We conducted a large spectroscopic survey of 336 red giants in the direction of the Leo II dwarf galaxy using Hectochelle on the Multiple Mirror Telescope, and we conclude that 175 of them are members based on their radial velocities and surface gravities. Of this set, 40 stars have never before been observed spectroscopically. The systemic velocity of the dwarf is 78.3 +/- 0.6 km s(-1) with a velocity dispersion of 7.4 +/- 0.4 km s(-1). We identify one star beyond the tidal radius of Leo II but find no signatures of uniform rotation, kinematic asymmetries, or streams. The stars show a strong metallicity gradient of -1.53 +/- 0.10 dex kpc(-1) and have a mean metallicity of -1.70 +/- 0.02 dex. There is also evidence of two different chemodynamic populations, but the signal is weak. A larger sample of stars would be necessary to verify this feature.

We present a chemodynamical analysis of the Leo V dwarf galaxy, based on the Keck II DEIMOS spectra of eight member stars. We find a systemic velocity for the system of nu(r) = 170.9(+2.1) (-1.9) km s(-1) and barely resolve a velocity dispersion for the system, with sigma nu(r) = 2.3(+3.2) (-1.6) km s(-1), consistent with previous studies of Leo V. The poorly resolved dispersion means we are unable to adequately constrain the dark-matter content of Leo V. We find an average metallicity for the dwarf of [ Fe/ H] =-2.48 +/- 0.21 and measure a significant spread in the iron abundance of its member stars, with -3.1 <= [ Fe/ H] <=-1.9 dex, which clearly identifies Leo V as a dwarf galaxy that has been able to self-enrich its stellar population through extended star formation. Owing to the tentative photometric evidence for the tidal substructure around Leo V, we also investigate whether there is any evidence for tidal stripping or shocking of the system within its dynamics. We measure a significant velocity gradient across the system, of dv d chi = -4.1(+2.8) (-2.6) km s(-1) arcmin(-1) ( or d nu/d chi=-71.9(vertical bar 50.8) (-45.6) km s(-1) kpc(-1)), which points almost directly towards the Galactic Centre. We argue that Leo V is likely a dwarf on the brink of dissolution, having just barely survived a past encounter with the centre of the Milky Way.

We present results from MMT/Hectochelle spectroscopy of 390 red giant candidate stars along the line of sight to the recently discovered Galactic satellite Crater 2. Modeling the joint distribution of stellar positions, velocities, and metallicities as a mixture of Crater 2 and Galactic foreground populations, we identify similar to 62 members of Crater 2, for which we resolve a line-of-sight velocity dispersion of sigma(nu los) = 2.7(-0.3)(+0.3) km s(-1) and a. mean velocity of <nu(los)> = 87.5(-0.4)(+0.4) km s(-1) (solar rest frame). We also resolve a metallicity dispersion of sigma([Fe/H]) = 0.22(-0.03)(+0.04) dex and a mean of <[Fe/H]> = 1.98(-0.1)(+0.1) dex that is 0.28 +/- 0.14 dex poorer than estimated from photometry. Despite Crater 2's relatively large size (projected halflight radius R-h similar to 1 kpc) and intermediate luminosity (M-V similar to -8), its velocity dispersion is the coldest that has been resolved for any dwarf galaxy. These properties make Crater 2 the most extreme low-density outlier in dynamical as well as structural scaling relations among the Milky Way's dwarf spheroidals. Even so, under assumptions of dynamical equilibrium and negligible contamination by unresolved binary stars, the observed velocity distribution implies a gravitationally dominant dark matter halo, with a dynamical mass of. 4.4(-0.9)(+1.2) x 10(6) M-circle dot and a mass-to-light ratio of 53(-11)(+15) M-circle dot/L-V,L-circle dot enclosed within a radius of similar to 1 kpc, where the equivalent circular velocity is 4.3(-0.5)(+0.5) km s(-1).

We present VIMOS-Very Large Telescope (VLT) spectroscopy of the Frontier Fields cluster MACS. J0416.1-2403 (z = 0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts over similar to 600 arcmin(2), including similar to 800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to similar to 2.2 r(200) (similar to 4Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster (M-200 similar to 0.9 x 10(15) M-circle dot and sigma(V r200) similar to 1000 km s(-1)) presenting two major features: (i) a bimodal velocity distribution, showing two central peaks separated by Delta V-rf similar to 1100 km s(-1) with comparable galaxy content and velocity dispersion, and (ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent sub-clump similar to 600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low-mass structure at z similar to 0.390, similar to 10' south of the cluster center, projected at similar to 3Mpc, with a relative line-of-sight velocity of Delta V-rf similar to 1700 km s(-1). The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the "universal" NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal an overall complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in agreement with recent findings from radio and deep X-ray data. In this article, we also release the entire redshift catalog of 4386 sources in the field of this cluster, which includes 60 identified Chandra X-ray sources and 105 JVLA radio sources.

We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a data set that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch data set, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from 0.30(-0.10)(+0.09) to 0.34(-0.11)(+0.11), depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (similar to 0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km s(-1) and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of three. for binary fractions on the higher end of what has been seen in other dwarf spheroidals.

Using a sample of nearly half a million galaxies, intersected by over 7 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we trace H alpha + [N II] emission from a galactocentric projected radius, r(p), of 5 kpc to more than 100 kpc. The emission flux surface brightness is alpha r(p) 1.9 +/- 0.4. We obtain consistent results using only the Ha or [N II] flux. We measure a stronger signal for the bluer half of the target sample than for the redder half on small scales, r(p) < 20 kpc. We obtain a 3 sigma detection of H alpha + [N II] emission in the 50-100 kpc r(p) bin. The mean emission flux within this bin is (1.10 +/- 0.35) x 10(-20) erg cm(-2) s(-1) angstrom(-1), which corresponds to 1.87 x 10(-20) erg cm(-2) s(-1) arcsec(-2) or 0.0033 Rayleigh. This detection is 34 times fainter than a previous strict limit obtained using deep narrow-band imaging. The faintness of the signal demonstrates why it has been so difficult to trace recombination radiation out to large radii around galaxies. This signal, combined with published estimates of n(H), leads us to estimate the temperature of the gas to be 12,000 K, consistent with independent empirical estimates based on metal ion absorption lines and expectations from numerical simulations.

We use the APOSTLE suite of cosmological simulations to examine the role of the cosmic ionizing background in regulating star formation (SF) in low-mass LCDM halos. In agreement with earlier work, we find that, after reionization, SF can only proceed in halos whose mass exceeds a redshift-dependent ``critical'' virial mass determined by the structure of LCDM halos and the thermal pressure of UV-heated gas. This critical mass increases from Mcrit~10^8 Msun at z~11$ to ~10^9.7 Msun at z=0, roughly following the average mass growth history of halos in that mass range. This implies that most halos above or below critical at present have remained so since early times. In particular, the halos of most galaxies today were already above-critical (and thus forming stars) at high redshift, providing a simple explanation for the ubiquitous presence of ancient stellar populations in dwarfs, regardless of luminosity. It also implies that Mcrit today represents a ``threshold'' mass below which the fraction of ``dark'' halos increases steeply. Sub-critical halos may still host luminous galaxies if they were above-critical at some point in the past. SF ceases if a halo falls into the sub-critical regime; depending on each halo's accretion history this can occur over a wide range of times, explaining why SF in many dwarfs seems to continue well past the reionization epoch. It also suggests a tantalizing explanation for the episodic nature of SF in some dwarfs, which, in this interpretation, would be linked to temporary halo excursions above and below the critical boundary. In the simulations, Mcrit(z) cleanly separates star-forming from non-star-forming systems at all redshifts, indicating that the ionizing UV background, and not stellar feedback, is what regulates the beginning and the end of SF in the faintest dwarfs. Galaxies in sub-critical halos should make up a sizable population of faint field dwarfs, distinct from those in more massive halos because of their lack of ongoing star formation. Although few such galaxies are known at present, the discovery of this population would provide strong support for our results. / Graduate

Galaxies are natural laboratories for testing fundamental physics on the nature of the dark matter. MOdified Newtonian Dynamics (MOND) has been tested for over 20 years on small and large scales. While there are several versions of how MOND extrapolates to the large scales, and these versions are not yet fully successful, the original Bekenstein-Milgrom version of MOND is fully predictive and works very well on galaxy scales. However, little work has been done to explore this theory beyond fitting the rotation curves and Tully-Fisher relation of isolated disc galaxies. So far little is known of MONDian elliptical galaxies accelerating in any galaxy cluster. A defining feature of MOND is that internal dynamics of the galaxy depends on the overall acceleration of the galaxy. The existence of cuspy triaxial equilibria for elliptical galaxies is the minimal requirement to MOND. With the PhD project here, I constructed and then further studied the evolution and stability of gravitationally bound systems resembling like cuspy elliptical galaxies, both in isolation and when embedded in a uniform external field. I also studied the escape speeds from spiral galaxies, in particular by comparing the potentials of the Milky Way Galaxy in the Cold Dark Matter (CDM) and MOND frameworks.

Early-type galaxies (ETGs) are typically thought of as 'red and dead' with little to no star formation and old stellar populations. Their detailed kinematics measured locally suggest an interesting array of formation mechanisms and high-redshift observations are starting to reveal a two-phase evolutionary path for the most massive galaxies. In this thesis, I take a combined approach to studying the formation of ETGs. I look to distant quiescent galaxies in one of the densest regions of the early Universe and at the fossil record of a local galaxy to shed light on some of the unsolved mysteries of how ETGs evolved. Using the unique multiplexed instrument, the K-band Multi-Object Spectrograph (KMOS), the evolution of galaxies at both low and high redshift were studied as part of this thesis. I maximised the capabilities of this multi-integral field unit (IFU) near-infrared (NIR) instrument to study different aspects of ETG evolution. With 24 separate IFUs, many quiescent galaxies were efficiently observed in a massive high-redshift cluster as part of the KMOS Cluster Survey. Coupling KMOS spectroscopy with Hubble Space Telescope photometry, I studied the ages, kinematics, and structural properties of the galaxies. I then analysed the detailed properties of a massive local ETG with interesting kinematics, IC 1459. Coupling the NIR IFU data from KMOS with a large mosaic of optical data from the Multi-Unit Spectroscopic Explorer, I was able to study the spatially resolved kinematics, stellar populations, and initial mass function of the galaxy. The work presented in this thesis provides some interesting clues as to the formation of ETGs and possible diversity of their evolutionary paths.

One of the key goals of Milky Way science is measuring the distribution of dark matter in the Galaxy. Through the study of Galactic dynamics, inferences can be made about the structure of the Galaxy, and hence the dark matter distribution. To this end, we present a study of methods useful for modelling and understanding dynamical systems in the Galaxy. A natural choice of coordinate system when studying dynamical systems is the canonical system of angle-action coordinates. We present methods for estimating the angle-actions in both axisymmetric and triaxial potentials. These fall into two categories: non-convergent and convergent. The non-convergent methods are fast approaches, mostly based on approximations to Stäckel potentials. We investigate the accuracy of these methods for realistic Galactic potentials. The slower convergent methods operate by constructing generating functions to take us from simple analytically-tractable potentials to our target potential. Tidal streams should prove useful for constraining the large-scale dark matter distribution in the Galaxy. Armed with our new angle-action tools, we investigate the properties of known streams in a realistic Galactic potential. We present a simple algorithm for constraining the Galactic potential using a tidal stream, which exploits the expected structure of a stream in the angle-frequency space of the true potential. We expand this approach into a fully probabilistic scheme that allows for handling of large errors, missing data and outliers. We close by discussing another tool useful for modelling the dynamics of the Galaxy: extended distribution functions for the Galactic disc. We present a simple extension of an action-based distribution function from Binney (2010) that includes metallicity information, and compare the model predictions with current data. These models are essential for incorporating the selection effects of any survey, and reveal the important chemo-dynamic correlations that expose the history and evolution of the Galaxy.