We perform a spectroscopic analysis of 492 450 galaxy spectra from the first two years of observations of the Sloan Digital Sky Survey (SDSS) III/Baryonic Oscillation Spectroscopic Survey (BOSS) ...collaboration. This data set has been released in the ninth SDSS data release, the first public data release of BOSS spectra. We show that the typical signal-to-noise ratio of BOSS spectra, despite being low, is sufficient to measure stellar velocity dispersion and emission line fluxes for individual objects. We show that the typical velocity dispersion of a BOSS galaxy is ∼240 km s−1. The typical error in the velocity dispersion measurement is 14 per cent, and 93 per cent of BOSS galaxies have velocity dispersions with an accuracy of better than 30 per cent. The distribution in velocity dispersion is redshift independent between redshifts 0.15 and 0.7, which reflects the survey design targeting massive galaxies with an approximately uniform mass distribution in this redshift interval. We show that emission lines can be measured on BOSS spectra. However, the majority of BOSS galaxies lack detectable emission lines, as is to be expected because of the target selection design towards massive galaxies. We analyse the emission line properties and present diagnostic diagrams using the emission lines O ii, Hβ, O iii, Hα and N ii (detected in about 4 per cent of the galaxies) to separate star-forming objects and active galactic nuclei (AGN). We show that the emission line properties are strongly redshift dependent and that there is a clear correlation between observed frame colours and emission line properties. Within in the low-z sample (LOWZ) around 0.15 < z < 0.3, half of the emission line galaxies have low-ionization nuclear emission-line region (LINER)-like emission line ratios, followed by Seyfert-AGN-dominated spectra, and only a small fraction of a few per cent are purely star-forming galaxies. AGN and LINER-like objects, instead, are less prevalent in the high-z sample (CMASS) around 0.4 < z < 0.7, where more than half of the emission line objects are star forming. This is a pure selection effect caused by the non-detection of weak Hβ emission lines in the BOSS spectra. Finally, we show that star-forming, AGN and emission line free galaxies are well separated in the g − r versus r − i target selection diagram.
We present five new satellites of the Milky Way discovered in Sloan Digital Sky Survey (SDSS) imaging data, four of which were followed up with either the Subaru or the Isaac Newton Telescopes. They ...include four probable new dwarf galaxies--one each in the constellations of Coma Berenices, Canes Venatici, Leo, and Hercules--together with one unusually extended globular cluster, Segue 1. We provide distances, absolute magnitudes, half-light radii, and color-magnitude diagrams for all five satellites. The morphological features of the color-magnitude diagrams are generally well described by the ridge line of the old, metal-poor globular cluster M92. In the past two years, a total of 10 new Milky Way satellites with effective surface brightness k sub(u) 28 mag arcsec super(-2) have been discovered in SDSS data. They are less luminous, more irregular, and apparently more metal-poor than the previously known nine Milky Way dwarf spheroidals. The relationship between these objects and other populations is discussed. We note that there is a paucity of objects with half-light radii between 640 and 6100 pc. We conjecture that this may represent the division between star clusters and dwarf galaxies.
Abstract
We measure the quasar two-point correlation function over the redshift range 2.2 < z < 2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a homogeneous subset of the ...data consisting of 27 129 quasars with spectroscopic redshifts - by far the largest such sample used for clustering measurements at these redshifts to date. The sample covers 3600 deg2, corresponding to a comoving volume of 9.7 (h
−1 Gpc)3 assuming a fiducial Λ cold dark matter cosmology, and it has a median absolute i-band magnitude of −26, k-corrected to z= 2. After accounting for redshift errors we find that the redshift-space correlation function is fitted well by a power law of slope −2 and amplitude s
0 = (9.7 ± 0.5) h
−1 Mpc over the range 3 < s < 25 h
−1 Mpc. The projected correlation function, which integrates out the effects of peculiar velocities and redshift errors, is fitted well by a power law of slope −1 and r
0 = (8.4 ± 0.6) h
−1 Mpc over the range 4 < R < 16 h
−1 Mpc. There is no evidence for strong luminosity or redshift dependence to the clustering amplitude, in part because of the limited dynamic range in our sample. Our results are consistent with, but more precise than, previous measurements at similar redshifts. Our measurement of the quasar clustering amplitude implies a bias factor of b ≃ 3.5 for our quasar sample. We compare the data to models to constrain the manner in which quasars occupy dark matter haloes at z∼ 2.4 and infer that such quasars inhabit haloes with a characteristic mass of 〈M〉≃ 1012
h
−1 M⊙ with a duty cycle for the quasar activity of 1 per cent.
We present a new public archive of light-motion curves in Sloan Digital Sky Survey (SDSS) Stripe 82, covering 99° in right ascension from to and spanning in declination from to , for a total sky area ...of ∼249 deg2. Stripe 82 has been repeatedly monitored in the u, g, r, i and z bands over a seven-year baseline. Objects are cross-matched between runs, taking into account the effects of any proper motion. The resulting catalogue contains almost 4 million light-motion curves of stellar objects and galaxies. The photometry are recalibrated to correct for varying photometric zero-points, achieving ∼20 and 30 mmag rms accuracy down to 18 mag in the g, r, i and z bands for point sources and extended sources, respectively. The astrometry are recalibrated to correct for inherent systematic errors in the SDSS astrometric solutions, achieving ∼32 and 35 mas rms accuracy down to 18 mag for point sources and extended sources, respectively. For each light-motion curve, 229 photometric and astrometric quantities are derived and stored in a higher level catalogue. On the photometric side, these include mean exponential and point spread function (PSF) magnitudes along with uncertainties, rms scatter, χ2 per degree of freedom, various magnitude distribution percentiles, object type (stellar or galaxy), and eclipse, Stetson and Vidrih variability indices. On the astrometric side, these quantities include mean positions, proper motions as well as their uncertainties and χ2 per degree of freedom. The light-motion curve catalogue presented here is complete down to r∼ 21.5 and is at present the deepest large-area photometric and astrometric variability catalogue available.
We announce the discovery of a new satellite of the Milky Way in the constellation of Bootes at a distance of 660 kpc. It was found in a systematic search for stellar overdensities in the north ...Galactic cap using Sloan Digital Sky Survey Data Release 5. The color-magnitude diagram shows a well-defined turnoff, red giant branch, and extended horizontal branch. Its absolute magnitude is M sub(v) 6 -5.8 mag, which makes it one of the faintest galaxies known. The half-light radius is 6220 pc. The isodensity contours are elongated and have an irregular shape, suggesting that Boo may be a disrupted dwarf spheroidal galaxy.
We have detected stellar halo streams in the solar neighborhood using data from the seventh public data release of the Sloan Digital Sky Survey (SDSS), which includes the directed stellar program ...Sloan Extension For Galactic Understanding and Exploration (SEGUE). In order to derive distances to each star, we used the metallicity-dependent photometric parallax relation from Ivezic et al. We examine and quantify the accuracy of this relation by applying it to a set of globular and open clusters observed by the SDSS/SEGUE and comparing the resulting sequence to the fiducial cluster sequences obtained by An et al. Our final sample consists of 22,321 nearby (d <= 2 kpc), metal-poor (Fe/H <=-0.5) main-sequence stars with six-dimensional estimates of position and space velocity . We characterize the orbits of these stars through suitable kinematic proxies for their 'effective' integrals of motion, angular momentum, eccentricity, and orbital polar angle and compare the observed distribution to expectations from a smooth distribution in four Fe/H bins. The metallicities provide an additional dimension in parameter space that is well suited to distinguish tidal streams from those of dynamical origin. On this basis, we identify at least five significant 'phase-space overdensities' of stars on very similar orbits in the solar neighborhood to which we can assign unambiguously peaked Fe/H distributions. Three of them have been identified previously, including the halo stream discovered by Helmi et al. at a significance level of sigma = 12.0. In addition, we find at least two new genuine halo streams, judged by their kinematics and Fe/H, at sigma = 2.9 and 4.8, respectively. For one stream the stars even show coherence in the configuration space, matching a spatial overdensity of stars found by Juric et al. at (R, z) (9.,0.8) kpc. Our results demonstrate the practical power of our search method to detect substructure in the phase-space distribution of nearby stars without making a priori assumptions about the detailed form of the gravitational potential.
In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. ...Its color-magnitude diagram (CMD) shows a well-defined subgiant branch, main sequence, and turnoff, from which we estimate a distance of 630 kpc and a projected size of 6250 x 125 pc super(2). The CMD suggests a composite population with some range in metallicity and/or age. Based on its extent and stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named Ursa Major II (UMa II) after its constellation. Using SDSS data, we find an absolute magnitude of Mv6-3.8, which would make it the faintest known satellite galaxy. UMall's isophotes are irregular and distorted with evidence for multiple concentrations; this suggests that the satellite is in the process of disruption.
The Hercules-Aquila Cloud Belokurov, V; Evans, N. W; Bell, E. F ...
The Astrophysical journal,
03/2007, Letnik:
657, Številka:
2
Journal Article
Recenzirano
We present evidence for a substantial overdensity of stars in the direction of the constellations of Hercules and Aquila. The cloud is centered at a Galactic longitude of l - 40 and extends above and ...below the Galactic plane by at least 50. Given its off-centeredness and height, it is unlikely that the Hercules-Aquila cloud is related to the bulge or thick disk. More likely, this is a new structural component of the Galaxy that passes through the disk. The cloud stretches 680 in longitude. Its heliocentric distance lies between 10 and 20 kpc so that the extent of the cloud in projection is 620 kpc by 615 kpc. It has an absolute magnitude of Mu = -13, and its stellar population appears to be comparable to, but somewhat more metal-rich than, M92.
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