The properties of astrophysical masers are governed by the physical conditions of circumstellar envelopes of evolved stars, implying a connection between maser and mass-loss phenomena. Although similar studies to another type of mass-losing star, Asymptotic Giant Branch (AGB) stars, have been conducted, a quantitative understanding for the case of Red Supergiants (RSGs) is still largely lacking. Recently, more and more galactic massive clusters are discovered and studied, which provide a coeval environment to investigate the evolution of cool massive evolved stars with similar distance and metallicity. Among them, Westerlund 1 (Wd1) is one of the most massive open clusters, classified as Super Star Clusters (SSCs), within the Milky Way harboring 4 RSGs. We have 2 goals in this project. We aim to investigate the relationship between SiO maser detection and mass-loss behavior of RSGs in massive clusters, in order to explore the possibility of developing SiO maser as an evolutionary indicator of RSGs. We also aim to determine the kinematic properties of Wd1 with the aid of SiO maser. We report on observation of 43 GHz SiO (v = 1, J = 1–0) maser towards Wd1 conducted with Australia Telescope Compact Array (ATCA). We also make use of archival 22 GHz H2O maser (616–523) in help of studying kinematic of Wd1. We derive the maser detection information and stellar velocities from maser data. We also compile an extra sample of 36 RSGs, which surveyed in SiO maser before, within massive clusters, e.g. Red Supergiant Cluster 1 (RSGC1), Red Supergiant Cluster 2 (RSGC2), Perseus OB association 1 (Per OB 1) and Mercer et al.’s #8 (Mc8), and organize their photometric data from 2MASS, GLIMPSE, MSX, AKARI and WISE to derive their spectral energy distributions (SEDs). Luminosity, effective temperature and mass-loss rate are derived from fitting the SEDs with DUSTY model in order to search for correlations between mass-loss rate, SiO maser properties and evolution of RSGs. We detected SiO maser emission towards 2 RSGs (W 237 and W 26) in Wd1. These 2 RSGs also emit H2O maser as revealed from archival H2O maser observation data. We noticed that SiO masers tend to be detected towards RSGs with higher luminosity and mass-loss rate. We also determined the kinematic distance of Wd1 to be 3.3 kpc. From that result, we conclude that SiO maser is an effective evolution indicator for RSGs, which traces RSGs with high massloss rate. We also show that the age of RSGs in Wd1 is 10 ± 2 Myr which support the multi-generation star formation scenario in Wd1. / published_or_final_version / Physics / Master / Master of Philosophy

Bright optical nebulae are a relatively common feature of galaxy clusters with a central depression in their intracluster gas temperature suggestive of an X-ray cooling flow. In my thesis, I have measured, for the first time, the velocity field of nearly the entire optical nebula associated with NGC 1275, the central cD (giant elliptical) galaxy of the Perseus cluster. This nebula is the brightest example with the largest projected size in the sky. Our primary scientific objective is to address the physical processes that give rise to the complex morphology of this nebula, which comprises a multitude of mostly approximately radial but also a number of tangential emission-line _laments. This nebula spans up to ～140 kpc in the north-south direction, extending far beyond the half-light radius of NGC 1275. Popular models for the nature of the nebula invoke either an X-ray cooling flow, in which case the filaments should possess a velocity profile consistent with free fall, or gas drawn out from the central galaxy by buoyantly rising bubbles inflated by radio jets from the AGN, in which case the filaments should show a reversal in velocity along their lengths. We find that the velocity field of the nebula is incredibly complex, and in several important respects contradicts model predictions based on slit spectroscopy. We find that filaments previously thought to be very long integral structures actually comprise multiple shorter filaments that each have their own distinct kinematics. Furthermore, filaments that are apparently aligned and adjacent to each other often possess entirely different kinematics. We searched for filaments with velocity profiles consistent with free fall, but we could only find very few examples beyond the central bright nebular region where overlapping filaments complicate measurements of the individual filament kinematics. We also searched for filaments that show a reversal in velocity along their lengths, but again could find only several examples. Although the combination of a residual X-ray cooling flow and relatively cool gas drawn out by buoyant X-ray bubbles remains the most viable explanation for the nature of the nebula, both the morphology and kinematics of this nebula is complicated by the action of various X-ray bubbles that are currently expanding or rising through the nebula. As such, the velocity field of the filaments reflect the effects of the X-ray bubbles on the bulk flows within the intracluster medium, and trace streamlines that reveal motions in the surrounding X-ray gas. We point out evidences that support the idea that some filaments are being dragged by rising X-ray bubbles, others represent large-scale vortices behind bubbles, and yet others are draping the surface of and pushed outwards by expanding X-ray bubbles. / published_or_final_version / Physics / Master / Master of Philosophy

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In this thesis, I explore how the environments of both galaxy and cluster-scale strong gravitational lenses affect studies of cosmology and the properties of the earliest galaxies.Galaxy-scale lenses with measured time delays can be used to determine the Hubble constant, given an accurate lens model. However, perturbations from structures along the line of sight can introduce errors into the measurement. I use data from a survey towards known lenses in group environments to calculate the external shear in these systems, which is typically marginalized over in standard lens analyses. In three of six systems where I compare the independently-calculated environment shear to lens model shears, the quantities disagree at greater than 95% confidence. We explore possible sources of this disagreement. Using these data, I generate fiducial lines of sight and insert mock lenses with assumed input physical and cosmological parameters and find that those parameters can be recovered with∼ 5-10% scatter when uncertainties in my characterization of the environment are applied. The lenses in groups have larger bias and scatter. I predict how well new time delay lenses from LSST will constrain H_0 and find that an ensemble of 500 quad lenses will recover H_0 with∼ 2% bias with∼ 0.3% precision.On larger scales, galaxy cluster lenses can magnify the earliest galaxies into detectability. While past studies have focused on single massive clusters, I investigate the properties of lines of sight, or ``beams", containing multiple cluster-scale halos in projection. Even for beams of similar total mass, those with multiple halos have higher lensing cross sections on average. The optimal configurations for maximizing the cross section are also those that maximize faint z∼ 10 detections. I present a new selection technique to identify beams in wide-area photometric surveys that contain high total masses and often multiple clusters in projection as traced by luminous red galaxies. I apply this technique to the Sloan Digital Sky Survey and present the 200 most promising beams. Several are confirmed spectroscopically to be among the highest mass beams known with some containing multiple clusters. These are among the best fields to search for faint high-redshift galaxies.