Improved prospects for the detection of new Large Magellanic Cloud planetary nebulae

Abstract

The LargeMagellanic Cloud (LMC) contains the nearest large extragalactic population of planetary nebulae (PNe). A shallow viewing angle and low interstellar reddening towards the LMC potentially means a larger, more complete flux-limited population can be assembled than for any other galaxy. These advantages appear to be reflected by the small gap between the catalogued (∼700 PNe) and estimated (1000 ± 250 PNe) population size. With more detailed multi-wavelength studies the catalogued number of LMC PNe may fall, potentially widening this gap. We demonstrate here that the gap can be further bridged with improved optical and nearinfrared imaging surveys. We present three [O III]-selected PNe discovered from ESO WFI observations of the 30 Doradus region and one serendipitous discovery from near-infrared VistaMagellanic Cloud (VMC) survey observations. TheWFI PNe have resolved [O III] and Hα nebulae that verify their PN nature and their [O III] fluxes place them 6–7 mag (m5007 = 20–21 mag) fainter than the bright-end of the planetary nebula luminosity function (PNLF). Their faintness, small angular size and surrounding complex emission-line background explains why previous Hα surveys of the region did not select them. We estimate there may be as many as 50–75 similar PNe awaiting discovery in the central 5 × 5 degrees of the LMC. The VMC survey routinely detects PNe as red resolved nebulae that may allow some of this expected population to be recovered without traditional narrow-band imaging surveys. We demonstrate this potential with the first new VMC-selected PN which has a rare Wolf-Rayet [WC9]–[WC11] central star.