Extended red objects and stellar-wind bow shocks in the Carina Nebula

Abstract

We report the results of infrared photometry on 39 extended red objects (EROs) in the Carina Nebula, observed with the Spitzer Space Telescope. Most EROs are identified by bright, extended 8.0 um emission, which ranges from 10'' to 40'' in size, but our sample also includes 4 EROs identified by extended 24 um emission. Of particular interest are nine EROs associated with late O or early B-type stars and characterized by arc-shaped morphology, suggesting dusty, stellar-wind bow shocks. These objects are preferentially oriented towards the central regions of the Carina Nebula, suggesting that these bow shocks are generally produced by the interactions of OB winds with the bulk expansion of the H II region rather than high proper motion. We identify preferred regions of mid-infrared color space occupied by our bow shock candidates, which also contain bow shock candidates in M17 and RCW 49 but are well-separated from polycyclic aromatic hydrocarbon emission or circumstellar discs. Color cuts identify an additional 12 marginally-resolved bow shock candidates, 10 of which are also associated with known late O or early B stars. H II region expansion velocities derived from bow shock candidate standoff distances are ~10 km/s, assuming typical H II region gas densities, comparable to expansion velocities derived from bow shocks in M17 and RCW 49. One candidate bow shock provides direct evidence of physical interaction between the massive stellar winds originating in the Trumpler 15 and Trumpler 14 clusters, supporting the conclusion that both clusters are at similar heliocentric distances.