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

TL;DR

The ACES survey provides high-resolution 3mm continuum images of the Galactic Center, combining ALMA and GBT data to map large-scale structures and distinguish different emission sources, with data processing and validation details.

Contribution

This work presents the first large-scale, high-resolution 3mm continuum survey of the Galactic Center, including data processing, combined imaging with GBT, and validation against previous observations.

Findings

Achieved RMS noise of ~0.1 mJy per 2.5" beam in the mosaic.

In-band spectral indices help distinguish emission types.

Good overall agreement with previous ALMA data, with some discrepancies.

Abstract

The ALMA Central Molecular Zone Exploration Survey, ACES, has mapped $\gtrsim1000$ square arcminutes at 3 mm toward the center of our Galaxy. ACES provides the first large-scale, high-resolution ($\sim2.5$") view of the central $\sim200$ 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 $\sim0.1$ mJy per $\sim2.5$" beam, though there is a tail of substantially higher noise toward 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 millimeter Extended Nucleus Survey (TENS), a new 10"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 toward the brightest sources.