- ID:
- ivo://CDS.VizieR/J/ApJ/702/1230
- Title:
- Rotation measure image of the sky
- Short Name:
- J/ApJ/702/1230
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have re-analyzed the NRAO VLA Sky Survey (NVSS) data to derive rotation measures (RMs) toward 37543 polarized radio sources. The resulting catalog of RM values covers the sky area north of declination -40{deg} with an average density of more than one RM per square degree. We have identified five regions of the sky where the foreground median RM is consistently less than 1rad/m^2^ over several degrees. These holes in the foreground RM will be useful for future studies of possible small-scale fluctuations in cosmic magnetic field structures. In addition to allowing measurement of RMs toward polarized sources, the new analysis of the NVSS data removes the effects of bandwidth depolarization for |RM|>~100rad/m^2^ inherent in the original NVSS source catalog.
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- ID:
- ivo://CDS.VizieR/J/other/JApA/32.567
- Title:
- Rotation measures in A2255 at 18, 21, 25, 85cm
- Short Name:
- J/other/JApA/32.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Polarized radio emission is detected at various scales in the Universe. In this document, I will briefly review our knowledge on polarized radio sources in galaxy clusters and at their outskirts, emphasizing the crucial information provided by the polarized signal on the origin and evolution of such sources. Successively, I will focus on Abell 2255, which is known in the literature as the first cluster for which filamentary polarized emission associated with the radio halo has been detected. By using RM (plasma Rotation Measure) synthesis on our multi-wavelength WSRT observations, we studied the 3-dimensional geometry of the cluster, unveiling the nature of the polarized filaments at the borders of the central radio halo. Our analysis points out that these structures are relics lying at large distance from the cluster center.
- ID:
- ivo://CDS.VizieR/J/ApJ/878/92
- Title:
- Rotation measures in radio source pairs
- Short Name:
- J/ApJ/878/92
- Date:
- 03 Mar 2022 08:14:01
- Publisher:
- CDS
- Description:
- Faraday rotation measures (RMs) of extragalactic radio sources provide information on line-of-sight magnetic fields, including contributions from our Galaxy, source environments, and the intergalactic medium (IGM). Looking at differences in RMs, {Delta}RM, between adjacent sources on the sky can help isolate these different components. In this work, we classify adjacent polarized sources in the NRAO VLA Sky Survey (NVSS) as random or physical pairs. We recompute and correct the uncertainties in the NVSS RM catalog, since these were significantly overestimated. Our sample contains 317 physical and 5111 random pairs, all with Galactic latitudes |b|>=20{deg}, polarization fractions >=2%, and angular separations between 1.5' and 20'. We find an rms {Delta}RM of 14.9+/-0.4 and 4.6+/-1.1rad/m^2^ for the random and physical pairs, respectively. This means that polarized extragalactic sources that are close on the sky but at different redshifts have larger differences in RM than two components of one source. This difference of ~10rad/m^2^ is significant at 5{sigma} and persists in different data subsamples. While there have been other statistical studies of {Delta}RM between adjacent polarized sources, this is the first unambiguous demonstration that some of this RM difference must be extragalactic, thereby providing a firm upper limit on the RM contribution of the IGM. If the {Delta}RMs originate local to the sources, then the local magnetic field difference between random sources is a factor of 2 larger than that between components of one source. Alternatively, attributing the difference in {Delta}RMs to the intervening IGM yields an upper limit on the IGM magnetic field strength of 40nG.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/21
- Title:
- Rotation measures of extragalactic radio sources
- Short Name:
- J/ApJ/755/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) toward 641 polarized extragalactic radio sources in the Galactic longitude range 100{deg}-117{deg}, within 30{deg} of the Galactic plane. For |b|<15{deg}, we observe a symmetric RM distribution about the Galactic plane. This is consistent with a disk field in the Perseus arm of even parity across the Galactic mid-plane. In the range 15{deg}<|b|<30{deg}, we find median RMs of -15+/-4rad/m2 and -62+/-5rad/m2 in the northern and southern Galactic hemispheres, respectively. If the RM distribution is a signature of the large-scale field parallel to the Galactic plane, then this suggests that the halo magnetic field toward the outer Galaxy does not reverse direction across the mid-plane. The variation of RM as a function of Galactic latitude in this longitude range is such that RMs become more negative at larger |b|. This is consistent with an azimuthal magnetic field of strength 2{mu}G (7{mu}G) at a height 0.8-2kpc above (below) the Galactic plane between the local and the Perseus spiral arm. We propose that the Milky Way could possess spiral-like halo magnetic fields similar to those observed in M51.
- ID:
- ivo://CDS.VizieR/J/ApJ/663/258
- Title:
- Rotation measures of extragalactic sources in SGPS
- Short Name:
- J/ApJ/663/258
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new Faraday rotation measures (RMs) for 148 extragalactic radio sources behind the southern Galactic plane (253{deg}<=l<=356{deg}, |b|<=1.5{deg}), and use these data in combination with published data to probe the large-scale structure of the Milky Way's magnetic field. We show that the magnitudes of these RMs oscillate with longitude in a manner that correlates with the locations of the Galactic spiral arms. The observed pattern in RMs requires the presence of at least one large-scale magnetic reversal in the fourth Galactic quadrant, located between the Sagittarius-Carina and Scutum-Crux spiral arms. To quantitatively compare our measurements to other recent studies, we consider all available extragalactic and pulsar RMs in the region we have surveyed, and jointly fit these data to simple models in which the large-scale field follows the spiral arms.
- ID:
- ivo://CDS.VizieR/J/other/RAA/14.942
- Title:
- Rotation measures of radio point sources
- Short Name:
- J/other/RAA/14.9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compiled a catalog of Faraday rotation measures (RMs) for 4553 extragalactic radio point sources published in literature. These RMs were derived from multi-frequency polarization observations. The RM data are compared to those in the NRAO VLA Sky Survey (NVSS) RM catalog. We reveal a systematic uncertainty of about 10.0+/-1.5rad/m^2^ in the NVSS RM catalog. The Galactic foreground RM is calculated through a weighted averaging method by using the compiled RM catalog together with the NVSS RM catalog, with careful consideration of uncertainties in the RM data. The data from the catalog and the interface for the Galactic foreground RM calculations are publicly available on the webpage: http://zmtt.bao.ac.cn/RM/ .
- ID:
- ivo://CDS.VizieR/J/A+A/549/A56
- Title:
- Rotation Measure synthesis of WSRT obs.
- Short Name:
- J/A+A/549/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotation Measure synthesis (RM synthesis) of the Westerbork Synthesis Radio Telescope (WSRT) observations at 2m wavelength of the FAN region at l=137deg, b=+7deg shows the morphology of structures in the ionized interstellar medium.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/1
- Title:
- Rotation reversals in the polarization in OJ 287
- Short Name:
- J/ApJ/862/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained a smooth time series for the electric vector position angle (EVPA) of the blazar OJ 287 at centimeter wavelengths, by making +/-n{pi} adjustments to archival values from 1974 to 2016. The data display rotation reversals in which the EVPA rotates counterclockwise for ~180{deg} and then rotates clockwise by a similar amount. The timescale of the rotations is a few weeks to a year, and the scale for a double rotation, including the reversal, is 1-3yr. We have seen four of these events in 40yr. A model consisting of two successive outbursts in polarized flux density, with EVPAs counterrotating, superposed on a steady polarized jet, can explain many of the details of the observations. Polarization images support this interpretation. The model can also help to explain similar events seen at optical wavelengths. The outbursts needed for the model can be generated by the supermagnetosonic jet model of Nakamura+ (2010ApJ...721.1783N) and Nakamura & Meier (2014ApJ...785..152N), which requires a strong helical magnetic field. This model produces forward and reverse pairs of fast and slow MHD waves, and the plasma inside the two fast/slow pairs rotates around the jet axis, but in opposite directions.
- ID:
- ivo://CDS.VizieR/J/ApJ/898/102
- Title:
- Rotation velocity & dynamical mass of gal. from HI sp.
- Short Name:
- J/ApJ/898/102
- Date:
- 21 Mar 2022 08:49:45
- Publisher:
- CDS
- Description:
- The integrated 21cm HI emission profile of a galaxy encodes valuable information on the kinematics, spatial distribution, and dynamical state of its cold interstellar medium. The line width, in particular, reflects the rotation velocity of the galaxy, which, in combination with a size scale, can be used to constrain the dynamical mass of the system. We introduce a new method based on the concept of the curve of growth to derive a set of robust parameters to characterize the line width, asymmetry, and concentration of the integrated HI spectra. We use mock spectra to evaluate the performance of our method, to estimate realistic systematic uncertainties for the proposed parameters, and to correct the line widths for the effects of instrumental resolution and turbulence broadening. Using a large sample of nearby galaxies with available spatially resolved kinematics, we demonstrate that the newly defined line widths can predict the rotational velocities of galaxies to within an accuracy of <~30km/s. We use the calibrated line widths, in conjunction with the empirical relation between the size and mass of HI disks, to formulate a prescription for estimating the dynamical mass within the HI-emitting region of gas-rich galaxies. Our formalism yields dynamical masses accurate to ~0.3dex based solely on quantities that can be derived efficiently and robustly from current and future extragalactic HI surveys. We further extend the dynamical mass calibration to the scale of the dark matter halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/199
- Title:
- RRL and continuum data of 21 Galactic H II regions
- Short Name:
- J/ApJ/806/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Elemental abundance patterns in the Galactic disk constrain theories of the formation and evolution of the Milky Way. H II region abundances are the result of billions of years of chemical evolution. We made radio recombination line and continuum measurements of 21 H II regions located between Galactic azimuth Az=90{deg}-130{deg}, a previously unexplored region. We derive the plasma electron temperatures using the line-to-continuum ratios and use them as proxies for the nebular [O/H] abundances, because in thermal equilibrium the abundance of the coolants (O, N, and other heavy elements) in the ionized gas sets the electron temperature, with high abundances producing low temperatures. Combining these data with our previous work produces a sample of 90 H II regions with high-quality electron temperature determinations. We derive kinematic distances in a self-consistent way for the entire sample. The radial gradient in [O/H] is -0.082+/-0.014 dex/kpc for Az=90{deg}-130{deg}, about a factor of 2 higher than the average value between Az=0{deg}-60{deg}. Monte Carlo simulations show that the azimuthal structure we reported for Az=0{deg}-60{deg} is not significant because kinematic distance uncertainties can be as high as 50% in this region. Nonetheless, the flatter radial gradients between Az=0{deg}-60{deg} compared with Az=90{deg}-130{deg} are significant within the uncertainty. We suggest that this may be due to radial mixing from the Galactic Bar whose major axis is aligned toward Az~30{deg}.
