Deep Searches for High Redshift Molecular Absorption
S. J. Curran and J. K. Webb
%We present the results of our millimetre wavelength scans for new redshifted %molecular absorbers towards visually dim quasars. Millimetre-band scans of the frequency space towards optically dim quasars is potentially a highly efficient method for detecting new high redshift molecular absorption systems. Here we describe scans towards 7 quasars over wide bandwidths (up to 23 GHz) with sensitivity limits sufficient to detect the 4 redshifted absorbers already known. With wider frequency bands, highly efficient searches of large numbers of possibly obscured objects will yield many new molecular absorbers.
curran-jd21.tex
%&latex209 
\documentstyle[11pt,newpasp,twoside]{article} %original

\markboth{S. J. Curran, J. K. Webb, M. T. Murphy \& N. Kuno}{ASP Conf. Ser. Style}
\pagestyle{myheadings}
%\nofiles %supresses .aux file and therefore bibtex

% Some definitions I use in these instructions.

\def\emphasize#1{{\sl#1\/}}
\def\arg#1{{\it#1\/}}
\let\prog=\arg

\def\edcomment#1{\iffalse\marginpar{\raggedright\sl#1\/}\else\relax\fi}
\marginparwidth 1.25in
\marginparsep .125in
\marginparpush .25in
\reversemarginpar

%%%%% AUTHORS - PLACE YOUR OWN MACROS HERE %%%%%
\def\kms{km ${\rm s}^{-1}$}
\def\eg{{\it e.g.\ }}
\def\ie{{\it i.e.\ }}
\def\cf{{\it c.f.\ }}
\def\nb{{\it N.B.\ }}
\def\etal{{\it et al.\ }}
\def\etc{{\it etc.\ }}
\def\mag{$^{\rm m}$}
\def\ch2{$\chi^2$}
\def\dg{$^{\circ}$}
\def\dgm{^{\circ}} %already in math mode
\def\min{$^{\prime}$}
\def\sec{$^{\prime\prime}$}
\def\hr{$^h$}
\def\mn{$^m$}
\def\dtt{\delta T/T}
\def\half{$\frac{1}{2}$}
\def\quar{$\frac{1}{4}$}
\def\inv{$^{-1}$}
\def\Lo{L$_\odot$}
\def\Mo{M$_\odot$}
\def\Mom{{\rm M}_\odot} %for when already in math mode 
\def\Moy{M$_\odot$~yr$^{-1}$}
\def\SFR{L$_\odot ~{\rm M}_\odot^{-1}$}
\def\SFRC{L$_\odot ~{\rm M}_\odot^{-1},$}
\def\SFRF{L$_\odot ~{\rm M}_\odot^{-1}.$}
\def\um{$\mu m$}
\def\erf{\mbox{erf}}
\def\erfc{\mbox{erfc}}%
\def\AU {{\footnotesize AU}}
\def\solmass {$\hbox{M}_\odot$}
\def\solm {$\hbox{M}_\odot$}
\def\solum {$\hbox{L}_\odot$}
\def\Loc {$\hbox{L}_\odot$,}
\def\Los {$\hbox{L}_\odot$.}
\def\rhounit {$\hbox{M}_\odot\ts \hbox{pc}^{-3}$}
\def\kms {\hbox{${\rm km\ s}^{-1}$}}
\def\kmss {\hbox{${\rm km\ s}^{-1}$.}}
\def\kmsc {\hbox{${\rm km\ s}^{-1}$,}}
\def\kmsp {\hbox{${\rm km\ s}^{-1}{\rm pc}^{-1}$}} % km s-1 parsec-1
\def\vlsr {\hbox{${\rm v}_{\rm lsr}$}}
\def\delv{\hbox{$\Delta v_{1/2}$}}
\def\ccm {$\hbox{{\rm cm}}^{-3}$}    %cm-3
\def\scm  {$\hbox{{\rm cm}}^{-2}$}    %cm-2
\def\cm {$\hbox{{\rm cm}}^{-1}$}    %cm-1
\def\cmsix  {$\hbox{{\rm cm}}^{-6}$}  %cm-6
\def\arcsec {\hbox{$^{\prime\prime}$}}
\def\farcs{\hbox{$.\!\!^{\prime\prime}$}}
\def\h {\hbox{$^{\rm h}$}} %hours
\def\m {\hbox{$^{\rm m}$}} %min
\def\s {\hbox{$^{\rm s}$}} %sec
\def\arcmin {\hbox{$^{\prime}$}}
\def\deg {\hbox{$^{\circ}$}} %degrees
\def\Jyb {\hbox{${\rm Jy\ beam}^{-1}$}}
\def\MOLH {\hbox{${\rm H}_2$}}  %H2
\def\WAT {\hbox{${\rm H_{2}O}$}} %H2O
\def\HTWO {\hbox{${\rm H_{2}O}$}}
\def\MOLO {\hbox{${\rm O}_2$}}  %O2
\def\HDO {\hbox{${\rm HDO}$}}  %HDO%
\def\rr {\rightarrow}
\def\imp {$\Rightarrow$}
\def\mimp {\Rightarrow} 
\def \AL {$\alpha $}     %  gr. alpha
\def \BE {$\beta $}     % gr. beta
\def \GA {$\gamma $}    % gr. gamma
\def \HI {H{\sc \,i}}

\def\lapp{\ifmmode\stackrel{<}{_{\sim}}\else$\stackrel{<}{_{\sim}}$\fi}
\def\gapp{\ifmmode\stackrel{>}{_{\sim}}\else$\stackrel{>}{_{\sim}}$\fi}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}
\title{Deep Searches for High Redshift Molecular Absorption}
\author{S. J. Curran and J. K. Webb}
%\affil{School of Physics, University of New South Wales, Sydney NSW 2052, Australia}
\affil{School of Physics, University of New South Wales, NSW 2052, Australia}
\author{M. T. Murphy}
\affil{Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK}
\author{N. Kuno}
\affil{Nobeyama Radio Observatory, Nagano 384-1305, Japan} 
%\affil{Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano, 384-1305, Japan} 
%\author{Y. M. Pihlstr\"{o}m}
%\affil{National Radio Astronomy Observatory, Socorro, NM 87801, USA}
%\author{J. K. Webb}
%\affil{School of Physics, University of New South Wales, Sydney N.S.W. 2052, Australia}   
  
\begin{abstract}
%We present the results of our millimetre wavelength scans for new redshifted
%molecular absorbers towards visually dim quasars.
Millimetre-band scans of the frequency space towards optically dim
quasars is potentially a highly efficient method for detecting new
high redshift molecular absorption systems. Here we describe scans
towards 7 quasars over wide bandwidths (up to 23 GHz) with sensitivity
limits sufficient to detect the 4 redshifted absorbers already
known. With wider frequency bands, highly efficient searches of
large numbers of possibly obscured objects will yield many new
molecular absorbers.

\end{abstract}

\section{Introduction}

Webb et al. (these proceedings) discussed constraints on possible
variations in fundamental constants offered by quasar absorption lines. Optical studies
(Webb et al. 1999; Murphy et al. 2003) find a
statistically significant variation of the fine-structure constant,
$\Delta\alpha/\alpha \approx (-0.54 \pm 0.12)\times 10^{-5}$, over the
redshift range $0.2 < z_{\rm abs} < 3.7$.  Comparison between \HI-21cm and
molecular rotational (millimetre) absorption lines can yield an order of
magnitude better precision (per absorption system) than these purely
optical constraints (Drinkwater et al. 1998; Carilli et al. 2000; Murphy
et al. 2001): a statistical sample of \HI-21cm/mm comparisons will provide
an important cross-check on varying-$\alpha$. Currently, however, only 4
such redshifted millimetre absorption systems are known (Wiklind, these
proceedings). To increase this number we have employed the following
search strategies:

\begin{enumerate}
  \item Deep integrations of damped Lyman-alpha absorbers (DLAs),
    the highest column density ($N_{\rm HI}\gapp10^{20}$ cm$^{-2}$)
    quasar absorbers known. Since we observe at a known redshift
    and therefore frequency, optical depth limits better than $\tau\lapp0.1$
    are often obtained. The DLA results are discussed in detail by Curran et al. (2004).
    \item Scanning the frequency space towards visually dim millimetre
      bright quasars in search of a possible absorber responsible for
      the visual obscuration. Here we summarise our results as obtained
      with the Swedish-ESO Sub-millimetre Telescope (SEST) and 
      Nobeyama Radio Observatory's 45-m telescope (NRO).
\end{enumerate}
%\newpage
\section{Results}
From an extensive literature search we selected four millimetre-loud
quasars yet to be optically identified (Table 1, top).
\begin{table}
\begin{center}
\caption{The SEST (top) and NRO (bottom) search results. $V$ is
the visual magnitude with the Galactic extinction, $A_B$,
given. $z_{\rm em}$ is the quasar redshift, $S$ the approximate
flux density in Jy at the observed frequency band, $\nu$, and $\tau$ is the
typical $3\sigma$ optical depth limit (quoted for a resolution of 1 \kms, see Curran et al. 2002).}
\begin{tabular}{l c c c c c   c  c }			
\noalign{\smallskip}
\tableline
\noalign{\smallskip}
Quasar & $V$ & $A_B$ & $z_{\rm em}$ & Ref & $S$ & $\nu$ [GHz] & $\tau$ \\
% & & & & HCN/HCO$^+$ & CO & \\
\noalign{\smallskip}
\tableline
\noalign{\smallskip}
0500+019 & 21.2 & 0.289 & 0.58457 & 2 & 0.5 & 78.30--80.90 & 2\\
...&...& ...& ...&...&0.5 & 85.50--86.50 & 0.8\\
...&...& ...& ...&...&0.5 & 112.10--113.10 & 0.8\\
...&...& ...& ...&...&0.4 & 130.00--141.40 & 1 \\
0648--165 & -- & 2.456 & -- & -- & 1.6 & 78.30--80.90 & 0.2 \\
...&...& ...& ...&...&1.5 & 83.90--90.50 & 0.2\\
...&...& ...& ...&...&0.7 & 138.00--141.40 & 0.5 \\
...&...& ...& ...&...&0.6 & 142.80--149.40 & 0.7 \\
0727--115 & 22.5 & 1.271 & -- & -- & 2.9 & 78.30--80.90 & 0.2 \\
...&...& ...& ...&...& 2.7 & 83.90--90.50 & 0.1 \\
...&...& ...& ...&...&1.5 & 138.00--141.40 & 0.2 \\
...&...& ...& ...&...&1.2 & 142.80--148.60 & 0.4 \\
1213--172 & 21.4 & 0.253 & -- & -- &  1.0& 78.30--80.90 & 0.4 \\
...&...& ...& ...&... & 0.9 & 83.90--90.50 & 0.4 \\
...&...& ...& ...&... & 0.5 &138.00--141.40 & 0.8 \\
...&...& ...& ...&... & 0.4& 142.80--151.00 & 1\\
\noalign{\smallskip}
\tableline
\noalign{\smallskip}
0742+103 & $\sim24$ &0.111 & -- & --& 0.6 & 46.90--47.50  & --\\
...&...& ...& ...&...&0.4&77.25--87.50 & 0.9\\
...&...& ...& ...&...&0.4&88.45--89.35 & 0.4\\
1600+335 & 23.2& 0.137 &1.1 & 3 &0.7 &46.90--47.50 & 2\\
...&...& ...&...&...&0.5& 77.25--87.50 &0.5\\
...&...& ...&...&...&0.5& 88.45--89.35 &0.4\\
1655+077 & 20.1 &0.66& 0.621 & 1 &1.5 &46.90--47.50 &1 \\
...&...& ...& ...&...&1.2&77.25--87.50 &0.7\\ 
...&...& ...& ...&...&1.2&88.45--89.35 &0.3\\ 
\noalign{\smallskip}
\tableline
\noalign{\smallskip}
\end{tabular}
{References: (1) Wilkes (1986), (2) Carilli et al. (1998), (3) Snellen et al.~(2000).}
%\citet{wil86}, (2) \citet{cmr+98}, (3) \citet{ssm+00}.}
%\label{t1} %float is put after label - change \ref{t1} to 1, etc
\end{center}
\end{table}
%tried to put table 2 on own but just wasted space
For each of these we performed a spectral scan along the
line-of-sight. The high sensitivity and large bandwidth (1 GHz),
combined with the possibility of observing simultaneously with two
receivers, permitted us to scan a range of $\approx10$ GHz in both the
2-mm and 3-mm bands. Over these ranges we reached optical depth limits
in both bands sensitive enough the detect the 4 known redshifted
millimetre absorbers (Table 1 cf. $\tau\approx0.7{\rm ~to~}\approx2$
at $\gapp4$ \kms ~resolution), although no $\geq3\sigma$ absorption
features were found (Murphy, Curran \& Webb 2003).

Of the remaining visually dim quasars, 10 have 3-mm flux densities
$\gapp0.5$ Jy. Four of these are located in the north and with the
NRO\footnote{The fact that each of the 6 AOSs on the NRO only covers
0.25 GHz is compensated by the high efficiency of the 45-m antenna (4
Jy K$^{-1}$ cf. 25 Jy K$^{-1}$ at SEST).} we were able to observe the
three listed in Table 1.  While the 6-mm limits are poor, again at
3-mm our search is sensitive enough to detect the 4 known absorbers
over the observed redshift range: For the $J=0\rightarrow1$,
$1\rightarrow2$ and $2\rightarrow3$ of transitions CO, HCN and
HCO$^+$, i.e. the most commonly detected transitions in the 4 known
absorbers, the observed frequencies give a 50\% coverage for 0742+103
up to $z\approx3$ and 30\% for both 1600+335 and 1655+077 up to the
emission redshift\footnote{Note that we have included the possibility
of HCN or HCO$^+$ $0\rightarrow1$ Galactic absorption towards all 3
sources as well as HCN or HCO$^+$ $1\rightarrow2$ in the host of
1600+335.}. The coverage for the SEST sources are discussed in Murphy,
Curran \& Webb (2003); for the above transitions up to 90\% is achieved
due to the large bandwidth and dual receiver capability.


%\citet{sjss95}

%\begin{figure}
%	\vspace{5.4cm} \setlength{\unitlength}{1in}
%\special{psfile=coverage-crop.eps hoffset=-210 voffset=-155 hscale=100 vscale=100 angle=0}
%\caption{Redshift coverage...}
%\label{f1}
%\end{figure}

%\newpage

%\section{Summary}

%see i-table2.tex for abstract/summary version

%as usual - paste in .bbl and comment these out


%This research has made use of the NASA/IPAC Extragalactic
%Database (NED) which is operated by the Jet Propulsion Laboratory,
%California Institute of Technology, under contract with the National
%Aeronautics and Space Administration.

%\bibliographystyle{/home/sjc/styles/apj}
%\bibliography{aa,ref}
%\expandafter\ifx\csname natexlab\endcsname\relax\def\natexlab#1{#1}\fi
%need for mn2e to work properly

\begin{references}

\reference {Carilli}, C.~L., {Menten}, K.~M., {Reid}, M.~J., {Rupen}, M.~P., \& {Yun},
  M.~S. 1998, ApJ, 494, 175

\reference {Carilli}, C.~L., {Menten}, K.~M., {Stocke}, J.~T., {Perlman}, E., {Vermeulen},
  R., {Briggs}, F., {de Bruyn}, A.~G., {Conway}, J., \& {Moore}, C.~P. 2000,
  PhRvL, 85, 5511

\reference Curran, S.~J., Murphy, M.~T., Webb, J.~K., Rantakyr\"{o}, F., Johansson, L.
  E.~B., \& Nikoli\'{c}, S. 2002, A\&A, 394, 763

\reference Curran, S.~J., Murphy, M.~T., Pihlstr\"{o}m, Y.~M., Bolatto, A.~D., Bower,
  G.~C., \& Webb, J.~K. 2004, MNRAS, in preparation


\reference  {Drinkwater}, M.~J., {Webb}, J.~K., {Barrow}, J.~D., \& {Flambaum}, V.~V. 1998,
  MNRAS, 295, 457

\reference Murphy, M.~T., Curran, S.~J., \& Webb, J.~K. 2003, MNRAS, 342,
  830

\reference Murphy, M.~T., Webb, J.~K., \& Flambaum, V.~V. 2003, MNRAS,
  accepted (astro-ph/0306483)

\reference Murphy, M.~T., Webb, J.~K., Flambaum, V.~V., Drinkwater, M.~J., Combes, F., \&
  Wiklind, T. 2001, MNRAS, 327, 1244

\reference {Snellen}, I.~A.~G., {Schilizzi}, R.~T., {Miley}, G.~K., {de Bruyn}, A.~G.,
  {Bremer}, M.~N., \& {R{\" o}ttgering}, H.~J.~A. 2000, MNRAS, 319, 445

\reference {Steppe}, H., {Jeyakumar}, S., {Saikia}, D.~J., \& {Salter}, C.~J. 1995, A\&AS,
  113, 409

\reference {Webb}, J.~K., {Flambaum}, V.~V., {Churchill}, C.~W., {Drinkwater}, M.~J., \&
  {Barrow}, J.~D. 1999, PhRvL, 82, 884

%\reference {Wiklind}, T. \& {Combes}, F. 1996, in ESO Symposia, ed. P.~Shaver (Springer), 86

\reference {Wilkes}, B.~J. 1986, MNRAS, 218, 331

\end{references}

\end{document}
