- ID:
- ivo://CDS.VizieR/J/A+A/633/A154
- Title:
- HDBSCAN star, galaxy, QSO classification
- Short Name:
- J/A+A/633/A154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classification will be an important first step for upcoming surveys that will detect billions of new sources such as LSST and Euclid, as well as DESI, 4MOST and MOONS. The application of traditional methods of model fitting and colour-colour selections will face significant computational constraints, while machine-learning (ML) methods offer a viable approach to tackle datasets of that volume. While supervised learning methods can perform very well for classification tasks, the creation of representative and accurate training sets is a resource and time consuming task. We present a viable alternative using an unsupervised ML method to separate stars, galaxies and QSOs using photometric data. The heart of our work uses HDBSCAN to find the star, galaxy and QSO clusters in a multidimensional colour space. We optimized the hyperparameters and input attributes of three separate HDBSCAN runs, each to select a particular object class, and thus treat the output of each separate run as a binary classifier. We subsequently consolidate the output to give our final classifications, optimized on their F1 scores. We explore the use of Random Forest and PCA as part of the pre-processing stage for feature selection and dimensionality reduction. Using our dataset of ~50000 spectroscopically labelled objects we obtain an F1 score of 98.9, 98.9 and 93.13 respectively for star, galaxy and QSO selection using our unsupervised learning method. We find that careful attribute selection is a vital part of accurate classification with HDBSCAN. We applied our classification to a subset of the SDSS spectroscopic catalogue and demonstrate the potential of our approach in correcting misclassified spectra useful for DESI and 4MOST. Finally, we create a multiwavelength catalogue of 2.7 million sources using the KiDS, VIKING and ALLWISE surveys and publish corresponding classifications and photometric redshifts.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/481/673
- Title:
- HDF flanking fields and related data
- Short Name:
- J/ApJ/481/673
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- File flanking.dat contains Unpublished Catalogue of Galaxies identified by the DEEP Team in the Flanking Fields. This is the source catalogue that Vogt et al. (1997ApJ...479L.121V), Phillips et al. (1997ApJ...489..543P), Guzman et al. (1997ApJ...489..559G), and Mendez & Guzman (1998A&A...333..106M) used to select objects. The photometry in this catalogue was carried out using circular apertures of 3 arcsec diameter, as described by Phillips et al. (1997ApJ...489..543P). These will present small differences (~0.12mag, rms) relative to published values for the sample of 51 compact galaxies that were analysed by Phillips et al. (1997ApJ...489..543P) and Guzman et al. (1997ApJ...489..559G). This is because for the papers, the I(814) magnitudes were recalculated using elliptical apertures to 8 arcsec. The differences should only be significant in the case of galaxies with larger apparent sizes or with elongated shapes.
- ID:
- ivo://CDS.VizieR/J/ApJ/538/29
- Title:
- HDF-N Caltech faint galaxy redshift survey. X.
- Short Name:
- J/ApJ/538/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A redshift survey has been carried out in the region of the Hubble Deep Field North using the Low Resolution Imaging Spectrograph (LRIS) at the Keck Observatory. The resulting redshift catalog, which contains 671 entries, is a compendium of our own data together with published LRIS/Keck data.
- ID:
- ivo://CDS.VizieR/J/MNRAS/358/149
- Title:
- HDFN SCUBA Super-map. III
- Short Name:
- J/MNRAS/358/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new submillimetre (submm) super-map in the Hubble Deep Field North (HDF-N) region (Great Observatories Origins Deep Survey North, GOODS-N, field), containing 40 statistically robust sources at 850um. This map contains additional data, and several new sources, including one of the brightest blank-sky extragalactic submm sources ever detected. We have used the Advanced Camera for Surveys (ACS) Hubble Space Telescope (HST) images and ground-based near-infrared (IR) observations from the Great Observatories Origins Deep Survey (GOODS), along with deep radio observations, to develop a systematic approach for counterpart identification. With the depth achieved by this survey, optical counterparts have been found for all the radio-detected (RD) submm sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/172
- Title:
- HeCS-red: Hectospec surveys of redMaPPer clusters
- Short Name:
- J/ApJ/862/172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use dense redshift surveys to explore the properties of galaxy clusters selected from the redMaPPer catalog. Our new survey, Hectospec Cluster Survey of red-sequence-selected clusters (HeCS-red), includes 10589 new or remeasured redshifts from MMT/Hectospec observations of 27 redMaPPer clusters at redshifts z=0.08-0.25 with large estimated richnesses (richness estimate {lambda}>64). Our spectra confirm that each candidate cluster corresponds to a large overdensity in redshift space. The redMaPPer photometric redshifts have a slight bias toward higher redshifts. We measure the relation between velocity dispersion {sigma}p and {lambda}. The relation shows intrinsic scatter of 24% (and a range of 2x) in velocity dispersion at fixed richness. We extend our analysis to HeCS-red-ext, a sample that includes several clusters selected by X-ray flux or Sunyaev-Zeldovich signal. The heterogeneous sample of 121 clusters in HeCS-red-ext shows similar intrinsic scatter in the {sigma}p-{lambda} relation as the HeCS-red sample, but the range of {sigma}p at fixed richness increases to 3x. We evaluate the membership probability estimates Pmem for individual galaxies provided by redMaPPer. The spectroscopic membership fraction is larger than Pmem for 0.05<=P_mem_<=0.7; conversely, the spectroscopic membership fraction is smaller than P_mem_ at P_mem_>=0.8. We compare spectroscopic richness estimates with redMaPPer richness estimates and find good agreement on average, but a range of a factor of two in spectroscopic richness at fixed redMaPPer richness. Overall, within the high-richness and low-redshift cut of our sample, spectroscopically estimated parameters such as velocity dispersion correlate well with photometric richness estimates, although the relations contain substantial scatter.
- ID:
- ivo://CDS.VizieR/J/ApJ/767/15
- Title:
- Hectospec Cluster Survey (HeCS)
- Short Name:
- J/ApJ/767/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The infall regions of galaxy clusters represent the largest gravitationally bound structures in a {Lambda}CDM universe. Measuring cluster mass profiles into the infall regions provides an estimate of the ultimate mass of these halos. We use the caustic technique to measure cluster mass profiles from galaxy redshifts obtained with the Hectospec Cluster Survey (HeCS), an extensive spectroscopic survey of galaxy clusters with MMT/Hectospec. We survey 58 clusters selected by X-ray flux at 0.1<z<0.3. The survey includes 22680 unique MMT/Hectospec redshifts for individual galaxies; 10145 of these galaxies are cluster members. For each cluster, we acquired high signal-to-noise spectra for ~200 cluster members and a comparable number of foreground/background galaxies. The cluster members trace out infall patterns around the clusters. The members define a very narrow red sequence. We demonstrate that the determination of velocity dispersion is insensitive to the inclusion of bluer members (a small fraction of the cluster population). We apply the caustic technique to define membership and estimate the mass profiles to large radii. The ultimate halo mass of clusters (the mass that remains bound in the far future of a {Lambda}CDM universe) is on average (1.99+/-0.11)M_200_, a new observational cosmological test in essential agreement with simulations. Summed profiles binned in M_200_ and in L_X_demonstrate that the predicted Navarro-Frenk-White form of the density profile is a remarkably good representation of the data in agreement with weak lensing results extending to large radius. The concentration of these summed profiles is also consistent with theoretical predictions.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/63
- Title:
- Hectospec survey of SZ clusters (HeCS-SZ)
- Short Name:
- J/ApJ/819/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We estimate cluster masses and velocity dispersions for 123 clusters from optical spectroscopy to compare the Sunyaev-Zeldovich (SZ) mass proxy and dynamical masses. Our new survey, HeCS-SZ (Hectospec Cluster Survey of SZ-selected clusters), includes 7721 new or remeasured redshifts from MMT/Hectospec observations of 21 SZ-selected clusters at redshifts z=0.05-0.20. We supplement the Hectospec data with spectra from the Sloan Digital Sky Survey (SDSS) and cluster data from the Cluster Infall Regions in SDSS project and the Hectospec Cluster Survey, our Hectospec survey of clusters selected by X-ray flux. We measure the scaling relation between velocity dispersion and SZ mass estimates from the integrated Compton parameter for an SZ-complete sample of 83 clusters. The observed relation agrees very well with a simple virial scaling from mass (based on SZ) to velocity dispersion. The SZ mass estimates (calibrated with hydrostatic X-ray mass estimates) are not significantly biased compared to dynamical mass estimates under the assumption of small velocity bias of galaxies compared to dark matter particles. Significant mass bias in SZ mass estimates could relieve tension between cosmological results from Planck SZ cluster counts and Planck CMB data. In principle, SZ mass bias and velocity bias of galaxies could conspire to yield good agreement, but the required velocity bias is {sigma}_galaxy_~0.77{sigma}_DM_, outside the range of recent models of velocity bias in the literature. More likely, SZ mass bias and velocity bias are both small, and the tension between SZ cluster counts and CMB data requires another explanation.
- ID:
- ivo://CDS.VizieR/J/A+A/513/A15
- Title:
- Heidelberg InfraRed Optical Cluster Survey, HIROCS
- Short Name:
- J/A+A/513/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a survey for distant clusters of galaxies that identified clusters as local overdensities in the 3D galaxy distribution. Optical and near-IR imaging in B, R, i, z, and H are used to derive photometric redshifts for objects as faint as m*+1 at a redshift of 1.5. We outline the astrometric and photometric data reduction. The 3D cluster search, based on the photometric redshifts, is described.
- ID:
- ivo://CDS.VizieR/J/ApJS/217/11
- Title:
- HeI* in broad absorption line QSOs
- Short Name:
- J/ApJS/217/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Neutral helium multiplets, HeI*{lambda}{lambda}3189, 3889, 10830, are very useful diagnostics for the geometry and physical conditions of the absorbing gas in quasars. So far only a handful of HeI* detections have been reported. Using a newly developed method, we detected the HeI*{lambda}3889 absorption line in 101 sources of a well-defined sample of 285 MgII broad absorption line (BAL) quasars selected from SDSS DR5. This has increased the number of HeI* BAL quasars by more than one order of magnitude. We further detected HeI*{lambda}3189 in 50% (52/101) of the quasars in the sample. The detection fraction of HeI* BALs in MgII BAL quasars is ~35% as a whole, and it increases dramatically with increasing spectral signal-to-noise ratio (S/N), from ~18% at S/N<=10 to ~93% at S/N>=35. This suggests that HeI* BALs could be detected in most MgII LoBAL quasars, provided the spectra S/N is high enough. Such a surprisingly high HeI* BAL fraction is actually predicted from photoionization calculations based on a simple BAL model. The result indicates that HeI* absorption lines can be used to search for BAL quasars at low z, which cannot be identified by ground-based optical spectroscopic surveys with commonly seen UV absorption lines. Using HeI*{lambda}3889, we discovered 19 BAL quasars at z<0.3 from the available SDSS spectral database. The fraction of HeI* BAL quasars is similar to that of LoBAL objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/81
- Title:
- HeII photoionization rates of quasars
- Short Name:
- J/ApJ/847/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HeII transverse proximity effect-enhanced HeII Ly{alpha} transmission in a background sightline caused by the ionizing radiation of a foreground quasar-offers a unique opportunity to probe the morphology of quasar-driven HeII reionization. We conduct a comprehensive spectroscopic survey to find z~3 quasars in the foreground of 22 background quasar sightlines with Hubble Space Telescope/COS HeII Ly{alpha} transmission spectra. With our two-tiered survey strategy, consisting of a deep pencil-beam survey and a shallow wide-field survey, we discover 131 new quasars, which we complement with known SDSS/BOSS quasars in our fields. Using a restricted sample of 66 foreground quasars with inferred HeII photoionization rates greater than the expected UV background at these redshifts ({Gamma}_QSO_^HeII^>5x10^-16^s^-1^) we perform the first statistical analysis of the HeII transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest {Gamma}_QSO_^HeII^ only one (previously known) quasar is associated with a significant HeII transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average HeII transmission near the foreground quasars at 3{sigma} significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on {Gamma}_QSO_^HeII^. Our detection places a purely geometrical lower limit on the quasar lifetime of t_Q_>25Myr. Improved modeling would additionally constrain quasar obscuration and the mean free path of HeII-ionizing photons.
