3,111 research outputs found
A Melanic Pieris Rapae from Michigan (Lepidoptera: Pierdae)
The Arthur J. Yates collection of Michigan Lepidoptera, recently donated to Michigan State University (see Fischer, 1967), contained a striking melanic male cabbage butterfly [Pieris rapae (Linnaeus)] (Figs. 1, 2) now incorporated into the MSU series. Yates collected the specimen on 29 May 1934 in Roseville, Macomb County, near the western shore of Lake St. Clair in southeastern Michigan. An examination of the androconia and genitalia, using the characters described by Chang (1963), assured proper identification of the specimen. Although we have found no record of a similar rapae taken in North America, there are some named European forms of various species of Pieris that resemble our specimen
A Very Hot, High Redshift Cluster of Galaxies: More Trouble for Omega_0 = 1
We have observed the most distant (z=0.829) cluster of galaxies in the
Einstein Extended Medium Sensitivity Survey, with the ASCA and ROSAT
satellites. We find an X-ray temperature of 12.3 +3.1/-2.2 keV for this
cluster, and the ROSAT map reveals significant substructure. The high
temperature of MS1054-0321 is consistent with both its approximate velocity
dispersion, based on the redshifts of 12 cluster members we have obtained at
the Keck and the Canada-France-Hawaii telescopes, and with its weak lensing
signature. The X-ray temperature of this cluster implies a virial mass ~ 7.4 x
10^14 h^-1 solar masses, if the mean matter density in the universe equals the
critical value, or larger if Omega_0 < 1. Finding such a hot, massive cluster
in the EMSS is extremely improbable if clusters grew from Gaussian
perturbations in an Omega_0 = 1 universe. Combining the assumptions that
Omega_0 = 1 and that the intial perturbations were Gaussian with the observed
X-ray temperature function at low redshift, we show that the probability of
this cluster occurring in the volume sampled by the EMSS is less than a few
times 10^{-5}. Nor is MS1054-0321 the only hot cluster at high redshift; the
only two other EMSS clusters already observed with ASCA also have
temperatures exceeding 8 keV. Assuming again that the initial perturbations
were Gaussian and Omega_0 = 1, we find that each one is improbable at the <
10^{-2} level. These observations, along with the fact that these luminosities
and temperatures of the high- clusters all agree with the low-z L_X-T_X
relation, argue strongly that Omega_0 < 1. Otherwise, the initial perturbations
must be non-Gaussian, if these clusters' temperatures do indeed reflect their
gravitational potentials.Comment: 20 pages, 4 figures, To appear in 1 Aug 1998 ApJ (heavily revised
version of original preprint
A General Precipitation-Limited L_X-T-R Relation Among Early-Type Galaxies
The relation between X-ray luminosity (L_X) and ambient gas temperature (T)
among massive galactic systems is an important cornerstone of both
observational cosmology and galaxy-evolution modeling. In the most massive
galaxy clusters, the relation is determined primarily by cosmological structure
formation. In less massive systems, it primarily reflects the feedback response
to radiative cooling of circumgalactic gas. Here we present a simple but
powerful model for the L_X-T relation as a function of physical aperture R
within which those measurements are made. The model is based on the
precipitation framework for AGN feedback and assumes that the circumgalactic
medium is precipitation-regulated at small radii and limited by cosmological
structure formation at large radii. We compare this model with many different
data sets and show that it successfully reproduces the slope and upper envelope
of the L_X-T-R relation over the temperature range from ~0.2 keV through >10
keV. Our findings strongly suggest that the feedback mechanisms responsible for
regulating star formation in individual massive galaxies have much in common
with the precipitation-triggered feedback that appears to regulate
galaxy-cluster cores.Comment: Submitted to ApJ, 9 pages, 3 figures (v2 fixes a few small typos
The narrow X-ray tail and double H-alpha tails of ESO 137-002 in Abell 3627
We present the analysis of a deep Chandra observation of a ~2L_* late-type
galaxy, ESO 137-002, in the closest rich cluster A3627. The Chandra data reveal
a long (>40 kpc) and narrow tail with a nearly constant width (~3 kpc) to the
southeast of the galaxy, and a leading edge ~1.5 kpc from the galaxy center on
the upstream side of the tail. The tail is most likely caused by the nearly
edge-on stripping of ESO 137-002's ISM by ram pressure, compared to the nearly
face-on stripping of ESO 137-001 discussed in our previous work. Spectral
analysis of individual regions along the tail shows that the gas throughout it
has a rather constant temperature, ~1 keV, very close to the temperature of the
tails of ESO 137-001, if the same atomic database is used. The derived gas
abundance is low (~0.2 solar with the single-kT model), an indication of the
multiphase nature of the gas in the tail. The mass of the X-ray tail is only a
small fraction (<5%) of the initial ISM mass of the galaxy, suggesting that the
stripping is most likely at an early stage. However, with any of the single-kT,
double-kT and multi-kT models we tried, the tail is always "over-pressured"
relative to the surrounding ICM, which could be due to the uncertainties in the
abundance, thermal vs. non-thermal X-ray emission, or magnetic support in the
ICM. The H-alpha data from SOAR show a ~21 kpc tail spatially coincident with
the X-ray tail, as well as a secondary tail (~12 kpc long) to the east of the
main tail diverging at an angle of ~23 degrees and starting at a distance of
~7.5 kpc from the nucleus. At the position of the secondary H-alpha tail, the
X-ray emission is also enhanced at the ~2 sigma level. We compare the tails of
ESO 137-001 and ESO 137-002, and also compare the tails to simulations. Both
the similarities and differences of the tails pose challenges to the
simulations. Several implications are briefly discussed.Comment: 15 pages, 6 figures, accepted for publication in Ap
Star Formation, Radio Sources, Cooling X-ray Gas, and Galaxy Interactions in the Brightest Cluster Galaxy in 2A0335+096
We present deep emission-line imaging taken with the SOAR Optical Imaging
Camera of the brightest cluster galaxy (BCG) in the nearby (z=0.035) X-ray
cluster 2A0335+096. We analyze long-slit optical spectroscopy, archival VLA,
Chandra X-ray, and XMM UV data. 2A0335+096 is a bright, cool-core X-ray
cluster, once known as a cooling flow. Within the highly disturbed core
revealed by Chandra X-ray observations, 2A0335+096 hosts a highly structured
optical emission-line system. The redshift of the companion is within 100 km/s
of the BCG and has certainly interacted with the BCG, and is likely bound to
it. The comparison of optical and radio images shows curved filaments in
H-alpha emission surrounding the resolved radio source. The velocity structure
of the emission-line bar between the BCG nucleus and the companion galaxy
provides strong evidence for an interaction between the two in the last ~50
Myrs. The age of the radio source is similar to the interaction time, so this
interaction may have provoked an episode of radio activity. We estimate a star
formation rate of >7 solar mass/yr based on the Halpha and archival UV data, a
rate similar to, but somewhat lower than, the revised X-ray cooling rate of
10-30 solar masses/year estimated from XMM spectra by Peterson & workers. The
Halpha nebula is limited to a region of high X-ray surface brightness and cool
X-ray temperature. The detailed structures of H-alpha and X-ray gas differ. The
peak of the X-ray emission is not the peak of H-alpha emission, nor does it lie
in the BCG. The estimated age of the radio lobes and their interaction with the
optical emission-line gas, the estimated timescale for depletion and
accumulation of cold gas, and the dynamical time in the system are all similar,
suggesting a common trigger mechanism.Comment: Accepted AJ, July 2007 publication. Vol 134, p. 14-2
A 70 Kiloparsec X-Ray Tail in the Cluster A3627
We present the discovery of a 70 kpc X-ray tail behind the small late-type galaxy ESO 137-001, in the nearby, hot (T = 6.5 keV) merging cluster A3627, from both Chandra and XMM-Newton observations. The tail has a length-to-width ratio of ∼10. It is luminous (L0.5–2 keV ∼ 1041 ergs s-1), with a temperature of ∼0.7 keV and an X-ray Mgas of ∼109 M⊙ (∼10% of the galaxy\u27s stellar mass). We interpret this tail as the stripped interstellar medium of ESO 137-001 mixed with the hot cluster medium, with this blue galaxy being converted into a gas-poor galaxy. Three X-ray point sources are detected in the axis of the tail, which may imply active star formation there. The straightness and narrowness of the tail also imply that the turbulence in the intracluster medium is not strong on scales of 20–70 kpc
Chandra detection of the intracluster medium around 3C294 at z=1.786
We present a Chandra observation of the powerful radio galaxy 3C294 showing
clear evidence for a surrounding intracluster medium. At a redshift of 1.786
this is the most distant cluster of galaxies yet detected in X-rays. The radio
core is detected as a point source, which has a spectrum consistent with a
heavily-absorbed power law implying an intrinsic 2-10 keV luminosity of ~10^45
erg/s. A small excess of emission is associated with the southern radio
hotspots. The soft, diffuse emission from the intracluster medium is centred on
the radio source. It has an hour-glass shape in the N-S direction, extending to
radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of
this extended component is fit by a thermal model with temperature ~5 keV, or
by gas cooling from above 7 keV at rates of ~400-700 Msolar/yr. The rest-frame
0.3-10 keV luminosity of the cluster is ~4.5x10^44 erg/s. The existence of such
a cluster is consistent with a low density universe.Comment: 5 pages, 6 figures, accepted by MNRA
No planet for HD 166435
The G0V star HD166435 has been observed by the fiber-fed spectrograph ELODIE
as one of the targets in the large extra-solar planet survey that we are
conducting at the Observatory of Haute-Provence. We detected coherent,
low-amplitude, radial-velocity variations with a period of 3.7987days,
suggesting a possible close-in planetary companion. Subsequently, we initiated
a series of high-precision photometric observations to search for possible
planetary transits and an additional series of CaII H and K observations to
measure the level of surface magnetic activity and to look for possible
rotational modulation. Surprisingly, we found the star to be photometrically
variable and magnetically active. A detailed study of the phase stability of
the radial-velocity signal revealed that the radial-velocity variability
remains coherent only for durations of about 30days. Analysis of the time
variation of the spectroscopic line profiles using line bisectors revealed a
correlation between radial velocity and line-bisector orientation. All of these
observations, along with a one-quarter cycle phase shift between the
photometric and the radial-velocity variationss, are well explained by the
presence of dark photospheric spots on HD166435. We conclude that the
radial-velocity variations are not due to gravitational interaction with an
orbiting planet but, instead, originate from line-profile changes stemming from
star spots on the surface of the star. The quasi-coherence of the
radial-velocity signal over more than two years, which allowed a fair fit with
a binary model, makes the stability of this star unusual among other active
stars. It suggests a stable magnetic field orientation where spots are always
generated at about the same location on the surface of the star.Comment: 9 pages, 8 figures, Accepted for publication in A&
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