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## (from tabmap V6.0 (2016-08-18)) 2024-05-09T23:01:34 #--------------------------------------------------------------------------- #-- J/ApJS/177/39 Survey of low-redshift OVI absorbers (Tripp+, 2008) #-------------------------------------------------------------------------- #---Table: J/ApJS/177/39/./appendix.dat Appendix: comments on line identification, blending, hot pixel contamination, and saturation in individual systems (490 records) # Note I2 --- Note number # Text A77 --- Text of note -------------------------------------------------------------------------------- No| te|Text --|----------------------------------------------------------------------------- 1|3C 249.1, z_abs_=0.24676. In this system, HI Ly{beta} is mildly blended with 1| an unrelated line. However, most of the Ly{beta} profile is free from the 1| blend, and the unblended portion of Ly{beta} provides useful constraints 1| and was included in the fit. Hot pixels are present in the STIS spectrum 1| on both the blue and red sides of the OVI {lambda}1037.62 line 1| (see Fig. 5). The OVI identification is secure because the 1| {lambda}1031.93 and {lambda}1037.62 profiles agree well in the regions 1| that are not affected by hot pixels. However, the regions affected by 1| hot pixels were excluded from the fit. 2|3C 249.1, z_abs_=0.30811. Both lines of the OVI doublet are detected at high 2| significance at this redshift (see Fig. 7). However, the OVI profiles are 2| strongly saturated in the component at v=0km/s. In addition, hot pixels are 2| present in the core of the OVI {lambda}1031.93 line. Consequently, the line 2| parameters are highly uncertain for the v=0km/s component. 3|3C 249.1, z_abs_=0.31364. The OVI {lambda}1037.62 line at this redshift is 3| only detected at the 1.9{sigma} level. However, the strength of the 2{sigma} 3| feature is in good agreement with the expected strength implied by the 3| well-detected OVI {lambda}1031.93 line. In addition, the 3| OVI {lambda}1031.93 line is well-aligned with the HI Ly{alpha}, Ly{beta}, 3| and Ly{gamma} lines detected at this redshift. The metal profiles 3| marginally suggest the presence of a second component, but better S/N 3| is required to verify and measure the second component. 4|3C 273.0, z_abs_=0.00334. The blue side of the Ly{beta} profile is blended 4| with a Galactic H2 absorption line (Sembach et al., 2001ApJ...561..573S). 4| Consequently, only the red side of the Ly{beta} line (which is free from 4| blending) was used to constrain the fit. The OVI {lambda}1037.62 line is 4| severely blended with Galactic H2 absorption, so only the 4| OVI {lambda}1031.93 line can be measured. The OVI {lambda}1031.93 line is 4| affiliated with a well-detected HI absorber at the same redshift 4| (Sembach et al., 2001ApJ...561..573S). This absorber clearly shows evidence 4| of multiple components in the HI Ly{alpha} profile (see Fig. 33). The OVI 4| profile, on the other hand, only shows one clear component. However, the 4| OVI line is broad and shallow, and the breadth of the OVI feature is 4| consistent with the velocity range spanned by the HI absorption. The degree 4| of velocity-centroid alignment of the OVI with HI is ambiguous; the OVI is 4| aligned, to within the 2{sigma} uncertainty, with both HI components derived 4| from profile fitting in Table 3. Following the conventions outlined in 4| Section 2.3.2, we assign the OVI to the broader HI component. In addition, 4| as discussed in Section 4.2, the breadth of the HI component at v=-8km/s 4| depends critically on the number of components assumed for the fit. 5|3C 273.0, z_abs_=0.12003. At this redshift, the OVI doublet is covered by 5| both the STIS and the FUSE spectrum of 3C 273.0. Both lines of the OVI 5| doublet are clearly detected in the FUSE spectrum of 3C 273.0 (see 5| Fig. 3 in Tripp et al., 2006ASPC..348..341T). In the STIS spectrum, the OVI 5| lines are located in a region of rapidly decreasing S/N. The STIS spectrum 5| shows the OVI 1037.62 line at 4.0{sigma} significance, but the significance 5| of the 1031.93 line is <2{sigma}. Consequently, we base our fit on the FUSE 5| data, but we note that fitting the STIS data yields consistent (but 5| noisier) results. 6|3C 273.0, z_abs_=0.15779. The OVI 1031.93 line is detected at 4.5{sigma} 6| significance, but the weaker OVI {lambda}1037.62 line is not detected. The 6| OVI identification is favored based on the precise alignment of the 6| OVI {lambda}1031.93 candidate with an HI Ly{alpha} line at the same 6| redshift (see Fig. 18). 7|3C 351.0, z_abs_=0.21811. Figure 38 shows the HI Ly{alpha} and OVI lines that 7| we detect in this system; the top panels show the absorption profiles and 7| the bottom panel compares the OVI N_a_(v) profiles. The OVI {lambda}1031.93, 7| {lambda}1037.62 lines are detected at the 5.5{sigma} and 3.7{sigma} levels, 7| respectively, and the N_a_(v) profiles are in good agreement. The OVI 7| profiles are broad and shallow and, hence, are sensitive to continuum 7| placement. Thom & Chen (2008ApJ...683...22T) do not agree with this system 7| identification; the most likely source of this discrepancy is continuum 7| placement, but differences in data reduction procedures could play a role. 7| Higher S/N observations with the Cosmic Origins Spectrograph (COS) would be 7| valuable for confirmation of broad and shallow lines such as these. Similar 7| component structure is evident in the OVI {lambda}1031.93 and 7| {lambda}1037.62 profiles, and the similarity of the component structure 7| favors a multicomponent fit. However, the OVI profiles are moderately noisy. 7| We flag these measurements with a colon, because while three components are 7| suggested by the OVI data, better S/N is needed to robustly establish that 7| three components are present. If we fit the OVI lines with a single 7| component instead of the three-component fit listed in Table 3, we obtain 7| b(O^vi^)=82{+/-}13km/s and logN(O^vi^)=14.06{+/-}0.05 for the single line. 8|3C 351.0, z_abs_=0.22111. An archival FUSE spectrum of 3C 351.0 shows that 8| this is an optically thick Lyman limit absorber with N(H^i^)>10^17^/cm2. The 8| Ly{alpha} profile is strongly saturated but shows complex structure at the 8| edges of the profile. This structure could be partly due to damping wings, 8| but this profile structure cannot be unambiguously attributed to damping 8| wings. Consequently, the HI column density is highly uncertain. The 8| OVI {lambda}1031.93 line is severely blended with the Galactic 8| SiII {lambda}1260.42 line, and consequently, {lambda}1031.93 cannot be 8| measured. However, many metal lines are detected at the redshift of this 8| strong Lyman limit system including transitions of CII, NII, SiII, SiIII, 8| and SiIV. The OVI {lambda}1037.62 line is identified based on its alignment 8| with the other metals at this redshift. All available HI lines are strongly 8| saturated at the velocities of the metal lines, so the degree of alignment 8| of the OVI and HI lines cannot be evaluated. However, analysis of the low- 8| and high-ionization metals lines indicates the presence of multiple phases, 8| so this system is classified as a complex absorber. 9|H1821+643, z_abs_=0.02438. HI Ly{beta} is mildly blended with a Galactic H2 9| absorption line (see K. R. Sembach et al. 2008, in preparation), but the 9| Ly{beta} line is mostly free from the blend. The blended portion of 9| Ly{beta} was excluded from the fit. OVI {lambda}1037.62 is lost in a 9| blend with Milky Way FeII and H2 absorption. The OVI identification is 9| based on the precise alignment of OVI {lambda}1031.93 with Ly{alpha} and 9| Ly{beta} lines at the same redshift. 10|H1821+643, z_abs_=0.12143. Thom & Chen (2008ApJ...683...22T) challenge this 10| OVI identification, noting that "there is strong absorption at the OVI 1037 10| position, but no OVI 1031, which should be easily detected, given the 10| strength of the weaker supposed OVI 1037 line." However, as discussed in 10| detail by Tripp et al. (2001ApJ...563..724T), the OVI {lambda}1037.62 line 10| is significantly blended with strong HI Ly{delta} absorption from the 10| absorber at z_abs_=0.22496 (Fig. 2 in Tripp et al., 2001ApJ...563..724T), 10| and it appears that Thom & Chen (2008ApJ...683...22T) have not taken this 10| serious blend into account. Moreover, Thom & Chen base their conclusions on 10| the STIS data only, which have S/N<~3/pixel in this wavelength range, 10| whereas the FUSE observations we used have S/N>~13/pixel here. When the FUSE 10| data are employed and the Ly{delta} blend is accounted for, we find 10| compelling evidence supporting this system. Because of the strong blend, our 10| OVI measurements are based on the {lambda}1031.93 line alone. The 10| OVI {lambda}1031.93 line is detected at the 6.9{sigma} level in our data. 10| While the blend hampers confirmation based on the {lambda}1037.63 line, we 10| note that there are no other clear identifications for the 6.9{sigma} line 10| at the {lambda}1031.93 wavelength. This is not an HI Ly{alpha} line because 10| the redshift places the line blueward of the Ly{alpha} region, nor is it a 10| higher Lyman series HI line because corresponding strong HI lines would be 10| obvious in the STIS spectrum but are not evident. 11|H1821+643, z_abs_=0.21331. The OVI {lambda}1037.62 line is blended with weak, 11| high-velocity SII {lambda}1259.52 absorption from Milky Way gas (see Savage 11| et al., 1995ApJ...449..145S, and Tripp et al., 2003AJ....125.3122T for 11| information about the Galactic high-velocity gas toward H1821+643). 11| Comparison of the Galactic SII {lambda}1259.52 and {lambda}1253.81 lines 11| shows that there is excess optical depth in the {lambda}1259.52 line, 11| and the excess is consistent with the expected contribution from the 11| OVI {lambda}1037.62 line at z_abs_=0.21331 (based on the strength of 11| the unblended OVI {lambda}1031.93 line), which supports the identification 11| of OVI at this redshift. In addition, the OVI {lambda}1031.93 line is 11| aligned with HI Ly{alpha}, {beta}, and {gamma} lines at the same zabs. 12|HE 0226-4110, z_abs_=0.01747. The OVI {lambda}1037.62 line is blended with 12| OVI {lambda}787.71 at z_abs_=0.34035 (see Lehner et al., 2006ApJS..164....1L 12| and our Fig. 29). The OVI identification is favored based on the precise 12| alignment of the OVI {lambda}1031.93 candidate with an HI Ly{lamba} line 12| at the same redshift. We note that the comparison of the Na profiles in 12| Figure 18 does not show the absorption in the wings of the Ly{alpha} 12| line very clearly; Figure 29 more clearly shows how the HI line is 12| slightly broader than the OVI lines. 13|HE 0226-4110, z_abs_=0.20701. Detailed analysis of this system has been 13| presented by Savage et al. (2005ApJ...626..776S). The HI Ly{gamma} line is 13| recorded in both the STIS spectrum and the FUSE spectrum of HE 0226-4110. 13| The apparent component structure in the STIS recording of the Ly{gamma} 13| line is incompatible with the FUSE recording of Ly{gamma} and with the 13| other (higher) Lyman series lines (see Savage et al., 13| 2005ApJ...626..776S), and the STIS Ly{gamma} line was excluded from the fit. 14|HE 0226-4110, z_abs_=0.35525. A weaker line offset by +40 km/s is present 14| next to the main component that is clearly detected in the 14| OVI {lambda}1031.93 and {lambda}1037.62 profiles at this redshift. The 14| +40km/s feature does not appear to be OVI, because it is not confirmed by 14| the {lambda}1037.62 line. However, the +40km/s feature would be 14| relatively weak in the {lambda}1037.62 transition, and it could be 14| hidden by noise. Following Lehner et al. (2006ApJS..164....1L), we do 14| not include the 40km/s component in the OVI measurements; higher S/N 14| data are needed to establish the identity of this feature. 15|HE 0226-4110, z_abs_=0.42670. At this redshift, the Ly{alpha} is redshifted 15| beyond the long-wavelength cutoff of our STIS spectrum, and the Ly{beta} 15| line is not detected. The OVI identification is based on the good agreement 15| of the OVI1031.93 and {lambda}1037.62 profiles (see Lehner et al., 15| 2006ApJS..164....1L). The OVI1031.93 line is partially affected by hot 15| pixels that were excluded from the fit. We note that identification of 15| this system depends critically on the STIS warm-hot pixel correction 15| algorithm. If we turn off the hot-pixel repair algorithm, we find 15| that the OVI1037.62 line is largely filled in by warm pixels. It is 15| important to obtain future observations of this system with COS in 15| order to test the reliability of the identification and to expand 15| the utility of this system with additional information (e.g., 15| better HI absorption constraints). 16|HE 0226-4110, z_abs_=0.49246. This complex, multispecies system has been 16| analyzed in detail by Ganguly et al. (2006ApJ...645..868G). The OVI 16| component at v=0km/s is uncertain due to substantial saturation. The 16| OVI1037.62 line is partially blended with Galactic CIV (see Fox et al., 16| 2005ApJ...630..332F), but the distinctive component structure seen in the 16| OVI1031.93 profile can be clearly recognized in the in the {lambda}1037.62 16| profile as well (see Ganguly et al., 2006ApJ...645..868G), so the 16| identification is secure, and the weaker OVI components are well-constrained 16| by the OVI1031.93 line. 17|HS 0624+6907, z_abs_=0.33979. HI Ly{beta} is mildly blended with an unrelated 17| line. However, most of the Ly{beta} profile is free from the blend, and the 17| unblended portion of Ly{beta} was included in the fit. As shown in the left 17| panel of Figure 39, hot pixel features are present within the OVI1031.93 17| line and at the red edge of the OVI1037.62 profile. Fortunately, in this 17| case the QSO was observed on two different dates (in 2002 January and 17| February; see Table 1), and the position of the spectrum on the detector was 17| shifted between these two dates. Inspection of the data reveals that the hot 17| pixel features are only present in the 2002 February data. As shown in the 17| right panel of Figure 39, by masking and rejecting the affected hot pixels 17| in the February data, we can suppress this problem with a minimal loss of 17| the S/N. 18|HS 0624+6907, z_abs_=0.37053. In this proximate absorber, HI Ly{alpha} is not 18| detected despite good S/N (see Fig. 7). As shown in Figure 7, the OVI 18| identification is quite secure; both lines of the OVI doublet show multiple 18| components and are in excellent agreement. 19|PG 0953+415, z_abs_=0.06807. We have carried out extensive investigations of 19| this absorber in previous papers (Savage et al., 2002ApJ...564..631S; Tripp 19| et al., 2006ApJ...643L..77T). Comparison of the OVI1031.93 and 19| {lambda}1037.62 lines indicates moderate saturation, and application of 19| the method of Jenkins (1996ApJ...471..292J) indicates that N(OVI) could 19| be 0.25dex higher. 20|PG 0953+415, z_abs_=0.14231. The Ly{beta} profile is partially blended with 20| an HI Ly{delta} line from z_abs_=0.23351. The blended part of the Ly{beta} 20| line was not used in the fit. However, the Ly{alpha} line has a complex 20| profile with many components (see Tripp & Savage, 2000ApJ...542...42T), 20| and the unblended portion of the Ly{beta} line provides useful 20| constraints for the fit. 21|PG 0953+415, z_abs_=0.22974. In this proximate absorber of PG 0953+415, 21| HI Ly{alpha} is not detected despite good S/N. The OVI identification is 21| based on the good agreement of the OVI lines over a large portion of both 21| profiles; the {lambda}1031.93 and 1037.62 profiles agree well over ~20pix 21| between v=-30 and 40km/s. However, the OVI profiles are discrepant at 21| v<-30km/s. While this discrepancy has the appearance of a hot pixel feature, 21| comparison of the data from 1998 December 4 and 11 shows the same profile 21| structure. The location of the spectrum on the detector was shifted between 21| 1998 December 4 and 11, so this discrepancy cannot be due to hot pixels. We 21| conclude that the OVI1031.93 line is blended with an unrelated Ly{alpha} 21| line on the blue side of the profile. This part of the {lambda}1031.93 21| profile was excluded from the Voigt profile fit. 22|PG 0953+415, z_abs_=0.23351. A Ly{delta} line with approximately correct 22| strength is detected at this redshift, but was not used in the fit due to 22| blending with Ly{beta} from the complex, multicomponent absorber at 22| z_abs_=0.14231 23|PG 1116+215, z_abs_=0.05927. Both lines of the OVI doublet are detected and 23| in excellent agreement at v=0km/s (see Fig. 29). The OVI1031.93 line is 23| also detected at v=-84km/s, but the OVI1037.62 line is not significantly 23| detected at that velocity. A small portion of the detected OVI1031.93 23| component at v=-84km/s is blended with Galactic H2 (see Sembach et al., 23| 2004, Cat. <J/ApJS/155/351>). The v=-84km/s component is also identified as 23| OVI, based on the good agreement of the OVI and HI Ly{alpha} line shapes 23| at v=-84km/s (not including the portion blended with H2, which was also 23| excluded from the fit), as shown in Figure 18. 24|PG 1116+215, z_abs_=0.13849. The OVI doublet at this redshift is detected 24| with both FUSE and STIS (see Sembach et al., 2004, Cat. <J/ApJS/155/351>). 24| The fit reported here is based on the STIS data. This system, which has a 24| high HI column and is detected in many Lyman series lines, has been 24| analyzed in detail by Sembach et al. (2004, Cat. <J/ApJS/155/351>). The 24| OVI lines are aligned with the HI lines, but analysis of the many 24| low-ionization metal absorption lines detected in this system clearly 24| establishes that this is a complex multiphase absorber (see Sembach 24| et al., 2004, Cat. <J/ApJS/155/351>). 25|PG 1116+215, z_abs_=0.16553. The HI components at v=-12, 143, 170, and 25| 342km/s are well-constrained by the detected absorption lines. Additional 25| absorption is clearly and significantly detected in other velocity ranges 25| in the Ly{alpha} profile, e.g., at v~70km/s, and components were added to 25| the fit to account for this additional absorption. However, these 25| components are not well-constrained due to blending with the adjacent 25| features. 26|PG 1116+215, z_abs_=0.17340. The OVI1031.93 line is detected at 5.8{sigma} 26| significance and is well-aligned with an HI line at the same redshift. In 26| addition, the OVI1037.62 line is detected with the expected wavelength and 26| relative strength at 2.9{sigma}. 27|PG 1216+069, z_abs_=0.12360. The Ly{alpha} profile has good S/N and shows 27| clear inflections and asymmetries that reveal the complicated component 27| structure including at least eight components; four of the components are 27| clearly evident in the Ly{beta} profile as well (see Fig. 4). However, all 27| of the components are either strong and significantly saturated (in both 27| Ly{alpha} and Ly{beta}) or are highly blended with adjacent strong 27| components. Moreover, some of the saturated components show that there are 27| errors in the flux zero level of the Ly{alpha} line, and the Ly{beta} line 27| is relatively noisy. Ly{gamma} lines are also evident (see Tripp et al., 27| 2005ApJ...619..714T), but the Ly{gamma} data are too noisy to usefully 27| constrain the fits. The HI component parameters are highly uncertain due to 27| these combined problems. Both lines of the OVI doublet are strong and are 27| clearly detected with component structure similar to the Ly{beta} 27| components. The apparent column density profiles of the OVI doublet are in 27| good agreement (see Fig. 4), which suggests that the OVI lines are not badly 27| saturated. However, the OVI profiles are also relatively noisy. 28|PG 1216+069, z_abs_=0.26768. The OVI1037.62 line cannot be measured, because 28| it is lost in a blend with a strongly saturated HI Ly{beta} absorption line 28| from z_abs_=0.28189. As shown in Figure 40, the OVI identification at 28| z_abs_=0.26768 is based on the alignment of OVI1031.93 with Ly{alpha} and 28| Ly{beta} at the same redshift. At this redshift, initial inspection 28| identified a candidate CIII977.02 line that is somewhat blended with 28| NV1238.82 absorption from the Milky Way. The CIII candidate cannot be a 28| second component of Galactic NV absorption, because it is not evident in the 28| profile of the other line of the NV doublet. However, closer inspection 28| reveals that this line is not CIII, but rather is the HI Ly{gamma} line from 28| the strong HI system at z_abs_=0.27353, so we can only place an upper limit 28| on CIII absorption at this redshift. 29|PG 1259+593, z_abs_=0.04637. Only the OVI1031.93 line is detected at this 29| redshift (OVI1037.62 is redshifted into a relatively noisy region of the 29| FUSE spectrum that is only recorded by the SiC channels). Nevertheless, 29| the identification is secure, because the OVI1031.93 profile has a 29| distinctive two-component structure that matches the component structure 29| seen in the CIII and CIV lines detected at the same redshift. An 29| unrelated OIV787.71 line is located near the Ly{gamma} profile; the 29| region affected by the OIV feature was excluded from the fit. 30|PG 1259+593, z_abs_=0.21949. Several components due to Galactic SII1250.58 30| are located on the blue side of the Ly{beta} line (see Richter et al., 30| 2004ApJS..153..165R); the velocity range affected by the Milky Way SII 30| absorption was excluded from the fit. 31|PG 1259+593, z_abs_=0.31972. The OVI1037.62 line is quite weak and mildly 31| blended with high-velocity NiII absorption from the Milky Way (see Richter 31| et al., 2004ApJS..153..165R). As shown in the right panels of Figure 40, 31| the OVI1031.93 line is clearly detected, and an absorption feature with 31| the right relative strength (compared to {lambda}1031.93) is present at 31| the expected wavelength of OVI1037.62, but because it is weak and 31| blended with Galactic NiII, our fit is based on the OVI1031.93 line only. 32|PG 1444+407, z_abs_=0.22032. The HI Ly{alpha} and OVI1031.93, {lambda}1037.62 32| lines for this absorption system are shown in the left panels of Figure 41. 32| The OVI1031.93 line at z_abs_=0.22032 is blended with the Galactic 32| SII1259.52 line. However, comparison of the Galactic SII1253.81 and 32| SII1259.52 profiles shows a clear and significant excess of absorption at 32| the expected velocity of OVI1031.93 at z_abs_=0.22032. Moreover, the 32| excess absorption has precisely the expected strength compared to the 32| (unblended) OVI1037.62 line, as can be seen in the comparison of the 32| OVI^Na(v)^ profiles shown in Figure 41. Only the unblended portion of 32| OVI1031.93 was included in the fit. 33|PG 1444+407, z_abs_=0.26738. The Ly{beta} line is slightly blended with an 33| unrelated weak line; the region affected by the blend was excluded from the 33| fit. More importantly, the Ly{alpha} line is located at the peak of the 33| broad Ly{alpha} emission line, and this introduces significant continuum 33| placement uncertainty. We note that a broad and shallow feature is 33| located just blueward of the Ly{alpha} line. This feature could be due 33| to additional weak HI absorption, but its significance is highly 33| dependent on the uncertain continuum placement. Consequently, we did 33| not include the broad, shallow feature in the fit. 34|PHL 1811, z_abs_=0.07765. Only the stronger OVI1031.93 line is detected 34| at >3{sigma} significance. However, many metals are detected at this 34| redshift including CII1334.53, SiII1260.42, CIII977.02, CIV1548.20, 34| (marginal) SiIV1393.76, and several HI Lyman series lines. The strongest 34| CIV component shows a ~-25km/s offset from the lower ionization metals, 34| but the OVI1031.93 line is aligned with the CIV1548.20 transition. 35|PHL 1811, z_abs_=0.15786. The Ly{alpha} profile at z_abs_=0.15786 is blended 35| with OI1302.17 absorption from the Lyman-limit system at z_abs_=0.08092 (see 35| Jenkins et al., 2005ApJ...623..767J; see also our Fig. 35). The narrow core 35| in this blend is predominantly due to the Lyman-limit OI line. However, 35| close inspection of this profile (see Fig. 38) reveals weak component 35| absorption straddling the narrow core on the short- and long-wavelength 35| sides. We cannot corroborate that the weaker components are also OI; 35| similar component structure is not clearly evident in the other profiles of 35| low-ionization metals in this Lyman-limit absorber, which suggests that 35| these weaker components could be unrelated to the OI and could be Ly{alpha} 35| at z_abs_=0.15786. However, better S/N data are needed to reliably determine 35| the origin of the weak components and to accurately deblend and measure 35| their parameters, so we flag this absorption with a colon in Table 3 to 35| reflect the substantial uncertainty of this Ly{alpha} case. 36|PHL 1811, z_abs_=0.17650. At this redshift, OVI1031.93 falls in the 36| saturated core of the Milky Way damped Ly{alpha} line. The OVI1037.62 line 36| is identified based on its alignment with multiple Lyman series lines, and 36| this is supported by the detection of CIII977.02 and SiIII1206.5 in this 36| absorber. However, we note that the OVI is offset by ~-25km/s compared to 36| the CIII and SiIII lines. 37|PKS 0312-770, z_abs_=0.15890. OVI1031.93 is detected at 5.6{sigma} 37| significance, and the corresponding OVI1037.62 line is also detected, but 37| only at 2.4{sigma} significance. As shown in Figure 41, the N_a_(v) 37| profiles of the two lines of the OVI doublet are in good agreement, and 37| the marginal detection of the {lambda}1037.62 line supports the OVI 37| identification. The OVI identification is also supported by the precise 37| alignment of the OVI1031.93 line with HILy{alpha} at the same redshift. 38|PKS 0312-770, z_abs_=0.19827. OVI1031.93 is detected at 4.7{sigma} 38| significance, but the OVI1037.62 line is not significantly detected in the 38| data at full resolution. However, as shown in the left panels of Figure 42, 38| if we mildly bin the data to 7km/s pixels to improve the S/N, we find a 38| feature in the spectrum at the expected wavelength of the 1037.62 line 38| that is fully consistent with the detected OVI1031.93 line [compare the 38| N_a_(v) profiles shown in the bottom left panel of Fig. 42]. The OVI 38| identification is bolstered by the close alignment of OVI1031.93 with 38| Ly{alpha} and Ly{beta} at the same redshift (see Fig. 42, left). 39|PKS 0312-770, z_abs_=0.20266. All accessible HI lines in the STIS bandpass 39| (Ly{alpha}, Ly{beta}, Ly{gamma}) are strong and highly saturated. Moreover, 39| the Ly{beta} and Ly{gamma} profiles show complex component structure with 39| at least five distinct components. Since most of the HI components are 39| black in the line cores, the HI profile parameters are poorly constrained, 39| and we have not attempted to fit the HI lines. Brief inspection of an 39| archival FUSE spectrum reveals that this is an optically thick Lyman limit 39| absorber. While the HI component properties are poorly constrained, 39| comparison of the low- and high-ionization metal lines reveals that this is 39| a complex multiphase system (see Section 2.4.1 and Fig. 3). In addition, the 39| individual components are spread over a large velocity range with low- and 39| high-ionization components detected at velocities ranging from -204 to 39| +135km/s. 40|PKS 0405-123, z_abs_=0.16692. Many Lyman series lines are available for 40| constraining the HI column density at this redshift, and the absence of 40| strong Lyman limit absorption places a firm upper limit on the total HI 40| column density (Prochaska et al., 2004, Cat. <J/ApJ/617/718>). 40| Nevertheless, the parameters of the individual HI components are highly 40| uncertain in this system. The Lyman series lines clearly require a 40| multicomponent fit, but the close spacing and blending of the 40| components causes the component parameter uncertainties to be substantial. 40| Thus, the degree of alignment of the HI and OVI components is highly 40| uncertain. Nevertheless, comparison of the low- and high-ionization metal 40| lines shows that this is a complex multiphase case (see Chen & Prochaska, 40| 2000ApJ...543L...9C). 41|PKS 0405-123, z_abs_=0.36156. The HI Ly{alpha} and OVI1031.93, 41| {lambda}1037.62 absorption profiles and apparent column densities are 41| compared in the right panels of Figure 42. The OVIN_a_(v) profiles are seen 41| to be in reasonable agreement. We note that the OVI1037.62 profile shows a 41| small excess of absorption on the blue side compared to the 1031.93 line; 41| this could be due to blending with an unrelated line (several unrelated 41| lines are readily apparent in the vicinity of {lambda}1037.62), but this 41| could also simply be a noise feature. An inflection is also evident in the 41| Ly{alpha} profile at the velocity of the OVI lines. It is interesting to 41| note that this system has a relatively high N(HI) and is detected in several 41| Lyman series lines, but no OVI absorption is evident at the velocity of the 41| main component where the strong HI lines are found (see Fig. 42). Instead, 41| the OVI is in the wing of the profile near the weak HI inflection component. 41| Several other absorbers show similar offsets between the strong main HI 41| absorption component and the OVI lines (see Fig. 18). 42|PKS 0405-123, z_abs_=0.36335. The OVI1031.93 line is detected at the 42| 4.5{sigma} level, but OVI1037.62 is measured at only 1.7{sigma} 42| significance. However, the apparent column density profiles of the two OVI 42| lines agree precisely; the wavelength separation and relative strength of 42| the lines makes the OVI identification compelling. The corresponding HI 42| absorption is relatively weak, and moreover, the HI Ly{alpha} line is 42| strongly blended with Galactic CI and CI* absorption lines from the CI1656 42| multiplet. We can see that HI Ly{alpha} absorption is present at this 42| redshift because the Galactic CI*1657.38 line is clearly too strong compared 42| to other CI* lines in the PKS 0405-123 spectrum. However, the HI Ly{alpha} 42| line is difficult to measure reliably due to this strong blending with 42| Galactic CI*1657.38. 43|PKS 0405-123, z_abs_=0.49501. In this case, the HI Ly{alpha} line is 43| redshifted beyond the long wavelength cutoff of the STIS spectrum, but 43| Ly{beta} and Ly{gamma} are detected at the 4.1{sigma} and 2.0{sigma} 43| levels, respectively. This absorber is detected in a variety of metals 43| (Prochaska et al., 2004, Cat. <J/ApJ/617/718>), and many of the metal 43| profiles, including the OVI lines, show evidence of multiple components. 43| However, it should be noted that there is a discrepancy evident in one 43| of the components of the OVI1031.93,1037.62 lines. To show this, we 43| compare the apparent column density profiles of the OVI1031.93, 43| 1037.62 lines in Figure 43. We also compare the OVI1031.93 N_a_(v) profile 43| to those of CIII977.02, OIV787.71, and OV629.73 in Figure 43. The 43| OVI1031.93, 1037.62 profiles agree well in the stronger component at 43| v~0km/s.Looking closely at the strongest component, we can see that the 43| profile is asymmetric with a sharp edge on the red side and a more gradually 43| decreasing apparent column density on the blue side. This asymmetry suggests 43| that the main feature is a blend of two components, and this is corroborated 43| by the CIII and OIV profiles, which also show an extra component on the blue 43| side. A third component is evident at v~70km/s in the CIII and OIV 43| transitions. This component appears to be present in the OV and OVI profiles 43| as well, but at a somewhat lower velocity (v=57km/s). However, there is a 43| 2-3 pixel offset between the peak of the OVI1031.93 and {lambda}1037.62 43| profiles in the v=57km/s component (see Fig. 43), in contrast to the v~0km/s 43| component in which the OVI profiles agree well. Initially, this offset 43| appeared to be due to a hot pixel feature falling in the middle of the 43| OVI1031.93 line, but this cannot be the cause, because the PKS 0405-123 43| observations were obtained on two separate occasions (see Table 1), and the 43| spectrum detector position was shifted between the two visits. The same 43| component structure is evident in the OVI profiles extracted separately from 43| the two visits, so this problem is not due to a hot-pixel feature. Apart 43| from this small offset, the N_a_(v) profiles of the OVI lines at v=57km/s 43| appear to be quite consistent; the relative strength and shape of the two 43| lines are in agreement. This suggests that the offset could be caused by an 43| instrumental calibration problem. For example, the STIS geometric distortion 43| can cause offsets of this magnitude if not properly corrected (Walsh et al., 43| 2001, Instrument Science Report STIS 2001-02; Maiz-Apellaniz & Ubeda, 43| 2004, Instrument Science Report STIS 2004-01), and some problems with the 43| distortion correction have been noted (Maiz-Apellaniz & Ubeda, 2004, 43| Instrument Science Report STIS 2004-01). Evidence of wavelength calibration 43| problems have also been noted when comparing lines that should have 43| identical component structure (e.g., Jenkins & Tripp, 2001ApJS..137..297J; 43| Tripp et al., , 2005ApJ...619..714T). While we have found these problems to 43| be relatively rare, the stability of the STIS geometric distortion 43| correction has not been studied systematically, and it remains possible 43| that the discrepancy in the v=57km/s component is caused by a calibration 43| problem such as this. Nevertheless, we flag the OVI lines in the v=57km/s 43| component with a colon in Table 3, because of this disagreement, and we 43| treat this component as an insecure identification. With the new COS, it 43| will be possible to reobserve PKS 0405-123 to determine if the offset is 43| due to a STIS instrumental problem. The OVI1037.62 line at this redshift 43| falls close to Galactic CIV1550.78 (which is the source of the extra 43| absorption evident at v<-40km/s in Fig. 43), but from the corresponding 43| Galactic CIV1548.20 line, we can see that the Milky Way C iv has little 43| impact on the redshifted OVI1037.62 profile. We give this system an 43| uncertain classification due to the insecure identification of the OVI 43| component at v=57km/s and the fact that the Ly{alpha} profile, which is 43| needed to detect low-N(HI) components, has not been observed at high 43| resolution. 44|PKS 1302-102, z_abs_=0.19159. The profile-fitting code obtains its best fit 44| to the HI lines with a narrow and deep component superimposed on a broad and 44| shallow component at the same velocity. The absorption that requires the 44| broad component could be nearly as well-fit with multiple narrower 44| components, and higher S/N is required to break this degeneracy. Only 44| OVI1031.93 is detected, but the OVI line is precisely aligned with the HI 44| lines, and CIII977.02 and SiIII1206.50 are also detected with good 44| significance at this redshift. 45|PKS 1302-102, z_abs_=0.22563. Some parts of the Ly{beta} profile are affected 45| by blends; those regions of Ly{beta} were excluded from the fit. The 45| OVI1037.62 line is also located next to an unrelated strong line. However, 45| the OVI1031.93 and 1037.62 N_a_(v) profiles show excellent agreement over 45| most of the velocity range where {lambda}1031.93 is clearly detected, and 45| the velocity range of the OVI1037.62 line that is affected by the adjacent 45| interloper was excluded from the fit. 46|TON 28, z_abs_=0.13783. The OVI1037.62 line is only detected at the 46| 2.2{sigma} level, but as shown in Figure 44, its wavelength and relative 46| strength agree with the corresponding OVI1031.93 line. In addition, we can 46| see from this figure that the OVI lines are aligned with a clearly detected 46| component in the corresponding HI Ly{alpha} line. 47|TON 28, z_abs_=0.27340. The HI Ly{alpha} line is strongly blended with Milky 47| Way CIV1548.20. However, the HI at this redshift is securely identified and 47| measured based on the well-detected Ly{beta} and Ly{gamma} lines, and 47| comparison of the Galactic CIV1548.20 and 1550.78 apparent column density 47| profiles verifies that substantial extra optical depth (due to the blended 47| Ly{alpha} line) is present in the Galactic CIV1548.20 profile. --------------------------------------------------------------------------------