119 research outputs found
Body Theology
Body Theology investigates the human body as a place where landscape, myth and bacteria intersect to create numerous imaginary realms. Horizon lines shift or disappear completely, and the overall dark palette sets a tone intended to evoke mystery. In these paintings, it may be difficult to determine whether inside is outside, up is down, big is small, or figure is ground. I embrace this ambiguity and invite the viewer to participate in a visual and metaphorical adventure. My painting process is traditional: from a white ground, many layers of semi-transparent oil paint begin with loose and rhythmic brush strokes. I enjoy how the nature of the paint itself reflects the fluidity and luminosity found in both inner and outer worlds. I never know exactly what the finished image will look like when I begin. Unforeseen problems require creative solutions, new forms and ideas emerge from the destruction of old ones, and my own understanding of the picture evolves through formal development and intuition
Millihertz X-ray variability during the 2019 outburst of black hole candidate Swift~J1357.20933
Swift J1357.20933 is a black-hole candidate X-ray transient, which
underwent its third outburst in 2019, during which several multi-wavelength
observations were carried out.~Here, we report results from the \emph{Neil
Gehrels Swift} and \emph{NICER} observatories and radio data from
\emph{AMI}.~For the first time,~millihertz quasi-periodic X-ray oscillations
with frequencies varying between ~1--5~ were found in
\emph{NICER} observations and a similar feature was also detected in one
\emph{Swift}--\textsc{XRT} dataset.~Our spectral analysis indicate that the
maximum value of the measured X-ray flux is much lower compared to the peak
values observed during the 2011 and 2017 outbursts.~This value is ~100
times lower than found with \emph{MAXI} on MJD~58558 much (~68 days)
earlier in the outburst, suggesting that the \emph{Swift} and \emph{NICER}
fluxes belong to the declining phase of the 2019 outburst.~An additional soft
component was detected in the \textsc{XRT} observation with the highest flux
level, but at a relatively low ~~, and which we fitted with a disc component at a
temperature of ~keV.~The optical/UV magnitudes obtained from
\emph{Swift}--\textsc{UVOT} showed a correlation with X-ray observations,
indicating X-ray reprocessing to be the plausible origin of the optical and UV
emission.~However, the source was not significantly detected in the radio
band.~There are currently a number of models that could explain this
millihertz-frequency X-ray variability; not least of which involves an X-ray
component to the curious dips that, so far, have only been observed in the
optical.Comment: 14 pages, Accepted for publication in MNRA
High resolution AMI Large Array imaging of spinning dust sources: spatially correlated 8 micron emission and evidence of a stellar wind in L675
We present 25 arcsecond resolution radio images of five Lynds Dark Nebulae
(L675, L944, L1103, L1111 & L1246) at 16 GHz made with the Arcminute
Microkelvin Imager (AMI) Large Array. These objects were previously observed
with the AMI Small Array to have an excess of emission at microwave frequencies
relative to lower frequency radio data. In L675 we find a flat spectrum compact
radio counterpart to the 850 micron emission seen with SCUBA and suggest that
it is cm-wave emission from a previously unknown deeply embedded young
protostar. In the case of L1246 the cm-wave emission is spatially correlated
with 8 micron emission seen with Spitzer. Since the MIR emission is present
only in Spitzer band 4 we suggest that it arises from a population of PAH
molecules, which also give rise to the cm-wave emission through spinning dust
emission.Comment: accepted MNRA
Precision Measurements of the Cluster Red Sequence using an Error Corrected Gaussian Mixture Model
The red sequence is an important feature of galaxy clusters and plays a
crucial role in optical cluster detection. Measurement of the slope and scatter
of the red sequence are affected both by selection of red sequence galaxies and
measurement errors. In this paper, we describe a new error corrected Gaussian
Mixture Model for red sequence galaxy identification. Using this technique, we
can remove the effects of measurement error and extract unbiased information
about the intrinsic properties of the red sequence. We use this method to
select red sequence galaxies in each of the 13,823 clusters in the maxBCG
catalog, and measure the red sequence ridgeline location and scatter of each.
These measurements provide precise constraints on the variation of the average
red galaxy populations in the observed frame with redshift. We find that the
scatter of the red sequence ridgeline increases mildly with redshift, and that
the slope decreases with redshift. We also observe that the slope does not
strongly depend on cluster richness. Using similar methods, we show that this
behavior is mirrored in a spectroscopic sample of field galaxies, further
emphasizing that ridgeline properties are independent of environment.Comment: 33 pages, 14 Figures; A typo in Eq.A11 is fixed. The C++/Python codes
for ECGMM can be downloaded from:
https://sites.google.com/site/jiangangecgmm
First results from the Very Small Array -- I. Observational methods
The Very Small Array (VSA) is a synthesis telescope designed to image faint
structures in the cosmic microwave background on degree and sub-degree angular
scales. The VSA has key differences from other CMB interferometers with the
result that different systematic errors are expected. We have tested the
operation of the VSA with a variety of blank-field and calibrator observations
and cross-checked its calibration scale against independent measurements. We
find that systematic effects can be suppressed below the thermal noise level in
long observations; the overall calibration accuracy of the flux density scale
is 3.5 percent and is limited by the external absolute calibration scale.Comment: 9 pages, 10 figures, MNRAS in press (Minor revisions
AMI observations of unmatched Planck ERCSC LFI sources at 15.75 GHz
The Planck Early Release Compact Source Catalogue includes 26 sources with no
obvious matches in other radio catalogues (of primarily extragalactic sources).
Here we present observations made with the Arcminute Microkelvin Imager Small
Array (AMI SA) at 15.75 GHz of the eight of the unmatched sources at
declination > +10 degrees. Of the eight, four are detected and are associated
with known objects. The other four are not detected with the AMI SA, and are
thought to be spurious.Comment: 6 pages, 5 figures, 4 table
Microwave observations of spinning dust emission in NGC6946
We report new cm-wave measurements at five frequencies between 15 and 18GHz
of the continuum emission from the reportedly anomalous "region 4" of the
nearby galaxy NGC6946. We find that the emission in this frequency range is
significantly in excess of that measured at 8.5GHz, but has a spectrum from
15-18GHz consistent with optically thin free-free emission from a compact HII
region. In combination with previously published data we fit four emission
models containing different continuum components using the Bayesian spectrum
analysis package radiospec. These fits show that, in combination with data at
other frequencies, a model with a spinning dust component is slightly preferred
to those that possess better-established emission mechanisms.Comment: submitted MNRA
Further Sunyaev-Zel'dovich observations of two Planck ERCSC clusters with the Arcminute Microkelvin Imager
We present follow-up observations of two galaxy clusters detected blindly via
the Sunyaev-Zel'dovich (SZ) effect and released in the Planck Early Release
Compact Source Catalogue. We use the Arcminute Microkelvin Imager, a dual-array
14-18 GHz radio interferometer. After radio source subtraction, we find a SZ
decrement of integrated flux density -1.08+/-0.10 mJy toward PLCKESZ
G121.11+57.01, and improve the position measurement of the cluster, finding the
centre to be RA 12 59 36.4, Dec +60 04 46.8, to an accuracy of 20 arcseconds.
The region of PLCKESZ G115.71+17.52 contains strong extended emission, so we
are unable to confirm the presence of this cluster via the SZ effect.Comment: 4 tables, 3 figures, revised after referee's comments and resubmitted
to MNRA
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