Sloan Digital Sky Survey Filters Research Articles

The Importance of Having an Extended Point-spread Function in Low Surface-brightness Science

Abstract Obtaining and characterizing the extended point-spread function (PSF) is essential to extract accurate photometric information from deep imaging surveys. In this contribution, we present the extended PSFs of the Sloan Digital Sky Survey (SDSS). By stacking images of individual stars with different brightness, two-dimensional SDSS PSFs extending over 8 arcmin in radius for all the SDSS filters have been obtained. We demonstrate how to use the PSF models for correcting the scattered light field produced by the brightest stars in the Coma cluster central region field. This example shows the enormous importance of extended PSFs in the study of the low-surface brightness Universe, especially with the upcoming of ultra-deep surveys such as the Large Synoptic Survey Telescope (LSST). All PSF models and the scripts used to obtain them are publicly available and further details can be found in Infante-Sainz et al. (2020).

Observational Nonstationarity of AGN Variability: The Only Way to Go Is Down!

Abstract To gain insights into long-term active galactic nuclei (AGN) variability, we analyze an AGN sample from the Sloan Digital Sky Survey (SDSS) and compare their photometry with observations from the Hyper Suprime-Cam survey (HSC) observed yr after SDSS. On average, the AGN are fainter in HSC than SDSS. We demonstrate that the difference is not due to subtle differences in the SDSS versus HSC filters or photometry. The decrease in mean brightness is redshift dependent, consistent with expectations for a change that is a function of the rest-frame time separation between observations. At a given redshift, the mean decrease in brightness is stronger for more luminous AGN and for objects with longer time separation between measurements. We demonstrate that the dependence on redshift and luminosity of measured mean brightness decrease is consistent with simple models of Eddington ratio variability in AGN on long (Myr, Gyr) timescales. We show how our results can be used to constrain the variability and demographic properties of AGN populations.

The Sloan Digital Sky Survey extended point spread functions

ABSTRACT A robust and extended characterization of the point spread function (PSF) is crucial to extract the photometric information produced by deep imaging surveys. Here, we present the extended PSFs of the Sloan Digital Sky Survey (SDSS), one of the most productive astronomical surveys of all time. By stacking ∼1000 images of individual stars with different brightness, we obtain the bidimensional SDSS PSFs extending over 8 arcmin in radius for all the SDSS filters (u, g, r, i, z). This new characterization of the SDSS PSFs is near a factor of 10 larger in extension than previous PSFs characterizations of the same survey. We found asymmetries in the shape of the PSFs caused by the drift scanning observing mode. The flux of the PSFs is larger along the drift scanning direction. Finally, we illustrate with an example how the PSF models can be used to remove the scattered light field produced by the brightest stars in the central region of the Coma cluster field. This particular example shows the huge importance of PSFs in the study of the low-surface brightness Universe, especially with the upcoming of ultradeep surveys, such as the Large Synoptic Survey Telescope (LSST). Following a reproducible science philosophy, we make all the PSF models and the scripts used to do the analysis of this paper publicly available (snapshot v0.4-0-gd966ad0).

AN ACCURATE NEW METHOD OF CALCULATING ABSOLUTE MAGNITUDES ANDK-CORRECTIONS APPLIED TO THE SLOAN FILTER SET

We describe an accurate new method for determining absolute magnitudes, and hence also K-corrections, which is simpler than most previous methods, being based on a quadratic function of just one suitably chosen observed color. The method relies on the extensive and accurate new set of 129 empirical galaxy template SEDs from Brown et al. (2014). A key advantage of our method is that we can reliably estimate random errors in computed absolute magnitudes due to galaxy diversity, photometric error and redshift error. We derive K-corrections for the five Sloan Digital Sky Survey filters and provide parameter tables for use by the astronomical community. Using the New York Value-Added Galaxy Catalog we compare our K-corrections with those from kcorrect. Our K-corrections produce absolute magnitudes that are generally in good agreement with kcorrect. Absolute g, r, i, z-band magnitudes differ by less than 0.02 mag, and those in the u-band by ~0.04 mag. The evolution of rest-frame colors as a function of redshift is better behaved using our method, with relatively few galaxies being assigned anomalously red colors and a tight red sequence being observed across the whole 0.0 < z < 0.5 redshift range.

GIANT GALAXIES, DWARFS, AND DEBRIS SURVEY. I. DWARF GALAXIES AND TIDAL FEATURES AROUND NGC 7331

The Giant GAlaxies, Dwarfs, and Debris Survey concentrates on the nearby universe to study how galaxies have interacted in groups of different morphology, density, and richness. In these groups we select the dominant spiral galaxy and search its surroundings for dwarf galaxies and tidal interactions. This paper presents the first results from deep wide-field imaging of NGC 7331, where we detect only four low luminosity candidate dwarf companions and a stellar stream that may be evidence of a past tidal interaction. The dwarf galaxy candidates have surface brightnesses of mu_{r} ~ 23-25 mag/arcsec^{2} with (g-r) colors of 0.57-0.75mag in the Sloan Digital Sky Survey filter system, consistent with their being dwarf spheroidal galaxies (dSph). A faint stellar stream structure on the western edge of NGC 7331 has mu_{g} ~27 mag/arcsec^{2} and a relatively blue color of (g-r)=0.15mag. If it is tidal debris, then this stream could have probably formed from a rare type of interaction between NGC 7331 and a dwarf irregular or transition-type dwarf galaxy. We compare the structure and local environments of NGC 7331 to those of other nearby giant spirals in small galaxy groups. NGC 7331 has a much lower (2%) stellar mass in the form of early-type satellites than found for M31 and lacks the presence of nearby companions like luminous dwarf elliptical galaxies or the Magellanic Clouds. However, our detection of a few dSph candidates suggests that it is not deficient in low-luminosity satellites.

Spectral variability of quasars from multi-epoch photometric data in the Sloan Digital Sky Survey Stripe 82

We present a new approach to analysing the dependence of quasar variability on rest-frame wavelengths. We exploited the spectral archive of the Sloan Digital Sky Survey (SDSS) to create a sample of more than 9000 quasars in the Stripe 82. The quasar catalogue was matched with the Light Motion Curve Catalogue for SDSS Stripe 82 and individual first-order structure functions were computed. The structure functions are used to create a variability indicator that is related to the same intrinsic timescales for all quasars (1 to 2 yr in the rest frame). We study the variability ratios for adjacent SDSS filter bands as a function of redshift. While variability is almost always stronger in the bluer passband compared to the redder, the variability ratio depends on whether strong emission lines contribute to either one band or the other. The variability ratio-redshift relations resemble the corresponding colour index-redshift relations. From the comparison with Monte Carlo simulations of variable quasar spectra we find that the observed variability ratio-redshift relations are closely fitted assuming that (a) the r.m.s. fluctuation of the quasar continuum follows a power law-dependence on the intrinsic wavelength with an exponent -2 (i.e., bluer when brighter) and (b) the variability of the emission line flux is only about 10% of that of the underlying continuum. These results, based upon the photometry of more than 8000 quasars, confirm the previous findings by Wilhite et al. (2005) from 315 quasars with repeated SDSS spectroscopy. Finally, we find that quasars with unusual spectra and weak emission lines tend to have less variability than conventional quasars. This trend is opposite to what is expected from the dilution effect of variability due to line emission and may be indicative of high Eddington ratios in these unconventinal quasars.

The Period‐Luminosity Relation of RR Lyrae Stars in the SDSS Photometric System

We provide the first detailed study of the RR Lyrae period-luminosity (PL) relation in the ugriz bandpasses of the Sloan Digital Sky Survey (SDSS) filter system. We argue that tight, simple PL relations are not present in the SDSS filters, except for the redder bandpasses i and (especially) z. However, for all bandpasses, we show that, by incorporating terms involving a (fairly reddening-independent) pseudo-color C_0 = (u-g)_0 - (g-r)_0, tight (non-linear) relations do obtain. We provide theoretically calibrated such relations in the present paper, which should be useful to derive precise absolute magnitudes (hence distances) and intrinsic colors (hence reddening values) to even {\em individual} field RR Lyrae stars. For applications to cases where photometry in all five passbands may not be available, we also provide simple (though less precise) average PL relations for the i and z bandpasses, which read as follows: M_z = 0.839 - 1.295 log P + 0.211 log Z, M_i = 0.908 - 1.035 log P + 0.220 log Z. Similarly, simple period-color relations for (r-i)_0, (g-r)_0, and (u-z)_0 are also provided.

Detection of Cosmic Magnification with the Sloan Digital Sky Survey

We present an 8 sigma detection of cosmic magnification measured by the variation of quasar density due to gravitational lensing by foreground large scale structure. To make this measurement we used 3800 square degrees of photometric observations from the Sloan Digital Sky Survey (SDSS) containing \~200,000 quasars and 13 million galaxies. Our measurement of the galaxy-quasar cross-correlation function exhibits the amplitude, angular dependence and change in sign as a function of the slope of the observed quasar number counts that is expected from magnification bias due to weak gravitational lensing. We show that observational uncertainties (stellar contamination, Galactic dust extinction, seeing variations and errors in the photometric redshifts) are well controlled and do not significantly affect the lensing signal. By weighting the quasars with the number count slope, we combine the cross-correlation of quasars for our full magnitude range and detect the lensing signal at >4 sigma in all five SDSS filters. Our measurements of cosmic magnification probe scales ranging from 60 kpc/h to 10 Mpc/h and are in good agreement with theoretical predictions based on the WMAP concordance cosmology. As with galaxy-galaxy lensing, future measurements of cosmic magnification will provide useful constraints on the galaxy-mass power spectrum.

Blue Horizontal-Branch Stars in the Sloan Digital Sky Survey. I. Sample Selection and Structure in the Galactic Halo

We isolate samples of 733 bright (g 18) high Galactic latitude blue horizontal-branch stars with photometry and spectroscopy in the Sloan Digital Sky Survey (SDSS). Comparison of independent photometric and spectroscopic selection criteria indicates that contamination from F and blue straggler stars is less than 10% for bright stars (g 18), and this is qualitatively confirmed by proper motions based on the USNO-A catalog as first epoch. Analysis of repeated observations shows that the errors in radial velocity are ≈26 km s-1. A relation between absolute magnitude and color is established using the horizontal branches of halo globular clusters observed by SDSS. Bolometric corrections and colors are synthesized in the SDSS filters from model spectra. The redder stars agree well in absolute magnitude with accepted values for RR Lyrae stars. The resulting photometric distances are accurate to about 0.2 mag, with a median of about 25 kpc. Modest clumps in phase space exist and are consistent with the previously reported tidal stream of the Sagittarius dwarf galaxy.

Characterization of M, L, and T Dwarfs in the Sloan Digital Sky Survey

An extensive sample of M, L and T dwarfs identified in the Sloan Digital Sky Survey (SDSS) has been compiled. The sample of 718 dwarfs includes 677 new objects (629 M dwarfs, 48 L dwarfs) together with 41 that have been previously published. All new objects and some of the previously published ones have new optical spectra obtained either with the SDSS spectrographs or with the Apache Point Observatory 3.5m ARC telescope. Spectral types and SDSS colors are available for all objects; approximately 35% also have near-infrared magnitudes measured by 2MASS or on the Mauna Kea system. We use this sample to characterize the color--spectral type and color--color relations of late type dwarfs in the SDSS filters, and to derive spectroscopic and photometric parallax relations for use in future studies of the luminosity and mass functions based on SDSS data. We find that the (i*-z*) and (i*-J) colors provide good spectral type and absolute magnitude (M_i*) estimates for M and L dwarfs. Our distance estimates for the current sample indicate that SDSS is finding early M dwarfs out to about 1.5 kpc, L dwarfs to approximately 100 pc and T dwarfs to near 20 pc. The T dwarf photometric data show large scatter and are therefore less reliable for spectral type and distance estimation.

RR Lyrae Stars and Type Ia Supernovae: Discovery and Calibration of Astronomical Standard Candles

Accurate apparent and intrinsic luminosities of objects are very important in astronomy, for without them we cannot calculate accurate distances or scale the energy budget of physical models. This dissertation deals with observations of two of the most widely used astronomical standard (or standardizable) candles. The Sloan Digital Sky Survey (SDSS) is an important survey presently being carried out, which will provide photometry of roughly 10 objects over a 10,000 square degree area of sky (D. G. York et al. 2000, AJ, 120, 1579). One million spectra of galaxies will be obtained, and many high-redshift quasars will be discovered (see, e.g., X. Fan et al. 1999, AJ, 118, 1). Many new candidate variable stars in our Galaxy will also be identified, amongst them RR Lyrae stars (roughly one per square degree). Distances and velocities of a large number of such objects will allow us to refine models of the Galaxy’s halo and to measure the Galaxy’s mass. We observed a number of types of objects of interest in SDSS filters (RR Lyrae stars, Cepheids, cataclysmic variables, carbon stars, and asteroids) and showed to what extent these objects can be identified solely on the basis of their SDSS colors. Details can be found in a paper already published in this journal (K. Krisciunas, B. Margon, & P. Szkody 1998, PASP, 110, 1342). In particular, Figure 12 of that paper shows the color locus of bona fide RR Lyrae stars. We have observed one dozen RR Lyrae candidates identified from SDSS commissioning data and proved beyond a shadow of a doubt that all are RR Lyrae stars. Light curves of six candidates identified by B. Willman and S. Anderson are to be found in Z. Ivezic et al. (2000, AJ, 120, 963). Five of the other confirmed RR Lyrae stars are objects 5, 9, 134, 141, and 144 from Table 2 of Ivezic et al. Figure 1 shows the folded light curve of star 144. Owing to their luminosities ( at maximum), Type M ≈ 19.4 V Ia supernovae (SNe) are the most important standardizable candle used in extragalactic astronomy because they can be seen halfway across the visible universe. We use the word “standardizable” because, unlike RR Lyrae stars of identical metallicity, Type Ia SNe do not all have the same intrinsic luminosity. Those which rise faster and subsequently decline faster are intrinsically fainter at maximum compared to those which rise more slowly and decline more slowly. See M. M. Phillips et al. (1999, AJ, 118, 1766). As to an explosion mechanism, the favorite scenario is the deflagration of a carbonoxygen white dwarf which reaches the Chandrasekhar limit due to mass infall from a companion star (M. Livio 2000, preprint, astro-ph/0005344). Deflagration is a type of rapid, but subsonic, combustion in which the flame front is driven by turbulent heat exchange. It is also possible that some Type Ia SNe are due to a sub–Chandrasekhar-mass detonation of an accreted surface helium layer on a C-O white dwarf (P. Pinto, R. G. Eastman, & T. Rogers 2000, preprint, astro-ph/0008330). One of the potentially significant sources of error in determining the distance to a Type Ia SN is the contribution of extinction by dust in the host galaxy. What we need is a “wellbehaved” color index with the largest possible wavelength baseline. Since V) for standard Galactic dust, the A ≈ 3.1 # E(B V uncertainties in the color excess and the scale factor can lead to significant uncertainties in the extinction correction. J. H. Elias et al. (1985, ApJ, 296, 379) already showed that Type Ia SNe exhibit some degree of uniform V K color evolution, while B H photometry such as that of B. Leibundgut (1988, Ph.D. dissertation, Univ. Basel) is not as well behaved. Since K), the potential for A ≈ 1.21 # E(V H) ≈ 1.13 # E(V V smaller uncertainties for using V minus near-infrared colors AV was encouraging. New optical and near-infrared (JHK) photometry of Type Ia SNe, especially data obtained before B-band maximum, was needed. Y. D. Mayya et al. (1998, IAU Circ. 6907), S. Jha et al. (1999, ApJS, 125, 73), and P. Meikle (2000, MNRAS, 314, 782) have published data for the spectroscopically normal SN 1998bu, the distance of the host of which has also been measured with HST using Cepheids. We have obtained optical and infrared data for the spectroscopically normal Type Ia SNe 1999cl, 1999cp, 2000bk, and 2000ce and for the overluminous, slowly declining, spectroscopically peculiar SNe 1999aa, 1999gp, and 2000cx. Data for three of these have already been published (K. Krisciunas et al. 2000, ApJ, 539, 658).

A Catalog of Photometry for Las Campanas Redshift Survey Galaxies on the Sloan Digital Sky Survey System

We present high-quality photometry in the five Sloan Digital Sky Survey filters, u', g', r', i', and z', for 2195 galaxies with spectroscopic redshifts measured by the Las Campanas Redshift Survey. In addition, a polynomial photometric redshift estimator is derived, with an uncertainty of 0.035 out to z = 0.25.

L Dwarfs Found in Sloan Digital Sky Survey Commissioning Imaging Data

This paper describes the discovery of seven dwarf objects of spectral type L (objects cooler than the latest M dwarfs) in commissioning imaging data taken by the Sloan Digital Sky Survey (SDSS). Low-resolution spectroscopy shows that they have spectral types from L0 to L8. Comparison of the SDSS and the Two Micron All Sky Survey (2MASS) photometry for several of these objects indicates the presence of significant opacity at optical wavelengths. This comparison also demonstrates the high astrometric accuracy (better than 1'' for these faint sources) of both surveys. The L dwarfs are shown to occupy a distinctive region of color-color space as measured in the SDSS filters, which should enables their identification in a straightforward way. This should lead eventually to a complete sample of many hundreds of these low-mass objects, or about 1 per 15 deg2 to i' ≈ 20, in the complete SDSS data set.

Photometric Separation of Stellar Properties Using SDSS Filters

Using synthetic photometry of Kurucz model spectra, we explore the colors of stars as a function of temperature, metallicity, and surface gravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. The synthetic colors show qualitative agreement with the few published observations in these filters. We find that the locus of synthetic stars is basically two-dimensional for 4500 < T < 8000 K, which precludes simultaneous color separation of the three basic stellar characteristics we consider. Colors including u' contain the most information about normal stellar properties; measurements in this filter are also important for selecting white dwarfs. We identify two different subsets of the locus in which the loci separate by either metallicity or surface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly to G stars), the locus separates by metallicity; for photometric error of a few percent, we estimate metallicity to within ~0.5 dex in this range. In the range -0.15 < g' - r' < 0.00 (corresponding roughly to A stars), the locus shows separation by surface gravity. In both cases, we show that it is advantageous to use more than two colors when determining stellar properties by color. Strategic observations in SDSS filters are required to resolve the source of a ~5% discrepancy between synthetic colors of Gunn-Stryker stars, Kurucz models, and external determinations of the metallicities and surface gravities. The synthetic star colors can be used to investigate the properties of any normal star and to construct analytic expressions for the photometric prediction of stellar properties in special cases.