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1
Dale, J. E. "Feedback in star cluster formation." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598249.
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Massive stars emit strong fluxes of ionising radiation and their dynamical impact on their natal clusters is expected to be severe. The outflows generated expel residual gas from the cluster and can potentially gravitationally disrupt it. The loss of its reserves of molecular gas also prevents the cluster forming more stars. Star-formation and star cluster evolution cannot be fully understood without a proper treatment of feedback. I present a novel technique I have developed to allow the inclusion of the effects of ionising radiation in smoothed particle hydrodynamics (SPH) simulations of star clusters. The new algorithm is able to reproduce the results of simple analytical models and also gives results in good agreement with a more sophisticated Monte Carlo radiative transfer code when tested under highly anisotropic conditions. I simulate the effects of ionising radiation in globular clusters and compare my results with one-dimensional calculations with which I find good agreement. I investigate three cases in which different quantities of gas are distributed in my model cluster such that the as becomes fully ionised either during the HII region’s formation phase, or during its expansion phase, or such that the HII region is trapped inside the cluster core. I find gas expulsion to be quite efficient in the calculations in which the HII region escapes the core. I observe an instability in the second calculation which causes the shocked shell driven by the ionisation front to fragment as the HII region exits the core. The instability produces new structure from the smooth gas in the system, but this structure is rapidly destroyed by the radiation field and the effect of the instability on the evolution of the system is minimal. I also simulate feedback in the context of young embedded clusters, a highly inhomogeneous and anisotropic environment. I find that, again, photoionisation is able to produce novel structure in the ambient gas, causing it to fragment into filaments and beads. This fragmentation of the neutral gas, together with compression by hot ionised gas, which decreases the Jeans mass, lead me to conclude that feedback promotes star formation.
2
Adamo, A., J. E. Ryon, M. Messa, H. Kim, K. Grasha, D. O. Cook, D. Calzetti, et al. "Legacy ExtraGalactic UV Survey with The Hubble Space Telescope: Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 628." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624449.
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We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes similar to-2 and a truncation of a few times 10(5) M-circle dot. After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find massindependent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (<= 10(4) M-circle dot) clusters, suggesting that a massdependent component is necessary to fully describe the YSC disruption process in NGC 628.
3
Breen, Philip Gavin. "Dynamical evolution of idealised star cluster models." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8296.
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This thesis is concerned with the dynamical evolution of globular star clusters modelled as the classical gravitational N-body problem. The models in this thesis are idealised in order to allow the detailed study of particular dynamical aspects of the cluster evolution. Examples of properties which tend to be omitted are stellar evolution, primordial binaries and the effect of an external tidal gravitational field. The methods used in this thesis are gas models, N-body models and physical arguments. One of the main topics in this thesis is gravothermal oscillations in multicomponent star clusters. The evolution of one-component globular clusters, systems with equal particle masses, is quite well understood. However, the evolution of more realistic globular clusters, with a range of particle masses, is a much more complicated matter. The condition for the on-set of gravothermal oscillations in a one-component system is simply that the number of stars is greater than a certain number ( ≈7000). In a multi-component system the relationship between the number of stars at which the gravothermal oscillations first appear and the stellar mass distribution of a cluster is a complex one. In order to investigate this phenomenon two different types of multi-component systems were studied: two-component systems (the simplest approximation of a mass spectrum, Chapter 2) and ten-component systems (which were realisations of continuous power law IMFs, Chapter 3). In both cases the critical number of stars at which gravothermal oscillations first appear are found empirically for a range of stellar mass distributions. The nature of the oscillations themselves are investigated and it is shown that the oscillations can be understood by focusing on the behaviour of the heavier stars within the cluster. A parameter Nef (de nined Mtot/mmax where Mtot is the total mass and mmax is the maximum stellar mass) acts as an approximate stability boundary for multicomponent systems.The stability boundary was found to be at Nef ~- 12000. In this Chapter 4, globular star clusters which contain a sub-system of stellar-mass black holes (BH) are investigated. This is done by considering two-component models, as these are the simplest approximation of more realistic multi-mass systems, where one component represents the BH population and the other represents all the other stars. These systems are found to undergo a long phase of evolution where the centre of the system is dominated by a BH sub-system. After mass segregation has driven most of the BH into a compact sub-system, the evolution of the BH sub-system is found to be in uenced by the cluster in which it is contained. The BH sub-system evolves in such a way as to satisfy the energy demands of the whole cluster, just as the core of a one component system must satisfies the energy demands of the whole cluster. The BH sub-system is found to exist for a significant amount of time. It takes approximately 10trh;i, where trh;i is the initial half-mass relaxation time, from the formation of the compact BH sub-system up until the time when 90% of the sub-system total mass is lost (which is of order 103 times the half-mass relaxation time of the BH sub-system at its time of formation). Based on theoretical arguments the rate of mass loss from the BH sub-system (M2) is predicted to be (βζM)/(αtrh): where M is the total mass, trh is the half-mass relaxation time, and α, β, ζ are three dimensionless parameters. (see Section 4.3 for details). An interesting consequence of this is that the rate of mass loss from the BH sub-system is approximately independent of the stellar mass ratio (m2/m1) and the total mass ratio (M2/M1) (in the range m2/m1 ≥ 10 and M2/M1 ≈ 10-2, where m1, m2 are the masses of individual low-mass and high-mass particles respectively, and M1, M2 are the corresponding total mass). The theory is found to be in reasonable agreement with most of the results of a series of N-body simulations, and all of the models if the value of ζ is suitable adjusted. Predictions based on theoretical arguments are also made about the structure of BH sub-systems. Other aspects of the evolution are also considered such as the conditions for the onset of gravothermal oscillation. The final chapter (Chapter 5) of the thesis contains some concluding comments as well as a discussion on some possible future projects, for which the results in this thesis would be useful.
4
Pozzo, Monica. "The effect of high-mass stars on low-mass star formation." Thesis, Keele University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366445.
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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.
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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.
6
Canning, Rebecca Elizabeth Ann. "Star and filament formation in brightest cluster galaxies." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610523.
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Santoro, Fernando. "Semi analytical simulations of primordial star cluster formation." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288843.
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Simanton, Lesley Ann. "Star Cluster Populations in the Spiral Galaxy M101." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1437587267.
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Harris, William E., Stephanie M. Ciccone, Gwendolyn M. Eadie, Oleg Y. Gnedin, Douglas Geisler, Barry Rothberg, and Jeremy Bailin. "GLOBULAR CLUSTER SYSTEMS IN BRIGHTEST CLUSTER GALAXIES. III. BEYOND BIMODALITY." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/622870.
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We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the Hubble Space Telescope (HST) ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12,000 to 23,000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes are separated by similar or equal to 0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H] similar or equal to-2.4 to solar. There are, however, significant differences between galaxies in the relative numbers of metal-rich clusters, suggesting that they underwent significantly different histories of mergers with massive gas-rich halos. Last, the proportion of metal-poor GCs rises especially rapidly outside projected radii R >= 4 R-eff, suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.
10
Messa, M., A. Adamo, G. Östlin, D. Calzetti, K. Grasha, E. K. Grebel, F. Shabani, et al. "The young star cluster population of M51 with LEGUS – I. A comprehensive study of cluster formation and evolution." OXFORD UNIV PRESS, 2018. http://hdl.handle.net/10150/626277.
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Recently acquired WFC3 UV (F275W and F336W) imaging mosaics under the Legacy Extragalactic UV Survey (LEGUS), combined with archival ACS data of M51, are used to study the young star cluster (YSC) population of this interacting system. Our newly extracted source catalogue contains 2834 cluster candidates, morphologically classified to be compact and uniform in colour, for which ages, masses and extinction are derived. In this first work we study the main properties of the YSC population of the whole galaxy, considering a mass-limited sample. Both luminosity and mass functions follow a power-law shape with slope -2, but at high luminosities and masses a dearth of sources is observed. The analysis of the mass function suggests that it is best fitted by a Schechter function with slope -2 and a truncation mass at 1.00 +/- 0.12 x 10(5) M-circle dot . Through Monte Carlo simulations, we confirm this result and link the shape of the luminosity function to the presence of a truncation in the mass function. A mass limited age function analysis, between 10 and 200 Myr, suggests that the cluster population is undergoing only moderate disruption. We observe little variation in the shape of the mass function at masses above 1 x 10(4) M-circle dot over this age range. The fraction of star formation happening in the form of bound clusters in M51 is similar to 20 per cent in the age range 10-100 Myr and little variation is observed over the whole range from 1 to 200 Myr.
11
Chatzopoulos, Sotirios. "The old Nuclear Star Cluster in the Milky Way." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-184835.
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Fensch, Jérémy. "Star and stellar cluster formation in gas-dominated galaxies." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC207/document.
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Nous étudions la formation d’étoiles et d’amas d’étoiles dans les galaxies dominées par le gaz. Ce terme réfère en premier lieu aux galaxies de l’époque du pic de formation d’étoiles dans l’histoire de l’Univers, qui s’est déroulé vers z ~ 2, mais aussi à leurs analogues locaux, les galaxies naines de marées. En premier lieu, en utilisant des simulations numériques, nous montrons que les galaxies massives typiques de z=2, avec une fraction de gaz d’environ 50%, forment des structures gazeuses massives (10**7-8 masses solaires) et liées gravitationnellement, appelées grumeaux dans la suite. Ces grumeaux ne se forment dans des galaxies avec une fraction de gaz inférieure à 25%. Nous présentons ensuite une étude observationnelle d’un analogue local de grumeaux de galaxies à z=2, la galaxie naine de marée NGC 5291N. Une analyse des raies d’émission de cette galaxie montre la présence de chocs sur les pourtours de l’objet. La photométrie des amas d’étoiles de cette galaxie montre que les amas les plus jeunes (< 10 millions d’années) sont significativement moins massifs que les amas plus âgés. Ceci peut être le signe de fusions progressives d’amas et/ou d’une forte activité de formation stellaire dans ce système il y a environ 500 millions d’années.Dans un second lieu nous étudions comment la fraction de gaz influe sur la formation d’étoiles et d’amas stellaires dans des fusions de galaxies à z=2. En utilisant des simulations numériques nous montrons que ces fusions n’augmentent que relativement peu le taux de formation d’étoiles et d’amas stellaires comparativement aux fusions de galaxies locales, à faible fraction de gaz. Nous montrons que ceci est due à une saturation de plusieurs facteurs physiques, qui sont déjà présents naturellement dans les galaxies isolées à z=2 et sont donc comparativement peu accentués par les fusions. Il s’agit de la turbulence du gaz, des zones de champ de marée compressif et des flux de matières vers le noyau de la galaxie. Nous montrons aussi que les structures stellaires formées au sein des grumeaux de gaz sont préservées par la fusion : elles sont éjectées des disques et orbitent dans le halo de la galaxie résultante de la fusion, où elles peuvent devenir les progéniteurs de certains amas globulairesWe study the formation of stars and stellar clusters in gas-dominated galaxies. This term primarily refers to galaxies from the epoch of the peak of the cosmic star formation history, which occurred at z ~ 2, but also to their local analogues, the tidal dwarf galaxies.Firstly, using numerical simulations, we show that the massive galaxies at z = 2, which have a gas fraction of about 50%, form massive (10**7-8 solar masses) and gravitationally bound structures, which we call clumps thereafter. These clumps do not form in galaxies with a gas fraction below 25%. We then present an observational study of a local analogue of a z = 2 galactic clump, which is the tidal dwarf galaxy NGC 5291N. The analysis of emission lines show the presence of shocks on the outskirts of the object. Photometry of this galaxy’s stellar clusters show that the youngest clusters (< 10 million years) are significantly less massive than older clusters. This could be the sign of ongoing cluster mergers and/or of a strong star formation activity in this system about 500 million years ago).Secondly, we study how the gas fraction impacts the formation of stars and stellar clusters in galaxy mergers at z = 2. Using numerical simulations we show that these mergers only slightly increase the star and stellar cluster formation rate, compared to local galaxy mergers, which have a lower gas fraction. We show that this is due to the saturation of several physical quantities, which are already strong in isolated z=2 galaxies and are thus less enhanced by the merger. These factors are gas turbulence, compressive tides and nuclear gas inflows, We also show that the stellar structures formed in the gaseous clumps are preserved by the fusion: they are ejected from the disk and orbit in the halo of the remnant galaxy, where they may become the progenitors of some globular clusters
13
Pfuhl, Oliver. "The GRAVITY interferometer and the Milky Way’s nuclear star cluster." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-148778.
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Thomas, Claire F. "Environmental dependence of star formation in field and cluster galaxies." Thesis, Liverpool John Moores University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439066.
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Crnojević, D., D. J. Sand, D. Zaritsky, K. Spekkens, B. Willman, and J. R. Hargis. "DEEP IMAGING OF ERIDANUS II AND ITS LONE STAR CLUSTER." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621260.
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We present deep imaging of the most distant dwarf discovered by the Dark Energy Survey, Eridanus II (Eri II). Our Magellan/ Megacam stellar photometry reaches similar to 3 mag deeper than previous work and allows us to confirm the presence of a stellar cluster whose position is consistent with Eri II's center. This makes Eri II, at M-V = -7.1, the least luminous galaxy known to host a (possibly central) cluster. The cluster is partially resolved, and at MV = -3.5 it accounts for similar to 4% of Eri II's luminosity. We derive updated structural parameters for Eri II, which has a half-light radius of similar to 280 pc and is elongated (epsilon similar to 0.48) at a measured distance of D similar to 370 kpc. The color-magnitude diagram displays a blue, extended horizontal branch, as well as a less populated red horizontal branch. A central concentration of stars brighter than the old main-sequence turnoff hints at a possible intermediate-age (similar to 3 Gyr) population; alternatively, these sources could be blue straggler stars. A deep Green Bank Telescope observation of Eri II reveals no associated atomic gas.
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Wilking, B. A., C. J. Lada, and E. R. Young. "IRAS Observations of the Rho Ophiuchi Infrared Cluster: Spectral Energy Distributions and Luminosity Function." Steward Observatory, The University of Arizona (Tucson, Arizona), 1988. http://hdl.handle.net/10150/623919.
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Tsai, Chao-Wei. "Star cluster formation in the nuclear regions of nearby spiral galaxies." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1997620851&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Kuntschner, Harald. "The star formation history of early-type galaxies in the Fornax cluster." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4849/.
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We have measured central line strengths and line-strength gradients for a complete sample of early-type galaxies in the Fornax cluster, comprising 11 elliptical and 11 lenticular galaxies, more luminous than M(_B) = -17. We find that the centres of Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have metallicities varying roughly from half solar to 2.5 times solar. Line-strength gradients indicate that elliptical galaxies do not show age gradients with radius but do exhibit a decrease of ~ 0.4 dex in [Fe/H] between the centre and one effective radius. The centres of lenticular galaxies however exhibit a substantial spread to younger luminosity weighted ages indicating a more extended star formation history. Metallicity gradients are generally shallower than for ellipticals. Five of the faint S0s have experienced a central starburst on top of an underlying older stellar population. Our conclusions are based on several age/metallicity diagnostic diagrams in the Lick/IDS system comprising established indices such as [MgFe] and Hβ as well as new and more sensitive indices such as C4668, Fe3 and Hγ(_A). The inferred difference in the age distribution between lenticular and elliptical galaxies is a robust conclusion as the models generate consistent relative ages using different age and metallicity indicators even though the absolute ages remain uncertain. The absolute age uncertainty is caused by the effects of non-solar abundance ratios which are not accounted for in the stellar population models. We find that Es are generally overabundant in magnesium where the most luminous galaxies show stronger overabundances. The luminosity weighted stellar populations of young S0s are consistent with solar abundance ratios, however the bulges of the two large S0s in our sample have [Mg/Fe] > 0. We have analysed in detail the sources of scatter in the Mg-crg relation by investigating the effects of age, metallicity and [Mg/Fe] variations. We find that young stellar populations are responsible for most of the scatter towards weak Mg-absorption. However, for the roughly coeval ellipticals the scatter at a given ctq is correlated with [Mg/Fe variations; metallicity and age effects seem to be less important. The young luminosity weighted ages of the faint S0s in the Fornax cluster are consistent with the recent discovery that the fraction of S0 galaxies in intermediate redshift clusters is a factor of 2-3 lower than found locally, and suggests that a fraction of the cluster spiral galaxy population has evolved into these faint S0s in the 5 Gyrs interval from z = 0.5 to the present. One of the proposed transformation mechanisms is the galaxy harassment picture. The properties of young S0s with large bulge to disk ratios in our sample are remarkably similar to the proposed end-products of galaxy harassment. However, we note that there are young disky S0s which are unlikely to be the result of harassment. Two of the faintest lenticular galaxies in our sample have blue continua and extremely strong Balmer-line absorption suggesting starbursts < 2 Gyrs ago.
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Pierce, Michael John, and n/a. "Spectroscopy of extra-galactic globular clusters." Swinburne University of Technology, 2006. http://adt.lib.swin.edu.au./public/adt-VSWT20070731.104253.
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The focus of this thesis is the study of stellar populations of extra-galactic glob-
ular clusters (GCs) by measuring spectral indices and comparing them to simple
stellar population models. We present the study of GCs in the context of tracing
elliptical galaxy star formation, chemical enrichment and mass assembly.
In this thesis we set out to test how can be determined about a galaxy's formation
history by studying the spectra of a small sample of GCs. Are the stellar population
parameters of the GCs strongly linked with the formation history of the host galaxy?
We present spectra and Lick index measurements for GCs associated with 3 el-
liptical galaxies, NGC 1052, NGC 3379 and NGC 4649. We derive ages, metallicities
and a-element abundance ratios for these GCs using the x2 minimisation approach
of Proctor & Sansom (2002).
The metallicities we derive are quite consistent, for old GCs, with those derived
by empirical calibrations such as Brodie & Huchra (1990) and Strader & Brodie
(2004). For each galaxy the GCs observed span a large range in metallicity from
approximately [Z/H]=�2 to solar.
We find that the majority of GCs are more than 10 Gyrs old and that we can-
not distinguish any finer, age details amongst the old GC populations. However,
amongst our three samples we find two age distributions contrary to our expecta-
tions. From our sample of 16 GCs associated with the 1-2 Gyr old merger remnant
NGC 1052, we find no young GCs. If a significant population of GCs formed during
this merger we would expect those GCs to have low mass-to-light ratios and be
included in our sample of bright GCs. We find 4 young GCs in our sample of 38
around NGC 4649, an old massive cluster elliptical. There are no signs of recent
star formation and therefore we do not expect any GCs to have formed within the
galaxy. These results seem to indicate that the GC systems of elliptical galaxies are
not strongly associated with recent field star formation.
We find a correlation between the α-element abundance ratio and the metallicity
for all three samples. Using Thomas, Maraston & Korn (2004) models, we measure
much higher α abundance ratios for low metallicity GCs than high metallicity GCs.
With current data and models we are limited in both the accuracy and the detail
with which we can probe this relationship.
We suggest that there are some difficulties reconciling measured GC parameters
with our expectations and propose some future work which could help to resolve
these and other issues.
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Vincke, Kirsten [Verfasser], and Susanne [Gutachter] Pfalzner. "How star cluster evolution shapes protoplanetary disc sizes / Kirsten Vincke ; Gutachter: Susanne Pfalzner." Köln : Universitäts- und Stadtbibliothek Köln, 2018. http://d-nb.info/1191895785/34.
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Walsh, A. P. "New perspectives on magnetotail dynamic processes from combined cluster and double star observations." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/18606/.
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In this thesis, observations of the Earth's magnetotail from ESA's four Cluster and the two Sino-European Double Star spacecraft are presented. The observations are of intervals where data from the combination of Cluster and Double Star provide insights into the dynamics of the magnetotail that are not possible using data from one mission alone. In the first study, observations of three magnetic flux ropes are presented, two of which were detected near-simultaneously at Cluster and Double Star TC-1, while the third was detected by Cluster, along with a TCR a few minutes later. The observations represent the first observations of multiple flux ropes existing in the magnetotail simultaneously, providing evidence that flux rope orientation is influenced by neutral sheet tilt and provide further evidence that TCRs in the lobes are caused by the passage of flux ropes in the plasma sheet. In the second study, a detailed analysis of a plasma bubble is presented, including the first direct observations of the return flows around the flanks of the plasma bubble that are expected from theory and simulation. Furthermore a partially stagnant depleted wake behind the plasma bubble, not predicted by theory or simulation was discovered and the cross-tail extent of the bubble was measured to be 3RE. The first observations of near-Earth bubble features are also reported. Finally, in the third study, the substorm onset process itself is investigated using a wide array of space- and ground-based instrumentation. A pseudobreakup and later substorm onset are distinguished using both geomagnetic and auroral data and the establishment of the substorm current wedge is observed in-situ using the TC-2 and GOES12 spacecraft. A link between higher latitude geomagnetic activity and the fast flows and plasma sheet expansion related to the reconnection of lobe field lines is also posited.
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Scandariato, Gaetano. "The Initial Mass Function of the Orion Nebula Cluster from Near-Infrared Photometry." Doctoral thesis, Università di Catania, 2012. http://hdl.handle.net/10761/1027.
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The main goal of this thesis is the complete characterization of the IMF of the Orion Nebula Cluster (ONC) down to the Brown Dwarfs (BDs) regime, using ground-based Near-Infrared (NIR) photometric observations. The data taken in the framework of the Hubble Space Telescope (HST) Treasury Program on the ONC have been obtained with the wide-field imager Infrared Side Port Imager (ISPI) at the Blanco 4m telescope of CTIO, and cover an area of about 0.25 square degrees roughly centered on Theta1OriC. We observed the region in the JHKS bands with exposure times of 330 s. As a result of our survey, we provide
2MASS-calibrated astrometry and photometry for ~7000 sources in the ONC region.
Analyzing our photometric sample, we derive the contamination-completeness corrected (J,J-H) CMDs of the ONC, canceling out the contribution from the contaminant population. We also develop a statistical algorithm, which combines the CMD of the ONC with our reference isochrone and, taking into account the presence of extinction and NIR excess, derives the intrinsic Luminosity Function (LF) of the cluster. We finally combine the LF with our empirical NIR isochrone to derive a statistical estimate of the IMF at different distances from the cluster center. We find that the mass distribution of the cluster is peaked at ~0.16 M and falls off crossing the hydrogen burning limit, continuously decreasing in the BDs domain down to ~0.03 M . We also find that the substellar-to-stellar objects ratio in the ONC decreases with increasing distance from the cluster center, suggesting that BDs are preferentially formed in the deep gravitational potential well where the most massive stars of the Trapezium cluster are also found.
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Bai, Lei. "The Effects of Dense Cluster Environments on Galaxies and Intracluster Dust." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/193609.
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Dense cluster environment influences the properties of galaxies and their evolution. In order to understand this environmental effect and how it evolves with time, we study the infrared (IR) properties of galaxies in three rich clusters. The IR luminosities provide us with extinction-free measurements of the star formation rates (SFRs) of these cluster galaxies. We find a strong evolution in the IR luminosity function (LF) of two z ∼ 0:8 clusters when compared to two local clusters. The evolution rate of the IR LF found in these clusters is consistent with the evolution in field IR LFs. The similar evolution rate found in very different environments favors some internal mechanism, e.g., the gradual consumption of the gas fuel in galaxies, as being responsible for much of the star formation evolution. The mass-normalized integrated SFRs within 0.5R₂₀₀ of these clusters also shows an evolution trend, ∝ (1 + z)5. But this evolution has large scatter and may be affected by the mass selection effect of the sample. In the dense cluster core regions (r < 0.3 Mpc), we find evidence for enhanced SFR suppression. A substantial fraction of members in MS 1054-03 (z ∼ 0.8) are still forming stars actively. This cannot be explained by the scenario where the cluster is only passively accreting star-forming galaxies from the surrounding field, after which their star formation is quenched quickly. We also study the extended IR emission from the intracluster dust (ICD) in A2029. We only find weak signals at 24 and 70 μm and obtain upper limits for the ICD emission.
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Chatzopoulos, Sotirios [Verfasser], and Ortwin [Akademischer Betreuer] Gerhard. "The old Nuclear Star Cluster in the Milky Way / Sotirios Chatzopoulos. Betreuer: Ortwin Gerhard." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1075456584/34.
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Cai, Zheng. "Cosmic Structure Formation: From First Star to Large-scale Filamentary Structure." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/578387.
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Theory of cosmic structure formation outlines how stars, galaxies, clusters of galaxies, and large-scale structures formed out of primordial density fluctuations. It presents us a picture of cosmic mass assembly, and places strong constraints on cosmological model. Both observations and theories suggest that structures formation follows a "bottom up" process, in which small, low-mass component form first, and gradually develop into larger, more massive systems. This dissertation focuses on three crucial stages of cosmic structure formation: first generation stars, quasar host galaxies and the large-scale galaxy overdensities. In Chapter 1, I present an overview of structure formation, acquainting readers with a general picture from first object in the Universe to large-scale structures at later epochs. In Chapter 2 and Chapter 3, I derive strong constraints to the star formation rates (SFRs) of very massive Population III (Pop III) stars in two high redshift galaxies at z = 7. By probing the He II emission lines for both galaxies, I conclude that the contributions of very massive Pop III stars to total the SFRs are less than 3%. In Chapter 4, I move to more massive systems, quasar host galaxies at z ~ 3. Using damped Lyman alpha absorption systems as natural coronagraphs, I report that rest-frame far-UV emission of quasar host galaxy correlates strongly with quasar luminosity. This result suggests a co-evolution of supermassive black holes and their host galaxies. In Chapter 5, I develop a novel method for searching the most massive protoclusters at z = 2-3, by utilizing intergalactic Lyman alpha absorption. My investigations suggest that large intergalactic Lyman alpha absorption systems effectively trace the most overdense regions at large scale of ~ 15 h⁻¹ Mpc. In Chapter 6, I present our imaging observations of an extreme galaxy overdensity (protocluster) BOSS1441+4000, which is discovered using the techniques developed in Chapter 5. Furthermore, I report an intergalactic-scale Lyman alpha nebula detected at the density peak of BOSS1441+4000. This discovery, together with previously discovered Slug nebula, provide us a first look of intergalactic medium in emission in the early Universe. In the Chapter 7, I give a summary of this dissertation and discuss several future prospects.
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Lyo, A.-Ran Physical Environmental & Mathematical Sciences Australian Defence Force Academy UNSW. "The nearby young [special character] Chamaeleontis cluster as a laboratory for star formation and evolution." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Physical, Environmental and Mathematical Sciences, 2004. http://handle.unsw.edu.au/1959.4/38707.
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[Special characters cannot be displayed. Please see the pdf version of the Abstract for an accurate reproduction.] We studied the circumstellar discs, the initial mass function (IMF), mass distribution, binarity and the fundamental properties of the [special character] 9 Myr-old pre-main sequence (PMS) [special character] Chamaeleontis cluster. Using JHKL colour-colour and colour-excess diagrams, we found the circumstellar disc fraction to be [special character] 0.60 among the late-type members. Four stars with [special character] (K - L) > 0.4 were identified as experiencing ongoing accretion which was later confirmed by high-resolution spectroscopic study. Quantitative analysis of the H[special character] profiles found accretion in these four stars at rates comparable to that of two members of the similarly-aged TW Hydrae Association (TWA); rates 1 - 3 orders of magnitude lower than in younger classical T Tauri stars. Together these results suggest that, while the mass accretion rate decreases with age, PMS stars can retain their inner discs for [special character] 10 Myr. An optical photometric survey spanning 1.3 ?? 1.3 pc added two low-mass stars to the cluster inventory. Together with other recent surveys the population is likely to be significantly complete for primaries with masses M > 0.15M[special character]. The cluster now consists of 18 primaries and 9 confirmed and candidate secondaries, with [special character] 2-4 times higher multiplicity than seen in field dwarfs. The cluster IMF is consistent with that of rich young clusters and field stars. By extending the IMF to lower masses, we predict 20-29 low-mass stars and brown dwarfs may remain undiscovered. From study of the cluster???s spatial and mass distribution, we find the [special character] Cha cluster has significant mass segregation, with > 50 per cent of the stellar mass residing within the central 0.17 pc. Lastly we classified members of the cluster with low-resolution spectra, providing information about the fundamental properties of the PMS stars by comparison to standard dwarfs. Broadband VRI colours and pseudocontinuum indices derived for the cluster stars are indistinguishable from dwarfs at visual and red wavelengths. This suggests the temperature sequence for the PMS [special character] Cha cluster is similar to that of the dwarf sequence. Narrow-band spectral indices for the [special character] Cha cluster possibly indicate higher metallicity and strongly indicate lower surface gravity than the dwarf indices.
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Pfuhl, Oliver [Verfasser], and Reinhard [Akademischer Betreuer] Genzel. "The GRAVITY interferometer and the Milky Way’s nuclear star cluster / Oliver Pfuhl. Betreuer: Reinhard Genzel." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1027669182/34.
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Johnson, Helen Louise. "The evolution of gas kinematics in star-forming field and cluster galaxies since z~1." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12428/.
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A fundamental pursuit of astronomy is to understand how galaxies form and evolve. What drives the decline in the cosmic star formation rate density? Why are high redshift galaxies clumpy and turbulent? How can we explain the emergence of the Hubble sequence? To answer these questions we must unravel a complex interplay of different processes, including gas accretion, star formation, feedback, and environmental effects. Studying the gas kinematics of galaxies can provide valuable insight. In this thesis we use integral field spectroscopy to probe the evolution of star-forming field and cluster galaxies over the past 8 billion years. We first present a multi-wavelength analysis of 27 dusty starburst galaxies in a massive cluster at z~0.4. It is thought that starbursts represent an intermediate phase in the transition from spirals to S0s in dense environments. We combine H-alpha kinematics with far-infrared imaging and millimetre spectroscopy, and find that most galaxies are rotationally supported, with high angular momentum and large cold gas reservoirs. It appears that the starbursts have only recently been accreted to the cluster. To complete the transition to S0s, they must undergo a dynamical heating of the disk, increase in concentration, and reduce their angular momentum by ~40%. We conclude that the most likely way to achieve this is via multiple tidal interactions with other cluster members. We next study the velocity dispersion properties of 472 galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). Most galaxies at this epoch are rotationally supported, but dynamically hot and highly turbulent. In order to make robust kinematic measurements, we model the effects of beam smearing using a series of mock KMOS data cubes. We then combine KROSS with data from the SAMI survey (z~0.05) and an intermediate redshift MUSE sample (z~0.5), and find that while there is a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase in velocity dispersion with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. We also test the predictions of two analytic models which suggest that turbulence in the ISM is driven by gravitational instabilities or stellar feedback. However we find that further observations are required to rule-out either model. Finally, to understand the role of galaxy kinematics in “crystallising” the Hubble sequence, we study the HST images of 231 KROSS galaxies. We quantify differences in morphology using the asymmetry parameter. This metric correlates very well with our visual interpretation of “clumpiness”, however there are no strong trends as a function of galaxy kinematics. On average, the velocity dispersion of clumps is consistent with the underlying disk, and there is no evidence to suggest that these star-forming regions are preferentially located towards the outskirts of the galaxy. We propose that adaptive optics assisted IFU observations would provide further insight, allowing us to test clump evolution theories and to study the radial distribution of angular momentum.
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Lieberz, Patrick [Verfasser]. "From star formation to regional distribution: Influences on the embedded cluster mass function / Patrick Lieberz." Bonn : Universitäts- und Landesbibliothek Bonn, 2021. http://d-nb.info/1239730152/34.
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Anders, Peter. "Formation and evolution of star clusters in interacting galaxies." Doctoral thesis, [S.l.] : [s.n.], 2006. http://webdoc.sub.gwdg.de/diss/2006/anders.
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Bressert, Eli Walter. "The initial distribution of stars." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3890.
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The primary focus of my PhD is to quantify the spatial distribution of star-forming environments from optical to radio wavelengths using data from the Hubble Space Telescope, the Very Large Telescope, the Spitzer Space Telescope, the Herschel Space Observatory, and the Caltech Submillimeter Observatory. Towards the end of my PhD study I have developed theoretical models. With these observational and theoretical avenues I have led a series of research projects to (1) quantify the initial spatial structure of pre-stellar cores and proto-stars, (2) test whether massive stars can form in isolation or not, (3) and develop a theoretical model on how young massive clusters form. These research projects have been fruitful as my collaborators and I have shown that pre-stellar cores and stars form in a smooth continuum of surface densities from a few to thousands of stars per pc^2. These two works have important implications on our understanding of what a young stellar cluster is and how star forming environments can evolve to form field star populations or gravitationally bound clusters. In my second study my collaborators and I found evidence for isolated massive star formation in the active star forming region 30 Doradus, in the Large Magellanic Cloud. The result impacts the field of the initial mass function and star formation models. Massive stars forming in isolation is consistent with a stochastically sampled initial mass function. Additionally, the result would put constraints on theoretical models on massive star formation. Continuing my work on massive star forming environments my collaborators and I have developed a theoretical model on how young massive clusters form. From the models we argue that feedback energies can be contained by the gravitational potential well of the massive progenitors. Furthermore, we predict the physical properties the massive cluster progenitors in terms of initial gas mass, radii and flux brightness to enable a search for these objects in Galactic plane surveys and upcoming telescopes. Using the common thread of spatial distribution analysis of star formation I describe my future research plans, which entails studies on extragalactic scales in the conclusion.
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Aljassim, Mohammad A. "A 6-Year Study of Long Period Variable Stars in the Globular Cluster NGC 6388." Bowling Green State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1499442952467274.
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Pang, Xiaoying [Verfasser], and Eva [Akademischer Betreuer] Grebel. "A comprehensive study of the young star cluster HD 97950 in NGC 3603 / Xiaoying Pang ; Betreuer: Eva Grebel." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1179784731/34.
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Fabjan, Dunja. "The effect of star formation and feedback on the X-ray properties of simulated galaxy clusters." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3434.
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2008/2009The aim of this Thesis was to study the X--ray properties of the IntraCluster Medium (ICM) in a cosmological context resorting to high resolution hydrodynamical simulations. The thermodynamical and chemical properties of the ICM were inspected and studied within a set of galaxy clusters that were simulated with the TREE-SPH Gadget2 code (Springel 2005). This code included a detailed model of chemical evolution (Tornatore et al. 2007) as well as prescriptions for different physical processes: star formation, galactic winds and AGN feedback. We use this large set of simulated galaxy clusters with a twofold aim. First, we study the effect of different sources of feedback on the ICM observable properties, in particular on its metal enrichment and on thermo and chemo--dynamical properties when AGN feedback is at work. Second, we test the robustness of cluster mass proxies against the different physical processes included in the simulations. When exploring the effect on metal enrichment and its evolution we found that among different prescriptions for the stellar Initial Mass Function (IMF), the best results on Iron abundance profiles and global Iron evolution are found when applying the Salpeter IMF (Salpeter 1955). We also found that the positive evolution of the metal abundance in the central regions of simulated clusters can not be simply interpreted as a consequence of an excess of low--redshift star formation. Instead the evolution of the metallicity pattern is driven by the combined action of gas--dynamical processes, which redistribute already enriched gas, and of star formation, which acts both as a source and as a sink of metals (Fabjan et al. 2008, Borgani et al. 2008). Our analysis on the AGN feedback effect on ICM properties lends further support to the idea that a feedback source associated to gas accretion onto super-massive BHs is required by the observational properties of the ICM (e.g. McNamara & Nulsen 2007). However, our results also show that there are still a number of discrepancies between observations and the predictions made by simulations. This is especially true within the core regions of massive clusters, where a more efficient way of extracting and/or thermalising energy released by AGN is required. Our results further demonstrate that different astrophysical feedback sources leave distinct signatures on the pattern of chemical enrichment of the ICM. These differences are much more evident in the outskirts of galaxy clusters, which retain memory of the past efficiency that energy feedback had in displacing enriched gas from star-forming regions and in regulating star formation itself (Fabjan et al. 2010). The characterization of thermal and chemical properties in cluster external regions requires X--ray telescopes with large collecting area and an excellent control of the background, characteristics which should be eventually met by a future generation of X--ray satellites. In the last part of this Thesis we studied the effect that different physical processes included in the simulations have on the mass--observable scaling relations and their evolution with redshift. We focused on two cluster mass proxies, the gas mass M_gas and a new Y_X proxy defined by Kravtsov et al. (2006) as the product of gas mass and cluster temperature and test the robustness of the two relations, M_tot-M_gas and M_tot-Y_X, in simulations before including any observational effect. Furthermore we test the relations against the change of prescription for the physics that describes the ICM, such as viscosity, thermal conduction, star formation, galactic winds and AGN feedback. We found that the evolutions of both relations do not show any significant deviation from the predictions of the simple self--similar model. However we found that the Y_X proxy is less sensitive to the change of physical processes included in simulations. Since Y_X is by definition a measure of the thermal pressure support in the ICM, once the central cluster region is excised, the relation M_tot-Y_X is more stable against the change of physical processes included in the simulations (Fabjan et al., in preparation). In the future, the improved numerical resolution expected to be reached in simulations of the next generation needs to be accompanied by a suitable description of the subresolution physics, both concerning the star formation physics and and the AGN feedback. Within the latter, the inclusion of the jet injection by AGN would of course provide a physically meaningful description of the interplay between BH accretion and ICM properties. While Chandra, XMM and Suzaku will be pushed to their limits in these studies in the next few years, there is no doubt that a detailed knowledge of the ICM out the cluster virial boundaries and reaching very high redshift has to await for the advent of the next generation of X--ray telescopes (Giacconi et al. 2009, Arnaud et al.2009).
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Yu, Pui-ling, and 余佩玲. "Strong ram-pressure stripping and widespread star formation in the high-velocity system towards the center of the Perseus cluster." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2015. http://hdl.handle.net/10722/211150.
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I present spectroscopic imaging of the high-velocity system (HVS) towards the central cD galaxy (NGC 1275) in the Perseus Cluster at a high spectral resolution for the first time. Previous observation suggests that the HVS is a highly inclined dusty and gas-rich galaxy moving towards the center of NGC 1275 at a high speed of 3000 km/s relative to the systemic velocity of NGC 1275 through the hot intracluster medium (ICM). If this is the case, then the HVS should be undergoing intense ram-pressure stripping. However, there is tentative evidence for ram-pressure stripping in the HVS, and furthermore confined to a small region of the galaxy. Previous observations also point out that at the location where the HVS is seen, there are many star clusters seen towards the inner region of NGC 1275. The separation of young star clusters between those belong to NGC 1275 and those belong to the HVS is, however, not clearly defined.
The primary scientific objectives are to (i) search for evidence for ram-pressure stripping in the HVS, as well as signs of tidal interactions between the HVS and NGC 1275; and (ii) separate the numerous young star clusters seen towards the entire NGC 1275 into those associated with the HVS and those associated with NGC 1275. NGC 1275 and the HVS were observed simultaneously with the use of Potsdam Multi-Aperture Spectrophotometer. The main emission lines being studied are the Hα & [NII]λ6548,6483 lines in NGC 1275 and the HVS. I present maps of intensity distribution, velocity field and velocity dispersion of the Hαemission of the HVS, as well as the line ratio of the [NII] doublets lines to the Hα line in the HVS.
I find that the line ratio of [NII]/Hα is less than 0.1 throughout the entire body of the HVS, indicating metallicity is low in the HVS. I also find that the metallicity is decreasing with distance from the center, just like other normal spiral galaxies. I demonstrate that a large fraction of the young star clusters seen towards the inner regions of NGC 1275 are closely associated with bright Hα-emitting regions in the HVS, and trace the overall Hα-emitting body of the HVS, suggesting that some young star clusters are associated to the HVS. I find that there are two distributions of young star clusters in color-color space, providing a way to separate out the star clusters likely belong to the HVS. I present evidence that the HVS is experiencing intense ram-pressure stripping and also evidence suggesting that the HVS is possibly tidally interacting with NGC 1275.
The results demonstrate that the HVS is a dusty, gas-rich, low-metallicity galaxy that has been disrupted by ram-pressure stripping and possibly also tidal interactions. I show that the HVS exhibit widespread and vigorous (~3.6 MM_⊙ yr^(-1)) star formation over the last at least ~0.1 Gyr. The vigorous SFR of the HVS is in contrast to what suggested by the observed low metallicity (suggestive of relatively weak star-formation activity over the recent history). The SFR of the HVS is likely to be triggered by the same process that produces global distortion on the HVS, here ram pressure stripping and possibly tidal interaction are in consideration.published_or_final_version
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Master
Master of Philosophy
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Iwasa, Mao. "Lidov-Kozai mechanism in shrinking Massive Black Hole binaries." Kyoto University, 2018. http://hdl.handle.net/2433/232233.
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Rudnick, Gregory, Jacqueline Hodge, Fabian Walter, Ivelina Momcheva, Kim-Vy Tran, Casey Papovich, Cunha Elisabete da, et al. "Deep CO(1–0) Observations of z = 1.62 Cluster Galaxies with Substantial Molecular Gas Reservoirs and Normal Star Formation Efficiencies." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627107.
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We present an extremely deep CO(1-0) observation of a confirmed z = 1.62 galaxy cluster. We detect two spectroscopically confirmed cluster members in CO(1-0) with signal-to-noise ratio >5. Both galaxies have log (M-star/M-circle dot) > 11 and are gas rich, with M-mol/(M-star + M-mol) similar to 0.17-0.45. One of these galaxies lies on the star formation rate (SFR)-M-star sequence, while the other lies an order of magnitude below. We compare the cluster galaxies to other SFR-selected galaxies with CO measurements and find that they have CO luminosities consistent with expectations given their infrared luminosities. We also find that they have gas fractions and star formation efficiencies (SFE) comparable to what is expected from published field galaxy scaling relations. The galaxies are compact in their stellar light distribution, at the extreme end for all high-redshift star-forming galaxies. However, their SFE is consistent with other field galaxies at comparable compactness. This is similar to two other sources selected in a blind CO survey of the HDF-N. Despite living in a highly quenched protocluster core, the molecular gas properties of these two galaxies, one of which may be in the process of quenching, appear entirely consistent with field scaling relations between the molecular gas content, stellar mass, star formation rate, and redshift. We speculate that these cluster galaxies cannot have any further substantive gas accretion if they are to become members of the dominant passive population in z < 1 clusters.
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Bogdanov, Slavko, Craig O. Heinke, Feryal Özel, and Tolga Güver. "NEUTRON STAR MASS–RADIUS CONSTRAINTS OF THE QUIESCENT LOW-MASS X-RAY BINARIES X7 AND X5 IN THE GLOBULAR CLUSTER 47 TUC." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622762.
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We present Chandra/ACIS-S subarray observations of the quiescent neutron star (NS) low-mass X-ray binaries X7 and X5 in the globular cluster 47 Tuc. The large reduction in photon pile-up compared to previous deep exposures enables a substantial improvement in the spectroscopic determination of the NS radius and mass of these NSs. Modeling the thermal emission from the NS surface with a non-magnetized hydrogen atmosphere and accounting for numerous sources of uncertainties, we obtain for the NS in X7 a radius of R = 11.1(-0.7)(+0.8) km for an assumed stellar mass of M = 1.4 M-circle dot (68% confidence level). We argue, based on astrophysical grounds, that the presence of a He atmosphere is unlikely for this source. Due to the excision of data affected by eclipses and variable absorption, the quiescent low-mass X-ray binary X5 provides less stringent constraints, leading to a radius of R = 9.6(-1.1)(+0.9) km, assuming a hydrogen atmosphere and a mass of M. =. 1.4 Me. When combined with all existing spectroscopic radius measurements from other quiescent low-mass X-ray binaries and Type I X-ray bursts, these measurements strongly favor radii in the 9.9-11.2 km range for a similar to 1.5 M-circle dot NS and point to a dense matter equation of state that is somewhat softer than the nucleonic ones that are consistent with laboratory experiments at low densities.
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Kotze, J. P. "Studying the environmental dependence of star formation properties of galaxies in the Abell 1437 galaxy cluster and its surrounding large scale structure." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/8801.
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Includes bibliographical references.It has become clear that the local galaxy environment plays a crucial role in the evolution of galaxies. Recent studies show a strong bimodal distribution of galaxy properties, with red, passive galaxies dominating the bimodal distribution in dense environments, compared to blue, actively star forming galaxies dominating the bimodal distribution in low density environments. Blue, star-forming galaxies are continuously transformed into red, passive galaxies through one or more processes while being accreted into higher density environments. The processes responsible for the observed transformation remain uncertain. We address these issues by performing an in-depth study of large-scale structure surrounding the galaxy cluster Abell 1437 at z = 0.135. We consider the colour and specific star formation rate distributions of galaxies as a function of environment. In this thesis we develop techniques to derive environmental samples which consist of a cluster, groups, filament and field. The large-scale structure surrounding the cluster is characterised through the use of a Friends-of-Friends algorithm based on spectroscopic data. This provides a reference from which we construct a photometric environmental catalogue using methods developed to find groups and define filamentary structure. To accomplish this, we construct a ugrizJHK multi-band dataset using a custom pipeline to derive a seeing matched photometric catalogue from Sloan Digital Sky Survey (SDSS) and UKIRT Deep Sky Survey (UKIDSS) imaging data. The photometric dataset is complemented by a near uniformly sampled spectroscopic dataset from the SDSS and Two Degree Field (2dF) survey. Stellar masses and star formation rates for the environmental samples are derived using the state-of-the-art magphys SED fitting code. The environmental samples we derive yield, within the uncertainties, similar galaxy populations than typically found in clusters, groups and the field. Red fractions were computed for the cluster, groups, filament and field sample for which we found 0.90 ± 0.13, 0.79 ± 0.01, 0.69 ± 0.02 and 0.58 ± 0.01 respectively. This is the first filament red fraction measurement made in this way. We studied the passive fraction of galaxies as a function of environment using specific star formation rates. Passive fractions were computed using two different definitions of passiveness, 1/tH (log(sSFR) = −10.07) and the minimum in the bimodal sSFR distribution (log(sSFR) = −11.0) as the division between active and passive galaxies. We found that the log(sSFR) = −11.0 bimodal divider is a natural division between active and passive galaxies and does not suffer from density-dependent selection effects. Quiescent fractions derived from the environmental samples reproduce previously known trends of star formation rates with environment. The filament environment is one of the least well studied environments since their low galaxy density makes them difficult to detect. We studied the fractional excess of star forming galaxies along the filament between Abell 1437 and the neighbouring region of overdensities, and find a significant increase in star formation activity. Although there have been hints of excess star formation in filaments previously, we claim our results to be of highest significance thus far.
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Moeckel, Nickolas Barry. "Massive stars, disks, and clustered star formation." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3303877.
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Klein, Fabian [Verfasser], and Rainer [Akademischer Betreuer] Spurzem. "Simulations of an accretion disk surrounding a supermassive black hole and its interaction with a nuclear star cluster / Fabian Klein ; Betreuer: Rainer Spurzem." Heidelberg : Universitätsbibliothek Heidelberg, 2018. http://d-nb.info/1177149672/34.
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Zeidler, Peter [Verfasser], and Eva K. [Akademischer Betreuer] Grebel. "Revealing the secrets of Westerlund 2 - A young massive star cluster observed with the Hubble Space Telescope / Peter Zeidler ; Betreuer: Eva K. Grebel." Heidelberg : Universitätsbibliothek Heidelberg, 2017. http://d-nb.info/1180739248/34.
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Belles, Pierre-Emmanuel Aime Marcel. "Formation of stars and star clusters in colliding galaxies." Thesis, University of Hertfordshire, 2013. http://hdl.handle.net/2299/10312.
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Mergers are known to be essential in the formation of large scale structures and to have a significant role in the history of galaxy formation and evolution. Besides a morphological transformation, mergers induce important bursts of star formation. These starburst are characterised by high Star Formation Efficiencies (SFEs) and Specific Star Formation Rates, i.e., high Star Formation Rates (SFR) per unit of gas mass and high SFR per unit of stellar mass, respectively, compared to spiral galaxies. At all redshifts, starburst galaxies are outliers of the sequence of star-forming galaxies defined by spiral galaxies. We have investigated the origin of the starburst-mode of star formation, in three local interacting systems: Arp 245, Arp 105 and NGC7252. We combined high-resolution JVLA observations of the 21-cm line, tracing the Hi diffuse gas, with UV GALEX observations, tracing the young star-forming regions. We probe the local physical conditions of the Inter- Stellar Medium (ISM) for independent star-forming regions and explore the atomic-to-dense gas transformation in different environments. The SFR/H i ratio is found to be much higher in central regions, compared to outer regions, showing a higher dense gas fraction (or lower Hi gas fraction) in these regions. In the outer regions of the systems, i.e., the tidal tails, where the gas phase is mostly atomic, we find SFR/H i ratios higher than in standard Hi-dominated environments, i.e., outer discs of spiral galaxies and dwarf galaxies. Thus, our analysis reveals that the outer regions of mergers are characterised by high SFEs, compared to the standard mode of star formation. The observation of high dense gas fractions in interacting systems is consistent with the predictions of numerical simulations; it results from the increase of the gas turbulence during a merger. The merger is likely to affect the star-forming properties of the system at all spatial scales, from large scales, with a globally enhanced turbulence, to small scales, with possible modifications of the initial mass function. From a high-resolution numerical simulation of the major merger of two spiral galaxies, we analyse the effects of the galaxy interaction on the star forming properties of the ISM at the scale of star clusters. The increase of the gas turbulence is likely able to explain the formation of Super Star Clusters in the system. Our investigation of the SFR–H i relation in galaxy mergers will be complemented by highresolution Hi data for additional systems, and pushed to yet smaller spatial scales.
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Cai, Chunlin. "Étude de la cinétique des particules dans les couches frontières de la magnétosphère terrestre à l'aide des observations des satellites CLUSTER et DOUBLE STAR." Toulouse 3, 2010. http://thesesups.ups-tlse.fr/979/.
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L'environnement spatial proche de la Terre est complexe et divers. La cinétique des ions joue un rôle clé pour comprendre la nature des phénomènes essentiels et les processus physiques prenant place dans le "Géospace". Au moyen de données à haute résolution enregistrées par les quatre satellites Cluster et les deux satellites Double Star, cette thèse étudie la cinétique des ions de faible énergie dans certaines couches frontières essentielles de la magnétosphère terrestre. Le rôle dominant joué par la cinétique des particules dans les formations de ces structures de plasma à petite échelle et les caractéristiques des processus de couplage à différentes échelles y sont résumésThe near-Earth space environment is complex and diverse. Particle kinetics plays a key role in understanding the nature of key phenomena and physical processes taking place in the Geospace. By means of the high-resolution data recorded by the multiple-point Cluster and Double star spacecraft, the present thesis investigated low energy ion kinetics in some crucial boundary layers of the terrestrial magnetosphere. The dominating roles played by the particle kinetics in the formations of those small-scale plasma structures and the feature of cross-scale coupling processes are summarized
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Cai, Chunlin. "Etude de la cinétique des particules dans les couches frontières de la magnétosphère terrestre à l'aide des observations des satellites CLUSTER et DOUBLE STAR." Phd thesis, Université Paul Sabatier - Toulouse III, 2010. http://tel.archives-ouvertes.fr/tel-00499367.
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L'environnement spatial proche de la Terre est complexe et divers. La cinétique des ions joue un rôle clé pour comprendre la nature des phénomènes essentiels et les processus physiques prenant place dans le "Géospace". Au moyen de données à haute résolution enregistrées par les quatre satellites Cluster et les deux satellites Double Star, cette thèse étudie la cinétique des ions de faible énergie dans certaines couches frontières essentielles de la magnétosphère terrestre. Le rôle dominant joué par la cinétique des particules dans les formations de ces structures de plasma à petite échelle et les caractéristiques des processus de couplage à différentes échelles y sont résumés.
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Karnath, Nicole. "The Transition Points in Young Stars and Young Star Clusters." University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564763305735395.
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Rosen, Anna L. "The Destructive Birth of Massive Stars & Massive Star Clusters." Thesis, University of California, Santa Cruz, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10274404.
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The injection of energy and momentum into the interstellar medium by young massive stars’ intense radiation fields and their fast, radiatively driven winds can have a profound influence on their formation and environment. Massive star forming regions are rare and highly obscured, making the early moments of their formation difficult to observe. Instead, we must turn to theory to elucidate the physics involved in the formation of massive stars and massive star clusters (MSCs), which can host thousands of massive stars. In my thesis, I developed analytical and numerical techniques to study the formation of massive stars and how stellar wind feedback affects the dynamics of gas that surrounds MSCs. To estimate the initial rotation rates of massive stars at birth, I developed a protostellar angular momentum evolution model for accreting protostars to determine if magnetic torques can spin down massive stars during their formation. I found that magnetic torques are insufficient to spin down massive stars due to their short formation times and high accretion rates. Radiation pressure is likely the dominate feedback mechanism regulating massive star formation. Therefore detailed simulation of the formation of massive stars requires an accurate treatment of radiation. For this purpose, I developed a new, highly accurate radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. With this new tool, I performed a suite of three-dimensional adaptive mesh refinement radiation-hydrodynamic simulations of the formation of massive stars from collapsing massive pre-stellar cores. I found that mass is channeled to the massive star via dense infalling filaments that are uninhibited by radiation pressure and gravitational and Rayleigh-Taylor instabilities. To determine the importance of stellar wind feedback in young MSCs, I used observations to constrain a range of kinetic energy loss channels for the hot gas produced by the shock-heating of stellar winds to explain the low X-ray luminosities observed in Hii regions. I demonstrated that the energy injected by stellar winds is not a significant contributor to stellar feedback in young MSCs.
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Cao, Orjales Jose Manuel. "A Study of AGN and their environments in the far-infrared." Thesis, University of Hertfordshire, 2014. http://hdl.handle.net/2299/14440.
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My Ph.D. has been composed of work involving the use of far–IR and submm observations of AGN. During this time it has focused on the in- terplay between AGN and their host galaxies and cluster environments. Understanding the role of AGN, and how they affect the evolution of both their host galaxies and surrounding environments, is a pressing concern in cosmological models of the universe, affecting as they do the chemical makeup, star formation rate, and morphology of their host galaxies. In Chapter 2, we focus on attempting to determine whether there is an inherent physical difference between Broad Absorption Line Quasars and non–BAL QSOs using Herschel observations taken at 250, 350 and 500 μm as part of the H–ATLAS (Eales et al. 2010) survey. BAL QSOs have been considered the most visible form of AGN feedback, and therefore are a prime starting point for understanding how galaxy evolution may be affected by the presence of an AGN. By using matched samples of 50 BAL and 329 non–BAL QSOs, we create weighted stacks at each wavelength, finding similar far–IR flux–densities for each sample within the errors. By SED modelling using a simple modified black body (Hildebrand 1983) fit to Mrk 231 and IZw1, we derive likely upper and lower limits for the BAL and non–BAL QSOs in each wavelength, again finding they are consistent within the errors. A bevy of statistical tests run on either population similarly finds no evidence to reject the null hypothesis they are drawn from the same parent population. These results would imply that HiBAL QSOs can be unified with ordinary QSOs within a simple orientation dependent scheme. We cannot make the same distinction for LoBALs or FeLoBALs, which the literature suggests may well be a separate evolutionary phase. In Chapter 3, we determine whether the presence of an AGN correlates to an overdensity of star–forming galaxies in the FIR, as has been found at shorter wavelengths (Falder et al. 2010). For the SHAGs study, 171 AGN were observed and selected at z∼1. By using observations at 250 μm, we are able to trace close to the peak of the grey–body SED created by reprocessing by dust of radiation from young O and B stars. Following data reduction, we determine number counts and correct for completeness within a 1Mpc radius of the central AGN. We find an overdensity on the order of around 0.4 sources per AGN, implying a degree of activity already significantly lower than at higher redshifts. This overdensity appears to be somewhat different between RL AGN and RQQ within 1Mpc. A cor- relation is found between radio luminosity and star formation overdensity, consistent with a stronger dependence found by Falder et al. (2010) at 3.6 μm, and there also appears to be a correlation between stellar mass and star formation overdensity for radio–loud QSOs. The galaxies in the environs of the AGN have LIRG–level luminosities, and are likely the pro- genitors of modern day S0 galaxies, whose population increases steadily from z∼1 to the present day (Postman et al. 2005; Smith et al. 2005). Our work with SCUBA–2, presented in Chapter 4, follows on from a prior sample of X–ray–absorbed QSOs (Stevens et al. 2005). This new sample is composed of more highly–absorbed X–ray QSOs and covers a larger area than the initial sample, so is ideal for an analysis of source counts around AGN at high–redshift. Data from the JCMT have been reduced, and completeness corrections and flux corrections applied to catalogues to determine the number counts around AGN. A comparison background, created using data from the Cosmology Legacy Survey has been used to derive comparison counts. The AGN have been investigated, yet none are detected above 3 at 850 μm, in contrast to the original sample. This may suggest that star formation in their host galaxies has been suppressed. Upon stacking in redshift and BAL classification, no difference in flux– density is apparent and the sources studied here have a similar stacked submm output to an unabsorbed QSO sample created for the original X– ray absorbed QSOs. However, over half of the sources here are BAL QSOs in contrast to the original absorbed QSO sample which contained only 1 BAL QSO. From the work in Chapter 2, one might expect BAL and non–BAL QSOs to have similar flux–densities. We argue that the sources studied in this thesis have likely undergone rapid evolution owing to a strong outflow, and as such star formation has been suppressed sufficiently that the submm emission is below the confusion noise. BAL winds may still be present, but essentially, the show is already over. A similar mechanism may already have occurred in unabsorbed QSOs if all QSOs pass through an X–ray–absorbed phase. With regard to source counts, we find that there is tentative evidence for an overdensity of sources around these AGN. The SFRs of the companion sources have been calculated using several greybody analogues, all of which imply a high degree of activity, suggesting these fields will evolve to become some of the most massive regions at the present epoch, in keeping with current theories of SMGs and high–redshift clusters.
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Pope, Alexandra, Alfredo Montaña, Andrew Battisti, Marceau Limousin, Danilo Marchesini, Grant W. Wilson, Stacey Alberts, et al. "Early Science with the Large Millimeter Telescope: Detection of Dust Emission in Multiple Images of a Normal Galaxy at z > 4 Lensed by a Frontier Fields Cluster." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623817.
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We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z > 4 and the strong lensing model (mu = 7.5) allows us to calculate an intrinsic IR luminosity of 9.7 x 10(10) L-circle dot and an obscured star formation rate of 14.6 +/- 4.5 M-circle dot yr(-1). The unobscured star formation rate from the UV is only 4.1 +/- 0.3 M-circle dot yr(-1), which means the total star formation rate (18.7 +/- 4.5 M-circle dot yr(-1)) is dominated (75%-80%) by the obscured component. With an intrinsic stellar mass of only 6.9 x 10(9) M circle dot, MACS0717_Az9 is one of only a handful of z. >. 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-beta) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe.
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Krayzel, Fabien. "Etude de phénomènes non-thermiques dans les amas d'étoiles jeunes : modélisation et analyse des données de H.E.S.S." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY079.
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Voilà plus d'un siècle que Victor Hess a montré l'origine cosmique de ce mystérieux rayonnement ionisant, et pourtant ce dernier n'a pas fini de livrer tous ces secrets. En deçà d'une énergie de l'ordre du PeV, les vestiges de supernovae sont les candidats les plus sérieux pour rendre compte de l'accélération de ces particules cosmiques. Si toutefois cette hypothèse demeure toujours d'actualité, alors qu'auparavant on le considérait comme un événement isolé dans la Galaxie, on constate plutôt aujourd'hui que ces explosions d'étoiles massives surviennent majoritairement au sein de grandes structures galactiques nommées superbulles. Ces objets sont formés par la combinaison des forts vents stellaires issus des étoiles massives ainsi que de plusieurs supernovae, tout ceci regroupé dans un espace de quelques dizaines ou centaines de parsecs.On peut dès lors se poser la question suivante : est-il possible que des amas d'étoiles jeunes, n'ayant pas encore connu d'épisode de supernova, puissent être des accélérateurs cosmiques.Pour ce type d'investigation, l'astronomie gamma est aux premières loges puisque contrairement au rayonnement cosmique chargé, ce type de messager céleste n'est pas dévié dans son voyage depuis la source jusqu'à nous.L'objet de ce travail est ainsi d'évaluer la possibilité pour ces amas d'étoiles jeunes, de recycler une partie de l'énergie mécanique transférée au milieu interstellaire dans l'accélération de particules et partant, dans l'émission d'un rayonnement non-thermique. Cette étude propose, à partir d'un spectre d'injection pour des particules chargées (proton et/ou électrons), de modéliser l'émission non-thermique attendue considérant les pertes que celles-ci subissent. Un catalogue d'amas potentiellement prometteurs est dressé ainsi qu'un classement de ceux-ci au regard du flux de gamma attendu. Une analyse des données des télescopes H.E.S.S. est conduite pour un certain nombre d'amas sélectionnés. Ce réseau de télescopes Cherenkov situé en Namibie est le plus performant dans sa catégorie. Il est dédié à l'observation des rayons gamma de très haute énergie.Une analyse des données du Fermi-LAT ont également été effectuées. Il s'agit cette fois d'un satellite dédié à la partie des hautes énergies du rayonnement gamma.Enfin, on contraint les paramètres de notre modèle grâce aux résultats issus de ces analyses.L'expérience H.E.S.S., qui a fonctionné à 4 télescopes dès 2003, est depuis 2012 au tout début de sa deuxième phase consistant en l'ajout d'un cinquième télescope de plus grand diamètre. On montre ici, grâce à des simulations de gerbes, la nécessité pour ce télescope de disposer d'un système de focus permettant l'ajustement de la distance caméra-miroirs conduisant à de meilleures performances (taux de déclenchement, résolution angulaire)More than one century ago, Victor Hess discovered the cosmical origin of the mysterious ionizing radiation. Yet, nowadays it still has a lot of secrets for us. Roughly below the PeV energy, the best candidates already proposed in 1934 were the supernovae remnants (SNR). These candidates still remain ; in the past we considered isolated SNRs, while today we rather think about SNRs inside big structures as superbubbles. These objects are formed by powerful stellar winds from massive stars combined with several SNRs gathered in a space of some decades or hundreds of parsecs. Observations show that the majority of the SNRs occurs in such regions. The point for us is to know if star clusters or associations of massive stars, not hosting any SNR, could also accelerate particles to very high energies and consequently emit gamma-rays.The gamma-ray astronomy is relevant in order to solve this type of riddle because the Very High Energy photons do not suffer of any deviation due to the Galactic magnetic field. It means that we can get informations from the source itself by detecting the gamma-ray radiation.In our study we assume that a part of the mechanical energy transferred to the interstellar medium can be used to accelerate charged particles, which will emit non-thermal radiations.First we assume a given injection spectrum (for electrons and/or protons), then we model the non-thermal emission expected considering particles losses.We deliver a catalogue of promising clusters and we rank them according to the expected strength of the gamma-ray flux.We conducted the analysis of H.E.S.S. data collected toward some selected clusters. The H.E.S.S. experiment is situated in Namibia and is the most efficient array of Cherenkov telescopes. We also used the Fermi-LAT public data. Fermi is a space-based telescope for High Energy gamma ray.Then we constrain our model with the obtained analysis results.The H.E.S.S. experiment had initially 4 telescopes in operation since 2003. In 2012, the second phase of the experiment started when a fifth larger one was added. We show here that it is relevant for this telescope to use a focus system in order to move the camera and change the distance camera-mirrors. The simulations show that the focus system leads to better performances (trigger rate, angular resolution)