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The G305 star forming complex : a panoramic view of the environment and star formationHindson, Luke Paul January 2012 (has links)
This thesis presents molecular line and radio continuum observations of the giant molecular cloud (GMC) complex known as G305. The energy input from high-mass stars in the form of powerful winds and ionising radiation is one of the primary feedback mechanisms in GMCs. This feedback is thought to play a dual role both dispersing and destroying the natal environment but also sweeping up and compressing molecular gas and potentially triggering new episodes of star formation. Despite their importance to the evolution of GMCs and galaxies as a whole, the physical processes behind the formation and evolution of high-mass stars remains poorly understood. We therefore set out to obtain wide-field observations of the ionised and molecular environment to study the impact of high-mass stars on the evolution of G305. Observations conducted with the Mopra telescope of the molecular gas traced by NH3 in the (1,1), (2,2) and (3,3) transition and CO (12CO, 13CO and C18O J = 1–0) reveals the reservoir for future star formation in G305 and allows the physical properties and kinematics of the region to be studied. We identify 15 large molecular clouds and 57 smaller molecular clumps towards G305. The physical properties of the molecular gas are consistent with G305 being amongst the most massive a vigorous star forming regions in the Galaxy. We find a total molecular gas mass of 2:5–6:5 105M indicating that there is a large reservoir for future star formation. By considering virial equilibrium within the molecular clumps we discover that only 14% of the molecular clumps in G305 are gravitationally unstable, however these clumps contain > 30% of the molecular mass in G305 suggesting there is scope for considerable future star formation. To study the ionised environment towards G305 we have obtained some of the largest and most detailed wide-area mosaics with the Australia Telescope Compact Array to date. These radio continuum observations were performed simultaneously at 5.5 and 8.8 GHz and by applying two imaging techniques we are able to resolve HII regions from the ultra-compact to classical evolutionary phase. This has allowed high-mass star formation within G305 to be traced over the extent and lifetime of the complex. We discover that more than half of the observable total ionising flux in G305 is associated with embedded high-mass star formation around the periphery of a central cavity that has been driven into the molecular gas by a cluster of optically visible massive stars. By considering the contribution of embedded and visible massive stars to the observed radio continuum we suggest that more than 45 massive stars exist within G305. Combination of these two studies and recent and ongoing star formation provides the most in depth view of G305 to date and allows the star formation history and impact of high-mass stars to be investigated. We find compelling morphological evidence that suggests triggering is responsible for at least some of the observed high-mass star formation and construct a star formation history for the region.
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Constraining the Evolution of Galaxies over the Interaction Sequence with Multiwavelength Observations and SimulationsLanz, Lauranne 18 October 2013 (has links)
Interactions are crucial for galaxy formation and profoundly affect their evolution. However, our understanding of the impact of interactions on star formation and activity of the central supermassive black hole remains incomplete. In the canonical picture of the interaction process, these processes are expected to undergo a strong enhancement, but some recent studies have not found this prediction to be true in a statistically meaningful sense. This thesis uses a sample of local interactions observed from the ultraviolet to the far-infrared and a suite of N-body hydrodynamic simulations of interactions to examine the evolution of star formation, stellar mass, dust properties, and spectral energy distributions (SEDs) over the interaction sequence. / Astronomy
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Studying star formation at low and high redshift with integral field spectroscopyBlanc, Guillermo 01 June 2011 (has links)
In this thesis I focus mainly in studying the process of star formation in both high redshift, and local star forming galaxies, by using an observational technique called integral field
spectroscopy (IFS). Although these investigations are aimed at studying the star formation properties of these objects, throughout this work I will
also discuss the geometric, kinematic, and chemical structures in the inter-stellar medium of these galaxies, which are intimately connected with
the process of star formation itself. The studies presented here were conducted under the umbrella of two different projects. First, the HETDEX Pilot Survey for Emission Line Galaxies, where I have studied the properties of Ly-alpha emitting galaxies across the 2<z<4 range, with an emphasis in trying to understand the process by which Ly-alpha photons, produced in large quantities in the active star forming regions, are able to escape the ISM of
these objects, allowing us to detect them in the Ly-alpha line. The second project from which results are presented here is the VIRUS-P Exploration of Nearby Galaxies (VENGA), an ongoing campaign to obtain spatially resolved spectroscopy over a broad wavelength range for large portions of the disks of 30 nearby spiral galaxies. In this thesis, the VENGA data is used to study the physical parameters that
set the rate of star formation in the different environments present
within galaxies in the local universe. / text
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The Molecular Interstellar Medium from z=0-6Narayanan, Desika T January 2007 (has links)
I investigate the emission properties of the molecular interstellar medium in protoplanetary disks and galaxy mergers, though focus largely on the latter topic. I utilize both numerical models as well as observations to relate the emission characteristics to physical models for the formation and evolution of gas giant planets and galaxies. The main results of this thesis follow. (1) Gas giant protoplanets may be detectable via self-absorption signatures in molecular emission lines with sufficiently high critical density. Given the spatial resolution of e.g. ALMA, gas giant planets in formation may be directly imageable. (2) Starburst and AGN feedback-driven winds in galaxies can leave imprints on the molecular line emission properties via morphological outflows and high velocity peaks in the emission line spectra. Methods for distinguishing between high velocity peaks driven by dynamics versus those driven by winds are discussed. (3) CO line widths on average trace the virial velocity of z ∼ 6 quasar host halos. Thus, if the earliest quasars formed in ∼1013 M ⊙ halos, they are predicted to have broad molecular line widths. Selection effects may exist which tend quasars selected for optical luminosity toward molecular line widths narrower than the slightline-dependent mean. (4) Using the SMT, I observe a roughly linear relation between infrared luminosity and CO (J=3-2) luminosity in local galaxies confirming the results of recently observed L(IR)-HCN (J=1-0) relations. Subsequent modeling shows that observed SFR-molecular line luminosity relations owe to the average fraction of subthermally excited gas in galaxies, and are simply reflective of the assumed Schmidt law governing the SFR.
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Analysis and interpretation of astrophysical optical emission-line spectra / Susan Ilani LoubserLoubser, Susan Ilani January 2005 (has links)
This study consists of a quantitative optical emission-line analysis of spectra
from five blue compact galaxies (Zw 0855, Mrk 1267, II Zw 33, Tol 2
& Tol 3), as well as a qualitative analysis of spectra from two galactic H
II regions (NGC 3603 & NGC 3576). It serves a two-fold purpose: first, to
understand the CCD reduction, spectra extraction and different nebular analysis
methods, together with their applications and limitations, preparatory
to studies using the Southern African Large Telescope (SALT) and second,
to extend current star formation related research to include extragalactic
starburst galaxies. The observations were carried out using the 1.9m telescope
(equipped with a grating spectroscope and CCD detector) of the South
African Astronomical Observatory (SAAO), during the period 1 to 7 March
2005. The necessary CCD data reduction, spectra extraction, wavelength
and flux calibration, Doppler shift as well as reddening correction procedures
were performed before the emission lines were identified and measured. A full
nebular analysis, including temperature, density, metallicity (oxygen abundance)
and other chemical abundance determinations, was performed on the
blue compact galaxies (BCGs). Two different nebular analysis packages viz.
IRAF's nebular and SNAPwere used, with all the results well within the
range of values expected for metal poor BCGs. Recommendations on the different methods and their applications are made. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2006.
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The Stellar Populations and Evolution of Virgo Cluster GalaxiesRoediger, Joel C. 25 August 2009 (has links)
Using a combination of optical and near-infrared photometry, we have studied both the resolved and integrated stellar populations for a sample of Virgo cluster galaxies spanning the full range of galaxian parameters. The derived stellar population properties are compared against galaxy structural and environmental measures to gauge the importance of these factors in establishing galaxy star formation histories and chemical evolution.
Although galaxy colours do not uniquely probe a galaxy's star formation history, meaningful results may be obtained if considered in a relative sense. We find that colour profiles reflect variations in both stellar age and metallicity within galaxies. We also uncover systematic variations in colour gradients, and thus age/metallicity gradients, along the Hubble sequence, such that age and metallicity gradients become increasingly negative toward later Hubble types. However, only weak correlations exist between galaxies' stellar populations and their structure and environment. The correlations we find suggest that the star formation histories of gas-rich galaxies are strongly influenced by gas removal within the cluster, while their chemical evolution is due to a combination of stellar mass-dependent enrichment and outflow retention.
The assembly of gas-poor giant galaxies is consistent with a hierarchical scenario wherein gas-rich mergers dominate by number. Gas-poor dwarfs differ from the giants, however, appearing as the product of environmentally-driven evolution. Spiral galaxies bridge the dwarf-giant gap, whereby merging and gas-stripping signatures are imprinted in their stars. Early-type spirals seem to have fallen into the cluster sooner than the later types, thereby ceasing star formation in their disks at earlier epochs. The bulges of both types, however, appear to have grown via merging. The nature of this merging (minor versus major) remains unknown. Irregular galaxies exhibit signs of a recent gravitational encounter that has redistributed both their stars and gas, the latter of which caused recent star formation. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-08-25 14:12:46.48
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Žvaigždžių spiečiai M31 galaktikos pietvakarinėje dalyje. Fotometrinė apžvalga ir populiacijos savybės / Star Clusters in the M31 Galaxy Southwest Field. Photometric Survey and Population PropertiesNarbutis, Donatas 30 December 2010 (has links)
Daugėjant įrodymų, kad žvaigždės formuojasi spiečiais, jų masių funkcijos ir evoliucijos savybes kol kas galima nustatyti empiriniais stebėjimais. Tačiau tirti žvaigždėdaros procesą mūsų Galaktikoje galima ribotai. Andromedos galaktika (M31) yra artimiausia žvaigždžių sistema, panaši į Galaktiką. Todėl ji tinkamiausia žvaigždžių spiečių populiacijai tirti, tačiau ilgą laiką buvo tirta ribotai dėl tankių žvaigždžių laukų stebėjimo sudėtingumo.
Naudojant „Subaru“ teleskopo Suprime-Cam plataus lauko nuotraukas, buvo ištirti žvaigždžių spiečiai M31 galaktikos disko srityje, kuri pagal cheminę sudėtį, žvaigždinį tankį ir mažą žvaigždėdaros spartą yra analogiška Saulės aplinkai mūsų Galaktikoje. Buvo sukurti, išbandyti ir pritaikyti duomenų analizės metodai ir programos tankiems plataus lauko vaizdams apdoroti ir pusiau išskiriamų žvaigždžių spiečių evoliuciniams parametrams nustatyti.
Pagrindiniai rezultatai: (1) žvaigždžių spiečių formavimosi spartos sustiprėjimas M31 galaktikoje įvyko prieš ~70 mln. m.; (2) maždaug 10% žvaigždžių spiečių gyvena ilgiau nei 100 mln. m.; (3) būdingoji ~10^4 Saulės masių spiečiaus gyvavimo trukmė yra ~300 mln. m.; (4) žvaigždžių spiečių masių pasiskirstymas panašus į kitų mažos žvaigždėdaros spartos galaktikų žvaigždžių spiečių pasiskirstymą ir jį gerai nusako Schechter'io funkcija, kurios charakteringoji masė ~2x10^5 Saulės masių. Tai rodo, kad M31 galaktikoje yra gausi vidutinės masės žvaigždžių spiečių populiacija, kuri mūsų Galaktikoje yra... [toliau žr. visą tekstą] / Observational evidence that star formation proceeds in a clustered manner raises a question on the mass function of star clusters and their evolution. However, we have a limited scope of these processes in the Milky Way galaxy. The M31 galaxy is the nearest stellar system similar to our Galaxy, therefore, it is the most suitable one to provide clues for understanding the star cluster population and the evolution of galactic structures. However, detailed study of stellar populations and star clusters is a challenging task for ground-based observations due to crowded stellar fields.
Using Subaru telescope Suprime-Cam wide-field images, a survey of clusters was carried out in the disk region of the M31 galaxy southwest field, which is a close analogue to that of the Solar neighborhood in terms of chemical composition, stellar density, and quiescent star formation. Data analysis methods and programs were developed, tested, and applied for crowded wide-field image reduction and evolutionary parameter determination of semi-resolved star clusters.
The main results are: (1) enhanced star cluster formation activity in M31 occurred ~70 Myr ago; (2) approximately 10% of stars born in star clusters remain there at 100 Myr age; (3) the characteristic lifetime of a cluster of ~10^4 solar masses mass is ~300 Myr; (4) the mass function of star clusters in M31 is similar to that in other low star formation activity galaxies and it is best described by the Schechter's function with a... [to full text]
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PHYSICAL CONDITIONS INCLUDING MAGNETIC FIELDS IN SEVERAL STAR FORMING REGIONS OF THE GALAXYLykins, Matt 01 January 2010 (has links)
This document describes studies of two independent regions of the interstellar medium (ISM). These studies have the common element that both pertain to regions in our Galaxy that are known to be associated with present-day star formation. These studies aim to help us understand the ISM, star formation, and ultimately where we came from, since, after all, our star, the Sun, is itself the product of star formation 4.5 billion years ago. The first project measured the Zeeman Effect on the 21 cm H I absorption line in order to create a map of the line of sight magnetic fields near a star forming region called W3. From the map of the field, it was possible to create a three dimensional model of the magnetic field morphology. Also, calculating the various energies associated with W3 revealed that it is most likely in virial equilibrium, not expanding or contracting.
The second project used an instrument on the Hubble Space Telescope (HST) to measure the abundance of iron in a neutral region near the Orion Nebula called Orion’s Veil. One of the goals of this project is to investigate whether solid dust grains can be destroyed by ionizing radiation by comparing the amount of solid iron in Orion’s Veil to the amount in the nearby ionized regions. By measuring the depletion of iron in the neutral Veil and comparing it to the depletion of iron the H+ regions of the Orion Nebula, it was possible to conclude that iron was not being released into the gas phase by ultraviolet photons. In addition, oscillator strengths for two Fe II transitions were measured.
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Deep radio imaging of the UKIDSS Ultra Deep Survey field : the nature of the faint radio population, and the star-formation history of the UniverseArumugam, Vinodiran January 2013 (has links)
The centrepiece of this thesis is a deep, new, high-resolution 1.4-GHz image covering the United Kingdom Infrared (IR) Telescope IR Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) legacy field. Deep pseudo-continuum observations were made using the Very Large Array, prior to its recent upgrade, in its A, B and DnC configurations. The resulting mosaic has a full-width-at-half-maximum synthesised beam width of ≈ 1.7 arcsec and a point-source sensitivity of ≈ 60μJy (6σ ) across the central 0.6 deg2, while conserving flux from sources of extended emission. The full image covers 1.3 deg2. I also present a catalogue containing over 1,000 radio emitters, having chosen the 6-σ threshold by maximising the number of radio sources with secure optical/near-IR counterparts. Most of the sources in the catalogue (≈ 90 per cent) lie in the sub-mJy flux density regime. Deep, complementary data covering a wide range of wavelengths was used to explore this faint radio population, whose nature remains controversial. It was found that 53 per cent of the sample comprise active galactic nuclei (AGN). AGN dominate at & 0.2mJy and remain a significant population down to 0.1mJy; at lower fluxes – the so-called μJy radio population – star-forming galaxies become dominant. The radio sample presented here was also matched to Hubble Space Telescope imaging of the UDS field (which is part of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey – CANDELS) to classify the faint radio population morphologically. These classifications were done using the Gini–M20 method. It was found that a low fraction of AGN and SFGs are undergoing interactions and mergers, 33 ± 9 and 13 ± 7 per cent, respectively. The merger fraction does not appear to have evolved significantly since z ∼ 3. This suggests that mergers have played a relatively minor role in the assembly of galaxies and super-massive black holes – certainly less significant than previously thought. Finally, I present a study of cosmic star-formation activity as a function of stellar mass and redshift, exploiting panchromatic stacking. Mid-IR–through–radio images, including new data from Herschel, are stacked at the positions of a K-selected (i.e. an approximately mass-selected) sample in the UDS field. Specific star-formation rates (SSFR, i.e. star-formation rate per stellar mass, or the rate at which a galaxy is converting its gas into stars) were derived from UDS radio luminosities measured here and stellar masses from the literature. The SSFR was found to be poorly correlated with stellar mass; it decreases with decreasing redshift; at a given mass, SSFR rises with redshift. These results indicate that at early epochs, galaxies were forming stars more efficiently and at a higher rate.
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Modeling submillimetre polarization of molecular cloud cores using successive parametrized coordinate transformationsFranzmann, Erica 20 August 2014 (has links)
We present a novel new method for modelling magnetized molecular cloud cores using submillimetre linear polarization maps from thermal dust emission. Our PolCat modelling software builds a three-dimensional core model via the use of consecutive parametrized coordinate transformations, and produces simulated polarization maps to fit to observational datasets. We utilize the Ferret evolutionary optimizer to search the parameter space to simultaneously minimize chi-squared for the intensity and polarization position angle maps separately.
We have applied PolCat to multiple test problems and several datasets from the SCUPOL Legacy Catalogue. We find that PolCat is able to distinguish between maps of twisted and non-twisted field geometries and identify twist symmetry. Preliminary fits to several datasets show that the best potential field geometries to our sample cores contain field twists. Further research using a larger number of maps is required to determine if twisted fields are commonplace in cores.
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