ALMA Central Molecular Zone Exploration Survey (ACES) – II. 3 mm continuum images

ABSTRACT The ALMA Central Molecular Zone Exploration Survey (ACES) has mapped $\gtrsim 1000$ square arcminutes at 3 mm towards the centre of our Galaxy. ACES provides the first large-scale, high-resolution ($\sim 2.5\,\rm arcsec$) view of the central $\sim 200$ parsecs of the Milky Way. In this work, we describe the continuum data processing and present the continuum data products. In the combined mosaic of 45 individual ALMA mosaics, the typical RMS noise achieved is $\sim 0.1$ mJy per $\sim 2.5\, \rm arcsec$ beam, though there is a tail of substantially higher noise towards regions with bright continuum structure, especially around Sgr A* and Sgr B2. In-band spectral indices are measurable for a small fraction of the brightest and most compact sources, enabling distinction between dust-dominated and free-free- or synchrotron-dominated sources. To recover emission on large angular scales, we present the GBT MUSTANG-2 Three millimetre Extended Nucleus Survey (TENS), a new 10 arcsec resolution survey of the CMZ, which we combine with the ACES image by feathering. To demonstrate the quality and reliability of the ACES data, we compare to previously published ALMA data obtained with higher resolution and sensitivity, finding overall good agreement with past results, but some disagreement towards the brightest sources.