We briefly present a new coordinate-invariant statistical test dedicated to the study of the orientations of transverse quantities of non-uniformly distributed sources on the celestial sphere. These ...quantities can be projected spin-axes or polarization vectors of astronomical sources.
Context.
The formation of molecular gas in interstellar clouds is a slow process, but can be enhanced by gas compression. Magneto-hydrodynamic (MHD) waves can create compressed quasi-periodic linear ...structures, referred to as striations. Striations are observed at the column densities at which the transition from atomic to molecular gas takes place.
Aims.
We explore the role of MHD waves in the CO chemistry in regions with striations within molecular clouds.
Methods.
We targeted a region with striations in the Polaris Flare cloud. We conducted a CO
J
= 2−1 survey in order to probe the molecular gas properties. We used archival starlight polarization data and dust emission maps in order to probe the magnetic field properties and compare against the CO morphological and kinematic properties. We assessed the interaction of compressible MHD wave modes with CO chemistry by comparing their characteristic timescales.
Results.
The estimated magnetic field is 38–76 µG. In the CO integrated intensity map, we observe a dominant quasiperiodic intensity structure that tends to be parallel to the magnetic field orientation and has a wavelength of approximately one parsec. The periodicity axis is ~17° off from the mean magnetic field orientation and is also observed in the dust intensity map. The contrast in the CO integrated intensity map is ~2.4 times higher than the contrast of the column density map, indicating that CO formation is enhanced locally. We suggest that a dominant slow magnetosonic mode with an estimated period of 2.1–3.4 Myr and a propagation speed of 0.30–0.45 km s
−1
is likely to have enhanced the formation of CO, hence created the observed periodic pattern. We also suggest that within uncertainties, a fast magnetosonic mode with a period of 0.48 Myr and a velocity of 2.0 km s
−1
could have played some role in increasing the CO abundance.
Conclusions.
Quasiperiodic CO structures observed in striation regions may be the imprint of MHD wave modes. The Alfvénic speed sets the dynamical timescales of the compressible MHD modes and determines which wave modes are involved in the CO chemistry.
The detailed characterization of scaling laws relating the observables of a cluster of galaxies to their mass is crucial for obtaining accurate cosmological constraints with clusters. In this paper, ...we present a comparison between the hydrostatic and lensing mass profiles of the cluster MACS J0647.7+7015 at
z
= 0.59. The hydrostatic mass profile is obtained from the combination of high resolution NIKA2 thermal Sunyaev-Zel’dovich and
XMM-Newton
X-ray observations of the cluster. The lensing mass profile, on the other hand, is obtained from an analysis of the CLASH lensing data based on the lensing convergence map. We find significant variation in the cluster mass estimate depending on the observable, the modeling of the data, and the knowledge of the cluster’s dynamical state. This might lead to significant systematic effects on cluster cosmological analyses for which only a single observable is generally used. From this pilot study, we conclude that the combination of high resolution Sunyaev-Zel’dovich, X-ray, and lensing data could allow us to identify and correct for these systematic effects. This would constitute a very interesting extension of the NIKA2 SZ Large Program.
We present the first degree-scale tomography map of the dusty magnetized interstellar medium (ISM) from stellar polarimetry and distance measurements. We used the RoboPol polarimeter at Skinakas ...Observatory to conduct a survey of the polarization of starlight in a region of the sky of about four square degrees. We propose a Bayesian method to decompose the stellar-polarization source field along the distance to invert the three-dimensional (3D) volume occupied by the observed stars. We used this method to obtain the first 3D map of the dusty magnetized ISM. Specifically, we produced a tomography map of the orientation of the plane-of-sky component of the magnetic field threading the diffuse, dusty regions responsible for the stellar polarization. For the targeted region centered on Galactic coordinates ( l , b ) ≈ (103.3°, 22.3°), we identified several ISM clouds. Most of the lines of sight intersect more than one cloud. A very nearby component was detected in the foreground of a dominant component from which most of the polarization signal comes and which we identified as being an intersection of the wall of the Local Bubble and the Cepheus Flare. Farther clouds, with a distance of up to 2 kpc, were similarly detected. Some of them likely correspond to intermediate-velocity clouds seen in H I spectra in this region of the sky. We found that the orientation of the plane-of-sky component of the magnetic field changes along distance for most of the lines of sight. Our study demonstrates that starlight polarization data coupled to distance measures have the power to reveal the great complexity of the dusty magnetized ISM in 3D and, in particular, to provide local measurements of the plane-of-sky component of the magnetic field in dusty regions. This demonstrates that the inversion of large data volumes, as expected from the P ASIPHAE survey, will provide the necessary means to move forward in the modeling of the Galactic magnetic field and of the dusty magnetized ISM as a contaminant in observations of the cosmic microwave background polarization.
We present the first application of the vector spherical harmonics technique to the proper motions of the catalogues UCAC4, XPM and PPMXL for stars in the 11 to 17 mag range. The results obtained ...from the all-sky and from the Northern and Southern Galactic hemispheres solutions are discussed. The all-sky solution gave the parameters of the standard Ogorodnikov–Milne model (coordinates of the solar motion apex, the Oort constants, the angular speed of the local Galactic rotation, the slope of the local rotational velocity curve) which practically coincide with the traditional least-squares estimates. Essentially new is the fact that the all-sky vector spherical harmonics analysis detected the same strong and reliable extra-model harmonics in all the catalogues under consideration. In addition, the Northern and Southern hemisphere solutions (again in all the catalogues) gave the sign changes of the same Ogorodnikov–Milne parameters. It was shown that both effects are generated by the retardation of the Galaxy rotation with the increase of the distance from the principal Galactic plane. Each catalogue shows small decrease of the gradient estimates towards the faint stars, but the mean values of the gradient derived from the catalogues are in good agreement, namely – UCAC4: 40.1 ± 0.2; PPMXL: 36.2 ± 0.4 and XPM: 37.7 ± 0.1 km s−1 kpc−1.
It has not been shown so far whether the diffuse Galactic polarized emission at frequencies relevant for cosmic microwave background (CMB) studies originates from nearby or more distant regions of ...our Galaxy. This questions previous attempts that have been made to constrain magnetic field models at local and large scales. The scope of this work is to investigate and quantify the contribution of the dusty and magnetized local interstellar medium to the observed emission that is polarized by thermal dust. We used stars as distance candles and probed the line-of-sight submillimeter polarization properties by comparing the emission that is polarized by thermal dust at submillimeter wavelengths and the optical polarization caused by starlight. We provide statistically robust evidence that at high Galactic latitudes (\(|b| \geq 60^\circ\)), the \(353\) GHz polarized sky as observed by \textit{Planck} is dominated by a close-by magnetized structure that extends between \(200\) and \(300\) pc and coincides with the shell of the Local Bubble. Our result will assist modeling the magnetic field of the Local Bubble and characterizing the CMB Galactic foregrounds.
In the context of cosmic microwave background polarization studies and the characterization of the Galactic foregrounds, the power spectrum analysis of the thermal dust polarization sky has led to ...intriguing evidence of an E/B asymmetry and a positive TE correlation. In this work, we produce synthesized dust polarization maps from a set of global magneto-hydrodynamic (MHD) simulations of Milky-Way-sized galaxies, and analyze their power spectra at intermediate angular scales (angular multipoles \(\ell \in \left60 ,\, 140\right\)). We study the role of the initial configuration of the large-scale magnetic field, its strength, and the feedback on the power spectrum characteristics. Using full-galaxy MHD simulations, we were able to estimate the variance induced by the peculiar location of the observer in the galaxy. We find that the polarization power spectra sensitively depend on the observer's location, impeding a distinction between different simulation setups. There is a clear statistical difference between the power spectra measured from within the spiral arms and those measured from the inter-arm regions. Also, power spectra from within supernova-driven bubbles share common characteristics, regardless of the underlying model. However, no correlation was found between the properties of the polarization power spectra and the local (with respect to the observer) mean values of physical quantities such as the density and the strength of the magnetic field. Finally, we find indications that the global strength of the magnetic field may play a role in shaping the power spectrum characteristics; as the global magnetic field strength increases, the E/B asymmetry and the TE correlation increase, whereas the viewpoint-induced variance decreases. However, we find no direct correlation with the strength of the local magnetic field that permeates the mapped region of the interstellar medium.
In the framework of studies of the CMB polarization and its Galactic foregrounds, the angular power spectra of thermal dust polarization maps have revealed an intriguing E/B asymmetry and a positive ...TE correlation. In interpretation studies of these observations, magnetized ISM dust clouds have been treated as filamentary structures only; however, sheet-like shapes are also supported by observational and theoretical evidence. In this work, we study the influence of cloud shape and its connection to the local magnetic field on angular power spectra of thermal dust polarization maps. We simulate realistic filament-like and sheet-like interstellar clouds, and generate synthetic maps of their thermal dust polarized emission using the software \(Asterion\). We compute their polarization power spectra in multipole range \(\ell \in 100,500\) and quantify the E/B power asymmetry through the \(R_{EB}\) ratio, and the correlation coefficient \(r^{TE}\) between T and E modes. We quantify the dependence of \(R_{EB}\) and \(r^{TE}\) values on the offset angle (between longest cloud axis and magnetic field) and inclination angle (between line-of-sight and magnetic field) for both cloud shapes embedded either in a regular or a turbulent magnetic field. We find that both cloud shapes cover the same regions of the (\(R_{EB}\), \(r^{TE}\)) parameter space. The dependence on inclination and offset angles are similar for both shapes although sheet-like structures generally show larger scatter. In addition to the known dependence on the offset angle, we find a strong dependence of \(R_{EB}\) and \(r^{TE}\) on the inclination angle. The fact that filament-like and sheet-like structures may lead to polarization power spectra with similar (\(R_{EB}\), \(r^{TE}\)) values complicates their interpretation. In future analyses, this degeneracy should be accounted for as well as the connection to the magnetic field geometry.
We investigate the geometry of the magnetic field towards the Radcliffe Wave,
a coherent 3-kpc-long part of the nearby Local Arm recently discovered via
three-dimensional dust mapping. We use ...archival stellar polarization in the
optical and new measurements in the near-infrared to trace the magnetic field
as projected on the plane of the sky. Our new observations cover the portion of
the structure that is closest to the Sun, between Galactic longitudes of
122$^\circ$ and 188$^\circ$. The polarization angles of stars immediately
background to the Radcliffe Wave appear to be aligned with the structure as
projected on the plane of the sky. The observed magnetic field configuration is
inclined with respect to the Galactic disk at an angle of 18$^\circ$. This
departure from a geometry parallel to the plane of the Galaxy is contrary to
previous constraints from more distant stars and polarized dust emission. We
confirm that the polarization angle of stars at larger distances shows a mean
orientation parallel to the Galactic disk. We discuss implications of the
observed morphology of the magnetic field for models of the large-scale
Galactic magnetic field, as well as formation scenarios for the Radcliffe Wave
itself.
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