% Tomotsugu GOTO and the SDSS Collaboration
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% "Frontier in Astroparticle Physics and Cosmology"
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\BookTitle{Frontier in Astroparticle Physics and Cosmology}
\CopyRight{\copyright 2004 by Universal Academy Press, Inc.}

\begin{document}

\BookTitle{\itshape Frontier in Astroparticle Physics and Cosmology}
\CopyRight{\copyright 2004 by Universal Academy Press, Inc.}
%\tableofcontents
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\chapter{The Origin of E+A Galaxies%   %%%%%%%%% <===== TITLE of the contribution
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%Instructions for the Preparation of 
%Manu\-scripts for the Symposium Proceedings
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\author{%
Tomotsugu GOTO and the SDSS Collaboration\\%%%%%% <== First author
{\it Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan}
}
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\AuthorContents{T.\ Goto} %%%%%%% <=== It is the data for CONTENTS. Please enter all author's name that should be inithialized.

\AuthorIndex{Goto}{T.} %%%%%%% <=== It is the data for AUTHOR INDEX. Please enter a author's name that should be inithialized.
%\AuthorIndex{Nagataki}{S.}%%%%%%% <=== It is the data for AUTHOR INDEX. Please enter a author's name that should be inithialized.

%
%\section*{Abstract}
%
%An introduction for preparing manuscripts for the proceedings of
%the the 6th RESCEU International Symposium on
%{\it Frontier in Astroparticle Physics and Cosmology}\/ 
%held on 4--7 November, 2003
%is given in the present paper.  
%This paper is written in the format to be used for all
%manuscripts and illustrates the final appearance for the symposium papers. It is
%very important to follow these instructions to both ensure that your manuscript is
%quickly accepted, and to present a consistent and professional looking symposium
%proceedings publication. 


\section{E+A Mystery}

 E+A galaxies are galaxies with strong Balmer absorption lines and with no
 significant emission in [OII] or H$\alpha$ lines.  
  The existence of strong Balmer absorption lines shows 
 that these galaxies have experienced a starburst within the last 1 Gyr.  At
 the same time, these galaxies do not show any sign of on-going star 
 formation as indicated by the lack of [OII] or H$\alpha$ emission lines.  
   Therefore, E+A galaxies are interpreted as a post-starburst galaxy ---
 a galaxy which truncated starburst suddenly. 
  However, for more than 20 years, the origin of this post-starburst
 phenomena remained a mystery. 
 Using the 100,000 galaxy spectra of the Sloan Digital Sky Survey,
 we tested three popular explanations to the E+A phenomenon.


\section{Are E+As Created by a Cluster-Related Mechanism?}

  At first, E+A galaxies were found in cluster regions. Therefore,
  cluster related physical mechanisms have been thought to be
  responsible for the E+A phenomena. However, in the left panel of
  Fig. 1, E+A galaxies show the same local galaxy density distribution
  as field (all) galaxies. These numerous field E+A galaxies
  cannot be explained with a cluster related physical mechanism.  

\section{Are E+As Dusty Starbursts?}

     Another possible explanation for E+A phenomena is a dusty starburst, where
    E+A galaxies are actually star-forming, but emission 
    lines are invisible in optical wavelengths due to the heavy
   obscuration by dust. 
    However, in the middle panel of Fig.1, all E+As have $r-K<1.1$, where
    the theoretical models predict  $r-K \sim 1.5$ for dusty starburst galaxies. In
    the left panel of Fig.1, no E+As show any sign of starburst in radio
    estimated (dust-free) star formation rate derived from the FIRST data. 


\section{Are E+As Meger/Interaction Origin?}

 Merger/Interaction between two galaxies also can induce star
 formation. In Table 1, we counted number of accompanying galaxies
 within 50 and 75 kpc around E+A galaxies and compared those with
 randomly selected normal galaxies. We use galaxies with $-23<Mr<-19.5$
 and statistically subtract background counts using the global galaxy
 number counts in the SDSS data. As shown in the table, E+As have more
 accompanying galaxies than normal galaxies. Especially E+As with the
 strongest H$\delta$ absorption (H$\delta$ EW $>7\AA$) have 8 times more
 accompanying galaxies within 50 kpc. Since this excess in the number of
 accompanying galaxies is significant, we conclude that E+As are most
 likely to have a merger/interaction origin \cite{PhD}\cite{PASJ}. 






\begin{table}[h]
%\begin{center}
\caption{
 Number of accompanying galaxies around all the E+A galaxies and E+As
 with H$\delta$ EW$>$7 are compared with that of 1000
 randomly picked galaxies. We use galaxies 
 with -23.0$<Mr^*<$-19.5 after $k$-correction within the radius of 50 and 75
 kpc. Fore/background galaxy number counts are  statistically subtracted. 
}\label{tab:ea2_nearby_galaxies}
\begin{tabular}{lll}
\hline
 Sample  & $N_{nearby\ galaxy}$ within 50 kpc  & $N_{nearby\ galaxy}$ within 75 kpc \\
\hline
\hline
 Random                         &   0.03$\pm$0.01 & 0.16$\pm$0.01  \\ 
 All E+As                       &   0.12$\pm$0.03 & 0.26$\pm$0.04  \\ 
 E+A with H$\delta$ EW$>$7 \AA  &   0.24$\pm$0.09 & 0.40$\pm$0.12  \\ 
\hline
\end{tabular}
%\end{center}
\end{table}




\begin{figure}[t]
  \begin{center}
    \includegraphics[height=10pc]{030430_ea_density_5th_ea.ps}%%%%%
%   \includegraphics[height=10pc]{/home/tomo/public_html/research/out/030416_ea2_rk_jk.ps}%%%%% 
    \includegraphics[height=10pc]{031120_ea2_rk_jk_resceu.ps}%%%%% 
%  \includegraphics[height=10pc]{/home/tomo/public_html/research/out/030430_radio_sfr_uplimit.ps}%%%%%
    \includegraphics[height=10pc]{031120_radio_sfr_uplimit_resceu.ps}%%%%%
  \end{center}
  \caption{(left) Local galaxy density distribution for E+As and all
 galaxies. (middle) SDSS-2MASS optical-near infrared color distribution.
 (right) Radio estimated star formation rate derived from the FIRST data.}
\end{figure}




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%   \bibitem{Aquasition Editor: UAP}   %%%%% This case: Book and/or Proceedings. 
%   K. Sato and M. Kawasaki, 
%  {\em Birth and Evolution of the Universe}
%  (2001) Universal Academy Press, Tokyo.
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    \bibitem{PhD}   %%%%% This case: Journal.
    T. Goto, PhD Thesis, 2003, The University of Tokyo, astro-ph/0310196
 
    \bibitem{PASJ}   %%%%% This case: Journal.
   T. Goto et al., 2003, PASJ, 55, 771
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%    N. Seiberg, 
%    Phys. Lett. B318 (1993) 469.

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%\chapter*{ Entry Form for the Proceedings }
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%\section{Title of the Paper}
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%\* The Origin of E+A Galaxies %%% EXAMPLE %%%
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%\item Full Name:                Tomotsugu Goto %%% EXAMPLE %%%
%\item First Name:               Tomotsugu %%% EXAMPLE %%%
%\item Middle Name:               %%% EXAMPLE %%%
%\item Surname:                  Goto %%% EXAMPLE %%%
%\item Initialized Name:         T. Goto %%% EXAMPLE %%%
%\item Affiliation:              University of Tokyo, Japan %%% EXAMPLE %%%
%\item E-Mail:                   tomo@jhu.edu %%% EXAMPLE %%%
%\item Ship the Proceedings to:  Dept of Physics \& Astronomy, 3400
%      N. Charles Street, Baltimore, MD, 21210, USA %%% EXAMPLE %%%
%\end{itemize}
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%%%%%%%%%%%%%%%%%% This item unit is just for one author.
%%\item %
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%%\item Full Name:                Johann Sebastian Bach
%%\item First Name:               Johann
%%\item Middle Name:              Sebastian 
%%\item Surname:                  Bach
%%\item Initialized Name:         J. S. Bach
%%\item Affiliation:              St. Thomas Church, Leiptzig, Germany
%%\item E-Mail:                   jsbach@somewhere
%%\item Ship the Proceedings to:  St. Thomas Church, Leiptzig, Germany
%%\end{itemize}
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%\end{list}

\end{document}

astro-ph0411519.extracted_bib
\begin{thebibliography}{99}%%%%%%%%%%
%
%   \bibitem{Laslie's Work}   %%%%% This case: Book.
%   L. Lamport,   
%  {\em LaTeX: A Document Preparation System.}
%  (1986) Addison-Wesley Pub., Massachusetts.
%
%   \bibitem{Aquasition Editor: UAP}   %%%%% This case: Book and/or Proceedings. 
%   K. Sato and M. Kawasaki, 
%  {\em Birth and Evolution of the Universe}
%  (2001) Universal Academy Press, Tokyo.
%  
    \bibitem{PhD}   %%%%% This case: Journal.
    T. Goto, PhD Thesis, 2003, The University of Tokyo, astro-ph/0310196
 
    \bibitem{PASJ}   %%%%% This case: Journal.
   T. Goto et al., 2003, PASJ, 55, 771
%  
%    \bibitem{Phys. Lett.}   %%%%% This case: Journal.
%    N. Seiberg, 
%    Phys. Lett. B318 (1993) 469.

\end{thebibliography}