Prime-Cam is a first-generation science instrument for the CCAT Observatory's six-meter aperture Fred Young Submillimeter Telescope (FYST), under construction at an elevation of 5600 m on Cerro Chajnantor in Chile's Atacama Desert. Prime-Cam will deliver over ten times greater mapping speed at submillimeter wavelengths than current facilities for unprecedented broadband and spectroscopic measurements in windows between 1.4 – 0.3 mm (220 – 850 GHz). When fully populated, Prime-Cam will field over 100,000 kinetic inductance detectors across seven independently optimized instrument modules. With Prime-Cam, the CCAT Collaboration will address a suite of science goals, from Big Bang cosmology, to galaxy evolution and star formation over cosmic time. Prime-Cam is scheduled for integration in FYST in late 2026, followed by a year of early science observations with the 280 and 350 GHz instrument modules. We discuss the design and in-lab testing of the 1.8-m diameter Prime-Cam receiver and 280 GHz instrument module, and give an update on deployment status and early science plans.

We present a new method for modelling the kinematics of galaxies from interferometric observations by performing the optimization of the kinematic model parameters directly in visibility-space instead of the conventional approach of fitting velocity fields produced with the CLEAN algorithm in real-space. We demonstrate our method on ALMA observations of $^{12}$CO (2$-$1), (3$-$2) or (4$-$3) emission lines from an initial sample of 30 massive 850$\mu$m-selected dusty star-forming galaxies with far-infrared luminosities $\gtrsim$$\,10^{12}\,$L$_{\odot}$ in the redshift range $z \sim\,$1.2$-$4.7. Using the results from our modelling analysis for the 12 sources with the highest signal-to-noise emission lines and disk-like kinematics, we conclude the following: (i) Our sample prefers a CO-to-$H_2$ conversion factor, of $\alpha_{\rm CO} = 0.92 \pm 0.36$; (ii) These far-infrared luminous galaxies follow a similar Tully$-$Fisher relation between the circularized velocity, $V_{\rm circ}$, and baryonic mass, $M_{\rm b}$, as more typical star-forming samples at high redshift, but extend this relation to much higher masses $-$ showing that these are some of the most massive disk-like galaxies in the Universe; (iii) Finally, we demonstrate support for an evolutionary link between massive high-redshift dusty star-forming galaxies and the formation of local early-type galaxies using the both the distributions of the baryonic and kinematic masses of these two populations on the $M_{\rm b}\,-\,\sigma$ plane and their relative space densities.

Aims. We study the dust content of massive (log(M-*/M-circle dot)>= 10.8) quiescent galaxies (QGs) at redshifts z = 0.5 - 3 to place constraints on the evolution of their cold interstellar medium (ISM) and thereby obtain insights into the processes of galaxy quenching throughout cosmic time. Methods. We used a robust sample of 458 colour-selected QGs covered by the A(3)COSMOS+A(3)GOODSS database to perform a stacking analysis in the uv domain and measured their mean dust masses from their stacked sub-millimetre luminosities. We used the CIGALE spectral energy distribution fitting code to obtain star formation histories and infer the time since quenching for all the QGs in our sample. We used this information to gain insight into the time evolution of the dust content after quenching. Results. Most QGs in our sample quenched around a redshift of z similar to 1.3, following the peak of cosmic star formation. The majority of QGs observed at z > 1 are recently quenched (i.e. quenched for no longer than 500 Myr), whereas the majority of QGs observed at z < 1 have already been quenched for a significant amount of time (greater than or similar to 1 Gyr). This implies that high-redshift galaxies (z greater than or similar to 2) are ideal for studying the mechanisms of quenching and its effects on the ISM, while lower-redshift galaxies are more suitable for studying the long-term effects of the QG environment on their ISM. We obtain upper limits on the dust mass fraction of the QG population that indicate a lower dust content in high-redshift massive QGs than what was found by earlier stacking studies, and significantly lower (by a factor of similar to 2-6) than that of normal star-forming galaxies. We also place constraints on the initial gas fraction right after quenching. We find that within the first similar to 600 Myr after quenching, QGs already lose on average greater than or similar to 70% of their cold ISM. Our findings support a gas consumption or removal scenario acting on short timescales.

We present [NII] 205 μm fine structure line observations of three submillimeter galaxies (SMGs) and three quasar host galaxies at 4≲z≲6 using the Institut de radioastronomie millimetrique (IRAM) interferometer. The [NII] emission is detected in three sources, and we report detections of the underlying dust continuum emission in all sources. The observed [NII]-to-infrared luminosity ratio spans at least 0.5 dex for our sources. Comparing our estimates with sources detected in the [NII] 205 μm at similar redshifts shows that the overall [NII]-to-IR luminosity ratio spans over a dex in magnitude from L_[NII]/L_IR 10^-4 - 10^-5 and follows the trend of the so-called [NII] fine structure line deficit observed in (ultra)-luminous infrared galaxies in the local Universe. The [CII]-to-[NII] luminosity ratio is >10 for most of our sources, indicating that the bulk of the [CII] 158 μm line emission (f([CII]^PDR)>75 neutral medium. From our analysis, we do not find significant differences in the [NII] 205 μm emission and the respective ratios between SMGs and QSOs, suggesting a negligible contribution to the boosting of [NII] 205 μm emission due to the active galactic nucleus (AGN) photoionization. Future investigations involving other fine structure lines and optical diagnostics will provide further insight into a suite of ionized medium properties and reveal the diversity between AGN and non-AGN environments.

We present wide-field mapping at 850 μ m and 450 μ m of the z = 2.85 protocluster in the HS 1549+19 field using the Submillimetre Common-User Bolometer Array 2. Spectroscopic follow-up of 18 bright sources selected at 850 μ m, using the Northern Extended Millimeter Array and Atacama Large Millimeter/submillimeter Array, confirms that the majority lie near z ≃ 2.85 and are likely members of the structure. Interpreting the spectroscopic redshifts as distance measurements, we find that the submillimeter galaxies (SMGs) span 123 pMpc ^2 in the plane of the sky and demarcate a 3600 pMpc ^3 “pancake”-shaped structure in three dimensions. We find that the high star formation rates of these SMGs result in a total star formation rate of 20,000 M _⊙ yr ^−1 from just the brightest galaxies in the protocluster. These rapidly star-forming SMGs can be interpreted as massive galaxies growing rapidly at large clustercentric distances before collapsing into a virialized structure. We find that the SMGs trace the Ly α surface density profile. Comparison with simulations suggests that HS 1549+19 could be building a structure comparable to the most massive clusters in the present-day Universe.

We present NII 205 μm fine structure line observations of three submillimeter galaxies (SMGs) and three quasar host galaxies (QSOs) at 4lesssimzlesssim6 using the Institut de radioastronomie millim'etrique (IRAM) interferometer. The NII emission is detected in three sources, and we report detections of the underlying dust continuum emission in all sources. The observed NII -to-infrared luminosity ratio spans at least 0.5 dex for our sources. Comparing our estimates with sources detected in the NII 205 μm at similar redshifts shows that the overall NII -to-IR luminosity ratio spans over 1 dex in magnitude from L_ NII /L_IR ∼ 10^-4 -- 10^-5 and follows the trend of the so-called NII fine structure line deficit observed in (ultra)-luminous IR galaxies in the local Universe. The CII -to- NII luminosity ratio is greater than ten for most of our sources, indicating that the bulk of the CII 158 μm line emission ( f CII ^PDR) >75%) arises from the neutral medium. From our analysis, we do not find significant differences in the NII 205 μm emission and the respective ratios between SMGs and QSOs, suggesting a negligible contribution to the boosting of NII 205 μm emission due to the active galactic nucleus (AGN) photoionization. Future investigations involving other fine structure lines and optical diagnostics will provide further insight into a suite of ionized medium properties and reveal the diversity between AGN and non-AGN environments. We present NII 205 μm fine structure line observations of three submillimeter galaxies (SMGs) and three quasar host galaxies (QSO) at 4lesssimzlesssim6 using the Institut de radioastronomie millim'etrique (IRAM) interferometer. The NII emission is detected in three sources, and we report detections of the underlying dust continuum emission in all sources. The observed NII -to-infrared (IR) luminosity ratio spans at least 0.5 dex for our sources. Comparing our estimates with sources detected in the NII 205 μm at similar redshifts shows that the overall NII -to-IR luminosity ratio spans over a dex in magnitude from L_ NII /L_IR ∼ 10^-4 -- 10^-5 and follows the trend of the so-called NII fine structure line deficit observed in (ultra)-luminous infrared galaxies in the local Universe. The CII -to- NII luminosity ratio is >10 for most of our sources, indicating that the bulk of the CII 158 μm line emission ( f CII ^PDR) >75%) arises from the neutral medium. From our analysis, we do not find significant differences in the NII 205 μm emission and the respective ratios between SMGs and QSOs, suggesting a negligible contribution to the boosting of NII 205 μm emission due to the active galactic nucleus (AGN) photoionization. Future investigations involving other fine structure lines and optical diagnostics will provide further insight into a suite of ionized medium properties and reveal the diversity between AGN and non-AGN environments.

Galaxy submillimetre number counts are a fundamental measurement in our understanding of galaxy evolution models. Most early measurements are obtained via single-dish telescopes with substantial source confusion, whereas recent interferometric observations are limited to small areas. We used a large database of ALMA continuum observations to accurately measure galaxy number counts in multiple (sub)millimetre bands, thus bridging the flux density range between single-dish surveys and deep interferometric studies. We continued the Automated Mining of the ALMA Archive in the COSMOS Field project (A$^3$COSMOS) and extended it with observations from the GOODS-South field (A$^3$GOODSS). The database consists of ~4,000 pipeline-processed continuum images from the public ALMA archive, yielding 2,050 unique detected sources. To infer galaxy number counts, we constructed a method to reduce the observational bias inherent to targeted pointings that dominate the database. This method comprises a combination of image selection, masking, and source weighting. The effective area was calculated by accounting for inhomogeneous wavelengths, sensitivities, and resolutions and for spatial overlap between images. We tested and calibrated our method with simulations. We derived the number counts in a consistent and homogeneous way in four different ALMA bands covering a relatively large area. The results are consistent with number counts from the literature within the uncertainties. In Band 7, at the depth of the inferred number counts, ~40% of the cosmic infrared background is resolved into discrete sources. This fraction, however, decreases with wavelength, reaching ~4% in Band 3. Finally, we used the number counts to test models of dusty galaxy evolution, and find a good agreement within the uncertainties.

We present NOrthern Extended Millimeter Array observations of CO(8-7), (9-8), and (10-9) lines, as well as the underlying continuum for two far-infrared luminous quasars: SDSS J2054-0005 at z = 6.0389 and SDSS J0129-0035 at z = 5.7788. Both quasars were previously detected in CO (2-1) and (6-5) transitions, making them candidates for studying the CO spectral line energy distribution (SLED) of quasars at z similar to 6. Utilizing the radiative transfer code CLOUDY, we fit the CO SLED with two heating mechanisms, including the photodissociation region (PDR) and X-ray-dominated region (XDR) for both objects. The CO SLEDs can be fitted by either a dense PDR component with an extremely strong far-ultraviolet radiation field (gas density n H similar to 106 cm-3 and field strength G 0 greater than or similar to 106) or a two-component model including a PDR and an XDR. However, the line ratios, including L TIR and previous [C ii]158 mu m and [C i]369 mu m measurements, argue against a very high PDR radiation field strength. Thus, the results prefer a PDR+XDR origin for the CO SLED. The excitation of the high-J CO lines in both objects is likely dominated by the central active galactic nucleus (AGN). We then check the CO (9-8)-to-(6-5) line luminosity ratio r 96 for all z similar to 6 quasars with available CO SLEDs (seven in total) and find that there are no clear correlations between r 96 and both L FIR and the AGN UV luminosities. This further demonstrates the complexity of the CO excitation powered by both the AGN and nuclear star formation in these young quasar host galaxies.

Galaxy submillimetre number counts are a fundamental measurement in our understanding of galaxy evolution models. Most early measurements are obtained via single-dish telescopes with substantial source confusion, whereas recent interferometric observations are limited to small areas. We used a large database of ALMA continuum observations to accurately measure galaxy number counts in multiple (sub)millimetre bands, thus bridging the flux density range between single-dish surveys and deep interferometric studies. We continued the Automated Mining of the ALMA Archive in the COSMOS Field project (A^3COSMOS) and extended it with observations from the GOODS-South field (A^3GOODSS). The database consists of  4,000 pipeline-processed continuum images from the public ALMA archive, yielding 2,050 unique detected sources. To infer galaxy number counts, we constructed a method to reduce the observational bias inherent to targeted pointings that dominate the database. This method comprises a combination of image selection, masking, and source weighting. The effective area was calculated by accounting for inhomogeneous wavelengths, sensitivities, and resolutions and for spatial overlap between images. We tested and calibrated our method with simulations. We derived the number counts in a consistent and homogeneous way in four different ALMA bands covering a relatively large area. The results are consistent with number counts from the literature within the uncertainties. In Band 7, at the depth of the inferred number counts,  40 sources. This fraction, however, decreases with wavelength, reaching  4 Band 3. Finally, we used the number counts to test models of dusty galaxy evolution, and find a good agreement within the uncertainties.

Aims. We aim to understand the physical mechanisms that drive star formation in a sample of mass-complete (>109.5 M⊙) star-forming galaxies (SFGs) at 1.2 ≤ ɀ < 1.6. Methods. We selected SFGs from the COSMOS2020 catalog and applied a uυ-domain stacking analysis to their archival Atacama Large Millimeter/submillimeter Array (ALMA) data. Our stacking analysis provides precise measurements of the mean molecular gas mass and size of SFGs down to a stellar mass of M★ ~ 109.5 M⊙, even though at these stellar mass galaxies on the main sequence (MS) are no longer detected individually in the archival ALMA data. We also applied an image-domain stacking analysis on their HST i-band and UltraVISTA J - and Ks-band images. This allowed us to trace the distribution of their stellar component. Correcting these rest-frame optical sizes using the Rhalf–stellar–light-to-Rhalf–stellar–mass conversion at rest 5000 Å, we obtain the stellar mass size of MS galaxies and compare them to the sizes of their star-forming component obtained from our ALMA stacking analysis. Results. Across the MS (−0.2 < ∆MS = log(SFR/SFRMS) < 0.2), the mean molecular gas fraction of SFGs increases by a factor of ~1.4, while their mean molecular gas depletion time decreases by a factor of ~1.8. The scatter of the MS could thus be caused by variations in both the star formation efficiency and molecular gas fraction of galaxies. The mean molecular gas fraction of MS galaxies decreases by a factor of ~7 from M★~ 109.7 M⊙ to ~1011.3 M⊙, while their mean molecular gas depletion time remains roughly the same at all stellar masses. This finding could be a hint that the bending of the MS at ɀ ~1.4 is primarily driven by variations in cold gas accretion. The majority of the galaxies lying on the MS have RFIR ≈ Rstellar. Their central regions are subject to large dust attenuation. Starbursts (SBs, ∆MS > 0.7) have a mean molecular gas fraction ~2.1 times larger and mean molecular gas depletion time ~3.3 times shorter than MS galaxies. Additionally, they have more compact star-forming regions (~2.5 kpc for MS galaxies vs. ~1.4 kpc for SBs) and systematically disturbed rest-frame optical morphologies, which is consistent with their association with major-mergers. SBs and MS galaxies follow the same relation between their molecular gas mass and star formation rate surface densities with a slope of ~ 1.1–1.2, that is, the so-called Kennicutt-Schmidt relation.

Context. The Fred Young Submillimeter Telescope (FYST) line intensity mapping (LIM) survey will measure the power spectrum (PS) of the singly ionized carbon 158 mu m fine-structure line, [CII], to trace the appearance of the first galaxies that emerged during and right after the epoch of reionization (EoR, 6 < z < 9). Aims. We aim to quantify the contamination of the (post-)EoR [CII] LIM signal by foreground carbon monoxide (CO) line emission (3 < J(up) < 12) and assess the efficiency to retrieve this [CII] LIM signal by the targeted masking of bright CO emitters. Methods. Using the IllustrisTNG300 simulation, we produced mock CO intensity tomographies based on empirical star formation rate-to-CO luminosity relations. Combining these predictions with the [CII] PS predictions of the first paper of this series, we evaluated a masking technique where the interlopers are identified and masked using an external catalog whose properties are equivalent to those of a deep Euclid survey. Results. Prior to masking, our [CII] PS forecast is an order of magnitude lower than the predicted CO contamination in the 225 GHz ([CII] emitted at z = 6.8 - 8.3) band of the FYST LIM survey, at the same level in its 280 GHz ([CII] emitted at z = 5.3 - 6.3) and 350 GHz ([CII] emitted at z = 4.1 - 4.8) bands, and an order of magnitude higher in its 410 GHz ([CII] emitted at z = 3.4 - 3.9) band. For our fiducial model, the optimal masking depth is reached when less than 10% of the survey volume is masked at 350 and 410 GHz but around 40% at 280 GHz and 60% at 225 GHz. At these masking depths we anticipate a detection of the [CII] PS at 350 and 410 GHz, a tentative detection at 280 GHz, whereas at 225 GHz the CO signal still dominates our model. In the last case, alternative decontamination techniques will be needed.

Aims. We have implemented a novel method to create simulated [CII] emission line intensity mapping (LIM) data cubes using COSMOS 2020 galaxy catalogue data. It allows us to provide solid lower limits for previous simulation-based model predictions and the expected signal strength of upcoming surveys. Methods. We applied [CII]158 mu m luminosity models to COSMOS 2020 to create LIM cubes covering a 1.2 x 1.2deg2 sky area. These models were derived using galaxy bulk property data from the ALPINE-ALMA survey over the redshift range of 4.4 < z < 5.9, while additional models were taken from the literature. The LIM cubes cover 3.42 < z < 3.87, 4.14 < z < 4.76, 5.34 < z < 6.31, and 6.75 < z < 8.27, matched to planned observations from the EoR-Spec module of the Prime-Cam instrument in the Fred Young Submillimeter Telescope (FYST). We also created predictions including additional galaxies below current detection limits by 'extrapolating' from the faint end of the COSMOS 2020 luminosity function, comparing these to predictions from the literature. In addition, we computed the signal-to-noise (S/N) ratios for the power spectra, using parameters from the planned FYST survey with predicted instrumental noise levels. Results. We find lower limits for the expected power spectrum using the likely incomplete empirical data: when normalised by 2 pi 2, the amplitudes at k = 1 Mpc-1 are 3.06 x 107, 1.43 x 107, 9.80 x 105, 2.77 x 105 (Jy sr-1)2 for the aforementioned redshift ranges. For the extrapolated sample, the power spectra are consistent with prior predictions, indicating that extrapolation is a viable method for creating mock LIM cubes. In this case, we expect a result of S/N> 1 when using FYST parameters. However, our high-redshift results remain inconclusive because of the poor completeness of COSMOS 2020 at z > 6.3. These predictions will be improved on the basis of future JWST data.

Context. Galaxy submillimetre number counts are a fundamental measurement in our understanding of galaxy evolution models. Most early measurements are obtained via single-dish telescopes with substantial source confusion, whereas recent interferometric observations are limited to small areas. Aims. We used a large database of ALMA continuum observations to accurately measure galaxy number counts in multiple (sub)millimetre bands, thus bridging the flux density range between single-dish surveys and deep interferometric studies. Methods. We continued the Automated Mining of the ALMA Archive in the COSMOS Field project (A(3)COSMOS) and extended it with observations from the GOODS-South field (A(3)GOODSS). The database consists of similar to 4000 pipeline-processed continuum images from the public ALMA archive, yielding 2050 unique detected sources, including sources with and without a known optical counterpart. To infer galaxy number counts, we constructed a method to reduce the observational bias inherent to targeted pointings that dominate the database. This method comprises a combination of image selection, masking, and source weighting. The e ffective area was calculated by accounting for inhomogeneous wavelengths, sensitivities, and resolutions and for the spatial overlap between images. We tested and calibrated our method with simulations. Results. We derived the number counts in a consistent and homogeneous way in four di fferent ALMA bands covering a relatively large area. The results are consistent with number counts retrieved from the literature within the uncertainties. In Band 7, at the depth of the inferred number counts, similar to 40% of the cosmic infrared background is resolved into discrete sources. This fraction, however, decreases with increasing wavelength, reaching similar to 4% in Band 3. Finally, we used the number counts to test models of dusty galaxy evolution, and find a good agreement within the uncertainties. Conclusions. By continuing the A3COSMOS and A3GOODSS archival e ffort, we obtained the deepest archive-based (sub)millimetre number counts measured to date over such a wide area. This database proves to be a valuable resource that, thanks to its substantial size, can be used for statistical analyses after having applied certain conservative restrictions.

The formation of the first supermassive black holes is expected to have occurred in some most pronounced matter and galaxy overdensities in the early universe. We have conducted a sub-mm wavelength continuum survey of 54 $z\sim6$ quasars using the Submillimeter Common-User Bolometre Array-2 (SCUBA2) on the James Clerk Maxwell Telescope (JCMT) to study the environments around $z \sim 6$ quasars. We identified 170 submillimeter galaxies (SMGs) with above 3.5$\sigma$ detections at 450 or 850 \um\, maps. Their FIR luminosities are 2.2 - 6.4 $\times$ 10$^{12} L_{\odot}$, and star formation rates are $\sim$ 400 - 1200 M$_{\odot}$ yr$^{-1}$. We also calculated the SMGs differential and cumulative number counts in a combined area of $\sim$ 620 arcmin$^2$. To a $4\sigma$ detection (at $\sim$ 5.5 mJy), SMGs overdensity is $0.68^{+0.21}_{-0.19}$($\pm0.19$), exceeding the blank field source counts by a factor of 1.68. We find that 13/54 quasars show overdensities (at $\sim$ 5.5 mJy) of $\delta_{SMG}\sim$ 1.5 - 5.4. The combined area of these 13 quasars exceeds the blank field counts with the overdensity to 5.5 mJy of \dsmg $\sim$ $2.46^{+0.64}_{-0.55}$($\pm0.25$) in the regions of $\sim$ 150 arcmin$^2$. However, the excess is insignificant on the bright end (e.g., 7.5 mJy). We also compare results with previous environmental studies of Lyman alpha emitters (LAEs) and Lyman-Break Galaxies (LBGs) on a similar scale. Our survey presents the first systematic study of the environment of quasars at $z\sim6$. The newly discovered SMGs provide essential candidates for follow-up spectroscopic observations to test whether they reside in the same large-scale structures as the quasars and search for protoclusters at an early epoch.

We present the resolved properties of the z = 2.82 hyperluminous infrared Galaxy (HyLIRG) HS1700.850.1, the brightest 850 mu m source found in the SCUBA-2 followup to the Keck Baryonic Structure Survey fields (S-850 mu m = 19.5 mJy), and amongst the most luminous starbursts known at any redshift.- Using the IRAM-NOEMA interferometer in the highest resolution A-configuration, we resolve the source into two components separated by similar to 8 kpc, visible as blue shifted and red shifted (CO)-C-12(5-4) lines, exhibiting the expected kinematic properties of a major merger between two gas rich Galaxies. The combined merger system is traced over 2.3 arcsec or 18.4 kpc. Each component of the merger shows ordered gas motions suggestive of a massive turbulent disc. We measure the dynamical masses of the blue and red discs as (1.5 +/- 0.2) x 10(11) and (0.71 +/- 0.22) x 10(11) M-circle dot, respectively. The more massi ve disc component shows broad wings in the CO line, offset by similar to 3 kpc from the disc centroid along the major axis, and extending to velocities similar to +/- 1000 km s (-1) from systemic velocity. We interpret this as either a possible bipolar outflowing component, or more likely a warping or tidal structure in the CO disc. Comparing the properties of HS1700.850.1 to other submillimeter detected galaxies with comparably bright 850 mu m luminosities suggests that ongoing gas-rich mergers, or at least a clustered/group environment lead to these most extreme starburst phases.

The formation of the first supermassive black holes is expected to have occurred in some most pronounced matter and galaxy overdensities in the early universe. We have conducted a submillimeter wavelength continuum survey of 54 z ∼ 6 quasars using the Submillimeter Common-User Bolometre Array-2 on the James Clerk Maxwell Telescope to study the environments around z ∼ 6 quasars. We identified 170 submillimeter galaxies (SMGs) with above 3.5 σ detections in 450 or 850 μ m maps. Their far-IR luminosities are (2.2–6.4) × 10 12 L ⊙ , and their star formation rates are ∼400–1200 M ⊙ yr −1 . We also calculated the SMGs’ differential and cumulative number counts in a combined area of ∼620 arcmin 2 . To a 4 σ detection (at ∼5.5 mJy), SMGs’ overdensity is 0.68 − 0.19 + 0.21 (±0.19), exceeding the blank-field source counts by a factor of 1.68. We find that 13/54 quasars show overdensities (at ∼5.5 mJy) of δ SMG ∼ 1.5–5.4. The combined area of these 13 quasars exceeds the blank-field counts with the overdensity to 5.5 mJy of δ SMG ∼ 2.46 − 0.55 + 0.64 (±0.25) in the regions of ∼150 arcmin 2 . However, the excess is insignificant on the bright end (e.g., 7.5 mJy). We also compare results with previous environmental studies of Ly α emitters and Lyman break galaxies on a similar scale. Our survey presents the first systematic study of the environment of quasars at z ∼ 6. The newly discovered SMGs provide essential candidates for follow-up spectroscopic observations to test whether they reside in the same large-scale structures as the quasars and search for protoclusters at an early epoch.

Characterizing the physical conditions (density, temperature, ionization state, metallicity, etc) of the interstellar medium is critical to our understanding of the formation and evolution of galaxies. Here we present a multi-line study of the interstellar medium in the host galaxy of a quasar at z 6.4, i.e., when the universe was 840 Myr old. This galaxy is one of the most active and massive objects emerging from the dark ages, and therefore represents a benchmark for models of the early formation of massive galaxies. We used the Atacama Large Millimeter Array to target an ensemble of tracers of ionized, neutral, and molecular gas, namely the fine-structure lines: [OIII] 88μm, [NII] 122μm, [CII] 158μm, and [CI] 370μm and the rotational transitions of CO(7-6), CO(15-14), CO(16-15), and CO(19-18); OH 163.1μm and 163.4μm; and H_2O 3(0,3)-2(1,2), 3(3,1)-4(0,4), 3(3,1)-3(2,2), 4(0,4)-3(1,3), 4(3,2)-4(2,3). All the targeted fine-structure lines are detected, as are half of the targeted molecular transitions. By combining the associated line luminosities, the constraints on the dust temperature from the underlying continuum emission, and predictions from photoionization models of the interstellar medium, we find that the ionized phase accounts for about one third of the total gaseous mass budget, and is responsible for half of the total [CII] emission. It is characterized by high density (n 180 cm^-3), typical of HII regions. The spectral energy distribution of the photoionizing radiation is comparable to that emitted by B-type stars. Star formation also appears to drive the excitation of the molecular medium. We find marginal evidence for outflow-related shocks in the dense molecular phase, but not in other gas phases. This study showcases the power of multi-line investigations in unveiling the properties of the star-forming medium in galaxies at cosmic dawn.

We present a detailed overview of the science goals and predictions for the Prime-Cam direct detection camera/spectrometer being constructed by the CCAT-prime collaboration for dedicated use on the Fred Young Submillimeter Telescope (FYST). The FYST is a wide-field, 6-m aperture submillimeter telescope being built (first light in mid-2024) by an international consortium of institutions led by Cornell University and sited at more than 5600 meters on Cerro Chajnantor in northern Chile. Prime-Cam is one of two instruments planned for FYST and will provide unprecedented spectroscopic and broadband measurement capabilities to address important astrophysical questions ranging from Big Bang cosmology through reionization and the formation of the first galaxies to star formation within our own Milky Way galaxy. Prime-Cam on the FYST will have a mapping speed that is over ten times greater than existing and near-term facilities for high-redshift science and broadband polarimetric imaging at frequencies above 300 GHz. We describe details of the science program enabled by this system and our preliminary survey strategies.

We investigate the molecular gas content ofz ∼ 6 quasar host galaxies using the Institut de Radioastronomie Millimétrique Northern Extended Millimeter Array. We targeted the 3 mm dust continuum, and the line emission from CO(6–5), CO(7–6), and [C I]2−1in ten infrared–luminous quasars that have been previously studied in their 1 mm dust continuum and [C II] line emission. We detected CO(7–6) at various degrees of significance in all the targeted sources, thus doubling the number of such detections inz ∼ 6 quasars. The 3 mm to 1 mm flux density ratios are consistent with a modified black body spectrum with a dust temperatureTdust ∼ 47 K and an optical depthτν = 0.2 at the [C II] frequency. Our study provides us with four independent ways to estimate the molecular gas mass,MH2, in the targeted quasars. This allows us to set constraints on various parameters used in the derivation of molecular gas mass estimates, such as the mass per luminosity ratiosαCOandα[CII], the gas-to-dust mass ratioδg/d, and the carbon abundance [C]/H2. Leveraging either on the dust, CO, [C I], or [C II] emission yields mass estimates of the entire sample in the rangeMH2 ∼ 1010–1011M⊙. We compared the observed luminosities of dust, [C II], [C I], and CO(7–6) with predictions from photo-dissociation and X-ray dominated regions. We find that the former provide better model fits to our data, assuming that the bulk of the emission arises from dense (nH > 104cm−3) clouds with a column densityNH ∼ 1023cm−2, exposed to a radiation field with an intensity ofG0 ∼ 103(in Habing units). Our analysis reiterates the presence of massive reservoirs of molecular gas fueling star formation and nuclear accretion inz ∼ 6 quasar host galaxies. It also highlights the power of combined 3 mm and 1 mm observations for quantitative studies of the dense gas content in massive galaxies at cosmic dawn.

We predict the three-dimensional intensity power spectrum (PS) of the [CII] 158$\,\mu$m line throughout the epoch of (and post) reionization at redshifts from $\approx$ 3.5 to 8. We study the detectability of the PS in a line intensity mapping (LIM) survey with the Fred Young Submillimeter Telescope (FYST). We created mock [CII] tomographic scans in redshift bins at $z\approx$ 3.7, 4.3, 5.8, and 7.4 using the Illustris TNG300-1 $\Lambda$CDM simulation and adopting a relation between the star formation activity and the [CII] luminosity ($L_{[CII]}$) of galaxies. A star formation rate (SFR) was assigned to a dark matter halo in the Illustris simulation in two ways: (i) we adopted the SFR computed in the Illustris simulation and, (ii) we matched the abundance of the halos with the SFR traced by the observed dust-corrected ultraviolet luminosity function of high-redshift galaxies. The $L_{[CII]}$ is related to the SFR from a semi-analytic model of galaxy formation, from a hydrodynamical simulation of a high-redshift galaxy, or from a high-redshift [CII] galaxy survey. The [CII] intensity PS was computed from mock tomographic scans to assess its detectability with the anticipated observational capability of the FYST. The amplitude of the predicted [CII] intensity power spectrum varies by more than a factor of 10, depending on the choice of the halo-to-galaxy SFR and the SFR-to-$L_{[CII]}$ relations. In the planned $4^{\circ} \times 4^{\circ}$ FYST LIM survey, we expect a detection of the [CII] PS up to $z \approx$ 5.8, and potentially even up to $z \approx $ 7.4. The design of the envisioned FYST LIM survey enables a PS measurement not only in small (<10 Mpc) shot noise-dominated scales, but also in large (>50 Mpc) clustering-dominated scales making it the first LIM experiment that will place constraints on the SFR-to-$L_{[CII]}$ and the halo-to-galaxy SFR relations simultaneously.