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- ID:
- ivo://CDS.VizieR/J/MNRAS/440/1248
- Title:
- SDSS DR7 voids and superclusters
- Short Name:
- J/MNRAS/440/1248
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of the interesting cosmological properties of voids in the Universe depends on the efficient and robust identification of such voids in galaxy redshift surveys. Recently, Sutter et al. have published a public catalogue of voids in the Sloan Digital Sky Survey Data Release 7 main galaxy and luminous red galaxy samples, using the void-finding algorithm ZOBOV, which is based on the watershed transform. We examine the properties of this catalogue and show that it suffers from several problems and inconsistencies, including the identification of some extremely overdense regions as voids. As a result, cosmological results obtained using this catalogue need to be reconsidered. We provide instead an alternative, self-consistent, public catalogue of voids in the same galaxy data, obtained from using an improved version of the same watershed transform algorithm. We provide a more robust method of dealing with survey boundaries and masks, as well as with a radially varying selection function, which means that our method can be applied to any other survey. We discuss some basic properties of the voids thus discovered, and describe how further information may be obtained from the catalogue. In addition, we apply an inversion of the algorithm to the same data to obtain a corresponding catalogue of large-scale overdense structures, or `superclusters'. Our catalogues are available for public download on the journal website.
- ID:
- ivo://CDS.VizieR/J/ApJS/204/5
- Title:
- SDSS DR7 white dwarf catalog
- Short Name:
- J/ApJS/204/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20407 white dwarf spectra, representing 19712 stars, and provide atmospheric model fits to 14120 DA and 1011 DB white dwarf spectra from 12843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated logg if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/894
- Title:
- SDSS galaxies classification
- Short Name:
- J/MNRAS/477/894
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an automated method for the detection of bar structure in optical images of galaxies using a deep convolutional neural network that is easy to use and provides good accuracy. In our study, we use a sample of 9346 galaxies in the redshift range of 0.009-0.2 from the Sloan Digital Sky Survey (SDSS), which has 3864 barred galaxies, the rest being unbarred. We reach a top precision of 94 per cent in identifying bars in galaxies using the trained network. This accuracy matches the accuracy reached by human experts on the same data without additional information about the images. Since deep convolutional neural networks can be scaled to handle large volumes of data, the method is expected to have great relevance in an era where astronomy data is rapidly increasing in terms of volume, variety, volatility, and velocity along with other V's that characterize big data. With the trained model, we have constructed a catalogue of barred galaxies from SDSS and made it available online.
- ID:
- ivo://CDS.VizieR/J/AJ/135/348
- Title:
- SDSS-II SNe survey: search and follow-up
- Short Name:
- J/AJ/135/348
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sloan Digital Sky Survey-II Supernova Survey has identified a large number of new transient sources in a 300deg^2^ region along the celestial equator during its first two seasons of a three-season campaign. Multi-band (ugriz) light curves were measured for most of the sources, which include solar system objects, galactic variable stars, active galactic nuclei, supernovae (SNe), and other astronomical transients. The imaging survey is augmented by an extensive spectroscopic follow-up program to identify SNe, measure their redshifts, and study the physical conditions of the explosions and their environment through spectroscopic diagnostics. During the survey, light curves are rapidly evaluated to provide an initial photometric type of the SNe, and a selected sample of sources are targeted for spectroscopic observations. In the first two seasons, 476 sources were selected for spectroscopic observations, of which 403 were identified as SNe. For the type Ia SNe, the main driver for the survey, our photometric typing and targeting efficiency is 90%. Only 6% of the photometric SN Ia candidates were spectroscopically classified as non-SN Ia instead, and the remaining 4% resulted in low signal-to-noise, unclassified spectra.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/115
- Title:
- SDSS-II SN Survey: host-galaxy spectral data
- Short Name:
- J/ApJ/821/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the largest single-survey sample of Type Ia supernovae (SNe Ia) to date, we study the relationship between properties of SNe Ia and those of their host galaxies, focusing primarily on correlations with Hubble residuals (HRs). Our sample consists of 345 photometrically classified or spectroscopically confirmed SNe Ia discovered as part of the SDSS-II Supernova Survey (SDSS-SNS). This analysis utilizes host-galaxy spectroscopy obtained during the SDSS-I/II spectroscopic survey and from an ancillary program on the SDSS-III Baryon Oscillation Spectroscopic Survey that obtained spectra for nearly all host galaxies of SDSS-II SN candidates. In addition, we use photometric host-galaxy properties from the SDSS-SNS data release such as host stellar mass and star formation rate. We confirm the well-known relation between HR and host-galaxy mass and find a 3.6{sigma} significance of a nonzero linear slope. We also recover correlations between HR and host-galaxy gas-phase metallicity and specific star formation rate as they are reported in the literature. With our large data set, we examine correlations between HR and multiple host-galaxy properties simultaneously and find no evidence of a significant correlation. We also independently analyze our spectroscopically confirmed and photometrically classified SNe Ia and comment on the significance of similar combined data sets for future surveys.
- ID:
- ivo://CDS.VizieR/J/ApJ/708/661
- Title:
- SDSS-II SN Survey: SNe II-P standardization
- Short Name:
- J/ApJ/708/661
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We apply the Standardized Candle Method (SCM) for Type II Plateau supernovae (SNe II-P), which relates the velocity of the ejecta of a SN to its luminosity during the plateau, to 15 SNe II-P discovered over the three season run of the Sloan Digital Sky Survey-II Supernova Survey. The redshifts of these SNe - 0.027<z<0.144 - cover a range hitherto sparsely sampled in the literature; in particular, our SNe II-P sample contains nearly as many SNe in the Hubble flow (z>0.01) as all of the current literature on the SCM combined. We find that the SDSS SNe have a very small intrinsic I-band dispersion (0.22mag), which can be attributed to selection effects. When the SCM is applied to the combined SDSS-plus-literature set of SNe II-P, the dispersion increases to 0.29mag, larger than the scatter for either set of SNe separately. We show that the standardization cannot be further improved by eliminating SNe with positive plateau decline rates, as proposed in Poznanski et al. (2009ApJ...694.1067P). We thoroughly examine all potential systematic effects and conclude that for the SCM to be useful for cosmology, the methods currently used to determine the FeII velocity at day 50 must be improved, and spectral templates able to encompass the intrinsic variations of Type II-P SNe will be needed.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/88
- Title:
- SDSS-II supernovae Ia cosmological analysis
- Short Name:
- J/ApJ/763/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the cosmological analysis of 752 photometrically classified Type Ia Supernovae (SNe Ia) obtained from the full Sloan Digital Sky Survey II (SDSS-II) Supernova (SN) Survey, supplemented with host-galaxy spectroscopy from the SDSS-III Baryon Oscillation Spectroscopic Survey. Our photometric-classification method is based on the SN classification technique of Sako et al. (2011, Cat. J/ApJ/738/162), aided by host-galaxy redshifts (0.05<z<0.55). SuperNova ANAlysis simulations of our methodology estimate that we have an SN Ia classification efficiency of 70.8%, with only 3.9% contamination from core-collapse (non-Ia) SNe. We demonstrate that this level of contamination has no effect on our cosmological constraints. We quantify and correct for our selection effects (e.g., Malmquist bias) using simulations. When fitting to a flat {Lambda}CDM cosmological model, we find that our photometric sample alone gives {Omega}_m_=0.24^+0.07^_-0.05_ (statistical errors only). If we relax the constraint on flatness, then our sample provides competitive joint statistical constraints on {Omega}_m_ and {Omega}_{Lambda}_, comparable to those derived from the spectroscopically confirmed Three-year Supernova Legacy Survey (SNLS3). Using only our data, the statistics-only result favors an accelerating universe at 99.96% confidence. Assuming a constant wCDM cosmological model, and combining with H_0_, cosmic microwave background, and luminous red galaxy data, we obtain w=-0.96^+0.10^_-0.10_, {Omega}_m_=0.29^+0.02^_-0.02_, and {Omega}_k_=0.00^+0.03^_-0.02_ (statistical errors only), which is competitive with similar spectroscopically confirmed SNe Ia analyses. Overall this comparison is reassuring, considering the lower redshift leverage of the SDSS-II SN sample (z<0.55) and the lack of spectroscopic confirmation used herein. These results demonstrate the potential of photometrically classified SN Ia samples in improving cosmological constraints.
- ID:
- ivo://CDS.VizieR/J/A+A/526/A28
- Title:
- SDSS-II supernovae NTT and NOT spectroscopy
- Short Name:
- J/A+A/526/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sloan Digital Sky Survey II (SDSS-II) Supernova Survey, conducted between 2005 and 2007, was designed to detect a large number of type Ia supernovae around z~0.2, the redshift "gap" between low-z and high-z supernova searches. The survey has provided multi-band (ugriz) photometric lightcurves for variable targets, and supernova candidates were scheduled for spectroscopic observations, primarily to provide supernova classification and accurate redshifts. We present supernova spectra obtained in 2006 and 2007 using the New Technology Telescope (NTT) and the Nordic Optical Telescope (NOT). We provide an atlas of supernova spectra in the range z=0.03-0.32 that complements the well-sampled lightcurves from SDSS-II in the forthcoming three-year SDSS supernova cosmology analysis. The sample can, for example, be used for spectral studies of type Ia supernovae, which are critical for understanding potential systematic effects when supernovae are used to determine cosmological distances. The spectra were reduced in a uniform manner, and special care was taken in estimating the uncertainties for the different processing steps. Host-galaxy light was subtracted when possible and the supernova type fitted using the SuperNova IDentification code (SNID). We also present comparisons between spectral and photometric dating using SALT lightcurve fits to the photometry from SDSS-II, as well as the global distribution of our sample in terms of the lightcurve parameters: stretch and colour.
- ID:
- ivo://CDS.VizieR/J/AJ/136/2306
- Title:
- SDSS-II Supernova survey, 2005
- Short Name:
- J/AJ/136/2306
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ugriz light curves for 146 spectroscopically-confirmed or spectroscopically-probable Type Ia supernovae (SNe) from the 2005 season of the Sloan Digital Sky Survey-II Supernova (SN) survey. The light curves have been constructed using a photometric technique that we call scene modeling, which is described in detail here; the major feature is that SN brightnesses are extracted from a stack of images without spatial resampling or convolution of the image data. This procedure produces accurate photometry along with accurate estimates of the statistical uncertainty, and can be used to derive photometry taken with multiple telescopes. We discuss various tests of this technique that demonstrate its capabilities. We also describe the methodology used for the calibration of the photometry, and present calibrated magnitudes and fluxes for all of the spectroscopic SNe Ia from the 2005 season.
