Using infrared and X-ray diagnostics, we study star--formation and black hole accretion in nearby and distant galaxies.We examine diagnostics of the hardness of the ionizing field in low--redshift starburst galaxies, to constrain the initial mass function. We obtain new measurements of HeI 1.7 micron/Br 10, a physically simple diagnostic, then test ISO mid--infrared line ratios, finding them reliable. Compared to new photoionization models, the ISO ratios in 27 nearby starburst galaxies are systematically low. This argues that solar--metallicity starbursts are deficient in massive stars, or that such stars are present but highly embedded.Using Spitzer, HST, Chandra, and ground-based data, we examine the multi-wavelength (0.4--24 micron) spectral energy distributions and X-ray properties of X-ray--selected active galactic nuclei (AGN) in several deep fields: the Chandra Deep Field South, the Lockman Hole, and the extended Groth Strip. We examine the 24 micron to X-ray flux and luminosity ratios for 157 AGN at z~1; the luminosity ratios have not strongly evolved since z~0, and we find no trend with X-ray column density. This means that highly--obscured AGN do not have exceptional infrared fluxes. We examine the SEDs of 45 bright X-ray and 24 micron sources: only 22% are classified as unobscured ``type 1'' AGN; 18% are classified as ULIRG-like SEDs; and the majority are classified as obscured (``type 2'') AGN or spiral--like SEDs. This supports the picture from X-ray surveys that much of the AGN activity in the distant universe is significantly obscured. We examine why 20% of X-ray--selected AGN are optically--faint; they lie at significantly higher redshifts (median z=1.6) than most X-ray--selected AGN, and their spectra are intrinsically red. Their contribution to the X-ray Seyfert luminosity function is comparable to that of optically--bright AGN at z>1, but they do not significantly alter the redshift distribution. Lastly, we investigate why half of X-ray--selected AGN lack signs of accretion in optical spectra. We find that these ``optically--dull'' AGN have Seyfert--like mid--infrared emission, which argues that they do not have abnormally--weak UV/optical continua. The axis ratios of their host galaxies argue that extinction by host galaxies plays a key role in hiding nuclear emission lines.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 107-109).

Inaug.-Diss. - Leipzig. / "Literaturverzeichnis": p. [v]-xiv.

Thesis (A.M.L.S.)--University of Michigan, 1958.

Thesis (M.S.) in Teaching--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 60-63).

Pro Gradu-tutkielmassa kartoitetaan Marsin Protonilus Mensaen ja Moreux-kraatterin alueelta löytyviä jäätikkömäisiä kohteita. Alue sijaitsee Marsin dikotomiarajalla, joka sisältää runsaasti merkkejä amatsoonisella aikakaudella tapahtuneesta jäätiköitymisestä. Protonilus Mensaen alueelta tehdyissä aiemmissa tutkimuksissa on löydetty paljon merkkejä jäätä sisältävistä laattamaisista LDA-muodostumista ja laaksojen pohjia täyttävistä LVF-muodostumista [Squyres 1978, 1979] ja [Levy et al. 2010]. Kyseistä aluetta ei ole kuitenkaan aiemmin kartoitettu laaja-alaisesti uuden sukupolven avaruusluotaimien tuottamaa kuvamateriaalia hyödyntäen. Tämän työn päämääränä on ollut kartoittaa Protonilus Mensaen alue uuden sukupolven Mars Global Surveyor-, Mars Express-, Mars Reconnaissance Orbiter- ja Mars Odyssey-luotaimien tuottaman kuvamateriaalin avulla. Työssä on etsitty merkkejä mahdollisesti eri aikakausina toimineista jäätiköitymisprosesseista. Toisen mielenkiintoisen tutkimusaiheen muodostavat merkit veden virtauksesta alueella. Lisäksi tutkielmassa käydään läpi veden ja jään historiaa, koska niiden merkitys Marsin historiassa on koko ajan kasvanut. Tämän vuoksi on tärkeää käydä läpi, kuinka nykyinen käsityksemme Marsin vedestä on muodostunut. Tämän tutkielman myötä lukija saa kattavan käsityksen Marsin veden historiasta sekä nykyhetkestä. Tutkimuksen aineistona käytetään erityisesti Mars Odyssey-luotaimen Mola-instrumentin tuottamaa topografiatietoja sekä muiden luotaimien CTX-, HiRISE- ja HRSC-kameroiden tuottamaa kuvamateriaalia. Mars Reconnaissance Orbiter-luotaimen CTX-kameran tarkat ja hyvälaatuiset kuvat ovat toimineet kartoituksen pohjamateriaalina. CTX-instrumentin avulla Protonilus Mensaen aluetta voidaan tutkia noin kuuden metrin resoluutiolla. HiRISE- ja HRSC-kameroiden tarkempia ja yksityiskohtaisempia kuvia on käytetty alueilta, joista niitä on ollut saatavilla. Topografiatiedon avulla on mahdollista ymmärtää alueen jäätikkömäisten muodostumien liikettä sekä merkkejä veden virtauksesta. Tutkielman historiaosuudessa on käytetty hyväksi aiempien tutkimusryhmien tuloksia 1970-luvulta 2010-luvulle. Kartoituksessa pääasiallisena työkaluna on käytetty ArcGis-kartoitusohjelmaa, jonka avulla voidaan kartoittaa tehokkaasti laajoja alueita. Pienempiä alueita kartoitettaessa on käytetty myös Photoshop-kuvankäsittelyohjelmaa. Kartoituksessa Marsin Protonilus Mensaen alueelta löytyi paljon jäätikkömäisiä muodostumia. Laattamaiset LDA-muodostumat keskittyvät sirpaloituneelle ylänköalueelle ja Moreux-kraatterin keskuskohouman ympärille. Protonilus Mensae-alueen vuorien ympärille on muodostunut vaihtelevan kokoisia LDA-muodostumia. Tutkitulta alueelta löydetyt LVF-muodostumat keskittyvät sirpaloituneen ylänköalueen laaksoihin ja noaakkisella ylänköalueella vanhoihin virtausuomiin. Kraattereiden täytteitä eli CCF-muodostumia löytyy jokaisen kraatterin pohjalta. Noaakkiselta ylänköalueelta löydettiin yksi muinainen kraatterijärvi, josta on lähtenyt uoma kohti alempana sijaitsevia alueita. Jäätikkömäiset muodostumat ovat sijoittuneet topografisesti usean kilometrin skaalalle. Merkkejä jään sublimoitumisesta löytyy jokaisesta Protonilus Mensaen geologisesta yksiköstä. Tehdyn Pro gradu-tutkielman pohjalta voidaan todeta, että Moreux-kraatterin ympäristö ja Protonilus Mensae-alue on kokenut merkittävän jäätiköitymisjakson myöhäisellä amatsoonisella aikakaudella. Yhteneviin tuloksiin ovat päätyneet useat dikotomiaraja-aluetta tutkineet työryhmät [Baker et al, 2010]; [Kress and Head, 2008]; [Morgan et al, 2009]. Jäätikkömäisten muodostumien ajoittaminen kraatterilaskujen perusteella on epävarmaa, koska Marsin olosuhteet voivat muuttua merkittävästi suhteellisen lyhyessä ajassa. Olosuhteiden muutokset vaikuttavat jään säilymiseen sekä sen kykyyn edetä. Edellä mainitut tekivät vaikuttavat siten, että kraattereiden tuhoutumisnopeus voi vaihdella merkittävästi. Protonilus Mensaen alueella on tapahtunut ainakin kaksi eri jäätiköitymisjaksoa. Laajempi jäätiköityminen on synnyttänyt puhkaisun Moreux-kraatteriin. Puhkaisun aiheuttaneet LDA- ja LVF-muodostumat ovat pahasti erodoituneet. Myöhäisempi jäätiköityminen ei ole edennyt yhtä pitkälle. Laajempi jäätiköitymisjakso on voinut esiintyä samoihin aikoihin kuin hespeerisen ajan suuret tulvat. Nestemäinen vesi on voinut olla merkittävä tekijä laajempien LDA- ja LVF-muodostumien synnyssä. Amatsoonisella aikakaudella tapahtunut jäätiköityminen on kuitenkin ollut paikallista ja jäätiköityminen on vaatinut juuri sopivat olosuhteet. Jäätä on kertynyt etenkin kraattereihin, vuorien rinteille ja laaksoihin. Alueelta läydetyt LDA-, LVF- ja CCF-muodostumat ovat hyvin samankaltaisia kuin muiltakin alueilta löytyneet vastaavat muodostumat. Niiden syntymekanismi on luultavasti ainakin osittain identtinen. Tutkittu alue on täynnä pieniä mielenkiintoisia jäätikkömäisiä muodostumia, joiden tutkimiseen tulevaisuudessa kannattaa panostaa. Erityisesti muinaisen kraatterijärven myöhäisen jäätiköitymisprosessin tutkiminen tarkemmin olisi hyvin mielenkiintoista. Sirpaloituneen ylängön LDA- ja LVF-muodostumien keskinäisten vuorovaikutusten tutkiminen vaatisi nykyistä tarkempaa topografia- ja kuvamateriaalia. Virtausalueelta löytynyt kuivunut allas tulisi kuvata tarkemmilla kameroilla, koska allas vaikuttaa olevan alueen viimeisin nestemäisen veden aiheuttama muodostuma.

Galaxy dynamics using simulation models has been an important research field during the last 50 years. In the beginning of the 20th century there were already extensive catalogs of galaxies which showed the large diversity of the galaxy shapes, although there was no theory to explain those. Nowadays, galaxy dynamics can be extensively studied by simulating the dark matter, star, and gas cloud orbits numerically, but before the era of modern computers constructing even a simple model was a considerable challenge. In the beginning of the 1940’s Erik Holmberg (University of Lund) introduced his new integration procedure for galaxy simulations (Holmberg, 1941) which can be considered as a pioneering study in galaxy dynamics. In his work, Holmberg replaced gravitation with light intensity, based on the fact that they both obey the same 1/r² attenuation with distance. He modeled the interaction of two galaxies with light bulbs and came out with the conclusion that some features of the galaxies, for example tails and intergalactic bridges, can be explained by gravitational tidal forces. Holmberg’s work was significant for being the first simulation of galaxy dynamics, which could be upgraded only 20 years later, when the first simulations with electronic computers were started. Despite the significance of the Holmberg’s simulations and the large number of citations they have received, there is no marks that the simulations would have been repeated. During the summer of 2013 I reconstructed the Holmberg’s experimental setting in the University of Oulu. The experiment was made two times: once using exactly the same parameters that Holmberg used, and another time with small changes in the initial parameters. In this thesis I introduce the Holmberg’s experiments and the theory behind that. In chapter 2, I give a brief overview of disk galaxies and methods used in galaxy simulations. In chapter 3, I present the theoretical basis of Holmberg’s analog simulation. Chapter 4 covers the hardware and the practical realization of the experiment. In chapter 4, I represent the results and compare them with the Holmberg’s results.

In this thesis we are interested in the evoluNon of disc galaxies. One of the most common ways to study it is by a deep analysis of the distribuNon of chemical abundances in the stellar populaNons of the disc component. Abundance gradients let us reconstruct the puzzle of the formaNon and evoluNon of this type of galaxies, once we learn about the different elements that are released to the interstellar medium at each stage of the life of stars. In this work we pay special aaenNon to the so-­‐called thick disc component of spiral galaxies, believing that it is a relic of the early galaxy and its understanding opens the door for a complete galaxy formaNon scenario. We analyse thick discs both with observaNonal data and simulaNons because we want to have a wider view of the situaNon and we think that such complementary approaches can help us maximise our knowledge and results. Our simulaNons with an enhanced feedback are the ones that best reproduce the measured data from the Milky Way. The trend for the variaNon of the mean metallicity with galacNc radius at different heights from the plane matches that in the Galaxy. It is negaNve in the mid-­‐plane of galaxies and then becomes posiNve at greatest heights. According to simulaNons, this behaviour is due to a populaNon of relaNvely young and metal-­‐rich stars formed in situ in the outer galaxy, which is missing in the inner thick disc. When looking at the same magnitudes but via observaNons from the CALIFA local universe galaxy sample, we see that the external galaxies exhibit a variety of different behaviours both for the metallicity and age radial gradients with height, in addiNon to the trend found in simulaNons and the Milky Way. We deduce that thick discs probably do not form through a unique mechanism but from a combinaNon of many of them. Finally we want to know the influence of the galacNc mass in the chemical evoluNon of a disc galaxy. By using a fiducial set of simulaNons and comparing the results to observaNonal data we conclude that the smallest systems in our set might have an incorrect feedback efficiency, and suggest that a mass-­‐dependent modulaNon of feedback might improve the result.

High-mass stars play a key role in the energetics and chemical evolution of molecular clouds and galaxies. However, the mechanisms that allow the formation of high-mass stars are far less clear than those of their low-mass counterparts. Most of the research on high-mass star formation has focused on regions currently undergoing star formation. In contrast, objects in the earlier prestellar stage have been more difficult to identify. Recently, it has been suggested that the cold, massive, and dense Infrared Dark Clouds (IRDCs) host the earliest stages of high-mass star formation. The chemistry of IRDCs remains poorly explored. In this dissertation, an observational program to search for chemical variations in IRDC clumps as a function of their age is described. An increase in N2H+ and HCO+ abundances is found from the quiescent, cold phase to the protostellar, warmer phases, reflecting chemical evolution. For HCO+ abundances, the observed trend is consistent with theoretical predictions. However, chemical models fail to explain the observed trend of increasing N2H+ abundances. Pristine high-mass prestellar clumps are ideal for testing and constraining theories of high-mass star formation because their predictions differ the most at the early stages of evolution. From the initial IRDC sample, a high-mass clump that is the best candidate to be in the prestellar phase was selected (IRDC G028.23-00.19 MM1). With a new set of observations, the prestellar nature of the clump is confirmed. High-angular resolution observations of IRDC G028.23-00.19 suggest that in order to form high-mass stars, the detected cores have to accrete a large amount of material, passing through a low- to intermediate-mass phase before having the necessary mass to form a high-mass star. The turbulent core accretion model is inconsistent with this observational result, but on the other hand, the observations support the competitive accretion model. Embedded cores have to grow in mass during the star-formation process itself; the mass is not set at early times as the turbulent core accretion model predicts. The observed gas velocity dispersion in the cores is transonic and mildly supersonic, resulting in low virial parameters (neglecting magnetic fields). The turbulent core accretion model assumes highly supersonic linewidths and virial parameters $sim$1, inconsistent with the observations, unless magnetic fields in the cores have strengths of the order of 1 mG.

<p> We develop, test, and apply a statistical photometric parallax method using main sequence turn off (MSTO) stars in the Sloan Digital Sky Survey (SDSS). We show using simulated data that if our density model is similar to the actual density distribution of our data, we can reliably determine the density model parameters of at least three major substructures in the Milky Way halo, and a smooth background component, using the computational resources available on MilkyWay@home (a twenty parameter fit). As a test for the new model, we fit the stellar density in SDSS stripe 19. After confirming that the model is working as intended on both simulated and observed SDSS stripe 19 data, we moved on to fitting stripes 10 through 23 in the SDSS north Galactic cap. We found an oblate halo with an average flattening of $0.58$. Seven streams were found in these fourteen stripes. The Sgr dwarf leading tidal tail detected in 8 stripes, with properties that are consistent with previous fits to the streams. The trailing tidal tail and the ''bifurcated'' stream were found at the previously identified distances. The Parallel Stream was traced across the sky at a distance of 15 kpc, and roughly tracks an orbit that was fit by previous authors to the Virgo Stellar Stream. A new stream, the Perpendicular Stream, was found at a distance of 15 kpc in the region of Virgo, but roughly perpendicular in orientation on the sky to the Parallel Stream. A stream possibly including the globular cluster NGC 5466 was also found at a distance between 5 and 15 kpc from the Sun.</p><p>