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Faraday tomography of a field centred on the extragalactic point source 3C 196 with the LOw Frequency ARray (LOFAR) revealed an intertwined structure of diffuse polarised emission with straight depolarisation canals and tracers of the magnetized and multi-phase interstellar medium (ISM), such as dust and line emission from atomic hydrogen (HI). This study aims at extending the multi-tracer analysis of LOFAR data to three additional fields in the surroundings of the 3C 196 field. For the first time, we study the three-dimensional structure of the LOFAR emission by determining the distance to the depolarisation canals. We use the Rolling Hough Transform to compare the orientation of the depolarisation canals with that of the filamentary structure seen in HI and, based on starlight and dust polarisation data, with that of the plane-of-the-sky magnetic field. Stellar parallaxes from $Gaia$ complement the starlight polarisation with the corresponding distances. Faraday tomography of the three fields shows a rich network of diffuse polarised emission at Faraday depths between $-10~{\rm rad~m^{-2}}$ and $+15~{\rm rad~m^{-2}}$. A complex system of straight depolarisation canals resembles that of the 3C 196 field. The depolarisation canals align both with the HI filaments and with the magnetic field probed by dust. The observed alignment suggests that an ordered magnetic field organises the multiphase ISM over a large area ($\sim$20$^{\circ}$). In one field, two groups of stars at distances below and above 200 pc, respectively, show distinct magnetic-field orientations. These are both comparable with the orientations of the depolarisation canals in the same field. We conclude that the depolarisation canals likely trace the same change of the magnetic field as probed by the stars, which corresponds to the edge of the Local Bubble., Comment: 14 pages, 11 figures, accepted for publication in A&A

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., Accepted for publication as a Letter in Astronomy and Astrophysics

We investigate the linear polarization produced by interstellar dust aligned by the magnetic field in the solar neighborhood (d< 50 pc). We also look for intrinsic effects from circumstellar processes, specifically in terms of polarization variability and wavelength dependence. We aim to detect and map dust clouds which give rise to statistically significant amounts of polarization of the starlight passing through the cloud, and to determine the interstellar magnetic field direction from the position angle of the observed polarization. High-precision broad-band (BVR) polarization observations are made of 361 stars in spectral classes F to G, in the magnitude range 4-9, with detection sensitivity at the level of or better than 10E-5 (0.001 %). Statistically significant (>3 sigma) polarization is found in 115 stars, and > 2 sigma detection in 178 stars, out of the total sample of 361 stars. Polarization maps based on these data show filament-like patterns of polarization position angles which are related to both the heliosphere geometry, the kinematics of nearby clouds, and the Interstellar Boundary EXplorer (IBEX) ribbon magnetic field. From long-term multiple observations, a number (18) of stars show evidence of intrinsic variability at the 10E-5 level. This can be attributed to circumstellar effects (e.g., debris disks and chromospheric activity). The star HD 101805 shows a peculiar wavelength dependence, indicating size distribution of scattering particles different from that of a typical interstellar medium., Comment: 18 pages, 8 figures, 13 tables

High-resolution spectroscopic observations (UV HST/STIS and optical) are used to characterize the physical state and velocity structure of the multiphase interstellar medium seen towards the nearby (170 pc) star HD102065, located behind the tail of a cometary-shaped, infrared cirrus-cloud, in the area of interaction between the Sco-Cen OB association and the Local Bubble. We analyze interstellar components present along the line of sight by fitting multiple transitions from CO, CH, CH+, C I, S I, Fe I, Mg I, Mg II, Mn II, P II, Ni II, C II, N I, O I, Si III, C IV, and Si IV. The absorption spectra are complemented by H I, CO and C II emission-line spectra, H$_2$ column-densities derived from FUSE spectra, and IRAS images. Gas components of a wide range of temperatures and ionization states are detected along the line of sight. Most of the hydrogen column-density is in cold, diffuse, molecular gas at low LSR velocity. This gas is mixed with traces of warmer molecular gas traced by H2 in the J>2 levels, in which the observed CH+ must be formed. We also identify three distinct components of warm gas at negative velocities down to -20 km/s. The temperature and gas excitation are shown to increase with increasing velocity shift from the bulk of the gas. Hot gas at temperatures of several 10^5 K is detected in the most negative velocity component in the highly-ionized species. This hot gas is also detected in very strong lines of less-ionized species (Mg II, Si II* and C II*) for which the bulk of the gas is cooler. We relate the observational results to evidence for dynamical impact of the Sco-Cen stellar association on the nearby ISM. We propose a scenario where the cirrus cloud has been hit a few 10^5 yr ago by a supernova blast wave originating from the Lower Centaurus Crux group of the Sco-Cen association., 16 pages, 9 figures, to be published in A&A

Context. Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than ∼100 pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations – including an important fraction whose members are Hipparcos stars – offer insights into the star formation process in low-density environments, shed light on the substellar domain, and could have played an important role in the recent history of the local interstellar medium. Aims. To study the kinematic evolution of young local associations and their relation to other young stellar groups and structures in the local interstellar medium, thus casting new light on recent star formation processes in the solar neighbourhood. Methods. We compiled the data published in the literature for young local associations. Using a realistic Galactic potential we integrated the orbits for these associations and the Sco-Cen complex back in time. Results. Combining these data with the spatial structure of the Local Bubble and the spiral structure of the Galaxy, we propose a recent history of star formation in the solar neighbourhood. We suggest that both the Sco-Cen complex and young local associations originated as a result of the impact of the inner spiral arm shock wave against a giant molecular cloud. The core of the giant molecular cloud formed the Sco-Cen complex, and some small cloudlets in a halo around the giant molecular cloud formed young local associations several million years later. We also propose a supernova in young local associations a few million years ago as the most likely candidate to have reheated the Local Bubble to its present temperature.

We present medium-resolution spectra (R ∼ 7.5 km s −1 ) of the interstellar NaI and CaII interstellar absorption lines observed towards 16 early-type stars with distances of 160-1 kpc in the line-of-sight towards the Orion-Eridanus Superbubble (OE-S). These data have been supplemented with measurements of NaI absorption towards a further 13 stars with similar sight-lines taken from the literature. We detect two major absorption components with velocities of Vlsr ∼ +7.0 and −8.0 km s −1 . The former component, seen in 70% of the sight-lines is associated with the boundary to the Local Bubble cavity located at a distance of 140-150 pc. The other absorption component is only detected towards a limited region of the sky bounded by (190 ◦ 220 pc within an area coincident with that of the 0.75 keV X-ray enhancement of the OE-S. Column density ratios, N(NaI)/N(CaII), for the most negative velocity components have values 500 pc. Finally, we place a similar distance limit for any coherently structured rear shell of neutral gas associated with expansion of the OE-S towards the galactic halo.

Solar wind interaction with neutral gas has been shown to generate soft X-rays, through the charge-exchange of highly ionized ions with neutral atoms and molecules in the interplanetary space and in the geocorona. The resulting diffuse emission can explain the non-cosmic long term enhancements (LTE) of ROSAT soft X-ray observations, which are produced by strong solar wind flux increases. This paper focuses on the emission pattern resulting from the impact on the interstellar gas of the average, “quiet” solar wind, i.e., the non variable signal “below” the LTEs. A sky map of the heliospheric emission is calculated, based on realistic hydrogen and helium atom distributions under the influence of solar conditions such as those prevailing during the ROSAT survey. It is shown that parallax effects linked to the ROSAT observing strategy have a strong influence on the resultant emission pattern. For a stationary solar wind the modeled emission has an anisotropy factor of $\simeq$1.8, and the emission maxima do not coincide with the interstellar wind axis direction. This emission is compared with the fraction of the ROSAT 0.25 keV emission assigned to hot ($T=10^{6}$ K) gas in the Local Interstellar Bubble and with the dense gas contour maps of the Bubble drawn from NaI absorption. Assuming constancy of the global pattern, but allowing for a variable scaling factor, the maximum heliospheric contribution is derived and this allows the placement of lower limits on the truly interstellar emission in many directions. After subtraction of the heliospheric emission, there is significant interstellar 0.25 keV emission from the Local Bubble “openings” to the lower halo, as expected, but also to neighbouring interstellar “bubbles”, as well as towards a number of regions along the galactic plane. There is evidence that there is hot gas emission attributable to our local cavity and generated throughout its volume, including along the galactic plane, but significantly weaker than initially thought. This would attenuate the discrepancy by a factor of about 4–5 between the hot gas pressure initially derived without heliospheric decontamination and the pressure of the embedded local diffuse clouds.

We present an absorption study of the interstellar gas at high positive galactic latitudes in the direction close to the axis of the Local Chimney (LC), which is an extension of the rarefied local cavity that reaches out from the galactic disk to a z-distance of at least 250 pc into the lower halo region. Our study includes high-resolution (R ∼ 1. 7k m s −1 ) spectral observations of the interstellar NaI and CaII absorption lines seen towards 6 early-type stars with distances ranging from 225 to 500 pc contained within a radius of ∼6 ◦ along the sight-line (l = 160 ◦ , b =+ 55 ◦ ). These visible data are supplemented with far-ultraviolet absorption measurements of the interstellar sight-lines towards two hot white dwarf stars, RE J1043+490 (d = 230 pc) and RE J1059+512 (d = 315 pc), taken with the NASA Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Our observations reveal interstellar gas clouds with velocities in the −20 to −60 km s −1 range that appear to be falling towards the galactic disk. In particular, we have detected absorption with a velocity of Vhelio ∼− 55 km s −1 towards two sight-lines (HD 89501 and HD 88545) that can be associated with an intermediate velocity (IV) cloud called the IV Arch. Our observations place a probable z-distance to this IVC of 275-320 pc, this being much nearer than previously thought. The far UV spectra of the two hot white dwarfs show only a few (∼10) interstellar absorption lines, which is indicative of the very low density phase of the interstellar gas contained within the LC region. We have derived relative elemental abundance ratios for C, N, O, Si, Ar and Fe for these two sight-lines and find that the abundance patterns are very similar to those found for other sight-lines in the local cavity. The high ionization line of OVIλ1032 A has been detected towards RE J1043+490 with a column density of 7 × 10 12 cm −2 , which is consistent with the average space density of this ion recently found in the Local Bubble region. Finally, we (tentatively) propose a possible connection between the formation of the Gould Belt, the Local Bubble cavity, the Local Chimney and the overlying IV Arch clouds.

We present intermediate results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, motivated by the availability of accurate and consistent parallaxes from the Hipparcos satellite. Equivalent widths of the interstellar NaI D-line doublet at 5890 A are presented for the lines-of-sight towards some 311 new target stars lying within ∼350 pc of the Sun. Using these data, together with NaI absorption measurements towards a fur- ther ∼240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ∼450 lines- of-sight already presented by (Sfeir et al. 1999), we show 3D absorption maps of the local distribution of neutral gas towards 1005 sight-lines with Hipparcos distances as viewed from a variety of different galactic projections. The data are synthesized by means of two complementary methods, (i) by mapping of iso-equivalent width contours, and (ii) by density distribution calculation from the inversion of column-densities, a method devised by Vergely et al. (2001). Our present data confirms the view that the local cavity is deficient in cold and neutral interstellar gas. The closest dense and cold gas "wall", in the first quadrant, is at ∼55-60 pc. There are a few isolated clouds at closer distance, if the detected absorption is not produced by circumstellar material. The maps reveal narrow or wide "interstellar tunnels" which connect the Local Bubble to surrounding cavities, as predicted by the model of Cox & Smith (1974). In particular, one of these tunnels, defined by stars at 300 to 600 pc from the Sun showing negligible sodium absorption, connects the well known CMa void (Gry et al. 1985), which is part of the Local Bubble, with the supershell GSH 238+00+09 (Heiles 1998). High latitude lines-of-sight with the smallest absorption are found in two "chimneys", whose directions are perpendicular to the Gould belt plane. The maps show that the Local Bubble is "squeezed" by surrounding shells in a complicated pattern and suggest that its pressure is smaller than in those expanding regions. We discuss the locations of several HI and molecular clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints on their distances. According to the velocity criteria, MBM 33−37, MBM 16−18, UT 3−7, and MBM 54−55 are closer than ∼100 pc, and MBM 40 is closer than 80 pc. Dense HI clouds are seen at less than 90 pc and 85 pc in the directions of the MBM 12 and MBM 41−43 clouds respectively, but the molecular clouds themselves may be far beyond. The above closest molecular clouds are located at the neutral boundary of the Bubble. Only one translucent cloud, G192−67, is clearly embedded within the LB and well isolated. These maps of the distribution of local neutral interstellar NaI gas are also briefly compared with the distribution of both interstellar dust and neutral HI gas within 300 pc.

We present Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) satellite measurements of the absorption and emission characteristics of interstellar gas associated with the Local Interstellar Chimney, which is an extension of the rarefied Local Bubble cavity that extends outward from the galactic disk towards the lower galactic halo. Far ultraviolet (FUV) diffuse background emission has been detected in the high ionization line of O VI ( λ 1032 A) for two lines-of-sight ($l = 162.7^{\circ}$, $b = +57.0^{\circ}$) and ($l = 156.3^{\circ}$, $b = +57.8^{\circ}$) at emission levels of $2500\pm700$ photons cm -2 s -1 sr -1 (LU) and $3300\pm1100$ LU respectively. These levels of O VI emission are very similar to those found for four other lines-of-sight sampled thus far by the $\it FUSE$ satellite, implying a fairly constant level of average O VI surface brightness emission at high galactic latitudes of about 2700 LU with a standard deviation of 450 LU. These emission-line data are supplemented by FUV interstellar absorption line measurements taken towards the hot DA white dwarf star, REJ 1032+532 ($l = 157.5^{\circ}$, $ b = +53.2^{\circ}$), whose distance of 116 pc places it within the Local Bubble region. No high ionization interstellar O VI λ 1032 A absorption has been detected $(N({\rm O~VI}) -2 ), which is consistent with the non-detections of interstellar C IV and Si IV absorption reported towards this star by Holberg et al. ([CITE]). Taken together, our FUV absorption and emission data may be explained by a scenario in which the O VI emission and absorption lines are $\it both$ formed at the conductive interface of the neutral boundary to the Local Bubble. For the presently sampled sight-lines we have found no correlation between the OVI emission line intensity and the associated 0.25 keV soft X-ray background flux as measured in the R1 and R2 bands by the $\it ROSAT$ satellite. The OVI line intensities also show no correlation with the soft X-ray background flux attributable to emission from the million degree K gas of the Local Hot Bubble as modeled by Kuntz & Snowden ([CITE]). Any (new) model of the Local Bubble must now be able to explain (i) the low levels of variability in both the O VI emission-line intensity and the associated soft X-ray background flux for galactic sight-lines > $|40|$°, (ii) the observed pressure of $P/k\sim 10\,000$ cm -3 K for the local hot interstellar gas, and (iii) the paucity of high ionization absorption lines observed within the local ISM and the sudden increase in their measured column density for distances beyond the Local Bubble neutral boundary.

Aims. The asymptotic giant-branch, long-period variable star Mira exhibits a 4 parsec long cometary tail in the far-ultraviolet. We address the issue of the origin of this structure and its emission process by simulating the transition of this star from the interstellar medium to the Local Bubble, which is a tenuous, high-pressure medium. Methods. We use the hydrodynamic and the magnetohydrodynamic modules of the PLUTO astrophysical code to carry out our simulations. We study the system without a cooling function, with a simplified exponential cooling function, and with a simplified nonequilibrium cooling function. Results. We find evidence that magnetohydrodynamics constrain the shape of the cometary tail and explain features of its farultraviolet emission. We suggest an emission process that involves C 0 excitation through inelastic electron collisions and a two-photon continuum to explain the luminosity of Mira’s tail.

Rotation Measure synthesis (RM synthesis) of the Westerbork Synthesis Radio Telescope (WSRT) observations at 2 m wavelength of the FAN region at l=137deg, b=+7deg shows the morphology of structures in the ionized interstellar medium. We interpret the diffuse polarized synchrotron emission in terms of coherent structures in the interstellar medium and the properties of the interstellar magnetic field. For the first time, cross-correlation is applied to identify and characterize polarized structures in Faraday depth space. Complementary information about the medium are derived from H$\alpha$ emission, properties of nearby pulsars, and optical polarized starlight measurements. Three morphological patterns are recognized, showing structures on scales from degrees down to the beam size. At low Faraday depth values, a low gradient across the imaged field is detected, almost aligned with the Galactic plane. Power spectra of polarized structures in Faraday depth space provide evidence of turbulence. A sign reversal in Faraday depth space indicates a reversal of the magnetic field component along the line of sight, from towards the observer and nearby to away from the observer at larger distances. The distance to the nearby, extended component is estimated to be lesser than 100 pc, which suggests that this structure corresponds to the Local Bubble wall. For the circular component, various physical interpretations are discussed. The most likely explanation is that the circular component seems to be the presence of a nearby (about 200 pc away) relic Stromgren sphere, associated with an old unidentified white dwarf star and expanding in a low-density environment., Comment: 16 pages, 16 figures, 4 tabs, accepted for publication in A&A

The Orion-Eridanus superbubble has been blown by supernovae and supersonic winds of the massive stars in the Orion OB associations. The formation history and current structure of the superbubble are still poorly understood. It possibly consists of a combination of nested shells along the line of sight. We have investigated the composite structure of the Eridanus side of the superbubble in the light of a new decomposition of the atomic and molecular gas. We used HI and CO emission lines to separate coherent gas shells in space and velocity, and we studied their relation to the warm ionised gas probed in H$\alpha$ emission, to the hot plasma emitting X-rays, and to the magnetic fields traced by dust polarised emission. We also constrained the relative distances to the clouds using dust reddening maps and X-ray absorption. We used the dust polarisation data to estimate the plane-of-sky components of the magnetic field in several clouds and along the outer rim of the superbubble. Our gas decomposition has revealed several shells inside the superbubble that span distances from about 150 pc to 250 pc. One of these shells forms a nearly complete ring filled with hot plasma. Other shells likely correspond to the layers of swept-up gas that is compressed behind the expanding outer shock wave. We used the gas and magnetic-field data downstream of the shock to derive a shock expansion velocity close to 20 km/s. Taking the X-ray absorption by the gas into account, we find that the pressure of the hot plasma inside the superbubble exceeds that in the Local Bubble. It comprises a mix of hotter (3-9 MK) and cooler (0.3-1.2 MK) gas along the lines of sight. The magnetic field along the western and southern rims and in the approaching wall of the superbubble appears to be shaped and compressed by the ongoing expansion. We find plane-of-sky magnetic strengths ranging from 3 to 15 $\mu$G along the rim., Comment: accepted for publication in A&A