3D mapping of the dense interstellar gas around the Local Bubble

Abstract

Abstract. 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 Å 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 further ∼240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ∼450 linesof-sight already presented by , 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 , 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.

O VI in the local interstellar medium

“…This is a strong indication that the distribution of material around the Sun is far from uniform and that interfaces are not seen in all directions. We already know from earlier studies of the LISM, culminating in the work of Lallement et al (2003), that boundary of the Local Bubble is not equidistant from the Sun in all directions. Nor is it a simple shape.…”

“…This is now provided by our interpretation of Figure 8. Figure 8 indicates the location of a selection of the stars listed in Table 3 and shows a number of slices through the local ISM based on the 3-D spatial distribution of neutral gas presented by Lallement et al (2003), but updated by Welsh et al (2010) with more recent information. On each of the projections shown, we have plotted the positions of detections of interstellar O VI along with the most sensitive non-detections.…”

The Magnificent Seven in the dusty prairie

“…These different components of the hydrogen column density are estimated by different measurement Fig. 2 The limits of using the Ferlet et al (1985) formula The sodium column density as derived from the density data by Lallement et al (2003) is shown in galactic cartesian coordinates at z=0; x is towards the galactic center which is at the right, y towards l=90 • is pointing up. The image spans 500 pc times 500 pc.…”

“…Current interstellar absorption treatment depends on chosen abundances and scattering cross-sections of the elements as well as on the 3D distribution of the interstellar medium. After a discussion of these factors we use the comprehensive 3D measurements of the Local Bubble by Lallement et al (2003) to construct two simple models of the 3D distribution of the hydrogen column density. We test these models by using a set of soft X-ray sources with known distances.…”

UV Capabilities to Probe the Formation of Planetary Systems: From the ISM to Planets

“…The local ISM The Sun lies inside the Local Bubble, a large ionised gas bubble that extends outwards from the Sun to a neutral hydrogen column density log N (H I) ≈ 19.2 (cm −2 units), corresponding to a geometrical size of 100-200 pc depending on the direction from the Sun. The Local Bubble's morphology has been identified by Na I absorption, which is formed in the cold gas than surrounds the Local Bubble and determines its shape (Lallement et al, 2003). The Local Bubble is thought to be an H II region formed by the explosions of supernovae and the strong winds of young hot stars in the Lower Centaurus Crux subgroup of the Scorpio-Centaurus Association (Maíz-Apellániz, 2001;Berghöfer and Breitschwerdt, 2002).…”