Recent observations have suggested that the C III] lambda 1907/1909 emission lines could be alternative diagnostic lines for galaxies in the reionization epoch. We use the F128N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to search for C III] emission in a sample of five galaxies at z = 5.7 in the Subaru Deep Field and the Subaru/XMM-Newton Deep Field. Using the F128N narrowband imaging, together with the broadband imaging, we do not detect C III] emission for the five galaxies with JAB ranging from 24.10 to 27.00 in our sample. For the brightest galaxy J132416.13+274411.6 in our sample (z = 5.70, J(AB) = 24.10), which has a significantly higher signal to noise, we report a C III] flux of 3.34 +/- 1.81 x 10(-18) erg s(-1)cm(-2), which places a stringent 3 sigma upper limit of 5.43 x 10(-18) erg s(-1)cm(-2) on C III] flux and 6.57 angstrom on the C III] equivalent width. Using the stacked image, we put a 3 sigma upper limit on the mean C III] flux of 2.55 x 10(-18) erg s(-1) cm(-2) and a 3 sigma upper limit on the mean C III] equivalent width of 4.20 angstrom for this sample of galaxies at z = 5.70. Combined with strong C III] detection reported among high-z galaxies in the literature, our observations suggest that the equivalent widths of C III] from galaxies at z > 5.70 exhibit a wide range of distribution. Our strong limits on C III] emission could be used as a guide for future observations in the reionization epoch.

Luminous high-redshift quasars can be used to probe of the intergalactic medium in the early universe because their UV light is absorbed by the neutral hydrogen along the line of sight. They help us to measure the neutral hydrogen fraction of the high-z universe, shedding light on the end of reionization epoch. In this paper, we present a discovery of a new quasar (PSO J006.1240+39.2219) at redshift z = 6.61 +/- 0.02 from Panoramic Survey Telescope & Rapid Response System 1.Including this quasar, there are nine quasars above z > 6.5 up to date. The estimated continuum brightness is M-1450 = -25.96 +/- 0.08. PSO J006.1240+39.2219 has a strong Ly alpha emission compared with typical low-redshift quasars, but the measured near-zone region size is R-NZ = 3.2 +/- 1.1 proper megaparsecs, which is consistent with other quasars at z similar to 6.

Theoretical models predict that some of the first stars ended their lives as extremely energetic pair-instability supernovae (PISNe). With energies approaching 10⁵³ ergs, these supernovae are expected to be within the detection limits of the upcoming James Webb Space Telescope (JWST), allowing observational constraints to be placed on the properties of the first stars. We estimate the source density of PISNe using a semi-analytic halo mass function based approach, accounting for the effects of feedback from star formation on the PISN rate using cosmological simulations. We estimate an upper limit of ~0.2 PISNe per JWST field of view at any given time. Feedback can reduce this rate significantly, e.g., lowering it to as little as one PISN per 4000 JWST fields of view for the most pessimistic explosion models. We also find that the main obstacle to observing PISNe from the first stars is their scarcity, not their faintness; exposures longer than a few times 10⁴ s will do little to increase the number of PISNe found. Given this we suggest a mosaic style search strategy for detecting PISNe from the first stars. Even rather high redshift PISNe are unlikely to be missed by moderate exposures, and a large number of pointings will be required to ensure a detection. / text

This thesis is a continuation of last year's work and it builds on earlier construction of a rover that will deploy an interferometer on the far side of the moon. The project is done in collaboration with (JPL) Jet Propulsion Laboratoryin Pasadena, California. Given the size of the mission, accuracy and time limit project has been split into several smaller projects. The areas that are the focus of this project are the suspension and the transition system. The transition system that is originated from the stage when the rover transforms from the transit mode to ready mode, and the suspension system, are in this thesis work presented by detailed conceptual design. The next step, not mentioned this thesis work, will be to perform aprimary structure design on the details. The project owner’s ultimate goal is to create a better understanding about the origins of the universe and its continual changing. This would give scientists an opportunity to study some of the most fundamental questions that are still are waiting for answers. Together with a group of energy engineers, Gustav Andersson and Emil Ericsson, we were caught by the very attractive project assignment, well aware that not many people get the chance or the opportunity to be involved or work with projects like this.

The fraction of ionizing photons escaping from high-redshift star-forming galaxies is a key obstacle in evaluating whether galaxies were the primary agents of cosmic reionization. We previously proposed using the covering fraction of low-ionization gas, measured via deep absorption-line spectroscopy, as a proxy. We now present a significant update, sampling seven gravitationally lensed sources at 4 < z < 5. We show that the absorbing gas in our sources is spatially inhomogeneous, with a median covering fraction of 66%. Correcting for reddening according to a dust-in-cloud model, this implies an estimated absolute escape fraction of similar or equal to 19% +/- 6%. With possible biases and uncertainties, collectively we find that the average escape fraction could be reduced to no less than 11%, excluding the effect of spatial variations. For one of our lensed sources, we have sufficient signal-tonoise ratio to demonstrate the presence of such spatial variations and scatter in its dependence on the Ly alpha equivalent width, consistent with recent simulations. If this source is typical, our lower limit to the escape fraction could be reduced by a further factor similar or equal to 2. Across our sample, we find a modest anticorrelation between the inferred escape fraction and the local star formation rate, consistent with a time delay between a burst and leaking Lyman continuum photons. Our analysis demonstrates considerable variations in the escape fraction, consistent with being governed by the small-scale behavior of star-forming regions, whose activities fluctuate over short timescales. This supports the suggestion that the escape fraction may increase toward the reionization era when star formation becomes more energetic and burst-like.

We present the HST WFC3/F275W UV imaging observations of A2218-Flanking, a lensed compact dwarf galaxy at redshift z approximate to 2.5. The stellar mass of A2218-Flanking is log(M-*/M-circle dot) = 9.14(-0.04)(+0.07) and SFR is 12.5(-7.4)(+3.8) M-circle dot yr(-1) after correcting the magnification. This galaxy has a young galaxy age of 127. Myr and a compact galaxy size of r(1/2) = 2.4 kpc. The HST UV imaging observations cover the rest-frame Lyman continuum (LyC) emission (similar to 800 angstrom) from A2218-Flanking. We firmly detect (14s) the LyC emission in A2218-Flanking in the F275W image. Together with the HST F606W images, we find that the absolute escape fraction of LyC is f(abs,esc) > 28%-57% based on the flux density ratio between 1700 and 800 angstrom (f(1700)/f(800)). The morphology of the LyC emission in the F275W images is extended and follows the morphology of the UV continuum morphology in the F606W images, suggesting that the f(800) is not from foreground contaminants. We find that the region with a high star formation rate surface density has a lower f(1700)/f(800) (higher f(800)/f(1700)) ratio than the diffused regions, suggesting that LyC photons are more likely to escape from the region with the intensive star-forming process. We compare the properties of galaxies with and without LyC detections and find that LyC photons are easier to escape in low-mass galaxies.

This thesis investigates the potential for detection and identification of primordial stars, galaxies, and supernovae at high redshift. Simulations indicate that the first Population III stars should appear in minihalos of mass M = 105-106 Msol at z ≈ 10-30. To assess the detectability of these objects, theoretical models of these stars and their surrounding HII regions are used. We assess the plausibility of detection with the upcoming James Webb Space Telescope (JWST), using the gravitational lensing provided by the galaxy cluster MACSJ0717.5+3745. The conclusion is that the detection of these objects is highly improbable but not impossible. To investigate the prospects of detecting and identifying the first galaxies, the spectral synthesis code Yggdrasil is introduced. According to this code, JWST may be able to detect Population III galaxies with stellar masses as low as 105 Msol at z ≈ 10 in unlensed fields. We find that, over limited redshift intervals, it could be possible to use Hubble Space Telescope (HST) and/or JWST broadband color criteria to single out Population III galaxy candidates. The prospects of detecting gravitationally lensed Population III galaxies with JWST and HST is investigated. A lower limit to detect ≈1 Population III galaxy of ε ≈ 10-2 (HST/CLASH) and ε ≈ 10-3 (JWST using MACS J0717.5+3745 as lens) is derived, where ε is the baryon fraction converted to Population III stars in a host halo. By fitting HST/CLASH data to Yggdrasil and comparison grids, two Population III galaxy candidates are discovered. These two candidates are the first Population III galaxy candidates discovered at z &gt; 6.5. A highly-magnified and doubly lensed extremely high-redshift (z ≈ 7.8) object is also identified. Finally the prospects of detecting core-collapse (CC) supernovae (SN) from the first galaxies at z ≈ 5-12 are investigated. The prediction is that no primordial SN is detectable, but 2-3 CC SN should be discovered by the HST/CLASH. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Submitted. Paper 6: Submitted. Paper 7: Manuscript.</p>

We investigate the evolution of dust content in galaxies from redshifts z = 0 to z = 9.5. Using empirically motivated prescriptions, we model galactic-scale properties-including halo mass, stellar mass, star formation rate, gas mass, and metallicity-to make predictions for the galactic evolution of dust mass and dust temperature in main-sequence galaxies. Our simple analytic model, which predicts that galaxies in the early universe had greater quantities of dust than their low-redshift counterparts, does a good job of reproducing observed trends between galaxy dust and stellar mass out to z approximate to 6. We find that for fixed galaxy stellar mass, the dust temperature increases from z = 0 to z = 6. Our model forecasts a population of low-mass, high-redshift galaxies with interstellar dust as hot as, or hotter than, their more massive counterparts; but this prediction needs to be constrained by observations. Finally, we make predictions for observing 1.1 mm flux density arising from interstellar dust emission with the Atacama Large Millimeter Array.

We introduce a new suite of radiation- hydrodynamical simulations of galaxy formation and reionization called Aurora. The Aurora simulations make use of a spatially adaptive radiative transfer technique that lets us accurately capture the small- scale structure in the gas at the resolution of the hydrodynamics, in cosmological volumes. In addition to ionizing radiation, Aurora includes galactic winds driven by star formation and the enrichment of the universe with metals synthesized in the stars. Our reference simulation uses 2 x 512(3) dark matter and gas particles in a box of size 25 h(-1) comoving Mpc with a force softening scale of at most 0.28 h(-1) kpc. It is accompanied by simulations in larger and smaller boxes and at higher and lower resolution, employing up to 2 x 1024(3) particles, to investigate numerical convergence. All simulations are calibrated to yield simulated star formation rate functions in close agreement with observational constraints at redshift z = 7 and to achieve reionization at z approximate to 8.3, which is consistent with the observed optical depth to reionization. We focus on the design and calibration of the simulations and present some first results. The median stellar metallicities of low- mass galaxies at z = 6 are consistent with the metallicities of dwarf galaxies in the Local Group, which are believed to have formed most of their stars at high redshifts. After reionization, the mean photoionization rate decreases systematically with increasing resolution. This coincides with a systematic increase in the abundance of neutral hydrogen absorbers in the intergalactic medium.

Η παρούσα εργασία έχει ως θέμα τις συνθήκες ναυσιπλοΐας και την έκφραση του ναυτικού βιώματος στις ελληνικές περιοχές κατά την περίοδο μεταξύ των μέσων του 9ου και του τέλους του 6ου αιώνα π.Χ. Η βάση εκκίνησης της έρευνας ήταν τα ομηρικά έπη, ενώ για την επεξεργασία του θέματος χρησιμοποιήθηκαν αρχαιολογικά και γραμματειακά δεδομένα προερχόμενα από τη συγκεκριμένη εποχή, αλλά και στοιχεία σχετικά με το θέμα προερχόμενα από προγενέστερες ή μεταγενέστερες εποχές. Επίσης συχνά έπρεπε να ανατρέξουμε σε πληροφορίες προερχόμενες από περιοχές εκτός του ελληνικού κόσμου, ώστε να μπορέσουμε να σχηματίσουμε την αναγκαία γενική εικόνα εντός της οποίας έγινε η πραγματεία του θέματος. Αρχικά, εξετάζονται τα ναυπηγικά δεδομένα, με βάση γραμματειακές πηγές (κυρίως, την περιγραφή του τρόπου ναυπήγησης της σχεδίας του Οδυσσέα), πρωτογενή ευρήματα (ναυάγια) και απεικονίσεις ή ομοιώματα καραβιών. Στο δεύτερο κεφάλαιο εξετάζεται το ομηρικό λεξιλόγιο για τα καράβια: λέξεις για τη μορφή, το σχήμα, τα δομικά στοιχεία, την πλεύση με κουπιά και με πανί, τα συστήματα διεύθυνσης, τον κατάπλου, ώστε να σχηματίσουμε μια όσο το δυνατόν λεπτομερή εικόνα για τα πλοία της Ιλιάδας και της Οδύσσειας. Στο τρίτο κεφάλαιο, η έρευνα εστιάζει στο το φυσικό περιβάλλον εντός του οποίου έπλεαν τα καράβια της ομηρικής εποχής: καιροί, ρεύματα, μορφολογία των ακτών, ορατότητα• επιπλέον, θα εξετάσουμε τις στρατηγικές πλεύσης που καθορίζονταν από το φυσικό περιβάλλον. Στο τέταρτο κεφάλαιο προσπαθούμε να διακρίνουμε τα κίνητρα που οδηγούσαν τους ναυτικούς στην επιλογή της μίας ή της άλλης διαδρομής, καθώς και να εξετάσουμε κάποιες βασικές ρότες. Στο πέμπτο κεφάλαιο διερευνώνται οι γενικότερες αιτίες που οδηγούσαν τους ανθρώπους της ομηρικής εποχής στο θαλάσσιο ταξίδι. Τέλος, στο έκτο κεφάλαιο, και μέσα στο πλαίσιο του θαλάσσιου ταξιδιού, εξετάζονται είναι οι σχέσεις που συνδέουν τον Οδυσσέα με την Ιθάκη, καθώς και η θέση της Ιθάκης στην αντίληψη των ναυτικών της αρχαιότητας. / The subject of this dissertation is the conditions of navigation and the expression of nautical experience in Greek societies between the middle of the 9th and the end of 6th centuries B.C. The base of the research is the Homeric epic. The main tools of research were archaeological and literary data from this era; also, we used relevant complementary evidence from earlier and subsequent ages. From time to time it was necessary to use the informatory context of non-Greek societies, in order to enlighten some obscure points and construct the big picture of our subject. At first, we discuss the construction of a ship, using literary sources (mainly, the account of raft building, in the second book of Odyssey), archaic ship relics and ship images or clay models. In the second chapter, we discuss the Homeric nautical vocabulary: words for the shape, the form, the construction of a ship, the sailing, the rowing, the rudder, the rigging and the harborage. The natural environment is the subject of the third chapter; weather, sea currents, coastlines, visibility from the sea and in the sea; besides, we tried to figure out the navigation strategies of Homeric era sailors in this environment and in these conditions. Consequently, we attempted to discern and understand the motives of a sailor to follow a sea route and we try to describe some of these routes. In the fifth chapter, we discuss the main reasons of sea venturing in Homeric era. Finally, we tried to look into the links between Odysseus and Ithaca, as well as the place of Ithaca in Greek nautical cosmos.