641 research outputs found
The EIU Student Life Survey: Explanations for Involvement
The research reported in this paper was designed to assist the EIU General Education Assessment Committee to understand the ways in which undergraduate students made use of their time on campus, both in-class and out-of-class. The results provided stakeholders with information to support student activities and student involvement. The survey instrument used for data collection is also attached
The slope of the black-hole mass versus velocity dispersion correlation
Observations of nearby galaxies reveal a strong correlation between the mass
of the central dark object M and the velocity dispersion sigma of the host
galaxy, of the form log(M/M_sun) = a + b*log(sigma/sigma_0); however, published
estimates of the slope b span a wide range (3.75 to 5.3). Merritt & Ferrarese
have argued that low slopes (<4) arise because of neglect of random measurement
errors in the dispersions and an incorrect choice for the dispersion of the
Milky Way Galaxy. We show that these explanations account for at most a small
part of the slope range. Instead, the range of slopes arises mostly because of
systematic differences in the velocity dispersions used by different groups for
the same galaxies. The origin of these differences remains unclear, but we
suggest that one significant component of the difference results from Ferrarese
& Merritt's extrapolation of central velocity dispersions to r_e/8 (r_e is the
effective radius) using an empirical formula. Another component may arise from
dispersion-dependent systematic errors in the measurements. A new determination
of the slope using 31 galaxies yields b=4.02 +/- 0.32, a=8.13 +/- 0.06, for
sigma_0=200 km/s. The M-sigma relation has an intrinsic dispersion in log M
that is no larger than 0.3 dex. In an Appendix, we present a simple model for
the velocity-dispersion profile of the Galactic bulge.Comment: 37 pages, 9 figure
HST STIS spectroscopy of the triple nucleus of M31: two nested disks in Keplerian rotation around a Supermassive Black Hole
We present HST spectroscopy of the nucleus of M31 obtained with STIS. Spectra
taken around the CaT lines at 8500 see only the red giants in the double
bright- ness peaks P1 and P2. In contrast, spectra taken at 3600-5100 A are
sensitive to the tiny blue nucleus embedded in P2, the lower surface brightness
red nucleus. P2 has a K-type spectrum, but the embedded blue nucleus has an
A-type spectrum with strong Balmer absorption lines. Given the small likelihood
for stellar collisions, a 200 Myr old starburst appears to be the most
plausible origin of the blue nucleus. In stellar population, size, and velocity
dispersion, the blue nucleus is so different from P1 and P2 that we call it P3.
The line-of-sight velocity distributions of the red stars in P1+P2 strengthen
the support for Tremaine s eccentric disk model. The kinematics of P3 is
consistent with a circular stellar disk in Keplerian rotation around a
super-massive black hole with M_bh = 1.4 x 10^8 M_sun. The P3 and the P1+P2
disks rotate in the same sense and are almost coplanar. The observed velocity
dispersion of P3 is due to blurred rotation and has a maximum value of sigma =
1183+-201 km/s. The observed peak rotation velocity of P3 is V = 618+-81 km/s
at radius 0.05" = 0.19 pc corresponding to a circular rotation velocity at this
radius of ~1700 km/s. Any dark star cluster alternative to a black hole must
have a half-mass radius <= 0.03" = 0.11 pc. We show that this excludes clusters
of brown dwarfs or dead stars on astrophysical grounds.Comment: Astrophysical Journal, Sep 20, 2005, 21 pages including 20 figure
M33: A Galaxy with No Supermassive Black Hole
Galaxies that contain bulges appear to contain central black holes whose
masses correlate with the velocity dispersion of the bulge. We show that no
corresponding relationship applies in the pure disk galaxy M33. Three-integral
dynamical models fit Hubble Space Telescope WFPC2 photometry and STIS
spectroscopy best if the central black hole mass is zero. The upper limit is
1500 M_sun. This is significantly below the mass expected from the velocity
dispersion of the nucleus and far below any mass predicted from the disk
kinematics. Our results suggest that supermassive black holes are associated
only with galaxy bulges and not with their disks.Comment: 8 pages, AJ accepted, November issu
The Demography of Massive Dark Objects in Galaxy Centres
We construct dynamical models for a sample of 36 nearby galaxies with Hubble
Space Telescope photometry and ground-based kinematics. The models assume that
each galaxy is axisymmetric, with a two-integral distribution function,
arbitrary inclination angle, a position-independent stellar mass-to-light ratio
Upsilon, and a central massive dark object (MDO) of arbitrary mass M_bh. They
provide acceptable fits to 32 of the galaxies for some value of M_bh and
Upsilon; the four galaxies that cannot be fit have kinematically decoupled
cores. The mass-to-light ratios inferred for the 32 well-fit galaxies are
consistent with the fundamental plane correlation Upsilon \propto L^0.2, where
L is galaxy luminosity. In all but six galaxies the models require at the 95%
confidence level an MDO of mass M_bh ~ 0.006 M_bulge = 0.006 Upsilon L. Five of
the six galaxies consistent with M_bh=0 are also consistent with this
correlation. The other (NGC 7332) has a much stronger upper limit on M_bh. We
consider various parameterizations for the probability distribution describing
the correlation of the masses of these MDOs with other galaxy properties. One
of the best models can be summarized thus: a fraction f ~0.97 of galaxies have
MDOs, whose masses are well described by a Gaussian distribution in log
(M_bh/M_bulge) of mean -2.27 and width ~0.07.Comment: 28 pages including 13 figures and 4 tables. Submitted to A
The Allen Telescope Array
The Allen Telescope Array, originally called the One Hectare Telescope (1hT) [1] will be a large array radio telescope whose novel characteristics will be a wide field of view (3.5 deg-GHz HPBW), continuous frequency coverage of 0.5 - 11 GHz, four dual-linear polarization output bands of 100 MHz each, four beams in each band, two 100 MHz spectral correlators for two of the bands, and hardware for RFI mitigation built in. Its scientific motivation is for deep SETI searches and, at the same time, a variety of other radio astronomy projects, including transient (e.g. pulsar) studies, HI mapping of the Milky Way and nearby galaxies, Zeeman studies of the galactic magnetic field in a number of transitions, mapping of long chain molecules in molecular clouds, mapping of the decrement in the cosmic background radiation toward galaxy clusters, and observation of HI absorption toward quasars at redshifts up to z=2. The array is planned for 350 6.1-meter dishes giving a physical collecting area of about 10,000 square meters. The large number of components reduces the price with economies of scale. The front end receiver is a single cryogenically cooled MIMIC Low Noise Amplifier covering the whole band. The feed is a wide-band log periodic feed of novel design, and the reflector system is an offset Gregorian for minimum sidelobes and spillover. All preliminary and critical design reviews have been completed. Three complete antennas with feeds and receivers are under test, and an array of 33 antennas is under construction at the Hat Creek Radio Observatory for the end of 2004. The present plan is to have a total of about 200 antennas completed by the summer of 2006 and the balance of the array finished before the end of the decade
The Allen Telescope Array: The First Widefield, Panchromatic, Snapshot Radio Camera for Radio Astronomy and SETI
The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to
deliver data at the Hat Creek Radio Observatory in Northern California.
Scientists and engineers are actively exploiting all of the flexibility
designed into this innovative instrument for simultaneously conducting surveys
of the astrophysical sky and conducting searches for distant technological
civilizations. This paper summarizes the design elements of the ATA, the cost
savings made possible by the use of COTS components, and the cost/performance
trades that eventually enabled this first snapshot radio camera. The
fundamental scientific program of this new telescope is varied and exciting;
some of the first astronomical results will be discussed.Comment: Special Issue of Proceedings of the IEEE: "Advances in Radio
Telescopes", Baars,J. Thompson,R., D'Addario, L., eds, 2009, in pres
The evolution of the star formation activity in galaxies and its dependence on environment
We study how the proportion of star-forming galaxies evolves between z=0.8
and z=0 as a function of galaxy environment, using the [OII] line in emission
as a signature of ongoing star formation. Our high-z dataset comprises 16
clusters, 10 groups and another 250 galaxies in poorer groups and the field at
z=0.4-0.8 from the ESO Distant Cluster Survey, plus another 9 massive clusters
at similar redshifts. As a local comparison, we use samples of galaxy systems
selected from the Sloan Digital Sky Survey at 0.04< z < 0.08. At high-z most
systems follow a broad anticorrelation between the fraction of star-forming
galaxies and the system velocity dispersion. At face value, this suggests that
at z=0.4-0.8 the mass of the system largely determines the proportion of
galaxies with ongoing star formation. At these redshifts the strength of star
formation (as measured by the [OII] equivalent width) in star-forming galaxies
is also found to vary systematically with environment. Sloan clusters have much
lower fractions of star-forming galaxies than clusters at z=0.4-0.8 and, in
contrast with the distant clusters, show a plateau for velocity dispersions , where the fraction of galaxies with [OII] emission does not
vary systematically with velocity dispersion. We quantify the evolution of the
proportion of star-forming galaxies as a function of the system velocity
dispersion and find it is strongest in intermediate-mass systems (sigma ~
500-600 km s^-1 at z=0). To understand the origin of the observed trends, we
use the Press-Schechter formalism and the Millennium Simulation and show that
galaxy star formation histories may be closely related to the growth history of
clusters and groups. We propose a scheme that is able to account for the
observed relations between the star-forming fraction and \sigma [abridged].Comment: 28 pages, 19 figures, ApJ in pres
Evaluation of the limitations and methods to improve rapid phage-based detection of viable Mycobacterium avium subsp. paratuberculosis in the blood of experimentally infected cattle
Background
Disseminated infection and bacteraemia is an underreported and under-researched aspect of Johneâs disease. This is mainly due to the time it takes for Mycobacterium avium subsp. paratuberculosis (MAP) to grow and lack of sensitivity of culture. Viable MAP cells can be detected in the blood of cattle suffering from Johneâs disease within 48 h using peptide-mediated magnetic separation (PMMS) followed by bacteriophage amplification. The aim of this study was to demonstrate the first detection of MAP in the blood of experimentally exposed cattle using the PMMS-bacteriophage assay and to compare these results with the immune response of the animal based on serum ELISA and shedding of MAP by faecal culture.
Results
Using the PMMS-phage assay, seven out of the 19 (37 %) MAP-exposed animals that were tested were positive for viable MAP cells although very low numbers of MAP were detected. Two of these animals were positive by faecal culture and one was positive by serum ELISA. There was no correlation between PMMS-phage assay results and the faecal and serum ELISA results. None of the control animals (10) were positive for MAP using any of the four detection methods. Investigations carried out into the efficiency of the assay; found that the PMMS step was the limiting factor reducing the sensitivity of the phage assay. A modified method using the phage assay directly on isolated peripheral blood mononuclear cells (without PMMS) was found to be superior to the PMMS isolation step.
Conclusions
This proof of concept study has shown that viable MAP cells are present in the blood of MAP-exposed cattle prior to the onset of clinical signs. Although only one time point was tested, the ability to detect viable MAP in the blood of subclinically infected animals by the rapid phage-based method has the potential to increase the understanding of the pathogenesis of Johneâs disease progression by warranting further research on the presence of MAP in blood
- âŠ