We present deep and high-resolution ( FWHM \sim 0 \aas@@fstack { \prime \prime } 4 ) near-infrared ( NIR ) imaging observations of the NGC 7538 IRS 1–3 region ( in JHK bands ) , and IRS 9 region ( in HK bands ) using the 8.2 m Subaru telescope .
The NIR analysis is complemented with GMRT low-frequency observations at 325 , 610 , and 1280 MHz , molecular line observations of H ^ { 13 } CO ^ { + } ( J =1–0 ) , and archival Chandra X-ray observations .
Using the ‘ J - H / H - K ’ diagram , 144 Class II and 24 Class I young stellar object ( YSO ) candidates are identified in the IRS 1–3 region .
Further analysis using ‘ K / H - K ’ diagram yields 145 and 96 red sources in the IRS 1-3 and IRS 9 regions , respectively .
A total of 27 sources are found to have X-ray counterparts .
The YSO mass function ( MF ) , constructed using a theoretical mass-luminosity relation , shows peaks at substellar ( \sim 0.08–0.18 ~ { } M _ { \odot } ) and intermediate ( \sim 1–1.78 ~ { } M _ { \odot } ) mass ranges for the IRS 1–3 region .
The MF can be fitted by a power law in the low mass regime with a slope of \Gamma \sim 0.54-0.75 , which is much shallower than the Salpeter value of 1.35 .
An upper limit of 10.2 is obtained for the star to brown dwarf ratio in the IRS 1–3 region .
GMRT maps show a compact H ii region associated with the IRS 1–3 sources , whose spectral index of 0.87 \pm 0.11 suggests optical thickness .
This compact region is resolved into three separate peaks in higher resolution 1280 MHz map , and the ‘ East ’ sub-peak coincides with the IRS 2 source .
H ^ { 13 } CO ^ { + } ( J =1–0 ) emission reveals peaks in both IRS 1–3 and IRS 9 regions , none of which are coincident with visible nebular emission , suggesting the presence of dense cloud nearby .
The virial masses are approximately of the order of 1000 ~ { } M _ { \odot } and 500 ~ { } M _ { \odot } for the clumps in IRS 1–3 and IRS 9 regions , respectively .