Sloan Digital Sky Survey Sources Research Articles

An Independent Measure of the Kinematic Dipole from SDSS

We utilize the Sloan Digital Sky Survey (SDSS) extended Baryon Oscillation Spectroscopic Survey and Baryon Oscillation Spectroscopic Survey catalogs with precise spectroscopic redshifts to estimate the kinematic redshift dipole caused by the proper motion of the solar system. We find that the velocity extracted from the kinematic dipole is consistent with cosmic microwave background (CMB) inferred values. Although the small sky coverage and limited number density of the SDSS sources constrain us from obtaining precise and robust measurements, we leverage the redshift dipole method to estimate the kinematic dipole. The velocity measurements in this study are insensitive to intrinsic clustering, associated with the source count dipole. The kinematic dipole measured in this work and its consistency with CMB values do not guarantee isotropy at large scales. The anisotropy (excess dipole) measured with the NRAO VLA Sky Survey and the Wide-field Infrared Survey Explorer Catalog could be due to the intrinsic distribution of galaxies. The results in this work focus solely on the kinematic dipole term.

AT 2020iko: A WZ Sge-type Dwarf Nova Candidate with an Anomalous Precursor Event

Abstract The ongoing Zwicky Transient Facility (ZTF) survey is generating a massive alert rate from a variety of optical transients and variable stars, which are being filtered down to subsets meeting user-specified criteria by broker systems such as the Arizona-NOIRLab Temporal Analysis and Response to Events System (ANTARES). In a beta implementation of the algorithm of Soraisam et al. on ANTARES, we flagged AT 2020iko from the ZTF real-time alert stream as an anomalous source. This source is located close to a red extended Sloan Digital Sky Survey source. In the first few epochs of detection, it exhibited a V-shaped brightness profile, preceded by nondetections both in ZTF and in the All-Sky Automated Survey for Supernovae extending to 2014. Its full light curve shows a precursor event, followed by a main superoutburst and at least two rebrightenings. A low-resolution spectrum of this source points to a dwarf nova (DN) nature. Although some of the features of AT 2020iko indicate an SU UMa-type DN, its large amplitude, presence of rebrightenings, and inferred supercycle period of ≥6 yr are in favor of AT 2020iko being a new WZ Sge-type DN candidate, a subset of rare DNe consisting of extreme mass-ratio (<0.1) binaries with an orbital period around the period minimum. The precusor event of AT 2020iko brightened by 6.5 mag, while its decay spanned 3–5 mag. We speculate this superoutburst is associated with a less expanded accretion disk than in typical superoutbursts in WZ Sge systems, with the large depth of the precursor decay implying an extremely small mass ratio. To the best of our knowledge, such a precursor event has not been recorded for any DN. This result serves to demonstrate the efficacy of our real-time anomaly search algorithm.

Identifying galaxies, quasars, and stars with machine learning: A new catalogue of classifications for 111 million SDSS sources without spectra

We used 3.1 million spectroscopically labelled sources from the Sloan Digital Sky Survey (SDSS) to train an optimised random forest classifier using photometry from the SDSS and the Widefield Infrared Survey Explorer. We applied this machine learning model to 111 million previously unlabelled sources from the SDSS photometric catalogue which did not have existing spectroscopic observations. Our new catalogue contains 50.4 million galaxies, 2.1 million quasars, and 58.8 million stars. We provide individual classification probabilities for each source, with 6.7 million galaxies (13%), 0.33 million quasars (15%), and 41.3 million stars (70%) having classification probabilities greater than 0.99; and 35.1 million galaxies (70%), 0.72 million quasars (34%), and 54.7 million stars (93%) having classification probabilities greater than 0.9. Precision, Recall, and F1 score were determined as a function of selected features and magnitude error. We investigate the effect of class imbalance on our machine learning model and discuss the implications of transfer learning for populations of sources at fainter magnitudes than the training set. We used a non-linear dimension reduction technique, Uniform Manifold Approximation and Projection, in unsupervised, semi-supervised, and fully-supervised schemes to visualise the separation of galaxies, quasars, and stars in a two-dimensional space. When applying this algorithm to the 111 million sources without spectra, it is in strong agreement with the class labels applied by our random forest model.

The environment of C- and S-shaped radio galaxies

We study the environment of radio galaxies with different morphological types using the Proctor sample, which was built from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey archive. Among the 15 radio galaxy types classified by Proctor, 199 C-shaped (i.e., wide- or narrow-angle tail) and 203 S-shaped (i.e., S- or Z-shaped) sources are selected in this work, which are located in the redshift range of 0.02 < z < 1, because these two subsamples are relatively larger than the other subsamples in the Proctor sample. By cross-matching these radio galaxies with the optical sources drawn from the Sloan Digital Sky Survey (SDSS) database and counting the SDSS sources with an r-band absolute magnitude brighter than −19 located within a 0.5 Mpc distance around each source (i.e., the richness), we find that the fraction of C-shaped sources with a richness above 10 is larger than that of S-shaped sources. We have also correlated the radio galaxies in our sample with the brightest cluster galaxies (BCGs) defined in the NASA/IPAC Extragalactic Database (NED), and infer that the C-shaped sources are more likely to be BCGs than the S-shaped sources. These results support the idea that C-shaped radio galaxies often reside in a richer environment than radio galaxies with other morphological types.

CFHTLenS: the Canada–France–Hawaii Telescope Lensing Survey – imaging data and catalogue products

We present data products from the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS). CFHTLenS is based on the Wide component of the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS). It encompasses 154 deg2 of deep, optical, high-quality, sub-arcsecond imaging data in the five optical filters u*g′r′i′z′. The scientific aims of the CFHTLenS team are weak gravitational lensing studies supported by photometric redshift estimates for the galaxies. This paper presents our data processing of the complete CFHTLenS data set. We were able to obtain a data set with very good image quality and high-quality astrometric and photometric calibration. Our external astrometric accuracy is between 60 and 70 mas with respect to Sloan Digital Sky Survey (SDSS) data, and the internal alignment in all filters is around 30 mas. Our average photometric calibration shows a dispersion of the order of 0.01–0.03 mag for g′r′i′z′ and about 0.04 mag for u* with respect to SDSS sources down to iSDSS ≤ 21. We demonstrate in accompanying papers that our data meet necessary requirements to fully exploit the survey for weak gravitational lensing analyses in connection with photometric redshift studies. In the spirit of the CFHTLS, all our data products are released to the astronomical community via the Canadian Astronomy Data Centre at http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/community/CFHTLens/query.html. We give a description and how-to manuals of the public products which include image pixel data, source catalogues with photometric redshift estimates and all relevant quantities to perform weak lensing studies.

Photometric redshift requirements for lens galaxies in galaxy-galaxy lensing analyses

Weak gravitational lensing is a valuable probe of galaxy formation and cosmology. Here we quantify the effects of using photometric redshifts (photo-z) in galaxy-galaxy lensing, for both sources and lenses, both for the immediate goal of using galaxies with photo-z as lenses in the Sloan Digital Sky Survey (SDSS) and as a demonstration of methodology for large, upcoming weak lensing surveys that will by necessity be dominated by lens samples with photo-z. We calculate the bias in the lensing mass calibration as well as consequences for absolute magnitude (i.e., k-corrections) and stellar mass estimates, for a large sample of SDSS Data Release 8 (DR8) galaxies. The redshifts are obtained with the template based photo-z code ZEBRA on the SDSS DR8 ugriz photometry. We assemble and characterise the calibration samples (~9k spectroscopic redshifts from four surveys) to obtain photometric redshift errors and lensing biases corresponding to our full SDSS DR8 lens and source catalogues. Our tests of the calibration sample also highlight the impact of observing conditions in the imaging survey when the spectroscopic calibration covers a small fraction of its footprint; atypical imaging conditions in calibration fields can lead to incorrect conclusions regarding the photo-z of the full survey. For the SDSS DR8 catalogue, we find sigma_z/(1+z)=0.096 and 0.113 for the lens and source catalogues, with flux limits of r=21 and r=21.8, respectively. We also explore the systematic uncertainty in the lensing signal calibration when using source photo-z, and both lens and source photo-z; given the size of existing training samples, we can constrain the lensing signal calibration (and therefore the normalization of the surface mass density) to within 2 and 4 per cent, respectively. [ABRIDGED]

THE LUMINOSITY AND MASS FUNCTIONS OF LOW-MASS STARS IN THE GALACTIC DISK. I. THE CALIBRATION REGION

We present measurements of the luminosity and mass functions of low-mass stars constructed from a catalog of matched Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) detections. This photometric catalog contains more than 25,000 matched SDSS and 2MASS point sources spanning ~30 deg2 on the sky. We have obtained follow-up spectroscopy, complete to J = 16, of more than 500 low-mass dwarf candidates within a 1 deg2 subsample, and thousands of additional dwarf candidates in the remaining 29 deg2. This spectroscopic sample verifies that the photometric sample is complete, uncontaminated, and unbiased at the 99% level globally, and at the 95% level in each color range. We use this sample to derive the luminosity and mass functions of low-mass stars over nearly a decade in mass (0.7 M ☉ > M * > 0.1 M ☉). The luminosity function of the Galactic disk is statistically consistent with that measured from volume-complete samples in the solar neighborhood. We find that the logarithmically binned mass function is best fit with an Mc = 0.29 log-normal distribution, with a 90% confidence interval of Mc = 0.20-0.50. These 90% confidence intervals correspond to linearly binned mass functions peaking between 0.27 M ☉ and 0.12 M ☉, where the best fit MF turns over at 0.17 M ☉. A power-law fit to the entire mass range sampled here, however, returns a best fit of α = 1.1 (where the Salpeter slope is α = 2.35); a broken power law returns α = 2.04 at masses greater than log M = –0.5 (M = 0.32 M ☉), and α = 0.2 at lower masses. These results agree well with most previous investigations, though differences in the analytic formalisms adopted to describe those mass functions, as well as the range over which the data are fit, can give the false impression of disagreement. Given the richness of modern-day astronomical data sets, we are entering the regime whereby stronger conclusions can be drawn by comparing the actual datapoints measured in different mass functions, rather than the results of analytic analyses that impose structure on the data a priori. Having validated this method to generate a low-mass luminosity function from matched SDSS/2MASS data sets, future studies will extend this technique to the entirety of the SDSS footprint.

Nature and completeness of galaxies detected in the Two Micron All Sky Survey

The Two Micron All Sky Survey (2MASS) provides the most comprehensive data set of near-infrared galaxy properties. We cross correlate the well-defined and highly complete spectroscopic selection of over 155 000 bright (r≤ 17.5 mag) galaxies in the Sloan Digital Sky Survey (SDSS) main galaxy sample (MGS) with 2MASS sources to explore the nature and completeness of the 2MASS (K-band) selection of nearby galaxies. Using estimates of total galaxy brightness direct from the 2MASS and SDSS public catalogues, corrected only for Galactic extinction, we find that 2MASS detects 90 per cent of the MGS brighter than r= 17 mag. We quantify the completeness of 2MASS galaxies in terms of optical properties from SDSS. For r≤ 16 mag, 94.6 per cent of the MGS is found in the 2MASS extended source catalogue (XSC). These detections span the representative range of optical and near-infrared galaxy properties, but with a surface brightness-dependent bias to preferentially miss sources at the extreme blue and low-concentration end of parameter space, which are consistent with the most morphologically late-type galaxy population. An XSC completeness of 97.6 per cent is achievable at bright magnitudes, with blue low-surface-brightness galaxies being the only major source of incompleteness, if one follows our careful matching criteria and weeds out spurious SDSS sources. We conclude that the rapid drop in XSC completeness at r > 16 mag reflects the sharp surface-brightness limit of the extended source detection algorithm in 2MASS. As a result, the r > 16 galaxies found in the XSC are over-representative in red early types and under-representative in blue late types. At r > 16 mag, the XSC suffers an additional selection effect from the 2–3 arcsec spatial resolution limit of 2MASS. Therefore, in the range 16 < r≤ 17 mag, 2MASS continues to detect 90 per cent of the MGS, but with a growing fraction found in the point-source catalogue (PSC) only. Overall, one-third of the MGS is detected in the 2MASS PSC but not the XSC. Careful consideration of the different selection effects of 2MASS and SDSS are required to produce useful matched samples. A combined K≤ 13.57 and r≤ 16 mag-limited selection provides the most representative inventory of galaxies in the local cosmos with near-infrared and optical measurements, and 92.2 per cent completeness. Using data from the SDSS Second Data Release, this sample contains 19 143 galaxies with a median redshift of 0.052.

Phase-resolved spectroscopy of the helium dwarf nova ‘SN 2003aw’ in quiescence

High time resolution spectroscopic observations of the ultracompact helium dwarf nova 'SN 2003aw' in its quiescent state at V similar to 20.5 reveal its orbital period at 2027.8 +/- 0.5 s or 33.80 min. Together with the photometric 'superhump' period of 2041.5 +/- 0.5 s, this implies a mass ratio q approximate to 0.036. We compare both the average and time-resolved spectra of 'SN 2003aw' and Sloan Digital Sky Survey (SDSS) J124058.03-015919.2. Both show a DB white dwarf spectrum plus an optically thin, helium-dominated accretion disc. 'SN 2003aw' distinguishes itself from the SDSS source by its strong calcium H & K emission lines, suggesting higher abundances of heavy metals than the SDSS source. The silicon and iron emission lines observed in the SDSS source are about twice as strong in 'SN 2003aw'. The peculiar 'double bright spot' accretion disc feature seen in the SDSS source is also present in time-resolved spectra of 'SN 2003aw', albeit much weaker.

Cosmological parameters from SDSS and WMAP

We measure cosmological parameters using the three-dimensional power spectrum P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data. Our results are consistent with a ``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt, tensor modes or massive neutrinos. Adding SDSS information more than halves the WMAP-only error bars on some parameters, tightening 1 sigma constraints on the Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes and the equation of state. Our results are in substantial agreement with the joint analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive consistency check with independent redshift survey data and analysis techniques. In this paper, we place particular emphasis on clarifying the physical origin of the constraints, i.e., what we do and do not know when using different data sets and prior assumptions. For instance, dropping the assumption that space is perfectly flat, the WMAP-only constraint on the measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running tilt, neutrino mass and equation of state in the list of free parameters, many constraints are still quite weak, but future cosmological measurements from SDSS and other sources should allow these to be substantially tightened.

Optical and Radio Properties of Extragalactic Sources Observed by the FIRST Survey and the Sloan Digital Sky Survey

We discuss the optical and radio properties of ~30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 15 with a Sloan Digital Sky Survey (SDSS) (optical, sensitive to r* ~ 22.2) source in 1230 deg2 of sky. The matched sample represents ~30% of the 108,000 FIRST sources and 0.1% of the 2.5 ? 107 SDSS sources in the studied region. SDSS spectra are available for 4300 galaxies and 1154 quasars from the matched sample and for a control sample of 140,000 galaxies and 20,000 quasars in 1030 deg2 of sky. Here we analyze only core sources, which dominate the sample; the fraction of SDSS-FIRST sources with complex radio morphology is determined to be less than 10%. This large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r* = 21 are optically resolved; the fraction of resolved objects among the matched sources is a function of the radio flux, increasing from ~50% at the bright end to ~90% at the FIRST faint limit. Nearly all optically unresolved radio sources have nonstellar colors indicative of quasars. We estimate an upper limit of ~5% for the fraction of quasars with broadband optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux?optical flux plane suggests the existence of the quasar radio dichotomy; 8% ? 1% of all quasars with i* 2.22) galaxies, especially those with r* > 17.5. Magnitude- and redshift-limited samples show that radio galaxies have a different optical luminosity distribution than nonradio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. For a given optical luminosity and redshift, the observed optical colors of radio galaxies are indistinguishable from those of all SDSS galaxies selected by identical criteria. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions and resulting selection effects are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. The fraction of radio galaxies whose emission-line ratios indicate an AGN (30%), rather than starburst, origin is 6 times larger than the corresponding fraction for all SDSS galaxies (r* < 17.5). We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies.

The Optical, Infrared and Radio Properties of Extragalactic Sources Observed by SDSS, 2MASS and FIRST Surveys

AbstractWe positionally match sources observed by the Sloan Digital Sky Survey (SDSS), the Two Micron All Sky Survey (2MASS), and the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey. Practically all 2MASS sources are matched to an SDSS source within 2 arcsec; ~11% of them are optically resolved galaxies and the rest are dominated by stars. About 1/3 of FIRST sources are matched to an SDSS source within 2 arcsec; ~80% of these are galaxies and the rest are dominated by quasars. Based on these results, we project that by the completion of these surveys the matched samples will include about 107stars and 106galaxies observed by both SDSS and 2MASS, and about 250,000 galaxies and 50,000 quasars observed by both SDSS and FIRST. Here we present a preliminary analysis of the optical, infrared and radio properties for the extragalactic sources from the matched samples. In particular, we find that the fraction of quasars with stellar colors missed by the SDSS spectroscopic survey is probably not larger than ~10%, and that the optical colors of radio-loud quasars are ~0.05 mag. redder (with 4σ significance) than the colors of radio-quiet quasars.

Optical and Infrared Colors of Stars Observed by the Two Micron All Sky Survey and the Sloan Digital Sky Survey

We discuss optical and infrared photometric properties of stars matched in the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) commissioning data for ~50 deg2 of sky along the celestial equator centered at l = 150°, b = -60°. About 98% (~63,000) of objects listed in the 2MASS Point Source Catalog in the analyzed area are matched within 2'' to an SDSS source. The matched sources represent 8% of the ~800,000 SDSS sources in this area. They are predominantly red sources, as expected, and 15% of them are resolved in SDSS imaging data although they are detected as point sources in 2MASS data. The distribution of positional discrepancies for the matched sources and the astrometric statistics for the multiply observed SDSS sources imply that the astrometric accuracy of both surveys is about 01 per coordinate (rms). For about 14,000 stars with the smallest photometric errors (10%) in both surveys, we present optical and infrared color-magnitude and color-color diagrams. We use optical (SDSS) colors to identify the stellar spectral sequence and show that stars of different spectral types can have similar infrared colors, thus making the classification of stars based on only 2MASS data very difficult. However, a broad separation into early and late spectral types (relative to type K0) is possible with a reliability of ~95% even with 2MASS colors alone. The distributions of matched sources in color-magnitude and color-color diagrams are compared with the predictions of a stellar population synthesis code. We find that the models are in fair overall agreement with the data. In particular, the total number counts agree to better than 10%, and the morphologies of the color-magnitude and color-color diagrams appear similar. The most significant discrepancies are found for the number ratio of early to late type stars (by about a factor of 2) and in the colors of M stars (up to 0.2 mag). The first disagreement indicates that some parameters of the standard Galactic structure model and/or initial mass function can be improved, and the second disagreement emphasizes known difficulties with the modeling of stellar atmospheres for cool stars.