We present Spitzer infrared, Galaxy Evolution Explorer UV, and Sloan Digitized Sky Survey and Southeastern Association for Research in Astronomy optical images of the peculiar interacting galaxy pair Arp 285 (NGC 2856/4), and compare with a new numerical model of the interaction. We estimate the ages of clumps of star formation in these galaxies using population synthesis models, carefully considering the uncertainties on these ages. This system contains a striking example of "beads on a string": a series of star-formation complexes 1 kpc apart. These "beads" are found in a tail-like feature that is perpendicular to the disk of NGC 2856, which implies that it was formed from material accreted from the companion NGC 2854. The extreme blueness of the optical/UV colors and redness of the mid-infrared colors implies very young stellar ages (4-20 Myr) for these star-forming regions. Spectral decomposition of these "beads" shows excess emission above the modeled stellar continuum in the 3.6 μm and 4.5 μm bands, indicating either contributions from interstellar matter to these fluxes or a second older stellar population. These clumps have -12.0 < M B< -10.6, thus they are less luminous than most dwarf galaxies. Our model suggests that bridge material falling into the potential of the companion overshoots the companion. The gas then piles up at apogalacticon before falling back onto the companion, and star formation occurs in the pile-up. There was a time delay of 500 Myr between the point of closest approach between the two galaxies and the initiation of star formation in this feature. A luminous (M B -13.6) extended (FWHM 1.3 kpc) "bright spot" is visible at the northwestern edge of the NGC 2856 disk, with an intermediate stellar population (400-1500 Myr). Our model suggests that this feature is part of a expanding ripple-like "arc" created by an off-center ring-galaxy-like collision between the two disks.

We present Spitzer mid-infrared imaging of a sample of 35 tidally distorted premerger interacting galaxy pairs selected from the Arp Atlas. We compare their global mid-infrared properties with those of normal galaxies from the SINGS Spitzer Legacy survey, and separate the disk emission from that of the tidal features. The [8.0 μm] - [24 μm], [3.6 μm] - [24 μm], and [5.8 μm] - [8.0 μm] colors of these optically selected interacting galaxies are redder on average than those of spirals, implying enhancements to the mass-normalized star formation rates (SFRs) of a factor of ∼2. Furthermore, the 24 μm emission in the Arp galaxies is more centrally concentrated than that in the spirals, suggesting that gas is being concentrated into the inner regions and fueling central star formation. No significant differences can be discerned in the shorter wavelength Spitzer colors of the Arp galaxies compared to the spirals, and thus these quantities are less sensitive to star formation enhancements. No strong trend of Spitzer color with pair separation is visible in our sample; this may be because our sample was selected to be tidally disturbed. The tidal features contribute ≤ 10% of the total Spitzer fluxes on average. The SFRs implied for the Arp galaxies by the Spitzer 24 μm luminosities are relatively modest, ∼1 M⊙ yr-1 on average.

We present Spitzer infrared imaging of the peculiar galaxy pair Arp 107 and compare with an optical Hα map and a numerical model of the interaction. The [3.6] - [4.5] colors of clumps in the galaxy do not vary around the ringlike primary spiral arm and are consistent with those of stars; thus, these bands are dominated by starlight. In contrast, the [5.8 μm] - [8.0 μm] colors are consistent with those of interstellar dust and vary by about 0.2 mag around the ring/spiral, with redder colors associated with regions with stronger star formation as indicated by Ha and mid-infrared luminosity. The [4.5 μm] - [5.8 μm] colors for clumps in this arm are bluer than dust and redder than stars and vary by 1.3 mag around the arm. This color is therefore a measure of the relative number of young stars to old stars, with a redder color indicating a higher proportion of young stars. There is a clear azimuthal sequence in the [4.5] - [5.8] color around the arm, indicating a sequence in average stellar age. The L HQ/L 8.0 μm ratio varies around the arm by a factor of ≈7; this variation may be due to extinction or to polycyclic aromatic hydrocarbon excitation by nonionizing photons. Our model of Arp 107 accounts for the general morphology of the system and explains the age variation along the arm as the result of differences in the time of maximum compression in the arm. Using Spitzer colors, we are able to distinguish background quasars and foreground stars from star-forming regions associated with Arp 107.

No description available.

OH Megamasers (OHMs) generally appear in luminous infrared regions i.e. merging galaxies. In this study we assume that OHMs may not be represented by their association with star formation solely, because of the possibility of a compact AGN source in the merging galaxies. In fact, previously classified starburst galaxies where OHMs are found are now optically observed as AGN. OHMs may also serve as a reasonable criterion for the evolutionary stage of the merger. This project focuses on observations from a multi-frequency analysis of merging regions with known OHMs. Optically, Hα and BVRI filters provided an environmental perspective of the "masing" components. In the radio, 18-cm data was used to determine the structure and position of the OHM. We studied the source IIZw096 and compared our results with two familiar OHM sources. We were able to look at each source at high radio resolutions and compare the structure and classification of each.

Depuis le milieu des années 1990, la taille des échantillons de galaxies situées à très grande distance (“redshift”) de nous, au tout début de la vie de l'univers a augmenté grace à la sensibilité croissante des télescopes optiques / infrarouge proche. Cependant, les propriétés des poussières continues dans ces galaxies sont mal connues en raison de l'absence d'observations profondes en infrarouge lointain et en sous-mm. Cette thèse explore les propriétés multi-longueur d'onde d'une population de galaxies observées ~ 2Gyr après le Big Bang. Notre échantillon comprend 22000 galaxies, et il a été sélectionné à partir de la discontinuité de Lyman. Nous utilisons une technique statistique, appelée analyse d'empilement, qui combine le signal provenant d'un grand nombre de sources individuellement non détectées dans le but d’ameliorer les limites de détection par rapport aux observations actuelles, à ces longueurs d'onde. Elle nous permet d'obtenir une distribution spectrale d’énergie complete de l’ultraviolet lointain à l’infrarouge lointain, et d'étudier la formation des étoiles et l'atténuation par la poussière sur ces galaxies. / Since the mid-1990s, the sample of galaxies in the early universe has been growing thanks to the increasing sensitivities in the Optical/NIR telescopes. However, their dust properties are poorly known due to the lack of deep far-infrared or sub-mm observations. This thesis explores the multi-wavelength properties of a population of galaxies observed ~2Gyr after the Big Bang. Our sample includes 22000 galaxies, and it has been selected by the classical U-dropout or Lyman Break technique. We use a statistical technique, called stacking analysis, that combines the signal from a large number of sources to lower the detection limits on the current long wavelengths observations. It allows us to obtain data over the full FUV-to-FIR spectral domain, and study the star formation and dust attenuation of these galaxies.

This thesis presents a starburst model for far-infrared/sub-millimeter/millimeter (FIR/sub-mm/mm) line emission of molecular and atomic gas in an evolving starburst region, which is treated as an ensemble of non-interacting hot bubbles which drive spherical shells of swept-up gas into a surrounding uniform gas medium. These bubbles and shells are driven by winds and supernovae within massive star clusters formed during an instantaneous starburst. The underlying stellar radiation from the evolving clusters affects the properties and structure of photodissociation regions (PDRs) in the shells, and hence the spectral energy distributions (SEDs) of the molecular and atomic line emission from these swept-up shells and the associated parent giant molecular clouds (GMCs) contains a signature of the stage evolution of the starburst. The physical and chemical properties of the shells and their structure are computed using a a simple well known similarity solution for the shell expansion, a stellar population synthesis code, and a time-dependent PDR chemistry model. The SEDs for several molecular and atomic lines ($^{12}$CO and its isotope $^{13}$CO, HCN, HCO$^+$, C, O, and C$^+$) are computed using a non-local thermodynamic equilibrium (non-LTE) line radiative transfer model. By comparing our models with the available observed data of nearby infrared bright galaxies, especially M 82, we constrain the models and in the case of M 82, provide estimates for the age of the recent starburst activity. We also derive the total H$_2$ gas mass in the measured regions of the central 1 kpc starburst disk of M 82. In addition, we apply the model to represent various stages of starburst evolution in a well known sample of nearby luminous infrared galaxies (LIRGs). In this way, we interpret the relationship between the degree of molecular excitation and ratio of FIR to CO luminosity to possibly reflect different stages of the evolution of star-forming activity within their nuclear regions. We conclude with an assessment of the strengths and weaknesses of this approach to dating starbursts, and suggest future work for improving the model.

This thesis presents a starburst model for far-infrared/sub-millimeter/millimeter (FIR/sub-mm/mm) line emission of molecular and atomic gas in an evolving starburst region, which is treated as an ensemble of non-interacting hot bubbles which drive spherical shells of swept-up gas into a surrounding uniform gas medium. These bubbles and shells are driven by winds and supernovae within massive star clusters formed during an instantaneous starburst. The underlying stellar radiation from the evolving clusters affects the properties and structure of photodissociation regions (PDRs) in the shells, and hence the spectral energy distributions (SEDs) of the molecular and atomic line emission from these swept-up shells and the associated parent giant molecular clouds (GMCs) contains a signature of the stage evolution of the starburst. The physical and chemical properties of the shells and their structure are computed using a a simple well known similarity solution for the shell expansion, a stellar population synthesis code, and a time-dependent PDR chemistry model. The SEDs for several molecular and atomic lines ($^{12}$CO and its isotope $^{13}$CO, HCN, HCO$^+$, C, O, and C$^+$) are computed using a non-local thermodynamic equilibrium (non-LTE) line radiative transfer model. By comparing our models with the available observed data of nearby infrared bright galaxies, especially M 82, we constrain the models and in the case of M 82, provide estimates for the age of the recent starburst activity. We also derive the total H$_2$ gas mass in the measured regions of the central 1 kpc starburst disk of M 82. In addition, we apply the model to represent various stages of starburst evolution in a well known sample of nearby luminous infrared galaxies (LIRGs). In this way, we interpret the relationship between the degree of molecular excitation and ratio of FIR to CO luminosity to possibly reflect different stages of the evolution of star-forming activity within their nuclear regions. We conclude with an assessment of the strengths and weaknesses of this approach to dating starbursts, and suggest future work for improving the model.

It has become clear in recent years that the study of interacting/merging galaxies plays an important role in understanding important astrophysical phenomena. This thesis presents an observational study of interacting/merging galaxies at radio frequencies. The observations have been carried out at extremely high resolution using very long baseline interferometry. The observations described here include: (1) A study of the high velocity Hi absorption associated with the peculiar galaxy NGC 1275; (2) A study of the radio continuum and Hi absorption of the ULIRG IRAS 172080014; (3) A study of the radio continuum and Hi absorption of the LIRG NGC 7674. Some of the most prominent results of these observations include: Detection of several narrow Hi absorption features in the high velocity system associated with NGC 1275. These Hi absorption lines were observed toward the strong radio nucleus 3C 84. The results indicate the existence of several Hi clouds with velocity differences and widths similar to those seen in Galactic neutral hydrogen absorption and similar to some of the Hi absorption seen in the Large Magellanic Cloud. The discovery of an extreme nuclear starburst region in the advanced merger system IRAS 172080014. Our results suggest a star formation rate of 84 M yr-1, and a supernova rate of 4 yr-1. Hi absorption is detected in multiple components with optical depths ranging between 0.3 and 2.5, and velocity widths between 58 and 232 km s-1. The detection of complex jet structures in the inner 1 kpc region of the galaxy NGC 7674. At full resolution, several compact sources are observed with brightness temperatures on the order of 107 K. While it is possible that one of these compact structures could host an AGN, they could also be shock-like features formed by the interaction of the jet with compact interstellar clouds in the nuclear region of this galaxy. At least eight Hi absorption lines are detected toward some of the continuum emission regions in NGC 7674. If the widest Hi feature in our observations is rotationally broadened by a central supermassive black hole, the implied dynamical mass is about 107 M.

We present multi-wavelength detections of nine candidate gravitationally lensed dusty starforming galaxies (DSFGs) selected at 218 GHz (1.4 mm) from the Atacama Cosmology Telescope (ACT) equatorial survey. Among the brightest ACT sources, these represent the subset of the total ACT sample lying in Herschel SPIRE fields, and all nine of the 218 GHz detections were found to have bright Herschel counterparts. By fitting their spectral energy distributions (SEDs) with a modified blackbody model with power-law temperature distribution, we find the sample has a median redshift of z = 4.1(-1.0)(+1.1) (68 per cent confidence interval), as expected for 218 GHz selection, and an apparent total infrared luminosity of log10(mu LIR/L-circle dot) = 13.86(-0.30)(+0.33), which suggests that they are either strongly lensed sources or unresolved collections of unlensed DSFGs. The effective apparent diameter of the sample is root mu d = 4.2(-1.0)(+1.7) kpc, further evidence of strong lensing or multiplicity, since the typical diameter of DSFGs is 1.0-2.5 kpc. We emphasize that the effective apparent diameter derives from SED modelling without the assumption of optically thin dust (as opposed to image morphology). We find that the sources have substantial optical depth (tau = 4.2(-1.9)(+3.7)) to dust around the peak in the modified blackbody spectrum (lambda(obs) <= 500 mu m), a result that is robust to model choice.