Thin layers and camouflage: hidden \u3cem\u3ePseudo-nitzschia\u3c/em\u3e spp. (Bacillariophyceae) populations in a fjord in the San Juan Islands, Washington, USA

Two sets of observations were made on the distribution of Pseudo-nitzschia taxa in a fjord in the San Juan Islands, Washington, USA. From May 21 to 31, 1996, we observed the spatio-temporal distribution of a dense bloom of P. fraudulenta. Microscopic observations of live material were compared to physical-optical water-column structure, currents and wind. At the start of the study, dense concentrations of Pseudo-nitzschia spp. were observed directly at the surface. Optical profiles indicated that most cells were concentrated in a thin layer at ~5 m depth, which appeared to be contiguous throughout the sound. Several days later, sustained winds forced a plume of lighter water over the surface of the sound, displacing the original water mass, with its entrained flora, to depth. The resulting near-bottom thin layer persisted for several days, and contained \u3e106 Pseudo-nitzschia spp. cells l-1. Microscopic examination of live cells from the deep layer revealed that colonies were alive and motile. In 1996 and again in 1998, we observed P. pseudodelicatissima living within colonies of Chaetoceros socialis. Water-column thin layers, near-bottom thin layers and populations of Pseudo-nitzschia spp. within C. socialis colonies could easily escape detection by routine monitoring procedures, and may be a potential source of unexplained toxicity events

Occurrence and mechanisms of formation of a dramatic thin layer of marine snow in a shallow Pacific fjord

Huge accumulations of diatom-dominated marine snow (aggregates \u3e0.5 mm in diameter) were observed in a layer approximately 50 cm thick persisting over a 24 h period in a shallow fjord in the San Juan Islands, Washington, USA. The layer was associated with the 22.4 σt density surface. A second thin layer of elevated phytoplankton concentration located at a density discontinuity 1.5 to 2 m above the marine snow layer occurred within a dense diatom bloom near the surface. At the end of the study period, isopycnals shoaled and the 2 layers merged. More than 80% of the diatom bloom consisted of Thalassiosira spp. (50 to 59%), Odontella longicruris (5 to 14%), Asterionellopsis glacialis, and Thalassionema nitzschioides. A much higher proportion of O. longicruris occurred in marine snow (about 53%) than among suspended cells suggesting that this species differentially aggregated. Most zooplankton avoided the mucus-rich aggregate layer. The layer of marine snow was formed when sinking aggregated diatoms reached neutral buoyancy at the 22.4 isopycnal, probably due to the presence of low salinity mucus resistant to salt exchange in the interstices of the aggregates. Rates of turbulent kinetic energy dissipation throughout the water column rarely exceeded 10-8 m2 s-3 and aggregates below the thin layer were largely detrital in composition indicating that small-scale shears due to turbulence did not erode the layer of marine snow. The accumulation of marine snow and phytoplankton in persistent, discrete layers at density discontinuities results in habitat partitioning of the pelagic zone, impacts the distribution and interactions of planktonic organisms as well as the intensity and location of biological processes in the water column, and helps maintain species diversity

Halo mass - concentration relation from weak lensing

We perform a statistical weak lensing analysis of dark matter profiles around tracers of halo mass from galactic- to cluster-size halos. In this analysis we use 170,640 isolated ~L* galaxies split into ellipticals and spirals, 38,236 groups traced by isolated spectroscopic Luminous Red Galaxies (LRGs) and 13,823 MaxBCG clusters from the Sloan Digital Sky Survey (SDSS) covering a wide range of richness. Together these three samples allow a determination of the density profiles of dark matter halos over three orders of magnitude in mass, from 10^{12} M_{sun} to 10^{15} M_{sun}. The resulting lensing signal is consistent with an NFW or Einasto profile on scales outside the central region. We find that the NFW concentration parameter c_{200b} decreases with halo mass, from around 10 for galactic halos to 4 for cluster halos. Assuming its dependence on halo mass in the form of c_{200b} = c_0 [M/(10^{14}M_{sun}/h)]^{\beta}, we find c_0=4.6 +/- 0.7 (at z=0.22) and \beta=0.13 +/- 0.07, with very similar results for the Einasto profile. The slope (\beta) is in agreement with theoretical predictions, while the amplitude is about two standard deviations below the predictions for this mass and redshift, but we note that the published values in the literature differ at a level of 10-20% and that for a proper comparison our analysis should be repeated in simulations. We discuss the implications of our results for the baryonic effects on the shear power spectrum: since these are expected to increase the halo concentration, the fact that we see no evidence of high concentrations on scales above 20% of the virial radius suggests that baryonic effects are limited to small scales, and are not a significant source of uncertainty for the current weak lensing measurements of the dark matter power spectrum. [ABRIDGED]Comment: 17 pages, 5 figures, accepted to JCAP pending minor revisions that are included in v2 here on arXi

Infrared luminosities of galaxies in the Local Volume

Near-infrared properties of 451 galaxies with distances D \leq 10 Mpc are considered basing on the all-sky two micron survey (2MASS). A luminosity function of the galaxies in the K-band is derived within [-25,-11] mag. The local (D < 8 Mpc) luminosity density is estimated to be 6.8*10^8 L_sun/Mpc^3 that exceeds (1.5+-0.1) times the global cosmic density in the K-band. Virial mass-to-K-luminosity ratios are determined for nearby groups and clusters. In the luminosity range of (5*10^{10} - 2*10^{13})L_sun, the groups and clusters follow the relation \lg(M/L_K) propto (0.27+-0.03) lg(L_K) with a scatter of \~0.1 comparable to errors of the observables. The mean ratio ~= (20-25) M_sun/L_sun for the galaxy systems turns out to be significantly lower than the global ratio, (80-90)M_sun/L_sun, expected in the standard cosmological model with the matter density of Omega_m =0.27. This discrepancy can be resolved if most of dark matter in the universe is not associated with galaxies and their systems.Comment: 15 pages, 7 figures. Astronomy Letters, submitte

Missing Dark Matter in the Local Universe

A sample of 11 thousand galaxies with radial velocities V_ LG < 3500 km/s is used to study the features of the local distribution of luminous (stellar) and dark matter within a sphere of radius of around 50 Mpc around us. The average density of matter in this volume, Omega_m,loc=0.08+-0.02, turns out to be much lower than the global cosmic density Omega_m,glob=0.28+-0.03. We discuss three possible explanations of this paradox: 1) galaxy groups and clusters are surrounded by extended dark halos, the major part of the mass of which is located outside their virial radii; 2) the considered local volume of the Universe is not representative, being situated inside a giant void; and 3) the bulk of matter in the Universe is not related to clusters and groups, but is rather distributed between them in the form of massive dark clumps. Some arguments in favor of the latter assumption are presented. Besides the two well-known inconsistencies of modern cosmological models with the observational data: the problem of missing satellites of normal galaxies and the problem of missing baryons, there arises another one - the issue of missing dark matter.Comment: 19 pages, 7 figures, 1 table (accepted

A Multiband Study of the Galaxy Populations of the First Four Sunyaev--Zeldovich Effect selected Galaxy Clusters

We present first results of an examination of the optical properties of the galaxy populations in SZE selected galaxy clusters. Using clusters selected by the South Pole Telescope survey and deep multiband optical data from the Blanco Cosmology Survey, we measure the radial profile, the luminosity function, the blue fraction and the halo occupation number of the galaxy populations of these four clusters with redshifts ranging from 0.3 to 1. Our goal is to understand whether there are differences among the galaxy populations of these SZE selected clusters and previously studied clusters selected in the optical and the X-ray. The radial distributions of galaxies in the four systems are consistent with NFW profiles with a galaxy concentration of 3 to 6. We show that the characteristic luminosities in $griz$ bands are consistent with passively evolving populations emerging from a single burst at redshift $z=3$. The faint end power law slope of the luminosity function is found to be on average $\alpha \approx -1.2$ in griz. Halo occupation numbers (to $m^*+2$) for these systems appear to be consistent with those based on X-ray selected clusters. The blue fraction estimated to $0.36L^*$, for the three lower redshift systems, suggests an increase with redshift, although with the current sample the uncertainties are still large. Overall, this pilot study of the first four clusters provides no evidence that the galaxy populations in these systems differ significantly from those in previously studied cluster populations selected in the X-ray or the optical.Comment: 12 pages, 12 figures and 3 tables. Accepted for publication in Ap

SPT-CL J0546-5345: A Massive z > 1 Galaxy Cluster Selected Via the Sunyaev-Zel'dovich Effect with the South Pole Telescope

We report the spectroscopic confirmation of SPT-CL J0546-5345 at = 1.067. To date this is the most distant cluster to be spectroscopically confirmed from the 2008 South Pole Telescope (SPT) catalog, and indeed the first z > 1 cluster discovered by the Sunyaev-Zel'dovich Effect (SZE). We identify 21 secure spectroscopic members within 0.9 Mpc of the SPT cluster position, 18 of which are quiescent, early-type galaxies. From these quiescent galaxies we obtain a velocity dispersion of 1179^{+232}_{-167} km/s, ranking SPT-CL J0546-5345 as the most dynamically massive cluster yet discovered at z > 1. Assuming that SPT-CL J0546-5345 is virialized, this implies a dynamical mass of M_200 = 1.0^{+0.6}_{-0.4} x 10^{15} Msun, in agreement with the X-ray and SZE mass measurements. Combining masses from several independent measures leads to a best-estimate mass of M_200 = (7.95 +/- 0.92) x 10^{14} Msun. The spectroscopic confirmation of SPT-CL J0546-5345, discovered in the wide-angle, mass-selected SPT cluster survey, marks the onset of the high redshift SZE-selected galaxy cluster era.Comment: ApJ, in pres

The Atacama Cosmology Telescope: Dynamical Masses and Scaling Relations for a Sample of Massive Sunyaev-Zel'dovich Effect Selected Galaxy Clusters

We present the first dynamical mass estimates and scaling relations for a sample of Sunyaev-Zel'dovich effect (SZE) selected galaxy clusters. The sample consists of 16 massive clusters detected with the Atacama Cosmology Telescope (ACT) over a 455 sq. deg. area of the southern sky. Deep multi-object spectroscopic observations were taken to secure intermediate-resolution (R~700-800) spectra and redshifts for ~60 member galaxies on average per cluster. The dynamical masses M_200c of the clusters have been calculated using simulation-based scaling relations between velocity dispersion and mass. The sample has a median redshift z=0.50 and a median mass M_200c~12e14 Msun/h70 with a lower limit M_200c~6e14 Msun/h70, consistent with the expectations for the ACT southern sky survey. These masses are compared to the ACT SZE properties of the sample, specifically, the match-filtered central SZE amplitude y, the central Compton parameter y0, and the integrated Compton signal Y_200c, which we use to derive SZE-Mass scaling relations. All SZE estimators correlate with dynamical mass with low intrinsic scatter (<~20%), in agreement with numerical simulations. We explore the effects of various systematic effects on these scaling relations, including the correlation between observables and the influence of dynamically disturbed clusters. Using the 3-dimensional information available, we divide the sample into relaxed and disturbed clusters and find that ~50% of the clusters are disturbed. There are hints that disturbed systems might bias the scaling relations but given the current sample sizes these differences are not significant; further studies including more clusters are required to assess the impact of these clusters on the scaling relations.Comment: 15 pages, 4 figures. Accepted for publication in The Astrophysical Journal; matches published version. Full Table 8 with complete spectroscopic member sample available in machine-readable form in the journal site and upon request to C. Sif\'o

Optical Spectroscopy of Type Ia Supernovae

We present 432 low-dispersion optical spectra of 32 Type Ia supernovae (SNe Ia) that also have well-calibrated light curves. The coverage ranges from 6 epochs to 36 epochs of spectroscopy. Most of the data were obtained with the 1.5m Tillinghast telescope at the F. L. Whipple Observatory with typical wavelength coverage of 3700-7400A and a resolution of ~7A. The earliest spectra are thirteen days before B-band maximum; two-thirds of the SNe were observed before maximum brightness. Coverage for some SNe continues almost to the nebular phase. The consistency of the method of observation and the technique of reduction makes this an ideal data set for studying the spectroscopic diversity of SNe Ia.Comment: Accepted for publication in the Astronomical Journal, 109 pages (including data table), 44 figures, full resolution figures at http://www.noao.edu/noao/staff/matheson/Iaspec.ps.g

UBVRI Light Curves of 44 Type Ia Supernovae

We present UBVRI photometry of 44 type-Ia supernovae (SN Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SN Ia to date, nearly doubling the number of well-observed, nearby SN Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SN Ia observed at high redshift. The decline rate of SN Ia U-band light curves correlates well with the decline rate in other bands, as does the U-B color at maximum light. However, the U-band peak magnitudes show an increased dispersion relative to other bands even after accounting for extinction and decline rate, amounting to an additional ~40% intrinsic scatter compared to B-band.Comment: 84 authors, 71 pages, 51 tables, 10 figures. Accepted for publication in the Astronomical Journal. Version with high-res figures and electronic data at http://astron.berkeley.edu/~saurabh/cfa2snIa