The South Pole Telescope has discovered 100 gravitationally lensed, high-redshift, dusty, star-forming galaxies (DSFGs). We present 0."5 resolution 870 mu m. Atacama Large Millimeter/submillimeter Array imaging of a sample of 47 DSFGs spanning z = 1.9-5.7, and construct gravitational lens models of these sources. Our visibility-based lens modeling incorporates several sources of residual interferometric calibration uncertainty, allowing us to properly account for noise in the observations. At least 70% of the sources are strongly lensed by foreground galaxies (mu(870) (mu m) > 2), with a median magnification of mu(870) (mu m) = 6.3, extending to mu(870) (mu m) > 30. We compare the intrinsic size distribution of the strongly lensed sources to a similar number of unlensed DSFGs and find no significant differences in spite of a bias between the magnification and intrinsic source size. This may indicate that the true size distribution of DSFGs is relatively narrow. We use the source sizes to constrain the wavelength at which the dust optical depth is unity and find this wavelength to be correlated with the dust temperature. This correlation leads to discrepancies in dust mass estimates of a factor of two compared to estimates using a single value for this wavelength. We investigate the relationship between the [C II] line and the far-infrared luminosity and find that the same correlation between the [C II]/L-FIR. ratio and Sigma(FIR). found for low-redshift star-forming galaxies applies to high-redshift galaxies and extends at least two orders of magnitude higher in SFIR. This lends further credence to the claim that the compactness of the IR-emitting region is the controlling parameter in establishing the "[C II] deficit."

We observed the [C II] line in 15 lensed galaxies at redshifts 1 < z <. 3 using HIFI on the Herschel Space Observatory and detected 14/15 galaxies at 3 sigma or better. High magnifications enable even modestly luminous galaxies to be detected in [C II] with Herschel. The [C II] luminosity in this sample ranges from 8x10(7) L-circle dot to 3.7x10(9) L-circle dot (after correcting for magnification), confirming that [C II] is a strong tracer of the ISM at high redshifts. The ratio of the [C II] line to the total far-infrared (FIR) luminosity serves as a measure of the ratio of gas to dust cooling and thus the efficiency of the grain photoelectric heating process. It varies between 3.3% and 0.09%. We compare the [C II]/FIR ratio to that of galaxies at z = 0 and at high redshifts and find that they follow similar trends. The [C II]/FIR ratio is lower for galaxies with higher dust temperatures. This is best explained if increased UV intensity leads to higher FIR luminosity and dust temperatures, but gas heating does not rise due to lower photoelectric heating efficiency. The [C II]/FIR ratio shows weaker correlation with FIR luminosity. At low redshifts highly luminous galaxies tend to have warm dust, so the effects of dust temperature and luminosity are degenerate. Luminous galaxies at high redshifts show a range of dust temperatures, showing that [C II]/FIR correlates most strongly with dust temperature. The [C II] to mid-IR ratio for the HELLO sample is similar to the values seen for low-redshift galaxies, indicating that small grains and PAHs dominate the heating in the neutral ISM, although some of the high [CII]/FIR ratios may be due to turbulent heating.

We present the Magellan/FIRE detection of highly ionized C IV lambda 1550 and O III]lambda 1666 in a deep infrared spectrum of the z = 6.11 gravitationally lensed low-mass galaxy RXC J2248.7-4431-ID3, which has previously known Ly alpha. No corresponding emission is detected at the expected location of He II lambda 1640. The upper limit on He II, paired with detection of O III] and C IV, constrains possible ionization scenarios. Production of C IV and O III] requires ionizing photons of 2.5-3.5 Ryd, but once in that state their multiplet emission is powered by collisional excitation at lower energies (similar to 0.5 Ryd). As a pure recombination line, He II emission is powered by 4 Ryd ionizing photons. The data therefore require a spectrum with significant power at 3.5 Ryd but a rapid drop toward 4.0 Ryd. This hard spectrum with a steep drop is characteristic of low-metallicity stellar populations, and less consistent with soft AGN excitation, which features more 4 Ryd photons and hence higher He II flux. The conclusions based on ratios of metal line detections to helium non-detection are strengthened if the gas metallicity is low. RXJ2248-ID3 adds to the growing handful of reionization-era galaxies with UV emission line ratios distinct from the general z = 2-3 population in a way that suggests hard ionizing spectra that do not necessarily originate in AGNs.

Modern cosmology predicts that a galaxy overdensity (e.g., protocluster) will be associated with a large intergalactic medium gas reservoir, which can be traced by Ly alpha forest absorption. We have undertaken a systematic study of the relation between Coherently Strong intergalactic Lya Absorption systems (CoSLAs), which have the highest optical depth (tau) in the tau distribution, and mass overdensities on the scales of similar to 10-20 h(-1) comoving Mpc. On such large scales, our cosmological simulations show a strong correlation between the effective optical depth (tau(eff)) of the CoSLAs and the three-dimensional mass overdensity. In spectra with moderate signal-to-noise ratio, however, the profiles of CoSLAs can be confused with individual high column density absorbers. For z > 2.6, where the corresponding Ly beta is redshifted to the optical, we have developed a selection technique to distinguish between these two alternatives. We have applied this technique to similar to 6000 sight lines provided by Sloan Digital Sky Survey III quasar survey at z = 2.6-3.3 with a continuum-to-noise ratio greater than 8, and we present a sample of five CoSLA candidates with tau(eff) on 15 h(-1) Mpc greater than 4.5x the mean optical depth. At lower redshifts of z < 2.6, where the background quasar density is higher, the overdensity can be traced by intergalactic absorption groups using multiple sight lines with small angular separations. Our overdensity searches fully use the current and next generation of Ly alpha forest surveys, which cover a survey volume of > 1 (h(-1) Gpc)(3). Systems traced by CoSLAs will yield a uniform sample of the most massive overdensities at z > 2 to provide stringent constraints to models of structure formation.

We present the discovery of nine quasars at z similar to 6 identified in the Sloan Digital Sky Survey (SDSS) imaging data. This completes our survey of z similar to 6 quasars in the SDSS footprint. Our final sample consists of 52 quasars at 5.7 < z << 6.4, including 29 quasars with z(AB) <= 20 mag selected from 11,240 deg(2) of the SDSS single-epoch imaging survey (the main survey), 10 quasars with 20 <= z(AB) <= 20.5 selected from 4223 deg2 of the SDSS overlap regions (regions with two or more imaging scans), and 13 quasars down to z(AB) approximate to 22 mag from the 277 deg2 in Stripe 82. They span a wide luminosity range of -29.0 <= M-1450 <= -24.5. This well-defined sample is used to derive the quasar luminosity function (QLF) at z similar to 6. After combining our SDSS sample with two faint (M-1450 >= -23 mag) quasars from the literature, we obtain the parameters for a double power-law fit to the QLF. The bright-end slope beta of the QLF is well constrained to be beta = -2.8 +/- 0.2. Due to the small number of low-luminosity quasars, the faint-end slope a and the characteristic magnitude M*(1450) are less well constrained, with alpha = -1.90(-0.44)(+0.58) and M* = -25.2(-3.8)(+1.2) mag. The spatial density of luminous quasars, parametrized as rho(M-1450 < -26, z) = rho(z = 6)10(k(z-6)), drops rapidly from z similar to 5 to 6, with k = -0.72 +/- 0.11. Based on our fitted QLF and assuming an intergalactic medium (IGM) clumping factor of C = 3, we find that the observed quasar population cannot provide enough photons to ionize the z similar to 6 IGM at similar to 90% confidence. Quasars may still provide a significant fraction of the required photons, although much larger samples of faint quasars are needed for more stringent constraints on the quasar contribution to reionization.

Environment is known to have a significant impact on the evolution of galaxies. This is most evident in the local Universe, where the oldest and most massive galaxies are found at the of massive galaxy clusters. Current theory predicts that galaxies will form earlier and evolve more rapidly in the densest regions of the Universe. What is not clear is how rapidly the of environment start to have an impact on galaxies, at what stage can we detect physical differences between galaxies in dense regions and those in the field? By the time galaxies are assembled in virialised clusters the effects are clear, but at higher redshift (z ≳ 2), in the unvirialised progenitors of clusters (protoclusters) the effects are harder to detect. In this thesis I study the impact of environment in a z =3.1 protocluster in the SSA22 field. I consider the fraction of mergers in the protocluster, comparing it to the fraction of mergers in field at a similar redshift. My classification is based on the morphology of Lyman break (LBGs), using HST ACS/F814W imaging, which probes the rest frame UV. I find a marginal enhancement of the merger fraction, 48±10 per cent for LBGs in the protocluster compared 30±6 per cent in the field, suggesting that galaxy-galaxy mergers are one of the key driving accelerated star formation and AGN growth in protocluster environments. Having considered the fraction of mergers in the protocluster I then turn my attention to the physical properties of LBGs. I use multiwavelength data and spectral energy distribution fitting to determine the mass of LBGs in the protocluster and in the field. I find no statistical evidence for an enhancement of mass in the protocluster, suggesting that the protocluster environment has not impacted the average mass of LBGs at this redshift. It is possible that the protocluster LBG population may become more massive than LBGs in the field at lower redshift, or the galaxies may cease to be detectable by the Lyman break method before a mass difference between the protocluster galaxies and field is observable. Finally I consider the Lyman-α blobs (LABs) within the protocluster. These are large (~10- 100kpc) scale regions of diffuse Lyman-α emission, thought to be associated with overdense regions. 35 LABs have been detected in the SSA22 protocluster, indicating the presence of large clouds of gas in the circumgalactic medium. A debate has arisen regarding the powering mechanism of the LABs, particularly between star forming processes (e.g. Lyman-α escaping from a star forming galaxy or photoionizing radiation escaping from a star forming galaxy or active galactic nuclei) and a cold accretion model. The latter involves gas gravitationally cooling as it falls into the centre of a dark matter halo to feed a central galaxy. Some of this energy heats the cold gas, which then emits Lyman-α as it cools. The cold gas accretion theory gained popularity because some LABs appear not to contain a luminous galaxy or AGN which could explain the observed emission. One suggestion is that the central galaxy could be hidden by dust and that this could explain the lack of a detection in UV or optical. I therefore use SCUBA2 850μm imaging to search for submm sources (dusty star forming galaxies) in the LABs. I detect submm sources in only two of the LABs at 3.5δ, however, stacking all the LABs gives an average flux density of S850 = 0.6±0.2mJy. This suggests that on average the LABs do contain a submm source which could be a dusty galaxy. However, stacking the LABs by size indicates that only the largest third (area ≳ 1800kpc²) have a mean detection, at 4.5δ, with S850 = 1.4±0.3mJy, suggesting that different mechanisms may dominate the larger and smaller LAB populations. I explore two possible mechanisms for powering the LABs, cold accretion and central star forming galaxies. I find that central star formation is more likely to be the dominant source of emission, with cold accretion playing a secondary role.

We report the results of a faint quasar survey in a one-square-degree field. The aim is to test the Y - K/g - z and J - K/i - Y color selection criteria for quasars at faint magnitudes to obtain a complete sample of quasars based on deep optical and near-infrared color-color selection and to measure the faint end of the quasar luminosity function (QLF) over a wide redshift range. We carried out a quasar survey based on the Y - K/g - z and J - K/i - Y quasar selection criteria, using the deep Y-band data obtained from our CFHT/WIRCam Y-band images in a two-degree field within the F22 field of the VIMOS VLT deep survey, optical co-added data from Sloan Digital Sky Survey Stripe 82 and deep near-infrared data from the UKIDSS Deep Extragalactic Survey in the same field. We discovered 25 new quasars at 0.5 < z < 4.5 and i < 22.5 mag within one-square-degree field. The survey significantly increases the number of faint quasars in this field, especially at z similar to 2-3. It confirms that our color selections are highly complete in a wide redshift range (z < 4.5), especially over the quasar number density peak at z similar to 2-3, even for faint quasars. Combining all previous known quasars and new discoveries, we construct a sample with 109 quasars and measure the binned QLF and parametric QLF. Although the sample is small, our results agree with a pure luminosity evolution at lower redshift and luminosity evolution and density evolution model at redshift z > 2.5.

We present a survey of the [C II] 158 mu m line and underlying far-infrared (FIR) dust continuum emission in a sample of 27 greater than or similar to 6 quasars using the Atacama Large Millimeter Array (ALMA) at similar to 1 '' resolution. The [C II] line was significantly detected (at > 5-sigma) in 23 sources (85%). We find typical line luminosities of L-[C (II]) = 10(9-10) L-circle dot, and an average line width of similar to 385 km s(-1). The [C II]-to-far-infrared luminosity ratios ([C II]/FIR) in our sources span one order of magnitude, highlighting a variety of conditions in the star-forming medium. Four quasar host galaxies are clearly resolved in their [C II] emission on a few kpc scales. Basic estimates of the dynamical masses of the host galaxies give masses between 2 x 10(10) and 2 x 10(11) M-circle dot, i.e., more than an order of magnitude below what is expected from local scaling relations, given the available limits on the masses of the central black holes (> 3 x 10(8) M-circle dot, assuming Eddington-limited accretion). In stacked ALMA [C II] spectra of individual sources in our sample, we find no evidence of a deviation from a single Gaussian profile. The quasar luminosity does not strongly correlate with either the [C II] luminosity or equivalent width. This survey (with typical on-source integration times of 8 minutes) showcases the unparalleled sensitivity of ALMA at millimeter wavelengths, and offers a unique reference sample for the study of the first massive galaxies in the universe.

We report the discovery and constrain the physical conditions of the interstellar medium of the highest-redshift millimeter-selected dusty star-forming galaxy to date, SPT-S J031132-5823.4 (hereafter SPT0311-58), at z = 6.900 +/- 0.002. SPT0311-58 was discovered via its 1.4 mm thermal dust continuum emission in the South Pole Telescope (SPT)-SZ survey. The spectroscopic redshift was determined through an Atacama Large Millimeter/submillimeter Array 3 mm frequency scan that detected CO(6-5), CO(7-6), and [C I](2-1), and subsequently was confirmed by detections of CO(3-2) with the Australia Telescope Compact Array and[C II] with APEX. We constrain the properties of the ISM in SPT0311-58 with a radiative transfer analysis of the dust continuum photometry and the CO and [C I] line emission. This allows us to determine the gas content without ad hoc assumptions about gas mass scaling factors. SPT0311-58 is extremely massive, with an intrinsic gas mass of M-gas = 3.3 +/- 1.9 x 10(11) M-circle dot. Its large mass and intense star formation is very rare for a source well into the epoch of reionization.

We present IRAM/NOEMA and JVLA observations of the quasar J1342+0928 at z = 7.54 and report detections of copious amounts of dust and [C Pi] emission in the interstellar medium (ISM) of its host galaxy. At this redshift, the age of the universe is 690 Myr, about 10% younger than the redshift of the previous quasar record holder. Yet, the ISM of this new quasar host galaxy is significantly enriched by metals, as evidenced by the detection of the [C 158 mu m cooling line and the underlying far-infrared (FIR) dust continuum emission. To the first order, the FIR properties of this quasar host are similar to those found at a slightly lower redshift (z similar to 6), making this source by far the FIR-brightest galaxy known at z greater than or similar to 7.5. The [C Pi]emission is spatially unresolved, with an upper limit on the diameter of 7 kpc. Together with the measured FWHM of the [C Pi]line, this yields a dynamical mass of the host of <1.5 x 10(11) M-circle dot Using standard assumptions about the dust temperature and emissivity, the NOEMA measurements give a dust mass of (0.6-4.3) x 10(8) M-circle dot The brightness of the [C Pi] luminosity, together with the high dust mass, imply active ongoing star formation in the quasar host. Using [C Pi]-SFR scaling relations, we derive star formation rates of 85-545 M-circle dot yr(-1) in the host, consistent with the values derived from the dust continuum. Indeed, an episode of such past high star formation is needed to explain the presence of similar to 10(8) M-circle dot of dust implied by the observations.