arXiv subjects

Jon Brinkmann

Publications and source records attributed to Jon Brinkmann.

At least 73 records · Page 4Linked to original sources

arXiv2004

Photometric Properties of Void Galaxies in the Sloan Digital Sky Survey

Using a nearest neighbor analysis, we construct a sample of void galaxies from the Sloan Digital Sky Survey (SDSS) and compare the photometric properties of these galaxies to the population of non-void (wall) galaxies. We trace the density field of galaxies using a volume-limited sample with z_{max}=0.089. Galaxies from the flux-limited SDSS with z\leq z_{max} and fewer than three volume-limited neighbors within 7h^{-1}Mpc are classified as void galaxies. This criterion implies a density contrast δρ/ ρ< -0.6 around void galaxies. From 155,000 galaxies, we obtain a sub-sample of 13,742 galaxies with z\leq z_{max}, from which we identify 1,010 galaxies as void galaxies. To identify an additional 194 faint void galaxies from the SDSS in the nearby universe, r~ 72 h^{-1}Mpc, we employ volume-limited samples extracted from the Updated Zwicky Catalog and the Southern Sky Redshift Survey with z_{max}=0.025 to trace the galaxy distribution. Our void galaxies span a range of absolute magnitude from M_r=-13.5 to M_r=-22.5. Using SDSS photometry, we compare the colors, concentration indices, and Sersic indices of the void and wall samples. Void galaxies are significantly bluer than galaxies lying at higher density. The population of void galaxies with M_r ~ M* +1 and brighter is on average bluer and more concentrated (later type) than galaxies outside of voids. The latter behavior is only partly explained by the paucity of luminous red galaxies in voids. These results generally agree with the predictions of semi-analytic models for galaxy formation in cold dark matter models, which indicate that void galaxies should be relatively bluer, more disklike, and have higher specific star formation rates.

astro-ph↗

arXiv2004

Spectroscopic Properties of Void Galaxies in the Sloan Digital Sky Survey

We study the spectroscopic properties of a sample of 10^3 void galaxies from the Sloan Digital Sky Survey (SDSS) and compare these with the properties of galaxies in higher density regions (wall galaxies). This sample of void galaxies covers the range of absolute magnitude from M_r=-13.5 to M_r=-22.5 in regions with density contrast delta < -0.6. In this paper we compare the equivalent widths of Halpha, [OII], [NII], Hbeta, and [OIII] of void and wall galaxies of similar luminosities and find that void galaxies have larger values, indicating that they are still forming stars at a high rate. A comparison of the Balmer break, as measured by the parameter Dn(4000), reveals that void galaxies have younger stellar populations than wall galaxies. Using standard techniques, we estimate Halpha and [OII] star formation rates of the void and wall galaxies and along with estimates of the stellar masses, we compute specific star formation rates. In most cases, we find that void galaxies have similar SFRs to wall galaxies but they are fainter and smaller mass. This means that, consistent with the EWs, void galaxies have higher specific star formation rates than wall galaxies.

astro-ph↗

arXiv2004

Three-point Correlation Functions of SDSS Galaxies in Redshift Space: Morphology, Color, and Luminosity Dependence

We present measurements of the redshift--space three-point correlation function of galaxies in the Sloan Digital Sky Survey (SDSS). For the first time, we analyze the dependence of this statistic on galaxy morphology, color and luminosity. In order to control systematics due to selection effects, we used $r$--band, volume-limited samples of galaxies, constructed from the magnitude-limited SDSS data ($14.5<r<17.5$), and further divided the samples into two morphological types (early and late) or two color populations (red and blue). The three-point correlation function of SDSS galaxies follow the hierarchical relation well and the reduced three-point amplitudes in redshift--space are almost scale-independent ($Q_z=0.5\sim1.0$). In addition, their dependence on the morphology, color and luminosity is not statistically significant. Given the robust morphological, color and luminosity dependences of the two-point correlation function, this implies that galaxy biasing is complex on weakly non-linear to non-linear scales. We show that simple deterministic linear relation with the underlying mass could not explain our measurements on these scales.

astro-ph↗

arXiv2004

Cosmological Parameters from Eigenmode Analysis of Sloan Digital Sky Survey Galaxy Redshifts

We present estimates of cosmological parameters from the application of the Karhunen-Loeve transform to the analysis of the 3D power spectrum of density fluctuations using Sloan Digital Sky Survey galaxy redshifts. We use Omega_m*h and f_b = Omega_b/Omega_m to describe the shape of the power spectrum, sigma8 for the (linearly extrapolated) normalization, and beta to parametrize linear theory redshift space distortions. On scales k < 0.16 h/Mpc, our maximum likelihood values are Omega_m*h = 0.264 +/-0.043, f_b = 0.286 +/- 0.065, sigma8 = 0.966 +/- 0.048, and beta = 0.45 +/- 0.12. When we take a prior on Omega_b from WMAP, we find Omega_m*h = 0.207 +/- 0.030, which is in excellent agreement with WMAP and 2dF. This indicates that we have reasonably measured the gross shape of the power spectrum but we have difficulty breaking the degeneracy between Omega_m*h and f_b because the baryon oscillations are not resolved in the current spectroscopic survey window function.

astro-ph↗

arXiv2004

The Environmental Dependence of the Relations between Stellar Mass, Structure, Star Formation and Nuclear Activity in Galaxies

We use a complete sample of galaxies drawn from the SDSS to study how structure, star formation and nuclear activity depend on local density and on stellar mass. Local density is estimated by counting galaxies above a fixed absolute magnitude limit within cylinders 2 Mpc in projected radius and +-500 km/s in depth. The stellar mass distribution of galaxies shifts by nearly a factor of two towards higher masses between low and high density regions. At fixed stellar mass, both star formation and nuclear activity depend strongly on local density, while structural parameters such as size and concentration are almost independent of it. The galaxy property most sensitive to environment is specific star formation rate. For galaxies with stellar masses less than 3 x 10^10 M_sun, the median SFR/M* decreases by more than a factor of 10 from low to high densities. This decrease is less marked for massive galaxies. At fixed stellar mass, twice as many galaxies host AGN with strong [OIII] emission in low density regions as in high. Massive galaxies in low-density environments also contain more dust. We have analyzed correlations between spectroscopic indicators that probe SFH on different timescales (D4000, Hdelta_A and SFR/M*). The correlations do not depend on environment, suggesting that the decrease in star formation has ocurred over long (>1 Gyr) timescales. Since structure does not depend on environment for more massive galaxies, trends in recent SFH, dust and AGN for these systems cannot be driven by processes that alter structure, e.g. mergers. The SFH-density correlation is strongest for small scale (< 1 Mpc) estimates of local density. Finally, we highlight a striking similarity between changes in the galaxy population as a function of density and as a function of redshift and we interpret this using N-body simulations.

astro-ph↗

arXiv2003

A Low Latitude Halo Stream around the Milky Way

We present evidence for a ring of stars in the plane of the Milky Way, extending at least from l = 180 deg to l = 227 deg with turnoff magnitude $g \sim 19.5$; the ring could encircle the Galaxy. We infer that the low Galactic latitude structure is at a fairly constant distance of R = 18 +/- 2 kpc from the Galactic Center above the Galactic plane, and has R = 20 +/- 2 kpc in the region sampled below the Galactic plane. The evidence includes five hundred SDSS spectroscopic radial velocities of stars within 30 degrees of the plane. The velocity dispersion of the stars associated with this structure is found to be 27 km/s at (l,b) = (198, -27), 22 km/s at (l,b) = (225, 28), 30 km/s at (l,b) = (188, 24), and 30 km/s at (l,b) = (182, 27) degrees. The structure rotates in the same prograde direction as the Galactic disk stars, but with a circular velocity of 110+/-25 km/s. The narrow measured velocity dispersion is inconsistent with power law spheroid or thick disk populations. We compare the velocity dispersion in this structure with the velocity dispersion of stars in the Sagittarius dwarf galaxy tidal stream, for which we measure a velocity dispersion of 20 km/s at (l, b) = (165, -55) deg. We estimate a preliminary metallicity from the Ca II (K) line and color of the turnoff stars of [Fe/H] = -1.6 with a dispersion of 0.3 dex and note that the turnoff color is consistent with that of the spheroid population. We interpret our measurements as evidence for a tidally disrupted satellite of $2 \times 10^7$ to $5 \times 10^8 \rm M_\odot$ which rings the Galaxy.

astro-ph↗

arXiv2003

The H alpha Luminosity Function of Morphologically Classified Galaxies in the Sloan Digital Sky Survey

We present a study of the H$α$ line emission from a sample of 1482 optically-selected, morphologically-classified bright galaxies (median redshift of 0.05) derived from the Sloan Digital Sky Survey. The luminosity function is calculated for each morphological class and for the total sample. The luminosity function fitted with the Schechter form gives a slope $α=-1.43\pm 0.10$ for the total sample and the H$α$ luminosity density is $10^{39.31\pm 0.04{+0.10\atop-0.07}}h$ erg s$^{-1}$Mpc$^{-3}$, where the first error is statistical and the second is systematic. This value is consistent with that derived by Gallego et al. (1995), but this agreement is caused by a fortuitous cancellation of their neglect of stellar absorption that affects the estimate of extinction corrections and a significant sample incompleteness of emission line galaxies. The fraction of H$α$ emitters monotonically increases from early (a few % for ellipticals) to late types (100% for irregular galaxies), whereas strong emitters exist in all classes of morphological types. We find that 83% of the luminosity density comes from spiral galaxies, 5% from irregular galaxies, and 9% from early type galaxies; a small number of morphologically disturbed galaxies contribute by 3%.

astro-ph↗

arXiv2003

Spatial Variations of Galaxy Number Counts in the SDSS I.: Extinction, Large-Scale Structure and Photometric Homogeneity

We study the spatial variation of galaxy number counts using five band photometric images from the Sloan Digital Sky Survey. The spatial variation of this sample of 46 million galaxies collected from 2200 sq. degrees can be understood as the combination of Galactic extinction and large-scale clustering. With the use of the reddening map of Schlegel, Finkbeiner & Davis (1998), the standard extinction law is verified for the colour bands from u to z within 5% in the region of small extinction values, E(B-V)<0.15. The residual spatial variations of the number counts suggests that the error of global calibration for SDSS photometry is smaller than 0.02 mag.

astro-ph↗

arXiv2003

SDSS J115517.35+634622.0: A Newly Discovered Gravitationally Lensed Quasar

We report the discovery of SDSSJ115517.35+634622.0, a previously unknown gravitationally lensed quasar. The lens system exhibits two images of a $z = 2.89$ quasar, with an image separation of $1{\farcs}832 \pm 0.007$ . Near-IR imaging of the system reveals the presence of the lensing galaxy between the two quasar images. Based on absorption features seen in the Sloan Digital Sky Survey (SDSS) spectrum, we determine a lens galaxy redshift of $z = 0.1756$. The lens is rather unusual in that one of the quasar images is only $0{\farcs}22\pm0{\farcs}07$ ($\sim 0.1 R_{\rm eff}$) from the center of the lens galaxy and photometric modeling indicates that this image is significantly brighter than predicted by a SIS model. This system was discovered in the course of an ongoing search for strongly lensed quasars in the dataset from the SDSS.

astro-ph↗

arXiv2003

Blue horizontal branch stars in the Sloan Digital Sky Survey: I. Sample selection and structure in the Galactic halo

We isolate samples of 733 bright (g < 18) and 437 faint (g > 18) high-Galactic latitude blue horizontal branch stars with photometry and spectroscopy in the Sloan Digital Sky Survey (SDSS). Comparison of independent photometric and spectroscopic selection criteria indicates that contamination from F and blue-straggler stars is less than 10% for bright stars (g<18) and about 25% for faint stars (g>18), and this is qualitatively confirmed by proper motions based on the USNO-A catalog as first epoch. Analysis of repeated observations shows that the errors in radial velocity are approximately 26 km/s. A relation between absolute magnitude and color is established using the horizontal branches of halo globular clusters observed by SDSS. Bolometric corrections and colors are synthesized in the SDSS filters from model spectra. The redder stars agree well in absolute magitude with accepted values for RR Lyrae stars. The resulting photometric distances are accurate to about 0.2 magnitudes, with a median of about 25 kpc. Modest clumps in phase space exist and are consistent with the previously reported tidal stream of the Sagittarius dwarf galaxy. The sample is tabulated in electronic form in the online version of this article, or by request to the authors.

astro-ph↗

arXiv2003

Blue horizontal branch stars in the Sloan Digital Sky Survey: II. Kinematics of the Galactic halo

We carry out a maximum-likelihood kinematic analysis of a sample of 1170 blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey presented in Sirko et al. (2003) (Paper I). Monte Carlo simulations and resampling show that the results are robust to distance and velocity errors at least as large as the estimated errors from Paper I. The best-fit velocities of the Sun (circular) and halo (rotational) are 245.9 +/- 13.5 km/s and 23.8 +/- 20.1 km/s but are strongly covariant, so that v_0 - v_halo = 222.1 +/- 7.7 km/s. If one adopts standard values for the local standard of rest and solar motion, then the halo scarcely rotates. The velocity ellipsoid inferred for our sample is much more isotropic [(sigma_r,sigma_theta,sigma_phi) = (101.4 +/- 2.8, 97.7 +/- 16.4, 107.4 +/- 16.6) km/s] than that of halo stars in the solar neighborhood, in agreement with a recent study of the distant halo by Sommer-Larsen et al. (1997). The line-of-sight velocity distribution of the entire sample, corrected for the Sun's motion, is accurately gaussian with a dispersion of 101.6 +/- 3.0 km/s.

astro-ph↗

arXiv2003

Halos around edge-on disk galaxies in the SDSS

We present a statistical analysis of halo emission for a sample of 1047 edge-on disk galaxies imaged in five bands by the Sloan Digital Sky Survey (SDSS). Stacking the homogeneously rescaled images of the galaxies, we can measure surface brightnesses as deep as mu_r~31 mag/arcsec^2. The results strongly support the almost ubiquitous presence of stellar halos around disk galaxies, whose spatial distribution is well described by a power-law $ρ\propto r^{-3}$, in a moderately flattened spheroid (c/a~0.6). The colour estimates in g-r and r-i, although uncertain, give a clear indication for extremely red stellar populations, hinting at old ages and/or non-negligible metal enrichment. These results support the idea of halos being assembled via early merging of satellite galaxies.

astro-ph↗

arXiv2003

Sagittarius Tidal Debris 90 kpc from the Galactic Center

A new overdensity of A-colored stars in distant parts of the Milky Way's stellar halo, at a dereddened SDSS magnitude of g_0 = 20.3, is presented. Identification of associated variable RR Lyrae candidates supports the claim that these are blue horizontal branch stars. The inferred distance of these stars from the Galactic center is 90 kpc, assuming the absolute magnitude of these stars is M_g_0 = 0.7 and that the Sun is 8.5 kpc from the Galactic center. The new tidal debris is within 10 kpc of same plane as other confirmed tidal debris from the disruption of the Sagittarius dwarf galaxy, and could be associated with the trailing tidal arm. Distances to the Sagittarius stream estimated from M stars are about 13% smaller than our inferred distances. The tidal debris has a width of at least 10 degrees, and is traced for more than 20 degrees across the sky. The globular cluster NGC 2419 is located within the detected tidal debris, and may also have once been associated with the Sagittarius dwarf galaxy.

astro-ph↗

arXiv2003

The near-IR properties and continuum shapes of high redshift quasars from the Sloan Digital Sky Survey

We present J-H-K' photometry for a sample of 45 high redshift quasars found by the Sloan Digital Sky Survey. The sample was originally selected on the basis of optical colors and spans a redshift range from 3.6 to 5.03. Our photometry reflects the rest-frame SED longward of Ly alpha for all redshifts. The results show that the near-IR colors of high redshift quasars are quite uniform. We have modelled the continuum shape of the quasars (from just beyond Ly alpha to ~4000 A) with a power law of the form f_nu \propto nu^alpha, and find =-0.57 with a scatter of 0.33. This value is similar to what is found for lower redshift quasars over the same restframe wavelength range, and we conclude that there is hardly any evolution in the continuum properties of optically selected quasars up to redshift 5. The spectral indices found by combining near-IR with optical photometry are in general consistent but slightly flatter than what is found for the same quasars using the optical spectra and photometry alone, showing that the continuum region used to determine the spectral indices can somewhat influence the results.

astro-ph↗

arXiv2003

SDSS J0903+5028: A New Gravitational Lens

We report the discovery of a new gravitationally lensed quasar from the Sloan Digital Sky Survey, SDSS J090334.92+502819.2. This object was targeted for SDSS spectroscopy as a Luminous Red Galaxy (LRG), but manual examination of the spectrum showed the presence of a quasar at z= 3.6 in addition to a red galaxy at z=0.388, and the SDSS image showed a second possible quasar image nearby. Follow-up imaging and spectroscopy confirmed the lensing hypothesis. In images taken at the ARC 3.5-meter telescope, two quasars are separated by 2.8 arc-seconds; the lensing galaxy is clearly seen and is blended with one of the quasar images. Spectroscopy taken at the Keck II telescope shows that the quasars have identical redshifts of z=3.6 and both show the presence of the same broad absorption line-like troughs. We present simple lens models which account for the geometry and magnifications. The lens galaxy lies near two groups of galaxies and may be a part of them. The models suggest that the groups may contribute considerable shear and may have a strong effect on the lens configuration.

astro-ph↗

arXiv2003

Galaxy Types in the Sloan Digital Sky Survey Using Supervised Artificial Neural Networks

Supervised artificial neural networks are used to predict useful properties of galaxies in the Sloan Digital Sky Survey, in this instance morphological classifications, spectral types and redshifts. By giving the trained networks unseen data, it is found that correlations between predicted and actual properties are around 0.9 with rms errors of order ten per cent. Thus, given a representative training set, these properties may be reliably estimated for galaxies in the survey for which there are no spectra and without human intervention.

astro-ph↗

arXiv2003

Angular Clustering with Photometric Redshifts in the Sloan Digital Sky Survey: Bimodality in the Clustering Properties of Galaxies

Understanding the clustering of galaxies has long been a goal of modern observational cosmology. Utilizing our photometric redshift technique a volume limited sample containing more than 2 million galaxies is constructed from the SDSS galaxy catalog. In the largest such analysis to date, we study the angular clustering as a function of luminosity and spectral type. Using Limber's equation we calculate the clustering length for the full data set as r0=5.77+/-0.10 Mpc/h. We find that r0 increases with luminosity by a factor of 1.6 over the sampled luminosity range, in agreement with previous redshift surveys. We also find that both the clustering length and the slope of the correlation function depend on the galaxy type. In particular, by splitting the galaxies in four groups by their rest-frame type we find a bimodal behavior in their clustering properties. Galaxies with spectral types similar to elliptical galaxies have a correlation length of 6.59 +/- 0.17 Mpc/h and a slope of the angular correlation function of 0.96 +/- 0.05 while blue galaxies have a clustering length of 4.51 +/- 0.19 Mpc/h and a slope of 0.68 +/- 0.09. The two intermediate color groups behave like their more extreme 'siblings', rather than showing a gradual transition in slope. We discuss these correlations in the context of current cosmological models for structure formation.

astro-ph↗

arXiv2003

A Merged Catalog of Clusters of Galaxies from Early SDSS Data

We present a catalog of 799 clusters of galaxies in the redshift range z_est = 0.05 - 0.3 selected from ~400 deg^2 of early SDSS commissioning data along the celestial equator. The catalog is based on merging two independent selection methods -- a color-magnitude red-sequence maxBCG technique (B), and a Hybrid Matched-Filter method (H). The BH catalog includes clusters with richness Λ>= 40 (Matched-Filter) and N_gal >= 13 (maxBCG), corresponding to typical velocity dispersion of σ_v >~ 400 km s^{-1} and mass (within 0.6 h^{-1) Mpc radius) >~ 5*10^{13} h^{-1} M_sun. This threshold is below Abell richness class 0 clusters. The average space density of these clusters is 2*10^{-5} h^3 Mpc^{-3}. All NORAS X-ray clusters and 53 of the 58 Abell clusters in the survey region are detected in the catalog; the 5 additional Abell clusters are detected below the BH catalog cuts. The cluster richness function is determined and found to exhibit a steeply decreasing cluster abundance with increasing richness. We derive observational scaling relations between cluster richness and observed cluster luminosity and cluster velocity dispersion; these scaling relations provide important physical calibrations for the clusters. The catalog can be used for studies of individual clusters, for comparisons with other sources such as X-ray clusters and AGNs, and, with proper correction for the relevant selection functions, also for statistical analyses of clusters.

astro-ph↗