paper

Powerful H Emission and Star Formation on the Interacting Galaxy System Arp 143: Observations with Spitzer and GALEX

arXiv:0812.0450 · doi:10.1088/0004-637X/693/2/1650

Abstract

We present new mid-infrared (m) and ultraviolet (1539 -- 2316 Å) observations of the interacting galaxy system Arp 143 (NGC 2444/2445) from the Spitzer Space Telescope and GALEX. In this system, the central nucleus of NGC 2445 is surrounded by knots of massive star-formation in a ring-like structure. We find unusually strong emission from warm H associated with an expanding shock wave between the nucleus and the western knots. At this ridge, the flux ratio between H and PAH emission is nearly ten times higher than in the nucleus. Arp 143 is one of the most extreme cases known in that regard. From our multi-wavelength data we derive a narrow age range of the star-forming knots between 2 Myr and 7.5 Myr, suggesting that the ring of knots was formed almost simultaneously in response to the shock wave traced by the H emission. However, the knots can be further subdivided in two age groups: those with an age of 2--4 Myr (knots A, C, E, and F), which are associated with m emission from PAHs, and those with an age of 7-8 Myr (knots D and G), which show little or no m emission shells surrounding them. We attribute this finding to an ageing effect of the massive clusters which, after about 6 Myr, no longer excite the PAHs surrounding the knots.

19 pages, 11 figures, including tables at the end; accepted by ApJ

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