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\title{A blind survey for molecular gas in a {$z$\/} = 2.84  proto-cluster of galaxies}


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\author
{ Scott Chapman,$^{1\ast}$ Colin Ross,$^{1}$ Manuel Aravena,$^{2}$ Andrew Blain,$^{3}$
Jim Geach,$^{4}$\\
Mark Gurwell,$^{5}$ Rob Ivison,$^{6}$Naveen Reddy,$^{7}$
Ian Smail,$^{8}$ Chuck Steidel$^{9}$\\
\\
\scriptsize{$^{1}$Department of Physics and Atmospheric Science, Dalhousie University, Coburg Road Halifax, B3H 4R2}\\
%\normalsize{An Unknown Address, Wherever, ST 00000, USA}\\
\scriptsize{$^{2}$European Southern Observatory, Alonso de C\'{o}rdoba 3107, Vitacura, Santiago, Chile,}\\
\scriptsize{$^{3}$Physics and Astronomy, University of Leicester, University Road Leicester, LE1 7RH}\\
\scriptsize{$^{4}$Department of Physics, Ernest Rutherford Building, 3600 rue University, McGill University, Montreal, QC, H3A 2T8, Canada}\\
\scriptsize{$^{5}$Harvard CfA}\\
\scriptsize{$^{6}$UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ}\\
\scriptsize{$^{7}$Department of Physics and Astronomy, UC Riverside, 900 University
Avenue, Riverside, CA 92521}\\
\scriptsize{$^{8}$Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE}\\
\scriptsize{$^{9}$Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MS 249-17, Pasadena, CA 91125, USA}\\
\\
\scriptsize{$^\ast$To whom correspondence should be addressed; E-mail:  scott.chapman@dal.ca.}
}

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\begin{sciabstract}
%  Galaxy evolution.
%  Survey for CO in the highest overdensity of galaxies known at {$z$\/}=2.84
Measuring the evolution of  molecular gas density is  critical to understand the formation of molecular gas and stars in galaxies.
However, the gas supplies, star formation efficiencies, and starburst modes  (merger driven versus quiescent disk) may vary strongly as a function of their local density, and comparing the CO properties of galaxies in protoclusters to the field will elucidate the stronger evolution seen in overdense regions.
In this letter, we describe a blind 3mm search for CO(3-2) molecular gas from $z\sim2.8$ galaxies  in  the most overdense galaxy cluster known at $z$$>$$2$, from the Keck Baryonic Structure Survey (Rudie et al.\ 2012). The extremely strong clustering of galaxies in angular scales and  along the line of sight effectively increases the number of galaxies observed within a single pointing with the IRAM-PdBI.
%The galaxy clusters have $>4\times$
%the surface density of Lyman-alpha emitters (LAEs) compared to the average among the rest of the sample of $\sim10$ fields covered to a similar depth.
From the known $\sim22$ PdBI-targeted galaxies in this structure and their SFRs, we expect to detect at most two CO line emitters, scaling from field galaxy studies. However, we find five CO lines with S/N$>$5 associated to known UV-bright protocluster galaxies, and as many as 8 $z\sim2.84$ CO line emitters in total.
This provides a solid  constraint on the evolving CO luminosity function in  overdense fields.
The higher than expected fraction of galaxies with large CO gas masses tells us that this overdense region is in a process of forming stars at a tremendous rate.
%{\bf MORE}
We compare gas/dynamical masses and the Millenium simulation to constrain how rare such structures are, finding that one is expected every $\sim$20 deg$^2$ on the sky.
We also constrain our findings empirically using the lack of similar clustering in the CO surveys of Bothwell et al.\ (2013) and Tacconi et al.\ (2010), and Daddi et al.\ (2010), where no additional CO sources beyond the targeted source are found in the vicinity of $>$50 PdBI fields.
 %
The higher detectability rate is likely because the cluster galaxies are more biased, and hence more massive, than the field, as found from the large measured stellar masses of 4 of 6 of our CO emitters.
This appears to be the gas equivalent of the reversal in the relation claimed at $z\sim1.5-2$ for star formation and environment, %(papers by vy tran and kodama) - 
with the cluster population having higher gas masses than the field.
%
%would be interesting to add these to the gas fraction-redshift plot from geach's 2011(?) paper.
%
\end{sciabstract}



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\section*{Introduction}

One of the major goals of modern observational cosmology is to understand how the gas in the diffuse interstellar medium (ISM) of galaxies converts into stars and how both phases evolve with cosmic time. A major advance has been the determination of the evolution of the SFR density of the Universe. Deep optical and radio surveys indicated that the SFR density steadily increases from $z=5$, with a peak at $z\sim3-1$, and steeply declines from $z=1$ to the present {Lilly1996, Madau1996, Cowie1999, Steidel1999, Giavalisco2004, Ouchi2004, Bouwens2007, Smolcic2009}. Although the contribution from luminous, merger-driven starburst galaxies at high-redshift to the SFR density appears to be significant, the population that drives such evolution appears to be formed by more quiescent massive star-forming galaxies {Daddi2007, Rodighiero2011}. The close relationship between the SFR and the amount of molecular gas in galaxies, from which stars form, suggest that the evolution of the SFR density is the result of the evolution of the molecular gas density in galaxies across cosmic times. 

Measuring the evolution of this molecular gas density is thus critical to understand the formation of molecular gas and stars in galaxies. For this, it is necessary to perform blind surveys of the sky that allow us to measure the molecular gas content in a CO flux limited sample as a function of redshift and luminosity [ e.g. observations in the local Universe and simulations by ] {Keres2003, Obreschkow2009a, Obreschkow2009b}. The technical limitations (e.g. bandwidth, sensitivity) of current submillimeter and radio facilities, along with the intrinsic faintness of the CO emission lines used to measure the amount of molecular gas in galaxies have, however, precluded such studies. 

\section*{Observations and Sample}

We have obtained a deep PdBI pointing tuned to redshifted CO(3-2) in the 3mm band for the H1549, % field and a single pointing in the 
%H1700 and Q2345 
galaxy overdensity field (Steidel et al.\ 2005, 2010), depicted in Fig.~1. 
%for which we have recently obtained  deep (S$_{850\mu m}$$\sim$0.8mJy rms) SCUBA-2 images (Figs.~3,4). 
Because of its minimal excitation requirements,  CO J=3-2 offers the best  view of the mass/distribution of star forming gas in a range of galaxy types/luminosities. %metal-enriched H$_2$ (e.g., Ivison et al.\ 2011, Riechers et al.\ 2011, Harris et al.\ 2011).
The extremely strong clustering of galaxies in angular scales and importantly along the line of sight, $\sim$2000~km/s line of sight depth for the FWHM of the galaxy N($z$), makes it possible to effectively increase the number of galaxies observed within the PdBI-WIDEX  pointing. %and single frequency tuning.

The  target field was chosen from the 24 survey fields of the Keck Baryonic Structure Survey (KBSS -- e.g., Rudie et al.\ 2012).  Several of these fields show strong galaxy overdensities (e.g., Steidel et al.\ 2000, 2005, 2010), and together represent a complete, unbiased census of  overdensities in a well-calibrated field galaxy survey at $z>2$.
%
The H1549  field targeted in this study represents the strongest overdensity ($z$$\sim$2.84) found in the KBSS,
%$z\sim2.8$ galaxy cluster was discovered as a strong redshift spike in the H1549 survey field from Steidel et al.\ (2010) 
and has $>5\times$
the surface density of Lyman-alpha emitters (LAEs) compared to the average among $\sim20$ fields covered to a similar depth, representing
%{\it In fact, as far as we are aware, H1549 is 
the richest field of Ly$alpha$-selected objects ever observed, at any redshift.

We have also observed this field with SCUBA2 at 850$\mu$m and 450$\mu$m down to a 1$\sigma$ RMS of 0.8~mJy.
The SCUBA2 map at 850$\mu$m is overlaid on the IRAC 4.5$\mu$m map in Fig.~1, where significantly detected CO(3-2) sources consistent with lying in the protocluster are highlighted.


We detect, at  $>5\sigma$ %and $\sim4\sigma$ level, 
the CO $3-2$ emission line from five galaxies known to be at $z\sim2.84$ with available spectroscopic redshifts (Table~1), an additional three known $z\sim2.84$ galaxies at $>3.5\sigma$, and one candidate $z\sim2.84$ CO emitter with no known optical counterpart (C1 in Table~1).
We find $L'_\mathrm{CO}$ ranges from $(3.9\pm1.1)\times10^{10}$ K km s$^{-1}$ pc$^2$ to $(1.3\pm0.4)\times10^{10}$ K km s$^{-1}$ pc$^2$. SCUBA2 detects at 850$\mu$m, an unresolved complex of emission encompassing 4 of the strongest CO line emitters in this structure, with 450$\mu$m emission detected over the central two sources. These galaxies are also detected with {\it Spitzer} at 24 $\mu$m.  The CO detected galaxies are shown individually in Fig.~2.


\section*{Results}

{\bf Constraints on optical-CO properties in a dense environment: }

 In Fig.~3 we show the predicted cosmic evolution of the space density of CO emitting galaxies as a function of CO luminosity (CO luminosity function) at redshifts $z$ = 0--2. 
%The space density of CO emitters measured in the local Universe (Keres et al.\ 2003) are shown. The space density derived from Aravena et al.\ (in press) 4 CO 
%detections in the COSMOS $z$=1.5 overdense field targeted with JVLA are highlighted, and compared to an estimate of space density of CO emitters derived from the 6 BzK star-forming galaxies at $z$=1.5 (Daddi et al. 2010).
%
Our CO survey of star forming galaxies in the H1549, H1700, and Q2345 clusters will add significantly to our understanding of the optical-CO properties and the gas fractions of star forming galaxies in overdense regions at $z$$\sim$2.5, characterizing the CO(3-2) of the higher gas mass range of galaxies individually, and the lower range of M$_{\rm H_2}$ on average (through stacking). 
Since the overdensities themselves are well characterised relative to the field, they will provide an important baseline for  comparing with the field luminosity function that is emerging from other studies (e.g., Walter et al.\ 2012, Geach et al.\ 2012). The dense environment will likely bias the evolution of galaxies in the region differently than in the field -- in fact we will be able to start to characterize the effect of the large overdensity on the gas supplies and star formation modes with our CO detections and stacked CO properties. 

Through our blind survey of  CO(3-2) gas in this field, we have begun to assess the importance and variation of gas supply to the 
reversal of the star formation-density relation at $z$$>$2 (e.g., Tran et al.\ 2011), understanding for the first time the star formation efficiencies leading to the 
exceptionally high levels of star formation found in our cluster cores.
We  use the sample of 40 CO-observed  SMGs (Bothwell et al.\ 2012) and the census of CO(3-2) in normal $z$=1-2 star forming galaxies (Tacconi et al.\ 2010, Daddi et al., 2010) as a "field" comparison.  
%can the motivation be made more quantitative - what flux limits/mass limits will you get to from the stacking, is it feasible that detections will be made at those limits (any theory predictions?)
CO emission is the standard probe of gas mass in these high-redshift galaxies, but suffers from uncertainties in CO -H$_2$ conversion (factor 4 difference between the Bothwell et al.\ SMGs and Tacconi et al.\ SF galaxies). A comparison of dynamical, stellar, and molecular gas masses in these galaxies will allow us to constrain the variation of CO-H$_2$ conversions across the protocluster population versus the field population (e.g., Genzel et al.\ 2012).
%, including variations from metallicity (LBGs versus Ly$\alpha$ emitters). 
We  thus begin to calibrate the average SF-efficiencies in star forming galaxies in  protoclusters versus the field.


\section*{Discussion}

In this work, we have presented deep CO $3-2$ line observations of galaxies located in a galaxy cluster candidate at $z=2.84$ using the IRAM PdBI. The candidate cluster was identified using the red-sequence technique and is associated to an overdensity of $\sim\times10$ of star-forming galaxies. We use the spatial clustering and expanded bandwidth of the PdBI to simultaneously observe the CO emission from 22 galaxies with available optical spectroscopic redshifts in a single pointing and frequency setting. 

%and with {\it Herschel} at 250 $\mu$m and 350 $\mu$m. While modeling of their dust properties indicates total IR luminosities of $5.7\times10^{11}\ L_\odot$ and $9.5\times10^{11}\ L_\odot$, respectively, characterization of their multi-wavelength SEDs suggests both are young star-forming galaxies that have formed a significant fraction of their stellar content, with stellar masses of $4.5\times10^{10}\ M_\odot$ and $6.0\times10^{10}\ M_\odot$, respectively. 

We performed a blind search for significant ($>3.5\sigma$) emission line peaks in the PdBI data cube around the position of optical sources that were selected to have spectroscopic redshift in the range $z=2.74-2.86$ covered by our PdBI 
frequency band. We find 6 sources in the protocluster at $>5\sigma$, and an additional 3 protocluster galaxies have detected CO line emission at lower signfiicance.

{\bf Chance probabilities and monte carlo experiment.}

% and limited to $K_S<23.5$. This selection criteria ensures an accurate photometric redshift, while selecting galaxies with stellar masses $>2\times10^9\ M_\odot$. We find that 2 of these selected optical galaxies are associated with significant emission line peaks ($>4\sigma$), which are thus identified as CO $1-0$ line emission candidates. Both galaxies, ID 51207 and ID 51380, are found to have photometric redshifts in the range $1.4-1.6$. Based on Monte Carlo simulations of the distribution of such emission line peaks in the field, we find that any optical galaxy that follows our selection criteria and is located within $1''$ from a candidate emission line peak is statistically unlikely to be associated to such peak by chance. In the case of ID 51207, such probability is $3.7\%$ while for ID 51380 we find 10\%. Using in parallel a Bayesian inference approach to select emission line peaks in the data cube, we recover both CO-emitting candidate sources. Here, the line identified with ID 51380 is found to have a probability of $70\%$ of being a CO emission line, however the line identified with ID 51207 is found to have a rather low probability of 13\%.  

We find CO based spectroscopic redshifts compared to optical redshifts as listed in Table~1.
%of 1.530 and 1.551 with $L'_\mathrm{CO}=(1.03\pm0.25)\times10^{10}$ K km s$^{-1}$ pc$^2$ and $L'_\mathrm{CO}=(1.12\pm0.26)\times10^{10}$ K km s$^{-1}$ pc$^2$ for ID 51207 and ID 51380, respectively. These galaxies, ID 51207 and ID 51380, are detected a
The 24 $\mu$m and 850 $\mu$m with {\it Spitzer} and {\it JCMT}  lead to IR luminosities ranging from $11.9\times10^{11}\ L_\odot$ to $3.3\times10^{11}\ L_\odot$. In 3 cases,  optical/IR SED suggest a $\sim$1 Gyr old, very massive star forming galaxy, with a stellar mass of $1.1\times10^{11}\ M_\odot$, while for two others the SED indicates that it corresponds to a young star-forming galaxy, with a stellar mass of $2.8\times10^{10}\ M_\odot$. 
For the quasar host and the companion galaxy next to it, we are unable to accurately constrain the stellar emission.

We measured the space density of CO galaxies compared to the space density of CO emitters estimated from UV-selected galaxies with high SFRs from Tacconi et al.\ (2010), and the 6 BzK galaxies significantly detected in CO emission by Daddi et al.\ (2010), and compared to predictions from semi-analytic simulations. Overall, we find that all observations are only roughly consistent with the simulations, despite the low number of detections of typical star-forming galaxies at high-redshift. Clearly, observations of molecular gas from a statistically significant sample of these galaxies is necessary to measure the evolution of CO luminosity function with redshift, and thus constrain models of galaxy formation and evolution. We conclude by discussing the advantages of performing deep CO observations of star-forming galaxies in clustered fields compared to blank-fields in the sky. 

\section*{Conclusions}

The determination of redshifts for galaxies based on (sub)millimeter and radio wavelength observations have been focused on the IR brightest sources, favored by the expanded bandwidth of such facilities. Based on the relationship between IR and CO luminosities, an IR bright galaxy, such as an SMG, is likely to also have bright CO emission. This facilitates a high significance ``blind''  CO emission line detection along the line of sight, leading to an accurate redshift measurement. In such studies, the position of their targets are known a priori, usually derived from large blank-field IR/submm surveys, permitting to spatially guide the CO observations, being thus not really ``blind'' CO detections %\citep
%{Weiss2009, Lestrade2010,  Lupu2010, Frayer2011,Scott2011, Cox2011, Riechers2011b, Combes2012}. However, serendipitous CO line detections, where the locations and redshifts of the gas-rich galaxies were  not anticipated have been reported %\citep
%{Daddi2009a, Daddi2009b, Lestrade2010}.

Blind spectroscopic imaging of the sky with large bandwidths have a huge potential for discovery of gas-rich, optically and IR faint galaxies, however they require deep integrations to ensure significant emission line detections, at the $\sim10\sigma$ level, and unequivocally identify the galaxies and their redshifts. In the absence of such high signal-to-noise detections, observations need to be guided by well-known optical, IR or radio positions and by accurate photometric redshifts. As shown in this work, focused line observations of clustered fields at high-redshift have the advantage to increase the likelihood of finding gas emission using a limited bandwidth. This approach reduces the required observing time compared to purely blank fields, where besides the need to cover a substantial area of the sky, it is necessary either to cover a reasonable range in frequency (e.g. a full 3 mm band for ALMA,% a full K or Q band with JVLA)
 in order to contain emission lines at different redshifts. %, or to perform ``spot-checks'' at a given redshift.





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\noindent {\bf Fig. 1.} 
%Please do not use figure environments to set
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%
Sources in the field of H1547 at different wavelengths. 
 The white circle represents the location of the PdBI pointing and primary beam (PB) FWHM.   Red contours show SCUBA2 850$\mu$m map at contours starting at 2$\sigma$ spaced by 1$\sigma$. Background image is IRAC 4.5$\mu$m -- the rest frame 1.6$\mu$m at $z=2.84$. Blue circles show the CO(3-2) detections in Table~1, drawn at the size of the PdBI beam ($\sim3''$).
Projected number density of galaxies with $z_\mathrm{phot}=2.80$--2.86 and SFR $>10$ M$_\odot$ yr$^{-1}$ in a $3'\times3'$ region around the cluster center. Should show with grayscale and contours  the density of galaxies in this field, $\delta_C$, given in terms of the average density $\delta_0$ of similarly selected galaxies in the h1549 field, $\delta = \delta_C/\delta_0$. %Contours range from 2 to 7 in steps of +1.

\noindent {\bf Fig. 2.} CO(3-2) line detections ($>5\sigma$) of  five  $z$$\sim$2.84 galaxies in the field.  The first spectrum and channel map shows the two central sources which are blended together in the PdBI beam, but separate out by 2$''$ in the respective channel maps of the two sources. The other three CO sources are relatively isolated, although both D14 and NB63 may have contributions from more than one galaxy. Three other candidate  CO detections are found at lower signficance (3.5-4.4$\sigma$). One further $>5\sigma$  source is not identified with any known optical galaxies, the high significance of the CO detection suggests it may be very faint, obscured, starbursting systems in the protocluster.
No other known galaxies are detected  outside of the protocluster.

\noindent {\bf Fig. 3.} 
Predicted (Obreschkow et al.\ 2009) cosmic evolution of the space density of CO emitting galaxies  %as a function of CO1-0 luminosity (CO luminosity function) 
at redshifts $z$=0 (gray solid line, plus Keres et al.\ 2003 measurements), $z$=1 (black dashed line), $z$=3 (black solid line). %The gray open circles show the space density of CO emitters measured in the local Universe (Keres et al.\ 2003). 
%The black filled circle shows 
Also shown, the space density of 2 CO detections from a JVLA pointing in the COSMOS field (black filled), %The gray open square represents the space density obtained considering only the 2 spectroscopically confirmed galaxies. The black open circle shows the estimate of space density of CO emitters derived from 
the 6 BzK star-forming galaxies at $z$=1.5 (Daddi et al.\ 2010 -- black open). Our PdBI observations will provide key constraints on the CO(3-2) luminosity distribution in  well characterized, highly overdense regions, which can be compared with the field population.

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%Webb T., et al., 2009, ApJ, 692,1561% $\bullet$
%\item[29.]
%Yang Y., et al.,  2012, ApJ, 744,178 
%J. Wynckin, L. Blinckin, F. Nodd, {\it J. Geophys. Res.} {\bf 103}, 727 (1998).
%\item[2.]
%Of course, these people really don't exist.
\end{itemize} 

\begin{table}
\label{tab:par}
 \flushleft{
  \caption{Main properties of  CO-detected proto-cluster galaxies.}
\begin{tabular}{llccccccc}
\hline
ID  &   RA / Dec & S$_{CO(3-2)}$  &  S/N &   L$'$(CO) & $\sigma$(CO) & z(UV) &  z(CO)   & comments \\   % & velocity (channel peak)
%{}  &   {}  & (Jy km/s) & {} & (Jy km/s Mpc$^2$) & (km/s)  &  &    &  \\   % & velocity (channel peak)
{}  &   {}  & (Jy km/s) & {} & (L$_\odot$) & (km/s)  &  &    &  \\   % & velocity (channel peak)
%     3mmflux broadline?
\hline
Q1549   	   & 15:51:52.45  +19:11:03.8 &  0.778 & 12.4 &  && 2.844  & 2.847  & QSO host \\  %   0.327 \\  %3000  18
MD17 	   & 15:51:53.77  +19:11:09.7 & 0.528 & 10.8 & &&2.845 & 2.856 &  3mm ctm detected  \\ %   0.904  3700
NB63	& 15:51:53.98    +19:10:41.8 & 0.505 &  6.4 & &&2.843 & 2.841 & A28-31, two merging CO sources? \\
Q1549nbr   & 15:51:52.57  +19:11:05.4 & 0.229 & 5.4 & &&--- & 2.839 & neighbour to QSO  \\  %   0.327 \\  %3000  27
D14      	& 15:51:53.21    +19:10:59.5  &  0.325 & 5.3 & && 2.851 & 2.853 & massive SF galaxy \\  %    0.582   0.440  3500
\hline
MD12    & 15:51:51.88    +19:10:41.2   & 0.553  & 4.5 &&& 2.851 & 2.847 & massive SF galaxy \\ %     0.448   0.451  3010
M15    &   15:51:51.26    +19:11:05.6 & 0.247 & 4.2 &&& 2.849 & 2.853 & \\ % (could be M15 too z=2.841)  3450  MD15/A32
NB133    &  15:51:54.76    +19:11:06.3  & 0.215 & 4.0 &&& 2.844 & 2.847 & \\  %2979   A-47
%C4nb    &    0.290  2.8   2.846 \\  %3005
%C6bx    &    0.114  2.8   2.844 \\  %2810
\hline
C1 & 15:51:50.80      +19:11:40.0 & 0.313 & 5.1 &&& n/a & 2.853 & no known optical counterpart \\
\hline
\end{tabular}
} 
%\medskip \flushleft{ }
\end{table}


%%%% FIGURES %%%%%

%\includegraphics[width=5.9cm,angle=0,clip]{h1549lco.jpg}
\includegraphics[width=10.8cm,angle=0]{h1549_irac_co.jpg}
%\includegraphics[width=15.8cm,angle=0]{q1549_pdb_lae_lbg.jpg}
%\includegraphics[width=6.8cm,angle=0]{q1549_S2_irac_spec_PDBIbeam}

\bigskip

%\includegraphics[width=15.8cm,angle=0]{comosaic.jpg}

\includegraphics[width=11.8cm,angle=0]{q1549main.jpg}

\includegraphics[width=11.8cm,angle=0]{h1549_md17clean.jpg}

\includegraphics[width=11.8cm,angle=0]{h1549_nb63clean.jpg}

\includegraphics[width=11.8cm,angle=0]{q1549nbr.jpg}

\includegraphics[width=11.8cm,angle=0]{h1549_d14clean.jpg}

\includegraphics[width=11.8cm,angle=0]{h1549_md12clean2.jpg}

\includegraphics[width=11.8cm,angle=0]{h1549_m15clean.jpg}

\includegraphics[width=11.8cm,angle=0]{h1549_nb133clean.jpg}

\includegraphics[width=11.8cm,angle=0]{h1549_c1blind.jpg}

%\includegraphics[width=15.8cm,angle=0]{comosaic.jpg}

\bigskip

\includegraphics[width=13.8cm,angle=0]{h1549lf.jpg}

\eject



%%%%%%%%%%%%
%%%% SUP %%%%%

\section*{SUPPLEMENTAL MATERIAL}

\subsection{Line and continuum diagnostics}

In Figs.\ A1-A3 we show the properties LCO, SFE, M* etc.
Conclude XYZ - sumarized in text -- see descriptions

\subsection{Description of datasets}

\subsubsection{Details of the IRAM-PdBI observations}


\subsubsection{SCUBA2 data and reductions, 450um map.}

%Describe SCUBA2 survey.  
Observations with the SCUBA2  camera on the JCMT were conducted in Band 2 weather conditions ($\tau_{225 GHz} \sim 0.07$) over 4 nights between 4th April and 20th June 2012 totalling 6 hours of on-sky integration. The mapping centre of the SCUBA�2 H1549 field is $\alpha$ = 15:51:52.47   +19:11:03.3, chosen as the apparent center of the galaxy over-density at $z=2.85$ (Steidel et al.\ 2010). A standard 3 arcmin diameter `daisy' mapping pattern was used, which keeps the pointing centre on one of the four SCUBA�2 sub-arrays at all times during exposure.

Individual 30 min scans are reduced using the dynamic iterative map-maker of the SMURF package (Jenness et al.\ 2011; Chapin et al.\ 2012 in prep). Raw data are first flat-fielded using ramps bracketing every science observation.
The map maker attempts to solve for noise and astronomical signal model components, refining a model until convergence is met, an acceptable tolerance has been reached, or a fixed number of iterations has been exhausted (in this case, 20). 
The signal from each bolometer's resulting data time stream is then re-gridded onto a map, according to the scan pattern, with the contribution to a given pixel weighted according to its time-domain variance.
%
The sky opacity at JCMT has been obtained by fitting extinction models to hundreds of standard calibrators observed since the commissioning of SCUBA�2 (Dempsey et al.\ 2012). The optical depth in the 850$\mu$m band was found to scale with the Caltech Submillimetre Observatory (CSO) 225 GHz optical depth. % as: ?850	= 26.0(?225 ?0.0196). 

Filtering of the time-series is performed in the frequency domain, with band-pass filters equivalent to angular scales of $2'' < \theta < 120''$ %(i.e. frequencies of f = v/?, where v is the scan speed). The reduction also includes the usual filtering steps of 
Spike removal ($>10\sigma$ deviations in a moving boxcar), DC step corrections are also applied, and bad bolometers flagged.
%Throughout the iterative map making process, bad bolome- ters (those significantly deviating from the model) are flagged and do not contribute to the final map. 
Maps from independent scans are co-added in an optimal stack using the variance of the data contributing to each pixel to weight spatially aligned pixels. %Fi- nally, since we are interested in (generally faint) extragalactic point sources, we apply 
A beam matched filter is then applied to improve point source detectability, resulting in a map that is convolved with an estimate of the 850$\mu$m beam. The average exposure time over the nominal 3 arcminute daisy mapping region %(in practice there is usable data beyond this) 
is approximately 1000 sec per 2?? ? 2?? pixel.

A beam-matched flux conversion factor (FCF) has %been found to be reasonably stable over this period, and the average FCFs agree (within error) to those derived
been derived from the subset of standard calibrators observed on the nights of the observations, %. Therefore we have adopted the canon- ical calibration of 
FCF850 = 60$\pm$6 Jy beam$^{-1}$ pW$^{-1}$. 
A correction of 10\% is included in order to compensate for flux lost due to filtering in the blank-field map.

Details of the SCUBA2 data and the full maps and analysis are presented in C.\ Ross et al.\ (in prep).

\subsubsection{ SMA 870$\mu$m mosaic of core region} %survey verifies detections of 6 sources, including weak CO emitter M15.}

The SCUBA2 map has highlighted an apparent overdensity of 850um continuum blended in the core region.
Large variations in CO(3-2) line luminosity to gas mass and dust mass mean that we cannot reliably use the detected CO sources to deconvolve the 850um emission.
We thus embarked on an SMA survey to resolve the core region of the protocluster at 870um effective wavelength.
The SMA map shown in Fig.\ A1 has resolved the SCUBA2 emission into at least 6 sources.

Describe SMA survey.  Details of the SMA data in C.\ Ross et al.\ (in prep)

DISCUSSION OF OVERDENSITY WITH RADIUS, SMA DATA, VS S2 DATA

It is of interest to explore how concentrated this core is relative to the outer regions of the protocluster.

\subsection{Line detection significance and statistics}

\subsubsection{Blind line detection.}

chance of finding lines associated and unassociated to UV galaxies

\subsubsection{Stacking on UV galaxies.}

3sigma detection once removing all those with $>4sigma$ lines.  Rob to verify with his code.

\subsubsection{ Chance probabilities and monte carlo experiment.}

measured spectra in random positions, finding no lines.


\subsection{Individual CO(3-2) line properties} 

Through our many new CO(3-2) detections in these fields, we  study the bulk CO width (halo dynamics), the offset from optical lines (winds), and the potential for internal blue-red offset measurements (kinematics), comparing to the handfuls of CO(3-2) measurements of SMGs and lensed LBGs in the literature (e.g.,  Riechers et al.\ 2010). 

\eject

\noindent {\bf Fig. 1.} 
SMA 870$\mu$m mosaic map  (40$''$ by 30$''$) of the $z$$\sim$2.84 H1549 protocluster field.
CO-emitters from the PdBI map are shown as blue circles, while the SCUBA2 contours are shown overlaid (white). The SMA has effectively detected at least 5 of the CO emitters at 870$\mu$m continuum, clearly explaining the unresolved SCUBA2 emission, and allowing for far-IR SEDs to be fit to individual CO-emitting galaxies, and gas/dust ratios to be estimated precisely.
These observations constrain the  ISM properties and elucidate   the effect of the large overdensity on the gas supplies, stellar masses, and star formation modes relative to the field population.  

\includegraphics[width=11.8cm,angle=0]{h1549sma.jpg}


\end{document}

%%%% END %%%
%%%%%%%%%%%





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{\bf References and Notes}

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1 (1929).
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% Your references go at the end of the main text, and before the
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\begin{scilastnote}
\item We've included in the template file \texttt{scifile.tex} a new
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\end{scilastnote}




