2,599 research outputs found
On How to Extend the NIR Tully-Fisher Relation to be Truly All-Sky
Dust extinction and stellar confusion by the Milky Way reduce the efficiency
of detecting galaxies at low Galactic latitudes, creating the so-called Zone of
Avoidance. This stands as a stumbling block in charting the distribution of
galaxies and cosmic flow fields, and therewith our understanding of the local
dynamics in the Universe (CMB dipole, convergence radius of bulk flows). For
instance, ZoA galaxies are generally excluded from the whole-sky Tully-Fisher
Surveys () even if catalogued. We show here that by
fine-tuning the near-infrared TF relation, there is no reason not to extend
peculiar velocity surveys deeper into the ZoA. Accurate axial ratios ()
are crucial to both the TF sample selection and the resulting TF distances. We
simulate the effect of dust extinction on the geometrical properties of
galaxies. As expected, galaxies appear rounder with increasing obscuration
level, even affecting existing TF samples. We derive correction models and
demonstrate that we can reliably reproduce the intrinsic axial ratio from the
observed value up to extinction level of about mag (
mag), we also recover a fair fraction of galaxies that otherwise would fall out
of an uncorrected inclination limited galaxy sample. We present a
re-calibration of the 2MTF relation in the NIR , , and -bands for
isophotal rather than total magnitudes, using their same calibration sample.
Both TF relations exhibit similar scatter at high Galactic latitudes. However,
the isophotal TF relation results in a significant improvement in the scatter
for galaxies in the ZoA, and low surface brightness galaxies in general,
because isophotal apertures are more robust in the face of significant stellar
confusion.Comment: 12 pages, 10 figures, 4 tables, accepted for publication in MNRA
Galaxy peculiar velocities in the Zone of Avoidance
Dust extinction and stellar confusion of the Milky Way hinder the detection
of galaxies at low Galactic latitude, creating the so-called Zone of Avoidance
(ZoA). This has hampered our understanding of the local dynamics, cosmic flow
fields and the origin of the Cosmic Microwave Background dipole. The ZoA () is also excluded from the "whole-sky" Two Micron All-Sky Survey
(2MASS) Redshift Survey (2MRS) and 2MASS Tully-Fisher Survey (2MTF). The latter
aims to provide distances and peculiar velocities for all bright inclined 2MASS
galaxies with \leq 11\hbox{.\!\!^{\rm m}}25. Correspondingly,
knowledge about the density distribution in the ZoA remains limited to
statistical interpolations. To improve on this bias we pursued two different
surveys to fill in the southern and northern ZoA. These data will allow a
direct measurement of galaxy peculiar velocities. In this paper we will present
a newly derived optimized Tully-Fisher (TF) relation that allow accurate
measures of galaxy distances and peculiar velocities for dust-obscured
galaxies. We discuss further corrections for magnitudes and biases and present
some preliminary results on flow fields in the southern ZoA.Comment: 6 pages, 3 figures, to appear in Proceedings of SAIP2013, the 58th
Annual Conference of the South African Institute of Physics, edited by Roelf
Botha and Thulani Jili (SAIP and University of Zululand, 2014). ISBN:
978-0-620-62819-
Calorons, Nahm's equations on S^1 and bundles over P^1xP^1
The moduli space of solutions to Nahm's equations of rank (k,k+j) on the
circle, and hence, of SU(2) calorons of charge (k,j), is shown to be equivalent
to the moduli of holomorphic rank 2 bundles on P^1xP^1 trivialized at infinity
with c_2=k and equipped with a flag of degree j along P^1x{0}. An explicit
matrix description of these spaces is given by a monad constructio
Alternative administration routes and delivery technologies for polio vaccines.
Global polio eradication is closer than ever. Replacement of the live attenuated oral poliovirus vaccine (OPV) by inactivated poliovirus vaccine (IPV) is recommended to achieve complete eradication. Limited global production capacity and relatively high IPV costs compared to OPV spur the need for improved polio vaccines. The target product profile of these vaccines includes not only dose sparing but also high stability, which is important for stockpiling, and easy application important for (emergency) vaccination campaigns. In this review, the current status of alternative polio vaccine delivery strategies is given. Furthermore, we discuss the feasibility of these strategies by highlighting challenges, hurdles to overcome, and formulation issues relevant for optimal vaccine delivery
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
Hyperbolic calorons, monopoles, and instantons
We construct families of SO(3)-symmetric charge 1 instantons and calorons on
the space H^3 x R. We show how the calorons include instantons and hyperbolic
monopoles as limiting cases. We show how Euclidean calorons are the flat space
limit of this family.Comment: 11 pages, no figures 1 reference added Published version available
at: http://www.springerlink.com/content/k0j4815u54303450
NIR Tully-Fisher in the Zone of Avoidance. -- III. Deep NIR catalogue of the HIZOA galaxies
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a deep near-infrared (NIR) photometric catalogue of sources from the Parkes HI Zone of Avoidance (HIZOA) survey, which forms the basis for an investigation of the matter distribution in the Zone of Avoidance. Observations were conducted between 2006 and 2013 using the Infrared Survey Facility (IRSF), a 1.4-m telescope situated at the South African Astronomical Observatory site in Sutherland. The images cover all 1108 HIZOA detections and yield 915 galaxies. An additional 105 bright 2MASS galaxies in the southern ZOA were imaged with the IRSF, resulting in 129 galaxies. The average -band seeing and sky background for the survey are 1.38 arcsec and 20.1 mag, respectively. The detection rate as a function of stellar density and dust extinction is found to depend mainly on the HI mass of the HI detected galaxies, which in principal correlates with the NIR brightness of the spiral galaxies. The measured isophotal magnitudes are of sufficient accuracy (errors 0.02 mag) to be used in a Tully-Fisher analysis. In the final NIR catalogue, 285 galaxies have both IRSF and 2MASS photometry (180 HIZOA plus 105 bright 2MASX galaxies). The -band isophotal magnitudes presented in this paper agree, within the uncertainties, with those reported in the 2MASX catalogue. Another 30 galaxies, from the HIZOA northern extension, are also covered by UKIDSS Galactic Plane Survey (GPS) images, which are one magnitude deeper than our IRSF images. A modified version of our photometry pipeline was used to derive the photometric parameters of these UKIDSS galaxies. Good agreement was found between the respective -band isophotal magnitudes. These comparisons confirm the robustness of the isophotal parameters and demonstrate that the IRSF images do not suffer from foreground contamination, after star removal, nor under-estimate the isophotal fluxes of ZoA galaxies.Peer reviewe
Driftscan Surveys in the 21cm Line with the Arecibo and Nancay Telescopes
Driftscan methods are highly efficient, stable techniques for conducting
extragalactic surveys in the 21cm line of neutral hydrogen. Holding the
telescope still while the beam scans the sky at the sidereal rate produces
exceptionally stable spectral baselines, increased stability for RFI signals,
and excellent diagnostic information about system performance. Data can be
processed naturally and efficiently by grouping long sequences of spectra into
an image format, thereby allowing thousands of individual spectra to be
calibrated, inspected and manipulated as a single data structure with standard
tools that already exist in astronomical software. The behavior of spectral
standing waves (multi-path effects) can be appraised and excised in this
environment, making observations possible while the Sun is up. The method is
illustrated with survey data from Arecibo and Nancay.Comment: 7 pages; Latex; 1 encapsulated postscript figure; 4 jpeg images; 1
gif image. Presented at the workshop `HI in the Local Universe', Sydney, May
13-15 1996. Accepted for publication by Publications of the Astronomical
Society of Australia. Complete manuscript with encapsulated figures is
available at
http://www.atnf.csiro.au/Publications/HI_workshop/proceedings.htm
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