The observational trend that disky elliptical galaxies exhibit younger luminosity- weighted ages than boxy ellipticals is investigated. The presence of a possible young stellar disk embedded in these galaxies is explored by comparing kinematics derived from the near-infrared Calcium II triplet (around 8600 Å) and Hβ (4863 Å) Balmer line, thought to be sensitive to older and younger stars respectively. Using synthetic stellar population spectra of these two wavelength regions, it is found that a young disk component produces observable differences in the kinematics derived from the two wavelength regions. Specifically, very young disks produce differences in the Gauss-Hermite coefficients, h(_3) and h(_4). Disks with an intermediate age produce offsets in the rotation velocities. Older disks produce clear two-component structure in the derived LOSVDs. Thus, diagnostic indicators are established which can be applied to observations. A comparison is presented of the major- and minor-axis kinematics derived from the Calcium II triplet and Hβ absorption features for a small sample of disky elliptical galaxies with enhanced Hβ absorption strength, indicative of a young component. For two galaxies in the sample, NGC 584 and NGC 821, Hβ gives a rotation velocity higher than that from the Calcium II triplet. These offsets are not consistent with the spectral models, since the offsets in velocity are not accompanied by the expected offsets in the other LOSVD parameters. This implies that the disks have either formed over time with a modest star- formation rate; or that the young stars in these systems are present in both the disk and spheroid components. From dynamical modelling of ground-based integral-field spectroscopy combined with HST STIS data, the disky elliptical NGC 821 is found to have a mass-to-light ratio of 4.12± 0.06 in I-band solar units, and harbours a central black hole of mass (3.41 ± 0.68) x 10(^7) M(_ʘ). This black hole mass is consistent with Gebhardt et al. (2002), who use the same STIS data with their independent modelling code. The phase-space distribution of the orbits in the model shows evidence for a two-component structure, which corresponds to a slowly rotating spheroidal component superimposed with a flattened, strongly rotating component. This second component, which has properties similar to a disk, accounts for 15% of the total system mass. Applying the two-component stellar population models, a disk of this mass would have formed 6 Gyr ago to produce the observed Hβ absorption. Such a disk is not consistent with the long-slit observations, as no offset was found between the Calcium II triplet and Hβ velocity dispersions. However, this cannot be strongly excluded due to the effects of metallicity and disk velocity dispersion on the spectral modelling.

No description available.

In this work I have examined the spatially resolved properties of the local early- type galaxy population. Using Hubble Space Telescope and ground based pho- tometry I constructed Jeans Anisotropic Multi Gaussian Expansion models of the SAURON sample of early-type galaxies, from which I determined the depth of the local gravitational potential well, quantified by the local escape velocity, Vesc. I found that Vesc correlated tightly with the three Lick indices: Mgb, Fe5015 and Hβ. The Mgb-Vesc relation within individual galaxies is identical to that between different galaxies; the relation is both local and global. The Mgb-Vesc relation is: log Mgb = (0.35 ± 0.01) log Vesc − (0.41 ± 0.03). While the metallicity, [Z/H] is cor- related with Vesc it does not show the same local and global behaviour. Age (t) and alpha enhancement ([α/Fe]) are only weakly correlated with Vesc. A combination of [Z/H] and t is tightly correlated with Vesc, with scatter comparable to the Mgb-Vesc relation, and does show the local and global behaviour. This combination is given by: log Vesc = 0.85[Z/H] + 0.43 log t. Using the volume limited ATLAS3D sample of 260 local ETGs I examined in detail the behaviour of the Mgb-Vesc relation and its dependence on other galaxy properties. I found that systematic deviations from the relation correlate with the local environmental density and molecular gas mass of a galaxy, and with the local [α/Fe] measurement. I found that there is a population of galaxies that do not follow the relation, found only at Vesc < 400 kms−1. These galaxies have negative gradients, high central Hβ indices and young (t < 3 Gyrs) ages. Using stellar population models I demonstrated that these negative gradient galaxies are perturbed from the relation by recent star formation and will return to the relation as they age. I also describe the observation, reduction and analysis of a new sample of ETGs in the core of the Coma cluster, the highest density environment in the local Universe, observed with the SWIFT Integral Field Spectrograph. I determined the fraction of slow rotators in the sample, comparing it to results from the ATLAS3D survey, and found an enhanced slow rotator fraction in the Coma cluster. I also determined the Fundamental Plane of Coma early-type galaxies, given by: log Re = (1.20 ± 0.22) log σe − (0.79 ± 0.09) log⟨Ie⟩.

In this thesis I present new interferometric ¹²CO observations of 30 early-type galaxies (ETGs). These galaxies were the brightest ~2/3 of CO detected ETGs from the complete, volume limited Atlas^3D survey. By including literature data I construct the largest ever sample of mapped ETGs, containing 41 objects, and use this sample to analyse the morphology, kinematics and origin of the molecular gas. Many of the galaxies in this sample have relaxed molecular discs, but polar structures, rings, bars and disturbed gas distributions are also present. Around half of the galaxies have molecular gas that follows the stellar light profile, similar to molecular gas in spirals, while others have molecular gas excesses, truncations, rings or composite profiles. The molecular gas extent is smaller in absolute terms in ETGs than in late-type galaxies, but the size distributions are similar once scaled by the galaxies optical/stellar characteristic scalelengths. Cluster environments, however, lead to systems having denser, more compact molecular reservoirs. I find that molecular gas is an excellent kinematic tracer, even in high-mass ETGs, and thus molecules may be the kinematic tracer of choice for probing the M/L evolution of galaxies over cosmic-time. I use this knowledge to construct the first ever early-type CO Tully-Fisher relation, and show that it is offset from the Tully-Fisher relation of spirals by 0.98±0.22 magnitudes at Ks-band. I find that a third of my sample galaxies have their molecular and ionised gas kinematically misaligned with respect to the stars, setting a strong lower limit on the importance of externally acquired gas (e.g. from mergers and cold accretion). The origin of the molecular gas seems to depend strongly on environment, with externally acquired material being common in the field but nearly completely absent in Virgo. Furthermore, my results suggest that galaxy mass may be an important independent factor associated with the origin of the gas, with the most massive fast-rotating galaxies in our sample always having kinematically aligned gas.

>Magister Scientiae - MSc

Supergiant stars of spectral types B and A are characterized by variable and structured winds, as revealed by variability of optical and ultraviolet spectral lines. Non- radial pulsations and magnetically supported loops have been proposed as explanations for these phenomena. The latter hypothesis is tested using a time series of 65 high-resolution (λ/∆λ ∼ 65, 000) circular polarization (Stokes I and V ) spectra of the late B type supergiant Rigel (β Ori, B8 Iae), obtained with the instruments ESPaDOnS and Narval at the Canada-France-Hawaii Telescope and the Bernard Lyot Telescope, respectively. Examination of the unpolarized (Stokes I) spectra using standard spectral analysis tools confirms complex line profile variability during the 5 month period of observations; the high spectral resolution allows the identification of a weak, transient Hα feature similar in behaviour to a High Velocity Absorption event. Analysis of the Stokes V spectra using the cross-correlation technique Least Squares Deconvolution (LSD) yields no evidence of a magnetic field in either LSD Stokes V profiles or longitudinal field measurements, with longitudinal field 1σ error bars of ∼ 12 G for individual observations, and a mean field in the best observed period of 3 ± 2 G. Synthetic LSD profiles fit to the observations using a Monte Carlo approach yield an upper limit on the surface dipolar field strength of Bdip ≤ 50 G for most orientations of the rotational and magnetic axes, lowered to Bdip ≤ 35 G if the mean LSD profile from the most densely time-sampled epoch (with an LSD SNR of ∼80,000) is used. A simple two-spot geometry representing the footpoints of a magnetic loop emerging from the photosphere yields upper limits on the spot magnetic fields of 60–600 G, depending on the filling factor of the spots. Given existing measurements of the mass loss rate and the wind terminal velocity, these results cannot rule out a magnetically confined wind as, for Bdip ≤ 15 G, η∗ ≥ 1. However, the detailed pattern of line profile variability seems inconsistent with the periodic wind modulation characteristic of known magnetic early-type stars, suggesting that magnetic fields do not play a dominant role in Rigel’s variable winds. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-04-29 02:10:41.308

This work is focused on a search for strong gravitational lenses in early-type galaxies (ETGs). The total number of samples is 4,706 galaxies encompassing a magnitude range 15.0 < i < 18.0 and colour 3.5 < (u-r) < 5.0. Two databases were employed as the source of K-band images (UKIDSS Large Area Survey) and g, r, i images (SDSS). All samples were fitted to a Sersic component and automatically processed using GALFIT (Peng et al. 2002; Peng et al. 2010) inside a Python script (Appendix A). The first classification generated 259 galaxies which are seen as single galaxies in their K-band images. These galaxies were then reclassified based on image contouring in g, r, i, and K filters and therefore resulted in three categories of samples: Sample A (99 galaxies), Sample B (96 galaxies), and Sample C (64 galaxies).

New results are described for the use of the Hanle effect in the photospheres of oblique magnetic rotators and of the Zeeman effect in stellar wind emission lines.

Stars with spectral type `A' (also called A-type stars or just A-stars) are bright intermediate mass stars (∼1.5-2.5 M⊙) that make up ∼1% of stars within 25 parsecs, and ∼20% of the brightest stars in the night sky (V < 3 mag). Most A-stars rotate rapidly with rotational velocities that range from ∼100 to ∼200 km/s in most cases, but can exceed 300 km/s. Such rapid rotation not only causes a star's observed properties (flux, temperature, and radius) to be inclination dependent, but also changes how the star evolves both chemically and structurally. Herein we conduct an interferometric survey of nearby A-stars using the CHARA Array. The long baselines of this optical/infrared interferometer enable us to measure the angular sizes of stars as small as ∼0.2 mas, and directly map the oblate shapes of rotationally distorted stars. This in turn allows us to more accurately determine their photospheric properties and estimate their ages and masses by comparing to evolution models that account for rotation. To facilitate this survey, we construct a census of all 232 A-stars within 50 parsecs (the 50PASS) and from that construct a sample of A-stars (the OSESNA) that lend themselves to interferometric observations with the CHARA Array (i.e., are in the northern hemisphere and have no known, bright, and nearby companions - 108 stars in total). The observations are interpreted by constructing a physical model of a rapidly rotating star from which we generate both photometric and interferometric model observations for comparison with actual observations. The stellar properties of the best fitting model are then compared to the MESA evolution models to estimate an age and a mass. To validate this physical model and the adopted MESA code, we first determine the ages of seven members of the Ursa Major moving group, which are expected to be coeval. With the exception of one star with questionable membership, these stars show a 1-σ spread in age of 56 Myr. This agreement validates our technique and provides a new estimate of the age for the group of 414 ± 23 Myr. We apply this validated technique to the directly-imaged `planet' host star κ Andromedae and determine its age to be 47+27-40 Myr. This implies the companion has a mass of 22+8-9 MJup and is thus more likely a brown dwarf than a giant planet. In total, we present new age and mass estimates for 55 nearby A-stars including six members of the Hyades open cluster, five stars with the λ Boötis chemical peculiarity, nine stars which have an infrared excess, possibly from a debris disk, and nine pulsating stars.

Star formation in the Milky Way is confined to star-forming regions (OB association, HII regions, and open clusters) in the Galactic plane. It is usually assumed that these regions are found preferably along spiral arms, as is observed in other spiral galaxies. However, young early-type stars are often found at high Galactic latitudes, far away from their birthplaces in the Galactic disc. These stars are called runaway stars, and it is believed that they were ejected from their birth- places early in their lifetimes by one of two mechanisms: ejection from a binary system following the destruction of the massive companion in a supernova type II event (the binary ejection mechanism), or ejection from a dense cluster following a close gravitational encounter between two close binaries (the dynamical ejection mechanism). The aims of our study were: to improve the current understanding of the nature of high Galactic latitude runaway stars, in particular by investigating whether the theoretical ejection mechanisms could explain the more extreme cases; to show the feasibility of using high Galactic latitude stars as tracers of the spiral arms. The main technique used in this investigation was the tracing of stellar orbits back in time, given their present positions and velocities in 3D space. This technique allowed the determination of the ejection velocities, flight times and birthplaces of a sample of runaway stars. In order to obtain reasonable velocity estimates several recent catalogues of proper motion data were used. We found that the evolutionary ages of the vast majority of runaway stars is consistent with the disc ejection scenario. However, we identified three outliers which would need flight times much larger then their estimated ages in order to reach their present positions in the sky. Moreover, the ejection velocity distribution appears to be bimodal, showing evidence for two populations of runaway stars: a “low” velocity population (89 per cent of the sample), with a maximum ejection velocity of about 300 kms−1, and a “high” velocity population, with ejection velo- cities of 400 – 500 kms−1. We argue that the observed bimodality and maximum ejection velocity of 500 kms−1 can be interpreted as a natural consequence of a variation of the binary ejection mechanism. A possible connection between the “high” velocity population and the so-called hypervelocity stars is also explored, resulting in the conclusion that some stars previously identified as hypervelocity may be in fact runaway stars. The feasibility of using stars as tracers of the spiral arms was tested on a local sample, in order to obtain better quality data and larger numbers. We found that the spiral arms pattern speeds estimated from this sample (24.9±5.2 kms−1 kpc−1) and from a selected sample of runaways (22.8 ± 7.8 kms−1 kpc−1) are consistent within the errors and also consistent with other published estimates. We concluded that our estimates combined with the ones obtained in other studies suggest a value in the range 20 − 25 kms−1 kpc−1 for the pattern speed. Moreover, we concluded that an adequate representation of the spiral arms is obtained given the former pattern speed estimate, even when applied to the sample of runaway stars.