[jQuery] A selector question

Hi, I have the following html and would like to find out how to select
#subgroup under #group2. I tried $(#group2 #subgroup) but that didn't
seem to work. Thank you.

<div id="main">
<div id="group1">
<div id="subgroup">
...
</div>
</div>

<div id="group2">
<div id="subgroup">
...
</div>
</div>

<div id="group3">
<div id="subgroup">
...
</div>
</div>
</div>