- ID:
- ivo://CDS.VizieR/J/ApJ/471/L5
- Title:
- Redshift clustering in the Hubble Deep Field
- Short Name:
- J/ApJ/471/L5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present initial results from a redshift survey carried out with the low-resolution imaging spectrograph on the 10m W. M. Keck Telescope in the Hubble Deep Field. In the redshift distribution of the 140 extragalactic objects in this sample, we find six strong peaks with velocity dispersions of ~400km/s. The areal density of objects within a particular peak, while it may be nonuniform, does not show evidence for strong central concentration. These peaks have characteristics (velocity dispersions, density enhancements, spacing, and spatial extent) similar to those seen in a comparable redshift survey in a different high Galactic latitude field (Cohen and coworkers), confirming that the structures are generic. They are probably the high-redshift counterparts of huge galaxy structures ("walls") observed locally.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/638/A27
- Title:
- Redshift database towards Shapley Supercluster
- Short Name:
- J/A+A/638/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a database and velocity catalogue towards the region of the Shapley Supercluster based on 18,129 measured velocities for 10,702 galaxies in the approximately 300 square degree area between 12:42:13.219<RA<14:16:59.210 and -38:29:35.70<Dec<-23:28:34.90. The data catalogue contains velocities from the literature found until 2015. It also includes 5,084 velocities, corresponding to 4617 galaxies, observed by us at Las Campanas and CTIO observatories and not reported individually until now. Of these, 2585 correspond to galaxies with no other previously published velocity measurement before 2015. Every galaxy in the velocity database has been identified with a galaxy extracted from the SuperCOSMOS photometric catalogues. We also provide a combined average velocity catalogue for all 10702 galaxies with measured velocities, adopting the SuperCOSMOS positions as a homogeneous base. A general magnitude cut-off at R2=18.0mag was adopted (with exceptions only for some of the new reported velocities). In general terms, we confirm the overall structure of the Shapley Supercluster, as found on earlier papers. However, the more extensive velocity data show finer structure, to be discussed in a future publication.
- ID:
- ivo://CDS.VizieR/J/AJ/130/2439
- Title:
- Redshift estimates in the SDSS DR2
- Short Name:
- J/AJ/130/2439
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have applied ClassX, an oblique decision tree classifier optimized for astronomical analysis, to the homogeneous multicolor imaging database of the Sloan Digital Sky Survey (SDSS), training the software on subsets of SDSS objects whose nature is precisely known via spectroscopy. We find that the software, using photometric data only, correctly classifies a very large fraction of the objects with existing SDSS spectra, both stellar and extragalactic. ClassX also accurately predicts the redshifts of both normal and active galaxies in SDSS. To illustrate ClassX applications in SDSS research, we (1) derive the object content of the SDSS Data Release 2 photometric catalog and (2) provide a sample catalog of resolved SDSS objects that contains a large number of candidate active galactic nucleus (AGN) galaxies (27,000), along with 63,000 candidate normal galaxies at magnitudes substantially fainter than the typical magnitudes of SDSS spectroscopic objects.
- ID:
- ivo://CDS.VizieR/J/A+A/363/517
- Title:
- Redshift from UBRI photometry method
- Short Name:
- J/A+A/363/517
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new method is developed for estimating photometric redshifts, using realistic template Spectral Energy Distributions (SEDs), extending over four decades in wavelength (i.e. from 0.05{mu}m to 1mm). The template SEDs are constructed for four different spectral types of galaxies (elliptical, spiral, irregular and starburst), satisfying the following characteristics: a) they are normalised to produce the observed colours of galaxies at z~0; b) incorporate the chemo-photometric spectral evolution of galaxies of different types, in agreement with the observations; c) allow treatment of dust contribution and its evolution with redshift, consistent with the spectral evolution models; d) include absorption and re-emission of radiation by dust and hence, realistic estimates of the far-infrared radiation; e) include correction for inter-galactic absorption by Lyman continuum and Lyman forest. Using these template SEDs, the photometric redshifts are estimated to an accuracy of {Delta}z=0.11. The simultaneous and self-consistent modelling of both the photometric and chemical evolution of galaxies and the effect of dust, makes this technique particularly useful for high redshift galaxies. The effects on the estimated photometric redshifts, due to assumptions in the evolutionary population synthesis models, are investigated and discussed. Also, the degeneracy in the predicted photometric redshifts and spectral types are examined, using a simulated galaxy catalogue.
1085. Redshift of 97 spirals
- ID:
- ivo://CDS.VizieR/J/A+A/310/353
- Title:
- Redshift of 97 spirals
- Short Name:
- J/A+A/310/353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Persistent claims have been made over the last ~15yr that extragalactic redshifts, when corrected for the Sun's motion around the Galactic centre, occur in multiples of ~24 or ~36km/s. A recent investigation by us of 40 spiral galaxies out to 1000km/s, with accurately measured redshifts, gave evidence of a periodicity ~37.2-37.7km/s. Here we extend our enquiry out to the edge of the Local Super cluster (~2600km/s), applying a simple and robust procedure to a total of 97 accurately determined redshifts. We find that, when corrected for related vectors close to recent estimates of the Sun's galactocentric motion, the redshifts of spirals are strongly periodic (P~37.6km/s). The formal confidence level of the result is extremely high, and the signal is seen independently with different radio telescopes. We also examine a further sample of 117 spirals observed with the 300-foot Green Bank telescope alone. The periodicity phenomenon appears strongest for the galaxies linked by group membership, but phase coherence probably holds over large regions of the Local Supercluster.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A53
- Title:
- Redshift reliability flags (VVDS data)
- Short Name:
- J/A+A/611/A53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Future large-scale surveys, as the ESA Euclid mission, will produce a large set of galaxy redshifts (>=10^6) that will require fully automated data-processing pipelines to analyze the data, extract crucial information and ensure that all requirements are met. A fundamental element in these pipelines is to associate to each galaxy redshift measurement a quality, or reliability, estimate. In this work, we introduce a new approach to automate the spectroscopic redshift reliability assessment based on machine learning (ML) and characteristics of the redshift probability density function. We propose to rephrase the spectroscopic redshift estimation into a Bayesian framework, in order to incorporate all sources of information and uncertainties related to the redshift estimation process and produce a redshift posterior probability density function (PDF). To automate the assessment of a reliability flag, we exploit key features in the redshift posterior PDF and machine learning algorithms.
- ID:
- ivo://CDS.VizieR/J/A+A/479/1
- Title:
- Redshifts and morphology in A3667
- Short Name:
- J/A+A/479/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The galaxy cluster A3667 was observed using the Two-degree Field (2dF) multifibre spectroscopic system on the Anglo-Australian Telescope in a program designed to examine the velocity structure in the region. Specifically, we sought evidence from the optical data for the putative cluster merger believed to be responsible for the observed radio and X-ray emission. We present 184 new redshifts in the region, of which 143 correspond to member galaxies of A3667. We find the cluster velocity distribution to be well modelled by a single Gaussian in agreement with previous results. In addition, new redshift-selected isodensity plots significantly reduce the prominence of the previously reported subgroup to the north-west of the main cluster. Instead, we find the galaxy distribution to be elongated and well mixed, with a high velocity dispersion and no significant evidence for substructure. These results are consistent with the axis of the proposed merger being close to the plane of the sky.
- ID:
- ivo://CDS.VizieR/J/A+A/492/345
- Title:
- Redshifts and SDSS photometry of A1942 galaxies
- Short Name:
- J/A+A/492/345
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a dynamical analysis of the galaxy cluster Abell 1942 based on a set of 128 velocities obtained at the European Southern Observatory. Data on individual galaxies are presented and the accuracy of the determined velocities as some properties of the cluster are discussed. We have also made use of publicly available Chandra X-ray data.
- ID:
- ivo://CDS.VizieR/J/A+A/415/9
- Title:
- Redshifts behind the Southern Milky Way
- Short Name:
- J/A+A/415/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of our efforts to unveil extragalactic large-scale structures behind the southern Milky Way, we here present redshifts for 764 galaxies in the Hydra/Antlia, Crux and Great Attractor region (266{deg}<=l<=338{deg}, |b|<=10{deg}), obtained with the Meudon-ESO Fibre Object Spectrograph (MEFOS) at the 3.6-m telescope of ESO. The observations are part of a redshift survey of partially obscured galaxies recorded in the course of a deep optical galaxy search behind the southern Milky Way (Kraan-Korteweg 2000, Cat. <J/A+AS/141/123>; Woudt & Kraan-Korteweg 2001, Cat. <J/A+A/380/441>). A total of 947 galaxies have been observed, a small percentage of the spectra (N=109, 11.5%) were contaminated by foreground stars, and 74 galaxies (7.8%) were too faint to allow a reliable redshift determination. With MEFOS we obtained spectra down to the faintest galaxies of our optical galaxy survey, and hence probe large-scale structures out to larger distances (v<=30000km/s) than our other redshift follow-ups using the 1.9-m telescope at the South African Astronomical Observatory (Kraan-Korteweg et al., 1995, Cat. <J/A+A/297/617>; Fairall et al., 1998, Cat. <J/A+AS/127/463>; Woudt et al., 1999, Cat. <J/A+A/352/39>) and the 64-m Parkes radio telescope (Kraan-Korteweg et al., 2002, Cat. <J/A+A/391/887>). The most distinct large-scale structures revealed in the southern Zone of Avoidance are discussed in context to known structures adjacent to the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/434/475
- Title:
- Redshifts for X-ray selected AGNs
- Short Name:
- J/A+A/434/475
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photometric redshift estimates for X-ray selected sources detected in the XMM/2dF survey. 5-band photometry for 193 sources has been obtained from the SDSS. We exclude 10 sources associated with Galactic stars. The tabulated data include the optical coordinate of all sources in our sample, their photometric redshift estimate, their r-band magnitude and g-r colour as well as their morphological classification (these optical parameters have been used in the discussion of our results). Spectroscopic redshifts are available only for a sub-sample of our data and are included in Table 1 together with the survey from which they have been obtained.
