Extreme BAL Quasars from the Sloan Digital Sky Survey
P. B. Hall
J. E. Gunn
G. R. Knapp
V. K. Narayanan
M. A. Strauss
The Sloan Digital Sky Survey %(SDSS) has discovered a population of %low-ionization broad absorption line %(LoBAL) quasars with various extreme properties. Many show absorption from metastable states of Fe\,{\sc ii} with varying excitations; several objects are almost completely absorbed bluewards of Mg\,{\sc ii}; at least one shows stronger absorption from Fe\,{\sc iii} than Fe\,{\sc ii}, indicating temperatures $T$$>$35000~K in the absorbing region; and one object even seems to have broad H$\beta$ absorption. %**delete next to keep on 1st page? Many of these extreme BALs are also heavily reddened, though `normal' BALs (particularly LoBALs) from SDSS also show evidence for internal reddening. %
Hall.tex
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\begin{document}
\title{Extreme BAL Quasars from the Sloan Digital Sky Survey}
%\author{P. B. Hall, J. E. Gunn, G. R. Knapp, V. K. Narayanan, M. A. Strauss}
\author{Patrick~B.~Hall,~J.~E.~Gunn,~G.~R.~Knapp,~V.~K.~Narayanan,~M.~A.~Strauss}
\affil{Princeton University Observatory, Princeton NJ 08544-1001}
\author{S. F. Anderson}
\affil{University of Washington}
\author{D. E. Vanden Berk}
\affil{Fermi National Accelerator Laboratory}
%\author{T. M. Heckman, J. H. Krolik, S. Malhotra, Z. I. Tsvetanov, W. Zheng}
\author{T. M. Heckman, J. H. Krolik, Z. I. Tsvetanov, W. Zheng}
\affil{The Johns Hopkins University}
\author{G. T. Richards, D. P. Schneider}
\affil{The Pennsylvania State University}
\author{X. Fan}
\affil{Institute for Advanced Study}
\author{D. G. York}
\affil{The University of Chicago}
\author{T. R. Geballe}
\affil{Gemini Observatory}
\author{M. Davis}
\affil{University of California at Berkeley}
\author{R. H. Becker}
\affil{Lawrence Livermore National Laboratory}
\author{R. J. Brunner}
\affil{California Institute of Technology}
%\author{R. C. Nichol}
%\affil{Carnegie Mellon University}
\begin{abstract}
The Sloan Digital Sky Survey %(SDSS) 
has discovered a population of %low-ionization 
broad absorption line %(LoBAL) 
quasars with various extreme properties.  
Many show absorption from metastable states of Fe\,{\sc ii} with varying
excitations; 
several objects are almost completely absorbed bluewards of Mg\,{\sc ii};
at least one shows stronger absorption from Fe\,{\sc iii} than Fe\,{\sc ii},
indicating temperatures $T$$>$35000~K in the absorbing region;
and one object even seems to have broad H$\beta$ absorption.
%**delete next to keep on 1st page?
Many of these extreme BALs are also heavily reddened, though `normal' BALs
(particularly LoBALs) from SDSS also show evidence for internal reddening.
%
\end{abstract}


\section{Introduction}

The Sloan Digital Sky Survey (York et al. 2000) is using dedicated instruments
on a 2.5m telescope (Gunn et al. 1998) to image 10$^4$ deg$^2$ of sky to
$\sim$23$^m$ in five bands (Fukugita et al. 1996)
and obtain spectra of $\sim$10$^6$ galaxies and $\sim$10$^5$ quasars
selected primarily as outliers from the stellar locus.
Its area, depth, and selection criteria make SDSS effective at finding
unusual quasars. %quasars with unusual properties.
%Visual inspection of the first 2326 SDSS quasars (Richards et al. 2001)
%yields 96 BAL quasars, 13 of which are also FIRST sources (Menou et al. 2001).
The first data release (Stoughton et al. 2001, in prep.). contains
$\sim$4500 spectroscopically confirmed quasars, including $\sim$200 BALs,
a few percent of which have extreme properties of one sort or another.
All these extreme BALs are LoBALs, which show absorption from both low-
and high-ionization transitions, instead of the more common HiBALs with
only high-ionization absorption.  Full analysis is underway 
(Hall et al. 2001, in prep.), but already these objects confirm 
the existence of a population of extreme BALs,
%that BALs as a population have a very wide range of properties, 
as suspected from previous discoveries of individual extreme BALs
(Becker et al. 1997, Djorgovski et al. 2001).


\section{BAL Quasars With Fe\,{\sc ii}* Absorption}

\begin{figure}
%%\plottwo{sp0357_51813_509_z2.11096.eps}{scalloped3.eps}
%\plottwo{sp0357_51813_509sm5_z2.11096.eps}{scalloped3.eps}
\plottwo{Hallfig1.eps}{Hallfig2.eps}
%\plottwo{edr1723p5553_z2.11096.eps}{scalloped3.eps}
\caption{BALs with Fe\,{\sc ii}* absorption. a) SDSS 1723+5553, $z$=2.11.
b) Comparison of 2000-2900\AA\ regions in SDSS~1723+5553 (bottom)
and two lower-$z$ FeLoBALs, SDSS~1128+0113 (middle, $z$=0.894)
and SDSS~1125+0029 (top, $z$=0.865); dashed lines show zero flux for each,
and vertical dotted lines show 
Fe\,{\sc ii}*2414\AA\ \& 2632\AA\ and Mg\,{\sc ii} 2798.}
\end{figure}

The rare %FeLoBALs (Becker et al. 2000), %(White et al. 2000) actually...
LoBAL quasars with absorption from metastable excited states of
Fe\,{\sc ii} (Fe\,{\sc ii}*) 
	have been dubbed FeLoBALs 
	(Becker et al. 2000; Hazard et al. 1987; Menou et al. 2001).
	They
are valuable because photoionization modelling of them can 
constrain $n_e$ %the electron density 
in the BAL clouds (e.g. de Kool et al. 2001).
%(Menou et al. 2001).
%
Fig. 1a shows a spectacular example, SDSS~1723+5553,
with absorption from over twenty transitions in at least a dozen elements.
Fig. 1b compares SDSS~1723+5553 to two lower-$z$ FeLoBALs with [O\,{\sc ii}]
emission line redshifts.  
Both low-$z$ objects show Fe\,{\sc ii}* absorption blueward of
2414\AA\ and 2632\AA\ from %Fe\,{\sc ii}*
states up to $\sim$1~eV
above ground, but SDSS~1125+0029 %(top)
also shows %Fe\,{\sc ii}*
absorption near 2500~\AA\ %which arises 
from even more excited levels.  
In both low-$z$ objects, the Mg\,{\sc ii} BAL absorption apparently
extends 2000~km\,s$^{-1}$ {\em redward} of the 
systemic $z$. %narrow-line [O\,{\sc ii}] redshift.
%**point out partial covering / scatlight? poln=?


%\section{BAL Quasars With Extreme Mg\,{\sc ii} Absorption}

\begin{figure}
%%\plottwo{sp0410_51816_621_z0.8773.eps}{sp0356_51779_546_z1.98_r2000_3100.eps}
%\plottwo{J0300p0048sm.eps}{sp0356_51779_546sm5.eps}
\plottwo{Hallfig3.eps}{Hallfig4.eps}
\caption{SDSS LoBALs with strong absorption blueward of Mg\,{\sc ii}.
a) SDSS~0300+0048 at $z$=0.8916.
b) SDSS~1730+5850 at $z$=1.98.}
\end{figure}

Some SDSS FeLoBALs show very abrupt drops in flux near
Mg\,{\sc ii}\,$\lambda\lambda$2796,2803 (e.g. SDSS~0300+0048 in Fig. 2a).
%(for convenience, we have dropped the `p' (preliminary) and `J' (J2000)
%in the SDSS object designations).
%
%We adopt $z$=0.8916, the redshift of an associated Mg\,{\sc ii} system.
%SDSS~0300+0048 also shows narrow associated Ca\,{\sc ii} H\&K absorption at 4
%different redshifts from 2350 to 3900~km\,s$^{-1}$ blueward of the Mg\,{\sc ii}
%redshift, 
SDSS~0300+0048 has associated Mg\,{\sc ii} absorption at $z$=0.8916, 
at least 4 narrow Ca\,{\sc ii} H\&K absorption systems located 2350 to
3900~km\,s$^{-1}$ blueward of the Mg\,{\sc ii} system, and
broad Ca\,{\sc ii} absorption extending a further 2000~km\,s$^{-1}$ blueward.
%broad Ca\,{\sc ii} absorption extending a further 2000~km\,s$^{-1}$ blueward
Broad, near-total Mg\,{\sc ii} absorption is associated with the highest-$z$
Ca\,{\sc ii} system, but broad Fe\,{\sc ii}* absorption 
is associated instead with the {\em strongest} Ca\,{\sc ii} system,
%**above OK?  or rephrase from orig:  %with the strongest Ca\,{\sc ii} system, 
at slightly lower $z$.
%
Fig. 2b shows SDSS~1730+5850, which is clearly a higher redshift analogue of
SDSS~0300+0048.  Our spectrum extends farther into the UV for this $z$$\sim$2
object, and shows a weak recovery at C\,{\sc iii}]\,$\lambda$1908 but
essentially zero flux below Al\,{\sc ii}\,$\lambda$1670.
%
%Heavily absorbed 
Quasars such as these at $z\geq2$ will obviously be greatly
%	$z\geq2$ quasars such as these will obviously be %greatly
underrepresented in optical surveys. %, if not completely missed.
%	Optical surveys will miss quasars such as these if they are at $z>2$.


\section{BAL Quasars With Fe\,{\sc iii} Absorption}

\begin{figure}
%%\plotone{sp0374_51791_136_z1.47548.eps}
%\plotone{J2215m0045_z1.47548.eps}
\plotone{Hallfig5.eps}
\caption{SDSS~2215$-$0045 at $z$=1.47548.  Note the absence of strong
Fe\,{\sc ii} absorption at 2200--2600\AA\ in the rest frame.
%(The top axis plots rest wavelengths at the emission-line $z$,
%not the absorption trough $z$.)
}
\end{figure}

Fig. 3 shows SDSS~2215$-$0045, a %clearly reddened 
LoBAL at $z$=1.47548
(measured from associated Mg\,{\sc ii} absorption, as with SDSS~0300+0048).
Its absorption troughs are unusual for a LoBAL:
they are very broad, %(reaching --18,000~km\,s$^{-1}$)
detached, and strongest near the high velocity end rather than at low velocity.
%**compare w/Sri\&Pet'01
By comparison to SDSS~1723+5553 (Fig. 1), %** %above,
we initially identified the strong
trough at $\lambda_{obs}$$\sim$4900\AA\ as Cr\,{\sc ii}.  However, the implied
abundance of Cr relative to Mg is implausible, and 
the expected corresponding Zn\,{\sc ii} is missing.
%no corresponding Zn\,{\sc ii} is seen, as would be expected.  
We now believe this absorption is due to Fe\,{\sc iii} (multiplet UV 48), with
additional Fe\,{\sc iii} (UV 34) absorption at $\lambda_{obs}$$\sim$4500\AA,
redward of Al\,{\sc iii}.
Since Fe\,{\sc ii} absorption is weak or absent,
the large Fe\,{\sc iii}/Fe\,{\sc ii} ratio suggests that the BAL clouds
in this object have $T$$>$35000~K, sufficient to collisionally ionize 
Fe\,{\sc ii} to Fe\,{\sc iii}.
Fe\,{\sc iii} absorption is seen in several other SDSS LoBALs (e.g. Fig. 4)
and in a few previously known LoBALs,
%**refs for previous Fe\,{\sc iii}  
%	Q~0059$-$2735 (Hazard et al. 1987)
%	FIRST 1556+3517 \& 0840+3633 (Becker et al. 1997)
%	PC~0227+0057 (Schneider et al. 1999; Halpern, pers. comm.)
%	(Becker et al. 2000)
%	(Djorgovski et al. 2001) %0012453/89
but nowhere as strongly (alone or relative to Fe\,{\sc ii})
as in SDSS~2215$-$0045.
%Lastly,
%Note the break in spectral slope at $\sim$2400\AA,
Note the different spectral slopes blueward \& redward of $\sim$2400\AA,
indicating reddening which must occur outside the BAL region since dust
cannot survive long at $T$$>$35000~K. %in such hot BAL clouds.
%**refs for previous Fe\,{\sc ii}  
%	Q~0059$-$2735 (Hazard et al. 1987)
%	Hawaii 167 (Cowie et al. 1994)
%	Mrk 231 (Smith et al. 1995)
%	Arp 102B (Halpern et al. 1996)
%	FIRST 1556+3517 \& 0840+3633 (Becker et al. 1997)
%	(Becker et al. 2000)
%	(Menou et al. 2001)

%For comparison, the BAL flow in Q2359-1241 has 2000$<$T$<$10000~K, as
%determined from the level populations of metastable \feii* %seen in absorption
%%	and $n_e>10^5$~cm$^{-3}$
%(Arav et al. 2001).
%%	but it is possible that other effects are at work
%%	(supersolar metallicities? a density bounded outflow?)
%A number of other SDSS, FIRST and DPOSS BALs show
%%	absorption at 2070\AA,
%%	but this is the only one where it is stronger than \mgii.
%%	Very few LoBALs like this one, with stronger
%\feiii\ absorption of strength comparable to \feii\
%and/or deeper \aliii\ than \mgii, so these hot BAL clouds
%are not unique to this object.

%In particular, PC~0227+0057 (Schneider et al. 1999)
%%has been identified (J. Halpern, pers. comm.) as
%is a somewhat similar object at $z$=1.5, but with %It has
%a less extreme ratio of
%\feiii\ to \feii\ absorption, suggesting cooler clouds than in 2215-0045.
%%\mgii\ and \feiii\ absorption but weak \feii\ absorption, although the latter
%%is still stronger than in SDSS~2215-0045, suggesting somewhat cooler clouds.
%A few other SDSS, FIRST and DPOSS BALs also show absorption at 2070\AA,
%but this is the only one where it is stronger than \mgii.


\section{A LoBAL With Broad H$\beta$ Absorption}

\begin{figure}
%%\plotone{weird2.ps}
%%\plotone{w2oir.ps}
%\plotone{w2oir2.eps}
\plotone{Hallfig6.eps}
\caption{Optical-NIR spectra of SDSS~0437$-$0045 at $z$=2.74389.
Strong lines are labelled at the expected wavelengths for emission (top)
and absorption (bottom).  Note the nearly complete absorption near the expected
wavelength of C\,{\sc iv}, and the probable broad H$\beta$ absorption.}
\end{figure}

Fig. 4 shows an optical (Keck) plus NIR (UKIRT) spectrum of SDSS~0437-0045
which reveals a strongly absorbed quasar with $z$=2.74389 from [O\,{\sc iii}].  
The absorption extends 2900~km\,s$^{-1}$ redward of this $z$ (cf. Fig.~2b).
Even more remarkable is the probable presence of H$\beta$ absorption
nearly 10$^4$~km\,s$^{-1}$ wide and of REW$\sim$100~\AA.
H$\beta$ absorption in AGN has previously been seen only in NGC~4151
(Anderson \& Kraft 1969; Sergeev et al. 1999),
but with %only $\leq$3~\AA\ REW and $\leq$1000~km\,s$^{-1}$ width.
$\leq$1000~km\,s$^{-1}$ width and $\leq$3~\AA\ REW.
This object is also unusual because the Fe{\sc iii} %UV 48
trough at $\sim$2070\AA\ has been seen to vary with nearly unprecendented
amplitude and speed.
%as great as ever observed.

\section{Heavily Reddened BAL Quasars}

\begin{figure}
%%\plotone{spSpec-51666-0309-569.eps}
%\plotone{sp0309_51666_569sm7.eps}
\plotone{Hallfig7.eps}
\caption{SDSS~1456$+$0114, an extremely reddened LoBAL at $z$=2.367.}
\end{figure}

SDSS has found evidence for a population of red quasars (Richards et al. 2001),
and BALs in general are redder than the typical quasar (Menou et al. 2001),
but for the most extreme objects the reddening is unambiguous.
Fig. 5 shows SDSS~1456+0114, an extremely reddened LoBAL %**FeLoBAL ?
(and FIRST source) at $z$=2.367  
(measured from weak C\,{\sc iii}], the only broad line visible).
Several other similar objects have been found by SDSS, but with even
weaker broad emission.  Since reddening does not affect equivalent widths,
this may indicate that in these objects the broad line region is even more
heavily reddened than the continuum.  This would be quite plausible if most
of the continuum light in those objects is scattered light, a hypothesis which
can easily be tested with polarization data.


\section{Discussion}

`Well, that was disturbing.' ---Fred Hamann, after this talk at the meeting.

We prefer to view these objects as invigorating.  
The area and depth of SDSS, plus its simple selection of quasar candidates as
outliers from the stellar locus, makes it efficient at finding quasars with
unusual properties.  Moreover, the discovery of typically several examples of
each type of extreme LoBAL quasar presented here means that a {\em population}
of extreme LoBAL quasars exists and that only now, with SDSS, are we beginning
to sample the full range of properties that exist in BAL outflows, and
thus around quasars on the whole.
%
%** It also is worth noting that we have found no extreme HiBALs to date;
%that is, no BALs with extreme absorption in CIV but not in MgII.


\acknowledgements
The Sloan Digital Sky Survey 
	(SDSS)
is a joint project of The University of
Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation
Group, The Johns Hopkins University, the Max-Planck-Institute for Astronomy %,
	(MPIA), 
the Max-Planck-Institute for Astrophysics %,
	(MPA), 
New Mexico State University, Princeton University,
the United States Naval Observatory, and the University of Washington.
Apache Point Observatory, site of the SDSS telescopes,
is operated by the Astrophysical Research Consortium %.
	(ARC).
Funding for %SDSS 
	the project 
has been provided by the Alfred P. Sloan Foundation,
the SDSS member institutions, the National Aeronautics and Space Administration,
the National Science Foundation, the U.S. Department of Energy, 
	the Japanese
Monbukagakusho, and the Max Planck Society.
The SDSS Web site is http://www.sdss.org/.

\begin{references}
%
\reference Anderson, K., \& Kraft, R. 1969, ApJ, 158, 859
%
\reference Becker, R., Gregg, M., Hook, I., McMahon, R., White, R., \& Helfand, D. 1997, ApJ, 479, L93 %**
%
\reference Becker, R., et al. 2000, ApJ, 538, 72
%
\reference de Kool, M., et al. 2001, ApJ, 548, 609
%
\reference Djorgovski, S. G., et al. 2001, to appear in Mining the Sky, eds. A.
Bandel et al. (Berlin: Springer-Verlag) (astro-ph/0012489)
%
\reference Fukugita, M., Ichikawa, T., Gunn, J., Doi, M., Shimasaku, K., \& Schneider, D. 1996, AJ, 111, 1748 %**
%
\reference Gunn, J. E., \& The SDSS Collaboration 1998, AJ, 116, 3040
%
\reference Hazard, C., McMahon, R., Webb, J., and Morton, D. 1987, ApJ, 323, 263
%
\reference Menou, K., \& The SDSS Collaboration 2001, ApJ, in press (astro-ph/0102410)
%
\reference Richards, G. T., \& The SDSS Collaboration 2001, AJ, 121, 2308
%
\reference Sergeev, S., Pronik, V., Sergeeva, E., \& Malkov, Y. 1999, A\&A 341, 740
%
\reference York, D. G., \& The SDSS Collaboration 2000, AJ, 120, 1579
%
%\reference White, R., et al. 2000, ApJS, 126, 133
\end{references}


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\end{document}

--the Richards paper says 2625 QSOs, not 2326, as you say
--why are you referencing me for the first 2326 quasars
  and where does the number 96 BALs come from?  It has been a while, but
  I don't think that the Menou paper used the same data that I did for
  the colors paper.  Not that it really matters though.
--page 3, section 5: any chance this might be Fe BAL material
                   near the H-beta region
                   rather than really H-beta BAL? (I admit I've never
                   seen that before either, though...)?
--would be good in abstract and elsewhere to say "internal reddening"
--you do not say if these are included in the Menou paper 
--------------------------------------------------------------------------------
--my only comment is that the figures could stand some lablelling, or the
  text could  include more explicit ref.  to wavelengths you are referring to. 
--Figures: The labels are all much too small, and are practically
  unreadable.  The y-axes need a label (f_\lambda, 10^{-17} erg/cm^2/s/A).
  Nowhere is it described what all the vertical lines are. 
--Emphasize that these objects have *wild* colors!
--Section 1: You mention this later, but I would put a sentence or two
  in here about the quasar target selection: we look at anything outside
  the stellar locus to first order, which allows us to find quasars with
  broad-band colors very different from "ordinary" quasars.  
--Acknowledgements: This is actually slightly out of date.  Go to
  www.sdss.org, and get the latest version of this. 


