The Effelsberg Bonn H I Survey (EBHIS)

Kerp, J.; Winkel, B.; Bekhti, N. Ben; Floeer, L.; Kalberla, P. M. W.

doi:10.1002/asna.201011548

Cited by 114 publications

(120 citation statements)

References 40 publications

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“…For our follow-up analysis we used data from the EffelsbergBonn H i Survey (EBHIS; Winkel et al 2010;Kerp et al 2011) and the Galactic All-Sky Survey (GASS; McClure-Griffiths et al 2009;Kalberla et al 2010), which are the most sensitive, highest angular resolution, large-scale surveys of Galactic H i emission ever made in the northern and southern sky. The former is currently undertaken with the 100-m telescope at Effelsberg, while the latter (using the 64-m Parkes telescope) was recently finished.…”

Section: Ebhis and Gass Datamentioning

confidence: 99%

“…For the remaining lines of sight we make use of the new large-area H i 21-cm surveys GASS (Galactic All-Sky survey, McClure-Griffiths et al 2009;Kalberla et al 2010) and EBHIS (Effelsberg-Bonn HI survey, Winkel et al 2010;Kerp et al 2011). Compared to BB08, this leads to a substantially increased number of H i spectra available for follow-up analyses.…”

Section: Introductionmentioning

confidence: 99%

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An absorption-selected survey of neutral gas in the Milky Way halo

Bekhti

Winkel

Richter

et al. 2012

A&A

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Aims. We aim at analysing systematically the distribution and physical properties of neutral and mildly ionised gas in the Milky Way halo, based on a large absorption-selected data set. Methods.Multi-wavelength studies were performed combining optical absorption line data of Ca ii and Na i with follow-up H i 21-cm emission line observations along 408 sight lines towards low-and high-redshift QSOs. We made use of archival optical spectra obtained with UVES/VLT. H i data were extracted from the Effelsberg-Bonn H i survey and the Galactic All-Sky survey.For selected sight lines we obtained deeper follow-up observations using the Effelsberg 100-m telescope.Results. Ca ii (Na i) halo absorbers at intermediate and high radial velocities are present in 40-55% (20-35%) of the sightlines, depending on the column density threshold chosen. Many halo absorbers show multi-component absorption lines, indicating the presence of sub-structure. In 65% of the cases, absorption is associated with H i 21-cm emission. The Ca ii (Na i) column density distribution function follows a power-law with a slope of β ≈ −2.2 (−1.4). Conclusions. Our absorption-selected survey confirms our previous results that the Milky Way halo is filled with a large number of neutral gas structures whose high column density tail represents the population of common H i high-and intermediate-velocity clouds seen in 21-cm observations. We find that Na i/Ca ii column density ratios in the halo absorbers are typically smaller than those in the Milky Way disc, in the gas in the Magellanic Clouds, and in damped Lyman α systems. The small ratios (prominent in particular in high-velocity components) indicate a lower level of Ca depletion onto dust grains in Milky Way halo absorbers compared to gas in discs and inner regions of galaxies.

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Section: Ebhis and Gass Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An absorption-selected survey of neutral gas in the Milky Way halo

Bekhti

Winkel

Richter

et al. 2012

A&A

Self Cite

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“…(1) Winkel et al (2016), Kerp et al (2011), Winkel et al (2010); (2) Planck Collaboration XI (2014); (3) this work. Röhser et al (2014) propose a natural evolutionary sequence from pure atomic to molecular IVCs in the fountain cycle.…”

Section: Introductionmentioning

confidence: 99%

High-resolution HI and CO observations of high-latitude intermediate-velocity clouds

Röhser

Kerp

Bekhti

et al. 2016

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Context. Intermediate-velocity clouds (IVCs) are HI halo clouds that are likely related to a Galactic fountain process. In-falling IVCs are candidates for the re-accretion of matter onto the Milky Way. Aims. We study the evolution of IVCs at the disk-halo interface, focussing on the transition from atomic to molecular IVCs. We compare an atomic IVC to a molecular IVC and characterise their structural differences in order to investigate how molecular IVCs form high above the Galactic plane. Methods. With high-resolution HI observations of the Westerbork Synthesis Radio Telescope and 12 CO(1 → 0) and 13 CO(1 → 0) observations with the IRAM 30 m telescope, we analyse the small-scale structures within the two clouds. By correlating HI and far-infrared (FIR) dust continuum emission from the Planck satellite, the distribution of molecular hydrogen (H 2 ) is estimated. We conduct a detailed comparison of the HI, FIR, and CO data and study variations of the X CO conversion factor. Results. The atomic IVC does not disclose detectable CO emission. The atomic small-scale structure, as revealed by the highresolution HI data, shows low peak HI column densities and low HI fluxes as compared to the molecular IVC. The molecular IVC exhibits a rich molecular structure and most of the CO emission is observed at the eastern edge of the cloud. There is observational evidence that the molecular IVC is in a transient and, thus, non-equilibrium phase. The average X CO factor is close to the canonical value of the Milky Way disk. Conclusions. We propose that the two IVCs represent different states in a gradual transition from atomic to molecular clouds. The molecular IVC appears to be more condensed allowing the formation of H 2 and CO in shielded regions all over the cloud. Ram pressure may accumulate gas and thus facilitate the formation of H 2 . We show evidence that the atomic IVC will evolve also into a molecular IVC in a few Myr.

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“…We use data from the new Effelsberg-Bonn H -Survey (EBHIS, Winkel et al 2010;Kerp et al 2011) Notes. The columns list (from left to right) the survey, the corresponding frequency, the angular resolution, and the average noise.…”

Section: Introductionmentioning

confidence: 99%

A dynamical transition from atomic to molecular intermediate-velocity clouds

Röhser

Kerp

Winkel

et al. 2014

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Context. Towards the high galactic latitude sky, the far-infrared (FIR) intensity is tightly correlated to the total hydrogen column density which is made up of atomic (H ) and molecular hydrogen (H 2 ). Above a certain column density threshold, atomic hydrogen turns molecular. Aims. We analyse gas and dust properties of intermediate-velocity clouds (IVCs) in the lower galactic halo to explore their transition from the atomic to the molecular phase. Driven by observations, we investigate the physical processes that transform a purely atomic IVC into a molecular one. Methods. Data from the Effelsberg-Bonn H -Survey (EBHIS) are correlated to FIR wavebands of the Planck satellite and IRIS. Modified black-body emission spectra are fitted to deduce dust optical depths and grain temperatures. We remove the contribution of atomic hydrogen to the FIR intensity to estimate molecular hydrogen column densities. Results. Two IVCs show different FIR properties, despite their similarity in H , such as narrow spectral lines and large column densities. One FIR bright IVC is associated with H 2 , confirmed by 12 CO (1 → 0) emission; the other IVC is FIR dim and shows no FIR excess, which indicates the absence of molecular hydrogen. Conclusions. We propose that the FIR dim and bright IVCs probe the transition between the atomic and molecular gas phase. Triggered by dynamical processes, this transition happens during the descent of IVCs onto the galactic disk. The most natural driver is ram pressure exerted onto the cloud by the increasing halo density. Because of the enhanced pressure, the formation timescale of H 2 is reduced, allowing the formation of large amounts of H 2 within a few Myr.

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The Effelsberg Bonn H I Survey (EBHIS)

Cited by 114 publications

References 40 publications

An absorption-selected survey of neutral gas in the Milky Way halo

An absorption-selected survey of neutral gas in the Milky Way halo

High-resolution HI and CO observations of high-latitude intermediate-velocity clouds

A dynamical transition from atomic to molecular intermediate-velocity clouds

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