Showing papers in "The Astronomical Journal in 2004"

The Second Data Release of the Sloan Digital Sky Survey

Abstract: The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its Second Data Release. This data release consists of 3324 deg2 of five-band (ugriz) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg2 of this area, and tables of measured parameters from these data. The imaging data reach a depth of r ≈ 22.2 (95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point-spread function magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 to 9200 A at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines and included in the Second Data Release. Further characteristics of the data are described, as are the data products themselves and the tools for accessing them.

A Catalog of Neighboring Galaxies

Abstract: We present an all-sky catalog of 451 nearby galaxies, each having an individual distance estimate D 10 Mpc or a radial velocity VLG -17.0, which contribute about 4% to the local luminosity density, and roughly 10%–15% to the local H I mass density. The H I mass-to-luminosity and the H I mass-to-total (indicative) mass ratios increase systematically from giant galaxies toward dwarfs, reaching maximum values about 5 in solar units for the most tiny objects. For the Local Volume disklike galaxies, their H I masses and angular momentum follow Zasov's linear relation, expected for rotating gaseous disks being near the threshold of gravitational instability, favorable for active star formation. We found that the mean local luminosity density exceeds 1.7–2.0 times the global density, in spite of the presence of the Tully void and the absence of rich clusters in the Local Volume. The mean local H I density is 1.4 times its "global" value derived from the H I Parkes Sky Survey. However, the mean local baryon density Ωb(< 8 Mpc) = 2.3% consists of only a half of the global baryon density, Ωb = (4.7 ± 0.6)% (Spergel et al., published in 2003). The mean-square pairwise difference of radial velocities is about 100 km s-1 for spatial separations within 1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. also We calculated the integral area of the sky occupied by the neighboring galaxies. Assuming the H I size of spiral and irregular galaxies to be 2.5 times their standard optical diameter and ignoring any evolution effect, we obtain the expected number of the line-of-sight intersections with the H I galaxy images to be dn/dz ~ 0.4, which does not contradict the observed number of absorptions in QSO spectra.

Stellar chemical signatures and hierarchical galaxy formation

Abstract: To compare the chemistries of stars in the Milky Way dwarf spheroidal (dSph) satellite galaxies with stars in the Galaxy, we have compiled a large sample of Galactic stellar abundances from the literature. When kinematic information is available, we have assigned the stars to standard Galactic components through Bayesian classification based on Gaussian velocity ellipsoids. As found in previous studies, the [α/Fe] ratios of most stars in the dSph galaxies are generally lower than similar metallicity Galactic stars in this extended sample. Our kinematically selected stars confirm this for the Galactic halo, thin-disk, and thick-disk components. There is marginal overlap in the low [α/Fe] ratios between dSph stars and Galactic halo stars on extreme retrograde orbits (V < -420 km s-1), but this is not supported by other element ratios. Other element ratios compared in this paper include r- and s-process abundances, where we find a significant offset in the [Y/Fe] ratios, which results in a large overabundance in [Ba/Y] in most dSph stars compared with Galactic stars. Thus, the chemical signatures of most of the dSph stars are distinct from the stars in each of the kinematic components of the Galaxy. This result rules out continuous merging of low-mass galaxies similar to these dSph satellites during the formation of the Galaxy. However, we do not rule out very early merging of low-mass dwarf galaxies, since up to one-half of the most metal-poor stars ([Fe/H] ≤ -1.8) have chemistries that are in fair agreement with Galactic halo stars. We also do not rule out merging with higher mass galaxies, although we note that the LMC and the remnants of the Sgr dwarf galaxy are also chemically distinct from the majority of the Galactic halo stars. Formation of the Galaxy's thick disk by heating of an old thin disk during a merger is also not ruled out; however, the Galaxy's thick disk itself cannot be comprised of the remnants from a low-mass (dSph) dwarf galaxy, nor of a high-mass dwarf galaxy like the LMC or Sgr, because of differences in chemistry. The new and independent environments offered by the dSph galaxies also allow us to examine fundamental assumptions related to the nucleosynthesis of the elements. The metal-poor stars ([Fe/H] ≤ -1.8) in the dSph galaxies appear to have lower [Ca/Fe] and [Ti/Fe] than [Mg/Fe] ratios, unlike similar metallicity stars in the Galaxy. Predictions from the α-process (α-rich freeze-out) would be consistent with this result if there have been a lack of hypernovae in dSph galaxies. The α-process could also be responsible for the very low Y abundances in the metal-poor stars in dSph's; since [La/Eu] (and possibly [Ba/Eu]) are consistent with pure r-process results, the low [Y/Eu] suggests a separate r-process site for this light (first-peak) r-process element. We also discuss SNe II rates and yields as other alternatives, however. In stars with higher metallicities ([Fe/H] ≥ -1.8), contributions from the s-process are expected; [(Y, La, and Ba)/Eu] all rise as expected, and yet [Ba/Y] is still much higher in the dSph stars than similar metallicity Galactic stars. This result is consistent with s-process contributions from lower metallicity AGB stars in dSph galaxies, and is in good agreement with the slower chemical evolution expected in the low-mass dSph galaxies relative to the Galaxy, such that the build-up of metals occurs over much longer timescales. Future investigations of nucleosynthetic constraints (as well as galaxy formation and evolution) will require an examination of many stars within individual dwarf galaxies. Finally, the Na-Ni trend reported in 1997 by Nissen & Schuster is confirmed in Galactic halo stars, but we discuss this in terms of the general nucleosynthesis of neutron-rich elements. We do not confirm that the Na-Ni trend is related to the accretion of dSph galaxies in the Galactic halo.

A new nonparametric approach to galaxy morphological classification

Abstract: We present two new nonparametric methods for quantifying galaxy morphology: the relative distribution of the galaxy pixel flux values (the Gini coefficient or G) and the second-order moment of the brightest 20% of the galaxy's flux (M20). We test the robustness of G and M20 to decreasing signal-to-noise ratio (S/N) and spatial resolution and find that both measures are reliable to within 10% for images with average S/N per pixel greater than 2 and resolutions better than 1000 and 500 pc, respectively. We have measured G and M20, as well as concentration (C), asymmetry (A), and clumpiness (S) in the rest-frame near-ultraviolet/optical wavelengths for 148 bright local normal Hubble-type galaxies (E–Sd) galaxies, 22 dwarf irregulars, and 73 0.05 < z < 0.25 ultraluminous infrared galaxies (ULIRGs). We find that most local galaxies follow a tight sequence in G-M20-C, where early types have high G and C and low M20 and late-type spirals have lower G and C and higher M20. The majority of ULIRGs lie above the normal galaxy G-M20 sequence because of their high G and M20 values. Their high Gini coefficients arise from very bright nuclei, while the high second-order moments are produced by multiple nuclei and bright tidal tails. All of these features are signatures of recent and on-going mergers and interactions. We also find that in combination with A and S, G is more effective than C at distinguishing ULIRGs from the normal Hubble types. Finally, we measure the morphologies of 491.7 < z < 3.8 galaxies from HST NICMOS observations of the Hubble Deep Field North. We find that many of the z ~ 2 galaxies possess G and A higher than expected from degraded images of local elliptical and spiral galaxies and have morphologies more like low-redshift ULIRGs.

The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)

Abstract: The second US Naval Observatory (USNO) CCD Astrograph Catalog, UCAC2 was released in 2003 July. Positions and proper motions for 48,330,571 sources (mostly stars) are available on 3 CDs, supplemented with Two Micron All Sky Survey photometry for 99.5% of the sources. The catalog covers the sky area from -90° to +40° declination, going up to +52° in some areas; this completely supersedes the UCAC1 released in 2001. Current epoch positions are obtained from observations with the USNO 8 inch (0.2 m) Twin Astrograph equipped with a 4K CCD camera. The precision of the positions are 15–70 mas, depending on magnitude, with estimated systematic errors of 10 mas or below. Proper motions are derived by using over 140 ground- and space-based catalogs, including Hipparcos/Tycho and the AC2000.2, as well as yet unpublished remeasures of the AGK2 plates and scans from the NPM and SPM plates. Proper-motion errors are about 1–3 mas yr-1 for stars to 12th magnitude, and about 4–7 mas yr-1 for fainter stars to 16th magnitude. The observational data, astrometric reductions, results, and important information for the users of this catalog are presented.

Near - infrared photometry and spectroscopy of L and T dwarfs: The Effects of temperature, clouds, and gravity

Abstract: We present new JHK photometry on the MKO-NIR system and JHK spectroscopy for a large sample of L and T dwarfs. Photometry has been obtained for 71 dwarfs, and spectroscopy for 56. The sample comprises newly identified very red objects from the Sloan Digital Sky Survey (SDSS) and known dwarfs from the SDSS and the Two Micron All Sky Survey (2MASS). Spectral classification has been carried out using four previously defined indices from Geballe et al. that measure the strengths of the near infrared water and methane bands. We identify nine new L8?9.5 dwarfs and 14 new T dwarfs from SDSS, including the latest yet found by SDSS, the T7 dwarf SDSS J175805.46+463311.9. We classify 2MASS J04151954-0935066 as T9, the latest and coolest dwarf found to date. We combine the new results with our previously published data to produce a sample of 59 L dwarfs and 42 T dwarfs with imaging data on a single photometric system and with uniform spectroscopic classification. We compare the near-infrared colors and absolute magnitudes of brown dwarfs near the L?T transition with predictions made by models of the distribution and evolution of photospheric condensates. There is some scatter in the Geballe et al. spectral indices for L dwarfs, suggesting that these indices are probing different levels of the atmosphere and are affected by the location of the condensate cloud layer. The near-infrared colors of the L dwarfs also show scatter within a given spectral type, which is likely due to variations in the altitudes, spatial distributions, and thicknesses of the clouds. We have identified a small group of late-L dwarfs that are relatively blue for their spectral type and that have enhanced FeH, H2O, and K I absorption, possibly due to an unusually small amount of condensates. The scatter seen in the H-K color for late-T dwarfs can be reproduced by models with a range in surface gravity. The variation is probably due to the effect on the K-band flux of pressure-induced H2 opacity. The correlation of H-K color with gravity is supported by the observed strengths of the J-band K I doublet. Gravity is closely related to mass for field T dwarfs with ages greater than108 yr and the gravities implied by the H-K colors indicate that the T dwarfs in our sample have masses in the range 15?75MJupiter. One of the SDSS dwarfs, SDSS J111010.01+011613.1, is possibly a very low mass object, with log g ~ 4.2?4.5 and mass ~ 10?15MJupiter.

L' AND M' Photometry Of Ultracool Dwarfs

Abstract: We have compiled L' (3.4-4.1 microns) and M' (4.6- 4.8 microns) photometry of 63 single and binary M, L, and T dwarfs obtained at the United Kingdom Infrared Telescope using the Mauna Kea Observatory filter set. This compilation includes new L' measurements of eight L dwarfs and 13 T dwarfs and new M' measurements of seven L dwarfs, five T dwarfs, and the M1 dwarf Gl 229A. These new data increase by factors of 0. 6 and 1.6, respectively, the numbers of ultracool dwarfs T (sub eff)

Northern sky variability survey: public data release

Abstract: The Northern Sky Variability Survey (NSVS) is a temporal record of the sky over the optical magnitude range from 8 to 15.5. It was conducted in the course of the first-generation Robotic Optical Transient Search Experiment (ROTSE-I) using a robotic system of four comounted unfiltered telephoto lenses equipped with CCD cameras. The survey was conducted from Los Alamos, New Mexico, and primarily covers the entire northern sky. Some data in southern fields between declinations 0° and -38° are also available, although with fewer epochs and noticeably lesser quality. The NSVS contains light curves for approximately 14 million objects. With a 1 yr baseline and typically 100–500 measurements per object, the NSVS is the most extensive record of stellar variability across the bright sky available today. In a median field, bright unsaturated stars attain a point-to-point photometric scatter of ~0.02 mag and position errors within 2''. At Galactic latitudes |b| < 20°, the data quality is limited by severe blending due to the ~14'' pixel size. We present basic characteristics of the data set and describe data collection, analysis, and distribution. All NSVS photometric measurements are available for on-line public access from the Sky Database for Objects in Time-Domain (SkyDOT) at Los Alamos National Laboratory. Copies of the full survey photometry may also be requested on tape.

A Survey of z > 5.7 Quasars in the Sloan Digital Sky Survey. IV. Discovery of Seven Additional Quasars* **

Abstract: The authors present the discovery of seven quasars at z > 5.7, selected from {approx} 2000 deg{sup 2} of multicolor imaging data of the Sloan Digital Sky Survey (SDSS). The new quasars have redshifts z from 5.79 to 6.13. Five are selected as part of a complete flux-limited sample in the SDSS Northern Galactic Cap; two have larger photometric errors and are not part of the complete sample. One of the new quasars, SDSS J1335+3533 (z = 5.93), exhibits no emission lines; the 3-{sigma} limit on the rest-frame equivalent width of Ly{alpha}+NV line is 5 {angstrom}. It is the highest redshift lineless quasar known, and could be a gravitational lensed galaxy, a BL Lac object or a new type of quasar. Two new z > 6 quasars, SDSS 1250+3130 (z = 6.13) and SDSS J1137+3549 (z = 6.01), show deep Gunn-Peterson troughs in Ly{alpha}. These troughs are narrower than those observed among quasars at z > 6.2 and do not have complete Ly{beta} absorption.

The Size Distribution of Trans-Neptunian Bodies*

Abstract: We search 0.02 deg 2 of the invariable plane for trans-Neptunian objects (TNOs) 25 AU or more distant using the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope. With 22 ks per pointing, the search is more than 50% complete for m606W � 29:2. Three new objects are discovered, the faintest with mean magnitude m ¼ 28:3 (diameter � 25 km), which is 3 mag fainter than any previously well-measured solar system body. Each new discovery is verified with a follow-up 18 ks observation with the ACS, and the detection efficiency is verified with implanted objects. The three detections are a factor of � 25 less than would be expected under extrapolation of the power-law differential sky density for brighter objects, � (m) � dN=dmd� / 10 � m with � � 0:63. Analysis of the ACS data and recent TNO surveys from the literature reveals departures from this power law at both the bright and faint ends. Division of the TNO sample by distance and inclination into ‘‘classical Kuiper belt’’ (CKB) and ‘‘Excited’’ samples reveals that � (m) differs for the two populations at 96% confidence, and both samples show departures from power-law behavior. A double power-law � (m) adequately fits all data. Implications of these departures include the following: (1) The total mass of the ‘‘classical’’ Kuiper belt is � 0.010 M� , only a few times Pluto’s mass, and is predominantly in the form of � 100 km bodies (barring a secondary peak in the mass distribution at sub‐10 km sizes). The mass of Excited objects is perhaps a few times larger. (2) The Excited class has a shallower bright-end magnitude (and, presumably, size) distribution; the largest objects, including Pluto, make up tens of percent of the total mass whereas the largest CKB objects are only � 2% of its mass. (3) The derived size distributions predict that the largest Excited body should be roughly the mass of Pluto, and the largest CKB body should have mR � 20—hence, Pluto is feasibly considered to have originated from the same physical process as the Excited TNOs. (4) The observed deficit of small TNOs occurs in the size regime where present-day collisions are expected to be disruptive, suggesting extensive depletion by collisions. The Excited and CKB size distributions are qualitatively similar to some numerical models of growth and erosion, with both accretion and erosion appearing to have proceeded to more advanced stages in the Excited class than in the CKB. (5) The lack of detections of distant TNOs implies that if a mass of TNOs comparable to the CKB is present near the invariable plane beyond 50 AU, that distant population must be composed primarily of bodies smaller than � 40 km. (6) There are too few small CKB objects for this population to be the reservoir of Jupiter-family comet precursors without a significant upturn in the population at diameters under 20 km. With optimistic model parameters and extrapolations, the Excited population could be the source reservoir. Implications of these discoveries for the formation and evolution of the outer solar system are discussed.

The Mass Accretion Rates of Intermediate-Mass T Tauri Stars

Abstract: We present Hubble Space Telescope ultraviolet spectra and supporting ground-based data for a sample of nine intermediate-mass T Tauri stars (IMTTSs; 1.5–4 M⊙). The targets belong to three star-forming regions: T Tau, SU Aur, and RY Tau in the Taurus clouds; EZ Ori, P2441, and V1044 Ori in the Ori OB1c association surrounding the Orion Nebula cluster; and CO Ori, GW Ori, and GX Ori in the ring around λ Ori. The supporting ground-based observations include nearly simultaneous UBV(R I)C photometry, 6 A resolution spectra covering the range 3900–7000 A, optical echelle observations in the range 5800–8600 A, and K-band near-infrared spectra. We use these data to determine improved spectral types and reddening corrections and to obtain physical parameters of the targets. We find that an extinction law with a weak 2175 A feature but high values of AUV/AV is required to explain the simultaneous optical-UV data; the reddening laws for two B-type stars located behind the Taurus clouds, HD 29647 and HD 283809, meet these properties. We argue that reddening laws with these characteristics may well be representative of cold, dense molecular clouds. Spectral energy distributions and emission-line profiles of the IMTTSs are consistent with expectations from magnetospheric accretion models. We compare our simultaneous optical-UV data with predictions from accretion shock models to get accretion luminosities and mass accretion rates () for the targets. We find that the average mass accretion rate for IMTTSs is ~3 × 10-8 M⊙ yr-1, a factor of ~5 higher than that for their low-mass counterparts. The new data extend the correlation between and stellar mass to the intermediate-mass range. Since the IMTTSs are evolutionary descendants of the Herbig Ae/Be stars, our results put limits to the mass accretion rates of their disks. We present luminosities of the UV lines of highly ionized metals and show that they are well above the saturation limit for magnetically active cool stars but correlate strongly with accretion luminosity, indicating that they are powered by accretion, in agreement with previous claims but using a sample in which reddening and accretion luminosities have been determined self-consistently. Finally, we find that the relation between accretion luminosity and Brγ luminosity found for low-mass T Tauri stars extends to the intermediate-mass regime.

Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program

Abstract: We present preliminary trigonometric parallaxes and proper motions for 22 L dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager on the US naval Observatory (USNO) 1.55 m Strand Astrometric Reflector. The results presented here are based on observations obtained between 2000 September and 2002 November; about half of the objects have an observational time baseline of t 1:3 yr and half t 2:0 yr. Despite these short time baselines, the astrometric quality is sufficient to produce significant new results, especially for the nearer T dwarfs. Seven objects are in common with the USNO optical CCD parallax program for quality control and seven in common with the European Southern Observatory 3.5 m New Technology Telescope parallax program. We compare astrometric quality with both of these programs. Relative to absolute parallax corrections are made by employing Two Micron All Sky Survey and/or Sloan Digital Sky Survey photometry for reference-frame stars. We combine USNO infrared and optical parallaxes with the best available California Institute of Technology (CIT) system photometry to determine MJ , MH, and MK values for 37 L dwarfs between spectral types L0 and L8 and 19 T dwarfs between spectral types T0.5 and T8 and present selected absolute magnitude versus spectral type and color diagrams, based on these results. Luminosities and temperatures are estimated for these objects. Of special interest are the distances of several objects that are at or near the L-T dwarf boundary so that this important transition can be better understood. The previously reported early to mid T dwarf luminosity excess is clearly confirmed and found to be present at J, H, and K. The large number of objects that populate this luminosity-excess region indicate that it cannot be due entirely to selection effects. The T dwarf sequence is extended to MJ 16:9 by 2MASS J041519 0935, which, at d 5:74 pc, is found to be the lluminous LOG (L=L )pa

The Star Formation History of the Small Magellanic Cloud

Abstract: We present the spatially resolved star formation and chemical enrichment history of the Small Magellanic Cloud (SMC) across the entire central 4° × 45 area of the main body, based on UBVI photometry from our Magellanic Clouds Photometric Survey. We find that (1) approximately 50% of the stars that ever formed in the SMC formed prior to 8.4 Gyr ago (z > 1.2 for WMAP cosmology); (2) the SMC formed relatively few stars between 8.4 and 3 Gyr ago; (3) there was a rise in the mean star formation rate during the most recent 3 Gyr punctuated by "bursts" at ages of 2.5, 0.4, and 0.06 Gyr; (4) the bursts at 2.5 and 0.4 Gyr are temporally coincident with past perigalactic passages of the SMC with the Milky Way; (5) there is preliminary evidence for a large-scale annular structure in the 2.5 Gyr burst; and (6) the chemical enrichment history derived from our analysis is in agreement with the age-metallicity relation of the SMC's star clusters. Consistent interpretation of the data required an ad hoc correction of 0.1–0.2 mag to the B-V colors of 25% of the stars; the cause of this anomaly is unknown, but we show that it does not strongly influence our results.

[O II] as a Star Formation Rate Indicator

Abstract: We investigate the [O II] emission line as a star formation rate (SFR) indicator using integrated spectra of 97 galaxies from the Nearby Field Galaxies Survey (NFGS). The sample includes all Hubble types and contains SFRs ranging from 0.01 to 100 M⊙ yr-1. We compare the Kennicutt [O II] and Hα SFR calibrations and show that there are two significant effects that produce disagreement between SFR([O II]) and SFR(Hα): reddening and metallicity. Differences in the ionization state of the interstellar medium do not contribute significantly to the observed difference between SFR([O II]) and SFR(Hα) for the NFGS galaxies with metallicities log (O/H) + 12 8.5. The Kennicutt [O II]-SFR relation assumes a typical reddening for nearby galaxies; in practice, the reddening differs significantly from sample to sample. We derive a new SFR([O II]) calibration that does not contain a reddening assumption. Our new SFR([O II]) calibration also provides an optional correction for metallicity. Our SFRs derived from [O II] agree with those derived from Hα to within 0.03–0.05 dex. We show that the reddening, E(B-V), increases with intrinsic (i.e., reddening-corrected) [O II] luminosity for the NFGS sample. We apply our SFR([O II]) calibration with metallicity correction to two samples: high-redshift 0.8 < z < 1.6 galaxies from the NICMOS Hα survey and 0.5 < z < 1.1 galaxies from the Canada-France Redshift Survey. The SFR([O II]) and SFR(Hα) for these samples agree to within the scatter observed for the NFGS sample, indicating that our SFR([O II]) relation can be applied to both local and high-z galaxies. Finally, we apply our SFR([O II]) to estimates of the cosmic star formation history. After reddening and metallicity corrections, the star formation rate densities derived from [O II] and Hα agree to within ~30%.

Spectroscopic properties of cool stars in the sloan digital sky survey: an analysis of magnetic activity and a search for subdwarfs

Abstract: We present a spectroscopic analysis of nearly 8000 late-type dwarfs in the Sloan Digital Sky Survey. Using the Hα emission line as an activity indicator, we investigate the fraction of active stars as a function of spectral type and find a peak near type M8, confirming previous results. In contrast to past findings, we find that not all M7–M8 stars are active. We show that this may be a selection effect of the distance distributions of previous samples, since the active stars appear to be concentrated near the Galactic plane. We also examine the activity strength (ratio of the luminosity emitted in Hα to the bolometric luminosity) for each star and find that the mean activity strength is constant over the range M0–M5 and declines at later types. The decline begins at a slightly earlier spectral type than previously found. We explore the effect that activity has on the broadband photometric colors and find no significant differences between active and inactive stars. We also carry out a search for subdwarfs using spectroscopic metallicity indicators and find 60 subdwarf candidates. Several of these candidates are near the extreme subdwarf boundary. The spectroscopic subdwarf candidates are redder by ~0.2 mag in g-r compared with disk dwarfs at the same r-i color.

A Deep Wide-Field, Optical, and Near-Infrared Catalog of a Large Area around the Hubble Deep Field North*

Abstract: We have conducted a deep multicolor imaging survey of 0.2 deg2 centered on the Hubble Deep Field North (HDF-N). We shall refer to this region as the Hawaii HDF-N. Deep data were collected in U, B, V, R, I, and z' bands over the central 0.2 deg2 and in HK' over a smaller region covering the Chandra Deep Field North. The data were reduced to have accurate relative photometry and astrometry across the entire field to facilitate photometric redshifts and spectroscopic follow-up. We have compiled a catalog of 48,858 objects in the central 0.2 deg2 detected at 5 σ significance in a 3'' aperture in either R or z' band. Number counts and color-magnitude diagrams are presented and shown to be consistent with previous observations. Using color selection we have measured the density of objects at 3 5.5 using the Lyman break technique suffer from more contamination by low-redshift objects than suggested by previous studies.

A Subaru Search for Lyα Blobs in and around the Protocluster Region At Redshift z = 3.1

Abstract: We report the properties of 35 robust candidate Lyα blobs (LABs), which are larger than 16 arcsec2 in isophotal area and brighter than 0.7 × 10-16 ergs s-1 cm-2, located in and around the protocluster region at redshift z = 3.1 discovered by Steidel et al. in the SSA22 field, based on wide-field (31' × 23') and deep narrowband (NB497; 4977 A, FWHM 77 A) and broadband (B, V, and R) images taken with the prime-focus camera on the Subaru Telescope. The two previously known giant LABs are the most luminous and the largest in our survey volume of 1.3 × 105 Mpc3. We reveal the internal structures of the two giant LABs and discover some bubble-like features, which suggest that intensive starburst and galactic superwind phenomena occurred in these objects in the past. The other 33 LABs have isophotal areas of ~16–78 arcsec2 and flux of (0.7–7) × 10-16 ergs s-1 cm-2. These 35 LABs show a continuous distribution of isophotal area and emission-line flux. The distributions of average surface brightness and morphology are widespread from relatively compact high surface brightness objects to very diffuse low surface brightness ones. The physical origins of these LABs may be (1) photoionization by massive stars or active galactic nuclei, or (2) cooling radiation from gravitationally heated gas, or (3) shock heating by starburst-driven galactic superwind. One-third of the LABs are apparently not associated with ultraviolet continuum sources that are bright enough to produce Lyα emission, assuming a Salpeter initial mass function. Of these LABs 90% are located inside the high surface density region of the 283 relatively compact and strong Lyα emitters selected in our previous study. This suggests that these LABs may be phenomena related to a dense environment at high redshift.

The 2MASS Wide-Field T Dwarf Search. III. Seven New T Dwarfs and Other Cool Dwarf Discoveries

Abstract: We present the discovery of seven new T dwarfs identified in the Two Micron All Sky Survey. Low-resolution (R � 150) 0.8‐2.5 � m spectroscopy obtained with the Infrared Telescope Facility (IRTF) SpeX instrument reveals the characteristic H2 Oa nd CH4 bands in the spectra of these brown dwarfs. Comparison with spectral standards observed with the same instrument enables us to derive classifications of T3 to T7 for the objects in this sample. Moderate-resolution (R � 1200) near-infrared spectroscopy for a subset of these discoveries reveal K i line strengths consistent with previously observed trends with spectral type. Follow-up imaging observations provide proper-motion measurements for these sources, ranging from less than 0B 1t o 1B55 yr � 1 . One object, 2MASS 0034+0523, has a spectrophotometric distance placing it within 10 pc of the Sun. This source also exhibits a depressed K-band peak reminiscent of the peculiar T dwarf 2MASS 0937+2931 and may be a metal-poor or old, high-mass brown dwarf. We also present low-resolution SpeX data for a set of M- and L-type dwarf, subdwarf, and giant comparison stars used to classify 59 additional candidates identified as background stars. These are primarily M5‐M8.5 dwarfs, many exhibiting H i Pa� , but include three candidate ultracool M subdwarfs and one possible early-type L subdwarf.

VLA H I Observations of Gas Stripping in the Virgo Cluster Spiral NGC 4522

Abstract: We present VLA H I observations at ~20'' 1.5 kpc resolution of the highly inclined, H I–deficient Virgo Cluster spiral galaxy NGC 4522, which is one of the clearest and nearest cases of ongoing intracluster medium–interstellar medium (ICM-ISM) stripping. H I is abundant and spatially coincident with the stellar disk in the center, but beyond R = 3 kpc the H I distribution in the disk is sharply truncated, and the only H I is extraplanar and all on the northwest side. Forty percent of the total H I, corresponding to 1.5 × 108 M⊙, is extraplanar and has likely been removed from the galaxy disk by an ICM-ISM interaction. The kinematics and the morphology of the H I appear more consistent with ongoing stripping and less consistent with gas fall-back, which may occur long after peak pressure. Some of the extraplanar gas has line widths (FWZI) of 150 km s-1, including a blueshifted tail of weaker emission, and much of the extraplanar gas exhibits a modest net blueshift with respect to the galaxy's disk rotational velocities, consistent with gas accelerated toward the mean cluster velocity. The southwest side of the galaxy has less H I in the disk but more H I in the halo, suggesting more effective gas removal on the side of the galaxy that is rotating into the ICM wind. In recent simulations of ICM-ISM interactions large surface densities of extraplanar gas like that in NGC 4522 are seen at relatively early stages of active stripping and not during later gas fall-back stages. The galaxy is 33 800 kpc from M87, somewhat outside the region of strongest cluster X-ray emission. The ram pressure at this location, assuming a static smooth ICM and standard values for ICM density and galaxy velocity, appears inadequate to cause the observed stripping. We consider the possibility that the ram pressure is significantly stronger than standard values, because of large bulk motions and local density enhancements of the ICM gas, which may occur in a dynamic, shock-filled ICM experiencing subcluster merging. The H I and Hα distributions are similar, with both truncated in the disk at the same radius and H II regions located throughout much of the extraplanar H I. This implies that the star-forming molecular ISM has been effectively stripped from the outer disk of the galaxy along with the H I. The inferred peak stripping rate of ~10 M⊙ yr-1 is much larger than the galaxy's total star formation rate of ~0.1 M⊙ yr-1, implying that the rate of triggered star formation due to ICM pressure is presently minor compared with the rate of gas lost as a result of stripping.

The Team Keck Treasury Redshift Survey of the GOODS-North Field

Abstract: We report the results of an extensive imaging and spectroscopic survey in the Great Observatories Origins Deep Survey (GOODS)-North field completed using DEIMOS on the Keck II telescope. Observations of 2018 targets in a magnitude-limited sample of 2911 objects to RAB = 24.4 yield secure redshifts for a sample of 1440 galaxies and active galactic nuclei (AGNs) plus 96 stars. In addition to redshifts and associated quality assessments, our catalog also includes photometric and astrometric measurements for all targets detected in our R-band imaging survey of the GOODS-North region. We investigate various sources of incompleteness and find the redshift catalog to be 53% complete at its limiting magnitude. The median redshift of z = 0.65 is lower than in similar deep surveys because we did not select against low-redshift targets. Comparison with other redshift surveys in the same field, including a complementary Hawaii-led DEIMOS survey, establishes that our velocity uncertainties are as low as σ ≈ 40 km s-1 for red galaxies and that our redshift confidence assessments are accurate. The distributions of rest-frame magnitudes and colors among the sample agree well with model predictions out to and beyond z = 1. We will release all survey data, including extracted one-dimensional and sky-subtracted two-dimensional spectra, thus providing a sizable and homogeneous database for the GOODS-North field, which will enable studies of large-scale structure, spectral indices, internal galaxy kinematics, and the predictive capabilities of photometric redshifts.

Star Formation Properties of a Large Sample of Irregular Galaxies

Abstract: We present the results of Hα imaging of a large sample of irregular galaxies. Our sample includes 94 galaxies with morphological classifications of Im, 26 blue compact dwarfs (BCDs), and 20 Sm systems. The sample spans a large range in galactic parameters, including integrated absolute magnitude (MV of -9 to -19), average surface brightness (20–27 mag arcsec-2), current star formation activity (0–1.3 M⊙ yr-1 kpc-2), and relative gas content (0.02–5 M⊙/LB). The Hα images were used to measure the integrated star formation rates, determine the extents of star formation in the disks, and compare azimuthally averaged radial profiles of current star formation to older starlight. The integrated star formation rates of Im galaxies normalized to the physical size of the galaxy span a range of a factor of 104 with 10% Im galaxies and one Sm system having no measurable star formation at the present time. The BCDs fall, on average, at the high star formation rate end of the range. We find no correlation between star formation activity and proximity to other cataloged galaxies. Two galaxies located in voids are similar in properties to the Sm group in our sample. The H II regions in these galaxies are most often found within the Holmberg radius RH, although in a few systems H II regions are traced as far as 1.7RH. Similarly, most of the star formation is found within three disk scale lengths RD, but in some galaxies H II regions are traced as far as 6RD. A comparison of Hα surface photometry with V-band surface photometry shows that the two approximately follow each other with radius in Sm galaxies, but in most BCDs there is an excess of Hα emission in the centers that drops with radius. In approximately half of the Im galaxies Hα and V correspond well, and in the rest there are small to large differences in the relative rate of falloff with radius. The cases with strong gradients in the LHα/LV ratios and with high central star formation rate densities, which include most of the BCDs, require a significant fraction of their gas to migrate to the center in the last gigayear. We discuss possible torques that could have caused this without leaving an obvious signature, including dark matter bars and past interactions or mergers with small galaxies or H I clouds. There is now a substantial amount of evidence for these processes among many surveys of BCDs. We note that such gas migration will also increase the local pressure and possibly enhance the formation of massive dense clusters but conclude that the star formation process itself does not appear to differ much among BCD, Im, and Sm types. In particular, there is evidence in the distribution function for Hα surface brightness that the turbulent Mach numbers are all about the same in these systems. This follows from the Hα distribution functions corrected for exponential disk gradients, which are log-normal with a nearly constant dispersion. Thus, the influence of shock-triggered star formation is apparently no greater in BCDs than in Im and Sm types.

Spectral Analysis and Classification of Herbig Ae/Be Stars

Abstract: We present an analysis of the optical spectra of 75 early-type emission-line stars, many of which have been classified previously as Herbig Ae/Be (HAeBe) stars. Accurate spectral types were derived for 58 members of the sample; high continuum veiling, contamination by nonphotospheric absorption features, or a composite binary spectrum prevented accurate spectral typing for the rest. Approximately half of our sample exhibited [O I] λ6300 forbidden-line emission down to our detection limit of 0.1 A equivalent width; a third of the sample exhibited Fe II emission (multiplet 42). A subset of 11 of the HAeBe sample showed abnormally strong Fe II absorption; 75% of this subset are confirmed UX Ori objects. Combining our spectral typing results with photometry from the literature, we confirm previous findings of high values of total-to-selective extinction (RV ~ 5) in our larger sample, suggesting significant grain growth in the environments of HAeBe stars. With this high value of RV, the vast majority of HAeBe stars appear younger than with the standard RV = 3.1 extinction law and are more consistent with being pre–main-sequence objects.

An Improved Proper-Motion Catalog Combining USNO-B and the Sloan Digital Sky Survey

Abstract: An improved proper-motion catalog is presented, combining the USNO-B and Sloan Digital Sky Survey (SDSS) catalogs in the area of sky covered by SDSS Data Release 1 (DR1; 2099 deg2). USNO-B positions are recalibrated using SDSS galaxies, and proper motions are recomputed including both the USNO-B and SDSS positions. Statistical errors in the USNO-B proper motions are decreased by roughly 20%?30%, systematic errors are greatly reduced, and the proper motions are placed on an absolute reference frame. Requiring a match to an SDSS object removes the large number of false high proper motion objects in USNO-B. The resultant catalog is 90% complete to g < 19.7, with statistical errors in the component proper motions of roughly 3?3.5 mas yr-1, substantially smaller systematic errors, and a contamination rate of less than 0.5%. A number of studies are currently underway using proper motions from this catalog. The catalog is available via ftp.

The fall of active galactic nuclei and the rise of star-forming galaxies: A close look at the Chandra Deep Field X-ray number counts

Abstract: We investigate the X-ray number counts in the 1?2 Ms Chandra Deep Fields (CDFs) to determine the contributions of faint X-ray source populations to the extragalactic X-ray background (XRB). X-ray sources were separated into active galactic nuclei (AGNs), star-forming galaxies, and Galactic stars primarily on the basis of their X-ray?to?optical flux ratios, optical spectral classifications, X-ray spectra, and intrinsic X-ray luminosities. Number count slopes and normalizations below 2 ? 10-15 ergs cm-2 s-1 were calculated in each band for all source types assuming a single power-law model. We find that AGNs continue to dominate the number counts in the 0.5?2.0 and 2?8 keV bands. At flux limits of ?2.5 ? 10-17 ergs cm-2 s-1 (0.5?2.0 keV) and ?2.0 ? 10-16 ergs cm-2 s-1 (2?8 keV), the overall AGN source densities are 7166 and 4558 sources deg-2, respectively; these are factors of ~10?20 higher than those found in the deepest optical spectroscopic surveys. Although still a minority, the number counts of star-forming galaxies climb steeply, such that they eventually achieve source densities of 1727 sources deg-2 (0.5?2.0 keV) and 711 sources deg-2 (2?8 keV) at the CDF flux limits. The number of star-forming galaxies will likely overtake the number of AGNs at ~1 ? 10-17 ergs cm-2 s-1 (0.5?2.0 keV) and dominate the overall number counts thereafter. Adopting XRB flux densities of (7.52 ? 0.35) ? 10-12 ergs cm-2 s-1 deg-2 for 0.5?2.0 keV and (1.79 ? 0.11) ? 10-11 ergs cm-2 s-1 deg-2 for 2?8 keV, the CDFs resolve a total of 89.5 percent and 92.6 percent of the extragalactic 0.5?2.0 and 2?8 keV XRBs, respectively. AGNs as a whole contribute ?83% and ?95% to these resolved XRB fractions, respectively, whereas star-forming galaxies comprise only ?3% and ?2%, respectively, and Galactic stars comprise the remainder. Extrapolation of the number count slopes can easily account for the entire 0.5?2.0 and 2?8 keV XRBs to within statistical errors. We also examine the X-ray number counts as functions of intrinsic X-ray luminosity and absorption, finding that sources with L0.5?8 keV > 1043.5 ergs s-1 and NH < 1022 cm-2 are the dominant contributors to the 0.5?2.0 keV XRB flux density, whereas sources with L0.5?8 keV = 1042.5?1044.5 ergs s-1 and a broad range of absorption column densities primarily contribute to the 2?8 keV XRB flux density. This trend suggests that even less intrinsically luminous, more highly obscured AGNs may dominate the number counts at higher energies, where the XRB intensity peaks. Finally, we revisit the reported differences between the CDF-North and CDF-South number counts, finding that the two fields are consistent with each other except for sources detected at 2?8 keV below F2?8 keV ? 1 ? 10-15 ergs cm-2 s-1, for which deviations gradually increase to ?3.9 ?.

The Gemini Deep Deep Survey. I. Introduction to the Survey, Catalogs, and Composite Spectra

Abstract: The Gemini Deep Deep Survey (GDDS) is an ultradeep (K < 20.6 mag, I < 24.5 mag) redshift survey targeting galaxies in the "redshift desert" between z=1 and z=2. The primary goal of the survey is to constrain the space density at high redshift of evolved high-mass galaxies. We obtained 309 spectra in four widely separated 30 arcmin2 fields using the Gemini North telescope and the Gemini Multi-Object Spectrograph (GMOS). The spectra define a one-in-two sparse sample of the reddest and most luminous galaxies near the I-K versus I color-magnitude track mapped out by passively evolving galaxies in the redshift interval 0.8 < z < 1.8. This sample is augmented by a one-in-seven sparse sample of the remaining high-redshift galaxy population. The GMOS spectrograph was operating in a nod-and-shuffle mode, which enabled us to remove sky contamination with high precision, even for typical exposures times of 20–30 hr per field. The resulting spectra are the deepest ever obtained. In this paper we present our sample of 309 spectra, along with redshifts, identifications of spectral features, and photometry. This makes the GDDS the largest and most complete infrared-selected survey probing the redshift desert. The seven-band (VRIzJHKs) photometry is taken from the Las Campanas Infrared Survey. The infrared selection means that the GDDS is observing not only star-forming galaxies, as in most high-redshift galaxy surveys, but also quiescent evolved galaxies. In our sample we have obtained 225 secure redshifts, 167 of which are in the redshift interval 0.8 < z < 2. About 25% of these show clear spectral signatures of evolved (pure old, or old + intermediate-age) stellar populations, while 35% show features consistent with either a pure intermediate-age or a young + intermediate-age stellar population. About 29% of the galaxies in the GDDS at 0.8 < z < 2 are young starbursts with strong interstellar lines. A few galaxies show very strong poststarburst signatures. Another 55 objects have less secure redshifts, 31 of which lie in the redshift interval 0.8 < z < 2. The median redshift of the whole GDDS sample is z = 1.1. Spectroscopic completeness varies from a low of ~70% for red galaxies to greater than 90% for blue galaxies. In this paper we also present, together with the data and catalogs, a summary of the criteria for selecting the GDDS fields, the rationale behind our mask designs, an analysis of the completeness of the survey, and a description of the data reduction procedures used. All data from the GDDS are publicly available.

The Galaxy-Mass Correlation Function Measured from Weak Lensing in the Sloan Digital Sky Survey

Abstract: We present galaxy-galaxy lensing measurements over scales 0.025 to 10 h-1 Mpc in the Sloan Digital Sky Survey (SDSS). Using a flux-limited sample of 127,001 lens galaxies with spectroscopic redshifts and mean luminosity L ~ L* and 9,020,388 source galaxies with photometric redshifts, we invert the lensing signal to obtain the galaxy-mass correlation function ξgm. We find ξgm is consistent with a power law, ξgm = (r/r0)-γ, with best-fit parameters γ = 1.79 ± 0.06 and r0 = (5.4 ± 0.7)(0.27/Ωm)1/γ h-1 Mpc. At fixed separation, the ratio ξgg/ξgm = b/r, where b is the bias and r is the correlation coefficient. Comparing with the galaxy autocorrelation function for a similarly selected sample of SDSS galaxies, we find that b/r is approximately scale-independent over scales 0.2–6.7 h-1 Mpc, with mean b/r = (1.3 ± 0.2)(Ωm/0.27). We also find no scale dependence in b/r for a volume-limited sample of luminous galaxies (-23.0 < Mr < -21.5). The mean b/r for this sample is b/rVlim = (2.0 ± 0.7)(Ωm/0.27). We split the lens galaxy sample into subsets based on luminosity, color, spectral type, and velocity dispersion and see clear trends of the lensing signal with each of these parameters. The amplitude and logarithmic slope of ξgm increase with galaxy luminosity. For high luminosities (L ~ 5 L*), ξgm deviates significantly from a power law. These trends with luminosity also appear in the subsample of red galaxies, which are more strongly clustered than blue galaxies.

Spectral Classification of Quasars in the Sloan Digital Sky Survey: Eigenspectra, Redshift, and Luminosity Effects

Abstract: We study 16,707 quasar spectra from the Sloan Digital Sky Survey (SDSS) (an early version of the First Data Release; DR1) using the Karhunen-Loeve transform (or principal components analysis). The redshifts of these quasars range from 0.08 to 5.41, the i-band absolute magnitudes from -30 to -22, and the resulting rest-frame wavelengths from 900 to 8000 A. The quasar eigenspectra of the full catalog reveal the following: first order—the mean spectrum; second order—a host-galaxy component; third order—the UV-optical continuum slope; fourth order—the correlations of Balmer emission lines. These four eigenspectra account for 82% of the total sample variance. Broad absorption features are found not to be confined in one particular order but to span a number of higher orders. We find that the spectral classification of quasars is redshift and luminosity dependent; as such there does not exist a compact set (i.e., less than ≈10 modes) of eigenspectra (covering 900–8000 A) that can describe most variations (i.e., greater than ≈95%) of the entire catalog. We therefore construct several sets of eigenspectra in different redshift and luminosity bins. From these eigenspectra we find that quasar spectra can be classified (by the first two eigenspectra) into a sequence that is defined by a simple progression in the steepness of the slope of the continuum. We also find a dependence on redshift and luminosity in the eigencoefficients. The dominant redshift effect is a result of the evolution of the blended Fe II emission (optical) and the Balmer continuum (the "small bump," λrest ≈ 2000–4000 A). A luminosity dependence is also present in the eigencoefficients and is related to the Baldwin effect—the decrease of the equivalent width of an emission line with luminosity, which is detected in Lyα, Si IV+O IV], C IV, He II, C III] and Mg II, while the effect in N V seems to be redshift dependent. If we restrict ourselves to the rest-wavelength regions 1150–2000 A and 4000–5500 A, the eigenspectra constructed from the wavelength-selected SDSS spectra are found to agree with the principal components by Francis et al. and the well-known "Eigenvector-1" of Boroson & Green, respectively. ASCII formatted tables of the eigenspectra are available.

New Cepheid Period-Luminosity Relations for the Large Magellanic Cloud: 92 Near-Infrared Light Curves

Abstract: Near-infrared J, H, and Ks photometric measurements of 92 Cepheids in the Large Magellanic Cloud are presented. The stars are spread over the face of the Cloud, their periods range from 3 to 100 days, and their light curves are sampled at an average of 22 phase points per star. The intensity-weighted mean magnitudes and colors define period-luminosity-color (PL or PLC) relations whose uncertainties due to differential metal abundance and reddening/extinction effects are minimal. The dispersions in the infrared PL, PLC, and extinction-free period-Wesenheit relations are extremely small, amounting to less than 0.10 mag (or 5% in distance). The orientation of the disk plane of the sample (inclination angle and line of nodes) agrees well with the 2001 results of van der Marel & Cioni. The PL and PLC fits are the best-determined such relationships yet found for any sample of Cepheids and establish a calibration that can be used to precisely anchor ground- and space-based near-infrared Cepheid data to external galaxies, as well as back to Cepheid calibrators in the Galaxy. As an example, we use the 1998 Galactic Cepheid calibration of Gieren and coworkers to obtain the distance modulus to the centroid of our LMC sample. The true modulus of the LMC is thus determined to be 18.50 ± 0.05 mag. Currently, the dominant source of uncertainty in this number is the scatter in the Galactic calibrator sample. The PLC fits and dispersions and the dependence of the PLC on metal abundance are compared with theoretical versions computed from the 1999 work of Alibert and coworkers. Overall, the agreement is excellent, indicating that at near-infrared wavelengths the slope and dispersion of the PLC depend very weakly on metal abundance. The shift in the JHK PLC relations is ~0.02 mag for a change in metal abundance from solar to one-half solar.

Dust Reddening in Sloan Digital Sky Survey Quasars

Abstract: We explore the form of extragalactic reddening toward quasars using a sample of 9566 quasars with redshifts 0 0.1, and less than 1% have EB-V > 0.2, where the extinction is relative to quasars with modal colors. Reddening is uncorrelated with the presence of intervening narrow-line absorption systems, but reddened quasars are much more likely to show narrow absorption at the redshift of the quasar than are unreddened quasars. Thus the reddening toward quasars is dominated by SMC-like dust at the quasar redshift.

Large-Scale Structure of Emission-Line Galaxies at z = 3.1*

Abstract: We obtained a deep wide-field (32' ? 24') narrowband (?c = 4977?,?? = 77?) image of a field including the protocluster at z = 3.1 in the SSA22a field studied by Steidel et al. using the Subaru Telescope. The field we observed is about 10 times as large as that studied by Steidel et al. We detected 283 highly confident strong Ly? emitter candidates at z ~ 3.1 down to 25.8 AB mag with the observed equivalent width larger than 154 ?. These strong Ly? emitter candidates show a highly nonuniform distribution with the beltlike region of high surface density, which is found to extend over ~60 Mpc in comoving scale. The average number density of the strong Ly? emitter candidates in this high-density region is 3 times as high as that of a blank field. The probability of finding such a large-scale high-density peak is as small as 0.1% in the context of the CDM structure formation scenario, if we assume a linear bias parameter b ~ 4. In addition to these strong Ly? emitters, we also detected 49 Ly? absorbers, which show significant deficit in the narrowband image. We further detected 74 extended emitters, which have significant fluxes over the areas of 18 arcsec2 or more. Interestingly, both these absorbers and extended emitters show sky distributions very similar to that of the strong Ly? emitters. This supports the reality of the large-scale structure at z = 3.1 and suggests that galaxy formation preferentially occurs in the high-density region of strong Ly? emitters.