High‐Velocity Clouds and the Local Intergalactic Medium

Richter, Philipp

doi:10.1002/9783527619030.ch2

Cited by 30 publications

(19 citation statements)

References 88 publications

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“…Although the gas density n h of the halo, before the injection of the HVCs, was probably low, n h was not zero. The local intergalactic medium has low volume densities, 10 −6 −10 −4 cm −3 (Richter 2006). If n h ≈ 10 −6 atoms cm −3…”

Section: Results Of the Dynamical Modelmentioning

confidence: 99%

Distribution of the high-velocity clouds in the Galactic halo

Olano¹

2008

A&A

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Context. There is a connection between the kinematics and sky distribution of the high velocity clouds (HVCs) and the spatial velocity and orbital plane of the Magellanic Clouds (MCs) that allow us to conclude that most HVCs were ejected from the Clouds, some hundreds of Myrs ago, probably by an encounter between the Large (LMC) and Small Magellanic Cloud (SMC). Aims. Based on the idea that HVCs have progenitors in the MCs, we attempt determine theoretical distances to the HVCs using observed data of the sky positions and radial velocities, and thus to map the spatial distribution of the HVCs. Methods. i) In the context of a kinematical model we have found an analytical formula that gives the distance of an HVC; ii) we have developed two dynamical models in order to study the orbits of the HVCs under the gravitational forces exerted by the Galaxy and the MCs and forces of resistance due to the movement of the HVCs through the Galactic gaseous disk. We have adopted the gravitational potential of the Milky Way given by a dark matter halo (Model 1) plus a massive thick disk partially composed by dark matter (Model 2). By means of a fitting to certain Galactic, MC and HVC conditions we have obtained values for the free parameters of the Models. We have obtained the dynamical distances to the HVCs by constructing the theoretical relationship between the radial velocity and the distance in the line of sight of each HVC. Results. The HVCs can be divided into three major groups: Population MS, Population W and Population A−C. Population MS comprises the Magellanic stream and the leading arm of the Magellanic system. The HVCs of this population are dispersed around the MCs within a volume of ≈200 kpc × 200 kpc × 60 kpc. Population W is situated at a mean distance of ≈15 kpc from the Sun, and has been braked by the gas of the Galactic disk. Population A−C includes Complexes A, C, H, L, M, and ACHVC. The dynamical models give two solutions for the distance of each HVC of Population A−C. The near-distance solutions place Population A−C at ≈6 kpc from the Sun, showing that this chain of HVCs started to interact with the outer parts of the Galactic gaseous disk about 100 Myr ago. While, the spatial distribution of Population A−C represented with the far distances has the shape of a gigantic ring with a radius of ≈125 kpc. Our results support the idea that the LMC-SMC encounter triggered a period of star formation bursts, in which part of the LMC bar was probably formed. The interactions of a few 10 5 massive stars formed in this era with the then-existing low metallicity ISM of the MCs would have created the HVCs

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Section: Results Of the Dynamical Modelmentioning

confidence: 99%

Distribution of the high-velocity clouds in the Galactic halo

Olano¹

2008

A&A

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“…Observations of the Milky Way and other nearby galaxies carried out in the 21 cm line have shown that spiral galaxies commonly also exhibit extraplanar H i structures that indicate inflows, outflows, and merger processes in these systems (see reviews by Wakker & van Woerden 1997;Richter 2006;Putman et al 2012). In the Milky Way, such extraplanar neutral gas structures manifest themselves as the so-called high-velocity clouds (HVCs), which have column densities within the range NHI ∼ 10 18 − 10 20 cm −2 .…”

Section: H I Gas Componentmentioning

confidence: 99%

“…During the last two decades, significant progress was achieved in our understanding of the distribution and physical properties of circumgalactic and intergalactic gas in the Local Group (hereafter LG; e.g., Wakker & van Woerden 1997;Richter 2006;Putman et al ⋆ snuza@aip.de 2012, for reviews on this topic). Recent observational campaigns including 21 cm radio observations of neutral hydrogen (e.g., Thilker et al 2004;Kalberla & Haud 2006;Kerp et al 2011), and absorption-line measurements of neutral and ionized gas in the optical and ultraviolet (UV; e.g., Sembach et al 2003;Collins et al 2005Collins et al , 2009Ben Bekhti et al 2008Richter et al 2009Richter et al , 2012]; Herenz et al 2013;Rao et al 2013) indicate the extreme multi-phase character of circumgalactic gas within the virial radii of the Milky Way and Andromeda galaxies.…”

Section: Introductionmentioning

confidence: 99%

The distribution of gas in the Local Group from constrained cosmological simulations: the case for Andromeda and the Milky Way galaxies

Nuza

Parisi

Scannapieco

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We study the gas distribution in the Milky Way and Andromeda using a constrained cosmological simulation of the Local Group (LG) within the context of the CLUES (Constrained Local UniversE Simulations) project. We analyse the properties of gas in the simulated galaxies at z = 0 for three different phases: 'cold', 'hot' and H i, and compare our results with observations. The amount of material in the hot halo (M hot ≈ 4 − 5 × 10 10 M ⊙ ), and the cold (M cold (r 10 kpc) ≈ 10 8 M ⊙ ) and H i (M HI (r 50 kpc) ≈ 3 − 4 × 10 8 M ⊙ ) components display a reasonable agreement with observations. We also compute the accretion/ejection rates together with the H i (radial and all-sky) covering fractions. The integrated H i accretion rate within r = 50 kpc gives ∼0.2 − 0.3 M ⊙ yr −1 , i.e. close to that obtained from high-velocity clouds in the Milky Way. We find that the global accretion rate is dominated by hot material, although ionized gas with T 10 5 K can contribute significantly too. The net accretion rates of all material at the virial radii are 6 − 8 M ⊙ yr −1 . At z = 0, we find a significant gas excess between the two galaxies, as compared to any other direction, resulting from the overlap of their gaseous haloes. In our simulation, the gas excess first occurs at z ∼ 1, as a consequence of the kinematical evolution of the LG.

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“…HVCs also have been brought into relation with primordial building blocks of galaxies in a hierarchical formation scenario (e.g., Oort 1966;Blitz et al 1999). A powerful method of analysing the characteristics of IVC and HVC gas at low redshifts is to analyse high-resolution ultraviolet (UV) and optical absorption spectra together with H i 21-cm emission data (Richter 2006;Ben Bekhti et al 2008). The combination of these data provides important information about the spatial distribution and the physical properties of the clouds.…”

Section: Introductionmentioning

confidence: 99%

High-resolution 21-cm observations of low-column density gas clumps in the Milky Way halo

Bekhti¹,

Richter²,

Winkel³

et al. 2009

A&A

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Aims. We study the properties of low-column density gas clumps in the halo of the Milky Way based on high-resolution 21-cm observations. Methods. Using interferometric data from the Westerbork Synthesis Radio Telescope (WSRT) and the Very Large Array (VLA), we studied H i emission at low-, intermediate-and high radial velocities along four lines of sight towards the quasars QSO J0003−2323, QSO B1331+170, QSO B0450−1310, and J081331+254503. Along these sightlines we had previously detected weak Ca ii and Na i absorbers in the optical spectra of these quasars.Results. The analysis of the high-resolution H i data reveals several compact and cold clumps of neutral gas at velocities similar to the optical absorption. The clumps have narrow H i line widths in the range of 1.8 ≤ v FWHM ≤ 13.0 km s Conclusions. Our high-resolution 21-cm observations indicate that many of the Ca ii and Na i absorbers seen in our optical quasar spectra are associated with low-column density H i clumps on small angular scales. This suggests that, next to the massive, highcolumn density neutral gas clouds in the halo (the common 21-cm low-, intermediate-, and high-velocity clouds, LVCs, IVCs, and HVCs), a population of low-mass, neutral gas structures exists in the halo and remain mostly unseen in the existing 21-cm all-sky surveys of IVCs and HVCs. One of our absorbers may be associated with the Magellanic Stream, two intermediate-velocity clouds are probably part of the Intermediate-Velocity Spur and the Low-latitude IV arch, respectively. The remaining systems could be located either in the lower halo or in the disk of the Milky Way. The estimated thermal gas pressures of the detected H i clumps are consistent with what is expected from theoretical models of gas in the inner and outer Milky Way halos.

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High‐Velocity Clouds and the Local Intergalactic Medium

Cited by 30 publications

References 88 publications

Distribution of the high-velocity clouds in the Galactic halo

Distribution of the high-velocity clouds in the Galactic halo

The distribution of gas in the Local Group from constrained cosmological simulations: the case for Andromeda and the Milky Way galaxies

High-resolution 21-cm observations of low-column density gas clumps in the Milky Way halo

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