2,239 research outputs found
DENIS Observations of Multibeam Galaxies in the Zone of Avoidance
Roughly 25% of the optical extragalactic sky is obscured by the dust and
stars of our Milky Way. Dynamically important structures might still lie hidden
in this zone. Various surveys are presently being employed to uncover the
galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from
(different) limitations and selection effects.
We illustrate the promise of using a multi-wavelength approach for
extragalactic large-scale studies behind the ZOA, i.e. a combination of three
surveys -- optical, systematic blind HI and near-infrared (NIR), which will
allow the mapping of the peculiar velocity field in the ZOA through the NIR
Tully-Fisher relation. In particular, we present here the results of
cross-identifying HI-detected galaxies with the DENIS NIR survey, and the use
of NIR colours to determine foreground extinctions.Comment: Accepted for publication in PASA. Proceedings of workshop "HI in the
Local Universe, II", held in Melbourne, Sept. 1998. 9 pages, LaTeX2e, 2
encapsulated PS figures, 3 JPEG figures, Full resolution figures 2, 3 and 4
and full resolution paper are at
ftp://ftp.iap.fr/pub/from_users/gam/PAPERS/HICONF
The Parkes HI Zone of Avoidance Survey
A blind HI survey of the extragalactic sky behind the southern Milky Way has
been conducted with the multibeam receiver on the 64-m Parkes radio telescope.
The survey covers the Galactic longitude range 212 < l < 36 and Galactic
latitudes |b| < 5, and yields 883 galaxies to a recessional velocity of 12,000
km/s. The survey covers the sky within the HIPASS area to greater sensitivity,
finding lower HI-mass galaxies at all distances, and probing more completely
the large-scale structures at and beyond the distance of the Great Attractor.
Fifty-one percent of the HI detections have an optical/NIR counterpart in the
literature. A further 27% have new counterparts found in existing, or newly
obtained, optical/NIR images. The counterpart rate drops in regions of high
foreground stellar crowding and extinction, and for low-HI mass objects. Only
8% of all counterparts have a previous optical redshift measurement. A notable
new galaxy is HIZOA J1353-58, a possible companion to the Circinus galaxy.
Merging this catalog with the similarly-conducted northern extension (Donley et
al. 2005), large-scale structures are delineated, including those within the
Puppis and Great Attractor regions, and the Local Void. Several
newly-identified structures are revealed here for the first time. Three new
galaxy concentrations (NW1, NW2 and NW3) are key in confirming the diagonal
crossing of the Great Attractor Wall between the Norma cluster and the CIZA
J1324.7-5736 cluster. Further contributors to the general mass overdensity in
that area are two new clusters (CW1 and CW2) in the nearer Centaurus Wall, one
of which forms part of the striking 180 deg (100/h Mpc) long filament that
dominates the southern sky at velocities of ~3000 km/s, and the suggestion of a
further Wall at the Great Attractor distance at slightly higher longitudes.Comment: Published in Astronomical Journal 9 February 2016 (accepted 26
September 2015); 42 pages, 7 tables, 18 figures, main figures data tables
only available in the on-line version of journa
Analysis of time-profiles with in-beam PET monitoring in charged particle therapy
Background: Treatment verification with PET imaging in charged particle
therapy is conventionally done by comparing measurements of spatial
distributions with Monte Carlo (MC) predictions. However, decay curves can
provide additional independent information about the treatment and the
irradiated tissue. Most studies performed so far focus on long time intervals.
Here we investigate the reliability of MC predictions of space and time (decay
rate) profiles shortly after irradiation, and we show how the decay rates can
give an indication about the elements of which the phantom is made up.
Methods and Materials: Various phantoms were irradiated in clinical and
near-clinical conditions at the Cyclotron Centre of the Bronowice proton
therapy centre. PET data were acquired with a planar 16x16 cm PET system.
MC simulations of particle interactions and photon propagation in the phantoms
were performed using the FLUKA code. The analysis included a comparison between
experimental data and MC simulations of space and time profiles, as well as a
fitting procedure to obtain the various isotope contributions in the phantoms.
Results and conclusions: There was a good agreement between data and MC
predictions in 1-dimensional space and decay rate distributions. The fractions
of C, O and C that were obtained by fitting the decay
rates with multiple simple exponentials generally agreed well with the MC
expectations. We found a small excess of C in data compared to what was
predicted in MC, which was clear especially in the PE phantom.Comment: 9 pages, 5 figures, 1 table. Proceedings of the 20th International
Workshop on Radiation Imaging Detectors (iWorid2018), 24-28 June 2018,
Sundsvall, Swede
Application of the Large-N_c limit to a Chiral Lagrangian with Resonances
It is shown that the implementation of the Large-- approximation helps
to get insight into the structure of, in principle, any QCD-like theory. As an
example, we will compute the NLO corrections to in the chiral limit
with a Lagrangian with Resonances.Comment: 9 pages, 1 figure. Talk given at the International School of
Subnuclear Physics (Erice 2002). To be published in the Proceeding
Calorons in Weyl Gauge
We demonstrate by explicit construction that while the untwisted
Harrington-Shepard caloron is manifestly periodic in Euclidean time,
with period , when transformed to the Weyl () gauge,
the caloron gauge field is periodic only up to a large gauge
transformation, with winding number equal to the caloron's topological charge.
This helps clarify the tunneling interpretation of these solutions, and their
relation to Chern-Simons numbers and winding numbers.Comment: 10 pages, 10 figures, a sign typo in equation 27 is correcte
Two New Planetary Nebulae Discovered in a Galaxy Search in the Southern Milky Way
Spectroscopic observations have been carried out for eleven objects believed
to be planetary nebulae on the basis of their optical appearance. They were
discovered in an ongoing deep search for galaxies in the Southern Milky Way
(Kraan-Korteweg & Woudt 1994). The objects were observed with the 1.9m
telescope of the South African Astronomical Observatory during our program for
obtaining redshifts of obscured galaxies in the ``Zone of Avoidance''. Of the
eleven objects, three proved too faint for a definite classification, four were
galaxies with radial velocities between v=3920 km/s and v=14758 km/s, but four
were confirmed as planetary nebulae (PNE). Their relative line strengths and
radial velocities have been determined. The PNE are on average fairly large
(23''-30''). Two of them (PNG 298.3+06.7 and PNG 323.6-04.5) were previously
unknown; for these we show H_alpha and [OIII] images.Comment: A&A accepted, 7 pages, 3 tables, 2 postscript figures, 2 GIF figures,
uses l-aa.sty, full paper including ps-figures available upon request at
ftp://gin.obspm.fr/depot/kraan/pn.ps.gz (7.8Mb
A Morphological-type dependence in the mu_0-log(h) plane of Spiral galaxy disks
We present observational evidence for a galaxy `Type' dependence to the
location of a spiral galaxy's disk parameters in the mu_0-log(h) (central disk
surface-brightness - disk scale-length) plane. With a sample of ~40 Low Surface
Brightness galaxies (both bulge- and disk-dominated) and ~80 High Surface
Brightness galaxies, the early-type disk galaxies (<=Sc) tend to define a
bright envelope in the mu_0-log(h) plane, while the late-type (>=Scd) spiral
galaxies have, in general, smaller and fainter disks. Below the defining
surface brightness threshold for a Low Surface Brightness galaxy (i.e. more
than 1 mag fainter than the 21.65 B-mag arcsec^(-2) Freeman value), the
early-type spiral galaxies have scale-lengths greater than 8-9 kpc, while the
late-type spiral galaxies have smaller scale-lengths. All galaxies have been
modelled with a seeing-convolved Sersic r^(1/n) bulge and exponential disk
model. We show that the trend of decreasing bulge shape parameter (n) with
increasing Hubble type and decreasing bulge-to-disk luminosity ratio, which has
been observed amongst the High Surface Brightness galaxies, extends to the Low
Surface Brightness galaxies, revealing a continuous range of structural
parameters.Comment: To be published in ApJ. Inc. three two-part figure
Reddening, Absorption, and Decline Rate Corrections for a Complete Sample of Type Ia Supernovae leading to a Fully Corrected Hubble Diagram to v<30,000kms-1
Photometric BVI and redshift data corrected for streaming motions are
compiled for 111 "Branch normal", 4 1991T-like, 7 1991bg-like, and 2 unusual
SNe Ia. Color excesses E(B-V)host of normal SNe Ia, due to the absorption of
the host galaxy, are derived by three independent methods leading to the
intrinsic colors at maximum of (B-V)00=-0.024, and (V-I)00=-0.265 if normalized
to a common decline rate of Dm_15=1.1. The strong correlation between redshift
absolute magnitudes (based on Ho=60), corrected only for the extrinsic Galactic
absorption, and the derived E(B-V)host leads to well determined, yet abnormal
absorption-to-reddening ratios of R_BVI=3.65, 2.65, and 1.35. Comparison with
the canonical Galactic values of 4.1, 3.1, 1.8 forces the conclusion that the
law of interstellar absorption in the path length to the SN in the host galaxy
is different from the local Galactic law. Improved correlations of the fully
corrected absolute magnitudes with host galaxy type, decline rate, and
intrinsic color are derived. The four peculiar 1991T-type SNe are significantly
overluminous as compared to Branch-normal SNe Ia. The overluminosity of the
seven 1999aa-like SNe is less pronounced. The seven 1991bg-types in the sample
constitute a separate class of SNeIa, averaging in B two magnitudes fainter
than the normal Ia. New Hubble diagrams in BVI are derived out to ~30,000kms-1
using the fully corrected magnitudes and velocities, corrected for streaming
motions. Nine solutions for the intercept magnitudes in these diagrams show
extreme stability at the 0.04 level using various subsamples of the data. The
same precepts for fully correcting SN magnitudes we shall use for the
luminosity recalibration of SNe Ia in the forthcoming final review of our HST
Cepheid-SN experiment for the Hubble constant.Comment: 49 pages, 15 figures, 8 tables, accepted for publication in the
Astrophysical Journa
Discovery of a Nearby Low-Surface-Brightness Spiral Galaxy
During the course of a search for compact, isolated gas clouds moving with
anomalous velocities in or near our own Galaxy (Braun and Burton 1998 A&A, in
press), we have discovered, in the data of the Leiden/Dwingeloo survey
(Hartmann and Burton 1997, Atlas of Galactic Neutral Hydrogen, CUP) of Galactic
hydrogen, the HI signature of a large galaxy, moving at a recession velocity of
282 km/s, with respect to our Galaxy. Deep multicolor and spectroscopic optical
observations show the presence of star formation in scattered HII regions;
radio HI synthesis interferometry confirms that the galaxy is rich in HI and
has the rotation signature of a spiral galaxy; a submillimeter observation
failed to detect the CO molecule. The radio and optical evidence combined
suggest its classification as a low-surface-brightness spiral galaxy. It is
located in close spatial and kinematic proximity to the galaxy NGC 6946. The
newly-discovered galaxy, which we call Cepheus 1, is at a distance of about 6
Mpc. It is probably to be numbered amongst the nearest few LSB spirals.Comment: 13 page LaTeX, requires aastex, 4 GIF figures. Accepted for
publication in the AJ, January 199
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