Sloan Digital Sky Survey Bands Research Articles

Applied Machine-Learning Models to Identify Spectral Sub-Types of M Dwarfs from Photometric Surveys

M dwarfs are the most abundant stars in the Solar Neighborhood and they are prime targets for searching for rocky planets in habitable zones. Consequently, a detailed characterization of these stars is in demand. The spectral sub-type is one of the parameters that is used for the characterization and it is traditionally derived from the observed spectra. However, obtaining the spectra of M dwarfs is expensive in terms of observation time and resources due to their intrinsic faintness. We study the performance of four machine-learning (ML) models—K-Nearest Neighbor (KNN), Random Forest (RF), Probabilistic Random Forest (PRF), and Multilayer Perceptron (MLP)—in identifying the spectral sub-types of M dwarfs at a grand scale by deploying broadband photometry in the optical and near-infrared. We trained the ML models by using the spectroscopically identified M dwarfs from the Sloan Digital Sky Survey (SDSS) Data Release (DR) 7, together with their photometric colors that were derived from the SDSS, Two-Micron All-Sky Survey, and Wide-field Infrared Survey Explorer. We found that the RF, PRF, and MLP give a comparable prediction accuracy, 74%, while the KNN provides slightly lower accuracy, 71%. We also found that these models can predict the spectral sub-type of M dwarfs with ∼99% accuracy within ±1 sub-type. The five most useful features for the prediction are r − z, r − i, r − J, r − H , and g − z, and hence lacking data in all SDSS bands substantially reduces the prediction accuracy. However, we can achieve an accuracy of over 70% when the r and i magnitudes are available. Since the stars in this study are nearby (d ≲ 1300 pc for 95% of the stars), the dust extinction can reduce the prediction accuracy by only 3%. Finally, we used our optimized RF models to predict the spectral sub-types of M dwarfs from the Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite, and we provide the optimized RF models for public use.

Interstellar Extinction in Galactic Cirri in SDSS Stripe 82

We have applied the method of star counts with Wolf diagrams to determine the interstellar extinction in five Galactic cirri in Sloan Digital Sky Survey (SDSS) Stripe 82. For this purpose, we have used the photometry of stars in the GALEX NUV filter and the photometry of red dwarfs in five SDSS bands and four SkyMapper Southern Sky Survey DR2 bands. We have identified the cirri as sky regions with an enhanced infrared emission from the Schlegel+1998 map. The extinction in them has been calculated relative to the nearby comparison regions with a reduced emission. The results for different filters agree well, giving the range of distances and the extinction law for each cirrus. The distances in the range 140--415 pc found are consistent with the 3D reddening maps. In the range between the $B$ and $V$ filters the extinctions found are consistent with the estimates from Schlegel+1998 for the Cardelli+1989 extinction law with $R_\mathrm{V}=3.1$. However, the extinctions found for all of the filters are best described not by the Cardelli+1989 extinction law with some $R_\mathrm{V}=3.1$, but by the inverse proportionality of the extinction and wavelength with its own coefficient for each cirrus. In one of the cirri our results suggest a very slight decrease in extinction with wavelength, i.e., a large contribution of gray extinction. In the remaining cirri a manifestation of gray extinction is not ruled out either. This is consistent with the previous measurements of the extinction law far from the Galactic midplane.

HYPERCALIBRATION: A PAN-STARRS1-BASED RECALIBRATION OF THE SLOAN DIGITAL SKY SURVEY PHOTOMETRY

ABSTRACT We present a recalibration of the Sloan Digital Sky Survey (SDSS) photometry with new flat fields and zero points derived from Pan-STARRS1. Using point-spread function (PSF) photometry of 60 million stars with 16 < r < 20, we derive a model of amplifier gain and flat-field corrections with per-run rms residuals of 3 millimagnitudes (mmag) in griz bands and 15 mmag in u band. The new photometric zero points are adjusted to leave the median in the Galactic north unchanged for compatibility with previous SDSS work. We also identify transient non-photometric periods in SDSS (“contrails”) based on photometric deviations co-temporal in SDSS bands. The recalibrated stellar PSF photometry of SDSS and PS1 has an rms difference of {9, 7, 7, 8} mmag in griz, respectively, when averaged over 15′ regions.

The SDSS–2MASS–WISE 10-dimensional stellar colour locus

We present the fiducial main-sequence stellar locus traced by 10 photometric colours observed by Sloan Digital Sky Survey (SDSS), Two Micron All Sky Survey (2MASS), and Wide-field Infrared Survey Explorer (WISE). Median colours are determined using 1052 793 stars with r-band extinction less than 0.125. We use this locus to measure the dust extinction curve relative to the r band, which is consistent with previous measurements in the SDSS and 2MASS bands. The WISE band extinction coefficients are larger than predicted by standard extinction models. Using 13 lines of sight, we find variations in the extinction curve in H, Ks, and WISE bandpasses. Relative extinction decreases towards Galactic anticentre, in agreement with prior studies. Relative extinction increases with Galactic latitude, in contrast to previous observations. This indicates a universal mid-IR extinction law does not exist due to variations in dust grain size and chemistry with Galactocentric position. A preliminary search for outliers due to warm circumstellar dust is also presented, using stars with high signal-to-noise ratio in the W3 band. We find 199 such outliers, identified by excess emission in Ks − W3. Inspection of SDSS images for these outliers reveals a large number of contaminants due to nearby galaxies. Six sources appear to be genuine dust candidates, yielding a fraction of systems with infrared excess of 0.12 ± 0.05 per cent.

Scalelength of disc galaxies

We have derived disc scalelengths for 30 374 non-interacting disc galaxies in all five Sloan Digital Sky Survey (SDSS) bands. Virtual Observatory methods and tools were used to define, retrieve and analyse the images for this unprecedentedly large sample classified as disc/spiral galaxies in the LEDA catalogue. Cross-correlation of the SDSS sample with the LEDA catalogue allowed us to investigate the variation of the scalelengths for different types of disc/spiral galaxies. We further investigate asymmetry, concentration and central velocity dispersion as indicators of morphological type, and are able to assess how the scalelength varies with respect to galaxy type. We note, however, that the concentration and asymmetry parameters have to be used with caution when investigating type dependence of structural parameters in galaxies. Here, we present the scalelength derivation method and numerous tests that we have carried out to investigate the reliability of our results. The average r-band disc scalelength is 3.79 kpc, with an rms dispersion of 2.05 kpc, and this is a typical value irrespective of passband and galaxy morphology, concentration and asymmetry. The derived scalelengths presented here are representative for a typical galaxy mass of 1010.8±0.54 M⊙, and the rms dispersion is larger for more massive galaxies. Separating the derived scalelengths for different galaxy masses, the r-band scalelength is 1.52 ± 0.65 kpc for galaxies with total stellar mass 109–1010 M⊙ and 5.73 ± 1.94 kpc for galaxies with total stellar mass between 1011 and 1012 M⊙. Distributions and typical trends of scalelengths have also been derived in all the other SDSS bands with linear relations that indicate the relation that connect scalelengths in one passband to another. Such transformations could be used to test the results of forthcoming cosmological simulations of galaxy formation and evolution of the Hubble sequence.

Supernovae in Low‐Redshift Galaxy Clusters: The Type Ia Supernova Rate

Supernova (SN) rates are a potentially powerful diagnostic of star formation history (SFH), metal enrichment, and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials, and simple SFH. However, a low-redshift cluster SN rate has never been published. We derive the SN rate in galaxy clusters at 0.06<z<0.19, based on type Ia supernovae (SNe Ia) that were discovered by the Wise Observatory Optical Transient Survey. As described in a separate paper, a sample of 140 rich Abell clusters was monitored, in which six cluster SNe Ia were found and confirmed spectroscopically. Here, we determine the SN detection efficiencies of the individual survey images, and combine the efficiencies with the known spectral properties of SNe Ia to calculate the effective visibility time of the survey. The cluster stellar luminosities are measured from the Sloan Digital Sky Survey (SDSS) database in the griz SDSS bands. Uncertainties are estimated using Monte-Carlo simulations in which all input parameters are allowed to vary over their known distributions. We derive SN rates normalized by stellar luminosity, in SNU units (SNe per century per 10^10 L_sun) in five photometric bandpasses, of 0.36+/-(0.22,0.14)+/-0.02 (B), 0.351+/-(0.210,0.139)+/-0.020 (g), 0.288+/-(0.172,0.114)+/-0.018 (r), 0.229+/-(0.137,0.091)+/-0.014 (i), 0.186+/-(0.111,0.074)+/-0.010 (z), where the quoted errors are statistical and systematic, respectively. The SN rate per stellar mass unit, derived using a color-luminosity-mass relation, is 0.098+/-(0.059,0.039)+/-0.009 SNe (century 10^10 M_sun)^-1. The low cluster SN rates we find are similar to, and consistent with, the SN Ia rate in local elliptical galaxies.

Inclination Dependent Luminosity Function of Spiral Galaxies

We study the inclination dependent luminosity function (LF) of spiral galaxies of the Sloan Digital Sky Survey (SDSS). Up to 60000 sample galaxies are selected from the 2nd data release of SDSS by fracdeVr &lt; 0.5. Magnitudes and other related photometric parameters are taken from NYU-VAGC(Blanton et al.2005). The apparent axis ratio (b/a)is used as an observational inclination indicator to define sub-samples. LFs of all 5 SDSS bands (u, g, r, i, z) are drawn for different sub-samples. Significant correlation is found between characteristic magnitudes (M*) of sub-samples and their inclinations, which can be fairly explained by dust extinction. A linear fit of the relation between M* and log(b/a) measures the M*(0) (for expected face-on spirals, with 0.2 ~ 0.3 mag brighter than that of LF of whole sample) and the intensity of dust extinction γ, for each band (Figure 1(a)). Additionally, since γ ∝ τ (optical depth), the wavelength dependent γ describes the extinction curve. Figure 1(b) shows a good linear fit that implies the extinction curve obeys the power law very well, with τλ = τV(λ/5500Å)−0.97±0.07. The power index n ~ 1 is shallower than that of the MW, LMC and SMC (n=1.1~1.5), but significantly steeper than the value of Charlot et al. (2000) (n=0.7), which under the assumption of a patchy distribution of dust in spiral galaxies. So our result implies that dust distributed in spirals, on average, are not as patchy as Charlot et al. assumed.

On the Luminosity Function of Galaxies in Groups in the Sloan Digital Sky Survey

Using galaxy groups identified in the Fourth Data Release of the Sloan Digital Sky Survey (SDSS), we compute the luminosity function for several subsamples of galaxies in groups. In all cases, the luminosity functions are well described by Schechter functions, down to the faintest magnitudes we probe, $M_{\rb}-5\log(h)\sim-16$. For the general luminosity function of galaxies in groups in the five SDSS bands, we observe that the characteristic magnitude is brighter in $\sim 0.5$ magnitudes compared to those obtained for field galaxies by Blanton et al.. Even when the observed faint end slope is steeper in galaxy groups, it is statistically comparable with the field value. We analyze the dependence of the galaxy luminosity function with system masses finding two clear trends: a continuous brightening of the characteristic magnitude and a steepening of the faint end slope as mass increases. The results in $\gb$, $\rb$, $\ib$ and $\zb$ bands show the same behavior. Using the $u-r$ color to split the galaxy sample into red and blue galaxies, we show that the changes observed as a function of the system mass are mainly seen in the red, passively evolving, galaxy population, while the luminosities of blue galaxies remain almost unchanged with mass. Finally, we observe that groups having an important luminosity difference between the two brightest galaxies of a system show a steeper faint end slope than the other groups. Our results can be interpreted in terms of galaxy mergers as the main driving force behind galaxy evolution in groups.

Color Separation of Galaxy Types in the Sloan Digital Sky Survey Imaging Data

We study the optical colors of 147,920 galaxies brighter than g* = 21, observed in five bands by the Sloan Digital Sky Survey (SDSS) over ~100 deg2 of high Galactic latitude sky along the celestial equator. The distribution of galaxies in the g*-r* versus u*-g* color-color diagram is strongly bimodal, with an optimal color separator of u*-r* = 2.22. We use visual morphology and spectral classification of subsamples of 287 and 500 galaxies, respectively, to show that the two peaks correspond roughly to early- (E, S0, and Sa) and late-type (Sb, Sc, and Irr) galaxies, as expected from their different stellar populations. We also find that the colors of galaxies are correlated with their radial profiles, as measured by the concentration index and by the likelihoods of exponential and de Vaucouleurs' profile fits. While it is well known that late-type galaxies are bluer than early-type galaxies, this is the first detection of a local minimum in their color distribution. In all SDSS bands, the counts versus apparent magnitude relations for the two color types are significantly different and demonstrate that the fraction of blue galaxies increases toward the faint end.

Galaxy Number Counts from the Sloan Digital Sky Survey Commissioning Data

We present bright galaxy number counts in five broad bands (u', g', r', i', z') from imaging data taken during the commissioning phase of the Sloan Digital Sky Survey (SDSS). The counts are derived from two independent stripes of imaging scans along the celestial equator, one each toward the northern and the southern Galactic cap, covering about 230 and 210 deg2, respectively. A careful study is made to verify the reliability of the photometric catalog. For galaxies brighter than r* = 16, the catalog produced by automated software is examined against eye inspection of all objects. Statistically meaningful results on the galaxy counts are obtained in the magnitude range 12 ≤ r* ≤ 21, using a sample of 900,000 galaxies. The counts from the two stripes differ by about 30% at magnitudes brighter than r* = 15.5, consistent with a local 2 σ fluctuation due to large-scale structure in the galaxy distribution. The shape of the number counts–magnitude relation brighter than r* = 16 is well characterized by N ∝ 100.6m, the relation expected for a homogeneous galaxy distribution in a "Euclidean" universe. In the magnitude range 16 < r* < 21, the galaxy counts from both stripes agree very well and follow the prediction of the no-evolution model, although the data do not exclude a small amount of evolution. We use empirically determined color transformations to derive the galaxy number counts in the B and I814 bands. We compute the luminosity density of the universe at zero redshift in the five SDSS bands and in the B band. We find B = 2.4 ± 0.4 × 108 L⊙ h Mpc-3, for a reasonably wide range of parameters of the Schechter luminosity function in the B band.