24 research outputs found
High Resolution BIMA Observations of CO, HCN, and 13CO in NGC 1068
We present high-resolution CO, HCN, and 13CO maps of the inner arcminute of
NGC 1068 made with the BIMA interferometer. Several features appear in the CO
map which have not previously been observed: (1) a firm detection of CO line
emission from a compact region centered on the nucleus of the galaxy; (2) the
detection of a triplet velocity structure characteristic of kinematically
independent regions shown on the spectrum of the unresolved nuclear emission ;
and (3) the detection of a molecular bar, the extent and position angle of
which are in good agreement with the 2 m stellar bar. The most intense CO
emission is nonnuclear; the structure and kinematics of this emission imply
that this gas is distributed along the inner spiral arms and not in a ring. The
bar's kinematic influence on the molecular gas in the spiral arms is modest,
with typical ordered noncircular motions of \la\ 30 \kms\ in the plane of the
galaxy. Interior to the spiral arms, the bar's influence is more dramatic, as
reflected by the twisted isovelocity contours in the CO and HCN velocity
fields. The surface density of molecular gas within the central 100 pc radius
of NGC 1068 is the same as that in the central 200 pc radius in the Milky Way
to within the uncertainties. There is evidence for an kinematic mode in
NGC 1068; we find the kinematic center of rotation to be displaced from the
radio continuum center by about 2.9", or 200 pc. The HCN image, in contrast to
the CO map, shows a strong concentration of emission centered on the nucleus.
The ratio of integrated intensities of the HCN emission to that of CO is about
0.6 and is the highest ratio measured in the central region of any galaxy.Comment: 35 pages of uuencoded, compressed postscript, 20 postscript figures
not included but available from [email protected] or from
ftp://astro.astro.umd.edu/pub/thelfer/n1068_figs.ps.Z To appear in The
Astrophysical Journal, V. 450, Sept. 199
Dense Gas in the Milky Way
We present a study of dense gas emission in the Milky Way in order to serve
as a basis for comparison with extragalactic results. This study combines new
observations of HCN, CS, and CO in individual GMCs and in the Milky Way plane
with published studies of emission from these molecules in the inner 500 pc of
the Milky Way. We find a strong trend in the fraction of emission from dense
gas tracers as a function of location in the Milky Way: in the bulge,
I_{HCN}/I_{CO} = 0.081 \pm 0.004, in the plane, I_{HCN}/I_{CO} = 0.026 \pm
0.008 on average, and over the full extent of nearby GMCs, I_{HCN}/I_{CO} =
0.014 \pm 0.020. Similar trends are seen in I_{CS}/I_{CO}. The low intensities
of the HCN and CS emission in the plane suggests that these lines are produced
by gas at moderate densities; they are thus not like the emission produced by
the dense, pc-scale star forming cores in nearby GMCs. The contrast between the
bulge and disk ratios in the Milky Way is likely to be caused by a combination
of higher kinetic temperatures as well as a higher dense gas fraction in the
bulge of the Milky Way.Comment: 34 pages LaTeX, AASTEX macros, includes 11 postscript figures. To
appear in ApJ 478, March 199
Unequal-mass boson-star binaries: Initial data and merger dynamics
We present a generalization of the curative initial data construction derived
for equal-mass compact binaries in Helfer {\it et al} (2019 Phys. Rev. D 99
044046; 2022 Class. Quantum Grav. 39 074001) to arbitrary mass ratios. We
demonstrate how these improved initial data avoid substantial spurious
artifacts in the collision dynamics of unequal-mass boson-star binaries in the
same way as has previously been achieved with the simpler method restricted to
the equal-mass case. We employ the improved initial data to explore in detail
the impact of phase offsets in the coalescence of equal- and unequal-mass boson
star binaries.Comment: 37 pages, 12 figures, to match published version in CQ
The Gravitational Afterglow of Boson Stars
In this work we study the long-lived post-merger gravitational wave signature
of a boson-star binary coalescence. We use full numerical relativity to
simulate the post-merger and track the gravitational afterglow over an extended
period of time. We implement recent innovations for the binary initial data,
which significantly reduce spurious initial excitations of the scalar field
profiles, as well as a measure for the angular momentum that allows us to track
the total momentum of the spatial volume, including the curvature contribution.
Crucially, we find the afterglow to last much longer than the spin-down
timescale. This prolonged gravitational wave afterglow provides a
characteristic signal that may distinguish it from other astrophysical sources.Comment: Movie: https://youtu.be/JE5FRG7kgvU Data:
https://github.com/ThomasHelfer/BosonStarAfterglo
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 Allen Telescope Array Pi GHz Sky Survey I. Survey Description and Static Catalog Results for the Bootes Field
The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array.
PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky
with an emphasis on synoptic observations that measure the static and
time-variable properties of the sky. During the 2.5-year campaign, PiGSS will
twice observe ~250,000 radio sources in the 10,000 deg^2 region of the sky with
b > 30 deg to an rms sensitivity of ~1 mJy. Additionally, sub-regions of the
sky will be observed multiple times to characterize variability on time scales
of days to years. We present here observations of a 10 deg^2 region in the
Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The
PiGSS image was constructed from 75 daily observations distributed over a
4-month period and has an rms flux density between 200 and 250 microJy. This
represents a deeper image by a factor of 4 to 8 than we will achieve over the
entire 10,000 deg^2. We provide flux densities, source sizes, and spectral
indices for the 425 sources detected in the image. We identify ~100$ new flat
spectrum radio sources; we project that when completed PiGSS will identify 10^4
flat spectrum sources. We identify one source that is a possible transient
radio source. This survey provides new limits on faint radio transients and
variables with characteristic durations of months.Comment: Accepted for publication in ApJ; revision submitted with extraneous
figure remove