Two-millimeter ALMA Cluster Observations (TACO)
An ALMA + JWST census of cosmic dust toward the faint end of the infrared luminosity function at z > 4, using massive galaxy clusters as cosmic telescopes.
Science motivation
Two-millimeter continuum observations are an efficient selector of dusty star-forming galaxies (DSFGs) at z > 4, providing some of the best constraints on the obscured cosmic star-formation rate density (CSFRD) when the Universe was only 1–2 Gyr old. Yet there is still no direct measurement of the faint end of the infrared luminosity function (IRLF; LIR < 1012 L⊙) at z > 4 — one of the largest uncertainties in the obscured CSFRD.
TACO attacks this problem by surveying massive galaxy clusters as natural gravitational telescopes. Strong lensing magnifies background sources, pushing the effective 2 mm source-count function down to ~0.01 mJy — roughly 30× deeper than blank-field studies. Combined with deep HST, JWST, Spitzer and Herschel imaging and high-quality lens models, TACO securely detects strongly magnified sub-L* DSFGs at z > 4 and aims for a decisive measurement of the high-redshift IRLF faint end.
The survey delivers three additional science goals:
- Measure the dust mass and emissivity of normal DSFGs at z > 2 by characterizing the Rayleigh–Jeans tail.
- Constrain the evolution of the cosmic molecular gas density through serendipitous CO line emitters in the data cubes.
- Study the foreground clusters themselves via CO(2–1) from member galaxies and the resolved Sunyaev–Zeldovich (SZ) effect.
Survey design
- Band / wavelength: ALMA Band 4, ~135–151 GHz (≈2 mm), dual-sideband continuum (with serendipitous line coverage).
- Targets: well-studied massive lensing clusters (Frontier Fields, CLASH, RELICS, SPT, Planck and MACS clusters) with existing HST/JWST imaging and public lens models.
- Angular resolution: ≈0.6″–2.5″ (synthesized-beam, robust 0.5), with a 1.5″-tapered product for extended-emission sensitivity.
- Depth: requested RMS ≈60 µJy beam−1; delivered median ≈40 µJy beam−1 over a ~4.6 arcmin2 (pb > 0.5) field per cluster.
- Scope: Cycle 9 — 35 cluster fields (19.5 h) and Cycle 12 — 38 fields (41 h); ~70 fields observed & continuum-imaged to date, building toward a full ALMA + JWST dust census out to z ~ 7.
Status
- Cycle 9 (2022.1.01356.S): observed and delivered — 31 cluster fields with calibrated Band-4 continuum data in hand.
- Cycle 12 (2025.1.00360.S): observed and delivered — 39 cluster fields with calibrated Band-4 data; continuum imaged (robust 0.5 + 1.5″ taper).
- Continuum: all delivered Cycle-9 and Cycle-12 fields imaged at two weightings (robust 0.5 native + 1.5″ taper); matched-filter source extraction across both cycles → combined photometry catalog (129 sources, v2.0).
- Spectral-line cubes (Cycle 9): dedicated CASA pipeline produces 60 km s−1 cubes per sideband × 2 weightings, with uv-continuum subtraction. 3 fields complete (PLCKG004-19, CLJ0152-13, PLCKG287+32); A2744 imaging.
Sample
All delivered & imaged ALMA Band-4 fields across Cycle 9 and Cycle 12. RMS values are per synthesized beam; “taper” refers to the 1.5″-tapered product. The cube ✓ tag marks fields with completed 60 km/s spectral-line cubes (Cycle 9).
| Cluster | Cycle | R.A. (J2000) | Dec. (J2000) | Beam (″) | RMS (µJy bm−1) |
RMS taper (µJy bm−1) |
Area pb>0.5 (arcmin2) | Line cubes |
|---|---|---|---|---|---|---|---|---|
| A1300 | 9 | 11:31:53.7 | -19:55:26 | 0.76×0.62 | 52 | 66 | 4.6 | — |
| A1835 | 9 | 14:01:01.8 | +02:52:26 | 0.91×0.75 | 47 | 55 | 4.6 | — |
| A2744 | 9 | 00:14:21.2 | -30:24:01 | 0.91×0.74 | 32 | 37 | 4.5 | imaging |
| A2813 | 9 | 00:43:24.9 | -20:37:12 | 0.75×0.72 | 61 | 75 | 4.5 | — |
| A370 | 9 | 02:39:53.3 | -01:34:38 | 1.39×1.14 | 38 | 39 | 4.6 | — |
| ACT0102-49 | 9 | 01:02:54.0 | -49:15:17 | 1.29×1.14 | 37 | 38 | 4.6 | — |
| AS1077 | 9 | 22:58:48.3 | -34:48:12 | 1.26×1.05 | 45 | 47 | 4.5 | — |
| Bullet | 9 | 06:58:35.2 | -55:57:11 | 1.27×1.21 | 40 | 41 | 4.6 | — |
| CLJ0152-13 | 9 | 01:52:43.0 | -13:57:30 | 1.02×0.94 | 42 | 45 | 4.6 | cube ✓ |
| MACS0025 | 9 | 00:25:30.2 | -12:22:49 | 0.79×0.72 | 63 | 78 | 4.5 | — |
| MACS0150-10 | 9 | 01:50:21.1 | +17:46:35 | 1.50×1.20 | 45 | 43 | 4.6 | — |
| MACS0257-22 | 9 | 02:57:41.1 | -22:09:18 | 1.21×1.01 | 38 | 39 | 4.5 | — |
| MACS0308+26 | 9 | 03:08:56.1 | +26:45:40 | 1.07×0.73 | 47 | 54 | 4.5 | — |
| MACS0416 | 9 | 04:16:08.8 | -24:04:22 | 1.59×1.07 | 37 | 38 | 4.6 | — |
| MACS0417 | 9 | 04:17:33.7 | -11:54:21 | 1.26×1.05 | 38 | 39 | 4.6 | — |
| MACS1149 | 9 | 11:49:35.6 | +22:24:00 | 0.91×0.61 | 53 | 63 | 4.6 | — |
| MACS1423 | 9 | 14:23:48.0 | +24:04:46 | 1.98×1.01 | 36 | 35 | 4.5 | — |
| MS0451 | 9 | 04:54:10.8 | -03:00:56 | 1.31×1.06 | 38 | 39 | 4.6 | — |
| MS1008-12 | 9 | 10:10:33.8 | -12:39:41 | 0.76×0.69 | 46 | 56 | 4.6 | — |
| PLCKG004-19 | 9 | 19:17:05.0 | -33:31:21 | 1.33×1.03 | 37 | 39 | 4.5 | cube ✓ |
| PLCKG287+32 | 9 | 11:50:50.4 | -28:04:52 | 0.75×0.62 | 52 | 67 | 4.6 | cube ✓ |
| RCS2327 | 9 | 23:27:27.7 | -02:04:31 | 1.27×1.06 | 39 | 40 | 4.6 | — |
| RXC0232-44 | 9 | 02:32:18.1 | -44:20:49 | 1.39×1.13 | 36 | 36 | 4.6 | — |
| RXC0911+17 | 9 | 09:11:11.2 | +17:46:35 | 0.90×0.72 | 32 | 38 | 4.6 | — |
| SDSS1209+26 | 9 | 12:09:23.7 | +26:40:28 | 0.98×0.60 | 52 | 63 | 4.6 | — |
| SPT0254-58 | 9 | 02:54:15.8 | -58:57:06 | 1.63×1.16 | 40 | 40 | 4.6 | — |
| SPT0546-53 | 9 | 05:46:37.3 | -53:45:33 | 1.26×1.13 | 38 | 38 | 4.6 | — |
| SPT0615-57 | 9 | 06:15:51.9 | -57:46:46 | 1.28×1.20 | 38 | 38 | 4.6 | — |
| SPT2106-58 | 9 | 21:06:04.4 | -58:44:37 | 1.08×0.88 | 30 | 31 | 4.4 | — |
| SPT2344-42 | 9 | 23:44:44.0 | -42:43:12 | 1.29×1.07 | 33 | 34 | 4.6 | — |
| WHJ0137 | 9 | 01:37:24.9 | -08:27:33 | 0.99×0.85 | 50 | 55 | 4.6 | — |
| Abell1689 | 12 | 13:11:29.8 | -01:20:33 | 1.04×0.90 | 33 | 37 | 4.5 | — |
| Abell209 | 12 | 01:31:52.5 | -13:36:41 | 0.77×0.62 | 45 | 59 | 4.5 | — |
| Abell2537 | 12 | 23:08:22.0 | -02:11:32 | 0.60×0.55 | 33 | 48 | 4.5 | — |
| Abell3192 | 12 | 03:58:53.2 | -29:55:47 | 0.86×0.70 | 36 | 46 | 4.5 | — |
| Abell383 | 12 | 02:48:03.4 | -03:31:45 | 0.93×0.70 | 43 | 54 | 4.5 | — |
| Abell521 | 12 | 04:54:06.9 | -10:13:25 | 0.86×0.71 | 40 | 50 | 4.5 | — |
| Abell68 | 12 | 00:37:06.8 | +09:09:24 | 0.89×0.80 | 39 | 48 | 4.5 | — |
| AbellS1063 | 12 | 22:48:44.0 | -44:31:51 | 0.68×0.55 | 37 | 52 | 4.5 | — |
| AbellS295 | 12 | 02:45:31.0 | -53:02:24 | 0.81×0.75 | 44 | 56 | 4.5 | — |
| GAMA10033 | 12 | 08:42:21.4 | +01:38:29 | 1.81×1.07 | 46 | 47 | 4.5 | — |
| MACSJ0035-20 | 12 | 00:35:26.2 | -20:15:45 | 0.75×0.61 | 45 | 59 | 4.5 | — |
| MACSJ0159-08 | 12 | 01:59:49.4 | -08:49:59 | 0.78×0.62 | 45 | 59 | 4.5 | — |
| MACSJ0257-23 | 12 | 02:57:08.8 | -23:26:05 | 0.92×0.76 | 40 | 49 | 4.5 | — |
| MACSJ0329-02 | 12 | 03:29:41.6 | -02:11:46 | 0.84×0.73 | 39 | 49 | 4.5 | — |
| MACSJ0429-02 | 12 | 04:29:36.0 | -02:53:07 | 0.96×0.86 | 40 | 46 | 4.5 | — |
| MACSJ0451+00 | 12 | 04:51:54.6 | +00:06:18 | 0.96×0.88 | 39 | 46 | 4.5 | — |
| MACSJ0553-33 | 12 | 05:53:23.0 | -33:42:29 | 0.86×0.70 | 39 | 48 | 4.5 | — |
| MACSJ0940+07 | 12 | 09:40:53.7 | +07:44:25 | 1.46×1.20 | 56 | 57 | 4.5 | — |
| MACSJ1115+01 | 12 | 11:15:52.0 | +01:29:56 | 0.72×0.67 | 40 | 51 | 4.5 | — |
| MACSJ1206-08 | 12 | 12:06:12.0 | -08:48:02 | 0.71×0.64 | 39 | 52 | 4.5 | — |
| MACSJ1311-03 | 12 | 13:11:01.8 | -03:10:40 | 1.05×0.92 | 34 | 38 | 4.4 | — |
| MACSJ1931-26 | 12 | 19:31:49.6 | -26:34:33 | 0.82×0.61 | 52 | 67 | 4.5 | — |
| MACSJ2129-07 | 12 | 21:29:26.1 | -07:41:28 | 1.10×0.87 | 55 | 62 | 4.4 | — |
| MACSJ2214-14 | 12 | 22:14:57.3 | -14:00:13 | 0.71×0.62 | 44 | 57 | 4.5 | — |
| MS2137-2353 | 12 | 21:40:15.2 | -23:39:40 | 0.90×0.61 | 53 | 69 | 4.5 | — |
| PLCKG171.9-40.7 | 12 | 03:12:57.2 | +08:22:12 | 1.05×0.79 | 40 | 48 | 4.5 | — |
| PLCKG308.3-20.2 | 12 | 15:18:49.2 | -81:30:28 | 0.86×0.48 | 36 | 49 | 4.5 | — |
| RXCJ0018+16 | 12 | 00:18:33.3 | +16:26:12 | 0.90×0.86 | 40 | 47 | 4.5 | — |
| RXCJ0032+18 | 12 | 00:32:11.3 | +18:07:31 | 0.96×0.83 | 40 | 47 | 4.5 | — |
| RXCJ0600 | 12 | 06:00:09.0 | -20:08:08 | 0.83×0.64 | 38 | 49 | 4.5 | — |
| RXCJ0940+17 | 12 | 09:49:51.8 | +17:07:10 | 1.47×1.24 | 51 | 52 | 4.5 | — |
| RXCJ1347 | 12 | 13:47:31.2 | -11:45:11 | 0.95×0.63 | 51 | 66 | 4.4 | — |
| RXCJ1532 | 12 | 15:32:53.7 | +30:20:59 | 1.27×0.89 | 46 | 51 | 4.5 | — |
| RXCJ2129+00 | 12 | 21:29:39.9 | +00:05:21 | 1.08×0.92 | 52 | 60 | 4.5 | — |
| RXCJ2211-03 | 12 | 22:11:45.9 | -03:49:44 | 0.83×0.63 | 46 | 59 | 4.5 | — |
| SMACSJ0723-73 | 12 | 07:23:18.4 | -73:27:18 | 1.03×0.82 | 36 | 41 | 4.5 | — |
| SMACSJ2031-40 | 12 | 20:31:53.3 | -40:37:31 | 1.00×0.72 | 42 | 51 | 4.5 | — |
| SMACSJ2131-40 | 12 | 21:31:04.9 | -40:19:21 | 1.01×0.74 | 44 | 53 | 4.5 | — |
| SPT2325 | 12 | 23:25:11.9 | -41:12:05 | 2.53×1.69 | 33 | 31 | 4.5 | — |
70 fields imaged (31 Cycle-9 + 39 Cycle-12) · median RMS ≈40 µJy beam−1 (native) / 48 µJy beam−1 (1.5″ taper) — exceeding the 60 µJy request.
Findings so far
- Continuum: 129 sources catalogued across the combined Cycle-9 + Cycle-12 sample (photometry catalog v2.0), including strongly lensed candidates behind the clusters; the median delivered depth (~40 µJy beam−1) beats the proposal request, enabling source counts well below the blank-field confusion limit.
- Spectral lines: a blind line search in the completed Cycle-9 cube fields is so far consistent with noise (no >6.5σ lines; 5σ limit ≈3–4 mJy per 60 km s−1 channel). A systematic line search across the full sample is still to come; CO / [C i] emitters may emerge in richer or more strongly-lensed fields.
Continuum maps, the v2.0 source catalog, and per-field spectral products are being assembled into a uniform internal team data release.
Highlights
A glimpse of the data — deep 2 mm continuum imaging of a rich cluster field, and a selection of detected sources with their multi-wavelength counterparts.
ACT0102-49 (El Gordo) — one of the richest fields, with seven ALMA 2 mm continuum sources (cyan) detected across the primary beam.
Selected continuum sources — El Gordo, the Bullet Cluster, and some of the brightest detections — each shown with ALMA 2 mm (native & 1.5″ tapered, with peak S/N), HST, and Spitzer/IRAC cutouts.
Team & data
The TACO team — Eiichi Egami, Fengwu Sun and Madison VanWyngarden.
PIs: Fengwu Sun (Westlake) & Eiichi Egami (Arizona). Key Builder: Madison VanWyngarden (Arizona). TACO builds on the JWST cluster programs MAGNIF and the Frontier-Field legacy, exploiting public HST/JWST imaging and lens models for source identification and de-lensing.
Data products: calibrated visibilities, continuum maps (two weightings), source catalogs, and continuum-subtracted 2 mm spectral cubes. An internal team release is in preparation; please contact the PIs for access.