58 research outputs found
ALMA Science Verification Data: Millimeter Continuum Polarimetry of the Bright Radio Quasar 3C 286
We present full-polarization observations of the compact, steep-spectrum
radio quasar 3C~286 made with the ALMA at 1.3~mm. These are the first
full-polarization ALMA observations, which were obtained in the framework of
Science Verification. A bright core and a south-west component are detected in
the total intensity image, similar to previous centimeter images. Polarized
emission is also detected toward both components. The fractional polarization
of the core is about 17\%, this is higher than the fractional polarization at
centimeter wavelengths, suggesting that the magnetic field is even more ordered
in the millimeter radio core than it is further downstream in the jet. The
observed polarization position angle (or EVPA) in the core is
\,, which confirms the trend that the EVPA slowly increases
from centimeter to millimeter wavelengths. With the aid of multi-frequency VLBI
observations, we argue that this EVPA change is associated with the
frequency-dependent core position. We also report a serendipitous detection of
a sub-mJy source in the field of view, which is likely to be a submillimeter
galaxy.Comment: 10 pages, 9 figures, Accepted for publication in the Ap
A Precise Distance to IRAS 00420+5530 via H2O Maser Parallax with the VLBA
We have used the VLBA to measure the annual parallax of the H2O masers in the
star-forming region IRAS 00420+5530. This measurement yields a direct distance
estimate of 2.17 +/- 0.05 kpc (<3%), which disagrees substantially with the
standard kinematic distance estimate of ~4.6 kpc (according to the rotation
curve of Brand and Blitz 1993), as well as most of the broad range of distances
(1.7-7.7 kpc) used in various astrophysical analyses in the literature. The
3-dimensional space velocity of IRAS 00420+5530 at this new, more accurate
distance implies a substantial non-circular and anomalously slow Galactic
orbit, consistent with similar observations of W3(OH) (Xu et al., 2006;
Hachisuka et al. 2006), as well as line-of-sight velocity residuals in the
rotation curve analysis of Brand and Blitz (1993). The Perseus spiral arm of
the Galaxy is thus more than a factor of two closer than previously presumed,
and exhibits motions substantially at odds with axisymmetric models of the
rotating Galaxy.Comment: 33 pages, 12 figures; Accepted by ApJ (to appear March 2009
Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
We are using the VLBA and the Japanese VERA project to measure trigonometric
parallaxes and proper motions of masers found in high-mass star-forming regions
across the Milky Way. Early results from 18 sources locate several spiral arms.
The Perseus spiral arm has a pitch angle of 16 +/- 3 degrees, which favors four
rather than two spiral arms for the Galaxy. Combining positions, distances,
proper motions, and radial velocities yields complete 3-dimensional kinematic
information. We find that star forming regions on average are orbiting the
Galaxy ~15 km/s slower than expected for circular orbits. By fitting the
measurements to a model of the Galaxy, we estimate the distance to the Galactic
center R_o = 8.4 +/- 0.6 kpc and a circular rotation speed Theta_o = 254 +/- 16
km/s. The ratio Theta_o/R_o can be determined to higher accuracy than either
parameter individually, and we find it to be 30.3 +/- 0.9 km/s/kpc, in good
agreement with the angular rotation rate determined from the proper motion of
Sgr A*. The data favor a rotation curve for the Galaxy that is nearly flat or
slightly rising with Galactocentric distance. Kinematic distances are generally
too large, sometimes by factors greater than two; they can be brought into
better agreement with the trigonometric parallaxes by increasing Theta_o/R_o
from the IAU recommended value of 25.9 km/s/kpc to a value near 30 km/s/kpc. We
offer a "revised" prescription for calculating kinematic distances and their
uncertainties, as well as a new approach for defining Galactic coordinates.
Finally, our estimates of Theta_o and To/R_o, when coupled with direct
estimates of R_o, provide evidence that the rotation curve of the Milky Way is
similar to that of the Andromeda galaxy, suggesting that the dark matter halos
of these two dominant Local Group galaxy are comparably massive.Comment: 35 pages, 7 figures, 7 table
The VSOP 5 GHz AGN Survey II. Data Calibration and Imaging
The VSOP mission is a Japanese-led project to study radio sources with
sub-milliarcsecond angular resolution using an orbiting 8-m telescope, HALCA
and global arrays of Earth-based telescopes. Approximately 25% of the observing
time has been devoted to a survey of compact AGN at 5 GHz which are stronger
than 1 Jy -- the VSOP AGN Survey. This paper, the second in a series, describes
the data calibration, source detection, self-calibration, imaging and modeling,
and gives examples illustrating the problems specific to space VLBI. The VSOP
Survey web-site which contains all results and calibrated data is described.Comment: 14 pages. To appear in Astrophysical Journal Supplemen
The VSOP 5 GHz AGN Survey: III. Imaging Results for the First 102 Sources
The VSOP mission is a Japanese-led project to study radio sources with
sub-milliarcsec resolution using an orbiting 8 m telescope, HALCA, along with
global arrays of Earth-based telescopes. Approximately 25% of the observing
time is devoted to a survey of compact AGN which are stronger than 1 Jy at 5
GHz-the VSOP AGN Survey. This paper, the third in the series, presents the
results from the analysis of the first 102 Survey sources. We present high
resolution images and plots of visibility amplitude versus projected baseline
length. In addition, model-fit parameters to the primary radio components are
listed, and from these the angular size and brightness temperature for the
radio cores are calculated. For those sources for which we were able to
determine the source frame core brightness temperature, a significant fraction
(53 out of 98) have a source frame core brightness temperature in excess of
10^12 K. The maximum source frame core brightness temperature we observed was
1.2 X 10^13 K. Explaining a brightness temperature this high requires an
extreme amount of relativistic Doppler beaming. Since the maximum brightness
temperature one is able to determine using only ground-based arrays is of the
order of 10^12 K, our results confirm the necessity of using space VLBI to
explore the extremely high brightness temperature regime.Comment: 33 Pages, 4 Figures (included separately as jpg files). Figure 2
separated into 26 files, figure 3 separated into 2 files. Accepted by Ap. J.
Supp. in May 200
The VSOP 5 GHz Active Galactic Nucleus Survey. V. Imaging Results for the Remaining 140
In 1997 February, the Japanese radio astronomy satellite HALCA was launched to provide the space-bourne element for the VLBI Space Observatory Program (VSOP) mission. Approximately 25% of the mission time was dedicated to the VSOP survey of bright compact active galactic nuclei (AGNs) at 5 GHz. This paper, the fifth in the series, presents images and models for the remaining 140 sources not included in the third paper in the series, which contained 102 sources. For most sources, the plots of the (u,v) coverage, the visibility amplitude versus (u,v) distance, and the high-resolution image are presented. Model fit parameters to the major radio components are determined, and the brightness temperature of the core component for each source is calculated. The brightness temperature distributions for all of the sources in the VSOP AGN survey are discussed
An Overview of the 2014 ALMA Long Baseline Campaign
A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to
make accurate images with resolutions of tens of milliarcseconds, which at
submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop
and test this capability, a Long Baseline Campaign (LBC) was carried out from
September to late November 2014, culminating in end-to-end observations,
calibrations, and imaging of selected Science Verification (SV) targets. This
paper presents an overview of the campaign and its main results, including an
investigation of the short-term coherence properties and systematic phase
errors over the long baselines at the ALMA site, a summary of the SV targets
and observations, and recommendations for science observing strategies at long
baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also
compared to VLA 43 GHz results, demonstrating an agreement at a level of a few
percent. As a result of the extensive program of LBC testing, the highly
successful SV imaging at long baselines achieved angular resolutions as fine as
19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now
possible, and opens up new parameter space for submm astronomy.Comment: 11 pages, 7 figures, 2 tables; accepted for publication in the
Astrophysical Journal Letters; this version with small changes to
affiliation
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