We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star formation at z similar to 2 to today. Measurements of galaxy rotation velocity V-rot, which quantify ordered motions, and gas velocity dispersion sigma(g), which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift over 0.1 < z < 2.5, spanning 10 Gyr. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported (V-rot > sigma(g)). By z = 2, 50% and 70% of galaxies are rotationally supported at low (10(9)-10(10) M-circle dot) and high (10(10)-10(11) M-circle dot) stellar mass, respectively. For V-rot > 3 sigma(g), the percentage drops below 35% for all masses. From z = 2 to now, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend toward rotational support with time, and higher-mass systems reach it earlier. This is largely due to a mass-independent decline in sigma(g) by a factor of 3 since z - 2. Over the same time period, V-rot increases by a factor of 1.5 in low-mass systems but does not evolve at high mass. These trends in V-rot and sigma(g) are at a fixed stellar mass and therefore should not be interpreted as evolutionary tracks for galaxy populations. When populations are linked in time via abundance matching, sigma(g) declines as before and V-rot strongly increases with time for all galaxy populations, enhancing the evolution in V-rot sigma(g). These results indicate that z = 2 is a period of disk assembly, during which strong rotational support is only just beginning to emerge.

Located in the Large Magellanic Cloud, R136 is a rare example of a nearby young and dense massive star cluster in which individual stars can be resolved. Often suggested as a globular cluster in formation, its study is of great interest and promises to provide insights into the early dynamical evolution of massive star clusters. This is crucial to understand more extreme and distant starburst clusters, which contribute to a significant fraction of all current star formation in the Local Universe, in particular in interacting galaxies. The majority of this thesis is based on multi-epoch spectroscopic observations in and around R136 obtained as part of the VLT-FLAMES Tarantula Survey (VFTS), an ambitious programme which targeted nearly 1 000 massive stars in the intricate 30 Doradus star-forming region. The motivations and observing strategy of this survey, designed to address key questions about the evolution of massive stars and clusters, are first introduced. The data reduction procedures applied to VFTS data are described, with an emphasis on the tasks accomplished in the context of this thesis. The VFTS data are first used to perform a detailed kinematic study of R136, determine its dynamical state, and evaluate the importance of gas expulsion in the early evolution of massive star clusters. Orbital motions of binary stars are found to dominate the line- of-sight velocity dispersion of the cluster, illustrating the risk of interpreting velocity dispersion measurements for unresolved extragalactic young massive clusters. However, once the detected binaries are rejected and the contribution of undetected binaries is accounted for through Monte Carlo simulations, the true velocity dispersion of the cluster is found to be low and consistent with it being in virial equilibrium. This suggests that gas expulsion has not had a dramatic effect on the early dynamical evolution of R136. Using the velocity measurements of R136 as a test case, a maximum likelihood method that fits the velocity dispersion of a cluster from a single epoch of radial velocity data is then tested. The method must be applied with care given the high binary fraction of massive stars and the large uncertainties in their binary orbital parameter distributions, but for typical velocity dispersions of young massive clusters (& 4 kms−1), it is shown that the velocity dispersion can be measured with an accuracy of 40% or better. This offers an efficient way of constraining the dynamics of these systems. The radial velocity measurements of apparently single stars in R136 are also used to investigate the internal rotation of the cluster, a potentially important but largely unexplored characteristic of young clusters. Evidence is found, at the 95% confidence level, for rotation of the cluster as a whole. A simple maximum likelihood method is presented to fit rotation curves to the data, from which a typical rotational velocity of 3 kms−1 is found. When compared to the low velocity dispersion of R136, this suggests that star clusters may form with as much as 20% of their kinetic energy in rotation. Finally, a smaller-scale survey of massive stars in the Wing of the Small Magellanic Cloud is introduced. As an example of the particularly interesting massive binaries that can be revealed by the synergy between large optical spectroscopic surveys of young clusters and observations at other wavelengths, the discovery of a new Be/X-ray pulsar binary and associated supernova remnant is reported. With a long spin period of over 1 000 seconds and a young age of 104 years constrained by its association with the supernova remnant, the pulsar in this system is quickly emerging as a unique object that challenges our understanding of the spin evolution of accreting neutron stars.

We present a recalibration of the M-BH-sigma(star) relation, based on a sample of 16 reverberation-mapped galaxies with newly determined bulge stellar velocity dispersions (sigma(star)) from integral-field spectroscopy (IFS), and a sample of 32 quiescent galaxies with publicly available IFS. For both samples, sigma(star) is determined via two different methods that are popular in the literature, and we provide fits for each sample based on both sets of sigma(star). We find the fit to the active galactic nucleus sample is shallower than the fit to the quiescent galaxy sample, and that the slopes for each sample are in agreement with previous investigations. However, the intercepts to the quiescent galaxy relations are notably higher than those found in previous studies, due to the systematically lower sigma(star) measurements that we obtain from IFS. We find that this may be driven, in part, by poorly constrained measurements of bulge effective radius (r(e)) for the quiescent galaxy sample, which may bias the sigma(star) measurements low. We use these quiescent galaxy parameterizations, as well as one from the literature, to recalculate the virial scaling factor f. We assess the potential biases in each measurement, and suggest f = 4.82 +/- 1.67 as the best currently available estimate. However, we caution that the details of how sigma(star) is measured can significantly affect f, and there is still much room for improvement.

Stars form when filaments and dense cores in molecular clouds fragment and collapse due to self-gravity. In the most basic analyses of gravitational stability, the competition between self-gravity and thermal pressure sets the critical (i.e. maximum stable) mass of spheres and the critical line density of cylinders. Previous work has considered additional support from magnetic fields and turbulence. Here, we consider the effects of non-ionizing radiation, specifically the inward radiation pressure force that acts on dense structures embedded in an isotropic radiation field. Using hydrostatic, isothermal models, we find that irradiation lowers the critical mass and line density for gravitational collapse, and can thus act as a trigger for star formation. For structures with moderate central densities, similar to 10(3) cm(-3), the interstellar radiation field in the Solar vicinity has an order unity effect on stability thresholds. For more evolved objects with higher central densities, a significant lowering of stability thresholds requires stronger irradiation, as can be found closer to the Galactic centre or near stellar associations. Even when strong sources of ionizing radiation are absent or extincted, our study shows that interstellar irradiation can significantly influence the star formation process.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: parachute shedding characteristics; near wake evolution; parachute inflation; canopy breathing; velocity field measurements. Includes bibliographical references (p. 126-131).

Orbit-based modeling is a powerful way to construct dynamical models of galaxies. It has been used to measure the masses of supermassive black holes (SMBHs), constrain dark matter halos, and to recover information about the orbit structure of galaxies. This type of modeling usually goes hand in hand with the study of elliptical galaxies, however its applicability extends much further than this. In this thesis, I apply the well-studied technique of orbit-based modeling to two different types of galaxies—NGC 4594 (Sa) and Fornax (dSph). In NGC 4594, I use orbit-based models to update the mass of the central SMBH, place new constraints on its dark matter halo, and analyze the internal moments of its distribution function. For Fornax, the focus is to determine the shape of the dark matter density profile as well as to learn what we can from the internal moments. / text

We examine the globular cluster system (GCS) of the isolated elliptical NGC 720 using the Gemini Multi-Object Spectrograph (GMOS) and have obtained spectra for 241 candidate globular clusters (GCs) extending to a galactocentric radius of 40 kpc. Of the 241 candidates, 120 are confirmed GCs, where 46 are members of the metal-poor, blue, population and 74 are members of the metal-rich, red, population. A (g-i)=0.50 colour split is used to identify the blue and red populations. We measure the full GCS to have a rotational velocity (Vrot) of 50 +/- 7 km/s with a position angle (PA) of 170 +/- 69 degrees. The red population has a Vrot = 97 +/- 14 km/s with PA = 147 +\- 18 degrees and the blue population has a Vrot = 79 +/- 7 km/s with PA = 89 +/- 18 degrees. The full GCS has an average velocity dispersion of 168 +/- 22 km/s, for the red population is 156 +/- 30 km/s and for the blue population is 181 +/- 33 km/s. The velocity dispersion pro file for all populations is constant with increasing radius, suggesting the presence of a dark matter halo. Using a tracer mass estimator, we have measured the mass out to 40 kpc as 1.8(+0.6/-0.1)x10^12 Msun for a potential which traces the dark matter pro file. We also estimate the M/L_V = 30 - 70. This study extends our survey of GCSs to isolated environments. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-01-31 11:30:54.389

No description available.

The Milky Way (MW) and M31 both harbour massive satellite galaxies, the Large Magellanic Cloud (LMC) and M33, which may comprise up to 10 per cent of their host's total mass. Massive satellites can change the orbital barycentre of the host-satellite system by tens of kiloparsec and are cosmologically expected to harbour dwarf satellite galaxies of their own. Assessing the impact of these effects crucially depends on the orbital histories of the LMC and M33. Here, we revisit the dynamics of theMW-LMC system and present the first detailed analysis of the M31-M33 system utilizing high-precision proper motions and statistics from the dark-matter-only Illustris cosmological simulation. With the latest Hubble Space Telescope proper motion measurements of M31, we reliably constrain M33' s interaction history with its host. In particular, like the LMC, M33 is either on its first passage (t(inf) < 2 Gyr ago) or if M31 is massive (>= 2 x 10(12) M-circle dot), it is on a long-period orbit of about 6 Gyr. Cosmological analogues of the LMC and M33 identified in Illustris support this picture and provide further insight about their host masses. We conclude that, cosmologically, massive satellites such as the LMC and M33 are likely completing their first orbits about their hosts. We also find that the orbital energies of such analogues prefer an MW halo mass similar to 1.5 x 10(12) M-circle dot and an M31 halo mass >= 1.5 x 10(12)M(circle dot). Despite conventional wisdom, we conclude it is highly improbable that M33 made a close (< 100 kpc) approach to M31 recently (t(peri) < 3 Gyr ago). Such orbits are rare (< 1 per cent) within the 4s error space allowed by observations. This conclusion cannot be explained by perturbative effects through four-body encounters amongst the MW, M31, M33, and the LMC. This surprising result implies that we must search for a new explanation for M33' s strongly warped gas and stellar discs.

We present results from a survey of the internal kinematics of 49 star-forming galaxies at z similar to 2 in the CANDELS fields with the Keck/MOSFIRE spectrograph, Survey in the near-Infrared of Galaxies with Multiple position Angles (SIGMA). Kinematics (rotation velocity V-rot and gas velocity dispersion sg) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. We find that by z similar to 2, massive star-forming galaxies (log M-*/M-circle dot less than or similar to 10.2) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation. These massive galaxies have values of V-rot sg that are factors of 2-5 lower than local well-ordered galaxies at similar masses. Such results are consistent with findings by other studies. We find that low-mass galaxies (log M-*/M-circle dot less than or similar to 10.2) at this epoch are still in the early stages of disk assembly: their kinematics are often dominated by gas velocity dispersion and they fall from the Tully-Fisher relation to significantly low values of V-rot. This "kinematic downsizing" implies that the process(es) responsible for disrupting disks at z similar to 2 have a stronger effect and/or are more active in low-mass systems. In conclusion, we find that the period of rapid stellar mass growth at z similar to 2 is coincident with the nascent assembly of low-mass disks and the assembly and settling of high-mass disks.