Dissertations / Theses on the topic 'Redshift Space'

The aim of this thesis is to analyze statistically the available QSO, LRG, galaxy and cluster samples in order to estimate the QSO-galaxy lensing anti-correlation signal and measure the mass of foreground galaxies and clusters and to estimate the QSO-LRG clustering amplitude, the QSO bias and their dependence on QSO luminosity. We also investigate the behaviour of the group-galaxy infall parameter and their rms velocity dispersions for different group memberships. The aim here is to make dynamical estimates of the group masses to check the QSO lensing results. We first cross-correlate the SDSS photo-z, g < 21, 1.0 < Z(_p) < 2.2 QSOs with g < 21 galaxies and clusters in the same areas. The anti-correlation found is somewhat less than the results of Myers et al. based on 2QZ QSOs. But contamination of the QSOs by low redshift NELGs and QSOs can cause underestimation of the anticorrelation lensing signal. Correcting for such low redshift contamination at the levels indicated by our spectroscopic checks suggests that the effect is generally small for QSO cross-correlations with g < 21 galaxies but may be an issue for fainter galaxy samples. Thus when this correction is applied to the photo-z QSO sample of Scranton et al. the anti-correlation increases and the agreement with the 2QZ results of Myers et al. is improved. When we also take into account the fainter r < 21 galaxy limit of Scranton et al. as opposed to g < 21 for Myers et al., the two observational results appear to be in very good agreement. We then measure the bias of QSOs as a function of QSO luminosity at fixed redshift (z < 1) by cross-correlating them with Luminous Red Galaxies (LRGs) in the same spatial volume, hence breaking the degeneracy between QSO luminosity and redshift. We use three QSO samples from 2SLAQ, 2QZ and SDSS covering a QSO absolute magnitude range -24.5 < M(_bj) < -21.5, and cross-correlate them with 2SLAQ (z ≈ 0.5) and AAOmega (z ≈ 0.7) photometric and spectroscopic LRGs in the same redshift ranges. The 2-D and 3-D cross-clustering measurements are generally in good agreement. Our (2SLAQ) QSO-LRG clustering amplitude (r(_0) = 6.8 (^+0.1_-0.3)h(^-1)Mpc) as measured from the semi-projected cross-correlation function appears similar to the (2SLAQ) LRG-LRG auto-correlation amplitude (r(_0) = 7.45 ± 0.35h(^-1)Mpc) and both are higher than the (2QZ-t-2SLAQ) QSO-QSO amplitude (r(_0) ≈ 5.0h(^-1)Mpc). Our measurements show remarkably little QSO-LRG cross- clustering dependence on QSO luminosity. Assuming a standard ACDM model and values for b(_LRG) measured from LRG autocorrelation analyses, we find b(_Q) = 1.45 ± 0.11 at M(_bj) ≈ -24 and b(_Q) = 1.90 ± 0.16 at M(_bj) ≈ -22. We also find consistent results for the QSO bias from a z-space distortion analysis of the QSO-LRG cross-clustering at z ≈ 0.55. The velocity dispersions fitted to QSO-LRG cross-correlation, ع (σ,π), at 680 kms(^-1) are intermediate between those for QSO-QSO and LRG-LRG clustering, as expected given the larger QSO redshift errors. The dynamical infall results give ẞ(_Q) = 0.55 ± 0.10, implying b(_Q) = 1.4 ± 0.2. Thus both the z-space distortion and the amplitude analyses yield b(_Q) ≈ 1.5 at M(_bj) ≈ -23. The implied dark matter halo mass inhabited by QSOs at z ≈ 0.55 is ~ 10(^13)h(^-1)M(_ʘ), again approximately independent of QSO luminosity. Prompted by the indications from QSO lensing that there may be more mass associated with galaxy groups than expected from virial analyses, we make new dynamical infall estimates of the masses associated with 2PIGG groups and clusters. We analyse the redshift distortions in the cluster-galaxy cross-correlation function as a function of cluster membership, cross-correlating z < 0.12 2PIGG clusters and groups with the full 2dF galaxy catalogue. We make estimates of the dynamical infall parameter, ẞ, and new estimates of the group velocity dispersions for group membership classes out to z < 0.12. We first find that, out to 30-40h(^-1)Mpc, the amplitude of the full 3-D redshift space cross-correlation function, ع (_cg), rises monotonically with group membership. We use a simple linear-theory infall model to fit ع (σ,π), in the range 5 < s < 40h(^-1) Mpc. We find that the ẞ versus membership relation for the data shows a minimum at intermediate group membership n ≈ 20 or L ≈ 2 x l0(^11)h(^-2)L(_ʘ), implying that the bias and hence M/L ratios rise by a significant factor (≈ 5x) both for small groups and rich clusters. The minimum for the mocks is at a 2 - 3x lower luminosity than for the data. However, the mocks also show a systematic shift between the location of the ẞ minimum and the M/L minimum at L ≈ l0(^11)h(^-2)L(_ʘ), given by direct calculation using the known DM distribution. Our overall conclusion is that bias estimates from dynamical infall appear to support the minimum in star-formation efficiency at intermediate halo masses. Nevertheless, there may still be significant systematic problems arising from measuring ẞ x (^1/_b) ∂P(_mass) /∂P(_gaiaxies) using large-scale infall rather than M/L using small-scale velocity dispersions

>Magister Scientiae - MSc
We begin by finding a system of differential equations for the background and linearly perturbed variables in the standard, ɅCDM model, using the Einstein Field Equations, and then solving these numerically. Later, we extend this to dynamical dark energy models parameterised by an equation of state, w, and a rest frame speed of sound, cs. We pay special attention to the large-scale behaviour of Δm, the gauge invariant, commoving matter density, since the approximation Δm ≃ δm, where δm is the longitudinal gauge matter density, is more commonly used, but breaks down at large scales. We show how the background is affected by w only, so measurements of perturbations are required to constrain cs. We examine how the accelerated expansion of the universe, caused by dark energy, slows down the growth rate of matter. We then show the matter power spectrum is not in itself useful for constraining dark energy models, but how redshift-space distortions can be used to extract the growth rate from the galaxy power spectrum, and hence how redshift-space power spectra can be used to constrain different dark energy models. We find that on small scales, the growth rate is more dependent on w, while on large scales, it depends more on cs.

Redshift Space Distortions (RSD) are an apparent anisotropy in the distribution of galaxies due to their peculiar motion. These features are imprinted in the correlation function of galaxies, which describes how these structures distribute around each other. RSD can be represented by a distortions parameter $\beta$, which is strictly related to the growth of cosmic structures. For this reason, measurements of RSD can be exploited to give constraints on the cosmological parameters, such us for example the neutrino mass. Neutrinos are neutral subatomic particles that come with three flavours, the electron, the muon and the tau neutrino. Their mass differences can be measured in the oscillation experiments. Information on the absolute scale of neutrino mass can come from cosmology, since neutrinos leave a characteristic imprint on the large scale structure of the universe. The aim of this thesis is to provide constraints on the accuracy with which neutrino mass can be estimated when expoiting measurements of RSD. In particular we want to describe how the error on the neutrino mass estimate depends on three fundamental parameters of a galaxy redshift survey: the density of the catalogue, the bias of the sample considered and the volume observed. In doing this we make use of the BASICC Simulation from which we extract a series of dark matter halo catalogues, characterized by different value of bias, density and volume. This mock data are analysed via a Markov Chain Monte Carlo procedure, in order to estimate the neutrino mass fraction, using the software package CosmoMC, which has been conveniently modified. In this way we are able to extract a fitting formula describing our measurements, which can be used to forecast the precision reachable in future surveys like Euclid, using this kind of observations.

Redshift Space Distortions (RSD) are an apparent anisotropy in the distribution of galaxies due to their peculiar motion. These features are imprinted in the correlation function of galaxies, which describes how these structures distribute around each other. RSD can be represented by a distortions parameter $\beta$, which is strictly related to the growth of cosmic structures. For this reason, measurements of RSD can be exploited to give constraints on the cosmological parameters, such us for example the neutrino mass. Neutrinos are neutral subatomic particles that come with three flavours, the electron, the muon and the tau neutrino. Their mass differences can be measured in the oscillation experiments. Information on the absolute scale of neutrino mass can come from cosmology, since neutrinos leave a characteristic imprint on the large scale structure of the universe. The aim of this thesis is to provide constraints on the accuracy with which neutrino mass can be estimated when expoiting measurements of RSD. In particular we want to describe how the error on the neutrino mass estimate depends on three fundamental parameters of a galaxy redshift survey: the density of the catalogue, the bias of the sample considered and the volume observed. In doing this we make use of the BASICC Simulation from which we extract a series of dark matter halo catalogues, characterized by different value of bias, density and volume. This mock data are analysed via a Markov Chain Monte Carlo procedure, in order to estimate the neutrino mass fraction, using the software package CosmoMC, which has been conveniently modified. In this way we are able to extract a fitting formula describing our measurements, which can be used to forecast the precision reachable in future surveys like Euclid, using this kind of observations.

In this thesis, we exploit the potential of existing QSO and galaxy surveys for investigating the nature of the large scale structure in the Universe. A detailed analysis of clustering and redshift- space distortions allows us to constrain cosmological parameters. We model the anisotropies due to dynamical and geometrical effects in the measured clustering pattern of distant QSOs from the 2dF QSO Survey (2QZ) and also Lyman break galaxies. The 2QZ is then combined with the QSO sample from the 2dF SDSS LRG and QSO Survey (2SLAQ) to study the luminosity dependence of QSO clustering. Using AT-body simulations, we estimate the statistical gains in the determination of cosmological parameters from future LRG surveys. We measure the clustering of distant QSOs from the 2QZ survey by performing a correlation analysis of redshift-space (z-space) distortions. To interpret the z-space correlation function measured in orthogonal directions, ع(σ,π)， we require an accurate model for the QSO real-space correlation function, ع (r). Motivated by the form for ع (r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard ACDM predictions, we use a double power-law model for ع (r). which gives a good fit to the z-space and projected correlation functions. By fitting functional forms of ع(σ,π) which include both dynamical and geometrical modelling, we find, as expected, that β (which parameterises the infall into overdense regions) and the density of the Universe (Ω(^0_M)) are degenerate. However, this degeneracy can be lifted by using linear theory predictions under different cosmological scenarios. Using the 2QZ survey, we obtain: βQAO (z=1.4) = 0.50 (^0.13_0.15), Ω(^0_M) = 0.35 (^+0.19_-0.13). The modelling of geometrical and dynamical anisotropies in the measured ع(σ,π) pattern is then applied to a sample of distant Lymari-break galaxies. The presence of feedback mechanisms in these z〜 3 star-forming galaxies heightens the importance of understanding the effects of z-space distortions. Despite the limited size of the fields, which hampers the determination of ع(r) at large scales, we find that a double-power law ع(s) parameterisation is consistent with the correlation function measurements. This double power law model is then used as an input for the ع(σ,π) fitting and subsequent constraining of cosmological parameters. This investigation reveals that: ßLBG (z= 3) = 0.25± (^+0.05_-0.05) and Ω(^0_M) = 0.55(^+0.45_-0.16). The combination of the 2QZ with the fainter 2SLAQ QSO sample reveals that QSO clustering does not depend strongly on luminosity. This result is consistent with models which predict that haloes of similar mass can harbour QSOs of different luminosities. By assuming ellipsoidal models for the collapse of density perturbations, we test this hypothesis and estimate the mass of the dark matter haloes which the QSOs inhabit. We find that halo mass does not seem to evolve strongly with redshift nor depend on QSO luminosity. Having determined the black hole mass associated with the QSOs, we investigate how it correlates with luminosity and redshift and ascertain the relation between Eddington efficiency and black hole mass. Our results suggest that: (i) black hole mass does not depend strongly on accretion efficiency and (іі) black holes associated with QSOs of different luminosities have similar masses. Finally, the Hubble Volume simulation is used to construct a mock sample of a future ΑΑΩ Luminous Red Galaxy (LRG) survey. The ultimate aims of this survey are to identify the baryon acoustic features in the LRG clustering signal and to determine the equation of state of dark energy. We apply the z-space distortion analysis developed previously in the thesis to infer the statistical gain in terms of determinations of ß(_LRG) (z~ 0.7) and Ω(+0_m) .This thesis exploits the wealth of information contained in cosmological surveys, and demonstrates how the use of tools such as clustering statistics or z-space distortion analyses permit the extraction of such information.

>Magister Scientiae - MSc
The growth rate of large-scale structure is a key probe of gravity in the accelerating Universe. Standard models of Dark Energy within General Relativity predict essentially the same growth rate, whereas Modified Gravity theories without Dark Energy predict a different growth rate. Redshift-space distortions lead to anisotropy in the power spectrum, and extracting the monopole and quadrupole allows us to determine the growth rate and thus test theories of gravity. We investigate redshift-space distortions in the intensity maps of the 21cm emission line of neutral hydrogen (HI) in galaxies after the Epoch of Reionization: HI intensity mapping delivers very accurate redshifts. We first use the standard approach based on the Fourier power spectrum. Then we explored an alternative approach, based on the spherical-harmonic angular power spectrum. Fisher forecasting was used to make predictions of the accuracy with which MeerKAT will measure the growth rate parameter, via the proposed MeerKAT Large Area Synoptic Survey (MeerKLASS). Then we extend the forecasts to consider the planned HI intensity mapping survey in Phase 1 of the Square Kilometre Array. These forecasts enable us to predict at what level of accuracy General relativity and various alternative theories could be ruled out.

In this Thesis I have exploited the most recent observational data from CMB, BAO and growth rate of LSS as well as N-body simulations of modified gravity, to investigate the spatial properties of the large scale structure of Universe by constraining cosmological parameters in the framework of alternative cosmologies. The research is focused on clustering and redshift space distortions as cosmological probe. In this context I have studied the degeneracies between modified gravity and massive neutrinos as well as the robustness of the methodology for constraining the linear growth rate including realistic systematics, implementing suitable parametrizations of the redshift-space distortions in the perspective of current and future galaxy surveys.

The history of our Universe spans 13.7 billions of years and could be divided into several stages from the Big Bang up to now. Around 370 000 years after the Big Bang (z~1100) the temperature of the Universe low- ered enough for the first simple atoms to form. Matter and radiation decoupled, and the Universe became transparent to radiation. Cosmic microwave background (CMB) photons that we detect nowadays were last scattered at z~1100 and, since then, have been traveling in straight line. This is the reason why CMB is usually defined as the picture of the Universe at that redshift. Right after the CMB was emitted, the Universe entered the so called Dark Ages when no sources of light exist. Studying the early Universe, one of the most important phases is the subsequent phase-transition named reionization, i.e. the process that reionized the matter in the Universe after the formation of the first sources of light, namely the first stars and galaxies. Consequently, the detection and study of these objects are the key to unveil the early stages of the history of the Universe. Imaging plays a more important role than spectroscopy in searching for high-redshift galaxies because it permits to observe more objects at the same time, better managing the telescope time. Deep surveys, obtained by observing the same sky area for several days, are the answer to the need for detections of high-redshift galaxies. This thesis is focused on the study of the galaxy population existing when the Universe was less than 1.5 Gyr old. When studying the early Universe, the detection of high-redshift sources depends strongly on the detection limit of the survey and the surface brightness of the objects themselves. Taking this into account, we made use of the deepest datasets currently available obtained with the Hubble Space Telescope (HST) in both the optical and near-infrared (NIR) domain to carefully study how these two issues affect the identification and photometry of high-redshift galaxies. The important role played by high-redshift galaxies in cosmic reionization is no longer debated and, lately, most of studies agreed on the key relevance of galaxies that are below the current detection limit. While we are waiting for the James Webb Space Telescope (JWST) to directly observe these faint galaxies, finding an alternative way to estimate their overall light contribution is mandatory. To this aim we developed a technique based on the power spectrum to analyze background fluctuations. Relying on a Lyman break-like approach we compared the power spectra of background signal derived from observations obtained in two adjacent bands to identify the light contribution from a population of galaxies lying within a specific redshift range. Then, Monte Carlo simulations permitted us to disentangle the information embedded in the light excess identified via power spectra, in particular deriving a constraint on the faint-end slope of the luminosity function. The UDF05 dataset, follow-up of the original Hubble Ultra Deep Field (HUDF), consists in observations in the optical bands obtained with the Advanced Camera for Survey (ACS). It permitted us to constrain the slope of the luminosity function at z~6 (0.95 Gyr after the Big Bang), which turned out the be steep enough to allow bright and faint galaxies at that redshift to account for the ionizing photon budget required for cosmic reionization. The subsequent analysis aimed at deriving similar constraints on the faint-end slope of the luminosity function at z~7-8 (between 0.64 and 0.77 Gyr after the Big Bang) using deep observations in the near-infrared obtained with the infrared channel of the Wide Field Camera 3 (WFC3-IR) during the HUDF09 program. Regarding z ∼ 8, the quality of the NIR dataset did not permit to disentangle any light produced by the faint galaxy population from the background noise and spurious signals. On the basis of the drop in the star formation rate density from z~6 to z~7 and beyond, there should be a more relevant contribution in terms of photoionizing photons at z~7 than at z~8 and we expected to be able to detect it. Unfortunately, the analysis at z~7 implied dealing with different detectors that are characterized by systematics that can not be erased by simply considering the ratio of the power spectra. Up to now the understanding of all WFC3/IR related problems is not as good as for ACS and a fur- ther analysis is needed before being able to use the IR dataset for the analysis of surface brightness fluctuations. Since a perfect reduction procedure of the images turned out to be an essential requirement to study any background signal, we performed an advanced data reduction to get an improved version of the deepest image of the Universe currently available, the so called eXtreme Deep Field (XDF). The goal was to create an image that allows to verify our findings on the faint-end slope of the luminosity function at z~6 since the XDF did not permit us to get any constraint on background fluctuations. We started from raw frames obtained from several proposals over 10 years and created hyperbiases and hyperdarks taking into account all the issues affecting ACS data, including the minor ones such as the herringbone effect. Then, we masked the satellite trails, aligned all the frames, and corrected for the chip-to-chip jump. We are still working on the dataset, in particular we are focused on modelling and correcting for the electronic ghost. Anyway, the preliminary check on photometry suggests a promising, even though small, achievement in term of signal to noise of the sources. The effect of surface brightness on the detection of primordial galaxies in deep surveys is directly depending on the cosmological surface brightness dimming that can be express in the form (1 + z)−4 and that affects all the sources. The strong dependence of surface brightness dimming with increasing redshift suggests the presence of a selection bias when searching for high-redshift galaxies, i.e. we tend to detect only those galaxies with a high surface brightness. Unresolved knots of emission are not affected by surface brightness dimming, thus allowing, in principle, to test clumpiness within high-redshift galaxies. We followed an empirical approach based on HST legacy datasets characterized by different depth to study the surface brightness dimming of galaxies. We selected a sample of Lyman-break galaxies at z~4 (1.5 Gyr after the Big Bang) detected in the XDF, HUDF, and the Great Observatories Origins Deep Survey (GOODS) datasets and found no significant trend when comparing the total magnitudes measured from images with different depth. Then, we compared our results to the prediction for mock sources derived from Monte Carlo simulations. In particular, considering different surface brightness profiles for the mock galaxies we were able to rule out all the extended profiles as fit for our data, getting a confirmation on the clumpy distribution of the light in high-redshift galaxies. The study of cosmological surface brightness dimming is also important since it could affect our prediction of what the upcoming JWST can observe at higher redshifts, where younger galaxies may exhibit a larger fraction of clumpiness. Our direct comparison showing that galaxies detected in GOODS do not become significantly brighter in the HUDF suggests that most of their light is compact and hints to the fact that JWST will likely not find diffuse star forming components. Finally, to complete the study on high-redshift galaxies we also focused on lower-redshift galaxies that could enter the high-redshift sample due to photometric scatter. In general interlopers are galaxies at z~1-2 showing colors similar to those of real dropout galaxies due to the 4000 A break. Even though their colors are likely to include them in the dropout sample, contaminants have a non negligible detection in the bands blueward of the Lyman-break. The preliminary study we performed using the multi-wavelength catalog obtained from CANDELS GOODS-South shows that the number counts of contaminants are significantly different from those of dropout galaxies at z~5-6 suggesting a clear difference in the luminosity functions of the two populations and little or no evolution in the population of interlopers entering the sample at different redshifts. Finally, we used the 3D-HST catalogs for the GOODS-South field that provided us with photometric data in ground based, HST, and Spitzer/IRAC bands as well as with photometric redshfits. This catalog allowed a study on the interlopers at z~4-5.
I 13.7 miliardi di anni di storia dell’Universo possono essere suddivisi in diverse fasi a partire dal Big Bang fino ad arrivare al giorno d’oggi. Dopo l’emissione della radiazione cosmica di fondo (CMB) avvenuta 370 000 anni dopo il Big Bang (z~1100), in seguito al disaccoppiamento fra materia e radiazione l’Universo e' divenuto trasparente a quest’ultima dando inizio alla fase chiamata eta' oscura (“Dark Ages”), durante cui non era presente alcuna sorgente di luce. Nello studio dell’Universo primordiale riveste un ruolo chiave lo studio della transizione di fase, nota come reionizzazione, avvenuta in seguito alla nascita delle prime stelle e galassie. Lo studio delle prime sorgenti di luce che hanno popolato l’Universo e', quindi, la chiave per scoprire l’Universo primordiale e capirne l’evoluzione. La ricerca di galassie ad alto redshift ha ottenuto una spinta fondamentale grazie alla fotometria e alle tecniche basate sull’acquisizione di immagini che, a differenza della spettroscopia, permettono lo studio simultaneo di piu` oggetti, ottimizzando il tempo di osservazione con i telescopi. In particolare le survey profonde, ottenute osservando la medesima regione di cielo per piu' giorni, sono la risposta alla necessita' di identificare il maggior numero possibile di oggetti. Questa tesi e' focalizzata sullo studio delle prime galassie, gia' formate a meno di 1.5 miliardi di anni dal Big Bang. Lo studio dell’Universo primordiale dipende fortemente sia dal limite in magnitudine delle survey che dalla brillanza superficiale delle galassie che vogliamo osservare. Per caratterizzare l’effetto di entrambi questi fattori, in questa tesi abbiamo analizzato dati ottenuti con il telescopio spaziale Hubble (HST) sia nelle bande ottiche, che in quelle del vicino infrarosso (IR). L’obiettivo del nostro studio e' stato capire come questi effetti influiscano e limitino l’identificazione e la caratterizzazione fotometrica delle galassie ad alto redshift. Il ruolo chiave giocato dalle prime galassie nell’ambito del processo di reionizzazione e' ormai assodato, ma studi recenti hanno mostrato come le galassie meno brillanti, e dunque al di sotto dell’attuale limite di osservabilita', possano aver avuto un’importanza maggiore rispetto alle galassie brillanti che sono state identificate fino ad ora. In attesa che il telescopio spaziale James Webb (JWST) possa osservare direttamente queste galassie poco brillanti, e' fondamentale trovare un modo alternativo per stimare quale sia il con- tributo di luce totale proveniente da questi oggetti. Proprio a tale scopo abbiamo sviluppato una tecnica, basata sull’utilizzo dello spettro di potenza, per analizzare le fluttuazioni del segnale di background. Basandoci su un approccio simile al tecnica del Lyman-break, utilizzata comunemente per l’identificazione di galassie ad alto redshift, abbiamo confrontato lo spettro di potenza del segnale di fondo in due bande adiacenti per isolare la luce prodotta da una popolazione di galassie deboli entro un ristretto intervallo di redshift. Grazie ad una serie di simulazioni di tipo Monte Carlo siamo riusciti a ricavare dall’eccesso di segnale nella banda piu' rossa un vincolo sulla pendenza α della funzione di luminosita' alle magnitudini piu' deboli. In particolare, utilizzando i dati del progetto UDF05, continuazione del programma Hubble Ultra Deep Field (HUDF), siamo riusciti ad ottenere un valore della pendenza α della funzione di luminosita' a magnitudini deboli a z~6 (corrispondente a 0.95 miliardi di anni dopo il Big Bang). I valori di α = −1.8 e α = −1.9 che abbiamo ottenuto tenendo o meno conto del clustering sono tali da permetterci di dire che la quantita' di fotoni ionizzanti prodotti da tutte le galassie a z~6 e' sufficiente a giustificare il processo di reionizzazione dell’idrogeno nell’Universo. L’analisi che abbiamo condotto successivamente e' indirizzata ad ottenere un valore di α a redshift piu' alto, nello specifico z~7-8 (corrispondenti, rispettivamente, a 0.64 e 0.77 miliardi di anni dopo il Big Bang). Con questo obiettivo abbiamo fatto uso delle osservazioni profonde ottenute nell’ambito del programma HUDF09 nel vicino infrarosso. Per quanto riguarda z~8, la qualita' delle immagini infrarosse non ci ha permesso di isolare alcun segnale prodotto dalle galassie deboli dal rumore di fondo e da segnali spuri. Sulla base del crollo della densita' del tasso di formazione stellare andando da z ~6 a redshift piu' alti il contributo, in termini di fotoni ionizzanti, delle galassie a z~7 dovrebbe essere maggiore rispetto a quello della popolazione a z~8 e quindi ci aspettavamo che isolare un segnale prodotto da quelle galassie fosse piu' facile che a z~8. In realta', pero', l’analisi a z~7 prevede il confronto di dati ottenuti con strumenti diversi, caratterizzati da problemi diversi ed effetti sistematici che non vengono eliminati semplicemente con- siderando il rapporto fra gli spettri di potenza, come accade, invece, nel caso di immagini ottenute con la stessa camera. Inoltre, al momento, la nostra conoscenza dei problemi della camera infrarossa Wide Field Camera 3 (WFC3/IR) di HST non e' ancora allo stesso livello di quella relativa alla camera Advanced Camera for Survey (ACS) ed e', quindi, necessario un ulteriore e piu' approfondito studio sugli effetti legati allo strumento prima di poter usare i dati infrarossi per lo studio delle fluttuazioni di background. Avendo constatato che una perfetta procedura di riduzione dei dati costituisce un requisito essenziale per poter studiare le fluttuazioni di background e, quindi, il segnale proveniente dalle galassie meno brillanti, il passo successivo e' stato ottenere una versione migliorata dell’immagine piu' profonda dell’Universo attualmente disponibile ottenuta nell’ambito del progetto eXtreme Deep Field (XDF). Il nostro obiettivo era di ottenere un’immagine tale da permetterci di verificare i nostri risultati sulla pendenza della funzione di luminosita' a z~6 dato che l’XDF non ci ha permesso di individuare alcuna fluttuazione nel segnale di fondo. Il nostro lavoro e' iniziato acquisendo dall’archivio le immagini non ridotte ottenute in di- versi progetti durante un arco temporale di 10 anni e creando i nostri hyperbias e hyperdark. In questo abbiamo potuto tenere in considerazione tutte le problematiche legate alla camera ACS, anche quelle minori, come l’herringbone effect, che spesso non vengono corrette dalla normale pipeline di riduzione dati. Successivamente abbiamo mascherato le tracce dei satelliti, allineato tutte le immagini e corretto per la differenze di livello di fondo esistenti fra un chip e l’altro. Al momento stiamo ancora lavorando su queste immagini, nello specifico con l’idea di modellare i ghost elettronici e correggere le immagini per questo problema. I test preliminari sulla fotometria delle nostre immagini sono promettenti e suggeriscono che ci sia un leggero guadagno in termini di rapporto segnale-rumore rispetto alla versione originale dell’XDF, ma solo un ulteriore lavoro ci permettera' di ottenere le immagini finali. La brillanza superficiale incide direttamente sull’identificazione di galassie primordiali in immagini profonde sulla base dall’effetto noto come dimming cosmologico. Questo consiste in una diminuzione della brillanza superficiale di tutti gli oggetti astronomici e- stesi che scala con il redshift stesso di un fattore (1+z)^4. La forte dipendenza dell’effetto dal redshift suggerisce un effetto di selezione per il quale si individuerebbero più' facilmente le galassie primordiali con un’alta brillanza superficiale rispetto a quelle piu' deboli. Va notato che, siccome l’effetto del dimming si ha soltanto su oggetti estesi, essendo legato alla brillanza superficiale, la ricerca di tracce di questo effetto puo' essere utilizzata per testare quale sia la distribuzione di luce nelle sorgenti ad alto redshift. Nello specifico il dimming puo' aiutare a capire se l’emissione di luce sia concentrata in strutture compatte o meno. Nel nostro studio abbiamo adottato un approccio empirico, confrontando dati provenienti da survey con profondita' diversa, ma ottenute tutte con lo stesso strumento, in particolare HST/ACS. Abbiamo concentrato la nostra attenzione su un campione di galassie a z~4 (corrispondente a 1.5 miliardi di anni dopo il Big Bang) identificate nelle immagini XDF, HUDF e GOODS e, confrontando le magnitudini totali derivate dalle diverse survey, non e' emerso alcun andamento nei dati che fosse imputabile al dimming cosmologico. Per completare il lavoro abbiamo, poi, effettuato delle simulazioni Monte Carlo per ricavare quale sarebbe il riscontro sui dati se il dimming fosse in atto a secondo del tipo di dis- tribuzione di luce nelle galassie ad alto redshift. Confrontando i risultati delle simulazioni con quelli ricavati dai dati e' stato possibile escludere i profili di brillanza superficiale caratteristici delle sorgenti estese. I nostri dati sono, quindi, in accordo con una distribuzione della formazione stellare ad alto redshift in strutture compatte, come sostenuto anche da altri gruppi di ricerca. In generale lo studio degli effetti del dimming cosmologico riveste un ruolo molto importante nella determinazione del tipo di oggetti che JWST potra' osservare. Essendo in grado di spingere il nostro orizzonte verso fasi della storia dell’Universo ancora piu' vicine al Big Bang, JWST permettera' di verificare in maniera piu' accurata sia la distribuzione della luce nelle galassie primordiali sia il contributo proveniente dalle sorgenti che al momento non riusciamo a vedere singolamente. Infine, per completare il nostro studio sulle galassie ad alto redshift abbiamo preso in considerazione gli oggetti a z~1-2 che possono contaminare i cataloghi di galassie primordiali. Lo spettro di questi oggetti mostra un break a 4000 A che puo' portarli ad avere dei colori molto simili a quelli delle vere galassie ad alto redshift. Cio' che distingue i contaminanti dalle vere galassie primordiali e' l’essere chiaramente identificabili nelle bande piu' blu del Lyman-break. Lo studio preliminare che e' stato condotto sulla base di due cataloghi pubblici multi- banda di tutte le sorgenti presenti nel campo GOODS-South mostra che la distribuzione del numero di contaminanti e delle vere galassie primordiali e' diversa nell’intervallo di redshift che abbiamo analizzato (z~4-5-6). Questo suggerisce che la popolazione contaminante abbia una funzione di luminosita' differente rispetto alle galassie ad alto redshift. Inoltre, si ricava dai dati che la distribuzione dei conteggi di contaminanti a basso red- shift mostra solo una leggera, se non assente, evoluzione. La popolazione contaminante e', quindi, sempre all’incirca la stessa, e questo e' confermato dal leggero spostamento del break a 4000 A richiesto perche' questi oggetti soddisfino i criteri di selezione in colore delle galassie a z ≥ 4. Anche i redshift fotometrici sono in accordo con l’ipotesi che i contaminanti siano oggetti a redshift piu' basso. Una piu' completa caratterizzazione della popolazione delle galassie che hanno colori simili a quelle primordiali sara' possibile quando nuovi cataloghi saranno resi disponibili.

The expansion of the universe is currently accelerating, as first inferred by Efstathiou et al. (1990), Ostriker & Steinhardt (1995) and directly determined by Riess et al. (1998) and Perlmutter et al. (1999). Current constraints are consistent with a time independent equation-of-state of w = -1, which is to be expected when a constant vacuum energy density dominates. But the Quantum Field Theory prediction for the magnitude of this vacuum energy is very much larger than that inferred (Weinberg, 1989; Koksma & Prokopec, 2011). It is entirely possible that the cause of the expansion has an alternative explanation, with both the inclusion of a quantum scalar field and modified gravity theories able to reproduce an expansion history close to, but potentially deviating from, that of a cosmological constant and cold dark matter. In this work I investigate the consistency of the VIMOS Public Extragalactic Redshift Survey (VIPERS) v7 census of the galaxy distribution at z = 0:8 with the expansion history and linear growth rate predicted by General Relativity (GR) when a Planck Collaboration et al. (2016) fiducial cosmology is assumed. To do so, I measure the optimally weighted redshift-space power spectrum (Feldman et al., 1994), which is anisotropic due to the coherent infall of galaxies towards overdensities and outflow from voids (Kaiser, 1987). The magnitude of this anisotropy can distinguish between modified theories of gravity as the convergence (divergence) rate of the velocity field depends on the effective strength of gravity on cosmological scales (Guzzo et al., 2008). This motivates measuring the linear growth rate rather than the background expansion, which is indistinguishable for a number of modified gravity theories. In Chapter 6 I place constraints of fσ8(0:76) = 0:44 ± 0:04; fσ8(1:05) = 0:28 ± 0:08; with the completed VIPERS v7 survey; the combination remains consistent with General Relativity at 95% confidence. The dependence of the errors on the assumed priors will be investigated in future work. Further anisotropy is introduced by the Alcock-Paczynski effect - a distortion of the observed power spectrum due to the assumption of a fiducial cosmology differing from the true one. These two sources of anisotropy may be separated based on their distinct scale and angular dependence with sufficiently precise measurements. Doing so degrades the constraints: fσ8(0:76) = 0:31 ± 0:10; fσ8(1:05) = -0:04 ± 0:26; but allows for the background expansion (FAP ≡ (1 + z)DAH=c) to be simultaneously constrained. Galaxy redshift surveys may then directly compare both the background expansion and linear growth rate to the GR predictions I find the VIPERS v7 joint-posterior on (fσ8; FAP ) shows no compelling deviation from the GR expectation although the sizeable errors reduce the significance of this conclusion. In Chapter 4 I describe and outline corrections for the VIPERS spectroscopic selection, which enable these constraints to be made. The VIPERS selection strategy is (projected) density dependent and may potentially bias measures of galaxy clustering. Throughout this work I present numerous tests of possible systematic biases, which are performed with the aid of realistic VIPERS mock catalogues. These also allow for accurate statistical error estimates to be made { by incorporating the sample variance due to both the finite volume and finite number density. Chapter 5 details the development and testing of a new, rapid approach for the forward modelling of the power spectrum multipole moments obtained from a survey with an involved angular mask. An investigation of the necessary corrections for the VIPERS PDR-1 angular mask is recorded. This includes an original derivation for the integral constraint correction for a smoothed, joint-field estimate of ¯n(z) and a description of how the mask should be accounted for in light of the Alcock- Paczynski effect. Chapter 7 investigates the inclusion of a simple local overdensity transform: 'clipping' prior to the redshift-space distortions (RSD) analysis. This tackles the root cause of non-linearity and potentially extends the validity of perturbation theory. Moreover, this marked clustering statistic potentially amplifies signatures of modified gravity and, as a density-weighted two-point statistic, includes information not available to the power spectrum. I show that a linear real-space power spectrum with a Kaiser factor and a Lorentzian damping yields a significant bias without clipping, but that this may be removed with a sufficiently strict transform; similar behaviour is observed for the VIPERS v7 dataset. Estimates of fσ8 for different thresholds are highly correlated due to the overlapping volume, but the bias for insufficient clipping can be calibrated and the correlation obtained using mock catalogues. A maximum likelihood value for the combined constraint of a number of thresholds is shown to achieve a ' 16% decrease in statistical error relative to the most precise single-threshold estimate. The results are encouraging to date but represent a work in progress; the final analysis will be submitted to Astronomy & Astrophysics as Wilson et al. (2016). In addition to this, an original extension of the prediction for a clipped Gaussian field to a clipped lognormal field is presented. The results of tests of this model with a real-space cube populated according to the halo occupation distribution model are also provided.

Powerful forces are at work in giant Ly α nebulae, a rare and mysterious population in the high redshift universe. Much like the spatially extended emission line halos around high redshift radio galaxies . but without the strong radio emission . Ly α nebulae (or Ly α 'blobs') boast copious Ly α emission (10⁴⁴ erg s⁻¹), large sizes (∼100 kpc), complex gas morphologies, and the company of numerous compact, star-forming galaxies, and may offer a window into dramatic episodes of massive galaxy formation. The small sample sizes and complex inner workings of Ly α nebulae have limited progress on understanding the their space density, environments, and physical conditions. This thesis strives to answer fundamental questions about Ly α nebulae and pave the way for understanding their role in the build up of massive galaxy systems. To address the frequency of collapse of these massive structures, we carried out the largest systematic Ly α nebula survey to date and measured the Ly α nebula space density. As an unbiased test of the environment of Ly α nebulae, we studied the surroundings of a Ly α nebula and confirmed that Ly α nebulae reside preferentially in overdense regions. To disentangle the sources of ionization, we took a census of all the compact ionization sources within a large Ly α nebula using high resolution imaging. Finally, we used photoionization modeling to put constraints on the physical conditions, the metallicity, and the sources of ionization within Ly α nebulae. Future work will be able to build on this thesis by expanding the systematic search for Ly α nebulae to other existing deep broad-band datasets, mapping the three-dimensional overdense structures in which Ly α nebulae live out to ≥ 50 (comoving) Mpc scales, and disentangling multiple sources of ionization within a larger sample of individual systems using deep optical and near-infrared spectroscopy and detailed photoionization modeling.

We test the galactic outflow model by probing associated galaxies of four strong intergalactic C IV absorbers at z = 5-6 using the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) ramp narrowband filters. The four strong C IV absorbers reside at z = 5.74, 5.52, 4.95, and 4.87, with column densities ranging from N-C IV = 10(13.8) to 10(14.8) cm(-2). At z = 5.74, we detect an i-dropout Ly alpha emitter (LAE) candidate with a projected impact parameter of 42 physical kpc from the C IV absorber. This LAE candidate has a Ly alpha-based star formation rate (SFRLy alpha) of 2 M-circle dot yr(-1) and a UV-based SFR of 4 M-circle dot yr(-1). Although we cannot completely rule out that this i-dropout emitter may be an [O II] interloper, its measured properties are consistent with the C IV powered galaxy at z = 5.74. For C IV absorbers at z = 4.95 and z = 4.87, although we detect two LAE candidates with impact parameters of 160 and 200 kpc, such distances are larger than that predicted from the simulations. Therefore, we treat them as nondetections. For the system at z = 5.52, we do not detect LAE candidates, placing a 3 sigma upper limit of SFRLy alpha approximate to 1.5 M-circle dot yr(-1). In summary, in these four cases, we only detect one plausible C IV source at z = 5.74. Combining the modest SFR of the one detection and the three nondetections, our HST observations strongly support that smaller galaxies (SFRLy alpha less than or similar to 2 M-circle dot yr(-1)) are main sources of intergalactic C IV absorbers, and such small galaxies play a major role in the metal enrichment of the intergalactic medium at z greater than or similar to 5.

The results are presented here of multi-wavelength observations centred on two fields of the Leiden-Berkeley Deep Survey, which form the basis for a study of the population and cosmic evolution of the high redshift, low power, Fanaroff & Riley class I (FRI) radio galaxies. These fields, Hercules.1 and Lynx.2, contain a complete sample of 81 radio sources with S_1.4GHz > 0.5 mJy within 0.6 square degrees. Wide-field, ~1.5 arcsec resolution, radio observations, along with near infra-red and optical imaging, and some multi-object spectroscopy, are used to select the best high-redshift FRI candidates, giving 37 in total. Currently, the host galaxy identification fraction is 86% with 11 sources remaining unidentified at a level of r > 25.2 (Hercules; 4 sources) or r > 24.4 (Lynx; 7 sources) and K > 20. Spectroscopic redshifts are determined for 49% of the sample and photometric redshift estimates are presented for the sample sources without spectra or previously published results. 95% of the 37 best FRI high-redshift candidate sources were then observed using sub-arcsecond radio resolution, with the aim of detecting extended emission with respect to compact core features - vital for unambiguous morphological classification. The nature of the radio observations meant that 10 extra sample sources could also be included in the data. Lower resolution data were also taken for the Lynx.2 field sources to provide a comparison with the 1.5 arcsec data. The classification of the entire radio sample is done in two stages. Sources which showed clear extension are classified by morphology alone, whereas sources with no obvious or weak extension were classified using a combination of morphology and flux density loss in the higher resolution data indicative of resolved out extended emission. Five groups are used for this - 'Certain FRIs', 'Likely FRIs', 'Possible FRIs', 'Unclassifiable sources' (for those not included in the higher resolution observations) and 'Not FRIs'. The final group numbers are 8, 10, 24, 33 and 6 for groups 1-5 respectively. The space densities of the maximum, probable and minimum FRIs are then calculated and compared to two previously published measurements of the local value, and with the behaviour of the strongest FRII sources. The results for all three groups show density enhancements of factors of 5-9 at z ~ 1.0 which implies cosmic evolution of the FRI population; this enhancement is also in very good agreement with that predicted by previous models. The behaviour of the FRI/FRII dividing luminosity, as a function of host galaxy absolute magnitude, at the different cosmic epochs of the sample, and for two different star formation histories, is also investigated. A shift to brighter absolute magnitudes is found to be inconsistent with the data but this conclusion is weak due to the lack of knowledge of the host galaxy stellar populations, and the small number of sources in the sample.

In the last years, more and more studies demonstrated the existence of a coevolution between active galactic nuclei and host galaxies. Starbursts are often accompanied by an enhanced nucleus activity and the physical properties of the two physical mechanisms seems to be correlated. Given the dusty nature of the region in which such mechanisms take place, their direct observation is strongly affected by extinction. The hidden UV and optical emission has been for a long time a big limitation to these studies for both the difficulty in detecting a consistent fraction of such sources and for the estimation of their intrinsic emission. However, the energy absorbed at shorter wavelengths is re-emitted by the heated dust, in the mid and far infrared (MIR and FIR). In this picture, the observations obtained with the Herschel and Spitzer space observatories play a major role. Exploring the spectral region spanning from the peak of stellar emission to the peak of dust emission, they allow to constrain the total amount of energy emitted by the underlying physical mechanisms and, consequently, their relative and absolute strength. Herschel and Spitzer observations are however necessary but not sufficient for these kind of studies. Reliable photometric redshifts can only be computed with a good spectra coverage at optical wavelengths. Moreover, when studying the AGN activity, keeping into account the mid-IR spectral region, where the dusty torus emission dominates, become crucial. The mid-IR spectral region can be explored, e.g. by the Akari space observatory With the work summarized in this thesis, we contributed to the study of the connection between AGN and host galaxy under different aspects. Our analysis focuses on the south ecliptic pole (SEP) area, that given its position, is subject to a low cirrus emission. First, we reduced a large dataset of optical images taken in the SEP field. The resulting mosaics are now available for further studies both in the same and different topics. Second, starting from our optical images, and other pubblicly and private available images and catalogs, we built a multiwavelength catalog of sources covering 7 square degrees in the SEP area. The photometric coverage of this catalog spans from the optical to the far-IR of the Herschel-SPIRE bands. Spitzer-IRAC and MIPS bands, beside Akari-IRC observations are also included. This catalog is already available for the scientific community. Our third contribution to the research in this field is represented by our analysis on a sub-sample of far-IR selected sources. Using SED fitting techniques, we analyzed the main properties of these galaxies (redshifts, stellar masses, star formation and AGN activity). Then we studied the contribution of each single physical mechanism (stars, AGN, star formation) to the total emission at different wavelengths. Finally we discussed the relations among these properties. Our multiwavelength results complement literature analysis undertaken in the X-rays, pointing toward the existence of a double ``main sequence'', one in the stellar mass (M*) versus SFR space and the other in the M* versus black hole accretion rate (BHAR) space. We conclude with the estimation of the M*-BHAR main sequence slope at z<0.5.
Negli ultimi anni, sempre più studi hanno dimostrato l'esistenza di una co-evoluzione tra nuclei galattici attivi e galassie ospiti. Fenomeni di starburst sono spesso accompagnati da una incrementata attività nucleare e le proprietà dei due meccanismi fisici sembrano essere correlate. Data la natura polverosa delle regioni nelle quali questi meccanismi si manifestano, l'osservazione diretta è fortemente influenzata dall'estinzione. L'emissione UV ed ottica nascosta ha costituito per lungo tempo una grande limitazione a questi studi sia per la difficoltà nella rilevazione di una frazione consistente di queste sorgenti, sia per per la stima della loro estinzione intrinseca. Comunque, l'energia assorbita a lunghezze d'onda minori è riemessa dalla polvere riscaldata, nel medio e lontano infrarosso (MIR e FIR). In questo contesto, le osservazioni ottenute con gli osservatori spaziali Herschel e Spitzer giocano un ruolo predominante. Esplorando le regioni spettrali tra il picco di emissione stellare ed il picco di emissione delle polveri, essi permettono di stimare la quantità totale di energia emessa dai meccanismi fisici coinvolti e, conseguentemente, la loro importanza relativa ed assoluta. Le osservazioni Herschel e Spitzer sono comunque necessarie ma non sufficienti per questo tipo di studi. Redshift fotometrici affidabili possono essere calcolati solo con una buona copertura spettrale alle lunghezze d'onda dell'ottico. Inoltre, nello studio dell'attività AGN, tenere in considerazione la regione spettrale del medio IR, dove domina l'emissione del toro di polveri, diventa cruciale. La regione spettrale del medio IR può essere indagata e.g. dall'osservatorio spaziale Akari. Con il lavoro sintetizzato in questa tesi, abbiamo contribuito allo studio della connessione tra AGN e galassia ospite sotto vari aspetti. La nostra analisi si focalizza nell'area del polo sud eclittico (SEP), che data la sua posizione, è soggetta ad una bassa emissione da cirri. Per prima cosa, abbiamo ridotto un vasto set di immagini ottiche riprese nel campo SEP. I mosaici risultanti sono ora disponbili per ulteriori studi relativi allo stesso argomento o ad altri. In secondo luogo, a partire dalle nostre immagini ottiche e da altre immagini e cataloghi sia pubblici che privati, abbiamo costruito un catalogo di sorgenti all'interno di 7 gradi quadrati nell'area SEP. La copertura fotometrica va dall'ottico al lontano infrarosso delle bande Herschel-SPIRE. Misurazioni Spitzer-IRAC e MIPS, insieme ad osservazioni Akari-IRC sono inoltre incluse. Questo catalogo è ora disponibile per la comunità scientifica. Il nostro terzo contributo alla ricerca in questo campo è rappresentato dall'analisi condotta su un sottocampione di sorgenti selezionate nel lontano IR. Usando tecniche di SED fitting, abbiamo analizzato le principali proprietà di queste galassie (redshift, massa in stelle, attività di formazione stellare e di AGN). Quindi, abbiamo studiato il contributo di ciascun singolo meccanismo fisico (stelle, AGN, formazione stellare) all'emissione a differenze lunghezze d'onda. Per ultimo, abbiamo discusso le relazioni tra queste proprietà. La nostra analisi multi-banda è complementare ad analisi di letteratura condotte nel dominio dei raggi X, le quali puntano verso l'esistenza di una doppia ``sequenza principale'', una nel piano massa stellare (M*) contro tasso di formazione stellare (SFR), e l'altra nel piano M* contro tasso di accrescimento del buco nero (BHAR). Per ultimo abbiamo stimato la pendenza della sequenza principale M*-BHAR a redshift z<0.5

In recent years, advances in deep optical, and especially deep near-infrared imaging with the Hubble Space Telescope (HST) and wide-field ground-based telescopes such as VISTA, have revolutionized our understanding of the cosmological evolution of galaxies and supermassive black-holes (as manifest through active galactic nuclei; AGN). In particular, the dynamic range provided by the survey `wedding cake' of available HST+ground-based optical/IR data offers new opportunities to push the meaningful statistical study of galaxy and AGN evolution out to high redshifts. Much recent attention has focused, unsurprisingly, on using these new data to push studies of galaxy formation back to within a billion years of the Big Bang, and exploring the role of young galaxies in driving cosmic hydrogen reionization during the crucial era corresponding to redshifts z ≃ 6-10. However, these data have not been as thoroughly exploited at intermediate redshifts, and have only recently been used to explore black-hole/AGN evolution. In this thesis I utilise the latest deep optical/near-infrared imaging and spectroscopy to explore three key facets of cosmological evolution. First, I present a new, robust measurement of the evolving rest-frame ultraviolet (UV) galaxy luminosity function (LF) over the key redshift range from z ≃ 2 to z ≃ 4. My results are based on the high dynamic range provided by combining the Hubble Ultra Deep Field (HUDF), CANDELS/GOODS-South, and UltraVISTA/COSMOS surveys. I utilise the unparalleled multi-frequency photometry available in this survey `wedding cake' to compile complete galaxy samples at z ≃ 2; 3; 4 via photometric redshifts (calibrated against the latest spectroscopy). This study is important as the peak of star-formation is shown to happen within a redshift range z = 2 - 4 and determining the exact epoch that the galaxies were forming most of their stars depends significantly on the UV luminosity density which requires robust measurements of the galaxy UV luminosity function and its accurate parameterization. My new determinations of the UV LF extend from M1500 ≃ -22 (AB mag) down to M1500 =-14.5, -15.5 and -16 at z ≃2, 3 and 4 respectively (thus reaching ≃ 3-4 magnitudes fainter than previous blank-field studies at z ≃ 2 - 3). At z ≃ 2 - 3 I find a much shallower faint-end slope (α = -1:32 ± 0:03) than the steeper values (α ≃ -1:7) reported in the literature, and show that this new measurement is robust. By z ≃ 4 the faint-end slope has steepened slightly, to α = -1:43 ± 0:04, and I show that these measurements are consistent with the overall evolutionary trend from z = 0 to z = 8. I then calculate the UV luminosity density (and hence unobscured star-formation density) and show that it peaks at z ≃ 2:5 - 3, when the Universe was ≃ 2:5 Gyr old. Second, I have used these data to revisit the possibility that X-ray AGN played a significant role in cosmic hydrogen reionization which is one of the major processes in the formation of the Universe we see today. Hence, it is really important to understand this phenomenon thoroughly by studying the properties of sources capable of ionising photons, such as star-forming galaxies and high redshift AGNs. Although most recent studies have suggested that the emerging population of young star-forming galaxies can bathe the Universe in sufficient high-energy photons to complete reionization by z ≃ 6, some authors have reasserted the potentially important role of high-redshift AGN in the hydrogen reionization process. In an effort to clarify this situation, I reinvestigate a claimed sample of 22 X-ray detected active galactic nuclei (AGN) at redshifts z > 4, which has reignited the debate as to whether young galaxies or AGN reionized the Universe. These sources lie within the GOODS-S/CANDELS field, and I examine both the robustness of the claimed X-ray detections (within the Chandra 4Ms imaging) and perform an independent analysis of the photometric redshifts of the optical/infrared counterparts. I confirm the reality of only 15 of the 22 reported X-ray detections, and moreover find that only 12 of the 22 optical/infrared counterpart galaxies actually lie robustly at z > 4. I recalculate the evolving far-UV (1500Å) luminosity density produced by AGN at high redshift, and find that it declines rapidly from z ≃ 4 to z ≃ 6, in agreement with several other recent studies of the evolving AGN luminosity function. The associated rapid decline in inferred hydrogen-ionizing emissivity contributed by AGN falls an order-of-magnitude short of the level required to maintain hydrogen ionization at z ≃ 6. I conclude that AGNs make a very minor contribution to cosmic hydrogen reionization. Finally, I have utilized the deep optical/near-infrared survey data to explore the prevalence of quenched/passive galaxies at high redshift. Applying a robust method to isolate passive galaxies from star-forming galaxies is the key to improving our understanding of the quenching process. Focusing primarily on the deep HUDF data-set, I have revisited the effectiveness of simple colour-colour (UVJ) selection techniques in isolating robust samples of quenched galaxies, and find that dust plays a more important role in this selection process than has been previously appreciated. Through careful SED fitting I successfully isolate a sample of apparently dust-free quiescent galaxies in the redshift range 0:5 < z < 4:5 but (at least in the HUDF) fail to find any galaxy which has remained truly quiescent for > 1 Gyr. I conclude by focusing on the properties of a refined/robust sample of apparently quenched galaxies at z > 3, and in particular establishing the contribution of quenched galaxies to stellar-mass density at early times. I conclude with a summary of my findings, and a brief discussion of the most promising avenues for future advances with the next generation of facilities, such as the James Webb Space Telescope (JWST).

With the Hubble Space Telescope and its near-infrared capabilities, it is now possible to probe deep into the epoch of reionization, improving our understanding of galaxy evolution through cosmic history. Whether it is via colour-selection or fitting the spectral energy distribution, it has now become routine to amass large samples of galaxies as distant as redshift z = 8, with the current frontier of observations at z = 9 - 10. The new Hubble Frontier Fields (HFF) programme provides the potential to study the most distant, intrinsically faint background galaxies through the gravitational lensing provided by a foreground galaxy cluster. This thesis presents a study of the galaxy population at z = 9 - 10 that exploits this phenomenon. In an initial search of the first two HFF cluster+parallel pointings, Abell 2744 and MACS J0416.1-240, we unveil twelve candidate high-redshift galaxies at 8:4 < z < 9:5, and are thus able to place constraints on the galaxy UV luminosity function at z = 9. For this study, we employ the "blank-field" method, whereby we confine attention to only the homogeneously deep, relatively low-magnification regions of the imaging. We are able to demonstrate evidence for a smooth decline in UV luminosity density between z ≃ 8 and z ≃ 9, in contrast to reports in the recent literature of a steep drop-off at these redshifts. We extend this study to include the new MACS J0717.5+3745 and MACS J1149+2223 cluster+parallel pointings, and supplement the search for z ≃ 9-10 galaxies with twenty CLASH cluster pointings. From a search over an area ≃ 130 sq. arcmin, we are able to present 33 galaxy candidates with photometric redshift solutions in the range 8:4 < zphot < 11:2. Our new results reinforce the argument for a smoothly-evolving LF between z ≃ 8 and z ≃ 9, which can be equally well modelled by a factor ≃ 2 drop in Φ* or a dimming of ≃ 0:5 mag in M*. We also find evidence that this smooth decline in the UV luminosity function, and hence UV luminosity density, continues to z ≃ 10. As well as considering the galaxy population at z = 9 - 10, this thesis presents a study of the stellar populations of galaxies at z ≥ 5. We are able to extend the luminosity baseline and measure the colour-magnitude relation at z = 5 - 8, through a combination of probing intrinsically faint galaxies behind cluster fields, in conjunction with both ultra-deep, pencil beam imaging such as the Hubble Ultra Deep Field (HUDF) and wider, shallower imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). This allows us to make inferences about the underlying stellar populations of galaxies at these epochs, and provides a unique insight into the colours of intrinsically faint, lensed galaxies as faint as M1500 ~ -14. We find that the data is consistent with an essentially unchanged average UV slope (β) for a given luminosity across the redshift range z = 5-8. We also find that the data favours a mild flattening of the colour-magnitude relation with redshift between z = 5 and z = 8.

Le modèle ΛCDM de la cosmologie repose sur l’existence d’une composante exotique, appelée énergie noire, pour expliquer l’accélération tardive de l’expansion de l’univers à z < 0.7. Des alternatives à cette constante cosmologique proposent de modifier la théorie de la gravitation basée sur la relativité générale aux échelles cosmologiques. Depuis l’automne 2014, le multi-spectrographe SDSS-eBOSS effectue un relevé de quasars dans un domaine en redshift peu exploré entre 0.8 ≤ z ≤ 2.2 dont l’un des objectifs majeurs est d’étendre les contraintes sur la nature de l’énergie noire et de tester la validité de la théorie de la relativité générale à plus haut redshift en utilisant les quasars comme traceurs de la matière.Dans cette thèse, nous mesurons et analysons la fonction de corrélation à deux points de l’échantillon de quasars obtenu après deux ans d'observation de eBOSS pour contraindre les distances cosmiques, à savoir la distance angulaire DA et le taux d'expansion H, ainsi que le taux de croissance des structures fσ8 à un redshift effectif Zeff = 1.52. Nous commençons par construire des catalogues des grandes structures qui prennent en compte la géométrie angulaire et radiale du relevé. Puis pour obtenir des contraintes robustes, nous identifions plusieurs sources d’effets systématiques, en particulier ceux liés à la modélisation et aux observations sont étudiées avec des « mock catalogues » dédiés qui correspondent à des réalisations fictives de l’échantillon de quasars eBOSS. Les paramètres cosmologiques de ces catalogues fictifs étant connus, ils sont utilisés comme référence pour tester notre procédure d’analyse. Les résultats de ce travail sur l’évolution des distances cosmiques sont compatibles avec les prédictions du modèle ΛCDM utilisant les paramètres de Planck et basé sur l’existence d’une constante cosmologique. La mesure du taux de croissance des structures est compatible avec la prédiction de ce modèle basé sur la relativité générale, ce qui étend ainsi la validité de la théorie aux échelles cosmologiques à grand redshift. Nous utilisons également notre mesure pour mettre à jour les contraintes sur les modèles d'extensions à ΛCDM et sur les scénarios de gravité modifiée. Ce travail de thèse constitue une première étude menée avec les données de quasars eBOSS et sera utilisée pour l’analyse de l’échantillon final à la fin 2019 ou l’on attend une amélioration de la précision statistique d’un facteur 2. Associé à BOSS, eBOSS ouvrira la voie pour les futurs programmes d’observation, comme le télescope au sol DESI et le satellite Euclid. Ces deux programmes sonderont intensivement l’époque de l’univers entre 1 < z < 2 en observant plusieurs millions de spectres, ce qui permettra d'améliorer d'un ordre de grandeur au moins les contraintes actuelles sur les paramètres cosmologiques
The ΛCDM model of cosmology assumes the existence of an exotic component, called dark energy, to explain the late-time acceleration of the expansion of the universe at redshift z < 0.7. Alternative scenarios to this cosmological constant suggest to modify the theory of gravitation based on general relativity at cosmological scales. Since fall 2014, the SDSS-IV eBOSS multi-object spectrograph has undertaken a survey of quasars in the almost unexplored redshift range 0.8 ≤ z ≤ 2.2 with the key science goal to complement the constraints on dark energy and extend the test of general relativity at higher redshifts by using quasars as direct tracers of the matter field.In this thesis work, we measure and analyse the two-point correlation function of the two-year data taking of eBOSS quasar sample to constrain the cosmic distances, i.e. the angular diameter distance DA and the expansion rate H, and the growth rate of structure fσ8 at an effective redshift Zeff = 1.52. First, we build large-scale structure catalogues that account for the angular and radial incompleteness of the survey. Then to obtain robust results, we investigate several potential systematics, in particular modeling and observational systematics are studied using dedicated mock catalogs which are fictional realizations of the data sample. These mocks are created with known cosmological parameters such that they are used as a benchmark to test the analysis pipeline. The results on the evolution of distances are consistent with the predictions for ΛCDM with Planck parameters assuming a cosmological constant. The measurement of the growth of structure is consistent with general relativity and hence extends its validity to higher redshift. We also provide updated constraints on extensions of ΛCDM and models of modified gravity. This study is a first use of eBOSS quasars as tracers of the matter field and will be included in the analysis of the final eBOSS sample at the end of 2019 with an expected improvement on the statistical precision of a factor 2. Together with BOSS, eBOSS will pave the way for future programs such as the ground-based Dark Energy Spectroscopic Instrument (DESI) and the space-based mission Euclid. Both programs will extensively probe the intermediate redshift range 1 < z < 2 with millions of spectra, improving the cosmological constraints by an order of magnitude with respect to current measurements

Les études détaillées d'amas de galaxies confirmés à grands redshifts sont peu nombreuses. L’objectif de cette Thèse est d’établir le premier catalogue d'amas confirmés spectroscopiquement à grand redshift et, pour la première fois à ces redshifts, d’étudier de manière statistique les propriétés des galaxies membres des amas. Dans cette Thèse, nous caractérisons et étudions 20 candidats amas à redshifts 1.4 < z < 2.8 parmi les candidats les plus prometteurs de l’échantillon CARLA. Nous réduisons et analysons des données spectroscopiques grism sans fente et imagerie proche-infrarouge des amas candidats, obtenues avec le télescope spatial Hubble. Nous mesurons plus de 700 redshifts au sein des champs observés, et confirmons spectroscopiquement 16 amas CARLA dans l’intervalle 1.4 < z < 2.8; ces amas sont associés à des noyaux galactiques actifs à fortes émissions radios (RLAGN) en leur centre, par sélection. Cet effort fait plus que doubler le nombre d’amas confirmés à ces redshifts. Nous étudions également le taux de formation stellaire des galaxies membres des amas en fonction de leur masses stellaires, et de la distance aux RLAGN. Nous trouvons que les galaxies membres massives sont situées sous la séquence principale jusqu’à z=2, ce qui suggère déjà à ces redshifts une évolution accélérée des galaxies massives au sein des amas. Nous trouvons également une concentration plus importante de membres actifs à plus petits rayons des RLAGN, jusqu’à z=2. Ceci est en accord avec un renversement de la relation densité vs. taux de formation stellaire pour nos amas CARLA à 1.4 < z < 2.0, ce qui suggère que les amas CARLA représentent une phase de transition de l’évolution des galaxies au sein des amas. Nous étudions également les populations stellaires de deux de nos amas confirmés à redshift z=2.0. Nous analysons les relations couleurs-couleurs et couleurs-magnitudes de ces deux amas et montrons que l’une des structures à z=2 possède une séquence rouge de galaxies passives. Globalement, nos résultats démontrent que les amas CARLA représentent des structures riches comprenant des populations mixtes de galaxies évoluées et massives sans formation stellaire, et des galaxies actives formant des étoiles. Cet échantillon sans précédent de 16 amas confirmés spectroscopiquement dans l’intervalle de redshift 1.4 < z < 2.8 constitue un échantillon idéal pour étudier statistiquement la phase de transition des amas de galaxies, ainsi que les mécanismes de suppression de la formation stellaire. (Abrégé)
Detailed studies of high-redshift confirmed galaxy clusters are based on a few individual objects. In this Thesis, we therefore aim at building the first sample of spectroscopically confirmed clusters at high-redshifts and, for the first time at these redshifts, statistically infer cluster member galaxy properties. In this Thesis, we study and characterize 20 cluster candidates at redshifts 1.4 < z < 2.8, which represent the most promising cluster candidates from the CARLA sample. We reduce and analyze slitless grism spectroscopic and near-infrared imaging data of the fields, obtained with the Hubble Space Telescope. We measure redshifts for over 700 star-forming sources in the 20 fields, and we spectroscopically confirm 16 CARLA clusters in the range 1.4 < z < 2.8; by selection, these clusters are associated with powerful radio-loud active galactic nuclei (RLAGN) at their center. This effort alone more than doubles the number of confirmed clusters at these redshifts. We study cluster member star-formation rates (SFRs) as a function of their stellar masses and distances from the RLAGN. We find that massive members are located below their star-forming main-sequence up to z=2. This implies that the massive star-forming end of the cluster population already followed an accelerated evolution at these high redshifts. We also find an increasing concentration of star-forming members with smaller radii relative to the RLAGN, at all redshifts up to z=2. Our 1.4 < z < 2.0 cluster members are therefore consistent with a reversal of the SFR-density relation. This is a first evidence showing that CARLA clusters represent a transition phase for cluster galaxy evolution. We also study stellar populations of two of our confirmed CARLA clusters at z=2.0. We study their color-color and color-magnitude relations and show that one of the two structures is comprised of a z=2 red sequence of passive candidate members. Together, these results provide clear evidence that our confirmed CARLA clusters represent rich structures comprised of mixed populations, including both evolved, passive, massive galaxies, and galaxies with ongoing star formation. Together, this unprecedented sample of 16 confirmed clusters at 1.4 < z < 2.8 constitutes an ideal sample for further statistical investigation of the cluster transition phase, including study of quenching mechanisms. (Abridged)

We present reduced data and data products from the 3D-HST survey, a 248-orbit HST Treasury program. The survey obtained WFC3 G141 grism spectroscopy in four of the five CANDELS fields: AEGIS, COSMOS, GOODS-S, and UDS, along with WFC3 H-140 imaging, parallel ACS G800L spectroscopy, and parallel I-814 imaging. In a previous paper, we presented photometric catalogs in these four fields and in GOODS-N, the fifth CANDELS field. Here we describe and present the WFC3 G141 spectroscopic data, again augmented with data from GO-1600 in GOODS-N (PI: B. Weiner). We developed software to automatically and optimally extract interlaced two-dimensional (2D) and one-dimensional (1D) spectra for all objects in the Skelton et al. (2014) photometric catalogs. The 2D spectra and the multi-band photometry were fit simultaneously to determine redshifts and emission line strengths, taking the morphology of the galaxies explicitly into account. The resulting catalog has redshifts and line strengths (where available) for 22,548 unique objects down to JH(IR) <= 24 (79,609 unique objects down to JH(IR) <= 26). Of these, 5459 galaxies are at z > 1.5 and 9621 are at 0.7 < z < 1.5, where Ha falls in the G141 wavelength coverage. The typical redshift error for JH(IR) <= 24 galaxies is sigma(z) approximate to 0.003 x (1 + z), i.e., one native WFC3 pixel. The 3 sigma limit for emission line fluxes of point sources is 2.1 x 10(-17) erg s(-1) cm(-2). All 2D and 1D spectra, as well as redshifts, line fluxes, and other derived parameters, are publicly available.(18)

Les relevés spectroscopiques de galaxies sont riches d'information cosmologique. Les ondes acoustiques qui se sont propagées dans l'Univers primordial ont laissé une signature dans la distribution de matière, appelée oscillations acoustiques de baryons (BAO), à une échelle caractéristique de 150 mégaparsecs. Mesurer cette échelle dans la distribution des galaxies permet de sonder le taux d'expansion de l'Univers au cours de son histoire. Par ailleurs, les mesures des décalages spectraux des galaxies sont sensibles à leur vitesse particulière (RSD), permettant par là même de mesurer le taux de croissance des structures et de tester la relativité générale à grande échelle. Cette thèse est consacrée à la mesure par spectre de puissance des BAO et des RSD dans l'échantillon de 173 736 galaxies à raies d'émission (ELG) de la collaboration eBOSS, à un décalage spectral effectif de 0.85. Un soin particulier a été apporté à la validation de l'implémentation du modèle théorique du spectre de puissance des galaxies, et à l'estimation et correction des systématiques observationnelles, grâce à des simulations réalistes. Les principales systématiques observationnelles de ce relevé proviennent des fluctuations de la densité de cibles avec la qualité de l'échantillon photométrique utilisé pour eBOSS, dont une version plus récente est exploitée pour le relevé spectroscopique de nouvelle génération DESI. En particulier, en plus de notables fluctuations dans la densité angulaire de cibles, de fortes variations de densité en décalage spectral ont été notées en fonction de la profondeur de l'imagerie, un effet mineur dans les autres relevés d'eBOSS. Les variations résiduelles de densité angulaire ont été atténuées en supprimant le contraste de densité au-delà d'une certaine échelle, tandis que les fluctuations dans la fonction de sélection radiale ont été prises en compte en divisant le relevé en sous-ensembles de profondeur photométrique équivalente. Ce faisant, le spectre de puissance mesuré est amorti à grande échelle, ce qui nécessite de corriger la prédiction théorique par des termes dits de contrainte intégrale, un projet original de cette thèse, qui a aussi permis d'améliorer certains procédés des analyses réalisées jusqu'alors. Les mesures RSD et BAO obtenues avec les ELG d'eBOSS sont combinées avec celles des autres relevés de grandes structures de la collaboration SDSS, et les implications cosmologiques sont exposées. Cette thèse se termine par un bilan des différentes systématiques observationnelles et d'analyse entachant la mesure cosmologique, et de pistes pour contrôler le budget systématique des futurs relevés spectroscopiques, comme DESI
Spectroscopic galaxy surveys contain a wealth of cosmological information. Acoustic waves that propagated in the primordial Universe left a signature on the matter distribution, called baryon acoustic oscillations (BAO), at a characteristic scale of 150 megaparsecs. Measuring this standard ruler in the distribution of galaxies provides access to the expansion history of the Universe. In addition, redshift measurements of galaxies are sensitive to their peculiar velocities (RSD), allowing to probe the growth rate of structure and test general relativity on large scales. This thesis is dedicated to the power spectrum analysis of BAO and RSD in the sample of 173,736 emission line galaxies (ELGs) of the eBOSS collaboration, at an effective redshift of 0.85. Special care was devoted to validate the implementation of the galaxy power spectrum theoretical model, and to estimate and correct observational systematics, with the help of realistic simulations. The main observational systematics of this sample stem from fluctuations of the galaxy target density with the quality of the photometric sample used for eBOSS, which is an early version of that utilised in the next generation spectroscopic survey DESI. In particular, besides the noticeable fluctuations of the angular density of targets, strong variations in the redshift density with imaging depth were noted - an effect which is usually assumed to be minor. Residual variations of the angular target density were mitigated by suppressing the density contrast above a certain scale, while fluctuations in the radial survey selection function were accounted for by dividing the data set in subsamples of equivalent photometric depth. Doing so, the measured galaxy power spectrum is damped at large scale, which requires to correct the theoretical prediction for the so-called integral constraints, an original work of this thesis that also allowed to improve some techniques of clustering analyses. The RSD and BAO measurements obtained with eBOSS ELGs are combined with the results from the other clustering samples of the SDSS collaboration, and cosmological implications are presented. This manuscript ends with a recap of different observational and analysis systematics hindering the cosmological measurements, and gives ideas to control the systematic budget of future spectroscopic surveys, like DESI

abstract: Quasars, the visible phenomena associated with the active accretion phase of super- massive black holes found in the centers of galaxies, represent one of the most energetic processes in the Universe. As matter falls into the central black hole, it is accelerated and collisionally heated, and the radiation emitted can outshine the combined light of all the stars in the host galaxy. Studies of quasar host galaxies at ultraviolet to near-infrared wavelengths are fundamentally limited by the precision with which the light from the central quasar accretion can be disentangled from the light of stars in the surrounding host galaxy. In this Dissertation, I discuss direct imaging of quasar host galaxies at redshifts z ≃ 2 and z ≃ 6 using new data obtained with the Hubble Space Telescope. I describe a new method for removing the point source flux using Markov Chain Monte Carlo parameter estimation and simultaneous modeling of the point source and host galaxy. I then discuss applications of this method to understanding the physical properties of high-redshift quasar host galaxies including their structures, luminosities, sizes, and colors, and inferred stellar population properties such as age, mass, and dust content.
Dissertation/Thesis
Ph.D. Astrophysics 2014

How galaxies form and evolve is one of the primary outstanding problems in extragalactic astronomy. I conduct a quantitative census of the relative importance of the major structural components (flattened and dynamically cold disk-dominated components versus puffy and dynamically hot spheroidal or triaxial bulges/ellipticals) in massive galaxies over cosmic time and across different environments in order to explore how galaxies evolve under the action of the various assembly mechanisms (major mergers, minor mergers, gas accretion, and internal secular processes) in these different regimes. I perform three inter-related analyses focusing on massive galaxies from z ~ 0 - 3 in both field and rich cluster environments. Important strengths of this thesis include the use of high-resolution, panchromatic imaging from some of the largest and deepest galaxy surveys with the Hubble Space Telescope (HST), Spitzer, and Chandra space telescopes, and also the inclusion of detailed comparisons between the empirical data and hierarchical ΛCDM-based models of galaxy evolution.
text

High resolution imaging and spectroscopy are invaluable tools for extragalactic astronomy. Galaxies with redshifts of 1 or more subtend a very small angle on the sky—typically, only about an arcsecond. Unfortunately, this is also approximately the angular resolution achieved with a ground-based telescope regardless of its aperture. Atmospheric turbulence ruins the image before it reaches the telescope but the emerging technology of adaptive optics (AO) gives the observer the possibility, within limitations, of correcting for these effects. This is the case for instruments such as the Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) and the Gemini North Telescope (Gemini) Altitude-Conjugate Adaptive Optics for the Infrared (Altair) systems. The alternative is to rise above the limitations of the atmosphere entirely and put the telescope in space, for example, the Hubble Space Telescope (HST) and its successor, the Next-Generation Space Telescope (NGST). I discuss several techniques that help overcome the limitations of AO observations with existing instruments in order to make them more comparable to imaging from space. For example, effective dithering and flat-fielding techniques as well as methods to determine the effect of the instrument on the image of, say, a galaxy. The implementation of these techniques as a software package called AOTOOLS is discussed. I also discuss computer simulations of AO systems, notably the Gemini Altair instrument, in order to understand and improve them. I apply my AO image processing techniques to observations of high-redshift radio galaxies (HzRGS) with the CFHT AOB and report on deep imaging in near-infrared (NIR) bands of 6 HzRGs in the redshift range 1.1 ≤ z ≤ 3.8. The NIR is probing the restframe visible light—mature stellar populations—at these redshifts. The radio galaxy is resolved in all of these observations and its ‘clumpier’ appearance at higher redshift leads to the main result—although the sample is very small—that these galaxy environments are undergoing mergers at high redshift. Finally, I look to the future of high resolution observations and discuss simulations of imaging and spectroscopy with the NGST. The computer software NGST VI/MOS is a ‘virtual reality’ simulator of the NGST observatory providing the user with the opportunity to test real observing campaigns.
Graduate