On the Automated and Objective Detection of Emission Lines in Faint-Object Spectroscopy

Modern spectroscopic surveys produce large spectroscopic databases, generally with sizes well beyond the scope of manual investigation. The need arises, therefore, for an automated line detection method with objective indicators for detection significance. In this paper, we present an automated and objective method for emission line detection in spectroscopic surveys and apply this technique to 1574 spectra, obtained with the Hectospec spectrograph on the MMT Observatory (MMTO), to detect Lyman alpha emitters near z ~ 2.7. The basic idea is to generate on-source (signal plus noise) and off-source (noise only) mock observations using Monte Carlo simulations, and calculate completeness and reliability values, (C, R), for each simulated signal. By comparing the detections from real data with the Monte Carlo results, we assign the completeness and reliability values to each real detection. From 1574 spectra, we obtain 881 raw detections and, by removing low reliability detections, we finalize 649 detections from an automated pipeline. Most of high completeness and reliability detections, (C, R) ~ (1.0, 1.0), are robust detections when visually inspected; the low C and R detections are also marginal on visual inspection. This method at detecting faint sources is dependent on the accuracy of the sky subtraction.Comment: 19 pages, 16 figures, submitted to MNRA

Spatially Resolved Gas Kinematics within a Lyα\alpha Nebula: Evidence for Large-scale Rotation

We use spatially extended measurements of Ly$\alpha$ as well as less optically thick emission lines from an $\approx$80 kpc Ly$\alpha$ nebula at $z\approx1.67$ to assess the role of resonant scattering and to disentangle kinematic signatures from Ly$\alpha$ radiative transfer effects. We find that the Ly$\alpha$, CIV, HeII, and CIII] emission lines all tell a similar story in this system, and that the kinematics are broadly consistent with large-scale rotation. First, the observed surface brightness profiles are similar in extent in all four lines, strongly favoring a picture in which the Ly$\alpha$ photons are produced in situ instead of being resonantly scattered from a central source. Second, we see low kinematic offsets between Ly$\alpha$ and the less optically thick HeII line ($\sim$100-200 km s$^{-1}$), providing further support for the argument that the Ly$\alpha$ and other emission lines are all being produced within the spatially extended gas. Finally, the full velocity field of the system shows coherent velocity shear in all emission lines: $\approx$500 km s$^{-1}$ over the central $\approx$50 kpc of the nebula. The kinematic profiles are broadly consistent with large-scale rotation in a gas disk that is at least partially stable against collapse. These observations suggest that the Ly$\alpha$ nebula represents accreting material that is illuminated by an offset, hidden AGN or distributed star formation, and that is undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of M(<R=20 kpc)$\sim3\times10^{11}$ $M_{\odot}$, this system may represent the early formation of a large Milky Way mass galaxy or galaxy group.Comment: Accepted to ApJ; 25 pages in emulateapj format; 15 figures, 4 table

A Successful Broad-band Survey for Giant Lya Nebulae I: Survey Design and Candidate Selection

Giant Lya nebulae (or Lya "blobs") are likely sites of ongoing massive galaxy formation, but the rarity of these powerful sources has made it difficult to form a coherent picture of their properties, ionization mechanisms, and space density. Systematic narrow-band Lya nebula surveys are ongoing, but the small redshift range covered and the observational expense limit the comoving volume that can be probed by even the largest of these surveys and pose a significant problem when searching for such rare sources. We have developed a systematic search technique designed to find large Lya nebulae at 2<z<3 within deep broad-band imaging and have carried out a survey of the 9.4 square degree NOAO Deep Wide-Field Survey (NDWFS) Bootes field. With a total survey comoving volume of ~10^8 h^-3_70 Mpc^3, this is the largest volume survey for Lya nebulae ever undertaken. In this first paper in the series, we present the details of the survey design and a systematically-selected sample of 79 candidates, which includes one previously discovered Lya nebula.Comment: Accepted to ApJ after minor revision; 25 pages in emulateapj format; 18 figures, 3 table

The Stripe 82 1-2 GHz Very Large Array Snapshot Survey: Multiwavelength Counterparts

We have combined spectrosopic and photometric data from the Sloan Digital Sky Survey (SDSS) with $1.4$ GHz radio observations, conducted as part of the Stripe 82 $1-2$ GHz Snapshot Survey using the Karl G. Jansky Very Large Array (VLA), which covers $\sim100$ sq degrees, to a flux limit of 88 $\mu$Jy rms. Cross-matching the $11\,768$ radio source components with optical data via visual inspection results in a final sample of $4\,795$ cross-matched objects, of which $1\,996$ have spectroscopic redshifts and $2\,799$ objects have photometric redshifts. Three previously undiscovered Giant Radio Galaxies (GRGs) were found during the cross-matching process, which would have been missed using automated techniques. For the objects with spectroscopy we separate radio-loud Active Galactic Nuclei (AGN) and star-forming galaxies (SFGs) using three diagnostics and then further divide our radio-loud AGN into the HERG and LERG populations. A control matched sample of HERGs and LERGs, matched on stellar mass, redshift and radio luminosity, reveals that the host galaxies of LERGs are redder and more concentrated than HERGs. By combining with near-infrared data, we demonstrate that LERGs also follow a tight $K-z$ relationship. These results imply the LERG population are hosted by population of massive, passively evolving early-type galaxies. We go on to show that HERGs, LERGs, QSOs and star-forming galaxies in our sample all reside in different regions of a WISE colour-colour diagram. This cross-matched sample bridges the gap between previous `wide but shallow' and `deep but narrow' samples and will be useful for a number of future investigations.Comment: 17 pages, 19 figures. Resubmitted to MNRAS after the initial comment

Quasars in the COSMOS Field

We obtained medium-resolution spectra of 336 quasar candidates in the COSMOS HST/Treasury field using the MMT 6.5-meter telescope and the Hectospec multi-object spectrograph. Candidates were drawn from the Sloan Digital Sky Survey (SDSS) DR1 catalog using quasar flags set by the SDSS multi-color quasar target selection algorithm. In this paper we present our discovery spectra from 1.39 square degrees (69.5% of the COSMOS field) and a discussion of the selection method and yields. We confirmed 95 quasars, including at least 2 BALs; 80 of these are new quasars that do not appear in previous quasar confirmation follow-up studies. The candidates additionally included 184 compact emission-line galaxies, a third of which are likely Type 2 AGN, and 12 stars. The quasars span a range in magnitude of 18.3<g<22.5 and a range in redshift of 0.2<z<2.3. Our results are consistent with a lower limit quasar surface density from SDSS color selection of 102 per square degree down to g=22.5 over the entire COSMOS field. This work is the first step toward the eventual goal of setting up a grid of quasar absorption line probes of the 2 square degree field, and of conducting a complete census of supermassive black holes in this well-studied survey region. The total quasar count at the conclusion of this study is 139, making COSMOS one of the most densely-sampled regions of sky where a grid of quasar sightlines can be used to probe the intervening volume.Comment: Accepted for publication in ApJ; emulateapj style; 25 pages, 13 figures, 4 table