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DID YOU KNOW DOCUMENT: SUPPLEMENTAL TEXT
Note: All integration times are “on source”, main array integration times assuming dual polarization and default weather conditions as assumed by the ALMA Observing Tool (unless otherwise noted). Times are calculated using the online ALMA Sensitivity Calculator tool available at the time of publication which is part of the ALMA Observing Tool; proposers should re-calculate integration times for themselves. They do not include estimates of overhead. For a full description of the assumptions made for the time estimates, please review Chapter 9 of the ALMA Technical Handbook.
Image a nearby star forming galaxy in molecular gas. [image: CO(1→0) of M83 from Muraoka et al. (2009a).] The example galaxy used in the science cases below, M83, has a declination of -29:51:57.0 and an assumed distance of 4.5 Mpc.
CO(J=3→2): 345.8 GHz, in Band 7. Field of view is 18" (400 pc).
Muraoka et al. (2009b) measure 30-150 K km/s in the CO(3→2) line over the central kpc, over a full width of ~ 150 km/s. A sensitivity of 200 mK in the central 0.5 kpc will yield a 5σ detection of Tb=1 K. Using 0.25" resolution (6 pc), 2 km/s channel width (to simultaneously resolve the line and the cloud), and 43 antennas, achieving a sensitivity of 200 mK in the main array with the default weather of 1.262mm (4th Octile) takes 1.69 hours. Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
HCN(J=1→0): 88.6 GHz, in Band 3. Field of view is 71" (1.5 kpc).
Muraoka et al. (2009a) detect bright HCN across the central 1.5 kpc of M83 (rms ~ 4 K km/s) but are sensitivity limited; emission is tentatively detected at the noise limit, but secure detections require pushing to higher sensitivity. To get a 5σ detection of a cloud with 4 K km/s intensity, assuming a 10 km/s channel width, 43 antennas, and 1.4" resolution (30 pc), or 80 mK (1 mJy) sensitivity, requires 16.2 minutes in the main array with the default weather of 5.186mm (7th Octile). Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
HCN(J=1→0): 88.6 GHz, in Band 3. Field of view is 71" (1.5 kpc).
The optical bar is 3.1' by 1.4' (4.1 kpc by 1.8 kpc), requiring a 17-pointing mosaic. Assuming a 10 km/s channel width, 1.4" resolution (30 pc), and 80 mK sensitivity, the goal can be achieved in 2.14 hours on source in the default weather band for Band 3 (7th Octile). Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
References:
Muraoka et al. (2009a). PASJ, 61, 163
Muraoka et al. (2009b). ApJ, 706, 1213
Redshifted ISM in galaxies. [image: VLA 1.4 GHz (red) and MIPS 24 μm (blue) image of a SMG overlaid with ALMA 870 μm contours (Hodge et al. 2013).]
Continuum, 350 GHz, Band 7. Field of view is 18" (2.3 Mpc, assuming DL=25.8 Gpc).
Assuming a flux density detectability curve extrapolated between those shown in Figures 4 and 8 of Blain et al. (2002) at ~ 350 GHz, a dusty, 1011 L☉ galaxy with T~ 40 K at z=3 has a brightness of 60 μJy. Note that the flux density as a function of redshift is fairly flat from 1 $<$ z $<$ 6, so this estimate holds for galaxies of this luminosity across significant redshift space. For a 5σ detection (rms=12 μJy), with 7.5 GHz bandwidth and 43 antennas, a source at Dec=-20 degrees can be detected with this sensitivity in 4.3 hours with the default weather of 0.913mm (3rd Octile). Assuming a beam size of 1.4" (250 kpc) ensures that the source remains unresolved; using this beam size, the sensitivity corresponds to 61 μK (5σ). The ACA is not required.
[CII]: 1900.5 GHz / [1+z] = 365.5 GHz, in Band 7. Field of view is 17" (3.2 Mpc, assuming DL=38.7 Gpc).
Assuming a [CII] flux from a normal, Milky Way-type galaxy of 1x108 K km/s pc2 (Fixsen et al. 1999, Baker 2009) at z=4.2, the expected flux is 38.6 mJy km/s. Assuming a 300 km/s linewidth and magnification of 10 (average value seen by Hezaveh et al. 2013), a 5σ detection of 1.3 mJy (in one 300 km/s velocity channel) requires 0.26 mJy rms sensitivity. For a source at Dec=-20, with a 1.4" beam (280 kpc), 300 km/s channel width, and 43 antennas, this can be achieved in 28.3 minutes on source with the default weather of 0.913mm (3rd Octile); achieving this sensitivity and fully resolving the line with five 60 km/s channels can be done in 2.4 hours. The ACA is not required.
Continuum, 265 GHz, Band 6. Field of view is 23" (12 Mpc, assuming DL=106 Gpc).
Assuming a flux density detectability curve extrapolated from the one shown in Figure 4 of Blain et al. (2002) for a 5x1012 L☉ galaxy at 1100 μm, a 1012 L☉ luminous IR galaxy (LIRG) with T=38K at z=10 - assuming these exist at z=10 - should be five times fainter than 1.5 mJy, or 0.3 mJy. Note that the flux density as a function of redshift is fairly flat. For a 5 sigma detection, we require an rms of 0.03 mJy (13 mK for an angular resolution of 0.2”). Using 7.5 GHz bandwidth and 43 antennas, we would require 19 minutes on source to observe one target with the default weather of 1.796mm (5th Octile).
References:
Baker (2009). ALMA detectability memo.
Blain et al. (2002). PhR, 369, 111
Fixsen et al. (1999). ApJ, 526, 207
Hezaveh et al. (2013). ApJ, 767, 132
Hodge et al. (2013). ApJ, 768, 91
Solar System objects. [image: CO(2-1) of comet Hale-Bopp from PdBI. (From ESO/ALMA document.)]
CO(J=3→2): 345.8 GHz, in Band 7. Field of view is 18" (1.2x104 km).
The angular diameter of Mars ranges from 3.5" (farthest from Earth, 2.67 AU) to 14" (closest to Earth, 0.67 AU); here, we assume a 10" diameter (0.94 AU, where 300 km=0.44"). Lellouch et al. (1991) measure an absorption feature of depth -40.5 K in the CO(3→2) line over the entire disk. Assuming 0.5" resolution, 100 m/s channel width, Dec=0, and 43 antennas, a 100σ detection of 0.4 K sensitivity can be achieved in 25.5 minutes on source with the default weather of 0.913mm (3rd Octile). The largest angular scale of Mars is 10" on the sky (7000 km) Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
Several lines (230-271 GHz) in Band 6. Field of view is 24" (1.2x104 km).
Following the work of de Val-Borro et al. (2013), several volatiles - HCN, CH3OH, H2CO, CS, and HNC from the comet C/2002 T7 (LINEAR) are detected with the SMT. The best sensitivity reached during the observations is ~ 15 mK in a ~ 30" beam. The comet has a water production rate of 3x1029 molecules/second and was observed at geocentric distances of 0.70-0.73 AU (heliocentric distances of 0.42-0.52 AU). In Cycle 9, ALMA can achieve five different tunings in one scheduling block to capture each line; assuming a declination of -20 degrees, observing frequency of 260 GHz, 43 antennas, and 1.9" beam (1500 km at 0.7 AU, ensuring that the nucleus is unresolved), a sensitivity of 15 mK in a 0.3 km/s channel can be reached in 50.6 minutes per tuning, or 4.2 hours on source for all five lines with the default weather of 1.796mm (5th Octile). Additional transitions of each molecule present across the band may allow the same science in fewer spectral tunings, but this integration time estimate is based on the specific transitions observed by de Val-Borro et al. (2013). Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
Continuum, 345 GHz, Band 7. Field of view is 18" (5.1x105 km).
Assuming a standard thermal model for KBOs (Stansberry et al. 2008) with a beaming parameter of 1.2 and a geometric albedo of 0.08, the expected disk-averaged brightness temperature is 49 K for a body with a diameter of 200 km that is 40 AU from the Sun. At its closest position to Earth (d=39 AU), the object has an apparent size of 0.0071", which yields a flux of ~ 0.14 mJy at 345 GHz. This emission will be unresolved with the smallest possible ALMA beam. Assuming 43 antennas, 7.5 GHz bandwidth, and Dec=0, a 5σ detection (28 μJy/beam rms) in a 0.2" beam (5700 km at 39 AU, which corresponds to 7.2 mK) is possible in 47.5 min of observing time with the default weather of 0.913mm (3rd Octile). The ACA is not required.
References:
de Val-Borro et al. (2013). A&A, 559, 48
Lellouch et al. (1991). P&SS, 39, 209
"Science with ALMA". ESO Science Case for ALMA document.
Stansberry et al. (2008). "The Solar System Beyond Neptune", Barucci, Boehnhardt, Cruikshank, & Morbidelli (eds.), University of Arizona Press (Tucson), p.161-179
Galactic clouds and star forming regions. [image: CO map of Orion taken with the JCMT (HARP/ACSIS) in 2007.]
Continuum, 343.5 GHz, Band 7. Field of view is 18" (0.013 pc), restricted to the central third (6", 0.004 pc) for on-axis polarization observations in Cycle 9.
Following the study of the polarized dust continuum of the binary protostar IRAS 16293 performed by Rao et al. (2009) with the SMA, two components are detected with flux densities of 6.85 and 4.62 Jy and with 0.5% and 1.0% polarization, respectively. The sensitivity reached in the study, which is sufficient to detect the polarized components at the ~ 7σ level, is 4 mJy/beam in a 3.1" x 2.0" beam (~ 7.2 mK). Assuming a distance of 150 pc, a beam of 0.5" corresponds to a resolution of 75 AU. Reaching a sensitivity of 7 mK with a beam of 0.5" [or 4x(0.5/2.4)2 = 0.17 mJy/beam] at a declination of -24.5 degrees with 43 antennas, 7.5 GHz bandwidth, and full polarization requires ~1.6 hours on source integration time with the default weather of 0.913mm (3rd Octile), which will be observed in a block of 3 hours in length to account for accurate polarization calibration. Note that due to the 3-hour minimum observing time required for good polarization calibration, the actual sensitivity achieved in this example will be considerably better.
Spectral Line Survey, 211-274.9 GHz, Band 6. Field of view is 26" (0.055 pc).
The declination of Orion is approximately -05:23:00. In early science verification data (with 16 ALMA antennas), Randall & Remijan (2012) detected on average 20 lines above 5σ per 200 MHz of bandwidth from the hot core Orion-KL (~ 5" in size) in a blind Band 6 spectral survey; in their observations, σ = 50 mJy/beam with a beam of 2.2" (~ 280 mK). The channels had 488 kHz spacing (0.6 km/s at 230 GHz), oriented in five separate tunings (with four 1.875 GHz spectral windows each) for a total of ~ 40 GHz of coverage within the 64 GHz band. A spectrum measured toward Orion-KL in Cycle 9 with 2.0" resolution (880 AU, assuming d=440 pc), and 43 antennas to three times deeper 100 mK rms sensitivity can be achieved 23 seconds with 976 kHz of channel width and the default weather of 1.796 mm (5th Octile). The OT gives the minimum time on source, 5 minutes (which yields an rms of 4.8 mJy or 28 mK). Covering the entire 64 GHz band would recover potentially 6,000 lines at the previous sensitivity; assuming that a factor of ~ 3 increase in sensitivity would return twice as many lines yields potentially 12,000 lines across the full Band 6. This can be done with 10 tunings (taking into account 0.2 MHz of overlap between tunings) – or about 4 distinct spectral scan setups, which requires about 42 minutes on source to cover the entirety of Band 6. Note that this estimation does not take into account time necessary to calibrate, which is likely to be significant compared to the on source integration time. Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
References:
JCMT outreach website. http://outreach.jach.hawaii.edu/pressroom/2007\_harpacsis/
Randall & Remijan (2012). Orion B6 spectral scan report (CSV-1507)
Rao et al. (2009). ApJ, 707, 921
Formation of galaxy clusters and cosmic structure. [image: Simulated galaxy cluster at z=0.2 at 350 GHz with lensed background galaxies and SZ emission (from ESO/ALMA document).]
Continuum, 92 GHz, Band 3. Field of view is 69" with 12-m array and 117" with the ACA.
Previous SZE images achieved noise levels as low as ~ 40 μJy/beam with a 10" beam at 90 GHz (e.g. Mroczkowski et al. 2012, Korngut et al. 2011), which is sufficient to identify and characterize merger shocks in the central regions of merging galaxy clusters. Assuming a declination of -20 degrees, bandwidth of 7.5 GHz, and 43 antennas in the main array, a 4 sigma detection of 40 μJy/beam x (5/10)2 = 10 μJy/beam in a 5" beam (40 μK) requires 65 minutes on source with the default weather of 5.186mm (7th Octile). Utilizing the 117” field of view of the ACA would be advantageous for large clusters to improve sensitivity to the extended bulk SZE within the clusters. The 7-m component of the ACA has beam size of ~ 23". Assuming that the 7-m Array requires twice the integration time of the main array (2.2 hours) to recover the extended emission, observations of the same cluster with a bandwidth of 7.5 GHz and 10 antennas in the 7-m Array would reach an rms of 92 μJy/beam in a 23" beam, or 25 μK. Note that to adequately map the ACA field of view with the 12-m array may require a small mosaic.
Continuum, 353 GHz, Band 7. Field of view is 18" (2.3 Mpc, assuming D$_{L}$=26.9 Gpc).
Following the study of Geach et al. (2005), in which a sample of 23 LABs in a z=3.1 overdensity were observed with the JCMT, the average flux of the targets is 3.0 mJy at 850 μm. To achieve a 20σ detection of each LAB, an rms of 150 μJy is required. Assuming a 7.5 GHz bandwidth and 43 antennas at the declination of the overdensity (Dec=0 degrees), the necessary integration time for one target is 2.1 minutes on source with the default weather of 0.913mm (3rd Octile); all 23 sources can be observed to this sensitivity in less than an hour on source. If a beam size of 1.0" (130 kpc) is specified, then the sources will be unresolved; using this beam size, the sensitivity corresponds to 1.5 mK. The ACA is not required.
References:
``Science with ALMA". ESO Science Case for ALMA document.
Geach et al. (2005). MNRAS, 363, 1398
Korngut et al. (2011). ApJ, 734, 10
Mroczkowski et al. (2012). ApJ, 761, 47
Resolve planetary disks around young stars. [image: HCO+ in transition disk HD142527 (Casassus et al. 2013), taken from visualization created by S. Perez.]
H2CO(J=3→2): 225.7 GHz, in Band 6. Field of view is 28" (0.017 pc).
Using the ALMA simulation performed by Qi, Oberg, \& Wilner (2013) of the H2CO transition in the disk surrounding Herbig Ae star HD 163296, made with 1 hour of observing time and a beam size of 0.3", the snow line is easily resolved. The SMA observations presented in the same study utilize 0.6 km/s channels, and the declination of the source is -21:57:21.9. To detect their faintest contour level, 25 mJy km/s, at 10 sigma in a 0.6 km/s channel requires an rms of 4.2 mJy in their assumed 0.3" beam (37 AU, assuming d=122 pc, or 1.12 K). This sensitivity is achievable in 12.1 minutes on source with 43 antennas and the default weather of 1.796mm (5th Octile). Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
HCO+(J=4→3): 356.7, in Band 7. Field of view is 17" (0.012 pc).
The Cycle 0 ALMA observations of Casassus et al. (2013) of the HCO+(4-3) imaging of the disk around the young star HD 142527 detect (and resolve) dense gas flowing across the gap in the disk. The observations utilize 0.1 km/s channels and reach a sensitivity of 15 mJy in a beam of 0.51"x0.33" (~ 0.8 K) in 52 minutes on source. In Cycle 9, these observations (repeated for the same target) can be achieved assuming a declination of -42:19:23.3, 0.1 km/s channels, 43 antennas, a 0.42" beam (59 AU, assuming d=140 pc), and rms of 0.8 K (14.7 mJy) in 13.9 minutes on source with the default weather of 0.913mm (3rd Octile). Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
Continuum, 353 GHz, Band 7. Field of view is 18" (0.010 pc).
Following the ALMA simulations of Gonzalez et al. (2012), a gap induced by a 1 Jupiter mass planet in a dust disk 40 AU from its parent star is detectable at 850 μm with a beam size 0.15" or better at a distance of 140 pc. From their Figure 12, the gap in a disk around a star in Ophiuchus (d=120 pc, Dec=-24 degrees) can be well resolved in an hour with 0.12" resolution. Utilizing a resolution of 0.12" in Band 7 yields a resolution equivalent to 15 AU at the distance of Ophiuchus. Assuming 7.5 GHz bandwidth, 43 antennas, and the other parameters specified above, the sensitivity reaches 19 μJy in 2.0 hours of integration time on source and the default weather of 0.913mm (3rd Octile), consistent with the sensitivity shown to be necessary in Figure 12 of Gonzalez et al. (2012). Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
Continuum, 353 GHz, Band 7. Field of view is 18" (58 AU).
Following the model of Moran, Kuchner, & Holman (2004) of the debris disk around ε Eri (Dec= -09:27:29.7), which hosts dense dust clumps being dynamically affected by a massive planet, the dust distribution (in addition to the clumps) can be well resolved by ALMA. At the distance of $\epsilon$ Eri (3.22 pc), 1 AU = 0.31". From the Moran model, a sensitivity of 0.7 mJy/beam (with a 1.85" beam) is required to recover the faintest emission at the edge of the disk, which corresponds to 19.7 μJy with a 0.31" beam, or 6.6 μJy rms for a 3σ detection. This sensitivity can be achieved with 43 antennas and 7.5 GHz bandwidth in 16.8 hours on source with the default weather of 0.913mm (3rd Octile). The dense clumps within the disk (brighter than ~ 48 μJy/beam) can be observed to 16 μJy sensitivity in much less time (~ 3 hours). Due to Epsilon Eri's large angular distribution on the sky, the ACA would likely be recommended to achieve the science goal.
Continuum, Band 6 (233 GHz), field of view is 28”.
Following the SV data of HL Tau as an example, a resolution of 33 mas corresponds to a linear scale of 4.6 AU at the distance of Taurus, or 1.6 AU at the distance of TW Hya. The time on source used to generate the Band 6 HL Tau image shown in the press release was 4.5 hours. In this time on source in Cycle 9, with 43 antennas, a bandwidth of 7.5 GHz and assuming a declination of +18 degrees, a sensitivity of 7.9 μJy can be reached with the default weather of 1.796mm (5th Octile). Depending on the extent of the disk in question, other configurations of the 12-m array may be needed, or even the ACA for more nearby disks.
References:
Casassus et al. (2013). Nature, 493, 191
Gonzalez et al. (2012). A&A, 547, A58
Moran, Kuchner & Holman (2004). ApJ, 612, 1163
Qi, Oberg & Wilner (2013). ApJ, 765, 34
Measure stellar activity. [image: CO(2→1) contours (Cox et al. 2000) over 2.15 μm continuum image (Sahai et al. 1998) of the Egg Nebula.]
CO(J=2→1): 230.5, in Band 6. Field of view is 27" (0.20 pc).
Following the Cycle 0 ALMA observations of Sahai et al. (2013) of the Boomerang Nebula (Dec= -54:31:11.4), outflowing CO(2→1) was imaged with 0.63 km/s resolution and a 2.4"x1.6" beam to a sensitivity of 7.5 mJy/beam (~ 43 mK in a 2.0" beam, or 3000 AU assuming d=1.5 kpc). In Cycle 9, assuming 43 antennas, this sensitivity and velocity resolution can be reached in 4.0 minutes on source with the default weather of 1.796mm (5th Octile). Note that the OT will enforce a minimum time on source of 5 minutes. Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
Continuum, 250 GHz, Band 6. Field of view is 25".
Following the model of Harper et al. (2013), the expected millimeter fluxes of nearby giant stars range from 6-80 mJy at 250 GHz. Most of the stars considered in their study will be unresolved even with the smallest Cycle 9 beam, but assuming 0.2" resolution, even the faintest of these stars will be detectable with a S/N of 50 (rms = 0.12 mJy/beam, or 55 mK) in 1.5 minutes of integration time on source (assuming 43 antennas, 7.5 GHz bandwidth, and a declination of -20 degrees and the default weather of 1.796mm (5th Octile)). Note that the OT will enforce a minimum time on source of 5 minutes. The ACA is not required.
Continuum, 100 GHz, Band 3. Field of view is 62" (7.8, 32 Mpc, assuming DL=25.8, 106 Gpc).
Following the GRB afterglow model plotted in Figure 6 of de Ugarte Postigo et al. (2012), 1-2 days after a typical burst, a z=3 (z=10) afterglow peaks around 0.3 (0.08) mJy in Band 3. For a 10σ detection of each afterglow, assuming an observation at Dec=-20 degrees, 7.5 GHz bandwidth, and 43 antennas, rms sensitivities of 0.03 mJy/beam (in a 1.0" beam - 125 kpc at z=3 - yields 3.7 mK) and 0.008 mJy/beam (in a 1.0" beam - 500 kpc at z=10 - yields 1.0 mK) are required. These are achievable in 8 minutes and 1.8 hours, respectively, with the default weather of 5.186mm (7th Octile). The ACA is not required.
References:
Cox et al. (2000). A&A, 353, L25
de Ugarte Postigo et al. (2012). A&A, 538, 44
Harper et al. (2013). MNRAS, 428, 2064
Sahai et al. (1998). ApJ, 492, L163
Sahai et al. (2013). ApJ, 777, 92
Accretion onto black holes. [image: CO(2-1) AGN extended torus model of NGC 1068 at ALMA resolution (Wada \& Tomisaka 2005).]
CO(J=2→1): 230.2, in Band 6. Field of view is 27" (2.1 kpc).
Following Davis et al. (2013), the mass of the central black hole in NGC 4526 (d=16.4 Mpc, Dec=+07:42) can be modeled using high-resolution observations of molecular gas [CO(2→1)] obtained with multiple configurations of CARMA. This work achieves a resolution of 0.25" (20 pc) and rms of 2.9 mJy/beam (~ 1 K) in 10 km/s channels. With 43 antennas, the galaxy can be observed with 0.20" (16 pc) resolution and 2 km/s channels, and similar sensitivity (1.3 mJy/beam, or 0.75 K) can be reached in 42 minutes on source with the default weather of 1.796mm (5th Octile). Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended. However, the sphere of influence of the black hole in this system is 20 pc (Davis et al. 2013), so extended emission is likely not relevant in this case.
CO(J=3→2), CO(J=7→6): 91.8 GHz (in Band 3), 214.0 GHz (in Band 6). Fields of view are 69", 29" (7.8, 3.3 Mpc, assuming DL=23.4 Gpc).
Here we replicate with ALMA the study by Schumacher et al. (2012), which utilizes PdBI observations of the CO ladder to derive the kinetic temperature and density of the gas in the host galaxy of obscured quasar AMS12. The redshifted CO(3→2) and CO(7-6) lines fall into available bands (3 and 6, respectively). The quoted sensitivities to reach are 0.7 mJy/beam (Band 3) and 2.0 mJy/beam (Band 6), each in 30 km/s channels; the source is unresolved in the Schumacher et al. observations. We flip the +59 degree declination of the source to be -59 degrees and assume 30 km/s channels, 43 antennas, and a 1.0" beam (110 kpc, assumed to keep the source unresolved); the necessary integration time in Band 3 is 12 minutes and in Band 6 is 1.2 minutes on source, with the default weather of 5.186mm (7th Octile) and 1.796mm (5th Octile), respectively. Note that the OT will set a minimum integration time of 5 minutes. Note that for the purposes of OT setup, these bands must be requested in separate Science Goals. The ACA is not required.
Continuum, 345 GHz, Band 7. Field of view is 18" (0.72 pc).
Haubois et al. (2012) present observations of 870 μm emission from the Galactic center with APEX, which they observe to decrease during infrared flares, with a sensitivity of 60 mJy/beam in a 19" beam. In a 1.0" beam (0.08 pc, assuming d=8.3 kpc), this corresponds to 60 mJy/beam x (1.0/19.0)2 = 0.17 mJy/beam. Sgr A* has a declination of -29 degrees, and assuming 43 antennas and 7.5 GHz bandwidth, this sensitivity can be reached in 1.6 minutes on source time with the default weather of 1.262mm (4th Octile). Note that the OT will set a minimum integration time on source of 5 minutes. Depending on the largest angular scale required to achieve the science goal, the ACA (and/or an additional 12-m configuration) may also be recommended.
References:
Davis et al. (2013). Nature, 494, 328
Haubois et al. (2012). A&A, 540, A41
Schumacher et al. (2012). MNRAS, 423, 2132
Wada & Tomisaka (2005). ApJ, 619, 93
