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Lee, Pawel. "Structure in star forming regions." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/12395/.
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Stars form in clumpy, highly substructured environments. In this thesis I set up N-body simulations of substructured star forming regions and investigate the impact that the substructure has on the survival of the star forming regions. I also present a broad range of methods used in other fields to quantify and identify structure. I discuss their strengths and shortcomings and assess their suitability for use in astronomical contexts. I use the Q and Λ methods to compare the distributions of class I and class II sources in observed star forming regions to learn more about the dynamical evolution of systems and infer whether they are bound or unbound.
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Gledhill, Timothy Michael. "Optical polarimetry of star forming regions." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6757/.
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Holdship, J. R. "Shock chemistry in star forming environments." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/10027644/.
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Molecules are abundant in many astrophysical environments. The observation of these molecules and the modelling of the chemistry that leads to their formation is a powerful tool for improving our understanding of the regions in which they are found. In this thesis, a chemical model is developed and applied to astrophysical shocks to understand a number of processes in star forming regions. Shocks often result in discontinuous changes in the temperature and density of the gases they affect. The turbulent fragmentation theory of star formation suggests that such shocks are responsible for the over-densities that lead to the formation and collapse of prestellar cores from molecular clouds. Focusing on low mass objects, a chemical model of prestellar cores formed through shocks is developed and compared to models of similarly dense gas formed through gravitational freefall. Observational predictions of shock induced differences in the chemistry of these cores are reported and compared to the literature. Not only are molecules abundant in the gas phase but they are also observed in solid state, frozen onto the surfaces of interstellar dust grains. This freeze out process is efficient in molecular clouds but the composition of these ices is poorly constrained for all but the most abundant molecules. Shocks represent a powerful tool to study these ices as they not only change the gas properties but can also sputter and shatter dust grains releasing frozen molecules into the gas phase. Observations of sulfur-bearing molecules in a protostellar outflow, L1157-B1, are presented and analysed, giving an overview of the sulfur content of the recently shocked gas. The abundances of important sulfur molecules are then compared to chemical models of C-type shocks in an attempt to constrain the main solid state form of sulfur before the shock and the shock properties of the observed outflow.
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Lacki, Brian Cameron. "Cosmic Rays in Star-Forming Galaxies." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313437011.
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Kalari, Venu Madhav. "Disc-accretion in star-forming regions." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.695381.
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In this thesis, I present new ultraviolet/optical/infrared photometric and spectroscopic observations of pre-main sequence stars (PMS) that have formed either in metal-poor conditions, or in the vicinity of strong ionising radiation. This includes observations of 235 Classical T Tauri stars in the Lagoon Nebula; 63 Classical T Tauril Herbig Ae stars in the Carina Nebula open cluster Trumpler 14; 24 intermediate mass T Tauri stars in the low-Z Sh 2-284 star-forming region; and one Herbig 8[e] PMS candidate in the metal-poor 30 Doradus region. I measure the accretion rates of these PMS stars using the intensities of the U/Halpha band excess measured through either optical spectra of imaging. Where possible, I use archive infrared photometry in the 1.2-8 micron wavelength range to estimate the PMS disc evolutionary stage. The influence of the surrounding environment on the accretion rate evolution of pre-main sequence stars in these regions is explored using the spatial, and temporal distributions of accretion rate, mass, age and disc stage of PMS stars. In the wide-field photometric data of the Lagoon Nebula, I find that the spatial distributions of PMS stars is a continuum, ranging from dense clustering to relative isolation. Strongly accretion PMS stars are generally clumped together, in close proximity to their natal molecular cloud, whereas weaker, older accretors are relatively space apart. Ionising radiation from early-type stars appears to positively affect accretion rates on scales of 2-3 pc, but no evidence for triggered star formation is found. In addition, the accretion rates measured from Halpha imaging correlate well to those estimated from U-band photometry. In wide-field photometric data of Trumpler 14, I discover a population of PMS candidates nearly 25 Myrs old. I argue that these PMS candidates are a foreground population, approximately 5 Myr old that belong to the Carina Nebula cluster Trumpler 16. Using Halpha spectra of 24 intermediate mass T Tauri stars in Sh 2-284 (Z-0.004), I demonstrate that there is little evidence for a systematic change in accretion rates with metallicity, contrary to previous literature results at Z-0.006-0.002 in the Magellanic Clouds. I suggest that previous studies are likely affected by detection limits and biases. I also present ultraviolet/optical spectra of the Herbig 8[e] PMS candidate VFTS 822 located in the 30 Doradus region of the Large Magellanic Cloud. I discuss the impact of the discovery of VFTS 822 for star formation studies in the Magellanic Clouds, external Galaxies .
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Contreras, Peña Carlos Eduardo. "Exteme variables in star forming regions." Thesis, University of Hertfordshire, 2015. http://hdl.handle.net/2299/15590.
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The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a constant rate during the early stages of their evolution appears to be challenged by observations of YSOs suffering sudden increases of the rate at which they gain mass from their circumstellar discs. Also, this idea that stars spend most of their lifetime with a low accretion rate and gain most of their final mass during short-lived episodes of high accretion bursts, helps to solve some long-standing problems in stellar evolution. The original classification of eruptive variables divides them in two separate subclasses known as FU Orionis stars (FUors) and EX Lupi stars (EXors). In this classical view FUors are at an early evolutionary stage and are still gaining mass from their parent envelopes, whilst EXors are thought to be older objects only surrounded by an accretion disc. The problem with this classical view is that it excludes younger protostars which have higher accretion rates but are too deeply embedded in circumstellar matter to be observed at optical wavelengths. Optically invisible protostars have been observed to display large variability in the near-infrared. These and some recent discoveries of new eruptive variables, show characteristics that can be attributed to both of the optically-defined subclasses of eruptive variables. The new objects have been proposed to be part of a new class of eruptive variables. However, a more accepted scenario is that in fact the original classes only represent two extremes of the same phenomena. In this sense eruptive variability could be explained as arising from one physical mechanism, i.e. unsteady accretion, where a variation in the parameters of such mechanism can cause the different characteristics observed in the members of this class. With the aim of studying the incidence of episodic accretion among young stellar objects, and to characterize the nature of these eruptive variables we searched for high amplitude variability in two multi-epoch infrared surveys: the UKIDSS Galactic Plane Survey (GPS) and the Vista Variables in the Via Lactea (VVV). In order to further investigate the nature of the selected variable stars, we use photometric information arising from public surveys at near- to farinfrared wavelengths. In addition we have performed spectroscopic and photometric follow-up for a large subset of the samples arising from GPS and VVV. We analyse the widely separated two-epoch K-band photometry in the 5th, 7th and 8th data releases of the UKIDSS Galactic Plane Survey. We find 71 stars with _K > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is mostly excluded from the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (27 stars). The analysis of the multi-epoch K-band photometry of 2010-2012 data from VVV covering the Galactic disc at |b| < 1◦ yields 816 high amplitude variables, which include known variables of different classes such as high mass X-ray binaries, Novae and eclipsing binaries among others. Remarkably, 65% of the sample are found concentrated towards areas of star formation, similar to the results from GPS. In both surveys, sources in SFRs show spectral energy distributions (SEDs) that support classification as YSOs. This indicates that YSOs dominate the Galactic population of high amplitude infrared variable stars at low luminosities and therefore likely dominate the total high amplitude population. Spectroscopic follow-up allows us to confirm the pre-main sequence nature of several GPS and VVV Objects. Most objects in both samples show spectroscopic signatures that can be attributed to YSOs undergoing high states of accretion, such as veiling of photospheric features and CO emission, or show FUor-like spectra. We also find a large fraction of objects with 2.12 μm H2 emission that can be explained as arising from shock-excited emission caused by molecular outflows. Whether these molecular outflows are related to outbursts events cannot be confirmed from our data. Adding the GPS and VVV spectroscopic results, we find that between 6 and 14 objects are new additions to the FUor class from their close resemblance to the near-infrared spectra of FUors, and at least 23 more objects are new additions to the eruptive variable class. For most of these we are unable to classify them into any of the original definitions for this variable class. In any case, we are adding up to 37 new stars to the eruptive variable class which would double the current number of known objects. We note that most objects are found to be deeply embedded optically invisible stars, thus increasing the number of objects belonging to this subclass by a much larger factor. In general, objects in our samples which are found to be likely eruptive variable stars show a mixture of characteristics that can be attributed to both of the optically-defined classes. This agrees well with the recent discoveries in the literature. Finally, we are able to derive a first rough estimate on the incidence of episodic accretion among class I YSOs in the star-forming complex G305. We find that _ 9% of such objects are in a state of high accretion. This number is in agreement with previous theoretical and observational estimates among class I YSOs.
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Mineo, Stefano. "X-ray emission from star-forming galaxies." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-134839.
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Maskoliūnas, Marius. "Investigation of star forming regions in Cepheus." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140203_133341-51153.
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The interstellar matter in the Galaxy is concentrated in a thin layer close to the galactic plane, mostly in spiral arms. Most of the interstellar matter is in a form of atomic and molecular gas and only 1% of its mass is in a form of small (0.01 – 0.1 µm) dust grains which absorb and scatter the light of stars and cause the interstellar extinction. A part of interstellar gas and dust are in a diffuse form and fill the space with density which exponentially decreases with the distance from the galactic plane. However, in the spiral arms gigantic molecular clouds are present which play an outstanding role in the evolution of the Galaxy, since in them star forming processes take place. Molecular and dust clouds, young star clusters and associations and other star forming regions are concentrated in the Milky Way plane.
However, due to gravitational and radiation interactions between the molecular clouds and the young massive stars, some fragments of spiral arms deviate from the galactic plane. One of such deviating branches from the Local (Orion) spiral arm is a huge elongated system of molecular and dust clouds located in the Cepheus constellation which is known as the Cepheus Flare. Most of the objects investigated in this dissertation belong to this branch of the Local spiral arm.
The objects selected for the investigation are star forming regions in the vicinity of the reflection nebula NGC 7023, a group of dark clouds TGU 619, the young open cluster NGC 7129 and the... [to full text]Paukščių tako Galaktikoje didžioji dalis tarpžvaigždinės medžiagos yra susitelkusi į ploną sluoksnį Galaktikos plokštumoje, daugiausiai spiralinėse vijose. Didžiąją dalį tarpžvaigždinės medžiagos sudaro atominės ir molekulinės dujos ir tik maždaug 1% masės yra mažos (0.01 – 0.1 µm) dydžio dulkelės, kurios sugeria ir išsklaido šviesą ir sukelia tarpžvaigždinės ekstinkcijos reiškinį. Spiralinėse vijose esantys molekuliniai debesys yra svarbūs Galaktikos evoliucijos procese, nes juose vyksta aktyvūs žvaigždžių formavimosi procesai. Molekuliniai ir dulkių debesys, jaunų žvaigždžių spiečiai ir asociacijos bei kitos žvaigždžių susidarymo sritys dažniausiai yra Galaktikos plokštumoje. Tačiau dėl gravitacinės ir radiacinės sąveikos tarp jaunų didelės masės žvaigždžių ir molekulinių debesų kai kuriose Paukščių Tako srityse žvaigždėdaros rajonai nukrypsta nuo Galaktikos plokštumos. Viename iš tokių rajonų Cefėjo žvaigždyno kryptimi dalis tarpžvaigždinių debesų ir žvaigždėdaros rajonų yra nukrypę nuo Galaktikos plokštumos link šiaurinio dangaus poliaus ir sudaro Paukščių Tako atšaką, literatūroje žinomą kaip Cepheus Flare. Dauguma šioje disertacijoje tyrinėjamų objektų priklauso šiai Cefėjo atšakai. Šio darbo tikslas yra Cefėjo žvaigždėdaros rajonų, žinomų kaip atspindžio ūkas NGC 7023, tamsiųjų debesų kompleksas TGU 619 ir jaunas spiečius NGC 7129 fotometrinis tyrimas, siekiant nustatyti šių objektų nuotolį ir tarpžvaigždinę ekstinkciją, jauno spiečiaus NGC 7129 ir... [toliau žr. visą tekstą]
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Juárez, Rodríguez Carmen. "Collapse scenarios in magnetized star-forming regions." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/459253.
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Turbulence, magnetic fields and gravity driven flows are important for the formation of new stars. Although magnetic fields have been proven to be important in the formation of stars, only a few works have been done combining magnetic field and kinematic information. Such studies are important to analyze both gravity and gas dynamics and be able to compare them with the magnetic field. In this thesis we will combine dust polarization studies with kinematic analysis towards different star-forming regions. We aim to study the physical properties at core scales (<0.1 pc) from molecular line and dust emission, and study the role of the magnetic field in their dynamic evolution. For this, we will use millimeter and submillimeter observational data taken towards low- and high- mass star-forming regions in different environments and evolutionary states.
The first project is the study of the physical, chemical and magnetic properties of the pre-stellar core FeSt1-457 in the Pipe nebula. We studied the emission of the molecular line N2H+(1-0) which is a good tracer of dense gas and therefore describes well the structure of the core. In addition, we detected more than 15 molecular lines and found a clear chemical spatial differentiation for molecules with nitrogen, oxygen and sulfur. Using the ARTIST radiative transfer code (Brinch & Hogerheijde 2010, Padovani et al., 2011, 2012, Jørgensen et al., 2014), we simulated the emission of the different molecules detected and estimated their abundance. In addition, we estimated the magnetic field properties of the core (using the Chandrasekhar-Fermi approximation) from polarization data previously obtained by Alves et al., (2014). Finally, we found interesting correlations between the polarization properties and the chemistry in the region.
The second project is the study of a high-mass star-forming region called NGC6334V. NGC6334V is in a more advanced evolutionary state and in an environment surrounded by other massive star-forming regions. During the project we studied the magnetic field from the polarized emission of the dust and also the kinematics of the gas from the molecular line emission of the different tracers of dense gas. From the molecular emission of the gas tracing the envelope of the dense core, we see two different velocity structures separated by 2 km/s and converging towards the potential well in the region. In addition, the magnetic field also presents a bimodal pattern following the distribution of the two velocity structures. Finally, we compared the observational results with 3D magnetohydrodynamic simulations of star-forming regions dominated by gravity.
The last project is the study of a lower-mass star-forming region, L1287. From the data obtained with the SMA, the dust continuum structure shows six main dense cores with masses between ~0.4 and 4 solar masses. The dense gas tracer DCN(3-2) shows two velocity structures separated by 2-3 km/s, converging towards the highest-density region, the young stellar object IRAS00338+6312, in a similar scenario to the one observed in the higher-mass case of NGC6334V.
Finally, the studies of the pre-stellar core FeSt1-457 and the massive region NGC6334V, show how the magnetic field has been overcome by gravity and is not enough to avoid the gravitational collapse. In addition, NGC6334V and the lower- mass region L1287 present very similar scenarios with the material converging from large scales (~0.1 pc) to the potential wells of both regions at smaller scales (~0.02 pc) through two dense gas flows separated by 2-3 km/s. In a similar scenario, FeSt1-457 is located just in the region where two dense gas structures separated by 3 km/s appear to converge.La turbulencia, el campo magnético y la gravedad juegan un papel importante en la formación estelar. Aunque se ha mostrado que el campo magnético es importante, sólo se han llevado a cabo un número limitado de trabajos combinando el estudio del campo magnético y la cinemática del gas. Este tipo de trabajos son esenciales para estudiar la gravedad y la dinámica del gas y poder compararlas con el campo magnético a las mismas escalas espaciales. En este trabajo combinamos estudios de polarización a partir de la emisión del polvo, con el análisis de la cinemática del gas en diferentes regiones de formación estelar. El objetivo es estudiar las propiedades físicas a escalas de núcleos densos (<0.1 pc) a partir de la emisión molecular y del polvo, y estudiar el papel del campo magnético en la evolución dinámica de las regiones. Para ello hemos utilizado datos observacionales milimétricos y submilimétricos. Los estudios se han realizado en 3 regiones de formación estelar. El núcleo pre- estelar FeSt 1-457 localizado en un entorno aislado y muy magnetizado en la nebulosa de la Pipa. NGC 6334 V, una región de mayor masa, en un estado evolutivo más avanzado y en un entorno rodeado de otras regiones de formación estelar masiva. Y L1287, una región menos masiva pero con características similares a NGC 6334 V, con presencia de gas de alta velocidad y fuentes centimétricas e infrarrojas. Los estudios del núcleo pre-estelar FeSt 1-457 y la región de formación estelar de alta masa NGC 6334 V, muestran como el campo magnético ha sido superado por la gravedad y no es suficiente para evitar el colapso gravitatorio. Además NGC 6334 V y la región de menor masa L1287 presentan escenarios muy similares, con el material convergiendo desde escalas grandes hacia los pozos de potencial de ambas regiones a escalas más pequeñas a través de flujos de gas denso separados por 2-3 km/s. En un escenario parecido, FeSt 1-457 se encuentra justo en la zona donde parecen converger dos flujos de gas denso separados por 3 km/s.
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Simon, Robert. "Multiline CN observations of star forming regions." [S.l. : s.n.], 1997. http://deposit.ddb.de/cgi-bin/dokserv?idn=955972264.
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Revelle, Melissa C. "OBSERVATIONS OF STAR FORMING REGION NGC 1333." Thesis, The University of Arizona, 2009. http://hdl.handle.net/10150/192971.
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Groppi, Christopher Emil. "Submillimeter heterodyne spectroscopy of star forming regions." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280414.
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The sub-mm wave portion of the electromagnetic spectrum is on the frontier of both scientific and technical research in astrophysics. Being a relatively young field, scientific advancement is driven by advancements in detector technology. In this thesis, I discuss the design, construction, testing and deployment of two sub-mm wave heterodyne array receivers. Polestar is a 4 pixel (2 x 2) heterodyne array built for operation in the 810 GHz atmospheric window. It is in operation at the AST/RO telescope at the South Pole. This receiver has increased imaging speed in this band at AST/RO by a factor of ∼20 compared to previous receiver systems. DesertStar is a 7 pixel, hexagonally close packed heterodyne array receiver built to operate in the 345 GHz atmospheric window at the Heinrich Hertz Telescope in Arizona. This system will be a facility instrument at the telescope, and will increase mapping speed over the existing dual polarization single beam receiver at the telescope now by a factor of ∼16. Both these receiver systems enable scientific projects requiring large area imaging that were previously impossible. I also discuss two scientific applications of sub-mm wave receiver systems. We have used multiple telescopes to observe several mm, sub-mm transitions and continuum emission towards the R CrA molecular cloud core. Originally thought to be associated with high mass star formation, we find that the driving source behind the mm-wave emission is a low mass protostar. The close proximity of R CrA allows us to achieve high spatial resolution even with single dish mm-wave and sub-mm wave telescopes. With this resolution, we are able to disentangle the effects of infall, rotation and outflow motions. We also use vibrationally excited HCN emission to probe the protostellar accretion disk in a sample of nearby high and low mass protostars of varying ages. While these observations are difficult with single dish telescopes, we show the promise of the technique, and report results on 4 sources.
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Tideswell, David Mark. "Chemical modelling of extragalactic star forming regions." Thesis, University of Manchester, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529246.
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Abel, Nicholas Paul. "DETERMINING PHYSICAL CONDITIONS IN STAR FORMING REGIONS." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_diss/428.
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This dissertation is a study of the physical conditions in star-forming regions, and combines observational data and theoretical calculations. We studied the physical conditions of Orions Veil, which is an absorbing screen that lies along the line of sight to the Orion H II region. We computed photoionization models of the Veil. We combined calculations with UV, radio, and optical spectra that resolve the Veil into two velocity components. We derive many physical parameters for each component seen in 21 cm absorption. We find the magnetic field energy dominates turbulent and thermal energies in one component while the other component is close to equipartition between turbulent and magnetic energies. We observe H2 absorption for highly excited levels. We find that the low ratio of H2/H0 in the Veil is due to the high UV flux incident upon the Veil. We detect blueshifted S+2 and P+2 ions which must arise from ionized gas between the neutral portions of the Veil and the Trapezium and shields the Veil from ionizing radiation. We determine the ionized and neutral layers of the Veil will collide in less than 85,000 years. The second part of this dissertation involved self-consistently calculating the thermal and chemical structure of an H II region and photodissociation region (PDR) that are in pressure equilibrium. This differs from previous work, which used separate calculations for each gas phase. Our calculations span a wide range of initial conditions. We describe improvements made to the spectral synthesis code Cloudy which made these calculations possible. These include the addition of a molecular network with ~1000 reactions involving 68 molecules and improved treatment of the grain physics. Archival data are used to derive important physical characteristics of observed H II regions and PDRs. These include stellar temperatures, electron densities, ionization parameters, UV flux, and PDR density. The contribution of the H II region to PDR emission line diagnostics is also calculated. Finally, these calculations are used to derive emission line ratios than can tell us the equation of state in star-forming regions.
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Christie, H. "Structure and depletion in star forming clouds." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1367071/.
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Observations of star forming molecular clouds reveal clumpiness on all scales, both in the spectra of molecules and thermal continuum emission from the solid component of the interstellar medium, the dust. Recent, high resolution maps have allowed us to probe down to extremely small scales at which we see clumps of radii just several hundredths of a parsec. A good knowledge of the structure of these regions, and of the chemical processes occurring within, is crucial if we want to properly understand the early stages of star formation and the resulting stellar population. However, observations of cold, dense environments are challenging. Molecules emit at long wavelengths which are notoriously difficult to observe. A comparison with models is also complicated by the fact that in these conditions molecules will freeze-out onto dust grain surfaces forming icy mantles. We know little about the rate at which this process occurs in interstellar conditions, or the chemical reactions that happen on the grain surfaces. In this thesis we present two alternative methods by which to investigate the underlying clumpy nature of a molecular cloud and consider freeze-out in such an environment. Small, quiescent regions of enhanced emission in several molecules (including ammonia and HCO+) have been observed near to Herbig-Haro objects (HHOs) in star forming clouds. It was suggested that these could be due to molecules in small dense clumps being liberated from the dust grain surface by radiation from the shock front. Chemical modelling later proved this theory to be viable, and it was further supported by observational surveys and more detailed modelling of specific regions. In chapter 2 we simulate a dense clump near to an HHO, adapting the chemical code used in the original models to allow the shock front to move past the clump, providing a more realistic description of the effect of the radiation field. Chapter 3 describes how the outputs from these models can be used to simulate observations of part of a molecular cloud made up of small, transient density enhancements irradiated by a passing shock front. We briefly compare our synthetic maps with HCO+ spectra in regions surrounding HHOs. Commonly, researchers use decomposition algorithms on 2D and 3D maps to pick out clumps of emission and evaluate their properties. The mass functions of these objects often appear to emulate the stellar initial mass function, which has led researchers to conclude that the stellar mass is set at a very early stage, prior to the switch on of the protostar. In Chapter 4 we introduce the Gould Belt clouds for which we have HARP CO and SCUBA data (the HARP maps are presented in Appendix B). It is these on which we perform the analysis described in the final 3 Chapters. In Chapter 5 we investigate four popular clumpfinding algorithms, testing them on both synthetic and real (HARP) data, and explore the impact of user defined input parameters on derived properties. We choose one algorithm, with one set of input parameters, and use this to analyse the distribution of CO clumps in five nearby molecular clouds. The results of this study are outlined in Chapter 6. Chapter 7 focuses on the process by which CO freezes-out (depletes) onto the surfaces of dust grains in dark clouds. A single value for the depletion of a particular molecule is difficult to achieve because of its strong dependence on environmental factors and the past evolution of a region. However, we have a consistent data set across a range of environments and so are able to perform a statistical study in which we compare hydrogen densities derived from dust emission with those calculated using the CO maps. We look for missing CO in the gas phase which we then assume to be the result of depletion.
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Pattison, Ian. "High-mass star-forming regions in M33." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422023.
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Harker, Justin J. "The star forming universe after z=1 /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2008. http://uclibs.org/PID/11984.
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Barsony, Mary Anne Scoville Nicholas Zabriskie Scoville Nicholas Zabriskie. "Outflows in high mass star-forming regions /." Diss., Pasadena, Calif. : California Institute of Technology, 1989. http://resolver.caltech.edu/CaltechETD:etd-09102008-084535.
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Visser, Anja Eveline. "Star forming cores in dark molecular clouds." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620970.
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Cunningham, Nichol. "Molecular outflows in massive star forming regions." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/11180/.
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This thesis presents millimetre continuum and molecular line observations exploring the properties of molecular outflows towards massive star forming regions. Massive stars produce some of the most energetic phenomena in the Galaxy, yet we still do not have a comprehensive understanding of how they actually form. Outflows are known to play a key role in this formation process and their properties, particularly how they change depending on the mass, luminosity and evolution of the driving source can shed light on how massive stars actually form. This thesis presents observations at both high (SMA 3 arcsecond) and low (JCMT 15 arcsecond) spatial resolution of the known jet/outflow tracers, SiO and 12CO, towards a sample massive star forming region drawn from the RMS survey. Furthermore, the presence of infall signatures is explored through observations of HCO+ and H13CO+, and the hot core nature of the regions is probed using tracers such as CH3CN, HC3N and CH3OH. SiO is detected towards approximately 50% of the massive young stellar objects and HII regions in the JCMT sample. The detection of SiO appears to be linked to the age of the RMS source, with the likely younger sources showing a stronger dependence with SiO. The presence of SiO also appears to be linked to the CO velocity, with SiO more efficiently tracing sources with higher velocity dispersions. In the MOPRA observations towards a sample of 33 RMS sources, CH3CN is detected towards 66% of the sources, with the redder likely younger sources having the largest rotational temperatures. This thesis presents the first interferometric SiO (5-4) and 12CO (2-1) observations, taken with the SMA, towards the massive star forming region G203.3166/NGC 2264-C. In this intermediate/massive star forming cluster, SiO is again tracing the youngest sources. Both the SiO and 12CO emission trace two bipolar, high velocity outflows towards the mm brightest, IR-dark, likely youngest sources in this region. In contrast the IR-bright RMS source, AFGL 989-IRS1, in NGC 2264-C displays no associated molecular outflow emission. Furthermore, the high resolution follow-up SMA observations towards G192.6005/S255IR and the first interferometric 12CO and SiO observations towards G194.9349 show a high velocity outflow traced by 12CO in each region. In both regions the outflow appears to be driven by the IR-bright RMS source. However, no high velocity SiO counterpart is observed in either region. Thus, the lack of associated SiO emission may be a sign of age in these regions.
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Fukue, Tsubasa. "Polarimetric Study of Star/Planet-Forming Regions." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124422.
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Suraphong, Yuma. "Intrinsic Structure of Star-Forming BzK Galaxies." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/152030.
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Smith, Penelope Ann. "The molecular content of star-forming galaxies." Thesis, University of Edinburgh, 1992. http://hdl.handle.net/1842/27428.
Full textAbstract:
An exciting development in observational astronomy over the last 15 years has been the opening up of the submillimetre and millimetre atmospheric windows, to the extent that observations of external galaxies are now possible. This thesis presents the results of a millimetre/submillimetre-wave study of several nearby, infrared-bright, vigorously star-forming galaxies, in an attempt to investigate their molecular hydrogen content. In particular, it seeks to evaluate the relative merits of the two most commonly adopted molecular hydrogen 'tracers' - millimetre-wave transitions of the CO molecule and its isotopes, and submillimetre continuum emission from warm dust grains. Observational and theoretical evidence suggests that the effects of active star formation (in the form of intense UV fields, supernovae, etc.) on the CO emission may render it unreliable as a tracer of H2 in such galaxies. Dust continuum emission offers the potential for an independent probe of the interstellar molecular gas in stardust systems. The first part of the thesis concerns 450 μm mapping of the nearby starburst galaxy M82. In contrast to what might be expected if the CO and dust were both reliably tracing molecular hydrogen, the 450 μm map shows striking spatial dissimilarities to 12 CO line maps of the same region. Consideration of isotopic CO data suggests that optical depth effects may in part explain the discrepancy, while the effect of the vigorous nuclear star formation on the excitation state of the CO may also be an important factor. The optically thin 450 μm continuum emission shows no strong evidence for dust temperature gradients across the galaxy and appears to trace reliably the distribution of the grains and hence the gas with which they are associated. As a follow-up to the M82 observations, 800 μm dust continuum maps were made of three more nearby star-forming galaxies, Maffei 2, M83 and IC342. Together with 450-1100 μm photometry, these data fill an important gap in the long-wavelength spectra of such galaxies, enabling a study of the molecular material with which the dust is mixed. It is found that a single-temperature, modified blackbody dust spectrum cannot fit the observed submillimetre fluxes, unless the emissivity spectral index βchar61 1 all the way to 100 μm, with corresponding dust temperatures ~45 K. While this scenario cannot be ruled out by current grain models, a multitemperature dust grain population seems more plausible for a composite object such as a galaxy. A two-temperature spectral fit suggests that ~90% of the dust may be cool (~20-25 K), somewhat surprising in a galaxy exhibiting observational evidence of vigorous nuclear star formation. Possible reasons for this, as well as the effect of a large cool-dust fraction on the derived gas column densities and masses, are discussed.
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Randriamanakoto, Rojovola Zara-Nomena. "Super star cluster candidates in the star-forming regions of luminous infrared galaxies." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/11807.
Full textAbstract:
Includes abstract.Includes bibliographical references (leaves 86-90).
We report on a study of super star cluster (SSC) candidates in the star-forming regions of a representative sample of local luminous infrared galaxies (LIRGs) using KS-band near-infrared (NIR) adaptive optics imaging with GEMINI/ALTAIR and VLT/NACO instruments. The evolution of the cosmic star formation rate (CSFR) indicates its rapid decline in the local Universe.
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Marquart, Thomas. "Star-forming Dwarf Galaxies : Internal motions and evolution." Doctoral thesis, Uppsala universitet, Observationell astrofysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-181481.
Full textAbstract:
The study of dwarf galaxies is important in order to better understand the physics of the young universe and how larger galaxies form and evolve. In this work we focus on Blue Compact Galaxies (BCGs) which havemuch enhanced star formation (starbursts), causing blue colours and strong emission line spectra. Investigating of the inner motions of BCGs provides a means for determining masses and understanding what triggered the current starburst. We have used the Very Large Telescope to perform challenging observations of the stellar motions in several BCGs, as seen in the near-infrared Ca-triplet absorption lines. By comparing these to the kinematics of the ionized interstellar medium, we were able to look into the role of feeback from stellar winds and supernova explosions, as well as further strengthen the notion that the merging of galaxies plays an important role. Spatially resolved spectroscopy can yield information about the 3D-structure of galaxies. We have used a Fabry-Perot interferometer to study the kinematics of the interstellar medium in two samples of galaxies, each containing about twenty objects. We find strong indications for ongoing galaxy mergers that correlate well with the strength of the star-formation activity. Furthermore, by estimating dynamical masses, BCGs are shown to be on average not dynamically supported by rotation. In addition, we have used data from the Sloan Digital Sky Survey to study the frequency of starbursts in the local universe and the connection to their descendants. We selected starbursts by the strength of emission in H-alpha, the first Balmer recombination line, and post-starbursts by the strength of absorption in H-delta. These are indicators of currently ongoing and recent, on the order of 100 Myr, star-formation, respectively. By modelling the stellar populations we derive ages and masses and can establish a link between starbursts and postbursts in a time sequence. We find that starbursts are active on a 100 Myr timescale but are rare objects in the local universe.
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Rundle, David. "Molecular line transfer calculations in star forming regions." Thesis, University of Exeter, 2010. http://hdl.handle.net/10036/111934.
Full textAbstract:
This thesis describes the development, benchmarking and application of a non-LTE, co-moving frame Monte Carlo molecular line radiative transfer module for TORUS. Careful attention has been paid to the convergence, acceleration and optimisation of the code. I present the results of the application of the code to various benchmarking scenarios, including a collapsing cloud, a circumstellar disc and a very optically thick cloud of interstellar water. Benchmarking is an essential step in verifying the accuracy and efficiency of the code which is vital if it is to be used to analyse real data. In all cases, the code was able to accurately reproduce either the expected analytical solution or (in the absence of such a solution) was able to produce results commensurate with the results of other codes. In order to facilitate the motivating radiative transfer calculations of a star-forming cluster simulated using smoothed particle hydrodynamics (SPH) performed in this thesis, it was first necessary to devise and test an algorithm that efficiently maps an irregular distribution of smoothed particle hydrodynamics (SPH) particles onto a regular adaptive mesh. Whilst the algorithm was designed with this in mind it has also been used to study the effects of radiative feedback in circumstellar discs as well create a synthetic survey of a simulated galaxy. Bate et al.'s particle representation was resampled onto an adaptive mesh to enable me to use TORUS to obtain non-LTE level populations of multiple molecular species throughout the cluster and create velocity-resolved datacubes by calculating the emergent intensity using raytracing. I compared line profiles of cores traced by N2H+ (1-0) to probes of low density gas (13CO and C18O (1-0)) surrounding the cores along the line-of-sight. The relative differences of the line-centre velocities were found to be small compared to the velocity dispersion, matching recent observations. The conclusion is that one cannot reject competitive accretion as a viable theory of star formation based on observed velocity profiles.
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Furness, James. "Observations of young high mass star forming regions." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515251.
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Duval, Florent. "Lyman-alpha radiative transfer in Star-forming galaxies." Doctoral thesis, Stockholms universitet, Institutionen för astronomi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-111550.
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This thesis focuses on the intrinsically strongest spectral signature of star-forming galaxies: the Lyman alpha recombination line of the hydrogen atom (hereafter Lya). Located at the wavelength of 1215.67 Å in the restframe far-ultraviolet spectra of star-forming galaxies, the Lya line proves to be a vital tracer and a powerful emission-line window to discover and to study the remote young star-forming galaxies of the early the Universe. Although intrinsically very strong, the Lya line is also a resonant line. As a consequence, the transport of Lya photons inside the interstellar medium (ISM) of star-forming galaxies is very complex and depends on many ISM quantities (HI mass, dust content, HI gas kinematics and ISM clumpiness). All this process has serious effects on the emergent features of the Lya line (strength, equivalent width and line profile) that need to be understood for ensuring a proper interpretation of all very promising Lya-oriented studies in astrophysics and cosmology. This is precisely the aim of this thesis to go deeper into our understanding of the complex radiative transport experienced by the Lya line in star-forming galaxies. In this work, we carry out both numerical and observational studies of Lya transport inside the ISM of galaxies. In Paper I and II, we perform detailed numerical studies that examine the effects of a clumpy ISM on the strength and the shape of the Lya line. Although poorly studied until now, the effects of a clumpy ISM on Lya have been routinely invoked to explain the origin of anomalously strong Lya line observed from high-redshift galaxies. Some analytical studies suggest indeed an higher transmission of Lya photons over UV continuum ones from clumpy ISMs, resulting in an enhanced Lya equivalent width EW(Lya). Our results show that although clumpiness facilitates the escape of Lya, it is highly unlikely that any real ISM should result in any enhancement of EW(Lya). Other possible causes are discussed in our papers, leading to the conclusion that the observed high EW(Lya) are more likely produced by cooling radiation or anisotropic escape of Lya radiation. Both Paper III and IV are related to the LARS project. This is an ambitious observational program in which 14 nearby star-forming galaxies have been observed with the Hubble Space Telescope (HST) with the aim to investigate how Lya is transported out of galaxies and what effects each ISM quantity produces on the Lya line. While Paper III examines the Lya properties and morphology of individual galaxies, Paper IV presents a detailed study of the surprising Lya emission line of Mrk1486 (the fifth galaxy of the sample).At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.
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Wilding, Timothy Colin. "Probing the star-forming history of external galaxies." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318465.
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Kumari, Nimisha. "Spatially-resolved studies of nearby star-forming galaxies." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283605.
Full textAbstract:
Spatially-resolved studies of nearby star-forming galaxies are essential to understand various physical and chemical phenomena at play in the interstellar medium in the galaxies, and consequently to obtain a comprehensive picture of galaxy formation and evolution. In this thesis, I perform spatially-resolved analyses of chemical abundances and star-formation in nearby star-forming galaxies - blue compact dwarf galaxies (BCDs) and spiral galaxies. I map various properties of H II regions and the surrounding gas within three BCDs, using integral field spectroscopic (IFS) data from the Gemini Multi-Object Spectrograph-North. While answering questions related to chemical homogeneity, ionisation mechanisms and stellar populations within BCDs, I address more profound issues, which go beyond the characterisation of studied BCDs and aim to explain global phenomena with broader implications. The BCD NGC 4449 hosts a metal-poor central star-forming region, which I explain by various scenarios related to the interplay between star-formation, metal-distribution and gas dynamics within galaxies. The BCD NGC 4670 shows an unusual negative relationship between the nitrogen-to-oxygen ratio and oxygen abundance at spatially-resolved scales. I explore this relation with chemical evolution models and by comparison to other star-forming galaxies and suggest that nitrogen enrichment, variations in star-formation efficiency or hydrodynamical effects may be responsible for the observed relation. For another BCD, SBS 1415+437, the spatially-resolved abundances on average agree with the integrated abundance, implying that low-redshift spatially-resolved results may be directly compared with unresolved high-redshift results. I study spiral galaxies to address long-standing issues related to the reliability of metallicity calibrators and the Schmidt Law of star-formation. Using IFS data of twenty-four spiral galaxies taken with the Multi-Unit Spectroscopic Explorer, I find that the current strong-line metallicity calibrators for H II regions are unsuitable for regions dominated by diffuse ionised gas (DIG). I devise new recipes for estimating the metal-content of the DIG. For another set of nine spiral galaxies, I use multi-wavelength data to show that the spatially-resolved Schmidt relation is very sensitive to the consideration of diffuse background, which is a component unrelated to the current star-formation. Removal of this component from the SFR tracers and the atomic gas results in similar local and global Schmidt relation. To conclude, the spatially-resolved analyses presented in this thesis have led to discoveries and further questions, which I will address in my ongoing and future works.
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Hermanowicz, Maciej Tomasz. "Populations of star forming regions in nearby galaxies." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648576.
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Lorenzoni, Silvio. "Star-forming galaxies in the epoch of reionization." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:0ad7e1e3-cba3-4cef-9ccc-db3bb9278d02.
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This work presents a search for galaxies at 6.5 < z < 9.8 based on the Lyman-break technique, using the latest HST WFC3 near-infrared data covering ∼ 150 arcmin^2 of the GOODS-South field. With these data, it is possible to find sufficient z ≈ 7−9 galaxies to fit both φ∗ and M∗ of the UV Schechter luminosity function. There is evidence for evolution in this luminosity function from z = 6−7 to z = 8−9, in the sense that there are fewer UV-bright galaxies at z ≈ 8 − 9, consistent with an evolution mainly in M∗. The candidate z ≈ 7 − 9 galaxies detected have insufficient ionizing flux to reionize the Universe, and it is probable that galaxies below our detection limit provide a significant UV contribution. The faint-end slope, α, is not well constrained. Adopting a similar faint-end slope to that determined at z = 3 − 6 (α = −1.7), and a Salpeter initial mass function, reionization could be achieved at z ≈ 7 for an escape fraction of ionizing photons fesc = 0.5 integrating the luminosity function down to M_UV= −15, while at z ≈ 8, for the same fesc, the ionizing photon budget still falls short even integrating down to M_UV = −8. A steeper faint end slope or a low-metallicity population (or a top-heavy IMF) might still provide sufficient photons for star-forming galaxies to reionize the Universe, but confirmation of this might have to await the James Webb Space Telescope.
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Craigon, Alison M. "The morphology and kinematics of star forming regions." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27550.
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To develop a complete picture of the early stages of star and planet formation, it is necessary to understand the molecular clouds from which they form. The physical properties of these clouds and the interactions between their gas and solid constituents are not well known. This thesis presents an observational study of the morphology and kinematics of carbon monoxide(CO) gas in molecular clouds. It forms part of a wider project to produce the first coupled gas-solid maps of a broad sample of starless and star forming clouds. Nine molecular clouds were observed with the James Clerk Maxwell Telescope, the Institut de Radio Astronomie Millimétrique 30 m Telescope and the Nobeyama 45 m Radio Telescope to produce large scale(14.6 × 14.6 arcmin), high resolution (15.3 arcsec) maps of CO emission. The COROLINE software was developed to derive maps from the observations which show how the CO gas is distributed; the temperature and density structures of the clouds; and how the morphology and kinematics of CO gas is influenced by embedded and nearby stars. A comprehensive analysis is made of Barnard 35A: a cloud heavily processed both internally by a young stellar object and externally by massive stars. The temperature, density and velocity structures of this cloud are explored in detail. Observational evidence is proposed for photoelectric heating through a correlation between the gas temperature and emission from PolyAromatic Hydrocarbons. A clump of enhanced emission ahead of a Herbig–Haro object is thought to be due to photodesorption of CO ice from the surface of dust grains. A chain of similar clumps, following an arc equidistant from the YSO, suggest that the outflow is precessing. This work concludes with the first coupled gas-solid maps. This thesis demonstrates the importance of understanding the often complex morphology and kinematics of a star forming region prior to considering the interactions between its gas and solid-phase species.
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Martin, Clare E. "Alfvén waves in low-mass star-forming regions." Thesis, University of St Andrews, 1999. http://hdl.handle.net/10023/14190.
Full textAbstract:
Low-mass star-forming regions have a lifetime which is greater than their dynamical time and must therefore be, in an average sense, in mechanical equilibrium. The work presented here proposes that an equilibrium exists between the self-gravity, gas pressure, and the magnetic field and the waves it supports. Specifically the equilibrium in the direction perpendicular to the ordered magnetic field is given by the Lorentz force, while that parallel to the field is given by an Alfvén wave pressure force. The work detailed in this thesis models a low-mass star-forming region as a one-dimensional gas slab with a magnetic field lying perpendicular to the layer. Analytical, self-consistent models are formulated to study the equilibrium parallel to the background magnetic field. It is found that both short-wavelength (modelled using the WKB approximation) and large-amplitude, long-wavelength Alfvén waves can provide the necessary support parallel to the magnetic field, generating model cloud thicknesses that are consistent with the observations. The effect of damping by the linear process of ion-neutral friction is considered. It is found that the damping of the waves is not a necessary condition for the support of the cloud although it is an advantage. The possible sources of these waves are discussed. The Alfvén waves are also found to make an important contribution to the heating of a low-mass star-forming region. By modelling the dominant heating and cooling mechanisms in a molecular cloud, it is discovered that a cloud supported against its self-gravity by short-wavelength Alfvén waves will be hotter at its outer edge than in the central regions. These models successfully describe a low-mass star-forming region in equilibrium between its self-gravity, the gas pressure and an Alfvén wave pressure force. The question of the stability of such an equilibrium is considered, specifically that of an isothermal gas slab supported by short-wavelength Alfvén waves. The initial results suggest that the presence of a magnetic field and its associated Alfvén waves have a stabilising effect on the layer, and encourage further consideration of the role of Alfvén waves in low-mass star-forming regions.
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Tafere, Melaku S. "Gas flows and feedback in star-forming galaxies." Master's thesis, Faculty of Science, 2018. http://hdl.handle.net/11427/30016.
Full textAbstract:
In this MSc thesis, I investigated the kinematics of Hα emission from the hot ionized and NaD absorption from cool neutral gas in a sample of 40 nearby Luminous Infrared Galaxies (LIRGs: LIR ≥1011L) from Supernovae and starbursts in the infrared, SUNBIRD survey imaged with the Southern African Large Telescope (SALT). This project can be seen in two major areas. The first is analyzing the emission and absorption spectra, in this case from the hot ionized gas and cool gas respectively. Two routines were used for the profile fitting, to get the centroid wavelength of both the emission and absorption lines; Gaussian and Gaussian-Hermite functions were used. The fitting result provides an indication of the origin of an outflowing gas; nuclear or disk driven?. Secondly, I plotted and compared the velocities of hot ionized and cool neutral gas. Three different methods were used to estimate the systemic velocity Vsys for the accurate estimation of outflowing velocity. For instance, an outflowing NaD upto 380 kms−1 and inflowing gas up to -100 kms−1 relative to Hα is seen at the optical nucleus of the NGC6240[PA=45] and NGC1204[PA=253] galaxies respectively. I tested if there was a relation between star formation rate (SFR) and an outflowing gas and also whether the inflowing gas triggering new nuclear SF. I find the gas of two of our targets escaping the potential well of the host galaxy. There was also an expectation that the out flowing velocity would correlate with SFR, unfortunately I do not see any correlation, though it needs further investigation of all offset velocities of the gas with respect to stellar absorption lines and it also requires detail analysis of the of projection or orientation effect on the galaxy.
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Randriamampandry, Solohery Mampionona. "Stellar masses of star forming galaxies in clusters." University of the Western Cape, 2010. http://hdl.handle.net/11394/3028.
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Magister Scientiae - MScWe determine the stellar mass of star forming galaxies in the X-ray luminous cluster MS 0451.6-0305 at z ∼ 0.54. The stellar masses are estimated from fitting model spectral energy distributions (SEDs) to deep, optical UBRIz observations obtained from WIYN 3.5m telescope and public NIR K-band image from Palomar Observatory telescope. The model SEDs are based on the stellar population synthesis (SPS) model of Bruzual & Charlot (2003) and Conroy et al. (2009) that span a wide range of age, star formation history, Initial Mass Function (IMF), metallicity and dust content. We measure stellar masses for galaxies down to M∗∼2×10⁸M(.) We find a tight correlation between stellar masses derived from the two SPSs. We compare the derived stellar masses to the dynamical masses for a set of 25 star forming galaxies. The dynamical masses are derived from high resolution, spectroscopic observations of emission lines from the DEIMOS spectrograph on the Keck telescope. A strong correlation is seen between the dynamical and stellar mass for the galaxies; and the star forming galaxies show fairly constant ratio between stellar and dynamical mass. When comparing to the field sample of Guzm ́an et al. (2003) of luminous compact blue galaxies, we see an excess of low mass galaxies in the cluster.
South Africa
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Asboth, Viktoria. "Studying dusty star-forming galaxies with Herschel-SPIRE." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55041.
Full textAbstract:
Observations suggest that almost half of the total light emitted by stars in the Universe is absorbed by dust, and the emission is re-radiated at far-infrared and submillimeter wavelengths. Dusty star-forming galaxies play a significant role in the stellar mass build-up at high redshift, but their contribution to the cosmic star formation rate density at z > 4 is still unknown, due to the currently limited availability of statistically significant high-redshift dusty galaxy samples. In this thesis we analyze data from two large area surveys, the HerMES Large Mode Survey (HeLMS) and the Herschel Stripe 82 Survey (HerS), observed with the Herschel-SPIRE instrument at far-infrared wavelengths of 250, 350 and 500 μm. We describe the process of constructing maps from detector data that provide an unbiased estimate of the sky signal, then we use a map-based detection method to assemble a large catalog of candidate z > 4 dusty star-forming galaxies detected in HeLMS. The large area of the survey allows us to detect a significant number of sources and we are able to determine the differential number counts of these galaxies at 500 μm. We find an excess of such high-redshift galaxies compared to model predictions, and our counts suggest strong evolution in their properties.
We examine the properties of our sources at different wavelengths. Follow-up observations with ALMA, SCUBA-2 and ACT strengthen our initial assumption that the detected population consists of high-z dusty galaxies with their spectrum dominated by thermal dust emission, best fitted with an optically thick modified blackbody. These follow-up observations also allow us to examine the biasing effects in our number counts due to blending of nearby sources. We also investigate the mean dusty star formation activity in moderate redshift massive galaxy clusters detected by the Atacama Cosmology Telescope. We find that, on average, there is an excess of far-infrared emission in the line of sight of these clusters. Finding dusty star-forming galaxies in massive clusters implies that the environment can affect the star formation activity in galaxies.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Hindson, Luke Paul. "The G305 star forming complex : a panoramic view of the environment and star formation." Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/9197.
Full textAbstract:
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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Draper, Peter Walter. "CCD polarimetry as a probe of regions of recent star-formation." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6597/.
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Chapter 1 of this thesis details the incorporation of a Charged Coupled Device (CCD) detector system with the Durham Imaging Polarimeter. The details include the physical characteristics of the device and the electronics and software associated with the device control and data storage. The introduction of the CCD detector system haa made necessary the inclusion of a super-achromatic half-wave plate in the polarimeter which has an inherent variability in its optic axis. Chapter 2of this work describes fully how suitable corrections for this effect can be made, and derives "first order" results. The CCD performance is examined in comparison with the detector used previously and hence the veracity of the new results is established. Chapter 3 is a relevant summary of the status of the astronomy of the immediate regions of recent star-formation. Chapter 4 describes multicolour polarimetry of NGC2261/R Mon covering the period 1979 to 1986. The data conclusively proves that the polarisation of R Mon must be due to effects close to R Mon (~ 14 astronomical units). This is evident because of the dynamic timescale of the variations of the polarisation of R Mon and the anomalous band of polarisations seen across the head of the nebula. The interpretation presented is an extension of the Elsasser and Staude (1978) method of polarising objects embedded within the confines of a nearly edge-on disk. Detailed polarisations within the main nebula body provide evidence for this extended interpretation and also for an extensive helical magnetic field which may extend into the disk. Also it is seen that R Mon must still be "shrouded" in material preventing light from directly reflecting in the main nebula body. It is not thought that the variations in the region close to R Mon are due to planetary bodies but to accretion from the disk. The results of this re-interpretation of the polarising mechanism are tentatively applied to other similar objects.
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Gómez, Ruiz Arturo [Verfasser]. "Molecular Outflows in Star Forming Regions / Arturo Gómez Ruiz." Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1052582044/34.
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Meger, Nicole. "BzKs in GOODS-N : z~2 star forming galaxies." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/7581.
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This thesis presents new deep near-infrared imaging data in one of the most
well studied regions of the sky, the Great Observatories Origins Deep Survey's
northern field (GOODS-N). In particular, we have produced a science grade
Ks-band (2.2 μm) source catalogue with a depth of KS(AB) = 23.8
magnitudes. With our K-selected sample, we use the BzK two-colour se
lection criterion to find galaxies lying at redshifts between 1.4 and 2.5. We
investigate the redshift distribution of these BzKs using spectroscopic redshifts
as well as a new photometric redshift catalogue and find respectively,
13% and 14% contamination from low redshift interlopers. We then com
pare the relationship between star formation rate and stellar mass with three
different star formation rate estimators, derived from the rest-frame ultra
violet, mid-infrared and radio properties. We obtain similar relationships
from each of these methods and discuss the inherent uncertainty in estimat
ing high redshift star formation rates. Finally, we test the BzK selection
method with two extreme z~2 galaxy populations. The BzK criterion is
able to select submillimetre galaxies at redshifts from 1.4 to 2.5 even though
they have extreme star formation rates, and it can also effectively select
highly dust obscured galaxies.
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Schmeja, Stefan. "Properties of turbulent star forming clusters: models versus observations." Phd thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980518660.
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Elston, Richard Joseph. "Search for rapidly star-forming galaxies at high redshift." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184574.
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We have conducted three surveys to try and locate distant star forming galaxies. The most general survey used deep 2μ images with optical CCD photometry to locate objects with peculiar SEDs. Using the IR data we should be able to locate rapidly star forming galaxies to z = 25. With a 3σ detection limit of 18.5 at K we have found no objects with z > 5 but we have found several blue objects at z < 4 in 16min² of sky. This suggests tha there is no extremely luminous early phase of galaxy formation. We have found several blue objects at z < 4 in 10min² of sky. Of particular interest is an object which has a flat SED from V to K but shows a strong spectral break between B and V and a weaker break at 5800Å. We suggest these may be Lyman limit and Lyman α forest absorption at z-3.8 in a galaxy forming ≈400M(⊙) year⁻¹ of stars. A large sample of galaxies (100 objects) selected to have similar properties (R – I < .5, B – R > 1) has also been found. From this sample it appears this possible high redshift star forming phase only contributes 1/10 of the metal present in disks or spheroids. We have also found 30 Lyman α emission line companions to 12 z = 3 quasars. These objects have Lyman α equivalent widths (50Å) and luminosities (V = 24) consistent with galaxies forming ≈100M(⊙) year⁻¹ of stars. Also, 2 of the quasars have 8 companions and may be in cluster environments. A final survey analyzed optical to IR SEDs of luminous blue radio galaxies at z > 1. In these objects we find SEDs indicative of star formation rates between 10 and 100M(⊙) year⁻¹ but interpretation is difficult due to the AGN component of the sources. While these data seem to suggest a significant star forming phase taking place in galaxies at z ≈ 3-4, interpreting this result is difficult since we cannot determine if we are observing disk or spheroidal populations. In the case of the quasar companions and the radio galaxies, consideration of their dense environments and current epoch morphology suggest that these may be spheroids but these galaxies may not be typical of galaxies in general.
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Afonso, JoseÌ Manuel Lourenço Coutinho. "On the star-forming properties of faint radio sources." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271584.
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Davies, Luke Jonathan Mark. "A multi-wavelength study of early star-forming galaxies." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539761.
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Rane, Akshaya. "Physical Conditions in a Galactic Star forming region W22." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_theses/158.
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This document describes study of an active star forming region in our galaxy (the Milky Way) known as W22. Physical conditions in these regions can help us in understanding star formation processes in the universe and hence the structure and evolution of the universe. Zeeman effect measurements in 18 cm OH absorption line were carried out in order to estimate the line of sight magnetic field strength in the molecular cloud associated with this star forming region. Other physical parameters such as hydrogen column density, optical depth, critical magnetic field were also determined from these measurements. The region was mapped at 18 cm and the distribution of molecular gas within this star forming complex was described.
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Parkes, I. M. "A search for star-forming galaxies at high redshift." Thesis, University of Edinburgh, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.660361.
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This thesis describes the first search for star formation in primeval galaxies (PGs) at redshifts z ≥ 7. Our method was to undertake deep near-infrared imaging in the J window (~ 1.0 - 1.5μm) using four narrowband filters of 2% FWHM. Over an area of sky of 3.0?1, no emission line object was found to a sensitivity limit of ≈ 10-18 Wm-2. Interpreting this limit in terms of a limit on Lyα emission, it has been possible to place the first constraints on star formation at redshifts 7≤ z ≤ 9. The search is also sensitive to other emission lines at lower redshifts, of particular interest are the constraints placed on Hα emission. This line is a direct tracer of star formation (Kennicutt et al., 1987) and, at the wavelengths of the narrowband filter, it probes redshifts 0.5 ≤ z ≤ 0.9. Constraints on the star formation rate at these redshifts are of great interest in the interpretation of the excess of faint blue objects seen in number counts (Tyson 1988, Lilly et al. 1991, Metcalfe et al. 1991, Jones et al., 1991). By assuming that there is no evolution in the comoving number density of galaxies out to z = 9, and that the luminosity function of objects at these redshifts can be represented by a Schechter function, it is possible to use the limits of the IRCAM search to place constraints on the characteristic Lyα luminosity L*(Lyα) of PGs. Two extremes for the bright phase Δtbright of each galaxy are considered. In Case 1, Δtbright spans the four narrowband filters (~ 108 years). In Case 2, the bright period is much shorter, and the specific case of the Partridge & Peebles (1966) model is considered (Δtbright = 3 X 107 years). The 95% confidence limits for Case 1 models constrain L*(Lyα) to less than 1.6 X 1037 W - 4.2 X 1037 W, depending on the cosmological model. These limits are consistent with the Case 1 predictions for Lyα luminosity.
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Giannetti, Andrea <1986>. "The evolution of massive clumps in star forming regions." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6216/.
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In this thesis two related arguments are investigated:
- The first stages of the process of massive star formation, investigating the physical conditions and -properties of massive clumps in different evolutionary stages, and their CO depletion;
- The influence that high-mass stars have on the nearby material and on the activity of star formation.
I characterise the gas and dust temperature, mass and density of a sample of massive clumps, and analyse the variation of these properties from quiescent clumps, without any sign of active star formation, to clumps likely hosting a zero-age main sequence star. I briefly discuss CO depletion and recent observations of several molecular species, tracers of Hot Cores and/or shocked gas, of a subsample of these clumps.
The issue of CO depletion is addressed in more detail in a larger sample consisting of the brightest sources in the ATLASGAL survey: using a radiative tranfer code I investigate how the depletion changes from dark clouds to more evolved objects, and compare its evolution to what happens in the low-mass regime.
Finally, I derive the physical properties of the molecular gas in the photon-dominated region adjacent to the HII region G353.2+0.9 in the vicinity of Pismis 24, a young, massive cluster, containing some of the most massive and hottest stars known in our Galaxy. I derive the IMF of the cluster and study the star formation activity in its surroundings.
Much of the data analysis is done with a Bayesian approach. Therefore, a separate chapter is dedicated to the concepts of Bayesian statistics.
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Noble, Allison. "Dusty star-forming galaxies within high-redshift galaxy clusters." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123107.
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We present a multi-wavelength perspective of star-forming galaxies within high-redshift galaxy clusters. The clusters derive from the Red-sequence Cluster Survey (RCS) and the Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS), and possess ample spectroscopic coverage, yielding numerous confirmed cluster members. This thesis consists of a collection of distinct but related works, focusing on environmental effects within the dense regions of clusters---some of the rarest structures in the Universe. We exploit the high sensitivities of cutting-edge infrared and submillimeter telescopes to glean the wealth of information encoded within the thermal portion of the spectral energy distribution, including infrared luminosities and dust temperatures. This allows us to uncover various trends within the star-forming population as a function of environment. Moreover, we develop a novel definition of environment, based on the phase space of radius and velocity, to account for the various accretion histories of galaxies onto clusters; it thereby probes the time-averaged density that each galaxy population has experienced. Using this tracer of environment, we find a significant depression in the star formation rate per unit stellar mass for star-forming galaxies within cluster cores at z~0.9 and z~1.2, in contrast to the flat trend that results from conventional definitions of environment. We also discover a population of galaxies that have lower dust temperatures compared to both infalling galaxies and those that were accreted at the earliest stages of the formation of the cluster. Taken together, these trends in star formation rate and dust temperature can help elucidate which, if any, quenching mechanisms are active within cluster environments. Finally, we report the serendipitous detection of an overdensity of submillimeter-bright galaxies located behind a merging z~0.9 supercluster, which could signify a highly star-forming protocluster at z~3.Nous présentons une analyse multi-fréquentielle de galaxies à formation d'étoiles situées à l'intérieur d'amas de galaxies fortement décalés vers le rouge. Ces amas en provenance du sondage Red-sequence Cluster Survey (RCS) et de son adaptation par Spitzer (SpARCS) possèdent une large couverture spectroscopique et contiennent plusieurs membres confirmés. Cette thèse représente une collection de travaux distincts mais reliés, qui se concentrent sur les effets environnementaux présents à l'intérieur des régions denses d'amas de galaxies, des structures parmi les plus rares de l'Univers. Nous exploitons la sensibilité élevée des télescopes infrarouges et submillimétriques de pointe pour collecter l'information encodée dans la portion thermale de la distribution spectrale d'énergie, ce qui inclue des mesures de luminosité infrarouge et des températures de poussière. Cette méthode nous permet de dévoiler plusieurs tendances en cours à l'intérieur de la population de galaxies à formation d'étoiles en fonction de l'environnement où se trouvent ces galaxies. De plus, nous développons une nouvelle définition de ce qui constitue l'environnement d'une galaxie basée sur l'espace de phase du rayon et de la vitesse. Cette définition tient compte des nombreux épisodes d'accrétion de galaxies par les amas de galaxies, traçant ainsi la densité moyenne connue par chaque population de galaxies. En utilisant ce nouveau traceur d'environnement, nous trouvons un manque important dans le taux de formation d'étoiles par unité de masse stellaire pour les galaxies à formation d'étoiles situées au coeur d'amas de galaxies entre z~0.9 et z~1.2, ce qui contraste avec le taux constant résultant d'une définition conventionnelle de l'environnement. Nous avons aussi découvert une population de galaxies ayant des températures de poussière plus basse que celles associées à des galaxies qui tombent ou qui ont été accrétées au début de la formation de l'amas de galaxies. Considérées ensemble, ces tendances caractérisant le taux de formation d'étoiles et la température de poussière peuvent aider à mettre en lumière les mécanismes de relaxation actifs à l'intérieur des amas de galaxies. Pour terminer, nous rapportons la détection fortuite d'une surdensité de galaxies submillimétriques situées derrière un superamas de galaxies à z~0.9, ce qui pourrait indiquer la présence d'un proto-amas à haute formation d'étoiles à z~3.
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Ruffle, Deborah Patricia. "The physical and chemical evolution of star forming regions." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300792.
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