2,514 research outputs found
Abell 3627: A Nearby, X-ray Bright, and Massive Galaxy Cluster
The cluster A3627 was recently recognized to be a very massive, nearby
cluster in a galaxy survey close to the galactic plane. We are reporting on
ROSAT PSPC observations of this object which confirm that the cluster is indeed
very massive. The X-ray emission detected from the cluster extends over almost
1 degree in radius. The X-ray image is not spherically symmetric and shows
indications of an ongoing cluster merger. Due to the strong interstellar
absorption the spectral analysis and the gas temperature determination are
difficult. The data are consistent with an overall gas temperature in the range
5 to 10 keV. There are signs of temperature variations in the merger region. A
mass estimate based on the X-ray data yields values of \msu \ if extrapolated to the virial radius of Mpc. In
the ROSAT energy band (0.1 - 2.4 keV) the cluster emission yields a flux of
about erg s cm which makes A3627 the 6
brightest cluster in the ROSAT All Sky Survey. The cluster was missed in
earlier X-ray surveys because it was confused with a neighbouring X-ray bright,
galactic X-ray binary (1H1556-605). The large X-ray flux makes A3627 an
important target for future studies.Comment: 14 pages, Latex file, including aaspp.sty, 9 postscript figures and 1
table, accepted for publication by the Astrophysical Journa
HI Bright Galaxies in the Southern Zone of Avoidance
A blind survey for HI bright galaxies in the southern Zone of Avoidance, (212
deg < l < 36 deg; |b| < 5 deg), has been made with the 21 cm multibeam receiver
on the Parkes 64 m radiotelescope. The survey, sensitive to normal spiral
galaxies to a distance of about 40 Mpc and more nearby dwarfs, detected 110
galaxies. Of these, 67 have no counterparts in the NASA/IPAC Extragalactic
Database. In general, the uncataloged galaxies lie behind thicker obscuration
than do the cataloged objects. All of the newly-discovered galaxies have HI
flux integrals more than an order of magnitude lower than the Circinus galaxy.
The survey recovers the Puppis cluster and foreground group (Kraan-Korteweg &
Huchtmeier 1992), and the Local Void remains empty. The HI mass function
derived for the sample is satisfactorily fit by a Schechter function with
parameters alpha = 1.51 +- 0.12, Phi* = 0.006 +- 0.003, and log M* = 9.7 +-
0.10.Comment: To appear in The Astronomical Journa
Calorons, instantons and constituent monopoles in SU(3) lattice gauge theory
We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge
configurations at non-zero temperature and compare periodic and anti-periodic
temporal boundary conditions for the fermions. It is demonstrated that for the
different boundary conditions often the modes are localized at different
space-time points and have different sizes. Our observations are consistent
with patterns expected for Kraan - van Baal solutions of the classical
Yang-Mills equations. These solutions consist of constituent monopoles and the
zero-modes are localized on different constituents for different boundary
conditions. Our findings indicate that the excitations of the QCD vacuum are
more structured than simple instanton-like lumps.Comment: Remarks added. To appear in Phys. Rev.
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
Chiral zero-mode for abelian BPS dipoles
We present an exact normalisable zero-energy chiral fermion solution for
abelian BPS dipoles. For a single dipole, this solution is contained within the
high temperature limit of the SU(2) caloron with non-trivial holonomy.Comment: 9 pages, 1 figure (in 2 parts), presented at the workshop on
"Confinement, Topology, and other Non-Perturbative Aspects of QCD", 21-27
Jan. 2002, Stara Lesna, Slovaki
Towards a Full Census of the Obscure(d) Vela Supercluster using MeerKAT
Recent spectroscopic observations of a few thousand partially obscured
galaxies in the Vela constellation revealed a massive overdensity on
supercluster scales straddling the Galactic Equator (l 272.5deg) at km/s. It remained unrecognised because it is located just beyond the
boundaries and volumes of systematic whole-sky redshift and peculiar velocity
surveys - and is obscured by the Milky Way. The structure lies close to the
apex where residual bulkflows suggest considerable mass excess. The uncovered
Vela Supercluster (VSCL) conforms of a confluence of merging walls, but its
core remains uncharted. At the thickest foreground dust column densities (|b| <
6 deg) galaxies are not visible and optical spectroscopy is not effective. This
precludes a reliable estimate of the mass of VSCL, hence its effect on the
cosmic flow field and the peculiar velocity of the Local Group. Only systematic
HI-surveys can bridge that gap. We have run simulations and will present
early-science observing scenarios with MeerKAT 32 (M32) to complete the census
of this dynamically and cosmologically relevant supercluster. M32 has been put
forward because this pilot project will also serve as precursor project for HI
MeerKAT Large Survey Projects, like Fornax and Laduma. Our calculations have
shown that a survey area of the fully obscured part of the supercluster, where
the two walls cross and the potential core of the supercluster resides, can be
achieved on reasonable time-scales (200 hrs) with M32.Comment: 10 pages, 3 figures, accepted for publication, Proceedings of
Science, workshop on "MeerKAT Science: On the Pathway to the SKA", held in
Stellenbosch 25-27 May 201
SNIa Host Galaxy Properties and the Dust Extinction Distribution
Supernovae Type Ia display a complex relation with their host galaxies. An
important prior to the fit of the supernovae's lightcurve is the distribution
of host galaxy extinction values that can be encountered. The SDSS-SN project
has published light curve fits using both MLCS2k2 and SALT2. We use the former
fits extinction parameter () to map this distribution of extinction
values.
We explore the dependence of this distribution on four observables; the
inclination of the host galaxy disk, radial position of the supernova, redshift
of the supernova and host, and the level of star-formation in the host galaxy.
The distribution of values encountered by supernovae is typically
characterised by: , with = 0.4 or 0.33.
We find that the inclination correction using an infinitely thin disk for the
SNIa is sufficient, resulting in similar exponential distributions for
high- and low-inclination disks. The distribution also depends on the
radial position in the disk, consistent with previous results on the
transparency of spiral disks. The distribution of values narrows with
increased star-formation, possibly due to the destruction or dispersion of the
dusty ISM by stellar winds prior to the ignition of the supernova.
In future supernova searches, certainly the inclination of the host galaxy
disk, should be considered in the construction of the \av \ prior with
as the most likely prior in each individual host galaxy's
case.Comment: 10 pages, 14 figures, accepted for publication by MNRA
New HI-detected Galaxies in the Zone of Avoidance
We present the first results of a blind HI survey for galaxies in the
southern Zone of Avoidance with a multibeam receiver on the Parkes telescope.
This survey is eventually expected to catalog several thousand galaxies within
Galactic latitude |b|<5 degrees, mostly unrecognised before due to Galactic
extinction and confusion. We present here results of the first three detections
to have been imaged with the Australia Telescope Compact Array (ATCA). The
galaxies all lie near Galactic longitude 325 degrees and were selected because
of their large angular sizes, up to 1.3 degrees. Linear sizes range from 53 to
108 kpc. The first galaxy is a massive 5.7x10^11 solar mass disk galaxy with a
faint optical counterpart, SGC 1511.1--5249. The second is probably an
interacting group of galaxies straddling the Galactic equator. No optical
identification is possible. The third object appears to be an interacting pair
of low column density galaxies, possibly belonging to an extended Circinus or
Centaurus A galaxy group. No optical counterpart has been seen despite the
predicted extinction (A(B) = 2.7 - 4.4 mag) not being excessive. We discuss the
implications of the results, in particular the low HI column densities (~10^19
atoms/sq.cm) found for two of the three galaxies.Comment: 17 pages, 8 figures (Fig.1 in three parts, Fig.5 in two parts). To
appear in Astronomical Journal (Dec 1998). See
http://www.atnf.csiro.au/research/multibea
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