The Properties of Galaxies in Low Density Regions from the ALFALFA Survey
M.C.~Toribio and J.M.~Solanes for the ALFALFA collaboration
%%% Abstract to run on from here. Galaxies detected in the 21-cm line of neutral hydrogen (H$\,${\footnotesize I}) from the on-going Arecibo Legacy Fast ALFA (ALFALFA) blind extragalactic H$\,${\footnotesize I}\ survey have been cross-correlated with Sloan Digital Sky Survey (SDSS) Data Release 7 \citep{Aba09} in order to define a reference sample of H$\,${\footnotesize I}\ content in regions of low galactic density. This observational sample will be used in the future to derive new standards of normal atomic gas content that allow a statistical investigation of the H$\,${\footnotesize I}\ properties of galaxies in differing environments of the local universe. As a previous step, we compare here morphological indicators, like color or light concentration index, of ALFALFA detections and non-detections in low density regions. Our examination is extended also to a small data set of isolated galaxies. This kind of analysis is necessary in order to characterize as accurately as possible the type of galaxies that ALFALFA is detecting.
epsf.tex
%%% -*-TeX-*-
%%% ====================================================================
%%%  @TeX-file{
%%%     author          = "Tom Rokicki",
%%%     version         = "2.7.3",
%%%     date            = "23 July 2005",
%%%     time            = "14:32:01 MDT",
%%%     filename        = "epsf.tex",
%%%     address         = "Tom Rokicki
%%%                        Box 2081
%%%                        Stanford, CA 94309
%%%                        USA",
%%%     telephone       = "+1 415 855 9989",
%%%     checksum        = "20914 644 3054 26594",
%%%     email           = "rokicki@cs.stanford.edu (Internet)",
%%%     codetable       = "ISO/ASCII",
%%%     copyright       = "This file is freely redistributable and
%%%                        placed into the public domain by Tomas
%%%                        Rokicki.",
%%%     keywords        = "PostScript, TeX",
%%%     supported       = "yes",
%%%     abstract        = "This file contains macros to support the
%%%                        inclusion of Encapsulated PostScript files
%%%                        in TeX documents.",
%%%     docstring       = "This file contains TeX macros to include an
%%%                        Encapsulated PostScript graphic.  It works
%%%                        by finding the bounding box comment,
%%%                        calculating the correct scale values, and
%%%                        inserting a vbox of the appropriate size at
%%%                        the current position in the TeX document.
%%%
%%%                        To use, simply use
%%%
%%%                        \input epsf % somewhere early on in your TeX file
%%%
%%%                        % then where you want to insert a vbox for a figure:
%%%                        \epsfbox{filename.ps}
%%%
%%%                        Alternatively, you can supply your own
%%%                        bounding box by
%%%
%%%                        \epsfbox[0 0 30 50]{filename.ps}
%%%
%%%                        This will not read in the file, and will
%%%                        instead use the bounding box you specify.
%%%
%%%                        The effect will be to typeset the figure as
%%%                        a TeX box, at the point of your \epsfbox
%%%                        command. By default, the graphic will have
%%%                        its `natural' width (namely the width of
%%%                        its bounding box, as described in
%%%                        filename.ps). The TeX box will have depth
%%%                        zero.
%%%
%%%                        You can enlarge or reduce the figure by
%%%                        using
%%%
%%%                          \epsfxsize = <dimen> \epsfbox{filename.ps}
%%%                        or
%%%                          \epsfysize = <dimen> \epsfbox{filename.ps}
%%%
%%%                        instead. Then the width of the TeX box will
%%%                        be \epsfxsize and its height will be scaled
%%%                        proportionately (or the height will be
%%%                        \epsfysize and its width will be scaled
%%%                        proportionately).
%%%
%%%                        The width (and height) is restored to zero
%%%                        after each use, so \epsfxsize or \epsfysize
%%%                        must be specified before EACH use of
%%%                        \epsfbox.
%%%
%%%                        A more general facility for sizing is
%%%                        available by defining the \epsfsize macro.
%%%                        Normally you can redefine this macro to do
%%%                        almost anything.  The first parameter is
%%%                        the natural x size of the PostScript
%%%                        graphic, the second parameter is the
%%%                        natural y size of the PostScript graphic.
%%%                        It must return the xsize to use, or 0 if
%%%                        natural scaling is to be used.  Common uses
%%%                        include:
%%%
%%%                           \epsfxsize  % just leave the old value alone
%%%                           0pt         % use the natural sizes
%%%                           #1          % use the natural sizes
%%%                           \hsize      % scale to full width
%%%                           0.5#1       % scale to 50% of natural size
%%%                           \ifnum #1 > \hsize \hsize \else #1\fi
%%%                                       % smaller of natural, hsize
%%%
%%%                        If you want TeX to report the size of the
%%%                        figure (as a message on your terminal when
%%%                        it processes each figure), use
%%%                        `\epsfverbosetrue'.
%%%
%%%                        If you only want to get the bounding box
%%%                        extents, without producing any output boxes
%%%                        or \special{}, then use \epsfgetbb{filename}.
%%%                        The bounding box corner coordinates are saved
%%%                        in the macros \epsfllx, \epsflly, \epsfurx,
%%%                        and \epsfury in PostScript units of big
%%%                        points.
%%%
%%%                        Revision history:
%%%
%%%                        ---------------------------------------------
%%%                        epsf.tex macro file:
%%%                        Originally written by Tomas Rokicki of
%%%                        Radical Eye Software, 29 Mar 1989.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Don Knuth, 3 Jan 1990.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Tomas Rokicki, 18 Jul 1990.
%%%                        Accept bounding boxes with no space after
%%%                        the colon.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 03 Dec 1991 [2.0].
%%%                        Add version number and date typeout.
%%%
%%%                        Use \immediate\write16 instead of \message
%%%                        to ensure output on new line.
%%%
%%%                        Handle nested EPS files.
%%%
%%%                        Handle %%BoundingBox: (atend) lines.
%%%
%%%                        Do not quit when blank lines are found.
%%%
%%%                        Add a few percents to remove generation of
%%%                        spurious blank space.
%%%
%%%                        Move \special output to
%%%                        \epsfspecial{filename} so that other macro
%%%                        packages can input this one, then change
%%%                        the definition of \epsfspecial to match
%%%                        another DVI driver.
%%%
%%%                        Move size computation to \epsfsetsize which
%%%                        can be called by the user; the verbose
%%%                        output of the bounding box and scaled width
%%%                        and height happens here.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 05 May 1992 [2.1].
%%%                        Wrap \leavevmode\hbox{} around \vbox{} with
%%%                        the \special so that \epsffile{} can be
%%%                        used inside \begin{center}...\end{center}
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 09 Dec 1992 [2.2].
%%%                        Introduce \epsfshow{true,false} and
%%%                        \epsfframe{true,false} macros; the latter
%%%                        suppresses the insertion of the PostScript,
%%%                        and instead just creates an empty box,
%%%                        which may be handy for rapid prototyping.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 14 Dec 1992 [2.3].
%%%                        Add \epsfshowfilename{true,false}.  When
%%%                        true, and \epsfshowfalse is specified, the
%%%                        PostScript file name will be displayed
%%%                        centered in the figure box.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 20 June 1993 [2.4].
%%%                        Remove non-zero debug setting of \epsfframemargin,
%%%                        and change margin handling to preserve EPS image
%%%                        size and aspect ratio, so that the actual
%%%                        box is \epsfxsize+\epsfframemargin wide by
%%%                        \epsfysize+\epsfframemargin high.
%%%                        Reduce output of \epsfshowfilenametrue to
%%%                        just the bare file name.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 13 July 1993 [2.5].
%%%                        Add \epsfframethickness for control of
%%%                        \epsfframe frame lines.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 02 July 1996 [2.6]
%%%                        Add missing initialization \epsfatendfalse;
%%%                        the lack of this resulted in the wrong
%%%                        BoundingBox being picked up, mea culpa, sigh...
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 25 October 1996 [2.7]
%%%                        Update to match changes in from dvips 5-600
%%%                        distribution: new user-accessible macros:
%%%                        \epsfclipon, \epsfclipoff, \epsfdrafton,
%%%                        \epsfdraftoff, change \empty to \epsfempty.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 18 May 2002 [2.7.1]
%%%                        Add write statements to echo input file
%%%                        names.  Prior to that change, an error in
%%%                        such a file could be quite hard to track
%%%                        down: a long list of TeX page numbers could
%%%                        suddenly be followed by ``TeX buffer
%%%                        capacity'' exceeded, without any indication
%%%                        of the file that was responsible.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, 16 May 2003 [2.7.2]
%%%                        Supply two critical percent characters that
%%%                        were mistakenly omitted in version 2.7.1,
%%%                        and resulted in a small amount of spurious
%%%                        horizontal space.
%%%
%%%                        ---------------------------------------------
%%%                        Revised by Nelson H. F. Beebe
%%%                        <beebe@math.utah.edu>, Karl Berry
%%%                        <karl@freefriends.org>, and Robin Fairbairns
%%%                        <Robin.Fairbairns@cl.cam.ac.uk>,
%%%                        23 July 2005 [2.7.3]
%%%                        Add critical \hbox{} wrapper in \epsfsetgraph
%%%                        so that \epsfbox{} does not conflict with
%%%                        LaTeX center environment when \epsfbox{} is
%%%                        surrounded by other horizonal objects.
%%%                        Improve macro readability by adding legal,
%%%                        but invisible-in-typeset-output, spaces.
%%%                        Ensure that verbose status reports come
%%%                        inside (filename ...) list.
%%%
%%%                        ---------------------------------------------
%%%                        The checksum field above contains a CRC-16
%%%                        checksum as the first value, followed by
%%%                        the equivalent of the standard UNIX wc
%%%                        (word count) utility output of lines,
%%%                        words, and characters.  This is produced by
%%%                        Robert Solovay's checksum utility.",
%%%  }
%%% ====================================================================

%\immediate \write16 {This is `epsf.tex' v2.0 <02 Dec 1991>}%
%\immediate \write16 {This is `epsf.tex' v2.1 <05 May 1992>}%
%\immediate \write16 {This is `epsf.tex' v2.2 <09 Dec 1992>}%
%\immediate \write16 {This is `epsf.tex' v2.3 <14 Dec 1992>}%
%\immediate \write16 {This is `epsf.tex' v2.4 <20 June 1993>}%
%\immediate \write16 {This is `epsf.tex' v2.5 <13 July 1993>}%
%\immediate \write16 {This is `epsf.tex' v2.6 <02 July 1996>}%
%\immediate \write16 {This is `epsf.tex' v2.7 <25 October 1996>}%
%\immediate \write16 {This is `epsf.tex' v2.7.1 <18 May 2002>}%
%\immediate \write16 {This is `epsf.tex' v2.7.2 <16 May 2003>}%
\immediate \write16 {This is `epsf.tex' v2.7.3 <23 July 2005>}%
%
\newread \epsffilein    % file to \read
\newif \ifepsfatend     % need to scan to LAST %%BoundingBox comment?
\newif \ifepsfbbfound   % success?
\newif \ifepsfdraft     % use draft mode?
\newif \ifepsffileok    % continue looking for the bounding box?
\newif \ifepsfframe     % frame the bounding box?
\newif \ifepsfshow      % show PostScript file, or just bounding box?
\epsfshowtrue          % default is to display PostScript file
\newif \ifepsfshowfilename % show the file name if \epsfshowfalse specified?
\newif \ifepsfverbose   % report what you're making?
\newdimen \epsfframemargin % margin between box and frame
\newdimen \epsfframethickness % thickness of frame rules
\newdimen \epsfrsize    % vertical size before scaling
\newdimen \epsftmp      % register for arithmetic manipulation
\newdimen \epsftsize    % horizontal size before scaling
\newdimen \epsfxsize    % horizontal size after scaling
\newdimen \epsfysize    % vertical size after scaling
\newdimen \pspoints     % conversion factor
%
\pspoints = 1bp        % Adobe points are `big'
\epsfxsize = 0pt       % default value, means `use natural size'
\epsfysize = 0pt       % ditto
\epsfframemargin = 0pt % default value: frame box flush around picture
\epsfframethickness = 0.4pt % TeX's default rule thickness
%
\def \epsfbox #1{%
    \global \def \epsfllx {72}%
    \global \def \epsflly {72}%
    \global \def \epsfurx {540}%
    \global \def \epsfury {720}%
    \def \lbracket {[}%
    \def \testit {#1}%
    \ifx \testit \lbracket
        \let \next = \epsfgetlitbb
    \else
        \let \next = \epsfnormal
    \fi
    \next{#1}%
}%
%
% We use \epsfgetlitbb if the user specified an explicit bounding box,
% and \epsfnormal otherwise.  Because \epsfgetbb can be called
% separately to retrieve the bounding box, we move the verbose
% printing the bounding box extents and size on the terminal to
% \epsfstatus.  Therefore, when the user provided the bounding box,
% \epsfgetbb will not be called, so we must call \epsfsetsize and
% \epsfstatus ourselves.
%
\def \epsfgetlitbb #1#2 #3 #4 #5]#6{%
   \epsfgrab #2 #3 #4 #5 .\\%
   \epsfsetsize
   \epsfstatus{#6}%
   \epsfsetgraph{#6}%
}%
%
\def \epsfnormal #1{%
    \epsfgetbb{#1}%
    \epsfsetgraph{#1}%
}%
%
\def \epsfgetbb #1{%
%
%   The first thing we need to do is to open the
%   PostScript file, if possible.
%
    \openin\epsffilein=#1
    \immediate \write16 {(#1}%
    \ifeof \epsffilein
        \errmessage{Could not open file #1, ignoring it}%
    \else                       %process the file
        {%                      %start a group to contain catcode changes
            % Make all special characters, except space, to be of type
            % `other' so we process the file in almost verbatim mode
            % (TeXbook, p. 344).
            \chardef \other = 12%
            \def \do ##1{\catcode`##1=\other}%
            \dospecials
            \catcode `\ = 10%
            \epsffileoktrue        %true while we are looping
            \epsfatendfalse        %[02-Jul-1996]: add forgotten initialization
            \loop                  %reading lines from the EPS file
                \read \epsffilein to \epsffileline
                \ifeof \epsffilein %then no more input
                \epsffileokfalse   %so set completion flag
            \else                  %otherwise process one line
                \expandafter \epsfaux \epsffileline :. \\%
            \fi
            \ifepsffileok
            \repeat
            \ifepsfbbfound
            \else
                \ifepsfverbose
                    \immediate \write16 {No BoundingBox comment found in %
                                         file #1; using defaults}%
                \fi
            \fi
        }%                      %end catcode changes
        \closein\epsffilein
    \fi                         %end of file processing
    \epsfsetsize                %compute size parameters
    \epsfstatus{#1}%
    \immediate \write16 {)}%
}%
%
% Clipping control:
\def \epsfclipon  {\def \epsfclipstring { clip}}%
\def \epsfclipoff {\def \epsfclipstring {\ifepsfdraft \space clip\fi}}%
\epsfclipoff % default for dvips is OFF
%
% The special that is emitted by \epsfsetgraph comes from this macro.
% It is defined separately to allow easy customization by other
% packages that first \input epsf.tex, then redefine \epsfspecial.
% This macro is invoked in the lower-left corner of a box of the
% width and height determined from the arguments to \epsffile, or
% from the %%BoundingBox in the EPS file itself.
%
% This version is for dvips:
\def \epsfspecial #1{%
     \epsftmp=10\epsfxsize
     \divide \epsftmp by \pspoints
     \ifnum \epsfrsize = 0%
       \relax
       \special{PSfile=\ifepsfdraft psdraft.ps\else#1\fi\space
		llx=\epsfllx\space
		lly=\epsflly\space
		urx=\epsfurx\space
		ury=\epsfury\space
		rwi=\number\epsftmp
		\epsfclipstring
               }%
     \else
       \epsfrsize=10\epsfysize
       \divide \epsfrsize by \pspoints
       \special{PSfile=\ifepsfdraft psdraft.ps\else#1\fi\space
		llx=\epsfllx\space
		lly=\epsflly\space
		urx=\epsfurx\space
		ury=\epsfury\space
		rwi=\number\epsftmp
		rhi=\number\epsfrsize
		\epsfclipstring
               }%
     \fi
}%
%
% \epsfframe macro adapted from the TeXbook, exercise 21.3, p. 223, 331.
% but modified to set the box width to the natural width, rather
% than the line width, and to include space for margins and rules
\def \epsfframe #1%
{%
 % method for detecting latex suggested by Robin Fairbairns, May 2005.
  \ifx \documentstyle \epsfundefined
    \relax
  \else
%    \leavevmode                   % so we can put this inside
                                  % a latex centered environment
    % The \leavevmode breaks under plain when this is inside a box,
    % because it forces the figure to be the entire \hsize.  On the
    % other hand, we need the \leavevmode for it to work in LaTeX,
    % because the {center} environment works by adjusting TeX's
    % paragraph parameters.
    %
    % Compare the LaTeX sequence
    % \begin{center}
    %   \epsfbox{tip.eps}q
    % \end{center}
    % (needs the \leavevmode to put the q right next to the image)
    %
    % with the plain TeX sequence:
    % \leftline{\vbox{\epsfbox{tip.eps}}q}
    % (had the q all the way over to the right, when \leavevmode was used)
  \fi
  %
  \setbox0 = \hbox{#1}%
  \dimen0 = \wd0                                % natural width of argument
  \advance \dimen0 by 2\epsfframemargin         % plus width of 2 margins
  \advance \dimen0 by 2\epsfframethickness      % plus width of 2 rule lines
  \relax
  \hbox{%
    \vbox
    {%
      \hrule height \epsfframethickness depth 0pt
      \hbox to \dimen0
      {%
	\hss
	\vrule width \epsfframethickness
	\kern \epsfframemargin
	\vbox {\kern \epsfframemargin \box0 \kern \epsfframemargin }%
	\kern \epsfframemargin
	\vrule width \epsfframethickness
	\hss
      }% end hbox
      \hrule height 0pt depth \epsfframethickness
    }% end vbox
  }% end hbox
  \relax
}%
%
\def \epsfsetgraph #1%
{%
   %
   % Make the vbox and stick in a \special that the DVI driver can
   % parse.  \vfil and \hfil are used to place the \special origin at
   % the lower-left corner of the vbox.  \epsfspecial can be redefined
   % to produce alternate \special syntaxes.
   %
   \ifvmode \leavevmode \fi
   \relax
   \hbox{% so we can put this in \begin{center}...\end{center}
     \ifepsfframe \expandafter \epsfframe \fi
     {\vbox to\epsfysize
     {%
        \ifepsfshow
            % output \special{} at lower-left corner of figure box
            \vfil
            \hbox to \epsfxsize{\epsfspecial{#1}\hfil}%
        \else
            \vfil
            \hbox to\epsfxsize{%
               \hss
               \ifepsfshowfilename
               {%
                  \epsfframemargin=3pt % local change of margin
                  \epsfframe{{\tt #1}}%
               }%
               \fi
               \hss
            }%
            \vfil
        \fi
     }%
   }}%
   \relax
   %
   % Reset \epsfxsize and \epsfysize, as documented above.
   %
   \global \epsfxsize = 0pt
   \global \epsfysize = 0pt
}%
%
%   Now we have to calculate the scale and offset values to use.
%   First we compute the natural sizes.
%
\def \epsfsetsize
{%
   \epsfrsize = \epsfury \pspoints
   \advance \epsfrsize by -\epsflly \pspoints
   \epsftsize = \epsfurx \pspoints
   \advance \epsftsize by -\epsfllx \pspoints
%
%   If `epsfxsize' is 0, we default to the natural size of the picture.
%   Otherwise we scale the graph to be \epsfxsize wide.
%
   \epsfxsize = \epsfsize{\epsftsize}{\epsfrsize}%
   \ifnum \epsfxsize = 0
      \ifnum \epsfysize = 0
	\epsfxsize = \epsftsize
        \epsfysize = \epsfrsize
	\epsfrsize = 0pt
%
%   We have a sticky problem here:  TeX doesn't do floating point arithmetic!
%   Our goal is to compute y = rx/t. The following loop does this reasonably
%   fast, with an error of at most about 16 sp (about 1/4000 pt).
%
      \else
	\epsftmp = \epsftsize
        \divide \epsftmp by \epsfrsize
	\epsfxsize = \epsfysize
        \multiply \epsfxsize by \epsftmp
	\multiply \epsftmp by \epsfrsize
        \advance \epsftsize by -\epsftmp
	\epsftmp = \epsfysize
	\loop
        \advance \epsftsize by \epsftsize
        \divide \epsftmp by 2
	\ifnum \epsftmp > 0
	   \ifnum \epsftsize < \epsfrsize
           \else
	      \advance \epsftsize -\epsfrsize
              \advance \epsfxsize \epsftmp
           \fi
	\repeat
	\epsfrsize = 0pt
      \fi
   \else
     \ifnum \epsfysize = 0
       \epsftmp = \epsfrsize
       \divide \epsftmp by \epsftsize
       \epsfysize = \epsfxsize
       \multiply \epsfysize by \epsftmp
       \multiply \epsftmp by \epsftsize
       \advance \epsfrsize by -\epsftmp
       \epsftmp = \epsfxsize
       \loop
	 \advance \epsfrsize by \epsfrsize
	 \divide \epsftmp by 2
       \ifnum \epsftmp > 0
	  \ifnum \epsfrsize < \epsftsize
          \else
	     \advance \epsfrsize by -\epsftsize
             \advance \epsfysize by \epsftmp
          \fi
       \repeat
       \epsfrsize = 0pt
     \else
       \epsfrsize = \epsfysize
     \fi
   \fi
}%
%
% Issue some status messages if the user requested them
%
\def \epsfstatus #1{% arg = filename
   \ifepsfverbose
     \immediate \write16 {#1: BoundingBox:
			  llx = \epsfllx \space lly = \epsflly \space
			  urx = \epsfurx \space ury = \epsfury \space}%
     \immediate \write16 {#1: scaled width = \the\epsfxsize \space
			  scaled height = \the\epsfysize}%
   \fi
}%
%
%   We still need to define the tricky \epsfaux macro. This requires
%   a couple of magic constants for comparison purposes.
%
{\catcode`\%=12 \global \let \epsfpercent=%\global \def \epsfbblit {%BoundingBox}}%
\global \def \epsfatend{(atend)}%
%
%   So we're ready to check for `%BoundingBox:' and to grab the
%   values if they are found.
%
%   If we find a line
%
%   %%BoundingBox: (atend)
%
%   then we ignore it, but set a flag to force parsing all of the
%   file, so the last %%BoundingBox parsed will be the one used.  This
%   is necessary, because EPS files can themselves contain other EPS
%   files with their own %%BoundingBox comments.
%
%   If we find a line
%
%   %%BoundingBox: llx lly urx ury
%
%   then we save the 4 values in \epsfllx, \epsflly, \epsfurx, \epsfury.
%   Then, if we have not previously parsed an (atend), we flag completion
%   and can stop reading the file.  Otherwise, we must keep on reading
%   to end of file so that we find the values on the LAST %%BoundingBox.
\long \def \epsfaux#1#2:#3\\%
{%
   \def \testit {#2}%           % save second character up to just before colon
   \ifx#1\epsfpercent           % then first char is percent (quick test)
       \ifx \testit \epsfbblit  % then (slow test) we have %%BoundingBox
            \epsfgrab #3 . . . \\%
            \ifx \epsfllx\epsfatend % then ignore %%BoundingBox: (atend)
                \global \epsfatendtrue
            \else               % else found %%BoundingBox: llx lly urx ury
                \ifepsfatend    % then keep parsing ALL %%BoundingBox lines
                \else           % else stop after first one parsed
                    \epsffileokfalse
                \fi
                \global \epsfbbfoundtrue
            \fi
       \fi
   \fi
}%
%
%   Here we grab the values and stuff them in the appropriate definitions.
%
\def \epsfempty {}%
\def \epsfgrab #1 #2 #3 #4 #5\\{%
   \global \def \epsfllx {#1}\ifx \epsfllx\epsfempty
      \epsfgrab #2 #3 #4 #5 .\\\else
   \global \def \epsflly {#2}%
   \global \def \epsfurx {#3}\global \def \epsfury {#4}\fi
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toribio.tex
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\markboth{M.C.\ Toribio and J.M.\ Solanes}{Properties of ALFALFA galaxies}   
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\begin{document}
\title{The Properties of Galaxies in 
Low Density Regions from the ALFALFA Survey}   %%% Fill in title
\author{M.C.~Toribio and J.M.~Solanes for the ALFALFA collaboration}   %%% Fill in author names
\affil{Departament d'Astronomia i Meteorologia and 
Institut de Ci\`encies del Cosmos, Universitat de Barcelona,
Mart\'i i Franqu\`es 1, E-08028 Barcelona, Spain}    %%% Fill in author affiliations

\begin{abstract} %%% Abstract to run on from here.
  Galaxies detected in the 21-cm line of neutral hydrogen (H$\,${\footnotesize I}) from
  the on-going Arecibo Legacy Fast ALFA (ALFALFA) blind extragalactic
  H$\,${\footnotesize I}\ survey have been cross-correlated with Sloan Digital Sky Survey
  (SDSS) Data Release 7 \citep{Aba09} in order to define a
  reference sample of H$\,${\footnotesize I}\ content in regions of low galactic
  density. This observational sample will be used in the future to
  derive new standards of normal atomic gas content that allow a
  statistical investigation of the H$\,${\footnotesize I}\ properties of galaxies in
  differing environments of the local universe. As a previous step, we compare 
  here morphological indicators, like color or light concentration index,
  of ALFALFA detections and non-detections   in low density regions. 
  Our examination is extended also 
  to a small data set of isolated galaxies. This kind of analysis is necessary in order to
  characterize as accurately as possible the type of galaxies that
  ALFALFA is detecting.
\end{abstract}


\section{Introduction}

The first study to establish rigorous standards of normalcy for
the H$\,${\footnotesize I}\ content of galaxies in the absence of external influences was
carried out by \citet{HG84}, who used 288 galaxies with neutral
hydrogen emission contained in the \emph{Catalogue of Isolated
  Galaxies} \citep[CIG,][]{Kar73} to define a control sample. In this
work, it was demonstrated that, for a given Hubble type, the optical
linear diameter of galaxies is the most accurate diagnostic tool for
the H$\,${\footnotesize I}\ mass. This measure of 
the H$\,${\footnotesize I}\ content was reviewed and
updated by \citet*{SGH96} using a sample of 532 
galaxies listed in the \citet{Zwi6168} magnitude-limited
Catalog of Galaxies and Clusters of Galaxies located in the lowest
density environments of the Pisces-Perseus supercluster region. 
The lack of H$\,${\footnotesize I}\ dedicated surveys in those days forced the authors to
deal with multiple galaxy data sets affected by 
incompleteness and selection effects 
that could not always be fully accounted for in the calculation 
of the standard measurements of the H$\,${\footnotesize I}\ content.

This situation is now changing rapidly thanks to the on-going Arecibo
Legacy Fast ALFA (ALFALFA) survey \citep{Gio05}, a blind, flux-limited
extragalactic survey of the sky accesible to the Arecibo's antenna
that is providing an homogeneous census of 21-cm line
sources over a cosmologically significant volume of the local
universe. In this work, we use the H$\,${\footnotesize I}\ dataset from ALFALFA that will
soon constitute the first massive public data release, to define
a standard sample for the comparison of the H$\,${\footnotesize I}\ content of galaxies
free of the potential observational biases mentioned above, and 
combine it with optical data from SDSS in order to inspect
some of the intrinsic properties of ALFALFA sources. 

The definition of a suitable standard of normalcy 
for the H$\,${\footnotesize I}\ content
necessitates a well-chosen control sample formed by galaxies 
with H$\,${\footnotesize I}\
properties as less affected by the environment as possible. This
requirement has led us to define our reference sample from ALFALFA
detections in regions of low galactic density. This procedure, which
is supported by previous works showing that the depletion 
of H$\,${\footnotesize I}\ gas
is a phenomenon essentially constrained to the inner regions of rich
clusters and the densest groups of galaxies 
\citep[e.g.][]{GH85, Sol01, Ver01}, ensures a sufficiently 
large sample that allows a thorough 
statistical treatment of data. 

In the present work, we also
investigate the properties of a much smaller dataset of isolated
galaxies, the objects which are presumably less affected by
environmental processes.


\section{Low Density Region galaxy sample}\label{LDR}

The ALFALFA catalog consists of $\sim$6800 H$\,${\footnotesize I}\ detections over
 $\sim$ 1440 deg$^2$ on the Northern Hemisphere
sky and with H$\,${\footnotesize I} -masses within the range 
$10^7 \leq h^2 M_{HI}/M_{\odot} \leq 10^{10}$.
We have restricted our attention to those ALFALFA galaxies 
which have an optical counterpart in SDSS and heliocentric velocities 
within the range $3000 \leq v_{\mathrm{hel}}\leq 15000$ \ km\ s$^{-1}$, in order
to avoid large distance uncertainties for the
closest objects as well as the gap in 21-cm line detections above
15000 \ km\ s$^{-1}$\ caused by radio frequency interference. For each candidate, 
and after correcting radial distances for peculiar motions following 
prescriptions by \citet{Bla05}, we calculate the 3D distance to the $6th$ nearest
neighbor in the SDSS complete spectroscopic survey (with $r$-band
magnitude $\leq$ 17.77 mag). The corresponding estimate of the local
density $\rho_6$ is corrected for Galactic extinction \citep{SFD98}
and magnitude-limit effects by using the SDSS luminosity function
\citep{Bla01}.

The Low Density Region (LDR) sample includes galaxies with local
density below a certain threshold $\rho_{\mathrm{thr}}$. By applying
the H$\,${\footnotesize I}-deficiency estimator \citep{GH83} updated with the
coefficients inferred in \cite{SGH96}, we find that the H$\,${\footnotesize I}\ content
of galaxies inhabiting regions with local density below
$\rho_{\mathrm{thr}}=0.5$~${\mathrm{galaxies/Mpc}}^3$ is not correlated with
the environment. We have also verified that this threshold allows to
discard practically all galaxies located within $\sim$2-3 virial radii
around rich Abell clusters.

In the top left panel of Figure~\ref{fig1}, we compare the distributions of
$g-r$ colors of SDSS and ALFALFA galaxies located in LDR 
in the volume of the sky (in \emph{z}-space) where both surveys
overlap. This comparison is repeated in the top right panel, but
restricted to the subsets of LDR galaxies that verify the criterion
used by \citet{Mal09} to identify disk galaxies (axis ratio $\leq
0.55$ or S\'ersic index $\leq 3$). As expected, most of ALFALFA
detections ($\sim 92\%$) satisfy it, while about one non-detection out
of every six is not a \citeauthor{Mal09}'s disk.

Inspection of the color distribution confirms that ALFALFA is
detecting mainly blue galaxies. Even among those objects classified as
disks by \citeauthor{Mal09}'s criterion, ALFALFA galaxies are also the
bluest. Given the flux-limited nature of the ALFALFA survey, this
behavior becomes more accentuated with distance, i.e.\ the galaxies
with the reddest colors, which are expected to be usually less rich in
H$\,${\footnotesize I}, are preferently detected at closer distances. 
We also find that ALFALFA detections tend to show large values of the inverse
concentration index, a characteristic of late-type galaxies.


\section{Isolated galaxy sample}\label{isolated}

We have compared the colors of the members of the LDR galaxy sample
defined in Section \ref{LDR} with those belonging to a data set of
isolated galaxies that are as unperturbed as possible by environmental
mechanisms. The latter has been defined applying different isolation
criteria, such as the one based on angular diameter used by
\citet{Kar73} in the CIG and its updated version adopted by
\citet{All05} for the SDSS. We have also defined our own isolation
criterion similar to others found in the literature that combine
photometric and spectroscopic information: a candidate galaxy $i$ is
considered to be isolated if any neighboring galaxy $j$ with apparent
magnitude $m_j \le m_i+1.5$ mag is located further away than 280
$h^{-1}$ kpc ($\sim$ 400 kpc for $h=$0.7).

As already revealed by previous works \citep[e.g.][]{Ver07}, while it
is true that isolated galaxies avoid the densest regions of the
universe, we find that some of them may inhabit regions of moderate
local density in which $\rho_6$ is larger than the density threshold
we have used to define our LDR sample. To avoid this problem, 
membership for our isolated galaxy sample is restricted to LDR objects only.

In sharp contrast with LDR galaxies, dominated by blue objects, the
color distribution of our isolated sample demonstrates that any technique 
used to identify isolated galaxies from the difference in apparent
magnitude between neighbors \emph{always} favours the selection of
brighter and, hence, redder objects (Figure~\ref{fig1}). This is consistent,
for instance, with the results reported in the work by \citet{All05},
in which they obtained an isolated galaxy sample from SDSS with a
concentration index distribution that suggested a morphological
composition fifty-fifty between early and late galaxy types.

On the other hand, we find that, from a statistical point of view, the
 H$\,${\footnotesize I}\ contents of our isolated 
galaxies are essentially identical to
those of our LDR sample galaxies, thus confirming that substantial gas
depletion takes place mainly in high density environments.


\section{Summary and Future Work}

We have introduced the reference data set of ALFALFA
detections that is going to be used in the calculation of new
standards of the H$\,${\footnotesize I}\ content of galaxies.
The present comparison 
between some characteristics of SDSS galaxies in LDR detected 
and undetected by the ALFALFA survey is just a first small step 
towards setting up a suitable 
framework for the investigation of the H$\,${\footnotesize I}\ content of
galaxies in a wide range of environments of the local universe.




\begin{figure}[t]
\includegraphics[width=\textwidth]{toribio_fig1.ps}

\caption{\emph{Top left:} SDSS $g-r$ color of a subset of the SDSS
  spectroscopic complete sample in the region overlapping with ALFALFA survey
  (solid). We have selected only galaxies in low density
  regions with velocities within $3000 \leq
  v_{\mathrm{hel}} \leq 15000$ \ km\ s$^{-1}$. The sample is splitted into
  objects whose H$\,${\footnotesize I}\ is detected by ALFALFA (dashed line), and
  non-detections (dotted line). \emph{Top right:} same as above, but only
  for those objects identified as disks according to the
  \citeauthor{Mal09}'s \citeyear{Mal09} criterion.  \emph{Bottom left:}
  same as above, but for objects classified as isolated applying our
  spectrophotometric criterion.}\label{fig1}

\end{figure}


\acknowledgements 
This work is supported by the Spanish Direcci\'on
General de Investigaci\'on Cient\'{\i}fica y T\'ecnica, under contract
AYA2007-60366. M.C.T.\ acknowledges support from a fellowship of the
Ministerio de Educaci\'on y Ciencia of Spain.



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\end{document}

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\begin{thebibliography}{}

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\bibitem[{Blanton} {et~al.}(2001){Blanton} {et~al.}]{Bla01}
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\bibitem[{Blanton} {et~al.}(2005){Blanton} {et~al.}]{Bla05}
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\bibitem[{Giovanelli} \& {Haynes}(1983){Giovanelli} \& {Haynes}]{GH83}
{Giovanelli}, R., \& {Haynes}, M.~P. 1983, \aj, 88, 881

\bibitem[{Giovanelli} \& {Haynes}(1985){Giovanelli} \& {Haynes}]{GH85}
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\bibitem[{Giovanelli} {et~al.}(2005){Giovanelli} {et~al.}]{Gio05}
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\bibitem[{Solanes} {et~al.}(2001)]{Sol01}
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