AGB phase and after the nebula is formed to give M76 its shape. Both explanations vary depending on the assumed direction of motion of the star in it its AGB phase, but both are consistent with models by Villaver, Manchado and García-Segura (2012) and Wareing et al. (2007). Moreover, we compare our data to those of other authors and find similar velocity ranges around an axis going from one lobe to another as spectral maps made by Ramos-Larios et al. (2017) and Bryce et al. (1996).
Departing from observational data analysis, Chapter 4 focuses on how we can probe further into the CGM by upgrading existing instruments, turning commonplace condensed matter methods into tools for astrophysics. More specifically, Chapter 4 discusses the possibility of switching FIREBall's current UV sensitive emCCD detectors, which rely on coating to be visible-blind and on cryogenic equipment that is heavy for a balloon flight, for devices made out of hexagonal boron nitride (hBN). hBN's main energy bandgap overlaps with the emission lines that FIREBall is interested in capturing, and it can be combined with graphene (which is isomorphic to hBN) to make high quality, quantum efficient devices. While we weren't able to finish full devices, Chapter 4 discusses their fabrication in detail as well as how our Siesta SISL simulations show that even small device defects might be acceptable for a detector. The chapter ends with considerations about how one might fit individual devices as multi-pixel detectors.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/0fb7-nc49 |
| Date | January 2023 |
| Creators | Cruvinel Santiago, Bárbara |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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