\documentstyle[twoside,epsfig,CJK]{carticle}
%\documentclass[twoside]{carticle}
%\usepackage{epsfig}
\pagestyle{empty}
\headsep=0.6cm %%%%%%%

\setcounter{page}{130}

%\input cchead.sty
%\input Vatola.sty

\def\thefootnoot{}

\textwidth=140mm \textheight=210mm \topmargin=0pt
\oddsidemargin=0pt \evensidemargin=0pt \footskip 0.2 truecm

%%...................
%\vspace*{1\baselineskip}
\doublerulesep=0pt
%%..................
% \renewcommand{\baselinestretch}{1.4} %%cc
\parindent=7.5mm

\setlength{\parskip}{0 true pt}
    \def\hang{\hangindent\parindent}
    \def\RE{\par\hang\textindent}
    \catcode`@=11
%%%双页
    \def\@evenhead{\underline{\parbox{\textwidth}
    {\small\rm\zihao{6}\songti\thepage\hfill
    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
%%%单页
    \def\@oddhead{\underline{\parbox{\textwidth}
    {\small\rm \zihao{6}\songti suppl.\hfill P. Reich: Large Scale
    Surveys of the Galaxy   %%（作者：题目名称）
    \vspace{1.5mm}
    \hfill\thepage}}} %%%%%%%
    \normalsize\rm
\zihao{5}\songti

    \begin{CJK}{GB}{song}
    \begin{document}


%%篇首
    \thispagestyle{empty}
    \vspace*{-1.5 true cm}
    \small\rm
    \zihao{6}\songti
    \noindent
    \\%%%[-0.5 true mm]
    Vol.44~ Suppl.
    \hfill\hspace{8mm} %%% if ``October/January'' then \hspace{8/10 mm} July
    \small ACTA ASTRONOMICA SINICA
    \hfill
      Feb.,~2003 \\[-1.5 true mm] %%January
    \rule {\textwidth}{0.12 true mm}\\[-3.2 true mm]
    \rule {\textwidth}{0.12 true mm}
%%%%%%%

\input{../newcom.ctx}

\renewcommand{\baselinestretch}{1}

\setcounter{footnote}{130}

\vs\vs\vs \bc {\Large\bf\zihao{2}\heiti
Large Scale Surveys of the Galaxy    %%（文题）
%\\[1ex]
%$\!\!^*$
}



\vs\vs{\normalsize Patricia Reich}  %%（本文作者）

\vs
(\footnotesize {\it Max-Planck-Institut f\"ur Radioastronomie, Auf dem H\"ugel 69,
53121 Bonn, Germany}) %%（本文作者单位）
\vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~~\small The radio emission from normal
 galaxies is weak and requires
the largest telescopes to observe them. In principal the best case to study
normal galaxies is our own one. However, our unfavourable location within
the Galaxy makes it necessary to conduct large-scale surveys at different
frequencies in order to derive physical properties of the Galaxy.

For a long time the 408\,MHz all-sky survey and the 1420\,MHz survey of the
northern sky have been the most reliable surveys to perform these studies.
In the last years the 1420\,MHz survey has been extended to an all-sky survey.
Also at 22, 45 and 2625\,MHz large portions of the Galaxy were recently
mapped, so that there is an unprecedented database for Galactic studies
available today. However, some care must be taken when comparing these surveys
as they come from rather different telescopes and use different
observing techniques.

\end{quotation}

%%%% 正文
 \para{\large\bf{1}~~ Introduction}

\vspace{4mm}
Since the beginning of radio astronomy radio continuum surveys at different
frequencies have been conducted in order to study our own Galaxy. For example
 the parameters of the thin and the thick disk or halo were modelled.
With these global parameters of the Galaxy, comparisons with those from
 other galaxies are possible.
 %and allow to classify the Galaxy.
The spectrum of the radio emission can be  computed and a
 separation of the thermal and non-thermal emission can be made.
Surveys provide an overall view to large
local features extending up to 100\dg like the prominent North Polar Spur
(NPS). Other large supernova remnants, HII region complexes,
loops and spurs are also outstanding features in the survey maps and
can be studied in some detail.

Beyond astronomical applications surveys are important in other fields.
The Galactic background is a major source of noise at low frequencies and
sets the limit for receiver sensitivities other than technology,
which constrains the sensitivity in the high frequency range.
It was recently realised that the 1.4\,GHz
 surveys are of special interest for coming 1.4\,GHz satellite measurements
of the
 ocean salinity or soil moisture, because these radiometers pick up
 Galactic emission by their sidelobes and ground reflections
(Kerr et al. 2002 and references
 therein). Furthermore surveys give a comprehensive overview
of the Galactic foreground emission, which has to be subtracted from cosmic
 microwave background measurements before studies of its fine structure
for cosmological information.
%
Finally absolutely calibrated sky surveys are needed to add
 missing large-scale components to interferometric data. Also
 relative measurements of limited fields made with large single dishes
like the Effelsberg telescope gain from adding correct large-scale
structures.
%Relative measurements have zero at the edges
% of a map and underlying large scale structures are lost, which however might
% be added from the survey maps.

\para{\large\bf{2}~~The Surveys}

\vspace{4mm}
In the following surveys will be described which at least  cover
a third of  the sky and  include emission on all
scales. This excludes  high
resolution source surveys by interferometers or single dishes. Finally
 the surveys need to be available in numerical form, which excludes a number
of older maps. More information and discussions of previous surveys
were already provided e.g. by Salter \& Brown (1988) and by Reich (1990).

For 20 years one all-sky survey was available to the  astronomical
community, namely the 408\,MHz survey by Haslam et al. (1982). In the eighties
 the 1420\,MHz survey of the northern sky was published (Reich 1982;
 Reich \& Reich
 1986), and then it took more than ten years to publish more large-scale
 surveys at other frequencies. At the low-frequency end a 22\,MHz survey
of the northern sky
(Roger et al. 1999), at 45\,MHz first the southern sky survey,
and then the northern sky
survey (Alvarez et al. 1997; Maeda et al. 1999) were finished. At the
high-frequency end
first the southern sky at 2326\,MHz (Jonas, Baart, \& Nicolson 1998) and
later at 1420\,MHz was published (Reich, Testori, \& Reich 2001).
 Merging
of the 1420\,MHz maps in the southern and northern sky gives an all-sky
survey superior in angular resolution and
 sensitivity when compared to the 408\,MHz survey. Tables 1 and 2 list some
basic parameters of the above mentioned surveys.

\vspace{-2mm}\bc{\small\bf

 Table 1~~   Large-scale surveys of the Galaxy: basic parameters 1
}\\[2mm]

\fns \tabcolsep 4mm
\begin{tabular}{cccl}
\hline\\[-3.6mm]\hline
 Frequency & HPBW & Coverage & Authors \\
   (MHz)   & (\dg)&          &  \\
\hline
     22    & 1.1$\times$1.7 & $-28\dg\leq\delta\leq+80\dg$ & Roger et al. 1999 \\
  45     & 3.6     & $+5\dg\leq\delta\leq+65\dg$ & Maeda et al. 1999 \\
     45  & 4.6$\times$2.4 & $-86\dg\leq\delta\leq+19\dg$ & Alvarez et al. 1997 \\
408   &   0.85     & all-sky & Haslam et al. 1982 \\
 1420    &  0.59    & $\delta\geq-19\dg$   & Reich 1982; Reich \& Reich 1986\\
 1420     & 0.59   &  $\delta\leq-10\dg $  & Reich, Testori, \& Reich, 2001\\
2625      & 0.333 & $-83\dg\leq\delta\leq+13\dg$ & Jonas, Baart, \& Nicolson 1998\\
 \hline\\[-3.6mm]\hline
 \end{tabular}
 \ec

\bc{\small\bf

 Table 2~~   Large-scale surveys of the Galaxy: basic parameters 2
}\\[2mm]

\fns \tabcolsep 4mm
\begin{tabular}{cccl}
\hline\\[-3.6mm]\hline
 Frequency &   Sensitivity & Available from\\
   (MHz)  &               &               \\
\hline
     22     &  5000\,K & tom.landecker@nrc.ca\\
     45     &   250\,K & maeda@hcmern.hyo-med.ac.jp\\
     45     & 250\,K &  halvarez@das.uchile.cl \\
            &        & jmay@das.uchile.cl\\
     408    & 2\,K   &www.mpifr-bonn.mpg.de/survey.html\\
    1420    & 50\,mK &www.mpifr-bonn.mpg.de/survey.html \\
    1420    & 50\,mK & www.mpifr-bonn.mpg.de/survey/plots.html \\
    2625    & 30\,mK & J.Jonas@ru.ac.za \\
 \hline\\[-3.6mm]\hline
 \end{tabular}
 \ec

The 820\,MHz survey of the northern sky by Berkhuijsen (1972) is
not listed in the tables, because its original resolution of
1\dg.2 is degraded to 5\dg to increase the signal-to-noise ratio
in the low-intensity area between 150\dg and 270\dg in Galactic
longitude and roughly 30\dg and 50\dg to 70\dg in latitude.
However, this survey is also available at
http://www.mpifr-bonn.mpg.de/survey.html together with other
Galactic plane surveys not being discussed here.

\vn{\bf{2.1~~The Telescopes}}

The surveys have been realised by using technically quite different
 telescopes. The
22\,MHz survey was observed  at the Dominion Radio Astrophysical Observatory
 in Penticton (Canada). The T-shaped telescope consists of 624 full-wavelength
 dipoles and has an extent of 1310 $\times$ 443\,m (Costain, Lacey, \& Roger 1969).

The 45\,MHz survey of the southern sky was observed at Maipu in
Chile. There 528
 full-wavelength east-west orientated dipoles are arranged in  a rectangular
 field of  106 $\times$ 73 metres (May et al. 1984).

The 46.5\,MHz survey of the northern sky was conducted with the MU-Radar located
 in Shigaraki (Japan), where 475 crossed 3-element Yagis are arranged in a
 circle with a diameter of 103 metres (Fukao et al. 1985a, 1985b).

The 408\,MHz survey was combined from maps made with three large single-dish
 telescopes at Jodrell Bank (England), Effelsberg (Germany) and Parkes (Australia).

The 1420\,MHz survey of the northern sky was carried out with the 25-m Stockert
telescope of Bonn University (Reich 1977).
% which is located very close to the  Effelsberg 100-m telescope.
 The southern sky has been observed using a 30-m antenna at Villa
Elisa (Testori et al. 2001) located in the southern area of
 Buenos Aires (Argentina).

The 2326\,MHz survey of the southern sky came from  the 26-m antenna at
Hartebeesthoek (Jonas 1999) in South Africa, which is 1100\,km away
 from the supervising
 Rhodes University.

Most of the low-frequency antennas are located at quite
remote, isolated places in order to avoid man-made interference,
which is an increasing problem at higher frequencies as well. As
a consequence the Stockert 25-m telescope was closed at the
end of the eighties.


\vn{\bf{2.2~~The Observation Techniques}}

The observing techniques for the surveys were as different as the
telescopes used. The low-frequency surveys utilise sky rotation at
constant declinations to cover the sky. The 2326\,MHz survey has
been observed exactly orthogonally by moving the telescope along
declination. The 1420\,MHz survey of the northern sky is made from
azimuth scans at three different fixed elevations. The ``nodding
scan technique'' (Haslam et al. 1974), which is rather efficient
to reduce receiver drift effects, has been applied for most parts
of the 408\,MHz survey and also for the 1420\,MHz survey of the
southern sky. Nodding scans were collected by moving the telescope
up and down in the meridian and use the sky rotation to cover
large areas. Starting this continuous procedure for a sequence of
nights at different sidereal times gives a fully sampled grid of
data, where up and down scans intersect.

\para{\large\bf{3}~~The 1420\,MHz Survey}

\vspace{4mm} A 1420\,MHz all-sky survey map has been combined by
adding the northern and southern  survey  in the overlapping area
in such a way that the weight of each survey decreases as its
declination is reaching the survey's limit. In that way
discontinuities at $\delta=-10\dg$ or at  $\delta=-19\dg$ were
avoided. Fig.\,1 shows this survey, for clarity degraded to a
resolution of 2\dg, in an equal-area projection in Galactic
coordinates centered at the Galactic Centre. The contours are
running in steps of 50\,mK up to 4.4\,K, 100\,mK up to 6.0\,K,
250\,mK up to 7\,K, 500\,mK up to 10\,K and in steps of 1\,K
further on. Contour labels are in K T$_{\rm B}$ (full beam
brightness). Arrows on contours point towards local minima.  The
map is at an absolute scale, where the cosmic microwave background
and unresolved sources contribute in total by 2.8\,K T$_{\rm B}$.
\begin{figure}[tbph]
\vs\center {\includegraphics [bb=0 0 283 519,scale=1.1]{f1.eps}}

  % \parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize
 Fig.\,1~~ The 1420\,MHz all-sky survey at a resolution of 2\dg}
 \end{figure}
 \begin{figure}[tbph]
\center {\includegraphics [bb=0 0 283 511,scale=1.1]{f2.eps}}

   %\parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize
Fig.\,2~~ Sketch of some prominent structures seen in Fig.1}
\end{figure}

 The maximum emission
along the Galactic plane reflects the high concentration of
emission in the Galactic disk. At 2\dg angular resolution most source
complexes merge with the diffuse unresolved emission. The local
 spiral arm towards
 Cygnus and Vela (longitudes about
90\dg and 270\dg, respectively) clearly show up. Our position at
about 8\,kpc distance from the Galactic Centre allows to trace the enhanced
high latitude
emission from the inner Galaxy and quite weak emission towards
the Galactic anticentre direction.

In Fig.\,2 some well-known individual features are labelled on a
1420 MHz map with just a few selected contours. The most intense
feature sticking out of the Galactic plane at about 30\dg Galactic
longitude is the North Polar Spur (NPS).
%Beside an overall increase of emission towards the Galactic plane the
%prominent NPS is visible.
It is believed to be the relic of a very old SNR located at just
 about 200\,pc distance. A comprehensive review on the NPS was made by
Salter (1983). In contrast, the two historic supernova remnants,
the Crab nebula and Cas A, are the two strongest unresolved
sources in the sky.

The Galactic Centre Spur (GCS) is
the second strongest spur in the map following the NPS reaching out
of the Galactic plane for more than 20\dg. It can be traced on maps
with higher angular resolution to about 1\dg
distance to the Galactic Centre and was proposed by
Sofue, Reich, \& Reich (1989) to be emerging from there. In that case
it is a well collimated feature
with a length of 4\,kpc and a width of just 200\,pc.


%In the Cygnus and Vela regions we are
%looking into the local spiral arm directly, so the intensities are
%relatively high there.
Some nearby galaxies as the Large Magellanic Cloud (LMC), the
Small Magellanic Cloud (SMC) and M31 (Andromeda Galaxy) are
visible as distinct sources at high Galactic latitudes. A number
of strong radio galaxies are marked in Fig.\,2 too. The rather
extended and partly resolved radio galaxy Centaurus A has recently
been rediscussed by Alvarez et al. (2000) including data from the
surveys listed in Table 1.

%Further radio galaxies are For A, Hyd A,
%and  Pic A.
%The thermal region near Ori A appears much stronger compared
%to the 408 MHz map (Figure 5 of Haslam et al. 1982).
\para{\large\bf{4}~~ The Spectral Index Distribution}

\vspace{4mm}
Spectral indices can in principle be calculated from any pair of
surveys, although
a careful analysis of all the calibration properties like scaling,
zero-level adjustments and systematics from the observing method must
be made to obtain reliable results. For example,
such an analysis was made by Reich \& Reich (1988a) %is referred to,
who derived a spectral
index map between 408\,MHz and 1420\,MHz for the northern sky.
Significant spectral index variations were noted, reflecting the
mixture of thermal and synchrotron emission along the
Galactic plane. The changes in the
energy spectrum of the relativistic electron component in the Galaxy also cause
spectral variations.
A particular puzzling feature of this spectral index map is the spectral
flattening towards high latitudes in the Galactic anticentre, which was
interpreted by Reich \& Reich (1988b) as evidence for a Galactic wind.
This could be interpreted in terms of the cooling-convection halo
models  proposed by Lerche \& Schlickeiser (1982).
Extending this work by including the new southern sky data
at 1420\,MHz confirms qualitatively the same spectral behaviour
for the southern sky (Reich et al., in prep.).

%\vspace{-2mm}
\bc
{\bf References}
\ec

\vspace{-5mm} \no \fns

 \nref  Alvarez H, Aparici J, May J, et al.  A\&AS, 1997, 124: 315
 \nref  Alvarez H, Aparici J, May J, et al.  A\&A, 2000, 355: 863
 \nref  Berkhuijsen E M.  A\&AS 1972, 5: 263
 \nref  Costain C H, Lacey J D, Roger R S.  IEEE Trans IP, 1969, 17: 162
 \nref  Fukao S, Sato T, Tsuda T, et al.  Radio Science, 1985a, 20: 1155
 \nref  Fukao S, Tsuda T, Sato T , et al.  Radio Science, 1985b, 20: 1169
 \nref  Haslam C G T, Wilson W E, Graham D A, et al.  A\&AS, 1974, 13: 359
 \nref  Haslam C G T, Salter C J, Stoffel H, et al. A\&AS, 1982, 47: 1
 \nref  Jonas J L, Baart E E, Nicolson G D.  MNRAS, 1998, 297: 977
 \nref  Jonas J L. 1999, Ph. D. Thesis, Rhodes University, South Africa
 \nref  Kerr Y H, Wigneron J P, Waldteufel P, et al. 2002, in Proc. SPIE
VOL. 4542, Remote Sensing for Agriculture, Ecosystems, and
Hydrology III, ed. M. Owe \& G. D'Uro, 72
 \nref  Lerche I, Schlickeiser R.  A\&A, 1982, 107: 148
 \nref  Maeda K, Alvarez H, Aparici J, et al. A\&AS, 1999, 140: 145
 \nref  May J, Reyes F, Aparici J, et al.  A\&A, 1984, 140: 377
 \nref  Reich P, Reich W.  A\&AS, 1986, 63: 205
 \nref  Reich P, Reich W.  A\&AS, 1988a, 74: 7
 \nref  Reich P, Reich W.  A\&A, 1988b, 196: 211
 \nref  Reich P, Testori J C,  Reich W. A\&A, 2001, 376: 861
 \nref  Reich W. 1977, Ph. D. Thesis, University of Bonn, Germany
 \nref  Reich W.  A\&AS, 1982, 48: 219
 \nref  Reich W. 1990, IAU No. 144, ``The Interstellar Disk-Halo
 Connection in Galaxies'', ed. H. Bloemen, p. 187
\nref  Roger R S, Costain C H, Landecker T L, et al. A\&AS, 1999,
137: 7 \nref  Salter C J.  BASI, 1983, 11: 1 \nref  Salter C J,
Brown R L. 1988, in ``Galactic and Extragalactic Radio
Astronomy'', eds. G.L. Verschuur \& K.I. Kellermann, p. 1 \nref
Sofue Y, Reich W, Reich P. ApJ, 1989, 341: 47 \nref  Testori J C,
Reich P , Bava J A, et al. A\&A, 2001, 368: 1123


\end{CJK}
\end{document}
