An Accurate Distance to High‐Velocity Cloud Complex C

Thom, Christopher; Peek, J. E. G.; Putman, M. E.; Heiles, Carl; Peek, Kathryn M. G.; Wilhelm, Ronald

doi:10.1086/589960

Cited by 137 publications

(198 citation statements)

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“…Ideally, one would study systematically diagnostic metal-ion ratios (such as Si ii/Si iii and C ii/C iv) as a function of distance to the absorbers. Measuring HVC distances is very difficult, however, and reliable distance estimates have been determined only for a very limited number of halo clouds (Ryans et al 1997a(Ryans et al , 1997bvan Woerden et al 1998;Wakker et al 2007Wakker et al , 2008; Thom et al 2006Thom et al , 2008 Article number, page 7 of 37 A&A proofs: manuscript no. cos_hvc_astroph 2011; Lehner et al 2012;Richter et al 2015).…”

Section: Absorption Fraction Vs Radial Velocitymentioning

confidence: 99%

“…Article number, page 12 of 37 Richter et al: The Milky Way CGM in absorption Wakker (2001; Wakker et al (2007Wakker et al ( ,2008; Thom et al (2006Thom et al ( ,2008Richter (2006); Richter et al (2015); Wakker et al (2017, in prep.). b Distance assumed in our model to calculate the total HVC mass and accretion rate (Sect.…”

Section: Interpretation Of Observed Trendsmentioning

confidence: 99%

“…The presence of low and high ions in the gas reflects its extreme multi-phase nature with temperatures ranging from T = 10 2 to 10 7 K. Recent studies imply that the bulk of the Milky Way CGM baryons reside in a diffuse (at gas densities n H ≤ 10 −3 cm −3 ), predominantly ionized gas phase that can be detected in UV and X-ray absorption lines of intermediate and high ions against extragalactic background point sources (e.g., Sembach et al 2003;Shull et al 2009;Richter et al 2008Richter et al , 2009Lehner et al 2012;Miller et al 2016). Another important finding from absorption spectroscopy is that most of the spatially extended neutral gas features that are seen in H i 21 cm emission are relatively nearby at distances d < 15 kpc (Ryans et al 1997a(Ryans et al , 1997bWakker et al 2007Wakker et al , 2008; Thom et al 2006Thom et al , 2008Lehner et al 2012;Richter et al 2015), ruling that that these objects represent pristine, extragalactic gas clouds (see discussion in Blitz et al 1999). Many of the ionized HVCs are located at similarly small distances deep within the potential well of the Milky Way (Lehner & Howk 2011;Lehner et al 2012), but some of observed high-ion absorbers possibly are related to LG gas Nicastro et al 2003).…”

Section: Introductionmentioning

confidence: 99%

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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

115

131

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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...

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Section: Absorption Fraction Vs Radial Velocitymentioning

confidence: 99%

Section: Interpretation Of Observed Trendsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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

115

131

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“…Optical absorption spectroscopy of halo stars that span a distance range of several kiloparsecs in the direction of known 21cm HVCs imply that most (if not all) of the HVCs are located within ∼ 60 kpc of the Milky Way (e.g., Wakker et al 2007Wakker et al ,2008; Thom et al 2006Thom et al ,2008Lehner et al ,2012. HVCs thus represent gaseous structures that are located in the inner and outer Galactic halo well within the virial radius of the Milky Way.…”

Section: Kinematics Of Local Circumgalactic Gasmentioning

confidence: 99%

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

et al. 2014

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In this article we discuss the importance of high-resolution absorption spectroscopy for our understanding of the distribution and physical nature of the gaseous circumgalactic medium (CGM) that surrounds the Milky Way. Observational and theoretical studies indicate a high complexity of the gas kinematics and an extreme multi-phase nature of the CGM in low-redshift galaxies. High-precision absorption-line measurements of the Milky Way's gas environment thus are essential to explore fundamental parameters of circumgalactic gas in the local Universe, such as mass, chemical composition, and spatial distribution. We shortly review important characteristics of the Milky Way's CGM and discuss recent results from our multi-wavelength observations of the Magellanic Stream. Finally, we discuss the potential of studying the warm-hot phase of the Milky Way's CGM by searching for extremely weak [Fe X] λ6374.5 and [Fe XIV] λ5302.9 absorption in optical QSO spectra.

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“…The puzzle of the origin of high velocity clouds (HVCs) is still with us more than 50 years after their initial discovery (Muller et al(1963)), and despite the enormous progress made in the past decades in understanding their distances, size, mass, metalicity, covering fraction, and ionization state (e.g., Wakker & van Woerden(1997), Lockman et al(2002), Fox et al(2006), Wakker et al(2008), Thom et al(2008), Shull et al(2009), Putman et al(2012), Lehner et al(2012)). HVCs are now known to exist around nearby galaxies in a population that exends at least 50 kpc from the host system (Thilker et al(2004), Grossi et al(2008), Westmeier et al(2008), Putman et al(2009).)…”

Section: Introductionmentioning

confidence: 99%

Accretion Onto the Milky Way: The Smith Cloud

Lockman

2015

Proc. IAU

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Abstract. Active gas accretion onto the Milky Way is observed in an object called the Smith Cloud, which contains several million solar masses of neutral and warm ionized gas and is currently losing material to the Milky Way, adding angular momentum to the disk. It is several kpc in size and its tip lies two kpc below the Galactic plane. It appears to have no stellar counterpart, but could contain a stellar population like that of the dwarf galaxy Leo P. There are suggestions that its existence and survival require that it be embedded in a dark matter halo of a few 10 8 solar masses.

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An Accurate Distance to High‐Velocity Cloud Complex C

Cited by 137 publications

References 58 publications

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

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

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

Accretion Onto the Milky Way: The Smith Cloud

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