1,960 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-
Large-scale variations of the dust optical properties in the Galaxy
We present an analysis of the dust optical properties at large scale, for the
whole galactic anticenter hemisphere. We used the 2MASS Extended Source Catalog
to obtain the total reddening on each galaxy line of sight and we compared this
value to the IRAS 100 microns surface brightness converted to extinction by
Schlegel et al (1998). We performed a careful examination and correction of the
possible systematic effects resulting from foreground star contamination,
redshift contribution and galaxy selection bias. We also evaluated the
contribution of dust temperature variations and interstellar clumpiness to our
method. The correlation of the near-infrared extinction to the far-infrared
optical depth shows a discrepancy for visual extinction greater than 1 mag with
a ratio A_V(FIR) / A_V(gal) = 1.31 +- 0.06. We attribute this result to the
presence of fluffy/composite grains characterized by an enhanced far--infrared
emissivity. Our analysis, applied to half of the sky, provides new insights on
the dust grains nature suggesting fluffy grains are found not only in some very
specific regions but in all directions for which the visual extinction reaches
about 1 mag.Comment: 10 pages, 11 figures, accepted for publication in A&
Recalibrating the Wide-field Infrared Survey Explorer (WISE) W4 Filter
We present a revised effective wavelength and photometric calibration for the
Wide-field Infrared Survey Explorer (WISE) W4 band, including tests of
empirically motivated modifications to its pre-launch laboratory-measured
relative system response curve. We derived these by comparing measured W4
photometry with photometry synthesised from spectra of galaxies and planetary
nebulae. The difference between measured and synthesised photometry using the
pre-launch laboratory-measured W4 relative system response can be as large as
0.3 mag for galaxies and 1 mag for planetary nebulae. We find the W4 effective
wavelength should be revised upward by 3.3%, from 22.1 micron to 22.8 micron,
and the W4 AB magnitude of Vega should be revised from m = 6.59 to m = 6.66. In
an attempt to reproduce the observed W4 photometry, we tested three
modifications to the pre-launch laboratory-measured W4 relative system response
curve, all of which have an effective wavelength of 22.8 micron. Of the three
relative system response curve models tested, a model that matches the
laboratory-measured relative system response curve, but has the wavelengths
increased by 3.3% (or 0.73 micron) achieves reasonable agreement between the
measured and synthesised photometry.Comment: Accepted for publication in Publications of the Astronomical Society
of Australia, 6 pages, 4 figures, 1 tabl
HI observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7
We present HI observations of the Sculptor Group starburst spiral galaxy NGC
253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for
the SKA precursor MeerKAT, under construction. The short baselines and low
system temperature of the telescope make it very sensitive to large scale, low
surface brightness emission. The KAT-7 observations detected 33% more flux than
previous VLA observations, mainly in the outer parts and in the halo for a
total HI mass of M. HI can be found at
large distances perpendicular to the plane out to projected distances of ~9-10
kpc away from the nucleus and ~13-14 kpc at the edge of the disk. A novel
technique, based on interactive profile fitting, was used to separate the main
disk gas from the anomalous (halo) gas. The rotation curve (RC) derived for the
HI disk confirms that it is declining in the outer parts, as seen in previous
optical Fabry-Perot measurements. As for the anomalous component, its RC has a
very shallow gradient in the inner parts and turns over at the same radius as
the disk, kinematically lagging by ~100 km/sec. The kinematics of the observed
extra planar gas is compatible with an outflow due to the central starburst and
galactic fountains in the outer parts. However, the gas kinematics shows no
evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the
star formation rate (SFR) is compatible with the starburst nature of NGC 253.Comment: 18 pages, 20 figures, 8 Tables. Accepted for publication to MNRA
The 2MASS Tully-Fisher Survey : Mapping the Mass in the Universe
The 2MASS Tully-Fisher Survey (2MTF) aims to measure Tully-Fisher (TF)
distances for all bright inclined spirals in the 2MASS Redshift Survey (2MRS)
using high quality HI widths and 2MASS photometry. Compared with previous
peculiar velocity surveys, the 2MTF survey provides more accurate width
measurements and more uniform sky coverage, combining observations with the
Green Bank, Arecibo and Parkes telescopes. With this new redshift-independent
distance database, we will significantly improve our understanding of the mass
distribution in the local universe.Comment: 4 pages, 3 figures, IAU Symposium 289 proceedin
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