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\Large \centerline {\bf Project Description} \normalsize

\section{Results from Prior NSF Support}
\subsection{High Elevation Antarctic Terahertz (HEAT) telescopes for Ridge A}
In 2010, the PI initiated an NSF-funded (ANT-0944335, 7/2010-6/2014)
program to build two 60~cm terahertz telescopes for robotic operation
at the summit of
the Antarctic high plateau with the dual purpose of site testing and
performing leading edge terahertz astronomy.  These High Elevation
Antarctic Terahertz 
(HEAT) telescopes operate from 150 to 610~$\mu$m and observe the
brightest and most diagnostic far-infrared lines in the
Galaxy. An international collaboration with Australia's University of
New South Wales provided the PLATeau Observatory for Ridge~A
(PLATO-R), a platform for power and satellite communication.  In
January 2012, PLATO-R and the first HEAT prototype were deployed to
Ridge~A and are operational as of this writing (Figure~\ref{heat}).  A servicing
mission to Ridge~A in which the second HEAT telescope will be
installed is scheduled for January 2013.  HEAT is the first automated
telescope on the Plateau with cryogenic receivers; it is showing that
the Ridge~A site is the best site on the planet from which to perform terahertz
observations, with 10$\times$ more observing days suitable for
200~$\mu$m observations than Chajnantor (e.g. ALMA).  Already,
a preliminary public data release of 809~GHz (370~$\mu$m) [CI] data
returned via Iridium satellite has been made\footnote{{\tt
    soral.as.arizona.edu/heat}}.  A primary data release
in CO J=7-6 and [CI]~$^3P_2$~-~$^3P_1$ for the first year of operation
will take place shortly after the recovery of the raw data in January 2013.  

\begin{figure}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{4.2in}{\includegraphics[scale=0.7,angle=0]{figures/RidgeA.eps}
\includegraphics[scale=0.42,angle=0]{figures/HEATimg.eps}}}
{\parbox{2.3in}{\caption{\label{heat} {\small (left) The PLATeau Observatory
    and 60~cm HEAT
    telescope at Ridge~A, Antarctica installed in January
    2012. (right) The first 0.6 sq.deg. 
integrated intensity map in 370 $\mu$m [CI] emission
returned by HEAT via onboard data processing and Iridium satellite
downlink. The highly extended emission observed directly probes
the {\it dark molecular gas}, i.e. H$_2$ clouds with little CO emission.}}}}
\end{minipage}
\end{figure}


\subsection{Bolocam Galactic Plane Survey, CAMPARE, URO}

Y. Shirley has been PI or Co-I on three NSF grants; presented here in
reverse chronological order.

(1) Astrophysics with the Bolocam Galactic Plane Survey (PI
Dr. Y. Shirley, Prof.  
Jason Glenn is co-I; NSF grant AST-1008577, 8/2010-8/2013):  This
proposal provides spectroscopic
followup of BGPS clumps in the Galactic plane.  In the first half of
the grant period, 
Y. Shirley led a team of observers that have completed 
HHT observations of all BGPS clumps $l > 7.5$ deg in the first and
second quadrants of the Galaxy.  The complete
spectroscopic catalog was released in the fall of 2012. 
The paper from the pilot spectroscopic survey of 1882 sources was accepted 
(Schlingman et al. 2011) and highlights from the characterization of
the BGPS clumps 
properties are shown in Figure~\ref{bgps}.   Over 75\% of clumps were detected
in HCO$^+$ 3-2 
indicating that kinematic distances will be derived for a significant
fraction of 
BGPS clumps.  The Schlingman et al.
survey found that the clumps do not obey a size-linewidth relation
indicating a breakdown in 
the supersonic scaling laws (Larson's laws) that apply to larger CO clouds.

\begin{figure}
   \centering
   \vspace*{5cm}
   \leavevmode
   \special{psfile=figures/f9a.eps hoffset=-270 voffset=170 hscale=30
      vscale=30 angle=-90}
   \special{psfile=figures/f9b.eps hoffset=-110 voffset=170 hscale=30
      vscale=30 angle=-90}
   \special{psfile=figures/f18a.eps hoffset=80 voffset=35 hscale=30
      vscale=30 angle=0}
   \special{psfile=figures/f25.eps hoffset=-250 voffset=-65 hscale=30
      vscale=30 angle=0}
   \special{psfile=figures/f24d.eps hoffset=-90 voffset=-65 hscale=30
      vscale=30 angle=0}
   \special{psfile=figures/f22a.eps hoffset=70 voffset=-65 hscale=30
      vscale=30 angle=0}
 \vskip 0.75in
\parbox{6.3in}{\caption{\label{bgps}\small Scientific highlights from the BGPS
    Spectroscopic followup.   
CLOCKWISE FROM TOP LEFT: 
(1,2) Detection statistics for 1882 sources observed in HCO$^+$ and
N$_2$H$^+$ 3-2 in the initial  
spectroscopic followup to the BGPS (Schlingman, Shirley, et al. 2011).
Over 3/4$^{th}$ of BGPS continuum  
sources show emission in HCO$^+$.  (3) The distribution of sources
with galactocentric radius trace major  
spiral arm features in the Milky Way.  (4) The subset of clumps with
the distance ambiguity resolved do not 
display a size-linewidth relationship.  (5) The clump crossing time is
slightly less than the free-fall 
time for BGPS clumps. (6) The clump mass spectrum is steeper ($-0.8$)
than observed for CO clumps ($-0.6$)  
in the Galaxy, but flatter than a Salpeter IMF ($-1.35$).}}
\end{figure}
\normalsize
 
(2) California-Arizona Minority Partnership for Astronomy Research and Education 
(PI is Prof. Alexander Rudolph, Y. Shirley is co-I, NSF AST-0847170,
7/2009 - 7/2014):   
CAMPARE is an education program designed to give under-represented
minorities a hands-on REU 
experience working at the University of Arizona.  The students are
selected from California 
Polytechnic State University. As a co-I, Y. Shirley mentors 1 student
each summer.   
The PI most recently worked with Stephen Jasso, who obtained 12m
observations of CS 2-1 \& HCN 1-0 toward a sample of dense cores
identified through extinction mapping 
of the cloud (courtesy of Dr. Charlie Lada).

(3) The Arizona Radio Observatory: Surveying the ISM Through Millimeter and
Sub-millimeter Spectroscopy (PI is Prof. Lucy Ziurys, Y. Shirley is
co-I, NSF 11-529 URO, 4/15/2012 - 03/31/2015):
This proposal provides funding for the Arizona Radio Observatory and upgrade of
observatory facilities for the next three years.
The URO funds thus far have been principally used for engineering development. 
Work has commenced on designing the proposed 4 mm receiver. Also,
preliminary design work for the proposed broad-band spectrometer was
begun. 

\subsection{Supercam: A 64-beam Heterodyne Array Receiver at 850~$\mu$m}

In 2005, this team initiated an NSF-funded (AST-0421499,
1/2005-12/2009, PI: C. Walker) program to design and construct the
first integrated heterodyne focal plane array at submillimeter
wavelengths: 64 beams in the astrophysically important 850~$\mu$m
atmospheric window.  Supercam was designed to be used at the Arizona
Radio Observatory (ARO) 10-meter Heinrich Hertz 
Telescope (HHT) on Mt. Graham, Arizona to conduct its key project, a 
Galactic Plane survey in the $^{12}$CO J=3$\rightarrow$2 line (the
purpose of this proposal).  
Each component of Supercam has been modularized in units of 
1$\times$8 rows of the full heterodyne array
(Figure~\ref{prototype}).  Thus, the mixer blocks, bias 
electronics, IF processors, and digital FFT spectrometers are
quantized into modules that
provide 8 detector ``pixels''  each.  This one-dimensional integration is
crucial to the realization of large format heterodyne arrays and has been
successfully completed by the Supercam team (Figure~\ref{prototype}). 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.37,angle=0]{figures/1x8_prototype_sm.eps}
\hfill
\includegraphics[scale=0.65,angle=0]{figures/supercam-focalplane.eps}
\caption{\label{prototype} {\small Left: The centerpiece of the
        Supercam heterodyne array is the integrated mixer
        block; comprised of 8 feedhorns, SIS mixers, MMIC low noise
        amplifiers, and nano IF \& DC connectors. The final 64-beam focal
        plane consists of 8 such mixer modules. Right: Zoom-in on the opened
        Supercam cryostat, showing the fully populated 64 beam focal
        plane.}}
\end{figure}


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.92,angle=0]{figures/map1.eps}
\hfill
\includegraphics[scale=1,angle=0]{figures/map2.eps}
\caption{\label{maps} {\small A sample of first light maps at 345~GHz made with
    Supercam at the HHT in late May, 2012.  Left:  Integrated intensity map
    of CO J=3-2 line emission over 40'x40' of the W3 molecular
    cloud. Right: 
    Channel maps spanning 24'x30' of the Cepheus~A molecular cloud show
    complex kinematics.  Each image represents the emission in 1~km/s bins from V$_{LSR}$ = -18 to -6 km/s.  Despite the poor
    early-summer weather and a reduced pixel count, these large-scale maps were
    made in a few hours each. }} 
\end{figure}

The full Supercam instrument was successfully installed on the HHT in
May 2012.  Despite the comparatively poorer
weather near the end of the observing season, Supercam achieved first
light and delivered more than 1 million spectra per day.  Supercam's
relay optics delivered a 23'' diffraction-limited beam and 60\% beam
efficiency in nearly every pixel.  Two sample maps from that
engineering run are shown in Figure~\ref{maps}.  The yield of
pixels with good sensitivity (T$_{rec}<100$K DSB) during the
engineering run was approximately 55\%. Optimization of devices in the focal plane is underway (Fall 2012), to
increase the yield of devices with excellent 
RF performance, with a target goal of 75\%.  The expected instrument
performance based on laboratory tests is shown in
Figure~\ref{perf}(left) and the corresponding mapping speed is shown
as a function of frequency in Figure~\ref{perf}(right), 
dominated by the atmospheric transmission in the 350~GHz band.  At the
frequencies of interest, near CO J=3-2 and HCO$^+$ J=4-3, the mapping
rate is approximately 4-5 hours per square degree, or {\bf 5-6 square
degrees per day}.  This sharply contrasts to the 4-5 days per square degree
that is typically expended at (easier) mm wavelengths using the ALMA Band 6
(1.3mm) prototype receiver at the HHT.  This is the specific enabling
result which motivates the Galactic Plane survey proposed here.  

\begin{figure}[!hbt]
\centering
\includegraphics[scale=1.05,angle=0]{figures/perf1.eps}
\hfill \includegraphics[scale=1.05,angle=0]{figures/perf2.eps}
\caption{\label{perf} {\small (left) Expected
        performance of Supercam based on laboratory receiver testing.
        The mean noise temperature of working devices is 90K DSB and
        the focal plane yield of good devices is projected to be 75\%.  (right)
        Corresponding mapping speeds at the HHT, assuming an
        rms noise level of 0.2~K~km/s in median winter weather at a
        zenith angle of 30$^o$.  Near the spectral lines of interest,
        the mapping speed will be approximately 5 square degrees per
        day. }}
\end{figure}

\section{Research Activities}

Supercam will enable
innumerable new astronomical research opportunities as an available PI
instrument at the HHT, open to all users.  However, 
its high angular and spectral resolution,
coupled with an exceptional field of view makes it {\it a truly exceptional
Galactic Survey instrument}, which provided the primary motivation for
its construction.  Here, we outline a first
Supercam ``key project'', a submillimeter CO and HCO$^+$ survey of the
Galactic Plane observable from Arizona.  

\subsection{Introduction: Critical questions this proposal will address}

The evolution of (the stellar population of) galaxies is
determined to a large extent by the life cycles of
interstellar clouds: their creation, star-forming properties, and
subsequent destruction by both natal and dying (massive) stars. 
(Figure~\ref{cycles}). 

\begin{figure}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{3in}{\includegraphics[scale=0.33,angle=0]{figures/LifeCycle-ISM.eps}}}
{\parbox{3.4in}{\caption{\label{cycles} {\small The life cycle of
        interstellar clouds, observed through carbon lines.  
The internal evolution
of a galaxy is defined by the transformation of dense, neutral
interstellar clouds into stars and star clusters, the interaction of
the interstellar medium (ISM) with young stars as a regulator of
further star formation, and the return of
enriched stellar material to the ISM by stellar death, eventually to
form future generations of stars.}}}}
\end{minipage}
\end{figure}

Although these clouds are largely comprised of
neutral hydrogen in both atomic and molecular form and atomic helium, these
species are notoriously difficult to detect under typical interstellar
conditions.  Atomic hydrogen is detectable in cold clouds via the
21~cm spin-flip transition, but cold (T$\sim$70K) atomic clouds are
often indistinguishable from the warm (T$\sim$8000K) neutral medium that
pervades the Galaxy.  Furthermore, neither atomic helium nor molecular hydrogen
(H$_2$) have accessible emission line spectra in the prevailing
physical conditions in cold interstellar clouds.   Thus, it is generally
necessary to probe the nature of the ISM via rarer trace elements. 
Carbon, for example, is found in ionized form (C$^+$) in neutral HI clouds,
eventually becoming atomic (C), then molecular as carbon monoxide (CO)
in dark molecular clouds.  The dominant ionization state(s) of carbon
that accompany each stage of a cloud's life are shown in red in Figure~\ref{cycles}.  
Though we are now beginning to understand star formation, the
formation, evolution and destruction of molecular clouds remains
shrouded in uncertainty. 

The need to understand the evolution of interstellar clouds as they
directly 
relate to star formation and galaxy evolution has become acute.  The
most recent decadal 
survey, ``Astro2010: New Worlds, New Horizons'', specifically
identifies the questions ``{\it What controls the mass-energy-chemical
cycles within galaxies}'', ``{\it how do stars form}'', ``{\it what
  determines the 
star formation rates and efficiencies in molecular clouds}'', and
``{\it what determines the properties of pre-stellar cloud cores and what
is the origin of the stellar mass function}'' as among the key
questions for radio and (sub)millimeter facilities in this decade.
Further, the specific recommendation is made: {\bf ``A large-field
  mapper operating at 
millimeter and submillimeter wavelengths is required to pave the way
for follow-up observations with ALMA''}.  Supercam is a
direct answer to this recommendation and is ready {\it\bf now}.


This project aims to increase our understanding of the
interactions between stars and the molecular clouds which form them.
Stars affect their environments through the direct input of kinetic
energy and by radiation which ionizes or heats adjacent molecular
gas.  This proposed survey will yield major new results targeted at
answering specific questions about molecular clouds, star formation,
and stellar feedback:

\smallskip
 {\bf(1)} How do molecular clouds form, evolve, and get disrupted?  How
  do typical atoms and grains cycle through the ISM; in particular,
  how do molecular clouds relate to the atomic hydrogen component of
  the ISM?  Is there statistical evidence that molecular clouds may be
  formed by colliding streams or filaments of HI as has been shown in
  hydrodynamical models \citep{heitsch06}?

\smallskip
{\bf(2)} How and under what conditions do molecular clouds form stars?
  What role does the underlying physical structure of molecular clouds and
  their dense cores have on the mass function of stars that result?

\smallskip
{\bf (3)} What are the effects of HII regions on their associated
  molecular clouds? To what extent does cloud compression caused by
  expanding HII regions trigger the formation of dense cores and
  subsequent star formation?  To what extent do the dynamical, heating
  and ionization effects of OB stars and their HII regions destroy
  associated molecular clouds?  

\smallskip
{\bf(4)} What is the evolutionary and dynamical state of molecular cloud
  cores?  

\smallskip
{\bf(5)} How does the Galactic environment impact the formation of clouds
  and stars?   What are the specific roles of spiral arms, central
  bars, and infall and other influences from outside the Galaxy?  Can
  star formation in the Milky Way be synthesized into a ``template''
  to help interpret star formation in distant, unresolved galaxies?


We will use Supercam, the aforementioned state-of-the-art 64-beam
heterodyne array to map a large, 240 square degree region of the
Galactic Plane in the J=3-2 transition of CO and the 
J=4-3 transition of HCO$^+$ from the HHT.  The proposed observations
exploit the unique capabilities of Supercam, namely
efficient, rapid, high-fidelity spectral mapping over large angular
scales.  The survey angular resolution, 23'', will
yield maps superior in resolution and sensitivity to any other imaging
data yet presented over comparably large areas of sky.  
We will also employ other available data to form as
comprehensive a picture as possible of the ISM and the stellar content of
Galactic interstellar clouds.  With detailed kinematic analyses,
it will be possible to compare our data with predictions of numerical
hydrodynamical models of the ISM and thereby to constrain the physical
mechanisms resulting from stellar energy injection and the resulting
feedback which regulates the star formation process.  We emphasize
that these properties can only be determined from well-sampled
large-area maps that cover a wide range of spatial scales.  {\bf Single-dish telescopes are key to making
high-fidelity images of the ISM with high spectral resolution and
spatial dynamic range}.  With the advent of ALMA, sensitive, high resolution
imaging of relatively small regions is now possible.  However,
large-scale imaging with ALMA is prohibitively time consuming; this is
a task most effectively performed by precision single-dish telescopes
outfitted with multi-beam receivers like Supercam.

\subsection{Properties of the Proposed Survey}

\noindent \fbox{\parbox{6.5in}{The following properties represent a definitive
survey that would not only provide the clearest view of the star
forming clouds in the Galaxy, but also serve as the definitive reference
for focused follow-up studies with the SMA, CARMA and ALMA
interferometers and LMT.  }}

\subsubsection{High Resolution Spectroscopic Imaging}

Techniques commonly used to diagnose the molecular ISM 
include submillimeter continuum mapping of dust
emission \citep{hild83} and dust extinction mapping at optical and
near-infrared wavelengths \citep{lada94}.  Large format detector
arrays in the infrared are now 
commonplace, and with the advent of bolometer arrays like SCUBA at the
JCMT and BOLOCAM at the CSO, both techniques have performed large area
maps of molecular material. In the past decade,
continuum surveys at mid-infrared (GLIMPSE \& MIPSGAL; Benjamin et
al. 2003), submillimeter 
(Hi-GAL; Molinari et al. 2010), and ATLASGAL; Schuller et al. 2009,
Contreras et al. 2012),
and millimeter 
wavelengths (BGPS, Aguirre et al. 2011) have  
cataloged dense star forming clumps throughout the Galaxy.  The Bolocam Galactic
Plane Survey (BGPS) has discovered over 8400 sources in the Galactic
plane (Rosolowsky et al. 2010).  However, these techniques have limited 
applicability to the study of the large-scale evolution of molecular
clouds due to the complete lack of kinematic information.   
Supercam will make it feasible, for the first time, to obtain
a complete spectral map of the Galactic plane in a moderate (CO J=3-2)
and dense (HCO$^+$ J=4-3) gas molecular tracer, for direct comparison
with these surveys.

The confluence of many clouds along most Galactic lines of sight can only 
be disentangled with spectral line techniques.  Fitting to a model of
Galactic rotation is often the
only way to determine each cloud's distance and location within the
Galaxy.  With
resolution of 1~\kms\ or better, a cloud's kinematic location can
be distinguished from other phenomena that alter the lineshape, such as 
turbulence, rotation, and local phenomena such as protostellar
outflows.  These kinematic components play a vital role in the
sculpting of interstellar clouds, and a survey that has the goal of
understanding their evolution must be able to measure them.  

Supercam resolves the
intrinsic profiles of Galactic CO and HCO$^+$ lines, with a per-channel
resolution of 0.2~\kms. Supercam's IF center frequency will be adjusted
to allow simultaneous observations of both lines, CO~3-2 in the lower
sideband and HCO$^+$~4-3 in the upper sideband.  Supercam's mixers are
optimized for double sideband operation, with a sideband ratio of $\sim$1. 
The spectral bandwidth will scale with the known CO velocity
dispersion \citep{dame01}: for the Outer Galaxy ($l>40^o$), all 64
pixels will observe both spectral lines simultaneously, with
110~\kms\ of bandwidth each.  In the Inner Galaxy
($l<40^o$), all 64 pixels will observe CO J=3-2, and 16 of them will
observe both lines simultaneously, with 220~\kms\ of bandwidth each
(comparable to the Galactic rotational velocity).
Local Oscillator (LO) doppler tracking will ensure that the Galactic
emission profiles stay within their spectral bandpasses.

\begin{figure}
\centering
\begin{minipage}{6.5in}
{\parbox{3.2in}{\includegraphics[scale=0.33,angle=0]{figures/IRDC1_HCOP.eps}}}
{\parbox{3.2in}{\caption{\label{W43} \small Integrated intensity maps ($\int T_{mb}\, dv$, $3\sigma$ contours) 
of G28.37$+$0.08 in HCO$^+$ J=3-2 obtained with the HHT
overlaid on greyscale 1.1mm images (Battersby et al. 2010).  Since the
excitation conditions for HCO$^+$ J=4-3 are not drastically different
from HCO$^+$ J=3-2, we expect the J=4-3 emission to be extended and mappable.}}}
\end{minipage}
\end{figure}

\subsubsection{A Submillimeter Survey in CO and HCO$^+$}

CO is second only to H$_2$ as the most abundant molecule in the ISM,
and it remains the most accurate, most sensitive tracer of
H$_2$ on large scales.  Molecular line surveys
have been performed over the entire sky in the light of the 2.6 millimeter 
$J=1-0$ line of \co, and have been used to synthesize our
best understanding of the molecular content of the Galaxy.  Still, our
understanding of Galactic molecular clouds is incomplete.  Early
results were obtained with large beams
\citep{dame87,dame01}, were undersampled \citep{solo87, scov87}; or had limited
areal coverage, e.g., the early FCRAO surveys -- \citep{carp95, star89, ball91, miec94}.  The Galactic
Ring Survey (GRS) at FCRAO is by far the most comprehensive survey of
the inner Galaxy to date \citep{simo01}.  However, this survey traces
only the $J=1-0$ line of \tco, which is less sensitive to warm, low-opacity,
high velocity gas such as produced by outflows, photodissociation
regions (PDRs), and shocks.  

\medskip
\noindent 
\fbox{\parbox{6.5in}{A more comprehensive view of molecular clouds can
therefore be gleaned from
measurement of the submillimeter lines of CO and its isotopes, in
combination with existing millimeter-wave observations. 
The gas probed by
higher-J transitions is best suited to addressing the proposed survey's driving questions-- it is the {\it energetic} gas that 1) participates
in molecular outflows, 2) senses radiation fields at the
photodissociated surfaces of clouds, and 3) is warmed by 
star-formation in cloud cores.  Higher-J line surveys like Supercam's
are also needed to 
properly interpret basic properties of clouds derived from 
existing CO~J=1-0 observations. }}

\medskip

 The CO J=3-2 transition at 345.8~GHz
($n_{crit} = 1.5\times 10^4$~cm$^{-3}$) yields the lowest-lying line that
significantly departs from the behavior seen in J=1-0 emission at
2.6mm, making it an ideal probe of the denser, more energetic portions
of clouds.  Similarly, HCO$^+$ J=4-3 is
among the best tracers of high density gas ($n_{crit} = 2\times
10^6$~cm$^{-3}$). In the 350~GHz atmospheric window, it has more accessible
excitation characteristics than CS J=7-6 or HCN J=4-3.  It is expected
to be often subthermally-excited and optically-thick; radiative
trapping reduces its effective excitation density to $n\sim
10^5$~cm$^{-3}$.  HCO$^+$ also has a straightforward chemistry that is closely
connected to CO.  Observing both species is therefore highly
synergistic. 

While HCO$^+$ emission will be more concentrated than CO, bright BGPS
sources such as those shown in Figure~\ref{W43} clearly show that HCO$^+$
emission is often extended (Battersby et al. 2010). 
Based on the brightness of HCO$^+$ 3-2 emission
and the typical gas kinetic temperature measured with NH$_3$
observations toward BGPS clumps 
($<T_k> \sim 15$ K; Dunham et al. 2011), we expect to map extended
HCO$^+$ $4-3$ emission in $\sim$1600 individual clumps in a first
quadrant survey alone.  The MALT90 survey \citep{malt90} in HCO$^+$
J=1-0 will provide a significant lever arm to constrain physical
conditions in dense clumps that both surveys share in common.

\begin{figure}[!bt]
\centering
\begin{minipage}{6.5in}
{\parbox{4in}{\includegraphics[scale=0.5,angle=0]{figures/345window.eps}}}
{\parbox{2.5in}{\caption{\label{trans} {\small a) The 345~GHz spectral
	line survey toward 
    three positions in the W3 molecular cloud by \cite{helm97}
    shows a rich diversity of spectral diagnostics.  b) Modeled
    submillimeter atmospheric transparency for the HHT on Mt. Graham
    in 75 percentile (top), median (middle), and 25 percentile (bottom)
    atmospheric conditions, derived from 24 hour 225~GHz
    radiometer measurements over the last 10 years.}}}}
\end{minipage}
\begin{minipage}{4in}
{\parbox{1.5in}{a)}}
{\parbox{1.5in}{b)}}
\end{minipage}
\end{figure}

The design of a 350~GHz spectroscopic survey is attractive; at this
frequency the HHT has 
high aperture efficiency and good atmospheric transmission more
than 50\% of the winter (Figure~\ref{trans}-b).

\subsubsection{Large Area Mapping: A Galactic Plane Survey}
\label{mapping}

A complete picture for how star formation proceeds throughout the Galaxy
can only be accomplished through Galactic plane surveys.  Studies of
star formation in other galaxies have derived a fundamental
relationship between the 
surface density of dense gas and the star formation rate 
(i.e. the Kennicutt-Schmidt Law, Kennicutt 2007, Gao\& Solomon
2004a,b, Bussmann et al. 2008, 
Baan et al. 2008, Juneau et al. 2009, Lada et al. 2012, Kennicutt \&
Evans 2012).   
The most recent molecular extragalactic surveys have pushed 
the spatial resolution of observations of CO to scales of $0.1$ kpc in
nearby galaxies (Bigiel et al. 2011).  Over the next few years, ALMA
observations 
will probe smaller scales and also trace the more relevant
dense gas from which stars form with high efficiency using 
molecular tracers such as HCO$^+$ and HCN.
A simultaneous effort is needed within our own Galaxy to build-up to the
scales probed by extragalactic observers to determine a star
formation relationship within  
the Milky Way.  Galactic plane 
surveys in dense molecular gas tracers can provide the needed
information on the surface density 
and fraction of dense molecular gas throughout the Galaxy. When
combined with infrared 
surveys, they can constrain the global star formation relation in the
Milky Way.  No complete survey of the first quadrant of the Galactic
plane currently exists in a submillimeter-wave, dense gas tracer.  

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.7,angle=0]{figures/Fig2Dame.eps}
\caption{\label{area} {\small The power of SuperCam:  a definitive
    chemical and kinematic survey of star forming clouds in \co\ J=3-2
    and HCO$^+$ J=4-3 over 240
    square degrees of the sky can be performed in 4 months of
    observing in median winter weather.
    A corresponding survey with a single
    pixel receiver would take 100\% of the HHT's observing time for 5 years. }}
\end{figure}

Figure~\ref{area} shows the proposed sky coverage of the SuperCam
submillimeter-wave Galactic plane survey.  From previous CO surveys it
is known that the scale height of CO emission toward the inner Galaxy 
is less than one degree \citep{dame87,dame01}.  
The interstellar pressure, abundances, and physical
conditions vary strongly as a function of Galactocentric radius, so it is
necessary to probe the inner Galaxy, the outer Galaxy, and the
$l=\pm 100^o$ tangent arms to obtain a statistically meaningful survey
that encompasses the broad dynamic range of physical conditions in the
Galaxy.  We propose therefore to 
probe the entire Galactic plane as seen from Arizona ($0
< l < 240^o$).  Below $l=90^o$, a {\it completely unbiased survey} will be
undertaken, covering 180 square degrees ($-1^o < b < 1^o$).  
This ``inner'' Galaxy survey will coincide
with several synergistic surveys (Section~\ref{synergies}), such as
the FCRAO-BU Galactic Ring Survey (GRS), GLIMPSE, a Spitzer Space
Telescope (SST) Legacy Program \citep{benj03}, and Hi-GAL \citep{higal}.
Above $l=90^o$, most of the CO emission is located at
higher Galactic latitude; 60~square degrees will be distributed
according to the \cite{dame01} survey to follow the CO J=1-0
distribution, while maximizing
synergies with the C2D and GLIMPSE(360) Spitzer programs
\citep{evans}, cloud cores seen by BGPS, and and other
Spitzer \& Herschel programs (Figure~\ref{area}). Further discussion
of the survey regions may be found in Section~\ref{survey} and the
data management document.  

\subsubsection{High Angular Resolution}

Angular resolution is a critical aspect to the science return of a new
Galactic plane survey.   Figure~\ref{resolution} depicts a synthetic
model cloud projected to distances of 
500~pc and 5~kpc.  Clearly, disentangling different clouds and cloud
components can only be accomplished with sub-arcminute angular
scales.  The angular resolution of Supercam in CO J=3-2 on the HHT
is 23$''$, equivalent to 0.9~pc at the
distance of the Galactic Center. 

\begin{figure}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{3.0in}{\includegraphics[scale=0.32,angle=0]{figures/resolution.eps}}}
{\parbox{3.4in}{\caption{\label{resolution} {\small {\bf The need for high angular
    resolution: } A synthetic model cloud
    seen in the \co\
    $J=3-2$ transition at a distance of 500~pc (left) and at 5~kpc,
    with beam sizes of $30''$ (top) and $2'$ (bottom).  The structure
    of the cloud is essentially lost in the larger beam.  In order to
    probe cloud structure and excitation over the entire Galactic
    disk, high angular resolution is vital. }}}}
\end{minipage}
\end{figure}


\subsubsection{High Sensitivity}
\label{sensitivity}

CO survives in the ISM in part because of
the UV shielding from dissociation provided by H$_2$; thus CO's
survivability depends upon a molecular, H$_2$-dominated
environment.  For typical molecular clouds, the sharp transition
from H to H$_2$ occurs by a visual
extinction of $\sim$1 magnitude in the local interstellar radiation
field, N(H)=$1.8\times 10^{21}$~cm$^{-2}$.
We therefore aim to detect all CO down to this hydrogen column density limit.
This corresponds to a 5$\sigma$ 
detection limit of N(CO)=$10^{15}$~cm$^{-2}$, which
implies an integrated intensity for cold gas 
(T$_{kin}$=10-50K) of 1~K~\kms\ in the
$J=3\rightarrow2$ transition at a gas density of $n_H=10^4$~cm$^{-3}$.
This sensitivity limit is achievable (at 5$\sigma$) within 12 seconds of
integration time per independent beam in {\it median} atmospheric
conditions (T$_{sys}\sim$700K) at the HHT, or 5 hours per
square degree, with 10'' spatial pixels.
Detection (or limits) on J=3$\rightarrow$2 in that time would
constrain the gas density, based upon the line brightness of
millimeter wave transitions.  In the same period of time,
Supercam would also reach a 5$\sigma$ limit of
1~K~\kms\ in HCO$^+$ J=4-3, which would detect around
65\% of the BGPS clumps observed by \cite{Schlingman11} in HCO$^+$ J=3-2.
 Targeted follow-up HCO$^+$ observations
with Supercam toward sources with a wide range of evolutionary stages
are expected in year 3 of the proposed effort.


\subsection{Survey Activities}

\subsubsection{Mapping Strategy}
\label{survey}

The most efficient mode of data collection with a focal plane 
array that produces high fidelity images is 
On-the-Fly (OTF) mapping.  In this mode, the telescope continuously 
scans back and forth across a field while the backends are 
read-out at a sufficent rate to eliminate aliasing and beam smearing.  
The primary advantage of OTF mapping with an array 
is that a given position on the sky is observed by all pixels in the 
array.  This redundancy removes any noise and gain inhomogeneities between 
pixels
and reduces the degree to which the data are correlated, as a singular 
off-source measurement is distributed to on-source data. 
Mapping projects at the HHT routinely and efficiently use the OTF technique.  

The broad coverage of the Galactic Plane Survey lends itself naturally
to efficient, 24-hour/day mapping.   Only the regions defined by $0 < l < 40^o$
enters the $30^o$ Sun-avoidance circle in December,
and $150 < l < 210^o$ during May-June.  With 64
pixels, SuperCam can reach the requisite sensitivity of
1$\sigma$=0.2~K~km/s over a full square degree in 5 hours 
(Section~\ref{sensitivity}).  A visibility diagram
(Figure~\ref{visibility}) shows the nominal observing 
strategy in which the entire survey can be accomplished in 4 months of
observing time-- total; two month-long campaigns in each of two
years. A corresponding survey with a single pixel receiver would take
100\% of the HHT's observing time for 5 years. The observing time
required for the proposed survey was guaranteed by 
Steward Observatory in the original Supercam MRI proposal (see letter
from P. Strittmatter).

\begin{figure}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{3.3in}{\includegraphics[scale=0.33,angle=-90]{figures/visibility.eps}}}
{\parbox{3in}{\caption{\label{visibility} {\small The entire Galactic
        Plane survey 
    can be accomplished in 4 months of observing time total; two
    month-long campaigns in each of two years.  This visibility
    diagram denotes how the Galactic Plane 
    will be partitioned for efficient observing. }}}}
\end{minipage}
\end{figure}

\subsubsection{Science Products and Dissemination}

The primary challenge of OTF mapping is data management, which becomes
particularly 
acute with an array for which the data rates are typically 100x larger than normal.
We have adopted the strategy developed at FCRAO for OTF mapping with
the 32 pixel SEQUOIA array, whereby
coadded and regridded data are written as a FITS cube, and headers for 
each scan are written into a SQL relational database. This approach 
facilitates efficient logging and retrieval of the data.
Our storage requirements for a 240 square degree map, gridded to 10$''$ spacing,
with 1024 spectral points per grid position, is $\sim$100~GB.  The total
disk requirements for the raw data will be about 6~TB. 
This volume can be readily handled by a single computer with a
redundant disk array for data integrity. 
Open access to these data products (with no proprietary period)
will be provided through a web browser interface that will parse the
SQL database and FITS data cubes.  

\smallskip
\noindent \fbox{\parbox{6.5in}{All science tools, packaged reduction software,
    data products and 
    science products will be made available from the Supercam survey's web
    page, at {\tt soral.as.arizona.edu/supercam}  }}
\smallskip

\subsubsection{Survey Science Analysis Strategy}

To extract physical information from the Supercam survey data, in
combination with copious ancillary data already available,
we will employ a variety of analysis tools and integrative activities.

\smallskip
\noindent 1) Coupled escape probability (CEP) \citep{cep} and Monte Carlo
  (MC) \citep{bernes79} {\bf radiative
  transfer models} will be used to constrain kinetic temperature,
  hydrogen (molecule) particle density, and total column
  density. Observed line ratios and intensities can be compared to CEP
  model grids that can be used to estimate the average physical
  conditions of each observed point.  For HCO$^+$ J=4-3, application
  of Monte Carlo 
  radiative transfer will be used to check the CEP solutions when
  applicable.  Applicable codes have already been developed by the
  proposing team (CEP:
  Kulesa, MC: D. Narayanan).

\smallskip
\noindent 2) {\bf Photodissociation region (PDR) models} aim to reproduce the
  physics, chemistry, and emergent spectra of the surfaces of
  molecular clouds exposed to energetic stellar radiation.  PDR codes
  were originally developed to model the interstellar clouds subject
  to intense UV fields, like those in massive star forming regions
  \citep{hollenbach85,vDB88}.  We
  will use modified versions of CLOUDY \citep{Ferland98} and the Meudon
  PDR code \citep{meudon} in combination with the radiative transfer
  models cited above, to derive physical models of the observed
  regions, allowing the radiative impact on any cloud to be derived. 

\smallskip
\noindent 3) {\bf Dynamical analyses.}  Besides the effects of their
  radiation, stars influence clouds by depositing kinetic energy in
  protostellar outflows, stellar winds, and shocks from supernovae.
  This energy input is expected to drive turbulent linewidths in
  clouds, but the nature of this link is poorly established. 
  To extract this kinematic information from
  the data set, we will first perform moment analyses of the CO and
  HCO$^+$ spectral line profiles.  Centroid maps outside the line
  cores constitute the standard technique for finding high velocity
  gas such as shocks and outflows \citep{walker93,groppi}.  The line
  width provides a measure of the velocity components coincident
  within a telescope beam and sets an upper limit on the turbulent
  velocity field.  Secondly, we will extract kinematic information
  through a principal component analysis (PCA), a statistical approach
  that emphasizes the underlying patterns and regularities within
  complex data sets while minimizing inferences derived from
  incidental features \citep{heyer97}. \cite{brunt} have demonstrated
  that PCA can recover the true 3-dimensional statistics of the
  velocity field, distinguishing incompressible, eddy-like flows from
  strong compressible motions that create shocks and generate density
  enhancements like cloud cores.  These analyses will allow us to
  define the inertial range in molecular clouds and the variation of
  turbulence within molecular clouds and dense cores.  

\smallskip
\noindent 4) {\bf Development of a Milky Way Template}.  At high-redshift,
(sub)mm-observations of molecular gas in galaxies 
are typically restricted to higher-rotational quantum number
transitions (J$\geq$3).  Because the ground state transition is the
principal tracer of star-forming molecular gas (H$_2$), some assumption
invariably has to be made regarding the excitation of CO.  This can
dominate the error budget in determining the gas mass of the 
galaxy, driving uncertainty in baryonic gas
fraction determinations of high-z galaxies. 
In the era of ALMA, these quantities are routinely being
measured in galaxies from z=0-6 in order to understand the baryon
cycle in galaxies that governs gas accretion from the intergalactic
medium, conversion into stars, and subsequent expulsion due to stellar
feedback. Our high-resolution CO (J=3-2) survey of the Galactic plane
will reduce this uncertainty.  By comparing Supercam data to the
FCRAO CO and \tco\ J=1-0 surveys of the Milky Way, we will be
able to construct CO (J=3-2)/(J=1-0) line ratio maps across the
Galaxy at parsec scales.  Comparisons of this data to young stellar
object counts 
for nearby clouds will allow us to parameterize the excitation in
terms of the star formation rate surface density, the observable
quantity most likely to correlate with molecular excitation, and most
readily observable for high-z galaxies.  
This comparison will also establish the Galactic Kennicutt-Schmidt Law.
We will compute Star Formation Rate to the surface brightness of CO
J=3-2 and HCO$^+$ J=4-3 relation for gas in a 
large range of physical conditions, determining the most complete
estimate of the Milky Way's molecular luminosity in a dense gas tracer.
This strongly connects the Milky Way to observations of other galaxies.  
These templates will allow
our team to not only inform future observations, and help constrain
the cosmic evolution of the baryonic gas fraction in galaxies.  With
observations and cosmological simulations showing dramatic differences
in the predicted gas fractions of high-z galaxies (Narayanan, Bothwell
\& Dave, 2012)%; MNRAS 426, 1179)
, the construction of these templates will be timely.


\begin{table}[!hbt]
\centering
\small
\begin{tabular}{|l|c|l|}
\hline
{\bf Participant} & {\bf Affiliation} & {\bf Partipation
  Activity} \\
\hline \hline
Craig Kulesa  & U. Arizona &  PI: Reviews \& approves operations plans and execution \\
 & & Reviews and approves science data products \\
 & & Coordinates collaborative followup observations. \\
\hline
Chris Walker & U. Arizona & Co-PI (Supercam PI): Leads science advising effort with students \\
 & & Responsible for instrument viability \\
 & & Shares responsibility for science operations, \& data products \\
\hline
Yancy Shirley & U. Arizona & Co-PI: Lead responsibility for dense gas
mapping in HCO$^+$ \\ 
 & & Shares student advising effort \\
\hline
John H. Bieging & U. Arizona & Integration of SuperCam data with 1.3mm
HHT survey \\ 
\hline
Ed Churchwell & Wisconsin & Advisor: Synergy with GLIMPSE survey \\
\hline
Paul Goldsmith & JPL & Advisor: Synergy with Herschel GOTC$^+$ survey
\\
\hline
Alyssa Goodman & Harvard & Advisor: Synergy with C2D \& COMPLETE surveys \\
\hline
Chris Groppi & Arizona State & Participates in science operations \& instrument upgrades \\
\hline
Mark Heyer & U. Mass & Advisor: Synergy with GRS survey, PCA analysis \\
\hline
Desika Narayanan & U. Arizona & Theoretical modeling, construction of Milky Way template \\
\hline
Gopal Narayanan & U. Mass & Advisor: Galactic Surveys \& Star formation regions \\
\hline
\end{tabular}
\caption{\label{roles} \small Activities of the Supercam Science Team}
\end{table}


\subsubsection{Roles of the Collaboration Participants}

Senior personnel who will use the Supercam instrument in this first ``key''
program at the HHT are listed in Table~\ref{roles}.  {\it In addition,
  numerous students will participate in the science 
development at the University of Arizona and participating organizations.}


\section{Project Impact}

\subsection{Educational Impact}

The training of students in the development and use of state-of-the-art
instrumentation  
is essential to the future of science. This is particularly true in
mm/submm astronomy where technological advances are occuring so rapidly.
Ironically, there are only a handful of laboratories in the world
where students 
gain hands-on experience in the design, fabrication, and fielding of
radio astronomy 
instrumentation. In the team's lab (SORAL: Steward Observatory Radio
Astronomy Laboratory), we have been fortunate to have had
a number of 
talented students pursue their research. Over the past 10 years the
lab has produced  
9 Ph.D.'s and numerous undergraduate senior projects. Most of the
Ph.D.'s are still 
pursuing astronomical research and a number of the undergraduates have
gone on to 
receive Ph.D's at other institutions. In recent years research in the
lab has drawn 
an increasing number of students from other departments, particularly
optical sciences and electrical engineering.  It is interest in
astronomy and the interdisciplinary nature of the research 
that attracts them to the SORAL lab.  In an effort to reach this
population of students, 
the Co-PI's and fellow faculty members in other departments are seeking to
establish an 
interdisciplinary program in astronomical instrumentation. Two of
Co-PI Walker's past
Ph.D. students have received majors and minors in different
departments.  Co-PI Walker currently 
has 4 graduate and 2 undergraduate students participating in
interdisciplinary studies. 

In the proposed budget, funds for only one graduate student are
requested. The use of Supercam on the HHT will be the focus of the
student's research. However, as is customary in the SORAL lab,
many other students will also participate in making the program a
success. Indeed, 
one of the most important aspects of training students 
is the experience gained in working in teams. Astronomical science and
instrumentation is 
becoming ever more complex, and requires the talents  
of many individuals. Providing students with both technical training
and team-work experience increases their probability of success. 

\subsection{Global Impact: Survey Synergies}
\label{synergies}

The proposed Galactic Plane survey with Supercam
will serve as a ``finding chart'' for future, focused surveys 
with ALMA and markedly enhance the value of numerous contemporary
surveys.  These data will be released openly to the astronomical
community, with no proprietary period. 

\subsubsection{BGPS and ATLASGAL continuum surveys}

The 1.3mm Bolocam Galactic Plane Survey and 850~$\mu$m ATLASGAL survey
from APEX represent the most comprehensive long-wavelength continuum surveys
of high column density, cold dust in the Galaxy.  As previously
described in Section~\ref{mapping}, we will map the kinematics and
column of HCO$^+$ toward $\sim10^3$ cold dust condensations, and
expect to map extended HCO$^+$ emission towards many of them.  With
Supercam's survey of dense gas, a linewidth-size relationship can be
computed, which is critical to 
studies of turbulence and basic scaling laws for star formation. 
Approximately 12\% of HCO$^+$ detections
from Schlingman et al. (2011) showed a self absorption profile (Figure
9) indicating that we will also identify many potential infall
candidates (see Reiter et al. 2011).  Co-PI Shirley will coordinate
efforts to maximize the scientific return from Supercam's dense gas
surveys in combination with the BGPS.

\subsubsection{GLIMPSE, MIPSGAL, and Hi-GAL}

The Spitzer Space Telescope Legacy program GLIMPSE, 
headed by E. Churchwell, provided a thermal infrared survey of the
Galactic plane that provides a complete census of star formation, the
stellar structure of the molecular ring, will map the warm
interstellar dust, constrain extinction laws as a function of
galactocentric radius and will detect all young embedded O and B
stars.  MIPSGAL extended the wavelength coverage to Spitzer's
24~$\mu$m band, and Herschel's Hi-GAL program is mapping 720
sq.deg. of the Galactic Plane in 5 bands from 60 to 600~$\mu$m.  
Supercam's Galactic Plane survey will provide the best corresponding
molecular cloud survey that will account for the 
dense cloud material that forms stars,  cloud interaction with
formed stars, and kinematic disruption by mass ejection, outflow, and supernova
remnants.  Collaborator E. Churchwell will provide guidance in 
interpreting Spitzer data for comparison with the Supercam survey. 

\subsubsection{ From Molecular Clouds to Young Stars}
A second Spitzer
Legacy proposal, ``From Cores to Disks'', or ``C2D'', surveyed a sample of
giant molecular clouds and complexes in infrared continuum emission
to provide a complete base for nearby star formation and to follow
the transition from starless cloud cores to low-mass disks. 
The COMPLETE survey \citep{complete} provided a 
reference study of the mm wave dust continuum emission and the
$J=1\rightarrow0$ lines of CO and $^{13}$CO using the FCRAO Sequoia
array.  Our target surveys of Outer Galaxy and high latitude 
GMC's add significant value by providing
higher-J CO data critical for the study of star forming
regions where many excitation components are often present and cannot
be disentangled with only one spectral line.   
Collaborator Alyssa Goodman (CfA)
will provide guidance in comparing COMPLETE data with the Supercam survey.

\subsubsection{Galactic Ring Survey} The FCRAO Galactic 
Ring Survey led by J. Jackson 
provided the most sensitive study of the inner Galaxy to
date, but only mapped the $^{13}$CO $J=1\rightarrow0$ line.
This proposed
study will improve upon the GRS resolution by up to a factor of 4 in 
area and yield the crucial higher-J lines that make proper
interpretation of existing CO surveys possible.  Collaborator Mark
Heyer (U.Mass) is a member of the GRS team and will provide
guidance interpreting the GRS \& Supercam data. 

\section {Project Management}
\label{management}

Transitioning Supercam from an instrument development to a scientific
workhorse is an exciting prospect that our team has been working
towards for years. Collectively the Supercam
team members represent many years of successful instrument development and
observing experience.  As related by Table~\ref{roles}, 
the main components of the organization are the PI, who has overall 
responsibility for the project and coordinates the activities of the 
participants; Co-PI's Walker and Shirley, who share in these
responsibilities and lead the student advising efforts; and the
distributed members of the science team who act as an advisory council
to the PI and Co-PIs to ensure that the project stays on course. 
A schedule of key project milestones and tasks is provided in
Figure~\ref{gantt}. 
Routine communications between project participants is essential.
There will be monthly science team telecons
to monitor progress and provide insight into solutions to
emerging problems, and redefine priorities as needed. A Supercam wiki
at Arizona will provide a resource for team communications and
documentation.  

\begin{figure}[!htb]
\centering
\begin{minipage}{6.5in}
{\parbox{5.7in}{\includegraphics[angle=0,scale=0.7]{figures/gantt.eps}}}
{\parbox{0.7in}{\caption{\small \label{gantt} Supercam Science
      Operations Timeline }}}
\end{minipage}
\end{figure}


\clearpage

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