1994A&A...291..960H

We present a comprehensive study of the LMC HII region N4A and its associated molecular cloud using a relatively large amount of data obtained with various observational techniques. We investigate the physical characteristics of the HII region, in particular the morphology, density structure, gas temperature, dust distribution, chemical abundances, etc. A low-brightness filamentary pattern is brought out in N4A. The possible causes of this feature (stellar wind, supernova explosion, magnetic fields, molecular cloud) are discussed. The overall extinction towards N4A is A_V∼0.4mag. However, it amounts to as high as 3.7 mag in the direction of a compact knot of ionized gas lying in front of the HII region. We investigate the physical parameters of the associated molecular cloud extensively observed in the transitions ¹²CO(1-0), ¹²CO(2-1) and ¹³CO(1-0). The cloud is unusual mainly because the emission ratio ¹²CO(2-1)/¹²CO(1-0) is ≫1 in its part close to N4A. This part is probably a thin molecular sheet in front of the HII region. Moreover, a prominent velocity structure is detected in the molecular cloud, with two main components at V_LSR=272.5 and 278.5km/s. The ionized gas is redshifted with respect to the CO velocity counterpart by as much as 14.6km/s. A molecular hydrogen mass of ∼3x10⁴M_☉ is derived for the main component of the molecular cloud.