Thesis (Ph.D.)--McMaster University (Canada), 1995. / Source: Dissertation Abstracts International, Volume: 57-03, Section: B, page: 1862. Adviser: W. E. Harris.

>Magister Scientiae - MSc / We have used the Spitzer Survey of Stellar Structure in Galaxies (S⁴G) as a representative sample of the local universe (total of 2352 galaxies in S⁴G) to make a catalog of offset disk barred galaxies. Using the combined variation of the position angle and the ellipticity (provided by ellipse fit) and also through visual inspection, we have been able to identify all offset structures in S⁴G. While primary bars are present in 2=3 of the disk galaxies in the visible universe, offset bars have a much lower fraction. Of the ̴ 1500 (3.6µm images) disk galaxies available in S⁴G, we classified only 49 as offset barred disk galaxies. We have determined basic properties (bar to total luminosity ratio, bar length, disk scale-length and bars of offset bars shape) using GALFIT, a widely used galaxy decomposition software package. Our main conclusion is that all the offset bars are boxy, independent of their offset from the galaxy center, or the mass of the host galaxy. Additionally we find that, the early type offset bars seem to be more boxy than the late types. The comparison of our offset sample with two other samples, respectively, low mass and high mass normal barred galaxies ("normal" for bars located at the photometric center of the host galaxy), reveals them to be at an intermediate position between the two normal samples. The bar length, disk scale-length and bar to total luminosity ratio are on average larger than the low mass normal and smaller than high mass normal barred galaxies. We have found, overall, a tighter correlation between the disk and bar properties for offset bars in comparison to the two normal samples. Our explanation is that, although the offset has no visible impact on the global shape of the bars, the process responsible for these disturbances seems to affect the star formation rate such that their disk and bars are on average more active than the normal barred galaxies in the same mass range, but not enough to surpass normal barred galaxies with much higher mass.

We present IRAM/NOEMA and JVLA observations of the quasar J1342+0928 at z = 7.54 and report detections of copious amounts of dust and [C Pi] emission in the interstellar medium (ISM) of its host galaxy. At this redshift, the age of the universe is 690 Myr, about 10% younger than the redshift of the previous quasar record holder. Yet, the ISM of this new quasar host galaxy is significantly enriched by metals, as evidenced by the detection of the [C 158 mu m cooling line and the underlying far-infrared (FIR) dust continuum emission. To the first order, the FIR properties of this quasar host are similar to those found at a slightly lower redshift (z similar to 6), making this source by far the FIR-brightest galaxy known at z greater than or similar to 7.5. The [C Pi]emission is spatially unresolved, with an upper limit on the diameter of 7 kpc. Together with the measured FWHM of the [C Pi]line, this yields a dynamical mass of the host of <1.5 x 10(11) M-circle dot Using standard assumptions about the dust temperature and emissivity, the NOEMA measurements give a dust mass of (0.6-4.3) x 10(8) M-circle dot The brightness of the [C Pi] luminosity, together with the high dust mass, imply active ongoing star formation in the quasar host. Using [C Pi]-SFR scaling relations, we derive star formation rates of 85-545 M-circle dot yr(-1) in the host, consistent with the values derived from the dust continuum. Indeed, an episode of such past high star formation is needed to explain the presence of similar to 10(8) M-circle dot of dust implied by the observations.

Nearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z(circle dot)/2. Such tests are particularly important for interpreting the surprising high-ionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + logO/H < 8.5) and present uniformly large specific star formation rates (sSFR similar to 10(2) Gyr(-1)). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching CIII] equivalent widths comparable to those seen in systems at z similar to 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + logO/H less than or similar to 8.0 (Z/Z(circle dot) less than or similar to 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.

We present a spectroscopic survey of high-redshift, luminous galaxies over four square degrees on the sky, aiming to build a large and homogeneous sample of Ly alpha emitters (LAEs) at z approximate to 5.7 and 6.5, and Lyman-break galaxies (LBGs) at 5.5 < z < 6.8. The fields that we choose to observe are well studied, such as by the Subaru XMM-Newton Deep Survey and COSMOS. They have deep optical imaging data in a series of broad and narrow bands, allowing for the efficient selection of galaxy candidates. Spectroscopic observations are being carried out using the multi-object spectrograph M2FS on the Magellan Clay telescope. M2FS is efficient enough to identify high-redshift galaxies, owing to its 256 optical fibers deployed over a circular field of view 30' in diameter. We have observed similar to 2.5 square degrees. When the program is completed, we expect to identify more than 400 bright LAEs at z approximate to 5.7 and 6.5, and a substantial number of LBGs at z >= 6. This unique sample will be used to study a variety of galaxy properties and to search for large protoclusters. Furthermore, the statistical properties of these galaxies will be used to probe cosmic reionization. We describe the motivation, program design, target selection, and M2FS observations. We also outline our science goals, and present a sample of the brightest LAEs at z approximate to 5.7 and 6.5. This sample contains 32 LAEs with Ly alpha luminosities higher than 10(43) erg s(-1). A few of them reach >= 3 x 10(43) erg s(-1), comparable to the two most luminous LAEs known at z >= 6, "CR7" and "COLA1." These LAEs provide ideal targets to study extreme galaxies in the distant universe.

We map the star formation history across M31 by fitting stellar evolution models to color-magnitude diagrams of each 83 '' x 83 '' (0.3 x 1.4 kpc, deprojected) region of the Panchromatic Hubble Andromeda Treasury (PHAT) survey outside of the innermost 6' x 12' portion. We find that most of the star formation occurred prior to similar to 8 Gyr ago, followed by a relatively quiescent period until similar to 4 Gyr ago, a subsequent star formation episode about 2 Gyr ago, and a return to relative quiescence. There appears to be little, if any, structure visible for populations with ages older than 2 Gyr, suggesting significant mixing since that epoch. Finally, assuming a Kroupa initial mass function from 0.1 to 100 M-circle dot, we find that the total amount of star formation over the past 14 Gyr in the area over which we have fit models is 5 x 10(10) M-circle dot. Fitting the radial distribution of this star formation and assuming azimuthal symmetry, (1.5 +/- 0.2). x 10(11) M-circle dot of stars has formed in the M31 disk as a whole, (9 +/- 2) x 10(10). M-circle dot of which has likely survived to the present after accounting for evolutionary effects. This mass is about one-fifth of the total dynamical mass of M31.

We describe how to estimate the velocity dispersions of ultradiffuse galaxies (UDGs) using a previously defined galaxy scaling relationship. The method is accurate for the two UDGs with spectroscopically measured dispersions, as well as for ultracompact galaxies, ultrafaint galaxies, and stellar systems with little or no dark matter. This universality means that the relationship can be applied without further knowledge or prejudice regarding the structure of a galaxy. We then estimate the velocity dispersions of UDGs drawn from two published samples and examine the distribution of total masses. We find, in agreement with the previous studies of two individual UDGs, that these systems are dark matter dominated systems, and that they span a range of at least 10(10) < M-200/M-circle dot < 10(12). These galaxies are not, as an entire class, either all dwarfs or all failed L-* galaxies. Estimates of the velocity dispersions can also help identify interesting subsets of UDGs, such as those that are likely to have the largest mass-to-light ratios, for subsequent spectroscopic study.

Imaging with the James Webb Space Telescope (JWST) will allow observations of the bulk of distant galaxies at the epoch of reionization. The recovery of their properties, such as age, color excess E(B-V), specific star formation rate (sSFR), and stellar mass, will mostly rely on spectral energy distribution fitting, based on the data provided by JWST's two imager cameras, namely the Near Infrared Camera (NIRCam) and the Mid Infrared Imager (MIRI). In this work we analyze the effect of choosing different combinations of NIRCam and MIRI broadband filters, from 0.6 to 7.7 mu m, on the recovery of these galaxy properties. We performed our tests on a sample of 1542 simulated galaxies, with known input properties, at z = 7-10. We found that, with only eight NIRCam broadbands, we can recover the galaxy age within 0.1 Gyr and the color excess within 0.06 mag for 70% of the galaxies. Additionally, the stellar masses and sSFR are recovered within 0.2 and 0.3 dex, respectively, at z = 7-9. Instead, at z = 10, no NIRCam band traces purely the lambda > 4000 angstrom regime and the percentage of outliers in stellar mass (sSFR) increases by > 20% (> 90%), in comparison to z = 9. The MIRI F560W and F770W bands are crucial to improve the stellar mass and the sSFR estimation at z = 10. When nebular emission lines are present, deriving correct galaxy properties is challenging at any redshift and with any band combination. In particular, the stellar mass is systematically overestimated in up to 0.3 dex on average with NIRCam data alone and including MIRI observations only marginally improves the estimation.

We construct UV/optical/IR spectral energy distributions for 29 star forming regions in the interacting galaxy Arp 107, using GALEX UV, Sloan Digitized Sky Survey optical, and Spitzer infrared images. In an earlier study utilizing only the Spitzer data, we found a sequence in the mid-infrared colors of star-forming knots along the strong tidal arm in this system. In the current study, we find sequences in the UV/optical colors along the tidal arm that mirror those in the mid-infrared, with blue UV/optical colors found for regions that are red in the mid-infrared, and vice versa. With single-burst stellar population synthesis models, we find a sequence in the average stellar age along this arm, with younger stars preferentially located further out in the arm. Models that allow two populations of different ages and dust attenuations suggest that there may be both a young component and an older population present in these regions. Thus the observed color sequences may be better interpreted as a sequence in the relative proportion of young and old stars along the arm, with a larger fraction of young stars near the end. Comparison with star forming regions in other interacting galaxies shows that the Arp 107 regions are relatively quiescent, with less intense star formation than in many other systems.

We present new radio continuum, 21 cm H I, and 2.6 mm CO data for the peculiar radio galaxy NGC 4410A and its companion NGC 4410B and compare with available optical and X-ray maps. Our radio continuum maps show an asymmetric double-lobed structure, with a high surface brightness lobe extending 3′.6 (∼100 kpc) to the southeast and a 6′.2 (∼180 kpc) low surface brightness feature in the north-west. Molecular gas is abundant in NGC 4410A, with MH2 ∼ 4 × 109 M⊙ (using the standard Galactic conversion factor) but is undetected in NGC 4410B. H I is less abundant, with MHI ∼ 109 M⊙ for the pair. Our H I map shows a 3 × 108 M⊙ H I tail extending 1′.7 (50 kpc) to the southeast of the pair, coincident with a faint optical tail and partially overlapping with the southeastern radio lobe. The H I tail is anticoincident with a 2′ (56 kpc) long X-ray structure aligned with a stellar bridge that connects the pair to a third galaxy. If this X-ray emission is associated with the group, we infer (3-8) × 108 M⊙ of hot gas in this feature. This may be either intracluster gas or shocked gas associated with the bridge. Our detection of abundant interstellar gas in this pair, including an H I-rich tidal tail near the south-eastern radio lobe, suggests that the observed distortions in this lobe may have been caused by the interstellar medium in this system. The gravitational interaction of the two galaxies and the subsequent motion of the interstellar medium in the system relative to the jet may have produced sufficient ram pressure to bend and distort the radio jet. An alternative hypothesis is that the jet was distorted by ram pressure due to an intracluster medium, although the small radial velocity of NGC 4410A relative to the group and the lack of diffuse X-ray emission in the group makes this less likely unless the group is not virialized or is in the process of merging with another group. Using our VLA data, we also searched for H I counterparts to the other 10 known members of the NGC 4410 group and CO from three other galaxies in the inner group. In our velocity range of 6690-7850 km s-1, we detected six other galaxies above our H I sensitivity limits of 2 × 108 M⊙ for the inner group and 4 × 108 M⊙ for the outer group. The total H I in the group is 1.4 × 1010 M⊙, 80% of which arises from four galaxies in the outer group. Three of these galaxies (VCC 822, VCC 831, and VCC 847) are spirals with MHI/LB ratios typical of field galaxies, while FGC 170A appears to be a gas-rich dwarf galaxy (MB ∼ -18, MHI ∼ 3 × 109 M⊙). In the inner group, the SBa galaxy NGC 4410D (VCC 934) was detected in H I and CO (MHI, ∼ 5 × 108 M⊙ and MH2 ∼ 8 × 108 M⊙) and has a 1′ (28 kpc) long H I tail that points toward the nearby disk galaxy NGC 4410F. NGC 4410F was also detected in H I (MHI ∼ 4 × 108 M⊙). The galaxies in the inner group appear to be somewhat deficient in H I compared to their blue luminosities, suggesting phase changes driven by galaxy-galaxy or galaxy-intracluster medium encounters.