No abstract

In a six-year program started in July 2014, the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) will conduct novel cosmological observations using the BOSS spectrograph at Apache Point Observatory. These observations will be conducted simultaneously with the Time Domain Spectroscopic Survey (TDSS) designed for variability studies and the Spectroscopic Identification of eROSITA Sources (SPIDERS) program designed for studies of X-ray sources. In particular, eBOSS will measure with percent-level precision the distance-redshift relation with baryon acoustic oscillations (BAO) in the clustering of matter. eBOSS will use four different tracers of the underlying matter density field to vastly expand the volume covered by BOSS and map the large-scale-structures over the relatively unconstrained redshift range 0.6 < z < 2.2. Using more than 250,000 new, spectroscopically confirmed luminous red galaxies at a median redshift z = 0.72, we project that eBOSS will yield measurements of the angular diameter distance d A (z) to an accuracy of 1.2% and measurements of H(z) to 2.1% when combined with the z > 0.6 sample of BOSS galaxies. With ∼ 195, 000 new emission line galaxy redshifts, we expect BAO measurements of d A (z) to an accuracy of 3.1% and H(z) to 4.7% at an effective redshift of z = 0.87. A sample of more than 500,000 spectroscopically-confirmed quasars will provide the first BAO distance measurements over the redshift range 0.9 < z < 2.2, with expected precision of 2.8% and 4.2% on d A (z) and H(z), respectively. Finally, with 60,000 new quasars and reobservation of 60,000 BOSS quasars, we will obtain new Lyα forest measurements at redshifts z > 2.1; these new data will enhance the precision of d A (z) and H(z) at z > 2.1 by a factor of 1.44 relative to BOSS. Furthermore, eBOSS will provide improved tests of General Relativity on cosmological scales through redshift-space distortion (RSD) measurements, improved tests for non-Gaussianity in the primordial density field, and new constraints on the summed mass of all neutrino species. Here, we provide an overview of the cosmological goals, spectroscopic target sample, demonstration of spectral quality from early data, and projected cosmological constraints from eBOSS. eBOSS 3 confidence, where w is the ratio of pressure to energy density for dark energy. Thus, current observations are generally consistent with the simplest picture where dark energy is described completely by Einstein's cosmological constant (Λ).New precise observations can unravel the origin of the accelerating universe; specifically, to determine if cosmic acceleration is caused by deviations in General Relativity (GR) on large scales or by a new form of (dark) energy. It is possible to decouple scenarios of acceleration that require dark energy from those that require modifications to GR by independently probing both cosmic expansion history and the structure growth rate. Four primary observational techniques are generally accepted as the most powerful toward obtaining that goal (e.g. Albrech...

As part of the Sloan Digital Sky Survey IV the extended Baryon Oscillation Spectroscopic Survey (eBOSS ) will improve measurements of the cosmological distance scale by applying the Baryon Acoustic Oscillation (BAO) method to quasar samples. eBOSS will adopt two approaches to target quasars over 7500 deg 2 . First, a "CORE" quasar sample will combine optical selection in ugriz using a likelihood-based routine called XDQSOz, with a mid-IR-optical color-cut. eBOSS CORE selection (to g < 22 OR r < 22) should return ∼ 70 deg −2 quasars at redshifts 0.9 < z < 2.2 and ∼ 7 deg −2 z > 2.1 quasars. Second, a selection based on variability in multi-epoch imaging from the Palomar Transient Factory should recover an additional ∼ 3-4 deg −2 z > 2.1 quasars to g < 22.5. A linear model of how imaging systematics affect target density recovers the angular distribution of eBOSS CORE quasars over 96.7% (76.7%) of the SDSS North (South) Galactic Cap area. The eBOSS CORE quasar sample should thus be sufficiently dense and homogeneous over 0.9 < z < 2.2 to yield the first few-percent-level BAO constraint nearz ∼ 1.5. eBOSS quasars at z > 2.1 will be used to improve BAO measurements in the Lyman-α Forest. Beyond its key cosmological goals, eBOSS should be the next-generation quasar survey, comprising > 500,000 new quasars and > 500,000 uniformly selected spectroscopically confirmed 0.9 < z < 2.2 quasars. At the conclusion of eBOSS, the SDSS will have provided unique spectra of over 800,000 quasars.

Enormous Lyα Nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys, or have targeted known sources such as ultraluminous quasi-stellar-objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Lyα absorptions (CoSLAs), we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at z = 2 − 3 (Cai et al. 2016a). In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Lyα nebular luminosity of L nebula = 5.1 ± 0.1 × 10 44 erg s −1 . Above the 2σ surface brightness limit of SB Lyα = 4.8 × 10 −18 erg s −1 cm −2 arcsec −2 , this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended C iv λ1549 and He ii λ1640 emission on 30 kpc scales. Note that the Lyα, He ii and C iv emission all have double-peaked line profiles. Each velocity component has a full-width-half-maximum (FWHM) of ≈ 700 − 1000 km s −1 . We argue that this Lyα nebula could be powered by shocks due to an AGN-driven outflow or/and photoionization by a strongly obscured source.

We presents results from a spectroscopic survey of z ∼ 5 quasars in the CFHT Legacy Survey (CFHTLS). Using both optical color selection and a likelihood method we select 97 candidates over an area of 105 deg 2 to a limit of i AB < 23.2, and 7 candidates in the range 23.2 < i AB < 23.7 over an area of 18.5 deg 2 . Spectroscopic observations for 43 candidates were obtained with Gemini, MMT, and LBT, of which 37 are z > 4 quasars. This sample extends measurements of the quasar luminosity function ∼1.5 mag fainter than our previous work in SDSS Stripe 82. The resulting luminosity function is in good agreement with our previous results, and suggests that the faint end slope is not steep. We perform a detailed examination of our survey completeness, particularly the impact of the Lyα emission assumed in our quasar spectral models, and find hints that the observed Lyα emission from faint z ∼ 5 quasars is weaker than for z ∼ 3 quasars at a similar luminosity. Our results strongly disfavor a significant contribution of faint quasars to the hydrogen-ionizing background at z = 5.

Motivated by the recent discovery of the near-ubiquity of Lyα emission around z 3 QSOs, we performed a systematic study of QSO circumgalactic Lyα emission at z ≈ 2, utilizing the unique capability of the Keck Cosmic Web Imager (KCWI) -a new wide-field, blue sensitive integral-field spectrograph (IFU). In this paper, we present KCWI observations on a sample of 16 ultraluminous Type-I QSOs at z = 2.1 − 2.3 with ionizing luminosities of L νLL = 10 31.1−32.3 erg s −1 Hz −1 . We found that 14 out of 16 QSOs are associated with Lyα nebulae with projected linear-sizes larger than 50 physical kpc (pkpc). Among them, four nebulae have enormous Lyα emission with the Lyα surface brightness SB Lyα > 10 −17 erg s −1 cm −2 arcsec −2 on the > 100 kpc scale, extending beyond the field of view of KCWI. Our KCWI observations reveal that most z ≈ 2 QSO nebulae have a more irregular morphology compared to those at z 3. In turn, we measure that the circularlyaveraged surface brightness (SB) at z ≈ 2 is 0.4 dex fainter than the redshift-corrected, median SB at z 3. The Lyα SB profile (SB Lyα ) of QSOs at z ≈ 2 can be described by a power law of SB Lyα,z≈2.3 = 3.7 × 10 −17 × (r/40) −1.8 erg s −1 cm −2 arcsec −2 , with the slope similar to that at z 3. The observed lower redshift-corrected, circularly-averaged SB may be mainly due to the lower covering factor of cool gas clouds in massive halos at z ≈ 2.

We present a study of ∼100 high redshift (z ∼ 2−4) extremely strong damped Lyman-α systems (ESDLA, with N(H i) ≥ 0.5 × 10 22 cm −2 ) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) Data Release 11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(H i) frequency distribution has a relatively shallow slope with power-law index −3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ∼1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star-forming regions. This indicates that ESDLAs arise from a line of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Ly α emission with L ESDLA (Ly α) (0.6 ± 0.2) × 10 42 erg s −1 in the core of ESDLAs (corresponding to about 0.1 L at z ∼ 2−3), obtained through stacking the fibre spectra (of radius 1 corresponding to ∼8 kpc at z ∼ 2.5). Statistical errors on the Ly α luminosity are of the order of 0.1 × 10 42 erg s −1 but we caution that the measured Ly α luminosity may be overestimated by ∼35% due to sky light residuals and/or FUV emission from the quasar host and that we have neglected flux-calibration uncertainties. We estimate a more conservative uncertainty of 0.2 × 10 42 erg s −1 . The properties of the Ly α line (luminosity distribution, velocity width and velocity offset compared to systemic redshift) are very similar to that of the population of Lyman-α emitting galaxies (LAEs) with L LAE (Ly α) ≥ 10 41 erg s −1 detected in long-slit spectroscopy or narrow-band imaging surveys. By matching the incidence of ESDLAs with that of the LAEs population, we estimate the high column density gas radius to be about r gas = 2.5 kpc, i.e., significantly smaller than the radius corresponding to the BOSS fibre aperture, making fibre losses likely negligible. Finally, the average measured Ly α luminosity indicates a star-formation rate consistent with the Schmidt-Kennicutt law, SFR (M yr −1 ) ≈ 0.6/ f esc , where f esc < 1 is the Ly α escape fraction. Assuming the typical escape fraction of LAEs, f esc ∼ 0.3, the Schmidt-Kennicutt law implies a galaxy radius of about r gal ≈ 2.5 kpc. Finally, we note that possible overestimation of the Ly α emission would result in both smaller r gas and r gal . Our results support a close association between LAEs and stro...

We present the discovery of eight quasars at ∼ z 6 identified in the Sloan Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have some overlap with each other, leading to repeat observations over an area spanning >4000 deg 2 (more than one-fourth of the total footprint). These overlap regions provide a unique data set that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the SDSS single-epoch data. Our quasar candidates were first selected as i-band dropout objects in the SDSS imaging database. We then carried out a series of follow-up observations in the optical and near-IR to improve photometry, remove contaminants, and identify quasars. The eight quasars reported here were discovered in a pilot study utilizing the overlap regions at high galactic latitude (| | >°b 30 ). These quasars span a redshift range of < < z 5.866.06 and a flux range of < < z 19.3 20.6 AB mag. Five of them are fainter than = z 20 AB mag, the typical magnitude limit of ∼ z 6 quasars used for the SDSS single-epoch images. In addition, we recover eight previously known quasars at ∼ z 6 that are located in the overlap regions. These results validate our procedure for selecting quasar candidates from the overlap regions and confirming them with follow-up observations, and they provide guidance to a future systematic survey over all SDSS imaging regions with repeat observations.