A New Orientation Indicator for Radio-Quiet Quasars

The velocities of the [O III] 5007 and optical Fe II emission lines, measured relative to the systemic redshifts of 2265 QSOs by Hu et al. (2008), show the signature of a disklike BLR structure with polar outflows. Objects with large [O III] outflows show no Fe II offset velocity and are seen pole-on. Objects with large Fe II inflow show no [O III] offset velocity and are seen edge-on. This interpretation is supported by the morphology of the radio-loud objects within the sample and by previous determinations of the geometry of the broad and narrow line regions. Analysis of the objects with neither Fe II or [O III] velocity offsets, however, show that the two groups also differ in Eddington ratio, and, within this subset, corresponding groups with high and low Eddington ratio but with the opposite orientation can be identified. Using these four subsets of the sample, the effects of orientation and Eddington ratio can be separated, and, in some cases, quantified. The changes in apparent continuum luminosity and broad H-beta width and strength suggest a model in which both continuum and H-beta are emitted from the surface of the disk, which is less flattened in high Eddington ratio objects. The effects of orientation on the derived properties, black hole mass and Eddington ratio, are significant, though not large. The [O III] outflow appears to influence the width of that line, as well as its centroid.Comment: 8 pages, 2 figures, 1 table, accepted for publication in ApJ Letter

Detection of a Dipole in the Handedness of Spiral Galaxies with Redshifts z ~ 0.04

A preference for spiral galaxies in one sector of the sky to be left-handed or right-handed spirals would indicate a parity violating asymmetry in the overall universe and a preferred axis. This study uses 15158 spiral galaxies with redshifts <0.085 from the Sloan Digital Sky Survey. An unbinned analysis for a dipole component that made no prior assumptions for the dipole axis gives a dipole asymmetry of -0.0408\pm0.011 with a probability of occurring by chance of 7.9 x 10-4. A similar asymmetry is seen in the Southern Galaxy spin catalog of Iye and Sugai. The axis of the dipole asymmetry lies at approx. (l, b) =(52{\deg}, 68.5{\deg}), roughly along that of our Galaxy and close to alignments observed in the WMAP cosmic microwave background distributions. The observed spin correlation extends out to separations ~210 Mpc/h, while spirals with separations < 20 Mpc/h have smaller spin correlations.Comment: To be published in Physics Letters

Photometric Response Functions of the SDSS Imager

The monochromatic illumination system is constructed to carry out in situ measurements of the response function of the mosaicked CCD imager used in the Sloan Digital Sky Survey (SDSS). The system is outlined and the results of the measurements, mostly during the first 6 years of the SDSS, are described. We present the reference response functions for the five colour passbands derived from these measurements, and discuss column to column variations and variations in time, and also their effects on photometry. We also discuss the effect arising from various, slightly different response functions of the associated detector systems that were used to give SDSS photometry. We show that the calibration procedures of SDSS remove these variations reasonably well with the resulting final errors from variant response functions being unlikely to be larger than 0.01 mag for g, r, i, and z bands over the entire duration of the survey. The considerable aging effect is uncovered in the u band, the response function showing a 30% decrease in the throughput in the short wavelength side during the survey years, which potentially causes a systematic error in photometry. The aging effect is consistent with variation of the instrumental sensitivity in u-band, which is calibrated out. The expected colour variation is consistent with measured colour variation in the catalog of repeated photometry. The colour variation is delta (u-g) ~ 0.01 for most stars, and at most delta (u-g) ~ 0.02 mag for those with extreme colours. We verified in the final catalogue that no systematic variations in excess of 0.01 mag are detected in the photometry which can be ascribed to aging and/or seasonal effects except for the secular u-g colour variation for stars with extreme colours.Comment: 54 pages, 18 figures, 7 tables, accepted for publication in A

Inclination-Independent Galaxy Classification

We present a new method to classify galaxies from large surveys like the Sloan Digital Sky Survey using inclination-corrected concentration, inclination-corrected location on the color-magnitude diagram, and apparent axis ratio. Explicitly accounting for inclination tightens the distribution of each of these parameters and enables simple boundaries to be drawn that delineate three different galaxy populations: Early-type galaxies, which are red, highly concentrated, and round; Late-type galaxies, which are blue, have low concentrations, and are disk dominated; and Intermediate-type galaxies, which are red, have intermediate concentrations, and have disks. We have validated our method by comparing to visual classifications of high-quality imaging data from the Millennium Galaxy Catalogue. The inclination correction is crucial to unveiling the previously unrecognized Intermediate class. Intermediate-type galaxies, roughly corresponding to lenticulars and early spirals, lie on the red sequence. The red sequence is therefore composed of two distinct morphological types, suggesting that there are two distinct mechanisms for transiting to the red sequence. We propose that Intermediate-type galaxies are those that have lost their cold gas via strangulation, while Early-type galaxies are those that have experienced a major merger that either consumed their cold gas, or whose merger progenitors were already devoid of cold gas (the ``dry merger'' scenario).Comment: Accepted for publication in ApJ. 7 pages in emulateap

Spectrophotometric Redshifts. A New Approach to the Reduction of Noisy Spectra and its Application to GRB090423

We have developed a new method, close in philosophy to the photometric redshift technique, which can be applied to spectral data of very low signal-to-noise ratio. Using it we intend to measure redshifts while minimising the dangers posed by the usual extraction techniques. GRB afterglows have generally very simple optical spectra over which the separate effects of absorption and reddening in the GRB host, the intergalactic medium, and our own Galaxy are superimposed. We model all these effects over a series of template afterglow spectra to produce a set of clean spectra that reproduce what would reach our telescope. We also model carefully the effects of the telescope-spectrograph combination and the properties of noise in the data, which are then applied on the template spectra. The final templates are compared to the two-dimensional spectral data, and the basic parameters (redshift, spectral index, Hydrogen absorption column) are estimated using statistical tools. We show how our method works by applying it to our data of the NIR afterglow of GRB090423. At z ~ 8.2, this was the most distant object ever observed. We use the spectrum taken by our team with the Telescopio Nazionale Galileo to derive the GRB redshift and its intrinsic neutral Hydrogen column density. Our best fit yields z=8.4^+0.05/-0.03 and N(HI)<5x10^20 cm^-2, but with a highly non-Gaussian uncertainty including the redshift range z [6.7, 8.5] at the 2-sigma confidence level. Our method will be useful to maximise the recovered information from low-quality spectra, particularly when the set of possible spectra is limited or easily parameterisable while at the same time ensuring an adequate confidence analysis.Comment: 6 pages, 6 figures. Accepted for publication in Astronomy and Astrophysic

Testing gravity with motion of satellites around galaxies: Newtonian gravity against Modified Newtonian Dynamics

The motion of satellite galaxies around normal galaxies at distances 50-500 kpc provides a sensitive test for the theories. We study the surface density and the velocities of satellites around isolated galaxies in the Sloan Digital Sky Survey. We find that the surface number-density of satellites declines with the projected distance as a power law with the slope -1.5-2. The rms velocities gradually decline: observations exclude constant velocities at a 10 sigma level. We show that observational data strongly favor the standard model: all three major statistics of satellites - the number-density profile, the line-of-sight velocity dispersion, and the distribution function of the velocities -- agree remarkably well with the predictions of the standard cosmological model. Thus, that the success of the standard model extends to scales (50-500) kpc, much lower than what was previously considered. MOND fails on these scales for models which assume any single power-law number-density profile of satellites and any constant velocity anisotropy by predicting nearly constant rms velocities of satellites. Satellite data can be fit by fine-tuned models, which require (1) specific non-power-law density profile, (2) very radial orbits at large distances (velocity anisotropy beta =0.6-0.7 at 200-300 kpc), and (3) 2-2.5 times more stellar mass than what is found in the galaxies. The external gravity force - a necessary component for MOND -- makes the situation even worse. We argue that a combination of satellite data and observational constraints on stellar masses make these models very problematic.Comment: 14 pages, 7 figures. Accepted for publication in Ap

Improved redshifts for SDSS quasar spectra

A systematic investigation of the relationship between different redshift estimation schemes for more than 91000 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6) is presented. The publicly available SDSS quasar redshifts are shown to possess systematic biases of Dz/(1+z)>=0.002 (600km/s) over both small (dz~0.1) and large (dz~1) redshift intervals. Empirical relationships between redshifts based on i) CaII H & K host galaxy absorption, ii) quasar [OII] 3728, iii) [OIII] 4960,5008 emission, and iv) cross-correlation (with a master quasar template) that includes, at increasing quasar redshift, the prominent MgII 2799, CIII] 1908 and CIV 1549 emission lines, are established as a function of quasar redshift and luminosity. New redshifts in the resulting catalogue possess systematic biases a factor of ~20 lower compared to the SDSS redshift values; systematic effects are reduced to the level of Dz/(1+z)<10^-4 (30km/s) per unit redshift, or <2.5x10^-5 per unit absolute magnitude. Redshift errors, including components due both to internal reproducibility and the intrinsic quasar-to-quasar variation among the population, are available for all quasars in the catalogue. The improved redshifts and their associated errors have wide applicability in areas such as quasar absorption outflows, quasar clustering, quasar-galaxy clustering and proximity-effect determinations.Comment: Accepted to MNRAS. The QSO redshift catalogue and QSO template spectrum can be downloaded from ftp://ftp.ast.cam.ac.uk/pub/phewett/ until 1st May 201

Cool White Dwarfs Identified in the Second Data Release of the UKIRT Infrared Deep Sky Survey

We have paired the Second Data Release of the Large Area Survey of the UKIRT Infrared Deep Sky Survey with the Fifth Data Release of the Sloan Digital Sky Survey to identify ten cool white dwarf candidates, from their photometry and astrometry. Of these ten, one was previously known to be a very cool white dwarf. We have obtained optical spectroscopy for seven of the candidates using the GMOS-N spectrograph on Gemini North, and have confirmed all seven as white dwarfs. Our photometry and astrometry indicates that the remaining two objects are also white dwarfs. Model analysis of the photometry and available spectroscopy shows that the seven confirmed new white dwarfs, and the two new likely white dwarfs, have effective temperatures in the range Teff = 5400-6600 K. Our analysis of the previously known white dwarf confirms that it is cool, with Teff = 3800 K. The cooling age for this dwarf is 8.7 Gyr, while that of the nine ~6000 K white dwarfs is 1.8-3.6 Gyr. We are unable to determine the masses of the white dwarfs from the existing data, and therefore we cannot constrain the total ages of the white dwarfs. The large cooling age for the coolest white dwarf in the sample, combined with its low estimated tangential velocity, suggests that it is an old member of the thin disk, or a member of the thick disk of the Galaxy, with an age 10-11 Gyr. The warmer white dwarfs appear to have velocities typical of the thick disk or even halo; these may be very old remnants of low-mass stars, or they may be relatively young thin disk objects with unusually high space motion.Comment: 37 pages (referee format), 4 tables, 7 figures, accepted to Ap

Assembly of the outer Galactic stellar halo in the hierarchical model

We provide a set of numerical N-body simulations for studying the formation of the outer Milky Ways's stellar halo through accretion events. After simulating minor mergers of prograde and retrograde orbiting satellite halo with a Dark Matter main halo, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions where a retrograde signal in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the Milky Way stellar halo. Our results show that, for satellites more massive than $\sim 1/40$ of the main halo, the dynamical friction has a fundamental role in assembling the final velocity distributions resulting from different orbits and that retrograde satellites moving on low inclination orbits deposit more stars in the outer halo regions end therefore can produce the counter-rotating behavior observed in the outer Milky Way halo.Comment: 5 pages, 3 figures, ApJL, accepte

Properties of Disks and Bulges of Spiral and Lenticular Galaxies in the Sloan Digital Sky Survey

A bulge-disk decomposition is made for 737 spiral and lenticular galaxies drawn from a SDSS galaxy sample for which morphological types are estimated. We carry out the bulge-disk decomposition using the growth curve fitting method. It is found that bulge properties, effective radius, effective surface brightness, and also absolute magnitude, change systematically with the morphological sequence; from early to late types, the size becomes somewhat larger, and surface brightness and luminosity fainter. In contrast disks are nearly universal, their properties remaining similar among disk galaxies irrespective of detailed morphologies from S0 to Sc. While these tendencies were often discussed in previous studies, the present study confirms them based on a large homogeneous magnitude-limited field galaxy sample with morphological types estimated. The systematic change of bulge-to-total luminosity ratio, $B/T$, along the morphological sequence is therefore not caused by disks but mostly by bulges. It is also shown that elliptical galaxies and bulges of spiral galaxies are unlikely to be in a single sequence. We infer the stellar mass density (in units of the critical mass density) to be $\Omega=$0.0021 for spheroids, i.e., elliptical galaxies plus bulges of spiral galaxies, and $\Omega=$0.00081 for disks.Comment: 30 pages, 9 figure