79 research outputs found
The HI content of the recently discovered field dwarf galaxy APPLES1
We present observations in a search for neutral hydrogen associated with the
recently detected field dwarf galaxy APPLES1, performed with the Parkes
radiotelescope. The observed radio spectrum shows no evident (> 3sigma rms)
line emission indicating an upper limit for the HI content of the galaxy of ~
10E6 solar masses and providing an upper value for the M(HI)/L(B) ratio equal
to 2.4 solar masses/solar luminosities. The low value of the HI content
suggested by the observations, together with the galaxy optical morphology,
might indicate that APPLES1 is a dwarf spheroidal. This indication is in
contrast with the evidence of recent star formation, which is typical for dwarf
irregular galaxies. This may suggest that APPLES1 belongs to the class of mixed
dwarf irregular/spheroidal transition-type galaxies. We also conclude that the
relatively low neutral gas mass in APPLES1 can be explained by an extended and
inefficient star formation process, without the need for a dramatic event such
as enhanced star formation or a past encounter with a massive galaxy or galaxy
group.Comment: 5 pages including 2 figures, accepted for publication in A&A Main
Journa
Radio Polarimetry of the ELAIS N1 Field: Polarized Compact Sources
We present deep polarimetric observations at 1420 MHz of the European Large
Area ISO Survey North 1 region (ELAIS N1) as part of the Dominion Radio
Astrophysical Observatory Planck Deep Fields project. By combining closely
spaced aperture synthesis fields, we image a region of 7.43 square degrees to a
maximum sensitivity in Stokes Q and U of 78 microJy/beam, and detect 786
compact sources in Stokes I. Of these, 83 exhibit polarized emission. We find
that the differential source counts (log N - log p) for polarized sources are
nearly constant down to p > 500 microJy, and that these faint polarized radio
sources are more highly polarized than the strong source population. The median
fractional polarization is (4.8 +/- 0.7)% for polarized sources with Stokes I
flux density between 1 and 30 mJy; approximately three times larger than
sources with I > 100 mJy. The majority of the polarized sources have been
identified with galaxies in the Spitzer Wide Area Infrared Extragalactic Survey
(SWIRE) image of ELAIS N1. Most of the galaxies occupy regions in the IRAC
5.8/3.6 micron vs. 8.0/4.5 micron color-color diagram associated with dusty
AGNs, or with ellipticals with an aging stellar population. A few host galaxies
have colors that suggests significant PAH emission in the near-infrared. A
small fraction, 12%, of the polarized sources are not detected in the SWIRE
data. None of the polarized sources in our sample appears to be associated with
an actively star-forming galaxy.Comment: 28 pages, 8 Figures. Figures 2 and 3 as separate gif images. Accepted
for publication in the Astrophysical Journa
HI Distribution and Kinematics of UGCA 86
We present 21-cm HI line and 408 MHz and 1.4 GHz continuum observations of
the dwarf galaxy UGCA 86 with the DRAO synthesis telescope. UGCA 86 is detected
in the continuum at 408 MHz (S_{408} = 120 +/- 30 mJy) and 1.4 GHz (S_{1400} =
79 +/- 3 mJy). The HI structure of UGCA 86 is complex, with two separate
components: a rotating disk and a highly elongated spur that is kinematically
disjunct from the disk. The HI disk is centered on the optical galaxy with
similar axial ratio and orientation of the major axis. An area of the disk with
a peculiar velocity of 25 km/s relative to the regular rotation of the disk is
found on the southern side, where most of the star formation is concentrated.
The spur is seen along the minor axis of UGCA 86 and overlaps in part with the
disk. Towards the optical center of UGCA 86, the velocity difference between
the spur and the disk is 40 km/s, about one third of the rotation velocity of
the HI disk at 6 kpc from the center. This implies a large radial component of
the orbital velocity of the spur, and therefore a significantly non-circular
orbit. The velocity dispersion of the disk is 8.8 km/s, whereas the velocity
dispersion of the spur varies from 10 km/s to 30 km/s. A possible tidal origin
of the spur is considered in view of the proximity of the large Scd galaxy IC
342. However, evidence that the spur is located far outside the plane of the HI
disk, and the absence of evidence for a warp in the outer HI disk, poses a
problem for the interpretation of the spur as a tidal tail induced by IC 342.
Detailed modelling of the IC 342/UGCA 86 system will be required before a tidal
origin of the spur can be dismissed conclusively. The possibility that the spur
is part of the nascent cloud of UGCA 86 or the remains of a small dwarf galaxy
is presented as an alternative interpretation.Comment: 27 pages, 11 figures, external as gif. A PDF file with figures
included is temporarily available from
http://www.ras.ucalgary.ca/~stil/ugca86.html Accepted for publication in the
Astrophysical Journa
The VLA Galactic Plane Survey
The VLA Galactic Plane Survey (VGPS) is a survey of HI and 21-cm continuum
emission in the Galactic plane between longitude 18 degrees 67 degr. with
latitude coverage from |b| < 1.3 degr. to |b| < 2.3 degr. The survey area was
observed with the Very Large Array (VLA) in 990 pointings. Short-spacing
information for the HI line emission was obtained by additional observations
with the Green Bank Telescope (GBT). HI spectral line images are presented with
a resolution of 1 arcmin x 1 arcmin x 1.56 km/s (FWHM) and rms noise of 2 K per
0.824 km/s channel. Continuum images made from channels without HI line
emission have 1 arcmin (FWHM) resolution. VGPS images are compared with images
from the Canadian Galactic Plane Survey (CGPS) and the Southern Galactic Plane
Survey (SGPS). In general, the agreement between these surveys is impressive,
considering the differences in instrumentation and image processing techniques
used for each survey. The differences between VGPS and CGPS images are small, <
6 K (rms) in channels where the mean HI brightness temperature in the field
exceeds 80 K. A similar degree of consistency is found between the VGPS and
SGPS. The agreement we find between arcminute resolution surveys of the
Galactic plane is a crucial step towards combining these surveys into a single
uniform dataset which covers 90% of the Galactic disk: the International
Galactic Plane Survey (IGPS). The VGPS data will be made available on the World
Wide Web through the Canadian Astronomy Data Centre (CADC).Comment: Accepted for publication in The Astronomical Journal. 41 pages, 13
figures. For information on data release, colour images etc. see
http://www.ras.ucalgary.ca/VGP
Polarized point sources in the LOFAR Two-meter Sky Survey: A preliminary catalog
The polarization properties of radio sources at very low frequencies (h45m–15h30m right ascension, 45°–57° declination, 570 square degrees). We have produced a catalog of 92 polarized radio sources at 150 MHz at 4.′3 resolution and 1 mJy rms sensitivity, which is the largest catalog of polarized sources at such low frequencies. We estimate a lower limit to the polarized source surface density at 150 MHz, with our resolution and sensitivity, of 1 source per 6.2 square degrees. We find that our Faraday depth measurements are in agreement with previous measurements and have significantly smaller errors. Most of our sources show significant depolarization compared to 1.4 GHz, but there is a small population of sources with low depolarization indicating that their polarized emission is highly localized in Faraday depth. We predict that an extension of this work to the full LOTSS data would detect at least 3400 polarized sources using the same methods, and probably considerably more with improved data processing
Probing magnetic fields in the circumgalactic medium using polarization data from MIGHTEE
The detection and study of magnetic fields surrounding galaxies is important
to understand galaxy evolution since magnetic fields are tracers for dynamical
processes in the circumgalactic medium (CGM) and can have a significant impact
on the evolution of the CGM. The Faraday rotation measure (RM) of the polarized
light of background radio sources passing through the magnetized CGM of
intervening galaxies can be used as a tracer for the strength and extent of
magnetic fields around galaxies. We use rotation measures observed by the
MIGHTEE-POL (MeerKAT International GHz Tiered Extragalactic Exploration
POLarisation) survey by MeerKAT in the XMM-LSS and COSMOS fields to investigate
the RM around foreground star-forming galaxies. We use spectroscopic catalogs
of star-forming and blue cloud galaxies to measure the RM of MIGHTEE-POL
sources as a function of the impact parameter from the intervening galaxy. We
then repeat this procedure using a deeper galaxy catalog with photometric
redshifts. For the spectroscopic star-forming sample we find a
redshift-corrected |RM| excess of 5.6 +/- 2.3 rad m-2 which corresponds to a
2.5 sigma significance around galaxies with a median redshift of z = 0.46 for
impact parameters below 130 kpc only selecting the intervenor with the smallest
impact parameter. Making use of a photometric galaxy catalog and taking into
account all intervenors with Mg < -13.6 mag, the signal disappears. We find no
indication for a correlation between redshift and RM, nor do we find a
connection between the total number of intervenors to the total |RM| . We have
presented tentative evidence that the CGM of star-forming galaxies is permeated
by coherent magnetic fields within the virial radius. We conclude that mostly
bright, star-forming galaxies with impact parameters less than 130 kpc
significantly contribute to the RM of the background radio source.Comment: 11 pages, 8 figures, accepted for publication in A&
PSR J1856+0245: Arecibo Discovery of a Young, Energetic Pulsar Coincident with the TeV Gamma-ray Source HESS J1857+026
We present the discovery of the Vela-like radio pulsar J1856+0245 in the
Arecibo PALFA survey. PSR J1856+0245 has a spin period of 81ms, a
characteristic age of 21kyr, and a spin-down luminosity Edot = 4.6 x 10^36
ergs/s. It is positionally coincident with the TeV gamma-ray source HESS
J1857+026, which has no other known counterparts. Young, energetic pulsars
create wind nebulae, and more than a dozen pulsar wind nebulae have been
associated with very-high-energy (100GeV-100TeV) gamma-ray sources discovered
with the HESS telescope. The gamma-ray emission seen from HESS J1857+026 is
potentially produced by a pulsar wind nebula powered by PSR J1856+0245; faint
X-ray emission detected by ASCA at the pulsar's position supports this
hypothesis. The inferred gamma-ray efficiency is epsilon_gamma = L_gamma/Edot =
3.1% (1-10TeV, for a distance of 9kpc), comparable to that observed in similar
associations.Comment: 13 pages, 1 figure, accepted for publication in The Astrophysical
Journal Letter
Search for Diffuse Neutral Hydrogen and HI Clouds in the NGC 2403 Group
We have observed the NGC 2403 group of galaxies using the Robert C. Byrd
Green Bank Telescope (GBT) in a search for faint, extended neutral hydrogen
clouds similar to the clouds found around the M81/M82 group, which is located
approximately 250 kpc from the NGC 2403 group along the same filament of
galaxies. For an HI cloud with a size < 10 kpc within 50 kpc of a group galaxy,
our 7-sigma mass detection limit is 2.2 x 10^6 M_sun for a cloud with a
linewidth of 20 km/s, over the velocity range from -890 to 1750 km/s. At this
sensitivity level we detect 3 new HI clouds in the direction of the group, as
well as the known galaxies. The mean velocity of the new clouds differs from
that of the group galaxies by more than 250 km/s, but are in the range of Milky
Way High Velocity Clouds (HVCs) in that direction. It is most likely that the
clouds are part of the Milky Way HVC population. If HI clouds exist in the NGC
2403 group, their masses are less than 2.2 x 10^6 M_sun. We also compared our
results to structures that are expected based on recent cosmological models,
and found none of the predicted clouds. If NGC 2403 is surrounded by a
population of dark matter halos similar to those proposed for the Milky Way in
recent models, our observations imply that their HI content is less than 1% of
their total mass.Comment: Accepted by A
The Metal Content of Dwarf Starburst Winds: Results from Chandra Observations of NGC 1569
(Abridged) We present deep, Chandra spectral imaging of the dwarf starburst
galaxy NGC 1569. The unprecedented spatial resolution allows us to spatially
identify the components of the integrated \x spectrum. Fitted spectral models
require an intrinsic absorption component and higher metal abundances than
previous studies indicated. Our results provide the first direct evidence for
metal-enriched winds from dwarf starburst galaxies.Comment: 44 pages and 22 figures. Figures available as single postscript file
from ftp://ftp.astro.caltech.edu/users/clm/n1569/fig_show.ps.gz Accepted for
publication in the Astrophysical Journa
Polarized point sources in the LOFAR Two-meter Sky Survey: A preliminary catalog
The polarization properties of radio sources at very low frequencies (<200
MHz) have not been widely measured, but the new generation of low-frequency
radio telescopes, including the Low Frequency Array (LOFAR: a Square Kilometre
Array Low pathfinder), now gives us the opportunity to investigate these
properties. In this paper, we report on the preliminary development of a data
reduction pipeline to carry out polarization processing and Faraday tomography
for data from the LOFAR Two-meter Sky Survey (LOTSS) and present the results of
this pipeline from the LOTSS preliminary data release region (10h45m - 15h30m
right ascension, 45 - 57 degrees declination, 570 square degrees). We have
produced a catalog of 92 polarized radio sources at 150 MHz at 4.3 arcminute
resolution and 1 mJy rms sensitivity, which is the largest catalog of polarized
sources at such low frequencies. We estimate a lower limit to the polarized
source surface density at 150 MHz, with our resolution and sensitivity, of 1
source per 6.2 square degrees. We find that our Faraday depth measurements are
in agreement with previous measurements and have significantly smaller errors.
Most of our sources show significant depolarization compared to 1.4 GHz, but
there is a small population of sources with low depolarization indicating that
their polarized emission is highly localized in Faraday depth. We predict that
an extension of this work to the full LOTSS data would detect at least 3400
polarized sources using the same methods, and probably considerably more with
improved data processing.Comment: 20 pages, 8 figures, 2 catalog tables (non-machine readable),
accepted for publication in A&
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