- ID:
- ivo://CDS.VizieR/J/A+AS/127/463
- Title:
- Crux region redshifts
- Short Name:
- J/A+AS/127/463
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In our systematic optical galaxy search behind the southern Milky Way, 3760 (mostly unknown) galaxies with diameters D>0.2' were identified in the Crux region (287{deg}<~l<~318{deg}, |b|<~10{deg}, Woudt & Kraan-Korteweg 1998, in press). Prior to this investigation, only 65 of these galaxies had known redshifts. In order to map the galaxy distribution in redshift space we obtained spectra for 226 bright (B_J_<~18.0mag) objects with the 1.9m telescope of the South African Astronomical Observatory (SAAO). Redshifts could be determined for 209 objects, of which 173 have good signal-to-noise ratios. Of the 36 tentative redshifts, four are confirmed through independent values in the literature. The redshifts of three objects indicate them to be galactic in origin. One of these confirms a suspected Planetary Nebula. For 17 of the galaxies, no redshift could be determined due to poor signal-to-noise ratios. In addition, 26 redshifts have have been measured in the Hydra-Antlia region investigated earlier (Kraan-Korteweg et al., 1995, Cat. <J/A+A/297/617>), of which one is a tentative estimate. Two main structures crossing the Galactic Plane in the Crux region have now become clear. A narrow, nearby filament from (l, b)=(340{deg}, -25{deg}) to the Centaurus cluster can be traced. This filament runs almost parallel to the extension of the Hydra-Antlia clusters found earlier and is part of what we have earlier termed the ``Centaurus Wall'' extending in redshift-space between 0<=v<=6000km/s (Fairall & Paverd 1995, in Wide-Field Spedctroscopy and the Distant Universe, p. 121). The main outcome of this survey however, is the recognition of another massive extended structure between 4000<=v<=8000km/s. This broad structure, dubbed the Norma Supercluster (Woudt et al. 1997, in press), runs nearly parallel to the Galactic Plane from Vela to ACO 3627 (its centre) from where it continues to the Pavo cluster. This massive structure is believed to be associated with the Great Attractor. The survey has furthermore revealed a set of cellular structures, similar to those seen in redshift space at higher galactic latitudes, but never before seen so clearly behind the Milky Way.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/375/1349
- Title:
- 6C** sample of steep-spectrum radio sources. II
- Short Name:
- J/MNRAS/375/1349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the 6C** sample to investigate the comoving space density of powerful, steep-spectrum radio sources. This sample, consisting of 68 objects, has virtually complete K-band photometry and spectroscopic redshifts for 32 per cent of the sources. In order to find its complete redshift distribution, we develop a method of redshift estimation based on the Kz diagram of the 3CRR, 6CE, 6C* and 7CRS radio galaxies. Based on this method, we derive redshift probability density functions for all the optically identified sources in the 6C** sample. Using a combination of spectroscopic and estimated redshifts, we select the most radio luminous sources in the sample. Their redshift distribution is then compared with the predictions of the radio luminosity function of Jarvis et al. (2001MNRAS.327..907J). We find that, within the uncertainties associated with the estimation method, the data are consistent with a constant comoving space density of steep-spectrum radio sources beyond z>2.5, and rule out a steep decline.
- ID:
- ivo://CDS.VizieR/J/MNRAS/458/3786
- Title:
- CSS and GPS radio sources sample
- Short Name:
- J/MNRAS/458/3786
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The dependence of the turnover frequency on the linear size is presented for a sample of Giga-hertz Peaked Spectrum and Compact Steep Spectrum radio sources derived from complete samples. The dependence of the luminosity of the emission at the peak frequency with the linear size and the peak frequency is also presented for the galaxies in the sample. The luminosity of the smaller sources evolve strongly with the linear size. Optical depth effects have been included to the 3D model for the radio source of Kaiser to study the spectral turnover. Using this model, the observed trend can be explained by synchrotron self-absorption. The observed trend in the peak-frequency-linear-size plane is not affected by the luminosity evolution of the sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/392/998
- Title:
- Damped Lyman{alpha} systems
- Short Name:
- J/MNRAS/392/998
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a sample of 21 damped Lyman alpha systems (DLAs) and 35 sub-DLAs, we evaluate the D-index=[EW({AA})/{Delta}v(km/s)]x1000 from high-resolution spectra of the MgII {lambda}2796 profile. This sample represents an increase in the sub-DLA statistics by a factor of 4 over the original D-index sample. We investigate various techniques to define the velocity spread ({Delta}v) of the MgII line to determine an optimal D-index for the identification of DLAs. The success rate of DLA identification is 50-55 per cent, depending on the velocity limits used, improving by a few per cent when the column density of FeII is included in the D-index calculation. We recommend the set of parameters that are judged to be most robust, have a combination of high DLA identification rate (57 per cent) and low DLA miss rate (6 per cent) and most cleanly separate the DLAs and sub-DLAs (Kolmogorov-Smirnov probability 0.5 per cent). These statistics demonstrate that the D-index is the most efficient technique for selecting low-redshift DLA candidates.
- ID:
- ivo://CDS.VizieR/J/MNRAS/371/221
- Title:
- Deep Chandra survey of the Groth Strip. II.
- Short Name:
- J/MNRAS/371/221
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we discuss the optical and X-ray spectral properties of the sources detected in a single 200-ks Chandra pointing in the Groth-Westphal Strip region. A wealth of optical photometric and spectroscopic data are available in this field providing optical identifications and redshift determinations for the X-ray population. The optical photometry and spectroscopy used here are primarily from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey with additional redshifts obtained from the literature. These are complemented with the deeper (r>>26mag) multiwaveband data (ugriz) from the Canada-France-Hawaii Telescope Legacy Survey to estimate photometric redshifts and to optically identify sources fainter than the DEEP2 magnitude limit (R_AB_>>24.5mag). We focus our study on the 2-10keV selected sample comprising 97 sources to the limit 8x10^-16^erg/s/cm^2^, this being the most complete in terms of optical identification rate (86 per cent) and redshift determination fraction (63 per cent; both spectroscopic and photometric).
- ID:
- ivo://CDS.VizieR/III/268
- Title:
- DEEP2 Redshift Survey, Data Release 4
- Short Name:
- III/268
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper describes a new catalog that supplements the existing DEEP2 Galaxy Redshift Survey photometric and spectroscopic catalogs with ugriz photometry from two other surveys: the Canada-France-Hawaii Legacy Survey (CFHTLS) and the Sloan Digital Sky Survey (SDSS). Each catalog is cross-matched by position on the sky in order to assign ugriz photometry to objects in the DEEP2 catalogs. We have recalibrated the CFHTLS photometry where it overlaps DEEP2 in order to provide a more uniform data set. We have also used this improved photometry to predict DEEP2 BRI photometry in regions where only poorer measurements were available previously. In addition, we have included improved astrometry tied to SDSS rather than USNO-A2.0 for all DEEP2 objects. In total this catalog contains ~27, 000 objects with full ugriz photometry as well as robust spectroscopic redshift measurements, 64% of which have r > 23. By combining the secure and accurate redshifts of the DEEP2 Galaxy Redshift Survey with ugriz photometry, we have created a catalog that can be used as an excellent testbed for future photo-z studies, including tests of algorithms for surveys such as LSST and DES.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/1850
- Title:
- Detecting damped Ly{alpha} absorbers
- Short Name:
- J/MNRAS/472/1850
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop an automated technique for detecting damped Ly{alpha} absorbers (DLAs) along spectroscopic lines of sight to quasi-stellar objects (QSOs or quasars). The detection of DLAs in large-scale spectroscopic surveys such as SDSS III sheds light on galaxy formation at high redshift, showing the nucleation of galaxies from diffuse gas. We use nearly 50000 QSO spectra to learn a novel tailored Gaussian process model for quasar emission spectra, which we apply to the DLA detection problem via Bayesian model selection. We propose models for identifying an arbitrary number of DLAs along a given line of sight. We demonstrate our method's effectiveness using a large-scale validation experiment, with excellent performance. We also provide a catalogue of our results applied to 162858 spectra from SDSS-III data release 12.
- ID:
- ivo://CDS.VizieR/VII/249
- Title:
- 6dF-DR2 Galaxy Survey
- Short Name:
- VII/249
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 6dF Galaxy Survey is measuring around 150000 redshifts and 15000 peculiar velocities from galaxies over the southern sky at |b|>10{deg}. When complete, it will be the largest survey of its kind by more than an order of magnitude. A total of 83014 sources now have their spectra, redshifts, and near-infrared and optical photometry available online and searchable through an Structured Query Language at www.wfau.roe.ac.uk/6dFGS/ .
- ID:
- ivo://CDS.VizieR/J/MNRAS/329/87
- Title:
- 2dF Galaxy Redshift Survey: galaxy clusters
- Short Name:
- J/MNRAS/329/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS, Cat. <VII/226>) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information is used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10 per cent, whereas the APM catalogue suffers only 5 per cent contamination. If we use the original catalogue centroids, the level of contamination rises to approximately 15 per cent for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at z~0.05 hat may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive a space density of {sigma}>1000km/s clusters of 3.6x10^-6^h^3^/Mpc^3^. This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum.
- ID:
- ivo://CDS.VizieR/J/MNRAS/329/227
- Title:
- 2dF Galaxy Redshift Survey. II.
- Short Name:
- J/MNRAS/329/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have cross-matched the 1.4-GHz NRAO VLA Sky Survey (NVSS, Condon 1998, Cat. <VIII/65>) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS, Colless, 2001, Cat. <VII/226>), covering an effective area of 325{deg}^2^ (about 20 per cent of the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio identifications - the largest and most homogeneous set of radio source spectra ever obtained. The 2dFGRS radio sources span the redshift range z=0.005 to 0.438, and are a mixture of active galaxies (60 per cent) and star-forming galaxies (40 per cent). About 25 per cent of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1 Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We make a new determination of the local radio luminosity function at 1.4 GHz for both active and star-forming galaxies, and derive a local star formation density of 0.022+/-0.004M_{sun}_/yr/Mpc^3^ (H_0_=50km/s/Mpc)
