Program: GS-2007A-Q-7

We propose to obtain T-ReCS N and Q broad band images of five southern hemisphere infrared dark clouds (IRDCs) showing different levels of star-formation activity and environmental conditions (isolated vs cluster star-formation modes). This sample has been derived from a much larger compilation of IRDCs and represent each of the different types of small clouds currently known. T-ReCS images will help to constrain the star-formation efficiency in isolated small IRDCs, searching for potential Class 0 and Class I extremely young protostars (ages of about 10^4 -- 10^5 yr) likely responsible for the far infrared color excesses detected by IRAS. For three of the proposed IRDCs, no near-infrared counterparts have been detected with K < 18.5 and thus the central objects must be extremely young and lie well embedded in the parent cloud material. T-ReCS spatial resolution (a few tenths of arcsec) will eliminate IRAS bin uncertainty (about 1 arcmin) and allow us to unambiguously identify the associated protostars. In the case of the two remaining clouds, one of them is associated with a embedded proto-cluster and thus T-ReCS data will allow us to investigate the IMF of this truly young cluster (age of about 10^6 yr). The other IRDC has a faint K-band source detected within the IRAS ellipse as well as other singspots of star-formation activity. N and Q band images of this cloud can better constrain the evolutionary stage of the central star.