The Effelsberg-Bonn H i Survey: Milky Way gas

Winkel, B.; Kerp, J.; Flöer, L.; Kalberla, P. M. W.; Bekhti, N. Ben; Keller, Reinhard; Lenz, Daniel

doi:10.1051/0004-6361/201527007

Cited by 176 publications

(214 citation statements)

References 46 publications

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“…For this analysis we have used the 4 -resolution GALFA-HI survey where available (Peek et al 2011) and we have complemented it with the 10.8 -resolution EBHIS survey elsewhere (Winkel et al 2016). As shown in Fig.…”

Section: Hi and Co Datamentioning

confidence: 99%

Cosmic rays, gas and dust in nearby anticentre clouds

Remy

Grenier

Marshall

et al. 2017

A&A

187

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Aims. We aim to explore the capabilities of dust emission and γ rays for probing the properties of the interstellar medium in the nearby anti-centre region, using γ-ray observations with the Fermi Large Area Telescope (LAT), and the thermal dust optical depth inferred from Planck and IRAS observations. We also aim to study massive star-forming clouds including the well known Taurus, Auriga, Perseus, and California molecular clouds, as well as a more diffuse structure which we refer to as Cetus. In particular, we aim at quantifying potential variations in cosmic-ray density and dust properties per gas nucleon across the different gas phases and different clouds, and at measuring the CO-to-H 2 conversion factor, X CO , in different environments. Methods. We have separated six nearby anti-centre clouds that are coherent in velocities and distances, from the Galactic-disc background in H i 21-cm and 12 CO 2.6-mm line emission. We have jointly modelled the γ-ray intensity recorded between 0.4 and 100 GeV, and the dust optical depth τ 353 at 353 GHz as a combination of H i -bright, CO-bright, and ionised gas components. The complementary information from dust emission and γ rays was used to reveal the gas not seen, or poorly traced, by H i , free-free, and 12 CO emissions, namely (i) the opaque H i and diffuse H 2 present in the Dark Neutral Medium at the atomic-molecular transition, and (ii) the dense H 2 to be added where 12 CO lines saturate. Results. The measured interstellar γ-ray spectra support a uniform penetration of the cosmic rays with energies above a few GeV through the clouds, from the atomic envelopes to the 12 CO-bright cores, and with a small ±9% cloud-to-cloud dispersion in particle flux. We detect the ionised gas from the H ii region NGC1499 in the dust and γ-ray emissions and measure its mean electron density and temperature. We find a gradual increase in grain opacity as the gas (atomic or molecular) becomes more dense. The increase reaches a factor of four to six in the cold molecular regions that are well shielded from stellar radiation. Consequently, the X CO factor derived from dust is systematically larger by 30% to 130% than the γ-ray estimate. We also evaluate the average γ-ray X CO factor for each cloud, and find that X CO tends to decrease from diffuse to more compact molecular clouds, as expected from theory. We find X CO factors in the anti-centre clouds close to or below 10 20 cm −2 K −1 km −1 s, in agreement with other estimates in the solar neighbourhood. Together, they confirm the long-standing unexplained discrepancy, by a factor of two, between the mean X CO values measured at parsec scales in nearby clouds and those obtained at kiloparsec scale in the Galaxy. Our results also highlight large quantitative discrepancies in 12 CO intensities between simulations and observations at low molecular gas densities.

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Section: Hi and Co Datamentioning

confidence: 99%

Cosmic rays, gas and dust in nearby anticentre clouds

Remy

Grenier

Marshall

et al. 2017

A&A

187

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“…Spectrally, data have velocity resolution of 1.32 km s −1 . While we use interferometer-only data to measure optical depths through the HVCs via H i continuum absorption, we have also made a cube with all spatial frequencies from the largest scales down to the resolution limit of the DRAO ST by incorporating single-dish H i data as observed by the Effelsberg H i Survey (EBHIS; Winkel et al 2016, with spatial and velocity resolutions of ∼11 and 1.4 km s −1 , respectively). After smoothing to the same resolution as the 4850-MHz total-power data of 2 .45, we inspected this data cube carefully for apparent associations between the radio continuum emission structure and the distribution of the neutral hydrogen gas (see Sect.…”

Section: Km Smentioning

confidence: 99%

G181.1+9.5, a new high-latitude low-surface brightness supernova remnant

Kothes

Reich

Foster

et al. 2017

A&A

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Context. More than 90% of the known Milky Way supernova remnants (SNRs) are within 5• of the Galactic plane. The discovery of the new high-latitude SNR G181.1+9.5 will give us the opportunity to learn more about the environment and magnetic field at the interface between disk and halo of our Galaxy. Aims. We present the discovery of SNR G181.1+9.5, a new high-latitude SNR, serendipitously discovered in an ongoing survey of the Galactic anti-centre High-Velocity Cloud complex, observed with the DRAO Synthesis Telescope in the 21 cm radio continuum and H i spectral line.Methods. We use radio continuum observations (including the linearly polarized component) at 1420 MHz (observed with the DRAO ST) and 4850 MHz (observed with the Effelsberg 100-m radio telescope) to map G181.1+9.5 and determine its nature as a SNR. High-resolution 21 cm H i line observations and H i emission and absorption spectra reveal the physical characteristics of its local interstellar environment. Finally, we estimate the basic physical parameters of G181.1+9.5 using models for highly-evolved SNRs. Results. G181.1+9.5 has a circular shell-like morphology with a radius of about 16 pc at a distance of 1.5 kpc some 250 pc above the mid-plane. The radio observations reveal highly linearly polarized emission with a non-thermal spectrum. Archival ROSAT X-ray data reveal high-energy emission from the interior of G181.1+9.5 indicative of the presence of shock-heated ejecta. The SNR is in the advanced radiative phase of SNR evolution, expanding into the HVC inter-cloud medium with a density of n HI ≈ 1 cm −3 . Basic physical attributes of G181.1+9.5 calculated with radiative SNR models show an upper-limit age of 16 000 yr, a swept-up mass of more than 300 M , and an ambient density in agreement with that estimated from H i observations. Conclusions. G181.1+9.5 shows all characteristics of a typical mature shell-type SNR, but its observed faintness is unusual and requires further study.

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“…In addition, the angular resolution and quality of their data, especially in H i, is significantly surpassed by the new all-sky surveys that are available today (Winkel et al 2016a;Kalberla & Haud 2015;Planck Collaboration I 2014).…”

Section: Introductionmentioning

confidence: 99%

All-sky census of Galactic high-latitude molecular intermediate-velocity clouds

Röhser

Kerp

Lenz

et al. 2016

A&A

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Context. The H i halo clouds of the Milky Way, and in particular the intermediate-velocity clouds (IVCs), are thought to be connected to Galactic fountain processes. Observations of fountain clouds are important for understanding the role of matter recycling and accretion onto the Galactic disk and subsequent star formation. Aims. Here, we quantify the amount of molecular gas in the Galactic halo. We focus on the rare class of molecular IVCs (MIVCs) and search for new objects. Methods. The H i-FIR correlation was studied across the entire northern and southern Galactic hemispheres at Galactic latitudes |b| > 20• to determine the amount and distribution of molecular gas in IVCs. We used the most recent large-scale H i and FIR data, the Effelsberg Bonn-H i Survey, the Parkes Galactic All-Sky Survey, and the Planck FIR surveys.Results. We present a catalogue of 239 MIVC candidates on the northern and southern Galactic hemispheres. Among these candidates, all previously known MIVCs are recovered except for one single source. The frequency of candidates differs significantly between the northern and southern Galactic hemispheres and between negative and positive LSR velocities as well.Conclusions. In our approach we analyse the local Galactic environment. Extrapolating our results to the entire Galaxy, the global inflow of atomic and molecular IVC gas onto the Milky Way may account for the major fraction of the gaseous mass that is required to sustain the current Galactic star formation rate.

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The Effelsberg-Bonn H i Survey: Milky Way gas

Cited by 176 publications

References 46 publications

Cosmic rays, gas and dust in nearby anticentre clouds

Cosmic rays, gas and dust in nearby anticentre clouds

G181.1+9.5, a new high-latitude low-surface brightness supernova remnant

All-sky census of Galactic high-latitude molecular intermediate-velocity clouds

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