ner_tags: O O O O O O B-Wavelength O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O B-Citation O O O O B-Wavelength O O O O B-Wavelength I-Wavelength O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O B-Wavelength O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O B-Wavelength I-Wavelength O O O B-CelestialObject I-CelestialObject O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O B-Wavelength I-Wavelength B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O B-Citation O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O B-Wavelength O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O
tokens: is of similar order to earlier UV-based measurements (∼1 M ⊙ yr −1 ; Shull et al. 2009 ; Lehner Howk 2011 ; R17 ), but higher than radio-based measurements derived from large 21 cm HVCs (≈0.08 M ⊙ yr −1 ; Putman et al. 2012 ) and higher than the flow rates derived for individual clouds like Complex C (≈0.1 M ⊙ yr −1 ; Wakker et al. 1999 ; Collins et al. 2003 ; Shull et al. 2011 ). This makes sense because most HVC mass is in ionized HVCs (Lehner Howk 2011 ). The ratio of the UV inflow rate to the 21 cm inflow rate quantifies the relative mass in ionized and neutral gas. Our inflow rate calculations indicate (H ii )/ N (H i ), equivalent to a mean HVC ionization fraction f H II = N (H ii )/ N (H i +H ii ) = 0.87. This is higher than the mean ionization fraction reported in large 21 cm HVCs such as Complex C and Complex A because such large clouds are atypical; most HVCs are ionized and not detected at 21 cm (Shull et al. 2009 ; Lehner Howk 2011 ; R17 ). For comparison with the HVC mass flow rates, the intermediate-velocity mass flow rates are of interest. These can be derived from optical observations of Ca ii and Na i absorption (Ben Behkti et al. 2012 ). The Ca ii and Na i doublets are much less saturated than UV resonance lines, particularly at intermediate velocities, resulting in cleaner measurements. Ben Behkti et al. ( 2012 ) report a population of Ca ii IVCs with a sky covering factor of ≈30%, a mean v GSR = −42 km s −1 , and an associated N (H i ) distribution peaking near log N (H i ) ≈ 19. Combining these numbers with a typical IVC distance of 2 kpc (Richter et al. 2017 ) we derive an H i mass flow rate of ≈0.04 M ⊙ yr −1 in these Ca ii IVCs. If a similar ionization correction N (H ii )/ N (H i ) = 6.6 applies to IVCs as to HVCs, then IVCs represent a total mass flow rate of ≈0.27 M ⊙ yr −1 , comparable to the HVC flow rate (this similarity occurs because the larger column densities of IVCs are compensated by their smaller velocities and distances). To fully explore this, a more thorough investigation of the IVC mass flow rates using UV data would be worthwhile, including a distinction into inflow and outflow and detailed ionization modeling. We emphasize that the HVC mass flow rates derived in this paper are effectively instantaneous , as they represent the mass flux contained in HVCs observed at the current epoch. Hydrodynamic simulations (Heitsch Putman 2009 ; Armillotta et al. 2017 ) show that HVC lifetimes are typically a few 100 Myr depending on HVC mass and the density contrast with the surrounding hot medium, after which the clouds will become disrupted and evaporated by coronal interactions. Caution should therefore be used in integrating our mass flow rates over long timescales to calculate the total mass delivered in and out of the disk, as the gas will change phase over time via evaporation and subsequent condensation (e.g., Fraternali 2017 ; Voit et al. 2019 ). Finally, we can use our HVC mass outflow rate measurement to