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Appendix A: Discussion on individual HVC sightlines

In the following we shortly discuss the HVC absorption properties individually for each line of sight and summarize the results from previous studies. The sightlines are sorted by Galactic longitude.

PKS 2155 − 304. The PKS 2155−304 sightline is located at l = 17.7, b =  −52.3; it thus passes the outer edge of HVC Complex GCN. HVC absorption is seen at high negative velocities. Only E140M data are available for this sightline. The data have good quality with a S/N of  ~ 18 per 3.2 km s^-1-wide pixel element at 1300 Å. HVC absorption is split into two groups (see Fig. B.4; Table B.1). The first group near v_LSR =  −150 km s^-1 is detected in C ii, Si ii, Si iii, Si iv and C iv and has three subcomponents at −111,−135 and −157 km s^-1. The second group is centred near −260 km s^-1 and is detected only in Si iii, Si iv and C iv. It has three subcomponents at −232,−254 and −280 km s^-1. Detailed analyses of the PKS 2155−304 sightline are presented by Sembach et al. (1999) and Collins et al. (2004). This sightline is also discussed in Sembach et al. (2003), Fox et al. (2006), Collins et al. (2009), and Winkel et al. (2011).

Mrk 509. The Mrk 509 sightline is located at l = 36.0, b =  −29.9 and passes through highly-ionized HVC gas at very high negative velocities. This HVC is associated with Complex GCN (see Winkel et al. 2011). Both E140M and E230M data are available for this sightline, but the S/N in the data is relatively low (~7 per 3.2 km s^-1-wide pixel element at 1300 Å). Absorption is detected in four components at v_LSR =  −263,−287,−273, and −311 km s^-1 in the lines of C ii, Si iii, Si iv and C iv (see Fig. B.2; Table B.1). Detailed studies of this HVC are presented in Sembach et al. (2004b) and Collins et al. (2004). Other studies that discuss this sightline are Sembach et al. (2003) and Winkel et al. (2011).

PHL 1811. The line of sight towards the Seyfert 1 galaxy PHL 1811 (l = 47.5, b =  −44.8) passes the outskirts of HVC Complex GCN and shows a complex HVC absorption pattern in the LSR veocity range between −100 and −300 km s^-1 (see Fig. B.3; Table B.1). Only E140M data are available for this sightline; the S/N is  ~ 7 per 3.2 km s^-1-wide pixel element at 1300 Å. Five absorption components are identified at velocities of v_LSR =  −163,−206,−240,−263, and −351 km s^-1 in the lines of C ii, O i, Si ii, Al ii, Si iii, Si iv, and C iv. The large number of components suggests a complex spatial distribution of HVC gas in Complex GCN in this direction (see also Winkel et al. 2011). A detailed study of the Complex GCN absorption towards PHL 1811 is presented in Richter et al. (2009). Other studies of relevance in this context are the ones by Fox et al. (2006), Ben Bekhti et al. (2008), Collins et al. (2009), and Winkel et al. (2011).

PG 1630 + 377. For the line of sight towards the quasar PG 1630 + 377 (l = 60.3, b =  + 42.9) only STIS data from the E230M grating are available (see Fig. B.3; Table B.3). HVC absorption is detected in Mg ii and Fe ii in three individual components at negative velocities at v_LSR =  −64,−99, and −155 km s^-1. With a S/N of  ~ 8 per 4.8 km s^-1 wide pixel element at 2796 Å the data quality is rather low. For the two absorption components near −100 km s^-1 the Mg ii absorption is saturated. We did not find any previous studies that discuss HVC absorption along this line of sight.

PG 1444 + 407. Along the line of sight towards the Seyfert 1 galaxy PG 1444 + 407 at l = 69.9 and b =  + 62.7 we identify one double-component high-velocity absorber at v_LSR ≈ −85 km s^-1 in the lines of Si ii, O i, C ii, and C iv (see Fig. B.3; Table B.3). The C iv component seems to be shifted to more negative velocities and the C ii absorption is strongly saturated. This indicates a two-phase HVC structure with an inner core that is surrounded by an ionized envelope. The data have a S/N ~ 8 per 3.2 km s^-1-wide pixel element at 1260 Å. This HVC absorber is located at the outer edge of Complex C. For further information see the sample of Wakker et al. (2011) and Shull et al. (2009).

PG 1718 + 481. The line of sight towards the QSO PG 1718 + 481 is located at l = 74.4, b =  + 34.8; it therefore pierces the outer environments of the HVC Complexes C and K. Unfortunately, only Fe ii λ2600 is covered by the E230M data, while E140 data are not available. The E230M data have a good S/N of  ~ 14 per 4.8 km s^-1-wide pixel element at 2600 Å. The Fe ii line shows three well-defined HVC components at radial velocities of v_LSR =  −81,−128, and −197 km s^-1 (see Fig. B.3; Table B.1). We did not find any previous paper that discusses the HVC absorption towards PG 1718 + 481.

NGC 7469. The line of sight towards NGC 7469 passes directly through the Magellanic Stream at l = 83.1, b =  −45.5. Consequently, the STIS data show a complex absorption pattern at high negative velocities in the range v_LSR =  −180 to −400 km s^-1. For this sightline only E140M data are available. The S/N in the data is  ~ 10 per 3.2 km s^-1-wide pixel element at 1300 Å. We fit five individual absorption components to the data at v_LSR =  −185,−251,−293,−335, and −366 km s^-1 (Fig. B.2; Table B.1). A detailed analysis of this sightline is presented in Fox et al. (2010).

3C 351. The 3C 351 sightline passes the HVC Complexes C and K at l = 90.1, b =  + 36.4. Only E140 M data are available for this sightline. The S/N in the data is relatively low (~6 per 3.2 km s^-1-wide pixel element at 1500 Å). A complex absorption pattern at high negative velocities is visible in the absorption lines of C ii, Al ii, Si ii, O i, Si iii, Si iv, and C iv (see Fig. B.1; Table B.1). We identify five absorption components at LSR velocities of −76, −89, −131, −166, and −192 km s^-1. HVC absorption in Complex C and Complex K has been studied in detail by Tripp et al. (2003) and Collins et al. (2007).

Mrk 290. The line of sight towards Mrk 290 (l = 91.5, b =  + 48.0) is known to pass through Complex C. Unfortunately there is only E230M data available to us, and only the two Fe ii lines are covered. We find HVC absorption near v_LSR =  −130 km s^-1 in three absorption components, but because of the low S/N (~8 per 4.8 km s^-1-wide pixel element at 2600 Å) and the saturation of the Fe ii lines a reliable measurement is not possible (see Fig. B.2; Table B.1). HVC absorption along this sightline is discussed also in Shull et al. (2011).

H1821 + 643. The H1821 + 643 sightline at l = 94.0, b =  + 27.4 is known to pass through the Outer Arm and the HVC Complexes C and K. Thus, the available E140M STIS spectrum shows a complex absorption pattern of high-velocity gas components in the velocity range −80 to −200 km s^-1. The E140M data are of good quality with a S/N of  ~ 11 per 3.2 km s^-1-wide pixel element at 1300 Å. We identify three distinct absorption components at v_LSR =  −84,−126, and −146 km s^-1 in the lines of C ii, O i, Si ii, Al ii, Si iii, Si iv, C iv, and others (see Fig. B.1; Table B.2). A detailed analysis of the HVCs towards H1821 + 643 is presented in Tripp et al. (2003). Other studies that discuss HVC absorption along this sightline are the ones by Sembach et al. (2003) and Collins et al. (2009).

PG 1634 + 706. The PG 1634 + 706 sightline passes HVC Complex C at l = 102.8, b =  + 36.6. Only E230M data are available for this sightline, so that Complex C absorption is detected only in the lines of Fe ii and Mg ii at LSR velocities in the range −100 to −230 km s^-1 (see Fig. B.3; Table B.1). The E230M data have a high S/N of  ~ 22 per 4.8 km s^-1-wide pixel element at 2800 Å. Three major absorption components are identified at v_LSR =  −125,−164, and −195 km s^-1. The latter component appears to be very broad in Mg ii and possibly is composed of several (unresolved) sub-components. We did not find any previous study in the literature that analyses the HVC absorption in the STIS E230M data towards PG 1634 + 706.

Mrk 279. The line of sight towards Mrk 279 pierces HVC Complex C at l = 115.0, b =  + 46.9. The available E140M data show strong HVC absorption at negative velocities in the range v_LSR =  −100 to −200 km s^-1 in the lines of C ii, Si ii, O i, Al ii, Si iii and Si iv. The data have good quality with a S/N of  ~ 14 per 3.2 km s^-1-wide pixel element at 1500 Å. Three individual components at v_LSR =  −145,−161, and −179 km s^-1 are fitted to the data (see Fig. B.1; Table B.1). There exist a number of detailed studies of the Complex C absorption towards Mrk 279 based on different spectral data (e.g., Gibson et al. 2001; Tripp et al. 2003; Collins et al. 2003; Collins et al. 2007).

PG 1259 + 593. The line of sight towards the QSO PG 1259 + 593 (l = 120.6, b =  + 58.0) passes HVC Complex C at negative LSR velocities; it represents one of the best-studied HVC sightlines in the literature. Because PG 1259 + 593 is relatively faint (V = 15.84 mag) the existing E140M data (obtained with more than 350 ksec integration time; see Sembach et al. 2003) has only an intermediate S/N of  ~ 7 per 3.2 km s^-1-wide pixel element at 1500 Å. Strong HVC absorption associated with Complex C is seen in two distinct absorption components at v_LSR =  −134 km s^-1 and v_LSR =  −116 km s^-1 in the lines of Si ii, C ii, Al ii, O i, Si iii, and many other ions (see Fig. B.3; Table B.1; also Richter et al. (2001), their Fig. 2). Detailed studies of HVC Complex C towards PG 1259 + 593 are presented in Richter et al. (2001), Sembach et al. (2003), Collins et al. (2003), and Fox et al. (2004).

Mrk 205. The sightline towards the Seyfert 1 galaxy Mrk 205 passes high-velocity gas at negative velocities at l = 125.5, b =  + 41.7, associated with HVC Complex C. The available E140M data have a very good S/N of  ~ 22 per 3.2 km s^-1-wide pixel element at 1300 Å. Three absorption components at v_LSR =  −106,−138, and −197 km s^-1 are identified in the lines of Si ii, C ii and O i (Fig. B.1; Table B.1). For a more detailed study of this sightline see Collins et al. (2007).

3C 249.1. The sightline towards the Seyfert 1 galaxy 3C 249.1 (l = 130.4, b =  + 38.5) passes the outskirts of Complex C. With a S/N of  ~ 8 per 3.2 km s^-1-wide pixel element at 1260 Å  the quality of the available E140M data is relatively low. We identify one HVC absorption component at v_LSR =  −135 km s^-1 in the lines of Si ii, C ii, and Si iii (see Fig. B.1; Table B.1). HVC absorption along this sightline is mentioned by Collins et al. (2009).

PG 0117 + 21. For the line of sight towards the quasar PG 0117 + 21 (l = 131.8, b =  −40.8) only E230M data are available. We identify one weak HVC absorber at v_LSR =  −134 km s^-1 in the lines of Mg ii and Fe ii (see Fig. B.1; Table B.3). The S/N of the data is low (~6 per 4.8 km s^-1- wide pixel element at 2796 Å). The HVC towards PG 0117 + 21 apparently is not connected with any large HVC complexes. We are not aware of any previous study that discusses the PG 0117 + 21 sightline with respect to HVC absorption.

NGC 3516. The line of sight toward NGC 3516 (l = 133.2, b =  + 37.6) passes through the outskirts of HVC Complex C. For this sightline E140M and E230M data are available, but only the E230M data have sufficient quality to measure HVC absorption features (S/N ~ 7 per 4.8 km s^-1-wide pixel element at 2800 Å.) One single absorption component is detetected at typical Complex C velocities of v_LSR =  −158 km s^-1 in the lines of Mg ii and Fe ii (see Fig. B.2; Table B.1). HVC absorption towards NGC 3516 is mentioned in the papers from Collins et al. (2009) and Shull et al. (2009).

NGC 4151. Along the sightline towards NGC 4151 (l = 155.1, b =  + 75.1) weak HVC absorption is observed at high positive radial velocities in the lines of C ii, Si ii, Fe ii, Mg ii, Si iii, and C iv in a single absorption component centred at v_LSR =  + 143 km s^-1 (Fig. B.2; Table B.1). Both the available E140M and E230M data have good S/N (~19 per 3.2 km s^-1-wide pixel element at 1300 Å). This HVC appears to be isolated without being connected to any known large HVC complex. A detailed study of this HVC is presented in Richter et al. (2009).

Mrk 132. The line of sight towards Mrk 132 is located at l = 158.9, b =  + 48.6, located between the two HVC Complexes B and C. Only E230M data are available to us. We find high-velocity absorption at negative velocities (v_LSR =  −139 km s^-1 and v_LSR =  −98 km s^-1), as well as absorption at positive velocities (v_LSR ≈ 80 km s^-1) in the lines of Mg ii and Fe ii (see Fig. B.1; Table B.1). The best fit for the positive-velocity absorption yields two components blending each other. With a S/N of  ~ 10 per 4.8 km s^-1- wide pixel element at 2796 Å the data are of medium quality. We are not away of any previous paper that discusses the properties of the HVCs towards Mrk 132.

PG 0953 + 415. The line of sight towards the Seifert 1 galaxy PG 0953 + 415 is located at l = 179.8 and b =  + 51.7 and passes high-velocity halo gas that possibly is related to HVC Complex M. For this sightline only E140 M data with intermediate S/N (~9 per 3.2 km s^-1-wide pixel element at 1300 Å) are available. We identify one HVC component at v_LSR =  −147 km s^-1 in the lines of C ii, Al ii, Si ii, and Si iii (see Fig. B.2; Table B.1). No previous study exists that analyses in detail the low-ion absorption near v_LSR =  −147 km s^-1, but the sightline has been studied by several authors to investigate highly-ionized gas in the Milky Way halo at positive radial velocities (Collins et al. 2005, 2009; Fox et al. 2009; Shull et al. 2009; Fabian et al. 2000).

PG 1116 + 215. High-velocity absorption towards PG 1116+ 215 (l  =  223.4, b =  + 68.2) is seen at positive LSR velocities between  + 170 and  + 220 km s^-1 in the lines of Si ii, C ii, O i, Fe ii, Mg ii, Si iii, C iv, and Si iv (see Fig. B.2; Table B.1). This multi-phase absorber is relatively isolated, but possibly is associated with the Magellanic Stream. For this sightline both E140M and E230M data with relatively good S/N (~10 per 3.2 km s^-1-wide pixel element at 1300 Å) are available. Two absorption components at v_LSR =  + 184 and  + 203 km s^-1 can be fitted to the data. The HVC absorption towards PG 1116 + 215 was studied in detail by Ganguly et al. (2005) and Richter et al. (2009). Other studies that discuss the HVC absorption along this sightlines are Sembach et al. (2004a), Collins et al. (2005, 2009) and Fox et al. (2006).

Ton S210. Along the line of sight towards Ton S210 (l = 225.0, b =  −83.2) high-velocity absorption is seen at high negative velocities between −140 and −260 km s^-1. Absorption near −170 km s^-1 is related to the compact high-velocity cloud CHVC 224.0−83.4 (Putman et al. 2002), while the absorption at higher velocities is of unknown origin. Both E140M and E230M data are available, but the S/N is low (S/N ~ 4 per 3.2 km s^-1-wide pixel element at 1500 Å). Three individual absorption components at v_LSR =  −172,−207, and −241 km s^-1 are identified in the lines of C ii, O i, Si ii, Mg ii, Fe ii, Si iii, Si iv and C iv (see Fig. B.4; Table B.1). A detailed analysis of the high-velocity gas towards Ton S210 is presented in Sembach et al. (2002) and Richter et al. (2009).

HE 0515−4414. The sightline towards HE 0515−4414 is located at l = 249.6, b =  −35.0 and passes through a region with some scattered H i clouds that possibly are connected to the Magellanic Stream. Only E230M data are available for this sightline, and the data have a low S/N of  ~ 5 per 4.8 km s^-1-wide pixel element at 2400 Å. We identify one HVC absorption component at v_LSR =  + 103 km s^-1 in the lines of Mg ii and Fe ii. Additional HVC absorption components possibly are present near  ~  + 200 km s^-1, but are blended with intergalactic absorption features (Fig. B.1; Table B.1). We did not find any previous paper that discusses the HVC absorption towards HE 0515−4414.

PG 1211 + 143. Relatively weak weak absorption at positive LSR velocities near v_LSR =  + 180 km s^-1 is seen along the line of sight towards the Seyfert 1 galaxy PG 1211 + 143 (l = 267.6, b =  + 74.3) in the lines of Si ii, C ii, O i, Si iii, and C iv (see Fig. B.3; Table B.1). For this line of sight, only E140M data are available. The S/N in the data is good (~15 per 3.2 km s^-1-wide pixel element at 1300 Å). Two distinct absorption components are observed at v_LSR =  + 170 km s^-1 and  + 188 km s^-1; the latter component is seen predominantly in the intermediate and high ions. This HVC is isolated, but possibly is associated with a compact high-velocity cloud (CHVC)  ~ 1.5 deg away (de Heij et al. 2002). A detailed study of this absorber is presented in Richter et al. (2009); other studies that mention this HVC are Fox et al. (2006) and Collins et al. (2009).

PG 1216 + 069. The Seyfert 1 galaxy PG 1216 + 069 is located at l = 281.1, b =  + 68.1. We find HVC absorption in the lines of Si ii, Si iii, and C iv in three individual components at high LSR-velocities of v_LSR =  + 210... + 270 km s^-1 in the available E140M data (see Fig. B.1; Table B.1). The detected absorbers seem to be unrelated to any known large HVC complex. The data quality is relatively low (S/N ~ 8 per 3.2 km s^-1- wide pixel element at 1260 Å). HVC absorption towards PG 1216 + 069 is also discussed in Shull et al. (2009).

NGC 3783. The line of sight towards the Seyfert 1 galaxy NGC 3783 at l = 287.5, b =  + 23.0 is a well-studied HVC sightline that passes through the Leading Arm (LA) of the Magellanic Stream with strong absorption features at high positive

velocities. For this sightline both E140M and E230M dataare available. The data have superb quality with a S/N of  ~ 25 per 3.2 km s^-1-wide pixel element at 1300 Å. Very strong disc and halo absorption from local disc and halo gas is seen in a single absorption trough in many lines in the velocity range between −60 and  + 120 km s^-1. This absorption component is not further considered in this paper. Absorption from the LA is seen in two strong components at v_LSR =  + 180 and  + 234 km s^-1 in the lines of Si ii, O i, Mg ii, Fe ii, Al ii, C ii, and Si iii (see Fig. B.2; Table B.3). There are several detailed studies of the LA absorption towards NGC 3783 (e.g., Lu et al. 1998; Sembach et al. 2001).

RXJ 1230.8 + 0115. In the direction of RXJ 1230.8 + 0115 (l = 291.3, b =  + 63.7) weak HVC absorption in the lines of Si ii, C ii, O i and Si iii is observed in two individual clouds at high positive velocities near  + 100 and  + 300 km s^-1 (only E140M data are available; Fig. B.27; Table B.3). The data are of intermediate quality with a S/N of  ~ 7 per 3.2 km s^-1-wide pixel element at 1300 Å. For each of the two clouds, the HVC absorption can be fitted with a single absorption component centred at v_LSR =  + 111 and  + 295 km s^-1, respectively (for C ii we add another component at v_LSR =  + 292 km s^-1). Both HVCs do not appear to be associated with any prominent HVC complex, but obviously respresent isolated gaseous halo strucures. A recent study of this HVC sightline is presented by Richter et al. (2009).

PKS 0312−770. The line of sight towards the Seyfert 1 galaxy PKS 0312−770 (l = 293.4, b =  −37.6) is known to pass the so-called “Magellanic Bridge” (MB), an extended gaseous structure that connects the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC; see Hindman et al. 1963). The MB is believed to be locted at a distance of  ~ 50−60 kpc (Harries et al. 2003). Thus, the MB does not represent a “classical” Galactic HVC but rather is a tidal feature and gas component of the Magellanic system. For this sightline both E140M and E230M spectra are available, but the average S/N is relatively low (S/N ~ 6 per 3.2 km s^-1-wide pixel element at 1500 Å). Strong high-velocity absorption from gas in the MB is visible in the lines of C ii, O i, Si ii, Si iii, Fe ii, and Mg ii. The STIS data indicate two main absorption components centred at v_LSR =  + 174 km s^-1 and v_LSR =  + 224 km s^-1 (see Fig. B.3; Table B.1). A detailed analysis of this sightline and the MB absorption is presented in Misawa et al. (2009).

Appendix B: Supplementrary tables and figures

	Fig. B.1 Continuum-normalized absorption profiles of low and high ions towards different QSO sightlines recorded with the E140M and E230M echelle gratings of STIS. The data are plotted against the LSR radial velocity. Identified HVC absorption components are marked with dashed lines. The red plotted lines render the best Voigt-profile fit.
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	Fig. B.2 Additional continuum-normalized absorption profiles of low and high ions towards different QSO sightlines recorded with the E140M and E230M echelle gratings of STIS. The data are plotted against the LSR radial velocity. Identified HVC absorption components are marked with dashed lines. The red plotted lines render the best Voigt-profile fit.
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	Fig. B.3 Additional continuum-normalized absorption profiles of low and high ions towards different QSO sightlines recorded with the E140M and E230M echelle gratings of STIS. The data are plotted against the LSR radial velocity. Identified HVC absorption components are marked with dashed lines. The red plotted lines render the best Voigt-profile fit.
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	Fig. B.4 Additional continuum-normalized absorption profiles of low and high ions towards different QSO sightlines recorded with the E140M and E230M echelle gratings of STIS. The data are plotted against the LSR radial velocity. Identified HVC absorption components are marked with dashed lines. The red plotted lines render the best Voigt-profile fit.
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