Lethal Parasites in Oysters from Coastal Georgia with Discussion of Disease and Management Implications

Extensive mortalities of oysters, Crassostrea virginica, occurred from 1985 through 1987 in coastal waters of Georgia. Fluid thioglycolate cultures of oysters collected from 16 of 17 locations revealed infections by the apicomplexan parasite Perkinsus marinus. An ascetosporan parasite, Haplosporidium nelsoni, was also observed in histopathological examination of oysters from 4 of the locations. While the range of H. nelsoni currently is recognized as the east coast of the United States from Maine to Florida, this is the first report of the parasite in Georgia waters. This paper documents the occurrence of these two lethal parasites in oysters from coastal waters of Georgia, along with potential disease and management implications. Results of an earlier independent and previously unpublished survey are also discussed which document the presence of P. marinus in Georgia as early as 1966

Circulation Flows: Cooling Flows with Bubble Return

The failure of the XMM-Newton and Chandra X-ray telescopes to detect cooling gas in elliptical galaxies and clusters of galaxies has led many to adopt the position that the gas is not cooling at all and that heating by an active nucleus in the central E or cD galaxy is sufficient to offset radiative cooling. In this paper we explore an idealized limiting example of this point of view in which hot, buoyant bubbles formed near the center return the inflowing, radiatively cooling gas to distant regions in the flow. We show that idealized steady state, centrally heated non-cooling flows can indeed be constructed. In addition, the emission-weighted temperature profiles in these circulating flows resemble those of normal cooling flows. However, these solutions are valid only (1) for a range of bubble parameters for which there is no independent justification, (2) for a limited spatial region in the cooling flow and (3) for a limited period of time after which cooling seems inevitable. Our exploration of non-cooling flows is set in the context of galaxy/group flows.Comment: 10 pages (emulateapj5) with 4 figures; accepted by The Astrophysical Journa

The need for speed : escape velocity and dynamical mass measurements of the Andromeda galaxy

Our nearest large cosmological neighbour, the Andromeda galaxy (M31), is a dynamical system, and an accurate measurement of its total mass is central to our understanding of its assembly history, the life-cycles of its satellite galaxies, and its role in shaping the Local Group environment. Here, we apply a novel approach to determine the dynamical mass of M31 using high velocity Planetary Nebulae (PNe), establishing a hierarchical Bayesian model united with a scheme to capture potential outliers and marginalize over tracers unknown distances. With this, we derive the escape velocity run of M31 as a function of galacto-centric distance, with both parametric and non-parametric approaches. We determine the escape velocity of M31 to be 470 ± 40  km s−1 at a galacto-centric distance of 15  kpc, and also, derive the total potential of M31, estimating the virial mass and radius of the galaxy to be 0.8±0.1×1012M⊙ and 240 ± 10  kpc, respectively. Our M31 mass is on the low-side of the measured range, this supports the lower expected mass of the M31-Milky Way system from the timing and momentum arguments, satisfying the H i constraint on circular velocity between 10 ≲ R/ kpc < 35, and agreeing with the stellar mass Tully-Fisher relation. To place these results in a broader context, we compare them to the key predictions of the ΛCDM cosmological paradigm, including the stellar-mass–halo-mass and the dark matter halo concentration–virial mass correlation, and finding it to be an outlier to this relation.PostprintPeer reviewe

Density Variations in the NW Star Stream of M31

The Pan Andromeda Archeological Survey (PAndAS) CFHT Megaprime survey of the M31-M33 system has found a star stream which extends about 120 kpc NW from the center of M31. The great length of the stream, and the likelihood that it does not significantly intersect the disk of M31, means that it is unusually well suited for a measurement of stream gaps and clumps along its length as a test for the predicted thousands of dark matter sub-halos. The main result of this paper is that the density of the stream varies between zero and about three times the mean along its length on scales of 2 to 20 kpc. The probability that the variations are random fluctuations in the star density is less than 10^-5. As a control sample we search for density variations at precisely the same location in stars with metallicity higher than the stream, [Fe/H]=[0, -0.5] and find no variations above the expected shot noise. The lumpiness of the stream is not compatible with a low mass star stream in a smooth galactic potential, nor is it readily compatible with the disturbance caused by the visible M31 satellite galaxies. The stream's density variations appear to be consistent with the effects of a large population of steep mass function dark matter sub-halos, such as found in LCDM simulations, acting on an approximately 10Gyr old star stream. The effects of a single set of halo substructure realizations are shown for illustration, reserving a statistical comparison for another study.Comment: ApJ revised version submitte

The X-ray Size-Temperature Relation for Intermediate Redshift Galaxy Clusters

We present the first measurements of the X-ray size-temperature (ST) relation in intermediate redshift (z~0.30) galaxy clusters. We interpret the local ST relation (z~0.06) in terms of underlying scaling relations in the cluster dark matter properties, and then we use standard models for the redshift evolution of those dark matter properties to show that the ST relation does not evolve with redshift. We then use ROSAT HRI observations of 11 clusters to examine the intermediate redshift ST relation; for currently favored cosmological parameters, the intermediate redshift ST relation is consistent with that of local clusters. Finally, we use the ST relation and our evolution model to measure angular diameter distances; with these 11 distances we evaluate constraints on Omega_M and Omega_L which are consistent with those derived from studies of Type Ia supernovae. The data rule out a model with Omega_M=1 and Omega_L=0 with 2.5 sigma confidence. When limited to models where Omega_M+Omega_L=1, these data are inconsistent with Omega_M=1 with 3 sigma confidence.Comment: ApJ: submitted April 7, accepted June 28, to appear Dec 1 (vol 544

XMM-Newton and Chandra Observations of the Galaxy Group NGC 5044. I. Evidence for Limited Multi-Phase Hot Gas

Using new XMM and Chandra observations we present an analysis of the temperature structure of the hot gas within a radius of 100 kpc of the bright nearby galaxy group NGC 5044. A spectral deprojection analysis of data extracted from circular annuli reveals that a two-temperature model (2T) of the hot gas is favored over single-phase or cooling flow (M_dot = 4.5 +/- 0.2 M_{sun}/yr) models within the central ~30 kpc. Alternatively, the data can be fit equally well if the temperature within each spherical shell varies continuously from ~T_h to T_c ~ T_h/2, but no lower. The high spatial resolution of the Chandra data allows us to determine that the temperature excursion T_h --> T_c required in each shell exceeds the temperature range between the boundaries of the same shell in the best-fitting single-phase model. This is strong evidence for a multi-phase gas having a limited temperature range. The cooler component of the 2T model has a temperature (T_c \~ 0.7 keV) similar to the kinetic temperature of the stars. The hot phase has a temperature (T_h ~ 1.4 keV) characteristic of the virial temperature of the \~10^{13} M_{sun} halo expected in the NGC 5044 group. However, in view of the morphological disturbances and X-ray holes visible in the Chandra image within R ~10 kpc, bubbles of gas heated to ~T_h in this region may be formed by intermittent AGN feedback. Some additional heating at larger radii may be associated with the evolution of the cold front near R ~50 kpc, as suggested by the sharp edge in the EPIC images.Comment: 18 pages, 10 figures, Accepted for publication in ApJ, some changes in presentation for consistency with paper 2 (astro-ph/0303054), includes detailed analysis of azimuthal spectral variations in the chandra image, conclusions unchanged from previous versio