The UM/CTIO
Magellanic Cloud
Emission Line Survey:
A Project Summary

The interstellar medium (ISM) is no longer thought to be a quiescent distribution of gas, but rather a dynamic and complex interaction of the ambient gas and dust with stellar winds, HII regions, planetary nebulae (PNe), supernovae (SNe), supernova remnants (SNRs), superbubbles, and gigantic supershells. Nowhere is this more apparent than in the Magellanic Clouds. Their relative proximity and low extinction make them the ideal laboratories in which to study the ISM, its constituents, its energetics, and its interaction with the underlying stellar populations.

We are now finishing the Magellanic Cloud Emission Line Survey, aka MCELS, an optical emission line survey of these two nearby galaxies which, together with parallel surveys at other wavelengths, will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (~1 pc) to global scales.

The MCELS project was undertaken to provide a deep, uniform dataset to study the ionized gas structures of the ISM in the Magellanic Clouds. Using advanced digital image subtraction techniques to remove the stellar continuum from the images, we can more accurately measure the emission-line fluxes. Using the three emission lines together through emission-line ratios also provides information about the physical processes which are driving the emission (e.g., the [S II]/Ha ratio can be used to differentiate shock-excited emission from photoionization-driven emission). With this information we are studying the samples of small scale objects such as PNe and SNRs as well as large scale structures such as superbubbles and supergiant shells.

Technical Details

• TELESCOPE: The UM/CTIO Curtis 0.6/0.9m Schmidt
• CAMERA: SITE 2048x2048 CCD, also STIS 2048x2048 CCD
• FIELD OF VIEW PER IMAGE: 1.7 square degrees (1.3x1.3 deg)
• RESOLUTION: 2.3Ó/pixel, ~5Ó resolution
• BANDS: 3 emission lines, 2 continuum
  • Ha 6568/28,
  • [S II] 6729/50,
  • [O III] 5012/40,
  • Continuum 6850/100,
  • Continuum 5130/155 (DDO51).

  The two "continuum: bands are used to allow for subtraction of non-emission-line sources (e.g., stars) in order to more accurately determine emission-line fluxes as well as map out deeper detail in the faint, diffuse emission.

• COVERAGE: The central 8x8 degrees of the Large Magellanic Cloud and of the central 3.5x4.5 degrees of the Small Magellanic Cloud. A total of ~80 square degrees covering most of the gaseous extent of both galaxies (see images above). Each spot is sampled approximately 8 times in 4 different regions of the detector to help eliminate flat fielding problems and other instrumental effects.

The data have been taken over a 5 year period starting in 1998, and are now undergoing final flux calibration and global uniformity quality assessment in preparation both for our analysis and the public data release.