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The Complex Line of Sight Towards Q2059\Gamma360 1
B. Leibundgut
European Southern Observatory, Karl­Schwarzschild­Strasse 2,
D­85748 Garching, Germany
J. Gordon Robertson
School of Physics, University of Sydney, NSW 2006, Australia
Abstract. Emission in a damped Lyman ff system towards Q2059\Gamma360
has been confirmed. Three objects with similar redshift have to be con­
sidered along the line of sight: the absorption system, a spatially ex­
tended emission, and the quasar itself. The velocity separation between
the DLA and the quasar is about 500 km s \Gamma1 , and is similar to the ve­
locity offset between the DLA and the emission. The emission itself is
traced to about 2 00 away from the quasar, which corresponds to 15 kpc
(H 0 = 50 km s \Gamma1 Mpc \Gamma1
,\Omega = 1). The emission line profile changes
with distance from the quasar sight line, although an interpretation as a
rotation curve is unlikely. If placed in front of the damped system, the
emission site moves with a considerable peculiar velocity, possibly indi­
cating a group or cluster of galaxies. Another possibility is that the size
of the absorber is very small and we are observing narrow­line emission
regions near the quasar.
1. Introduction
Spatial information about objects responsible for the damped absorptions in
quasar spectra is rare and has only recently been forthcoming. These observa­
tions should further elucidate the nature of these objects. Galactic disks are
inferred from the high column densities and disk dynamics as derived from the
profiles of unsaturated lines (Prochaska & Wolfe 1996) or spatially offset emis­
sion (Djorgovski et al. 1996, Lu, Sargent, & Barlow 1997). Alternatively, the
damped lines could be caused by small, dense clumps falling together to form
the large, present­day galaxies (Haehnelt et al. 1997). Emission from damped
Lyman ff absorbers (DLAs) has been detected in very few cases (Hunstead et
al. 1990, MÜller & Warren 1993, Pettini et al. 1995, Djorgovski et al. 1996,
MÜller, Warren, & Fynbo 1998, Leibundgut & Robertson 1998).
1 To appear in 'The Young Universe: Galaxy Formation and Evolution at Intermediate and High
Redshift, eds. S. d'Odorico, A. Fontana, E. Giallongo, San Francisco: Astronomical Society of
the Pacific
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4000 5000 6000 7000 8000
0
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l vac (Angstrom)
F
l
(erg
s
­1
cm
­2
A
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Figure 1. Low­resolution spectrum of Q2059\Gamma360 obtained by us
with EMMI at the NTT in July 1997. The wavelengths are given for
vacuum. The correction to heliocentric wavelengths is negligible.
2. Relationship of Quasar, Absorber, and Narrow Emission
The line of sight towards Q2059\Gamma360 contains a DLA at z = 3:08303 \Sigma 0:00007 as
determined from metal lines (Fig. 1; Pettini et al. 1995, Leibundgut & Robertson
1998, Robertson & Leibundgut 1998). The quasar redshift measured from the
Civ and the Ciii] lines is z QSO = 3:092 \Sigma 0:002, in excellent agreement with
the redshift reported by Warren et al. (1991) and the reconstruction of the
Lyff emission line (Leibundgut & Robertson 1998). Emission from Siiv+Oiv is
detected as well, but we cannot derive a redshift due to blending with a night
sky line. The Civ and the Lyff/Nv emission lines have similar equivalent widths
which indicates that the DLA is absorbing a major fraction of the quasar Lyff
emission line.
Lyfi absorption from the DLA is detected at 4192 š A. The low resolution
is not enough to show any structure in this line. Lyfl, although in the spectral
range, is not detected. We find another deep absorption at – = 4269 š A, possibly
another damped system at z = 2:51.
From our previous intermediate­dispersion spectroscopy we derive a column
density of the absorber of log(N) = 20:85 \Sigma 0:03 (Leibundgut & Robertson 1998).
This value is slightly higher than found previously (Pettini et al. 1995), but we
have accounted for the partial obliteration of the quasar emission line. There is
an offset of 40 km s \Gamma1 between the Lyff absorption and the metal lines.
Our earlier observations show that the DLA is flanked on the red side by
a narrow emission, which has been detected out to at least 2 00 away from the
2

4940 4950 4960 4970 4980 4990 5000
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2" S
0"
0.5" S
4940 4950 4960 4970 4980 4990 5000
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3.04 3.06 3.08 3.1 3.12
Lya redshift
l vac
(Angstrom)
F
l
(erg
s
­1
cm
­2
A
­1
)
Figure 2. Emission line coincident with the DLA towards
Q2059\Gamma360 for three different spatial positions. Scaled spectra of the
quasar have been subtracted to isolate the emission.
quasar sight line (Fig. 2). It appears to be separated into two emission sites
separated by about 300 km s \Gamma1 . The line profile changes with positional offset.
One emission component maintains its strength at all offsets, while the other
weakens away from the quasar sight line.
3. Discussion
The DLA cannot be located within the host galaxy of the quasar. The velocity
offset is more than 500 km s \Gamma1 , which is a lower limit as high­ionization lines
tend to be blueshifted in quasars (Tytler & Fan 1991, MÜller et al. 1998). This
is a substantial velocity for any galaxy size object. The DLA contains no high­
ionization absorption lines, like Nv, and the metallicity is not enhanced. The
most intriguing argument is that the DLA would have been completely ionized, if
positioned within the host galaxy of the quasar. The DLA is hence not associated
with the quasar and more like other intervening damped absorbers. This result
is similar to two other DLAs observed near the quasar redshift (MÜller et al.
1998).
The Lyff photons observed in the emitter could still come from clouds asso­
ciated with the quasar and scatter near the rim of the DLA (Warren & MÜller
1996, Charlot & Fall 1991). The extent of the emission of at least 15 kpc
(H 0 = 50 km s \Gamma1
,\Omega = 1) makes this proposition rather unlikely. Another pos­
sibility is that the Lyff photons are coming from narrow­line regions associated
with the quasar and the DLA acts as a coronograph eclipsing the quasar in Lyff.
The photons would then be scattered into the absorption by the seeing disk.
3

This requires a small size for the DLA (cf. Fig. 6 in Leibundgut & Robertson
1998) and possibly an agglomeration of small, dense clouds. The line profiles
of the emitter (Fig. 2) suggest such an interpretation with two emission com­
ponents and strengths dependent on the offset. There is no detectable velocity
shift in the lines but the redder component decreases in strength by a factor of
about 3 from the quasar sight line to 2 00 to the South.
The large velocity offset between the DLA and the emitter suggests that
absorber and emitter are not located in the same galaxy. Since the emission
is shifted to the red, but the emission site has to be in front of the DLA, this
implies a substantial peculiar velocity.
Infalling gas with velocities of the order of 100 to 300 km s \Gamma1 has been
proposed for observed line shifts in nearby star­forming and high­redshift galax­
ies (Lequeux et al. 1995, Heckman & Leitherer 1997, Franx et al. 1997). The
velocity difference we measure for the absorber­emitter system is larger.
4. Conclusions
We have found a galaxy­size object near a DLA absorbing system towards
Q2059\Gamma360. The DLA is not associated with the quasar or its host galaxy,
and is comparable to other intervening DLA systems. The velocity offsets be­
tween quasar, absorber, and emitter are substantial and exclude that they all
are embedded within a single galaxy. They are similar to velocity dispersions
observed in groups. The emitter redshift nearly coincides with the quasar red­
shift which may indicate a connection of these two emission sites. If so, this
implies a small spatial extent for the absorber.
References
Charlot, S., Fall, S.M. 1991, ApJ, 378, 471
Djorgovski, S.G., Pahre, M.A., Bechtold, J., Elston, R. 1996, Nature, 382, 234
Franx, M., Illingworth, G. D., Kelson, D. D., van Dokkum, P. G., Tran, K.­V.
1997, ApJ, 486, L75
Haehnelt, M.G., Steinmetz, M., Rauch, M. 1997, ApJ, in press (astro­ph/9706201)
Heckman, R. M., Leitherer, C. 1997, AJ, 114, 69
Hunstead, R. W., Pettini, M., Fletcher, A. B. 1990, ApJ, 356, 23
Leibundgut, B., Robertson, J. G. 1998, MNRAS, submitted
Lequeux, J., Kunth, D., Mas­Hesse, J. M., Sargent, W. L. W. 1995, A&A, 301,
18
Lu, L., Sargent, W. L. W., Barlow, T. A. 1997, ApJ, 484, L131
MÜller, P., Warren, S. J. 1993, A&A, 270, 43
MÜller, P., Warren, S. J., Fynbo, J. U. 1998, A&A, 330, 19
Pettini, M., Hunstead, R. W., King, D. L., Smith, L. J. 1995, QSO Absorption
Lines, ed. G. Meylan, (Berlin: Springer), 55
Prochaska, J.X., Wolfe, A.M., 1996 ApJ, 470, 403
4

Robertson, J. G., Leibundgut, B. 1998, Evolution of the Intergalactic Medium
from QSO Absorption Line Systems, eds. P. Petitjean, S. Charlot, Paris:
Editions Frontieres, in press
Tytler, D., Fan, X.­M. 1992, ApJS, 79, 1
Warren, S. J., Hewett, P. C., Osmer, P. S. 1991, ApJS, 76, 23
Warren, S. J., MÜller, P. 1996, A&A, 311, 25
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