Spectra of components A1 +A2 and B of the gravitational lens system MG 0414+0534 taken with the low-resolution imaging spectrograph on the Keck 10 m telescope show that the strong absorption feature seen in a low-resolution spectrum is due to a complex of Fe II lines at redshifts near that of the lensed quasar. The redshift of the lens remains unknown

Cohen, J. G.

Lawrence, C. R.

Oke, J. B.

Caltech Authors - Main

19
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THE ASTRONOMICAL JOURNAL VOLUME 110, NUMBER 6 DECEMBER 1995 
ABSORPTION LINES IN THE GRAVITATIONAL LENS SYSTEM MG 0414+0534 
C. R. Lawrence,1 J. G. Cohen, and J. B. Oke2 
Palomar Observatory 105-24, California Institute of Technology, Pasadena, California 91125 
Electronic mail: crl@jplsp.jpl.nasa.gov, jlc.@astro.caltech.edu, jbo@cygnus.dao.nrc.ca 
Received 1995 June 22; revised 1995 August 28 
ABSTRACT 
Spectra of components A1+A2 and B of the gravitational lens system MG 0414+0534 taken with the 
low-resolution imaging spectrograph on the Keck 10 m telescope show that the strong absorption feature 
seen in a low-resolution spectrum is due to a complex of Fe II lines at redshifts near that of the lensed 
quasar. The redshift of the lens remains unknown. © 1995 American Astronomical Society. 
1. INTRODUCTION 
The gravitational lens system MG 0414+0534 (Hewitt 
et al 1992) is remarkable for its unique optical/infrared 
spectrum, the wavelength dependence of the flux ratios of 
the components, and the strength of the absorption feature 
observed near 8660 Á in a low-resolution spectrum. In a 
companion paper (Lawrence et al. 1995a, this volume) we 
report a redshift of 2.639 for the background quasar. If the 
absorption feature observed near 8660 Â were intrinsic to the 
quasar, its rest wavelength would be about 2380 Á. Although 
Fe II absorption features near this wavelength are often seen 
in quasar spectra, their equivalent width is usually much 
smaller than observed in MG 0414+0534. Moreover, the 2" 
angular size of MG 0414+0534 means that light from the 
quasar passes through the lens itself. It seemed to us likely, 
therefore, that the absorption feature came from the lens, and 
that an unambiguous identification of the feature would give 
the lens redshift. 
Accordingly, spectra of MG 0414+0534 at a resolution of 
2.0 Â (FWHM) were taken with the W. M. Keck 10 m tele- 
scope on 1993 October 22 during an early engineering run of 
the low-resolution imaging spectrograph (LRIS; see Oke 
et al. 1995 and Cohen et al. 1993 for details). The slit was 
oriented to cover both A1+A2 and B. 
Early problems with the LRIS readout electronics resulted 
in very high readout noise and a time-dependent bias level 
with strong nonrandom features that could be removed only 
partially. Nevertheless, a strong absorption doublet was seen 
near 8650 À in both A1+A2 and B, with separation exactly 
as expected for Nal XX 5889.95, 5895.92 at a redshift of 
0.47. A third absorption feature near 8515 Á was unidenti- 
fied, although not attributable to any obvious instrumental or 
night sky problem. We were sufficiently confident of the 
identification to submit a manuscript claiming that we had 
measured the redshift of the lens, but nevertheless reob- 
served MG 0414+0534 with LRIS after the readout prob- 
lems were corrected. In this paper we report on the new 
observations, which have a SNR more than three times 
higher than the earlier ones, and which require a completely 
Present address: Astrophysics 169-506, JPL, Pasadena, CA 91109. 
2Present address: DAO, 5071 West Saamich Rd. RR5, Victoria, B.C. 
V8X 4M6, Canada. 
2583 Astron. J. 110 (6), December 1995 
different interpretation of the absorption seen in this interest- 
ing lens system. 
2. OBSERVATIONS AND DATA REDUCTION 
MG 0414+0534 was reobserved with the Keck 10 m tele- 
scope on 1994 November 7, using the low-resolution imag- 
ing spectrograph. The detector is a 2048X2048 thinned Tek- 
tronix CCD, with a peak quantum efficiency at 6500 Á of 
80%. A slit 3' long illuminates an area of about 2048X800 
pixels. The blue- and red-wavelength halves of the chip are 
read out through independent electronics. 
A 1200 line mm-1 grating blazed at 7500 Â was used 
with a 1" slit, giving a FWHM of arc lines and unresolved 
night sky lines of 2.0 Á. The grating tilt put the wavelength 
range 8000-9200 Â on the detector. The overall throughput 
of the detector, spectrograph, and telescope was about 22% 
over this range. 
The slit was rotated so that components A1+A2 (sepa- 
rated by Katz & Hewitt 1993) and B could be observed 
simultaneously. Two consecutive 3000 s exposures were 
made, followed by a dome flat and a neon discharge tube 
exposure, all with the telescope pointed at MG 0414+0534. 
The dAO star GD 191B2B (Oke 1990) was observed with the 
same grating tilt for calibration. 
Following bias subtraction and an adjustment for slightly 
different gains in the two sets of readout electronics, the flat 
frame was high-pass filtered, adjusted to have a mean value 
of unity, and used to flatten the object and arc frames. 
Sky emission was subtracted using third-order polynomial 
fits to sky regions roughly 100 pixels wide on both sides of 
MG 0414+0534. Many combinations of polynomial order 
and region fit were tried both in order to establish the opti- 
mum method of sky subtraction, and to get an idea of the 
uncertainty in the absorption profile due to sky subtraction 
itself. 
The profile of the spectrum of A1+A2 along the slit was 
wider than that of B, as expected from the 0"32 projected 
separation of A1 and A2 along the slit. The entire profile is 
well fit by three Gaussians whose widths are equal to that of 
B, with separations as expected from the radio image. The 
width of B was 3.5 pixels (0'.'80) in the first of the two 3000 
s exposures and 5.0 pixels (T.T4) in the second. The differ- 
ence in the widths between the two exposures is due in part 
© 1995 Am. Astron. Soc. 2583 0004-6256/95/110(6)/2583/3/$0.90 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
2584 LAWRENCE ETAL: THE REDSHIFT OF THE LENS IN MG 0414+0534 2584 
8500 8550 8600 8650 8700 
Wavelength (Angstroms) 8500 8550 8600 8650 8700 
Fig. 1. Spectra of MG 0414+0534 A1+A2 (upper panel) and B (lower 
panel) in the region near the absorption feature. The error spectra at the 
bottom of each panel are based on photon noise and random readout noise 
only, and are dominated by night sky emission. 
to the fact that the second exposure was observed at higher 
airmass (1.22-1.45, compared to 1.09-1.22 for the first). 
Even in the second exposure, however, the overlap of 
A1+A2 and B represents less than 5% of the total energy 
observed, and the spectra of A1+A2 and B were extracted 
separately using an optimal extraction routine. 
Sixteen lines identified in the Ne spectrum were used to 
establish the wavelength scale. The rms error in the fitted 
dispersion relation was 0.03 Â. Offsets between the wave- 
length scales of the arc spectrum and the MG 0414+0534 
spectra due to flexure in the spectrograph were determined 
and removed using the positions of 40 night sky lines. The 
residual wavelength error on the night sky lines was 0.05 À. 
Corrections for atmospheric extinction and instrumental 
response were determined from the spectrum of the standard 
star GD 191B2B, observed at the same grating angle. Spectra 
of A1+A2 and B from the two exposures were then aver- 
aged. Figure 1 shows the resulting calibrated spectra over the 
wavelength region where features were detected. The error 
spectra reflect only photon noise and the random component 
of readout noise. 
Fig. 2. Absorption features in A1+A2 (upper panel) and B (lower panel). 
The smooth curves are a polynomial fitted to the continuum plus Gaussians 
fitted to individual features. 
3. DISCUSSION 
The absorption feature seen in the 4-Shooter spectrum of 
Hewitt et al. (1992) is revealed in Fig. 1 to be a blend of 
many features. Other features are seen between 8500 and 
8550 Â. Fits to these features are shown in Fig. 2. The lines 
are fitted beautifully by four sets of three Fe n lines (rest 
wavelengths of 2343.495, 2373.737, and 2382.039 Â). Pa- 
rameters of the fits are given in Table 1. All wavelengths are 
heliocentric, in air. The central wavelengths of the lines in 
each set were constrained to be in the ratio 
2343.495:2373.737:2382.039. One of the 2373.737 lines co- 
incides with the lowest-redshift 2382.039 line, so its ampli- 
tude and width were fixed to equal those of the 2373.737 line 
seen near 8647 Â. Fits were also made with the line centers 
free to move independently. The rms differences between the 
constrained and unconstrained centers is only 0.16 Â in 
A1+A2 and 0.36 Â in B. These small changes are a con- 
vincing demonstration of the line identifications, and can be 
taken as an estimate of the uncertainties in the line centers. 
Uncertainties in the amplitudes are about 2 ¿¿K, with cor- 
responding uncertainties in the equivalent widths of 10% in 
A1+A2 and 20% in B. The stronger features are saturated, 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
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2585 LAWRENCE ETAL: THE REDSHIFT OF THE LENS IN MG 0414+0534 2585 
Table 1. Absorption features of MG 0414+0534. 
Name 
Center Ampi. FWHM Wobs 
(À) (^Jy) (Â) (À) 
A 
FeuA2343.495 . 
FeuA2373.737 . 
Fen A2382.039 . 
B 
Fe il A2343.495 . 
Feu A2373.737 . 
FeuA2382.039 . 
8511.32 
8518.70 
8537.01 
8541.83 
8621.12 
8628.60 
8647.14 
8652.03 
8651.34 
8658.84 
8677.45 
8682.35 
8511.87 
8518.59 
8537.74 
8542.05 
8621.68 
8628.49 
8647.88 
8652.24 
8651.89 
8658.73 
8678.19 
8682.57 
-13.1 
-26.6 
-11.9 
-14.5 
-6.4 
-24.6 
-5.5 
-5.5 
-23.6 
-30.2 
-23.3 
-24.6 
-5.0 
-7.3 
-4.9 
-4.0 
-1.7 
-3.5 
-0.6 
-0.6 
-6.6 
-7.0 
-4.6 
-7.7 
3.6 
4.0 
3.5 
2.5 
2.4 
2.4 
2.0 
2.0 
3.2 
5.2 
2.7 
2.7 
2.0 
3.8 
2.2 
3.1 
4.2 
2.4 
2.0 
2.0 
3.6 
4.6 
3.0 
2.4 
1.5 
3.4 
1.3 
1.2 
0.5 
1.8 
0.3 
0.3 
2.2 
4.7 
1.9 
2.0 
1.2 
3.3 
1.2 
1.4 
0.8 
0.9 
0.1 
0.1 
2.5 
3.4 
1.4 
1.9 
so the ratios of amplitudes among the four systems vary 
considerably. Many of the lines are resolved (recall that the 
width of night sky lines is 2.0 A), with corresponding veloci- 
ties at half maximum up to 170 km s-1. 
The redshifts of the four systems are 2.63172, 2.63487, 
2.64268, and 2.64474. We estimate an uncertainty of 
±0.00005 by adding the aforementioned rms differences of 
0.16 and 0.36 Â in quadrature. Referenced to the lowest- 
redshift system these redshifts correspond to velocity differ- 
ences of 0, 170, 800, and 1070 km s-1. The redshift of the 
quasar is given by Lawrence et al. (this volume) as 2.639 
±0.002, in mild conflict (given the uncertainties) with ab- 
sorption at z =2.64268 or 2.64474. It is clear that the Fell 
absorbers lie close to the quasar, but given the difficulty of 
determining an accurate redshift from a line as broad at Ha 
in MG 0414+0534 it will be hard to say exactly how close. 
The fact that there are four absorbing systems so close to the 
quasar along a single line of sight, separated by hundreds of 
kilometers per second, suggests that the quasar lies in a rich 
environment. 
The wavelength differences between the line centers of 
the four triplets in A and B are probably not significant. 
The equivalent widths of the lines are large, particularly 
in the second-lowest redshift system. The observed equiva- 
lent width determined from the low-resolution 4-Shooter 
spectrum in Hewitt et al (1992) was 20.8 Â, while the total 
observed Weq for the lines for image A1+A2 between 8620 
and 8683 Â (which give rise to the absorption feature in the 
4-Shooter spectrum) in Table 1 is 13.8 Á. The differences are 
almost certainly the result of the low resolution of the 
4-Shooter spectrum (FWHM=27 À), coupled with the night 
sky features. Direct comparison of the 4-Shooter and Keck 
spectra shows that there is no offset in the wavelength scales, 
but that the shape of the absorption feature in the 4-Shooter 
spectrum is distorted in a pattern similar to the envelope of 
the night sky lines in that wavelength range. 
The largest rest equivalent width for Fe II X2382.039 seen 
in a sample of 103 low- and intermediate-redshift quasars by 
Steidel & Sargent (1992) was 2.33 Á in Q0013-0029. The 
sum of the rest equivalent widths of five Fe II lines at z^l.97 
in Q0013—0029 is 6.81 Â. In MG 0414+0534 A1+A2 and 
B the largest rest equivalent widths seen are 1.29 and 0.94 Á, 
respectively. The sum of the rest equivalent widths for all 
twelve features is 6.08 Â in A1+A2 and 5.01 Á in B. Thus 
the iron absorption in MG 0414+0534 is unusual but not 
unprecedented. 
The reader is referred to Lawrence et al (1995) for more 
details on this interesting system, and on the significance of 
dusty gravitational lenses. 
This work is based on observations made at the W. M. 
Keck Observatory, jointly operated by the California Institute 
of Technology and the University of California. We are 
grateful to the Keck Foundation for its vision and generosity 
in support of astronomy. We thank D. Womble and W. Sar- 
gent for useful discussions. 
REFERENCES 
Cohen, J. G., Cromer, J. L., Southard, Jr., S., & Clowe, D. 1993, in PASP 
Conf. Ser. 61, Astronomical Data Analysis Software and Systems III, ed- 
ited by D. R. Crabtree, R. J. Hanisch, and J. Barnes (ASP, San Francisco), 
p. 469 
Hewitt, J. N., Turner, E. L., Lawrence, C. R., Schneider, D. P, & Brody, J. 
P. 1992, AJ, 104, 968 
Katz, C. A., & Hewitt, J. N. 1993, ApJ, 409, L9 
Lawrence, C. R., Elston, Richard, Jannuzi, B. T, & Turner, E. T. 1995, 
AJ, 110, 2570 
Oke, J. B. 1990, AJ, 99, 1621 
Oke, J. B., et al. 1995, PASP, 107, 375 
Steidel, C. C., & Sargent, W. L. W. 1992, ApJS, 80, 1 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 


English

Absorption Lines in the Gravitational Lens System MG 0414+0534

19
95
AJ
 
 
11
0.
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THE ASTRONOMICAL JOURNAL VOLUME 110, NUMBER 6 DECEMBER 1995 
ABSORPTION LINES IN THE GRAVITATIONAL LENS SYSTEM MG 0414+0534 
C. R. Lawrence,1 J. G. Cohen, and J. B. Oke2 
Palomar Observatory 105-24, California Institute of Technology, Pasadena, California 91125 
Electronic mail: crl@jplsp.jpl.nasa.gov, jlc.@astro.caltech.edu, jbo@cygnus.dao.nrc.ca 
Received 1995 June 22; revised 1995 August 28 
ABSTRACT 
Spectra of components A1+A2 and B of the gravitational lens system MG 0414+0534 taken with the 
low-resolution imaging spectrograph on the Keck 10 m telescope show that the strong absorption feature 
seen in a low-resolution spectrum is due to a complex of Fe II lines at redshifts near that of the lensed 
quasar. The redshift of the lens remains unknown. © 1995 American Astronomical Society. 
1. INTRODUCTION 
The gravitational lens system MG 0414+0534 (Hewitt 
et al 1992) is remarkable for its unique optical/infrared 
spectrum, the wavelength dependence of the flux ratios of 
the components, and the strength of the absorption feature 
observed near 8660 Á in a low-resolution spectrum. In a 
companion paper (Lawrence et al. 1995a, this volume) we 
report a redshift of 2.639 for the background quasar. If the 
absorption feature observed near 8660 Â were intrinsic to the 
quasar, its rest wavelength would be about 2380 Á. Although 
Fe II absorption features near this wavelength are often seen 
in quasar spectra, their equivalent width is usually much 
smaller than observed in MG 0414+0534. Moreover, the 2" 
angular size of MG 0414+0534 means that light from the 
quasar passes through the lens itself. It seemed to us likely, 
therefore, that the absorption feature came from the lens, and 
that an unambiguous identification of the feature would give 
the lens redshift. 
Accordingly, spectra of MG 0414+0534 at a resolution of 
2.0 Â (FWHM) were taken with the W. M. Keck 10 m tele- 
scope on 1993 October 22 during an early engineering run of 
the low-resolution imaging spectrograph (LRIS; see Oke 
et al. 1995 and Cohen et al. 1993 for details). The slit was 
oriented to cover both A1+A2 and B. 
Early problems with the LRIS readout electronics resulted 
in very high readout noise and a time-dependent bias level 
with strong nonrandom features that could be removed only 
partially. Nevertheless, a strong absorption doublet was seen 
near 8650 À in both A1+A2 and B, with separation exactly 
as expected for Nal XX 5889.95, 5895.92 at a redshift of 
0.47. A third absorption feature near 8515 Á was unidenti- 
fied, although not attributable to any obvious instrumental or 
night sky problem. We were sufficiently confident of the 
identification to submit a manuscript claiming that we had 
measured the redshift of the lens, but nevertheless reob- 
served MG 0414+0534 with LRIS after the readout prob- 
lems were corrected. In this paper we report on the new 
observations, which have a SNR more than three times 
higher than the earlier ones, and which require a completely 
Present address: Astrophysics 169-506, JPL, Pasadena, CA 91109. 2Present address: DAO, 5071 West Saamich Rd. RR5, Victoria, B.C. 
V8X 4M6, Canada. 
2583 Astron. J. 110 (6), December 1995 
different interpretation of the absorption seen in this interest- 
ing lens system. 
2. OBSERVATIONS AND DATA REDUCTION 
MG 0414+0534 was reobserved with the Keck 10 m tele- 
scope on 1994 November 7, using the low-resolution imag- 
ing spectrograph. The detector is a 2048X2048 thinned Tek- 
tronix CCD, with a peak quantum efficiency at 6500 Á of 
80%. A slit 3' long illuminates an area of about 2048X800 
pixels. The blue- and red-wavelength halves of the chip are 
read out through independent electronics. 
A 1200 line mm-1 grating blazed at 7500 Â was used 
with a 1" slit, giving a FWHM of arc lines and unresolved 
night sky lines of 2.0 Á. The grating tilt put the wavelength 
range 8000-9200 Â on the detector. The overall throughput 
of the detector, spectrograph, and telescope was about 22% 
over this range. 
The slit was rotated so that components A1+A2 (sepa- 
rated by Katz & Hewitt 1993) and B could be observed 
simultaneously. Two consecutive 3000 s exposures were 
made, followed by a dome flat and a neon discharge tube 
exposure, all with the telescope pointed at MG 0414+0534. 
The dAO star GD 191B2B (Oke 1990) was observed with the 
same grating tilt for calibration. 
Following bias subtraction and an adjustment for slightly 
different gains in the two sets of readout electronics, the flat 
frame was high-pass filtered, adjusted to have a mean value 
of unity, and used to flatten the object and arc frames. 
Sky emission was subtracted using third-order polynomial 
fits to sky regions roughly 100 pixels wide on both sides of 
MG 0414+0534. Many combinations of polynomial order 
and region fit were tried both in order to establish the opti- 
mum method of sky subtraction, and to get an idea of the 
uncertainty in the absorption profile due to sky subtraction 
itself. 
The profile of the spectrum of A1+A2 along the slit was 
wider than that of B, as expected from the 0"32 projected 
separation of A1 and A2 along the slit. The entire profile is 
well fit by three Gaussians whose widths are equal to that of 
B, with separations as expected from the radio image. The 
width of B was 3.5 pixels (0'.'80) in the first of the two 3000 
s exposures and 5.0 pixels (T.T4) in the second. The differ- 
ence in the widths between the two exposures is due in part 
© 1995 Am. Astron. Soc. 2583 0004-6256/95/110(6)/2583/3/$0.90 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
2584 LAWRENCE ETAL: THE REDSHIFT OF THE LENS IN MG 0414+0534 2584 
8500 8550 8600 8650 8700 
Wavelength (Angstroms) 8500 8550 8600 8650 8700 
Fig. 1. Spectra of MG 0414+0534 A1+A2 (upper panel) and B (lower 
panel) in the region near the absorption feature. The error spectra at the 
bottom of each panel are based on photon noise and random readout noise 
only, and are dominated by night sky emission. 
to the fact that the second exposure was observed at higher 
airmass (1.22-1.45, compared to 1.09-1.22 for the first). 
Even in the second exposure, however, the overlap of 
A1+A2 and B represents less than 5% of the total energy 
observed, and the spectra of A1+A2 and B were extracted 
separately using an optimal extraction routine. 
Sixteen lines identified in the Ne spectrum were used to 
establish the wavelength scale. The rms error in the fitted 
dispersion relation was 0.03 Â. Offsets between the wave- 
length scales of the arc spectrum and the MG 0414+0534 
spectra due to flexure in the spectrograph were determined 
and removed using the positions of 40 night sky lines. The 
residual wavelength error on the night sky lines was 0.05 À. 
Corrections for atmospheric extinction and instrumental 
response were determined from the spectrum of the standard 
star GD 191B2B, observed at the same grating angle. Spectra 
of A1+A2 and B from the two exposures were then aver- 
aged. Figure 1 shows the resulting calibrated spectra over the 
wavelength region where features were detected. The error 
spectra reflect only photon noise and the random component 
of readout noise. 
Fig. 2. Absorption features in A1+A2 (upper panel) and B (lower panel). 
The smooth curves are a polynomial fitted to the continuum plus Gaussians 
fitted to individual features. 
3. DISCUSSION 
The absorption feature seen in the 4-Shooter spectrum of 
Hewitt et al. (1992) is revealed in Fig. 1 to be a blend of 
many features. Other features are seen between 8500 and 
8550 Â. Fits to these features are shown in Fig. 2. The lines 
are fitted beautifully by four sets of three Fe n lines (rest 
wavelengths of 2343.495, 2373.737, and 2382.039 Â). Pa- 
rameters of the fits are given in Table 1. All wavelengths are 
heliocentric, in air. The central wavelengths of the lines in 
each set were constrained to be in the ratio 
2343.495:2373.737:2382.039. One of the 2373.737 lines co- 
incides with the lowest-redshift 2382.039 line, so its ampli- 
tude and width were fixed to equal those of the 2373.737 line 
seen near 8647 Â. Fits were also made with the line centers 
free to move independently. The rms differences between the 
constrained and unconstrained centers is only 0.16 Â in 
A1+A2 and 0.36 Â in B. These small changes are a con- 
vincing demonstration of the line identifications, and can be 
taken as an estimate of the uncertainties in the line centers. 
Uncertainties in the amplitudes are about 2 ¿¿K, with cor- 
responding uncertainties in the equivalent widths of 10% in 
A1+A2 and 20% in B. The stronger features are saturated, 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
19
95
AJ
 
 
11
0.
25
83
L 
2585 LAWRENCE ETAL: THE REDSHIFT OF THE LENS IN MG 0414+0534 2585 
Table 1. Absorption features of MG 0414+0534. 
Name 
Center Ampi. FWHM Wobs 
(À) (^Jy) (Â) (À) 
A 
FeuA2343.495 . 
FeuA2373.737 . 
Fen A2382.039 . 
B 
Fe il A2343.495 . 
Feu A2373.737 . 
FeuA2382.039 . 
8511.32 
8518.70 
8537.01 
8541.83 
8621.12 
8628.60 
8647.14 
8652.03 
8651.34 
8658.84 
8677.45 
8682.35 
8511.87 
8518.59 
8537.74 
8542.05 
8621.68 
8628.49 
8647.88 
8652.24 
8651.89 
8658.73 
8678.19 
8682.57 
-13.1 
-26.6 
-11.9 
-14.5 
-6.4 
-24.6 
-5.5 
-5.5 
-23.6 
-30.2 
-23.3 
-24.6 
-5.0 
-7.3 
-4.9 
-4.0 
-1.7 
-3.5 
-0.6 
-0.6 
-6.6 
-7.0 
-4.6 
-7.7 
3.6 
4.0 
3.5 
2.5 
2.4 
2.4 
2.0 
2.0 
3.2 
5.2 
2.7 
2.7 
2.0 
3.8 
2.2 
3.1 
4.2 
2.4 
2.0 
2.0 
3.6 
4.6 
3.0 
2.4 
1.5 
3.4 
1.3 
1.2 
0.5 
1.8 
0.3 
0.3 
2.2 
4.7 
1.9 
2.0 
1.2 
3.3 
1.2 
1.4 
0.8 
0.9 
0.1 
0.1 
2.5 
3.4 
1.4 
1.9 
so the ratios of amplitudes among the four systems vary 
considerably. Many of the lines are resolved (recall that the 
width of night sky lines is 2.0 A), with corresponding veloci- 
ties at half maximum up to 170 km s-1. 
The redshifts of the four systems are 2.63172, 2.63487, 
2.64268, and 2.64474. We estimate an uncertainty of 
±0.00005 by adding the aforementioned rms differences of 
0.16 and 0.36 Â in quadrature. Referenced to the lowest- 
redshift system these redshifts correspond to velocity differ- 
ences of 0, 170, 800, and 1070 km s-1. The redshift of the 
quasar is given by Lawrence et al. (this volume) as 2.639 
±0.002, in mild conflict (given the uncertainties) with ab- 
sorption at z =2.64268 or 2.64474. It is clear that the Fell 
absorbers lie close to the quasar, but given the difficulty of 
determining an accurate redshift from a line as broad at Ha 
in MG 0414+0534 it will be hard to say exactly how close. 
The fact that there are four absorbing systems so close to the 
quasar along a single line of sight, separated by hundreds of 
kilometers per second, suggests that the quasar lies in a rich 
environment. 
The wavelength differences between the line centers of 
the four triplets in A and B are probably not significant. 
The equivalent widths of the lines are large, particularly 
in the second-lowest redshift system. The observed equiva- 
lent width determined from the low-resolution 4-Shooter 
spectrum in Hewitt et al (1992) was 20.8 Â, while the total 
observed Weq for the lines for image A1+A2 between 8620 
and 8683 Â (which give rise to the absorption feature in the 
4-Shooter spectrum) in Table 1 is 13.8 Á. The differences are 
almost certainly the result of the low resolution of the 
4-Shooter spectrum (FWHM=27 À), coupled with the night 
sky features. Direct comparison of the 4-Shooter and Keck 
spectra shows that there is no offset in the wavelength scales, 
but that the shape of the absorption feature in the 4-Shooter 
spectrum is distorted in a pattern similar to the envelope of 
the night sky lines in that wavelength range. 
The largest rest equivalent width for Fe II X2382.039 seen 
in a sample of 103 low- and intermediate-redshift quasars by 
Steidel & Sargent (1992) was 2.33 Á in Q0013-0029. The 
sum of the rest equivalent widths of five Fe II lines at z^l.97 
in Q0013—0029 is 6.81 Â. In MG 0414+0534 A1+A2 and 
B the largest rest equivalent widths seen are 1.29 and 0.94 Á, 
respectively. The sum of the rest equivalent widths for all 
twelve features is 6.08 Â in A1+A2 and 5.01 Á in B. Thus 
the iron absorption in MG 0414+0534 is unusual but not 
unprecedented. 
The reader is referred to Lawrence et al (1995) for more 
details on this interesting system, and on the significance of 
dusty gravitational lenses. 
This work is based on observations made at the W. M. 
Keck Observatory, jointly operated by the California Institute 
of Technology and the University of California. We are 
grateful to the Keck Foundation for its vision and generosity 
in support of astronomy. We thank D. Womble and W. Sar- 
gent for useful discussions. 
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Cohen, J. G., Cromer, J. L., Southard, Jr., S., & Clowe, D. 1993, in PASP 
Conf. Ser. 61, Astronomical Data Analysis Software and Systems III, ed- 
ited by D. R. Crabtree, R. J. Hanisch, and J. Barnes (ASP, San Francisco), 
p. 469 
Hewitt, J. N., Turner, E. L., Lawrence, C. R., Schneider, D. P, & Brody, J. 
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Katz, C. A., & Hewitt, J. N. 1993, ApJ, 409, L9 
Lawrence, C. R., Elston, Richard, Jannuzi, B. T, & Turner, E. T. 1995, 
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© American Astronomical Society • Provided by the NASA Astrophysics Data System 


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Absorption Lines in the Gravitational Lens System MG 0414+0534

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