2,576 research outputs found
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
Bending and Breathing Modes of the Galactic Disk
We explore the hypothesis that a passing satellite or dark matter subhalo has
excited coherent oscillations of the Milky Way's stellar disk in the direction
perpendicular to the Galactic midplane. This work is motivated by recent
observations of spatially dependent bulk vertical motions within ~ kpc of the
Sun. A satellite can transfer a fraction of its orbital energy to the disk
stars as it plunges through the Galactic midplane thereby heating and
thickening the disk. Bulk motions arise during the early stages of such an
event when the disk is still in an unrelaxed state. We present simple toy-model
calculations and simulations of disk-satellite interactions, which show that
the response of the disk depends on the relative velocity of the satellite.
When the component of the satellite's velocity perpendicular to the disk is
small compared with that of the stars, the perturbation is predominantly a
bending mode. Conversely, breathing and higher order modes are excited when the
vertical velocity of the satellite is larger than that of the stars. We argue
that the compression and rarefaction motions seen in three different surveys
are in fact breathing mode perturbations of the Galactic disk.Comment: 12 pages, 12 figure
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
From Spitzer Galaxy Photometry to Tully-Fisher Distances
This paper involves a data release of the observational campaign: Cosmicflows
with Spitzer (CFS). Surface photometry of the 1270 galaxies constituting the
survey is presented. An additional ~ 400 galaxies from various other Spitzer
surveys are also analyzed. CFS complements the Spitzer Survey of Stellar
Structure in Galaxies, that provides photometry for an additional 2352
galaxies, by extending observations to low galactic latitudes (|b|<30 degrees).
Among these galaxies are calibrators, selected in K band, of the Tully-Fisher
relation. The addition of new calibrators demonstrate the robustness of the
previously released calibration. Our estimate of the Hubble constant using
supernova host galaxies is unchanged, H0 = 75.2 +/- 3.3 km/s/Mpc.
Distance-derived radial peculiar velocities, for the 1935 galaxies with all the
available parameters, will be incorporated into a new data release of the
Cosmicflows project. The size of the previous catalog will be increased by 20%,
including spatial regions close to the Zone of Avoidance.Comment: Accepted for publication in MNRAS, 16 pages, 14 figures, 6 table
Radio galaxies and their magnetic fields out to z <= 3
We present polarisation properties at GHz of two separate
extragalactic source populations: passive quiescent galaxies and luminous
quasar-like galaxies. We use data from the {\it Wide-Field Infrared Survey
Explorer} data to determine the host galaxy population of the polarised
extragalactic radio sources. The quiescent galaxies have higher percentage
polarisation, smaller radio linear size, and GHz luminosity of
W Hz, while the quasar-like
galaxies have smaller percentage polarisation, larger radio linear size at
radio wavelengths, and a GHz luminosity of W Hz, suggesting that the environment of the
quasar-like galaxies is responsible for the lower percentage polarisation. Our
results confirm previous studies that found an inverse correlation between
percentage polarisation and total flux density at GHz. We suggest that
the population change between the polarised extragalactic radio sources is the
origin of this inverse correlation and suggest a cosmic evolution of the space
density of quiescent galaxies. Finally, we find that the extragalactic
contributions to the rotation measures (RMs) of the nearby passive galaxies and
the distant quasar-like galaxies are different. After accounting for the RM
contributions by cosmological large-scale structure and intervening Mg\,{II}
absorbers we show that the distribution of intrinsic RMs of the distant
quasar-like sources is at most four times as wide as the RM distribution of the
nearby quiescent galaxies, if the distribution of intrinsic RMs of the
WISE-Star sources itself is at least several rad m wide.Comment: 12 pages, 8 figures, accepted for publication into MNRA
Variability Flagging in the Wide-field Infrared Survey Explorer Preliminary Data Release
The Wide-field Infrared Survey Explorer Preliminary Data Release Source Catalog contains over 257 million objects. We describe the method used to flag variable source candidates in the Catalog. Using a method based on the chi-square of single-exposure flux measurements, we generated a variability flag for each object, and have identified almost 460,000 candidate sources that exhibit significant flux variability with greater than ~7σ confidence. We discuss the flagging method in detail and describe its benefits and limitations. We also present results from the flagging method, including example light curves of several types of variable sources including Algol-type eclipsing binaries, RR Lyr, W UMa, and a blazar candidate
- …