An Extremely Luminous Galaxy at [CLC][ITAL]z[/ITAL][/CLC] = 5.74

We report the results of a wide-field narrowband survey for redshift z ∼ 5.7 Lyα emitters carried out with the 34' × 27' field-of-view SuprimeCam mosaic CCD camera on the Subaru 8.3 m telescope. Deep narrowband imaging of the SSA22 field through a 120 Å bandpass filter centered at a nominal wavelength of 8150 Å was combined with deep multicolor RIz' broadband imaging with SuprimeCam, then supplemented with BVRZ imaging taken with the 42' × 28' field-of-view CFH12K camera on the Canada-France-Hawaii 3.6 m telescope to select high-redshift galaxy candidates. Spectroscopic observations were made using the new wide-field multiobject DEIMOS spectrograph on the 10 m Keck II telescope for 22 of the 26 candidate objects. Eighteen of these objects were identified as z ∼ 5.7 Lyα emitters, and a further nineteenth object from the candidate list was identified based on an LRIS spectrum. At the 3.3 Å resolution of the DEIMOS observations the asymmetric profile for Lyα emission with its steep blue falloff can be clearly seen in the spectra of the identified galaxies. This is by far the largest spectroscopic sample of galaxies at these redshifts, and we use it to describe the distribution of equivalent widths and continuum color break properties for identified Lyα galaxies compared with the foreground population. The large majority (at least 75%) of the lines have rest-frame Lyα equivalent widths substantially less than 240 Å and can be understood in terms of young star-forming galaxies with a Salpeter initial mass function for the stars. With the narrowband selection criteria of I-N > 0.7 and N < 25.05 (AB magnitudes) we find a surface density of Lyα emitters of 0.03 arcmin-2 in the filter bandpass (Δz = 0.1) down to a limiting flux of just under 2 × 10-17 ergs cm-2 s-1. The luminosity function of the Lyα emitters is similar to that at lower redshifts to the lowest measurable luminosity of 1043 ergs s-1 as is the universal star formation rate based on their continuum properties. However, we note that the objects are highly structured in both their spatial and spectral properties on the angular scale of the fields (≈60 Mpc), and that multiple fields will have to be averaged to accurately measure their ensemble properties.

Observations of high-redshift galaxies in the emitted-wavelength regime around Lyα have renewed interest in the appearance of normal galaxies in the deep ultraviolet. This paper presents an analysis of spectrophotometry of the local Sc galaxy Messier 33 (NGC 598) obtained by Voyager 2, covering the range from below the Lyman limit to about 1250 A. The scanning nature of the observation preserves one dimension of spatial resolution across the galaxy. M33 exhibits net Lyα emission at equivalent width ≈ 100 A and observed flux 1.8 ± 0.4 × 10-9 ergs cm-2 s-1. The line emission is broadly concentrated toward the center, but there is no peak coincident with the giant H II region NGC 604. This may suggest that Lyα photons from spirals escape preferentially from the diffuse interstellar medium rather than from individual luminous H II regions. The global Lyα/Hα ratio is at least 3. We must see Lyα at the radial velocity range of M33 through substantial structure in the foreground H I of the Milky Way, since applying the mean column density averaged over large scales would give negligible transmission. Therefore, the actual Lyα intensity must be larger than measured. The continuum shows the Lyβ/O VI/C II λ 1030 and Lyγ/C III λ 980 complexes in absorption and a decline in flux toward the Lyman limit. The dominant sources of radiation between 912 and 1216 A are B stars, which is not surprising, since this is where their output peaks. The global spectrum declines only slightly in Fλ from 1500 to 1000 A then declines sharply toward the Lyman limit. The intrinsic stellar spectrum must rise again shortward of the Lyman limit in order to match the intensity of recombination lines such as Hα. The spectrum is very well fitted by a weighted sum of B-star reference spectra, which would correspond to a current main-sequence mass function of N(M) ∝ M-4.7±0.3, although the important role of evolved B stars means that this fit does not necessarily correspond to the actual mass distribution. The stellar population in NGC 604 has bluer deep-UV colors than the rest of the galaxy, and the continuum in the Voyager passband follows the trend of flatter gradients for shorter wavelengths found from UV Imaging Telescope imagery. The continuum shape is a close match for that shown in Hopkins Ultraviolet Telescope observations of two starburst systems, as is expected from the short lifetimes of stars responsible for the deep-UV radiation. A simple comparison of the continuum and line properties of M33 with those of star-forming galaxies at high redshifts indicates that it is both fainter and much larger than the objects we can now detect in the early universe, pointing out how strongly our sample is (and will remain for some time) biased in favor of objects that are both compact and have absolutely high star formation rates. However, the detection of Lyα in M33, with nontrivial metallicity, bolsters the argument that many of the objects with such emission at high redshift are star-forming galaxies rather than those powered by active nuclei. The starburst system Mrk 357 at z = 0.053 has significant Lyα as well, from an archival IUE observation, providing a further example of such emission from star-forming systems. Tabulated properties are shown for nearby B stars observed with the UV Spectrometer systems on Voyagers 1 and 2 used here as reference objects for crude spectral synthesis.

We describe narrowband and spectroscopic searches for emission-line star-forming galaxies in the redshift range 3-6 with the 10 m Keck II Telescope. These searches yield a substantial population of objects with only a single strong (EW 100 A) emission line, lying in the 4000-8500 A range. Spectra of the objects found in narrowband-selected samples at λ~5390 and ~6741 A show that these very high equivalent width emission lines are generally redshifted Lyα 1216 A at z~3.4 and 4.5. The density of these emitters above the 5 σ detection limit of 1.5×10−17 ergs cm-2 s-1 is roughly 15,000 deg-2 per unit z at both z~3.4 and 4.5. A complementary deeper (1 σ~10−18 ergs cm-2 s-1) slit spectroscopic search covering a wide redshift range but a more limited spatial area (200 arcsec2) shows that such objects can be found over the redshift range z=3-6, with the currently highest redshift detected being at z=5.64. The Lyα flux distribution can be used to estimate a minimum star formation rate in the absence of reddening of roughly 0.01 M☉ Mpc-3 yr-1 (H0=65 km s-1 Mpc-1, q0=0.5). Corrections for reddening are likely to be no larger than a factor of 2, since observed equivalent widths are close to the maximum values obtainable from ionization by a massive star population. Within the still significant uncertainties, the star formation rate from the Lyα-selected sample is comparable to that of the color-break-selected samples at z~3 but may represent an increasing fraction of the total rates at higher redshifts. This higher z population can be readily studied with large ground-based telescopes.

We report on a new survey for z ≈ 4.5 Lyα sources, the Large-Area Lyman Alpha (LALA) survey. Our survey achieves an unprecedented combination of volume and sensitivity by using narrowband filters on the new 81922 pixel CCD Mosaic camera at the 4 m Mayall telescope of Kitt Peak National Observatory. Well-detected sources with flux and equivalent width matching previously known high-redshift Lyα galaxies (i.e., observed equivalent width EW > 80 Å; 2.6 × 10-17 ergs cm-2 s-1 < line + continuum flux < 5.2 × 10-17 ergs cm-2 s-1, and a small uncertainty on the equivalent width, δEW < EW/4) have an observed surface density corresponding to 11,000 ± 700 deg-2 per unit redshift at z = 4.5. Variations in this surface density are apparent on comparison between counts in 6561 ± 40 and 6730 ± 40 Å filters. Early spectroscopic followup results from the Keck telescope included three sources meeting our criteria for good Lyα candidates. Of these, one is confirmed as a z = 4.52 source, another remains consistent with either z = 4.55 or z = 0.81, and the third is an [O III] λ5007 emitter at z = 0.34. These pilot spectroscopic results suggest that approximately one-third of our good candidates are bona fide Lyα emitters, implying a net density of ~4000 Lyα emitters per square degree per unit redshift.

We have used both the Low-Resolution Imaging Spectrograph and the High Resolution Echelle Spectrograph on the Keck telescopes to obtain spectra of 12 candidate members of the Hyades identified by Leggett & Hawkins. All of the objects are chromospherically active, late-type M dwarfs, with Hα equivalent widths varying from 1 to 30 A. Based on our measured radial velocities, the level of stellar activity, and other spectroscopic features, only one of the 12 stars has properties consistent with cluster membership. We consider how this result affects estimates of the luminosity and mass function of the Hyades. Five of the 11 field stars have weak K I λλ7665, 7699 and CaH absorption as compared with M dwarf standards of the same spectral type, suggesting a lower surface gravity. Two of these sources, LH 0416+14 and LH 0419+15, exhibit significant lithium 6708 A absorption. Based partly on parallax measurements by the US Naval Observatory (Harris et al.), we identify all five as likely to be young, pre–main-sequence objects in or near the Taurus-Auriga association at distances of between 150 and 250 pc. A comparison with theoretical models of pre–main-sequence stars indicates masses of less than 0.05 M⊙.

Most of the matter in the universe consists of hydrogen. The hydrogen in the intergalactic medium (IGM), the matter between the galaxies, underwent a change of its ionisation state at the epoch of reionisation, at a redshift roughly between 6>z>10, or ~10^8 years after the Big Bang. At this time, the mostly neutral hydrogen in the IGM was ionised but the source of the responsible hydrogen ionising emission remains unclear. In this thesis I discuss the most likely candidates for the emission of this ionising radiation, which are a type of galaxy called Lyman alpha emitters (LAEs). As implied by their name, they emit Lyman alpha radiation, produced after a hydrogen atom has been ionised and recombines with a free electron. The ionising radiation itself (also called Lyman continuum emission) which is needed for this process inside the LAEs could also be responsible for ionising the IGM around those galaxies at the epoch of reionisation, given that enough Lyman continuum escapes. Through this mechanism, Lyman alpha and Lyman continuum radiation are closely linked and are both studied to better understand the properties of high redshift galaxies and the reionisation state of the universe. Before I can analyse their Lyman alpha emission lines and the escape of Lyman continuum emission from them, the first step is the detection and correct classification of LAEs in integral field spectroscopic data, specifically taken with the Multi-Unit Spectroscopic Explorer (MUSE). After detecting emission line objects in the MUSE data, the task of classifying them and determining their redshift is performed with the graphical user interface QtClassify, which I developed during the work on this thesis. It uses the strength of the combination of spectroscopic and photometric information that integral field spectroscopy offers to enable the user to quickly identify the nature of the detected emission lines. The reliable classification of LAEs and determination of their redshifts is a crucial first step towards an analysis of their properties. Through radiative transfer processes, the properties of the neutral hydrogen clouds in and around LAEs are imprinted on the shape of the Lyman alpha line. Thus after identifying the LAEs in the MUSE data, I analyse the properties of the Lyman alpha emission line, such as the equivalent width (EW) distribution, the asymmetry and width of the line as well as the double peak fraction. I challenge the common method of displaying EW distributions as histograms without taking the limits of the survey into account and construct a more independent EW distribution function that better reflects the properties of the underlying population of galaxies. I illustrate this by comparing the fraction of high EW objects between the two surveys MUSE-Wide and MUSE-Deep, both consisting of MUSE pointings (each with the size of one square arcminute) of different depths. In the 60 MUSE-Wide fields of one hour exposure time I find a fraction of objects with extreme EWs above EW_0>240A of ~20%, while in the MUSE-Deep fields (9 fields with an exposure time of 10 hours and one with an exposure time of 31 hours) I find a fraction of only ~1%, which is due to the differences in the limiting line flux of the surveys. The highest EW I measure is EW_0 = 600.63 +- 110A, which hints at an unusual underlying stellar population, possibly with a very low metallicity. With the knowledge of the redshifts and positions of the LAEs detected in the MUSE-Wide survey, I also look for Lyman continuum emission coming from these galaxies and analyse the connection between Lyman continuum emission and Lyman alpha emission. I use ancillary Hubble Space Telescope (HST) broadband photometry in the bands that contain the Lyman continuum and find six Lyman continuum leaker candidates. To test whether the Lyman continuum emission of LAEs is coming only from those individual objects or the whole population, I select LAEs that are most promising for the detection of Lyman continuum emission, based on their rest-frame UV continuum and Lyman alpha line shape properties. After this selection, I stack the broadband data of the resulting sample and detect a signal in Lyman continuum with a significance of S/N = 5.5, pointing towards a Lyman continuum escape fraction of ~80%. If the signal is reliable, it strongly favours LAEs as the providers of the hydrogen ionising emission at the epoch of reionisation and beyond.

A mosaic of two 2k x 4k fully depleted, high resistivity CCD detectors was installed in the red channel of the Low Resolution Imaging Spectrograph for the Keck-I Telescope in June, 2009 replacing a monolithic Tektronix/SITe 2k x 2k CCD. These CCDs were fabricated at Lawrence Berkeley National Laboratory (LBNL) and packaged and characterized by UCO/Lick Observatory. Major goals of the detector upgrade were increased throughput and reduced interference fringing at wavelengths beyond 800 nm, as well as improvements in the maintainability and serviceability of the instrument. We report on the main features of the design, the results of optimizing detector performance during integration and testing, as well as the throughput, sensitivity and performance of the instrument as characterized during commissioning.

(abridged) Steidel & Sargent (1991a) found that the spectra of the components of the close quasar pairs Q1634+267A,B and Q2345+007A,B were in each case remarkably similar but that individual broad emission lines due to Ly_alpha, Si IV, C IV, and C III] exhibited differences in profile or equivalent width between the A and B components. If the A and B components of these objects result from gravitational lensing of a single QSO, the difference in light travel time for the two images is roughly 1 year for both pairs. Accordingly, the authors suggested that observations of the spectra of single QSOs would reveal similar changes in emission line profiles and equivalent widths on a time scale of a year or less. In order to test Steidel & Sargent's hypothesis, we obtained in 1992 high quality spectra of 30 quasars with z(em) ~ 1 selected from the brighter QSOs in the sample of Steidel & Sargent (1991b), which those authors had observed in 1989-90. We find that the spectra from the two epochs are remarkably similar for all QSOs, except for overall changes in fluxes and minor differences in continuum shape which are probably artifacts introduced by the observing procedures. However, there are also changes in the equivalent widths or shapes of the stronger emission lines on rest-frame time scales of 1-1.5 years in about two thirds of the QSOs. These observations, therefore, support the notion that the spectra of the components in lensed QSOs need not be exactly identical. Moreover, it should be expected that any differences between the components in such systems should change with time.

We have performed narrowband imaging of NGC 4631 in the [O III] 5007 and Hα lines, and long-slit spectroscopy using the Low-Resolution Imaging Spectrograph at the W. M. Keck Observatory. Hα and [O III] λ5007 are detected far from the disk, with the highest [O III]/Hα ratios coincident with the soft X-ray emission. Spectroscopy reveals that the ionization is higher than that of the Milky Way diffuse ionized gas (DIG), with an average ratio [O III]/Hβ ~ 1, rising to 6 in one region. We use the Balmer decrement to probe extinction in the halo. Extinction appears as high as 5 kpc above the disk. Distinct smaller scale variations of [O III], Hβ, and [S II] indicate that we are viewing multiple zones with distinct ionization conditions along the line of sight, in some cases separated by dust. This suggests that the gas has multiple phases and that the ionization may be much higher in some zones. A model using photoionized clouds reproduces the average trends in the line ratios. The inferred densities and pressures are high for halo gas but consistent with observations of other phases that may be colocated with this gas. A combination of high- and low-ionization gas is best for explaining the majority of the fluctuations. The high-ionization phase could be in shocks, but the velocity resolution is not adequate to prove or reject this possibility. Gas at 6 × 105 K discovered by ROSAT by Wang and colleagues in 1995 could be a source of radiatively cooling gas. We present a new model of optical line emission from cooling clouds and compare it to the data. We show that it can produce part or all of the observed [O III] and fluctuations, may generate part or all of the EDIG gas itself, and may contribute to the photoionization of the upper halo. Our most important conclusions are that the halo is complex and multicomponent and that average line-of-sight line ratios alone cannot be used to determine the ionization conditions.

We use a spectroscopic sample of 286 star-forming galaxies (SFGs) at 1<z<3 from the GMASS survey to study different star formation rate (SFR) estimators. Infrared (IR) data are used to derive empirical calibrations to correct ultraviolet (UV) and [OII]{\lambda}3727 luminosities for dust extinction and dust-corrected estimates of SFR. In the selection procedure we fully exploit the available spectroscopic information. On the basis of three continuum indices, we are able to identify and exclude from the sample galaxies in which old stellar populations might bring a non-negligible contribution to IR luminosity (LIR) and continuum reddening. Using Spitzer-MIPS and Herschel-PACS data we derive LIR for two-thirds of our sample. The LIR/LUV ratio is used as a probe of effective attenuation (AIRX) to search for correlations with continuum and spectroscopic features. The relation between AIRX and UV continuum slope ({\beta}) was tested for our sample and found to be broadly consistent with the literature results at the same redshift, though with a larger dispersion with respect to UV-selected samples. We find a correlation between the rest-frame equivalent width (EW) of the [OII]{\lambda}3727 line and {\beta}, which is the main result of this work. We therefore propose the [OII]{\lambda}3727 line EW as a dust attenuation probe and calibrate it through AIRX, though the assumption of a reddening curve is still needed to derive the actual attenuation towards the [OII]{\lambda}3727 line. We tested the issue of differential attenuation towards stellar continuum and nebular emission: our results are in line with the traditional prescription of extra attenuation towards nebular lines. A set of relations is provided that allows the recovery of the total unattenuated SFR from UV and [OII]{\lambda}3727 luminosities. (Abridged)

We have used the Low Resolution Imaging Spectrograph on the W. M. Keck I telescope to obtain spatially resolved spectroscopy of a small sample of six ‘post-starburst’ and three ‘dusty-starburst’ galaxies in the rich cluster CL 0016+16 at z=0.55. We use this to measure radial profiles of the Hδ and [OII]λ3727 lines which are diagnostic probes of the mechanisms that give rise to the abrupt changes in star formation rates in these galaxies. In the post-starburst sample we are unable to detect any radial gradients in the Hδ line equivalent width — although one galaxy exhibits a gradient from one side of the galaxy to the other. The absence of Hδ gradients in these galaxies is consistent with their production via interaction with the intracluster medium; however, our limited spatial sampling prevents us from drawing robust conclusions. All members of the sample have early-type morphologies, typical of post-starburst galaxies in general, but lack the high incidence of tidal tails and disturbances seen in local field samples. This argues against a merger origin and adds weight to a scenario where truncation by the intra-cluster medium is at work. The post-starburst spectral signature is consistent over the radial extent probed with no evidence of [OII]λ3727 emission and strong Hδ absorption at all radii, i.e. the post-starburst classification is not an aperture effect. In contrast the ‘dusty-starburst’ sample shows a tendency for a central concentration of [OII]λ3727 emission. This is most straightforwardly interpreted as the consequence of a central starburst. However, other possibilities exist such as a non-uniform dust distribution (which is expected in such galaxies) and/or a non-uniform starburst age distribution. The members of the sample exhibit late-type and irregular morphologies.

ABSTRACTEmission-line galaxies are important targets for understanding the chemical evolution of galaxies in the universe. Deep, narrowband imaging surveys allow detection and study of the flux and the equivalent widths (EWs) of the emission line studied. The present work has been developed within the context of the OTELO project, an emission-line survey using the tunable filters (TF) of OSIRIS, the first-generation instrument on the Gran Telescopio Canarias (GTC) 10.4 m telescope located in La Palma, Spain, that will observe through selected atmospheric windows that are relatively free of sky emission lines. With a total survey area of0.1 deg2 distributed in different fields, reaching a 5σ depth of 10-18 ergs cm-2 s-1 and detecting objects of EW < 0.3 Å, OTELO will be the deepest emission-line survey to date. As part of the OTELO preparatory activities, the objective of this study is to determine the best combination of sampling and full width at half-maximum (FWHM) for the OSIRIS tunable filters for deblending Hα from [N II] lines by analyzing the flux errors obtained. We simulated the OTELO data by convolving a complete set of synthetic H II galaxies in EWs, with different widths of the OSIRIS TFs. We estimated relative flux errors of the recovered Hα and [N II] λ6583 lines. We found that for the red TF, a FWHM of 12 Å and a sampling of 5 Å is an optimal combination that allows deblending Hα from the [N II] λ6583 line with a flux error lower than 20%. This combination will allow estimating SFRs and metallicities using the Hα flux and the N2 method, respectively.

We present the optical spectra of four newly discovered gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS). These observations were carried out using the Low-Resolution Imaging Spectrograph on the W. M. Keck-I Telescope as part of a programme to study galaxy-scale gravitational lenses. From our spectra, we found the redshift of the background source in CLASS B0128+437 (z s = 3.1240 ± 0.0042) and the lensing galaxy redshifts in CLASS B0445+123 (z 1 = 0.5583 ± 0.0003) and CLASS B0850+054 (z 1 = 0.5883 ± 0.0006). Intriguingly, we also discovered that CLASS B0631+519 may have two lensing galaxies (z 1,1 = 0.0896 ± 0.0001, z 1,2 = 0.6196 ± 0.0004). We also found a single unidentified emission line from the lensing galaxy in CLASS B0128+437 and the lensed source in CLASS B0850+054. We find the lensing galaxies in CLASS B0445+123 and CLASS B0631+519 (1, 2) to be early-type galaxies with Einstein radii of 2.8-3.0 h -1 kpc. The deflector in CLASS B0850+054 is a late-type galaxy with an Einstein radius of 1.6 h -1 kpc.

Investigation of Variations in Double-Peaked Broad Emission Lines of Radio Quasar B3 1637+436A

We define a large sample of galaxies for use in a study of the fundamental plane in the intermediate redshift cluster Cl 1358+62 at z = 0.33. We have analyzed high-resolution spectra for 55 members of the cluster. The data were acquired with the Low-Resolution Imaging Spectrograph on the Keck I 10 m telescope. A new algorithm for measuring velocity dispersions is presented and used to measure the internal kinematics of the galaxies. This algorithm has been tested against the Fourier fitting method so that the data presented here can be compared with those measured previously in nearby galaxies. We have measured central velocity dispersions suitable for use in a fundamental plane analysis. The data have a high signal-to-noise ratio (S/N) and the resulting random errors on the dispersions are very low, typically less that 5%. Uncertainties due to mismatch of the stellar templates have been minimized through several tests, and the total systematic error is of order ~5%. Good seeing enabled us to measure velocity dispersion profiles and rotation curves for most of the sample, and although a large fraction of the galaxies display a high level of rotation, the gradients of the total second moment of the kinematics are all very regular and similar to those in nearby galaxies. We conclude that the data therefore can be reliably corrected for aperture size in a manner consistent with nearby galaxy samples.