Contents of: J/ApJS/177/39/./appendix.dat

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## (from tabmap V6.0 (2016-08-18)) 2024-03-28T11:14:08
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#-- J/ApJS/177/39 Survey of low-redshift OVI absorbers (Tripp+, 2008)
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#---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
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 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.
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