11,551 research outputs found
The Nature of the Peculiar Virgo Cluster Galaxies NGC 4064 and NGC 4424
We present a detailed study of the peculiar HI-deficient Virgo cluster spiral
galaxies NGC 4064 and NGC 4424, using CO 1-0 interferometry, optical
imaging and integral-field spectroscopic observations, in order to learn what
type of environmental interactions have afected these galaxies. Optical imaging
reveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shaped
isophotes and shells. NGC 4064, which lies in the cluster outskirts, possesses
a relatively undisturbed outer stellar disk and a central bar. In both galaxies
H-alpha emission is confined to the central kiloparsec. CO observations reveal
bilobal molecular gas morphologies, with H-alpha emission peaking inside the CO
lobes, implying a time sequence in the star formation process.Gas kinematics
reveals strong bar-like non-circular motions in the molecular gas in both
galaxies, suggesting that the material is radially infalling. In NGC 4064 the
stellar kinematics reveal strong bar-like non-circular motions in the central 1
kpc. On the other hand, NGC 4424 has extremely modest stellar rotation
velocities (Vmax ~ 30 km s-1), and stars are supported by random motions as far
out as we can measure it. The observations suggest that the peculiarities of
NGC 4424 are the result of an intermediate-mass merger plus ram pressure
stripping. In the case of NGC 4064, the evidence suggests an already stripped
"truncated/normal" galaxy that recently suffered a minor merger or tidal
interaction with another galaxy. We propose that galaxies with
"truncated/compact" H-alpha morphologies such as these are the result of the
independent effects of ram pressure stripping, which removes gas from the outer
disk, and gravitational interactions such as mergers, which heat stellar disks,
drive gas to the central kpc and increase the central mass concentrations.Comment: 42 pages, 21 figure
Surface Brightness and Stellar Populations at the Outer Edge of the Large Magellanic Cloud: No Stellar Halo Yet
We present a high quality CMD for a 36'x 36' field located 8 degrees (7 kpc)
from the LMC center, as well as a precise determination of the LMC surface
brightness derived from the resolved stellar population out to this large
galactocentric radius. This deep CMD shows for the first time the detailed age
distribution at this position, where the surface brightness is V=26.5 mag/sq".
At a radius R=474' the main sequence is well populated from the oldest turnoff
at I=21.5 to the 2.5 Gyr turnoff at I=19.5. Beyond this radius, a relatively
strong gradient in the density of stars with ages in the 2.5-4 Gyr range is
apparent. There are some stars brighter and bluer than the main population,
quite uniformly distributed over the whole area surveyed, which are well
matched by a 1.5 Gyr isochrone and may be indicative of a relatively recent
star formation, or merger, event. The surface brightness profile of the LMC
remains exponential to this large galactocentric radius and shows no evidence
of disk truncation. Combining the information on surface brightness and stellar
population we conclude that the LMC disk extends (and dominates over a possible
stellar halo) out to a distance of at least 7 kpc. These results confirm that
the absence of blue stars in the relatively shallow off-center CMDs of dIrr
galaxies is not necessarily evidence for an exclusively old stellar population
resembling the halo of the Milky Way.Comment: ApJLett, in press 13 pages including 3 color figure
The twisted fourth moment of the Riemann zeta function
We compute the asymptotics of the fourth moment of the Riemann zeta function
times an arbitrary Dirichlet polynomial of length Comment: 28 pages. v2: added reference
Pomeron loops in zero transverse dimensions
We analyze a toy model which has a structure similar to that of the recently
found QCD evolution equations, but without transverse dimensions. We develop
two different but equivalent methods in order to compute the leading-order and
next-to-leading order Pomeron loop diagrams. In addition to the leading-order
result which has been derived from Mueller's toy model~\cite% {Mueller:1994gb},
we can also calculate the next-to-leading order contribution which provides the
correction. We interpret this result and discuss its
possible implications for the four-dimensional QCD evolution.Comment: 11 pages, 4 figure
Enhancement and evaluation of Skylab photography for potential land use inventories, part 1
The author has identified the following significant results. Three sites were evaluated for land use inventory: Finger Lakes - Tompkins County, Lower Hudson Valley - Newburgh, and Suffolk County - Long Island. Special photo enhancement processes were developed to standardize the density range and contrast among S190A negatives. Enhanced black and white enlargements were converted to color by contact printing onto diazo film. A color prediction model related the density values on each spectral band for each category of land use to the spectral properties of the various diazo dyes. The S190A multispectral system proved to be almost as effective as the S190B high resolution camera for inventorying land use. Aggregate error for Level 1 averaged about 12% while Level 2 aggregate error averaged about 25%. The S190A system proved to be much superior to LANDSAT in inventorying land use, primarily because of increased resolution
Seeking the Local Convergence Depth. I. TF Observations of the Clusters A168, A397, A569, A1139, A1228, and A1983
We present first results of an all-sky observing program designed to improve
the quality of the I band Tully-Fisher (TF) template and to obtain the reflex
motion of the Local Group with respect to clusters to z = 0.06. We are
obtaining between 5 and 15 TF measurements per cluster on a sample of 50
clusters at intermediate redshifts (0.02 < z < 0.06). Presentation of the data
for seven Abell clusters of galaxies is given here. This data incorporates
methods for estimating the true inclination of a spiral disk, an observational
parameter undervalued for small angular-sized galaxies or for galaxies observed
in poor seeing conditions.Comment: 21 pages, uses AAS LaTeX, 3 tables and 8 postscript figures (only
first page of fig. 6 included in this version); to appear in the Astronomical
Journa
Seeking the Local Convergence Depth. The Abell Cluster Dipole Flow to 200 Mpc/h
We have obtained new Tully-Fisher (TF) peculiar velocity measurements for 52
Abell galaxy clusters distributed throughout the sky between ~ 50 and 200
Mpc/h.The measurements are based on I band photometry and optical rotation
curves for a sample of 522 spiral galaxies, from which an accurate TF template
relation has been constructed. Individual cluster TF relations are referred to
the template to compute cluster peculiar motions.
The reflex motion of the Local Group of galaxies is measured with respect to
the reference frame defined by our cluster sample and the distant portion of
the Giovanelli et al. (1998) cluster set. We find the Local Group motion in
this frame to be 565+/-113 km/s in the direction (l,b)=(267,26)+/-10 when
peculiar velocities are weighted according to their errors. After optimizing
the dipole calculation to sample equal volumes equally, the vector is 509+/-195
km/s towards (255,33)+/-22. Both solutions agree, to within 1-sigma or better,
with the Local Group motion as inferred from the cosmic microwave background
(CMB) dipole. Thus, the cluster sample as a whole moves slowly in the CMB
reference frame, its bulk flow being at most 200 km/s.Comment: 11 pages, uses AAS LaTeX; to appear in the Astrophysical Journal
Letter
No Evidence for Orbital Loop Currents in Charge Ordered YBaCuO from Polarized Neutron Diffraction
It has been proposed that the pseudogap state of underdoped cuprate
superconductors may be due to a transition to a phase which has circulating
currents within each unit cell. Here, we use polarized neutron diffraction to
search for the corresponding orbital moments in two samples of underdoped
YBaCuO with doping levels and 0.123. In contrast to
some other reports using polarized neutrons, but in agreement with nuclear
magnetic resonance and muon spin rotation measurements, we find no evidence for
the appearance of magnetic order below 300 K. Thus, our experiment suggests
that such order is not an intrinsic property of high-quality cuprate
superconductor single crystals. Our results provide an upper bound for a
possible orbital loop moment which depends on the pattern of currents within
the unit cell. For example, for the CC- pattern proposed by Varma,
we find that the ordered moment per current loop is less than 0.013 for
.Comment: Comments in arXiv:1710.08173v1 fully addresse
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