Context. Gas within a galaxy is forced to establish pressure balance against gravitational forces. The shape of an unperturbed gaseous disk can be used to constrain dark matter models.Aims. We derive the 3D H i volume density distribution for the Milky Way out to a galactocentric radius of 40 kpc and a height of 20 kpc to constrain the Galactic mass distribution. Methods. We used the Leiden/Argentine/Bonn all sky 21-cm line survey. The transformation from brightness temperatures to densities depends on the rotation curve. We explored several models, reflecting different dark matter distributions. Each of these models was set up to solve the combined Poisson-Boltzmann equation in a self-consistent way and optimized to reproduce the observed flaring. Results. Besides a massive extended halo of M ∼ 1.8 × 1012 M , we find a self-gravitating dark matter disk with M = 2 to 3 × 10 11 M , including a dark matter ring at 13 < R < 18.5 kpc with M = 2.2 to 2.8 × 10 10 M . The existence of the ring was previously postulated from EGRET data and coincides with a giant stellar structure that surrounds the Galaxy. The resulting Milky Way rotation curve is flat up to R ∼ 27 kpc and slowly decreases outwards. The H i gas layer is strongly flaring. The HWHM scale height is 60 pc at R = 4 kpc and increases to ∼2700 pc at R = 40 kpc. Spiral arms cause a noticeable imprint on the gravitational field, at least out to R = 30 kpc. Conclusions. Our mass model supports previous proposals that the giant stellar ring structure is due to a merging dwarf galaxy. The fact that the majority of the dark matter in the Milky Way for R < ∼ 40 kpc can be successfully modeled by a self-gravitating isothermal disk raises the question of whether this massive disk may have been caused by similar merger events in the past. The substructure in the Galactic dark matter disk suggests a dissipative nature for the dark matter disk.

Context. Measurement of the Galactic neutral atomic hydrogen (H i) column density, N H i , and brightness temperatures, T B , is of high scientific value for a broad range of astrophysical disciplines. In the past two decades, one of the most-used legacy H i datasets has been the Leiden/Argentine/Bonn Survey (LAB). Aims. We release the H i 4π survey (HI4PI), an all-sky database of Galactic H i, which supersedes the LAB survey. Methods. The HI4PI survey is based on data from the recently completed first coverage of the Effelsberg-Bonn H i Survey (EBHIS) and from the third revision of the Galactic All-Sky Survey (GASS). EBHIS and GASS share similar angular resolution and match well in sensitivity. Combined, they are ideally suited to be a successor to LAB. Results. The new HI4PI survey outperforms the LAB in angular resolution (ϑ FWHM = 16 .2) and sensitivity (σ rms = 43 mK). Moreover, it has full spatial sampling and thus overcomes a major drawback of LAB, which severely undersamples the sky. We publish all-sky column density maps of the neutral atomic hydrogen in the Milky Way, along with full spectroscopic data, in several map projections including HEALPix.

Context. The Galactic All-Sky Survey (GASS) is a survey of Galactic atomic hydrogen (H i) emission in the southern sky observed with the Parkes 64-m Radio Telescope. The first data release (GASS I) concerned survey goals and observing techniques, the second release (GASS II) focused on stray radiation and instrumental corrections. Aims. We seek to remove the remaining instrumental effects and present a third data release. Methods. We use the HEALPix tessellation concept to grid the data on the sphere. Individual telescope records are compared with averages on the nearest grid position for significant deviations. All averages are also decomposed into Gaussian components with the aim of segregating unacceptable solutions. Improved priors are used for an iterative baseline fitting and cleaning. In the last step we generate 3D FITS data cubes and examine them for remaining problems. Results. We have removed weak, but systematic baseline offsets with an improved baseline fitting algorithm. We have unraveled correlator failures that cause time dependent oscillations; errors cause stripes in the scanning direction. The remaining problems from radio frequency interference (RFI) are spotted. Classifying the severeness of instrumental errors for each individual telescope record (dump) allows us to exclude bad data from averages. We derive parameters that allow us to discard dumps without compromising the noise of the resulting data products too much. All steps are reiterated several times: in each case, we check the Gaussian parameters for remaining problems and inspect 3D FITS data cubes visually. We find that in total ∼1.5% of the telescope dumps need to be discarded in addition to ∼0.5% of the spectral channels that were excluded in GASS II. Conclusions. The new data release (GASS III) facilitates data products with improved quality. A new web interface, compatible with the previous version, is available for download of GASS III FITS cubes and spectra.

We investigate data from the Galactic Effelsberg-Bonn Hi Survey (EBHIS), supplemented with data from the third release of the Galactic All Sky Survey (GASS III) observed at Parkes. We explore the all sky distribution of the local Galactic Hi gas with |v LSR | < 25 km s −1 on angular scales of 11 to 16 . Unsharp masking (USM) is applied to extract small scale features. We find cold filaments that are aligned with polarized dust emission and conclude that the cold neutral medium (CNM) is mostly organized in sheets that are, because of projection effects, observed as filaments. These filaments are associated with dust ridges, aligned with the magnetic field measured on the structures by Planck at 353 GHz. The CNM above latitudes |b| > 20 • is described by a log-normal distribution, with a median Doppler temperature T D = 223 K, derived from observed line widths that include turbulent contributions. The median neutral hydrogen (HI) column density is N HI 10 19.1 cm −2 . These CNM structures are embedded within a warm neutral medium (WNM) with N HI 10 20 cm −2 . Assuming an average distance of 100 pc, we derive for the CNM sheets a thickness of 0.3 pc. Adopting a magnetic field strength of B tot = (6.0 ± 1.8)µG, proposed by Heiles & Troland 2005, and assuming that the CNM filaments are confined by magnetic pressure, we estimate a thickness of 0.09 pc. Correspondingly the median volume density is in the range 14 n 47 cm −3 .

Context. Since 1973, it has been known that some H i high velocity clouds (HVCs) have a core-envelope structure. Recent observations of compact HVCs confirm this, but more general investigations have been missing so far. Aims. We study the properties of all major HVC complexes from a sample compiled in 1991 by Wakker & van Woerden (WvW). Methods. We use the Leiden/Argentine/Bonn all sky 21-cm line survey and decompose the profiles into Gaussian components. Results. We find the WvW line widths and column densities to be underestimated by ∼40%. In 1991, these line widths could not be measured directly, but had to be estimated with the help of higher resolution data. We find a well-defined multi-component structure for most of the HVC complexes. The cold HVC phase has lines with typical velocity dispersions of σ = 3 km s −1 and exists only within more extended broad line regions, typically with σ = 12 km s −1 . The motions of the cores relative to the envelopes are characterized by Mach numbers M = (v core − v envelope )/σ envelope ∼ 1.5. The center velocities of the cores within a HVC complex have typical dispersions of 20 km s −1 . The well-defined two-component structure of some prominent HVC complexes in the outskirts of the Milky Way is remakable: Complex H lies approximately in the Galactic plane, and the most plausible distance estimate of R ∼ 33 kpc places it at the edge of the disk. The Magellanic Stream and the Leading Arm (complex EP) reach higher latitudes and are probably more distant, R ∼ 50 kpc. There might be some indications for an interaction between HVCs and disk gas at intermediate velocities. This is possible for complex H, M, C, WB, WD, WE, WC, R, G, GCP, and OA, but not for complex A, MS, ACVHV, EN, WA, and P. Conclusions. The line widths, determined by us, imply that estimates of HVC masses, as far as those derived from the WvW database are concerned, need to be scaled up by a factor 1.4. Correspondingly, guesses for the external pressure of a confining coronal gas need to be revised upward by a factor of 2. The HVC multi-phase structure implies in general that currently the halo pressure is significantly underestimated. In consequence, the HVC multi-phase structure may indicate that most of the complexes are circumgalactic. HVCs have turbulent energy densities which are an order of magnitude larger than that of comparable clumps in the Galactic disk.