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The Fred Young Submillimeter Telescope (FYST), which is the telescope of the CCAT-prime project, will be located at 5600 m near the summit of Cerro Chajnantor in northern Chile, and will host the modular instrument called Prime-Cam. Two of the instrument modules in Prime-Cam will be a spectrometer with a resolving power of R ∼ 100 and populated with a detector array of several thousand KIDs (Kinetic Inductance Detectors). The main science goal of this spectrometer module, called EoR-Spec, is to probe the Epoch of Reionization (EoR) in the early universe using the Line Intensity Mapping (LIM) technique with the redshifted [CII] fine-structure line. This presentation provides an overview of the optical, mechanical, and spectral design of EoR-Spec, as well as of the detector array that will be used. The optical design consists of four silicon lenses that have anti-reflection metamaterial layers. A scanning Fabry-Perot Interferometer (FPI) will be located at the pupil and provides the spectral resolution over the full spectral coverage of 210 GHz to 420 GHz in two orders, resulting in a redshift coverage of the [CII] line from z = 3.5 to z = 8. The detector array consists of three subarrays of KIDs, two of which are tuned for the frequency range between 210 GHz and 315 GHz, and one that is tuned for the 315 GHz to 420 GHz range. The angular resolution will be between about 30'' to 50''. This presentation also addresses the spectral and spatial scanning strategy of EoR-Spec on FYST. EoR-Spec is expected to be installed into Prime-Cam about 1 year after first light of FYST. 

Abstract We present power spectra of the cosmic microwave background (CMB) anisotropy in temperature and polarization, measured from the Data Release 6 maps made from Atacama Cosmology Telescope (ACT) data. These cover 19,000 deg²of sky in bands centered at 98, 150 and 220 GHz, with white noise levels three times lower thanPlanckin polarization. We find that the ACT angular power spectra estimated over 10,000 deg², and measured to arcminute scales in TT, TE and EE, are well fit by the sum of CMB and foregrounds, where the CMB spectra are described by the ΛCDM model. Combining ACT with larger-scalePlanckdata, the joint P-ACT dataset provides tight limits on the ingredients, expansion rate, and initial conditions of the universe. We find similar constraining power, and consistent results, from either thePlanckpower spectra or from ACT combined withWMAPdata, as well as from either temperature or polarization in the joint P-ACT dataset. When combined with CMB lensing from ACT andPlanck, and baryon acoustic oscillation data from the Dark Energy Spectroscopic Instrument (DESI DR1), we measure a baryon density of Ω_bh²= 0.0226 ± 0.0001, a cold dark matter density of Ω_ch²= 0.118 ± 0.001, a Hubble constant ofH₀= 68.22 ± 0.36 km/s/Mpc, a spectral index ofn_s= 0.974 ± 0.003, and an amplitude of density fluctuations ofσ₈= 0.813 ± 0.005. Including the DESI DR2 data tightens the Hubble constant toH₀= 68.43 ± 0.27 km/s/Mpc; ΛCDM parameters agree between the P-ACT and DESI DR2 data at the 1.6σlevel. We find no evidence for excess lensing in the power spectrum, and no departure from spatial flatness. The contribution from Sunyaev-Zel'dovich (SZ) anisotropy is detected at high significance; we find evidence for a tilt with suppressed small-scale power compared to our baseline SZ template spectrum, consistent with hydrodynamical simulations with feedback. 

Abstract We present Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) maps of the Cosmic Microwave Background temperature and polarization anisotropy at arcminute resolution over three frequency bands centered on 98, 150 and 220 GHz. The maps are based on data collected with the AdvancedACT camera over the period 2017–2022 and cover 19,000 square degrees with a median combined depth of 10 μK arcmin. We describe the instrument, mapmaking and map properties and illustrate them with a number of figures and tables. The ACT DR6 maps and derived products are available on LAMBDA athttps://lambda.gsfc.nasa.gov/product/act/actadv_prod_table.html. We also provide an interactive web atlas athttps://phy-act1.princeton.edu/public/snaess/actpol/dr6/atlasand HiPS data sets in Aladin (e.g.https://alasky.cds.unistra.fr/ACT/DR4DR6/color_CMB). 

Abstract We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model, ΛCDM, and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from thePlanckmission. To break geometric degeneracies, we include ACT andPlanckCMB lensing data and baryon acoustic oscillation data from DESI Year-1. To test the dependence of our results on non-ACT data, we also explore combinations replacingPlanckwithWMAPand DESI with BOSS, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral indexdn_s/dlnk= 0.0062 ± 0.0052) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming (N_eff= 2.86 ± 0.13, which combined with astrophysical measurements of primordial helium and deuterium abundances becomesN_eff= 2.89 ± 0.11), for non-zero neutrino masses (∑m_ν< 0.089 eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation (N_idr< 0.134), or for early-universe variation of fundamental constants, including the fine-structure constant (α_EM/α_EM,0= 1.0043 ± 0.0017) and the electron mass (m_e/m_e,0= 1.0063 ± 0.0056). Our data are consistent with standard big bang nucleosynthesis (we findY_p= 0.2312 ± 0.0092), theCOBE/FIRAS-inferred CMB temperature (we findT_CMB= 2.698 ± 0.016 K), a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant (w= -0.986 ± 0.025), and the late-time growth rate predicted by general relativity (γ= 0.663 ± 0.052). We find no statistically significant preference for a departure from the baseline ΛCDM model. In fits to models invoking early dark energy, primordial magnetic fields, or an arbitrary modified recombination history, we findH₀= 69.9^+0.8_-1.5, 69.1 ± 0.5, or 69.6 ± 1.0 km/s/Mpc, respectively; using BOSS instead of DESI BAO data reduces the central values of these constraints by 1–1.5 km/s/Mpc while only slightly increasing the error bars. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored over ΛCDM by our data. 

First light observations of the 280-GHz instrument module of the Fred Young Submillimeter Telescope in the CCAT Collaboration are expected in 2026. The focal plane of this module will consist of three superconducting microwave kinetic inductance detector (MKID) arrays: two aluminum-based arrays and one titanium nitride array with a similar layout. We have designed, microfabricated, assembled, and characterized a large-format aluminum-based MKID array. The responsivity of the detectors matches design expectation and scales at various optical loading levels as expected for aluminum. We have determined the internal quality factors and optical efficiency of the detectors, feedhorn beam shape, and the detector band pass. The detectors are photon noise limited with the majority of the noise being white photon noise down to 1 Hz. The array matches simulated expectations and is ready for sensitive astronomical observations for CCAT. Certain commercial equipment, instruments, or materials are identified in this paper to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by NIST, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.