Gas Accretion onto the Milky Way

Richter, Philipp

doi:10.1007/978-3-319-52512-9_2

Cited by 38 publications

(29 citation statements)

References 216 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4 of this review. • The above items refer to the stellar components of the Galaxy, but there is also warmionized gas (in a halo or circum-galactic medium, Richter 2017, Zheng et al 2019, and cold gas mostly in the disk.…”

Section: Figurementioning

confidence: 99%

Streams, Substructures, and the Early History of the Milky Way

Helmi

2020

Annu. Rev. Astron. Astrophys.

303

169

View full text Add to dashboard Cite

The advent of the second data release of the Gaia mission, in combination with data from large spectroscopic surveys, is revolutionizing our understanding of the Galaxy. Thanks to these transformational data sets and the knowledge accumulated thus far, a new, more mature picture of the evolution of the early Milky Way is currently emerging. ▪ Two of the traditional Galactic components, namely, the stellar halo and the thick disk, appear to be intimately linked: Stars with halo-like kinematics originate in similar proportions from a heated (thick) disk and from a debris from a system named Gaia-Enceladus. Gaia-Enceladus was the last big merger event experienced by the Milky Way and was completed around 10 Gyr ago. The puffed-up stars now present in the halo as a consequence of the merger have thus exposed the existence of a disk component at z ∼ 1.8. This is likely related to the previously known metal-weak thick disk and may be traceable to metallicities [Fe/H] [Formula: see text] −4. As importantly, there is evidence that the merger with Gaia-Enceladus triggered star formation in the early Milky Way, plausibly leading to the appearance of the thick disk as we know it. ▪ Other merger events have been characterized better, and new ones have been uncovered. These include, for example, the Helmi streams, Sequoia, and Thamnos, which add to the list of those discovered in wide-field photometric surveys, such as the Sagittarius streams. Current knowledge of their progenitors’ properties, star formation, and chemical evolutionary histories is still incomplete. ▪ Debris from different objects shows different degrees of overlap in phase-space. This sometimes confusing situation can be improved by determining membership probabilities via quantitative statistical methods. A task for the next few years will be to use ongoing and planned spectroscopic surveys for chemical labeling and to disentangle events from one another using dimensions other than phase-space, metallicity, or [α/Fe]. ▪ These large surveys will also provide line-of-sight velocities missing for faint stars in Gaia releases and more accurate distance determinations for distant objects, which in combination with other surveys could also lead to more accurate age dating. The resulting samples of stars will cover a much wider volume of the Galaxy, allowing, for example, the linking of kinematic substructures found in the inner halo to spatial overdensities in the outer halo. ▪ All the results obtained so far are in line with the expectations of current cosmological models. Nonetheless, tailored hydrodynamical simulations to reproduce in detail the properties of the merger debris, as well as constrained cosmological simulations of the Milky Way, are needed. Such simulations will undoubtedly unravel more connections between the different Galactic components and their substructures, and will aid in pushing our knowledge of the assembly of the Milky Way to the earliest times. Expected final online publication date for the Annual Review of Astronomy, Volume 58 is August 18, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

show abstract

Section: Figurementioning

confidence: 99%

Streams, Substructures, and the Early History of the Milky Way

Helmi

2020

Annu. Rev. Astron. Astrophys.

303

169

View full text Add to dashboard Cite

show abstract

“…These phases range from from cold/neutral gas at relatively high densities (n H ≥ 10 −3 cm −3 ) to warm/hot ionized gas at low densities (n H < 10 −3 cm −3 ) where the gas cannot recombine efficiently (see review by Richter 2017).…”

Section: Interpretation Of Observed Trendsmentioning

confidence: 99%

“…cos_hvc_astroph so-called HVC "complexes", primarily to distinguish between gas clouds in the Milky Way halo that are spatially unrelated and may have different origins (Wakker & van Woerden 1997;Richter 2005Richter , 2017Putman et al 2012). The definition of these HVC complexes is based on the position in l and b of the detected 21 cm features and the radial velocity range in which they are observed (see, e.g., Wakker & van Woerden 1997;Wakker 2001).…”

Section: Identification Of Hvc Complexesmentioning

confidence: 99%

“…This is because we use an angular grid together with an absorption-selected (in l, b, v LSR ) sightline selection to define the HVC boundaries in our sample, while other studies define the area of the MS+LA based on the 21cm contours (e.g., Fox et al 2014). This aspect needs to be taken into account when comparing the HVC mass-and accretion-rate estimates from different surveys (see review by Richter 2017).…”

Section: Identification Of Hvc Complexesmentioning

confidence: 99%

“…We would like to note that these previous estimates are based on other data sets and different model assumptions, so that a direct comparison remains difficult. For a detailed discussion of observational and theoretical studies of the Milky Way's gas accretion we refer to the review by Richter (2017).…”

Section: The Total Gas Masses Of Hvcsmentioning

confidence: 99%

See 2 more Smart Citations

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

Richter

Nuza

Fox

et al. 2017

A&A

112

131

View full text Add to dashboard Cite

Context. The Milky Way is surrounded by large amounts of diffuse gaseous matter that connects the stellar body of our Galaxy with its large-scale Local Group (LG) environment. Aims. To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Methods. Along 270 sightlines we measure metal absorption in the lines of Si ii, Si iii, C ii, and C iv and associated H i 21 cm emission in HVCs in the velocity range |vLSR| = 100 − 500 km s −1 . With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the HVC absorption characteristics with that of Damped Lyman α absorbers (DLAs) and constrained cosmological simulations of the LG (CLUES project). Results. The overall sky-covering fraction of high-velocity absorption is 77 ± 6 percent for the most sensitive ion in our survey, Si iii, and for column densities log N (Si iii) ≥ 12.1. This value is ∼ 4 − 5 times higher than the covering fraction of 21 cm neutral hydrogen emission at log N (H i) ≥ 18.7 along the same lines of sight, demonstrating that the Milky Way's CGM is multi-phase and predominantly ionized. The measured equivalent-width ratios of Si ii, Si iii, C ii, and C iv are inhomogeneously distributed on large and small angular scales, suggesting a complex spatial distribution of multi-phase gas that surrounds the neutral 21 cm HVCs. We estimate that the total mass and accretion rate of the neutral and ionized CGM traced by HVCs is MHVC ≥ 3.0×10 9 M⊙ and dMHVC/dt ≥ 6.1M⊙ yr −1 , where the Magellanic Stream (MS) contributes with more than 90 percent to this mass/mass-flow. If seen from an external vantage point, the Milky Way disk plus CGM would appear as a DLA that would exhibit for most viewing angles an extraordinary large velocity spread of ∆v ≈ 400 − 800 km s −1 , a result of the complex kinematics of the Milky Way CGM that is dominated by the presence of the MS. We detect a velocity dipole of high-velocity absorption at low/high galactic latitudes that we associate with LG gas that streams to the LG barycenter. This scenario is supported by the gas kinematics predicted from the LG simulations. Conclusions. Our study confirms previous results, indicating that the Milky Way CGM contains sufficient gaseous material to feed the Milky Way disk over the next Gyr at a rate of a few solar masses per year, if the CGM gas can actually reach the MW disk. We dem...

show abstract

Large metallicity variations in the Galactic interstellar medium

Jenkins

Ledoux

et al. 2021

Nature

View full text Add to dashboard Cite

Gas Accretion onto the Milky Way

Cited by 38 publications

References 216 publications

Streams, Substructures, and the Early History of the Milky Way

Streams, Substructures, and the Early History of the Milky Way

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

Large metallicity variations in the Galactic interstellar medium

Contact Info

Product

Resources

About