NGC 602 Environment, Kinematics and Origins

Abstract

The young star cluster NGC 602 and its associated HII region, N90, formed in a relatively isolated and diffuse environment in the Wing of the Small Magellanic Cloud. Its isolation from other regions of massive star formation and the relatively simple surrounding HI shell structure allows us to constrain the processes that may have led to its formation and to study conditions leading to massive star formation. We use images from Hubble Space Telescope and high resolution echelle spectrographic data from the Anglo-Australian Telescope along with 21-cm neutral hydrogen (HI) spectrum survey data and the shell catalogue derived from it to establish a likely evolutionary scenario leading to the formation of NGC 602. We identify a distinct HI cloud component that is likely the progenitor cloud of the cluster and HII region which probably formed in blister fashion from the cloud's periphery. We also find that the past interaction of HI shells can explain the current location and radial velocity of the nebula. The surrounding Interstellar Medium is diffuse and dust-poor as demonstrated by a low visual optical depth throughout the nebula and an average HI density of the progenitor cloud estimated at 1 cm^-3. These conditions suggest that the NGC 602 star formation event was produced by compression and turbulence associated with HI shell interactions. It therefore represents a single star forming event in a low gas density region.Comment: Accepted for publication in PASP. 25 pages, 10 figure

Young Star Clusters in the Small Magellanic Cloud: Impact of Local and Global Conditions on Star Formation

“…Using the shell catalog derived from the 21 cm neutral hydrogen (Hi) spectrum survey data (Staveley-Smith et al 1997;Staminirovíc et al 1999) we identified a distinct Hi cloud component that is likely the progenitor cloud of the cluster and the Hii region which probably formed in blister fashion from the cloud's periphery. A comparison between Hi and Hii kinematics suggests that star formation in NGC 602 was triggered by compression and turbulence associated with Hi shell interaction ∼ 7 Myr ago (Nigra et al 2008).…”

Formation of Cold Filamentary Structure From Wind-Blown Superbubbles

“…A natural mechanism for assembling the large amounts of gas necessary for the formation of molecular clouds is from large-scale converging atomic flows, such as expanding shells (Elmegreen & Lada 1977;McCray & Kafatos 1987), colliding shells (Nigra et al 2008), or flows generated by large-scale gravitational instabilities (Yang et al 2007;Kim & Ostriker 2002, 2006. Gas in these collision environments is subject to a number of fluid instabilities that can cool and condense it enough for it to become molecular (Heitsch et al 2005).…”

Time resolved star formation in the SMC: the youngest star clusters

“…Even if the morphology of this association is reminiscent of an expanding bubble of gas, UCLES high-resolution spectra show very low velocity dispersion, excluding large-scale motions (Nigra et al 2008). Another possible explanation for the NGC 602 morphology is that we are observing a cavity eroded by the OB UV stellar radiation.…”

“…The SMC youngest star clusters 249 formation in NGC 602 was triggered by compression and turbulence associated with H i shell interaction ∼ 7 Myr ago (Nigra et al 2008).…”