AFGL 5157 NH$_3$: A new stellar cluster in the forming
  We present the analysis of Spitzer/IRAC and NIR imaging observation of AFGL
5157, an active star forming region. In the IRAC images, this region shows
strong PAH emissions in channel 4 and H$_2$ emissions in channel 2. Many of the
H$_2$ features are aligned to form jet-like structures. Three bipolar jets in
the NH$_3$ core region and a couple of jets northwest of the core have been
identified. We identify the possible driving agents of the bipolar jets and
show them to be very young. An embedded cluster has been detected in the NH$_3$
core; many members in the cluster show their SEDs increasing from JHK bands
toward longer wavelength, indicative of their early evolutionary stages.
Millimeter and sub-millimeter continuum emissions are found to coincide
spatially with these presumable Class 0/I sources, in the NH$_3$ core and the
NW subregion. The existence of H$_2$ bipolar jets and very young stellar
objects suggests that star formation is still going on at present epoch in
these subregions. Combining the information from previous studies, we propose a
sequential star formation scenario in the whole AFGL 5157 region.
