The Extraordinary `Superthin' Spiral Galaxy UGC7321. I. Disk Color Gradients and Global Properties from Multiwavelength Observations

We present B- and R-band imaging and photometry, H-alpha narrow-band imaging, NIR H-band imaging, and HI 21-cm spectroscopy of the nearby Sd spiral galaxy UGC7321. UGC7321 exhibits a remarkably thin stellar disk with no bulge component. The galaxy has a very diffuse, low surface brightness disk, which appears to suffer little internal extinction in spite of its edge-on geometry. The UGC7321 disk shows significant B-R color gradients in both the radial and vertical directions. These color gradients cannot be explained solely by dust and are indicative of changes in the mix of stellar ages and/or metallicity as a function of both radius and height above the galaxy plane. The outer regions of the UGC7321 disk are too blue to be explained by low metallicity alone (B-R<0.6), and must be relatively young. However, the galaxy also contains stellar populations with B-R>1.1, indicating it is not a young or recently-formed galaxy. The disk of UGC7321 is not a simple exponential, but exhibits a light excess at small radii, as well as distinct surface brightness zones. Together the properties of UGC7321 imply that it is an under-evolved galaxy in both a dynamical and in a star-formation sense. (Abridged)Comment: Accepted to the Astronomical Journal; 28 pages, 1 table and 21 figures (GIF and postscript

Cosmic shear statistics in the Suprime-Cam 2.1 sq deg field: Constraints on Omega_m and sigma_8

We present measurements of the cosmic shear correlation in the shapes of galaxies in the Suprime-Cam 2.1 deg^2 R_c-band imaging data. As an estimator of the shear correlation originated from the gravitational lensing, we adopt the aperture mass variance. We detect a non-zero E mode variance on scales between 2 and 40arcmin. We also detect a small but non-zero B mode variance on scales larger than 5arcmin. We compare the measured E mode variance to the model predictions in CDM cosmologies using maximum likelihood analysis. A four-dimensional space is explored, which examines sigma_8, Omega_m, Gamma and zs (a mean redshift of galaxies). We include three possible sources of error: statistical noise, the cosmic variance estimated using numerical experiments, and a residual systematic effect estimated from the B mode variance. We derive joint constraints on two parameters by marginalizing over the two remaining parameters. We obtain an upper limit of Gamma0.9 (68% confidence). For a prior Gamma\in[0.1,0.4] and zs\in[0.6,1.4], we find sigma_8=(0.50_{-0.16}^{+0.35})Omega_m^{-0.37} for flat cosmologies and sigma_8=(0.51_{-0.16}^{+0.29})Omega_m^{-0.34}$ for open cosmologies (95% confidence). If we take the currently popular LCDM model, we obtain a one-dimensional confidence interval on sigma_8 for the 95.4% level, 0.62<\sigma_8<1.32 for zs\in[0.6,1.4]. Information on the redshift distribution of galaxies is key to obtaining a correct cosmological constraint. An independent constraint on Gamma from other observations is useful to tighten the constraint.Comment: 12 pages, 12 figures, accepted for publication in Ap

The u'g'r'i'z' Standard Star Network

We present the 158 standard stars that define the u'g'r'i'z' photometric system. These stars form the basis for the photometric calibration of the Sloan Digital Sky Survey (SDSS). The defining instrument system and filters, the observing process, the reduction techniques, and the software used to create the stellar network are all described. We briefly discuss the history of the star selection process, the derivation of a set of transformation equations for the UBVRcIc system, and plans for future work.Comment: References to URLs in paper have been updated to reflect moved website. Accepted by AJ. 50 pages, including 20 pages of text, 9 tables, and 15 figures. Plain ASCII text versions of Tables 8 and 9 can be found at http://home.fnal.gov/~dtucker/ugriz/index.html (new URL

Subaru Deep Survey. IV. Discovery of a Large-Scale Structure at Redshift \simeq 5

We report the discovery of a large-scale structure of Lyman alpha emitters (LAEs) at z=4.86 based on wide-field imaging with the prime-focus camera (Suprime-Cam) on the Subaru telescope. We observed a 25' x 45' area of the Subaru Deep Field in a narrow band (NB, lambdaC=7126 A and FWHM=73 A) together with R and i'. We isolate from these data 43 LAE candidates down to NB=25.5 mag using color criteria. Follow-up spectroscopy of five candidates suggests the contamination by low-z objects to be ~ 20%. We find that the LAE candidates are clustered in an elongated region on the sky of 20 Mpc in width and 50 Mpc in length at z=4.86, which is comparable in size to present-day large-scale structures (we adopt H0=70 km/s/Mpc, Omega0=0.3, lambda0=0.7). This elongated region includes a circular region of 12 Mpc radius of higher surface overdensity (delta=2), which may be the progenitor of a cluster of galaxies. Assuming this circular region to be a sphere with a spatial overdensity of 2, we compare our observation with predictions by Cold Dark Matter models. We find that an Omega0=0.3 flat model with sigma8=0.9 predicts the number of such spheres consistent with the observed number (one sphere in our survey volume) if the bias parameter of LAEs is b \simeq 6. This value suggests that the typical mass of dark haloes hosting LAEs at z \simeq 5 is of the order of 10^12 Msolar. Such a large mass poses an interesting question about the nature of LAEs.Comment: 4 pages, 4 figures, uses emulateapj5.sty, ApJL, accepte

Detection of a Thick Disk in the edge-on Low Surface Brightness Galaxy ESO 342-G017: I. VLT Photometry in V and R Bands

We report the detection of a thick disk in the edge-on, low surface brightness (LSB), late-type spiral ESO 342-G017, based on ultra-deep images in the V and R bands obtained with the VLT Test Camera during Science Verification on UT1. All steps in the reduction procedure are fully described, which, together with an extensive analysis of systematic and statistic uncertainties, has resulted in surface brightness photometry that is reliable for the detection of faint extended structure to a level of V = 27.5 and R = 28.5 mag/square arcsec. The faint light apparent in these deep images is well-modeled by a thick exponential disk with an intrinsic scale height about 2.5 times that of the thin disk, and a comparable or somewhat larger scale length. Deprojection including the effects of inclination and convolution with the PSF allow us to estimate that the thick disk contributes 20-40% of the total (old) stellar disk luminosity of ESO 342-G017. To our knowledge, this is the first detection of a thick disk in an LSB galaxy, which are generally thought to be rather unevolved compared to higher surface brightness galaxies.Comment: Accepted for publication in Astronomy & Astrophysics; 18 pages, 12 figure

Statistical Properties of Bright Galaxies in the SDSS Photometric System

We investigate the photometric properties of 456 bright galaxies using imaging data recorded during the commissioning phase of the Sloan Digital Sky Survey (SDSS). Morphological classification is carried out by correlating results of several human classifiers. Our purpose is to examine the statistical properties of color indices, scale lengths, and concentration indices as functions of morphology for the SDSS photometric system. We find that $u'-g'$, $g'-r'$, and $r'-i'$ colors of SDSS galaxies match well with those expected from the synthetic calculation of spectroscopic energy distribution of template galaxies and with those transformed from $UBVR_CI_C$ color data of nearby galaxies. The agreement is somewhat poor, however, for $i'-z'$ color band with a discrepancy of $0.1-0.2$ mag. With the aid of the relation between surface brightness and radius obtained by Kent (1985), we estimate the averages of the effective radius of early type galaxies and the scale length of exponential disks both to be 2.6 kpc for $L^*$ galaxies. We find that the half light radius of galaxies depends slightly on the color bands, consistent with the expected distribution of star-forming regions for late type galaxies and with the known color gradient for early type galaxies. We also show that the (inverse) concentration index, defined by the ratio of the half light Petrosian radius to the 90% light Petrosian radius, correlates tightly with the morphological type; this index allows us to classify galaxies into early (E/S0) and late (spiral and irregular) types, allowing for a 15-20% contamination from the opposite class compared with eye-classified morphology.Comment: 18 pages, LaTeX (aaspp4), 16 PostScript figures. Accepted for publication in AJ (September issue

The Photometric Properties of Isolated Early-Type Galaxies

Isolated galaxies are important since they probe the lowest density regimes inhabited by galaxies. We define a sample of 36 nearby isolated early-type galaxies for further study. Our isolation criteria require them to have no comparable-mass neighbours within 2 B-band magnitudes, 0.67 Mpc in the plane of the sky and 700 km/s in recession velocity. New wide-field optical imaging of 10 isolated galaxies with the Anglo-Australian Telescope confirms their early-type morphology and relative isolation. We also present imaging of 4 galaxy groups as a control sample. The isolated galaxies are shown to be more gravitationally isolated than the group galaxies. We find that the isolated early-type galaxies have a mean effective colour of (B-R)_e = 1.54 +/- 0.14, similar to their high-density counterparts. They reveal a similar colour-magnitude relation slope and small intrinsic scatter to cluster ellipticals. They also follow the Kormendy relation of surface brightness versus size for luminous cluster galaxies. Such properties suggest that the isolated galaxies formed at a similar epoch to cluster galaxies, such that the bulk of their stars are very old. However, our galaxy modelling reveals evidence for dust lanes, plumes, shells, boxy and disk isophotes in four out of nine galaxies. Thus at least some isolated galaxies have experienced a recent merger/accretion event which may have induced a small burst of star formation. We derive luminosity functions for the isolated galaxies and find a faint slope of -1.2, which is similar to the `universal' slope found in a wide variety of environments. We examine the number density distribution of galaxies in the field of the isolated galaxies.Comment: 16 pages, Latex, 17 figures, 6 tables, MNRAS in pres

The Updated Zwicky Catalog (UZC)

The Zwicky Catalog of galaxies (ZC), with m_Zw<=15.5mag, has been the basis for the Center for Astrophysics (CfA) redshift surveys. To date, analyses of the ZC and redshift surveys based on it have relied on heterogeneous sets of galaxy coordinates and redshifts. Here we correct some of the inadequacies of previous catalogs by providing: (1) coordinates with <~2 arcsec errors for all of the Nuzc catalog galaxies, (2) homogeneously estimated redshifts for the majority (98%) of the data taken at the CfA (14,632 spectra), and (3) an estimate of the remaining "blunder" rate for both the CfA redshifts and for those compiled from the literature. For the reanalyzed CfA data we include a calibrated, uniformly determined error and an indication of the presence of emission lines in each spectrum. We provide redshifts for 7,257 galaxies in the CfA2 redshift survey not previously published; for another 5,625 CfA redshifts we list the remeasured or uniformly re-reduced value. Among our new measurements, Nmul are members of UZC "multiplets" associated with the original Zwicky catalog position in the coordinate range where the catalog is 98% complete. These multiplets provide new candidates for examination of tidal interactions among galaxies. All of the new redshifts correspond to UZC galaxies with properties recorded in the CfA redshift compilation known as ZCAT. About 1,000 of our new measurements were motivated either by inadequate signal-to-noise in the original spectrum or by an ambiguous identification of the galaxy associated with a ZCAT redshift. The redshift catalog we include here is ~96% complete to m_Zw<=15.5, and ~98% complete (12,925 galaxies out of a total of 13,150) for the RA(1950) ranges [20h--4h] and [8h--17h] and DEC(1950) range [-2.5d--50d]. (abridged)Comment: 34 pp, 7 figs, PASP 1999, 111, 43

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 similar to 100 deg(2) 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

The u\u27g\u27r\u27i\u27z\u27 Standard Star Setwork

We present the 158 standard stars that define the u\u27g\u27r\u27i\u27z\u27 photometric system. These stars form the basis for the photometric calibration of the Sloan Digital Sky Survey (SDSS). The defining instrument system and filters, the observing process, the reduction techniques, and the software used to create the stellar network are all described. We briefly discuss the history of the star selection process, the derivation of a set of transformation equations for the UBVRcIc system, and plans for future work. (Refer to PDF file for exact formulas)