We present star formation activity in the infrared dark cloud ( IRDC ) G53.2 , a remarkable IRDC located at Galactic coordinates ( l,b ) \sim ( 53 ^ { \circ } .2 , 0 ^ { \circ } .0 ) based on the census of young stellar object ( YSO ) candidates .
IRDC G53.2 was previously identified as several IRDCs in mid-IR images , but it is in fact a long ( \gtrsim 45 pc ) cloud , well consistent with a CO cloud at v \sim 23 km s ^ { -1 } ( or at d \sim 1.7 kpc ) .
We present a point-source catalog of IRDC G53.2 that contains \sim 370 sources from our photometry of the Spitzer MIPS 24 \mu m data and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Catalog .
The classification of the identified sources based on their spectral index and control field analysis to remove field star contamination reveals that IRDC G53.2 is an active star-forming region with \sim 300 YSO candidates .
We compare the YSO classification based on spectral index , mid-IR colors , and the wavelength range used , which results in consistent classification , except for flat-spectrum objects , with some ambiguity between Class I and II .
Comparison of the YSO population in IRDC G53.2 with those of other nearby star-forming clusters indicates that they are similar in age ; on the other hand , stronger association with mid-IR stellar sources in IRDC G53.2 compared with other IRDCs indicates that IRDC G53.2 is at a later evolutionary stage among IRDCs .
Spatial distribution of the YSO candidates in IRDC G53.2 shows a good correlation with ^ { 13 } CO column density and far-IR emission , and earlier-class objects tend to be more clustered in the regions with higher density .