Andrew. I. Harris

Context . Sagittarius C (Sgr C) is a massive but relatively quiescent complex at the western edge of the Galaxy’s Central Molecular Zone (CMZ). While the Sgr B2 region on the opposite side of the CMZ has been extensively studied, Sgr C has received comparatively little attention. Aims . We aim to characterize the kinematics and physical state of the atomic gas in the Sgr C region using spatially and velocity-resolved emission from the [CII] line. This line traces the multi-phase gas that consists of the warm ionized medium, the warm and cold diffuse atomic medium, and the warm dense molecular gas and provides a complement to molecular line, dust, infrared, and radio observations. Methods . We present a fully sampled 74 × 47 pc map of the [CII] 158 µm fine-structure line toward Sgr C, observed with the upGREAT receiver onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) airborne observatory. The data feature a spatial resolution of 0.55 pc and a spectral resolution of 1 km s ⁻¹ . We analyzed these observations in conjunction with ancillary maps of the J = 2–1 transition of CO and its isotopologues observed with the PI230 receiver at the Atacama Pathfinder Experiment (APEX) telescope. Results . [CII] emission is widespread throughout the region and shows a continuous structure that extends from Sgr A to Sgr C with a complex morphology. The majority of the emission arises from gas at negative radial velocities, consistent with the direction of Galactic rotation. The most prominent feature is the giant Sgr C HII region, where [CII] reveals an expanding, ring-like shell structure interpreted as a photodissociation region (PDR). We modeled the shell’s kinematics and derived an expansion velocity of ∼23 km s ⁻¹ and a dynamical age of ∼0.13 Myr. Our analysis suggests that stellar winds from the known massive stars are likely insufficient to power the observed expansion; this points toward alternative driving mechanisms such as a buried supernova. We find a striking spatial association between this shell and a nonthermal radio filament, which provides evidence that the shell’s expansion into the surrounding medium has triggered high-mass star formation at its edge.

We present the first results of V z -GAL, a high-redshift CO( J = 1–0) large survey with the Karl G. Jansky Very Large Array, targeting 92 Herschel-selected, infrared-luminous, dusty star-forming galaxies at redshifts 1–6. These sources are selected based on having redshifts and mid-/high- J CO transitions from the NOrthern Extended Millimeter Array z –GAL survey. We successfully detect CO( J = 1–0) emission in 90/92 galaxies at the expected positions and redshifts, including nine tentative detections at 2 σ –3 σ significance, and CO( J = 2–1) emission in 10 of these galaxies. The CO( J = 1–0) luminosities suggest apparent gas masses in the range μ M H 2 = (2–20) × 10 ¹¹ ( α _CO /4.0) M _⊙ , which implies gas depletion times of 50–600 Myr. These timescales show similar spread as local ULIRGs, suggesting a self-regulatory mechanism that maintains a consistent star formation rate per unit gas mass in starbursts across redshifts. To quantify the contribution of “excitation correction” factors to gas mass estimates, we calculate median CO line brightness temperature ratios of r ₂₁ = 0.88 ± 0.25, r ₃₁ = 0.61 ± 0.22, r ₄₁ = 0.49 ± 0.15, r ₅₁ = 0.47 ± 0.13, and r ₆₁ = 0.28 ± 0.13. Accounting for these corrections results in a reduced scatter in “gas mass–star formation rate” relations. We also find a median log( L ′ [ CI ] ( 3 P 1 − 3 P 0 ) / L ′ CO ( J = 1 − 0 ) ) = − 0.71 ± 0.12 for a subsample of 23 sources, consistent with the ratios derived for local star-forming galaxies. Together, our findings are in agreement with common conditions in the cold gas reservoirs among star-forming galaxies over a broad range in star formation modes, efficiencies, and scales.

We present SOFIA/upGREAT velocity-resolved spectral imaging and analysis of the λ158 μm [C ii] spectral line toward the central 80 by 43 pc region of the Central Molecular Zone of the Galaxy. The field we imaged with 14″ (0.6 pc) spatial and 1 km s⁻¹ spectral resolution contains the circumnuclear disk (CND) around the central black hole Sgr A*, the neighboring thermal Arched Filaments, the nonthermal filaments of the Radio Arc, and the three luminous central star clusters. [C ii] traces emission from the CND’s inner edge to material orbiting at a distance of approximately 6 pc. Its velocity field reveals no sign of inflowing material nor interaction with winds from the Sgr A East supernova remnant. Wide-field imaging of the Sgr A region shows multiple circular segments, including the thermal Arched Filaments, that are centered on a region that includes the Quintuplet cluster. We examine the possibility that the Arched Filaments and other large-scale arcs trace transient excitation events from supernova blast waves. Along the Arched Filaments, comparisons among far-infrared fine-structure lines show changes in the ionization state over small scales and that high-excitation lines are systematically shifted in position from the other lines. These also point to transient fast winds that produce shocks on the surface of the Arches cloud to produce additional local ultraviolet (UV) radiation to excite the Arched Filaments on a cloud surface illuminated by UV from hot stars.

We present SOFIA/upGREAT velocity-resolved spectral imaging and analysis of the 158 um [C II] spectral line toward the central 80 by 43\,pc region of the Central Molecular Zone of the Galaxy. The field we imaged with 14" (0.6 pc) spatial and 1 km/s spectral resolution contains the Circum-Nuclear Disk (CND) around the central black hole Sgr A*, the neighboring thermal Arched Filaments, the nonthermal filaments of the Radio Arc, and the three luminous central star clusters. [C II] traces emission from the CND's inner edge to material orbiting at a distance of approximately 6 pc. Its velocity field reveals no sign of inflowing material nor interaction with winds from the Sgr A East supernova remnant. Wide-field imaging of the Sgr A region shows multiple circular segments, including the thermal Arched Filaments, that are centered on a region that includes the Quintuplet cluster. We examine the possibility that the Arched Filaments and other large-scale arcs trace transient excitation events from supernova blast waves. Along the Arched Filaments, comparisons among far-IR fine structure lines show changes in ionization state over small scales and that high-excitation lines are systematically shifted in position from the other lines. These also point to transient fast winds that shocked on the surface of the Arches cloud to produce additional local UV radiation to excite the Arched Filaments on a cloud surface illuminated by UV from hot stars.

The CO Mapping Array Project (COMAP) Pathfinder is performing line intensity mapping of CO emission to trace the distribution of unresolved galaxies at redshiftz ∼ 3. We present an improved version of the COMAP data processing pipeline and apply it to the first two Seasons of observations. This analysis improves on the COMAP Early Science (ES) results in several key aspects. On the observational side, all second season scans were made in constant-elevation mode, after noting that the previous Lissajous scans were associated with increased systematic errors; those scans accounted for 50% of the total Season 1 data volume. In addition, all new observations were restricted to an elevation range of 35–65 degrees to minimize sidelobe ground pickup. On the data processing side, more effective data cleaning in both the time and map domain allowed us to eliminate all data-driven power spectrum-based cuts. This increases the overall data retention and reduces the risk of signal subtraction bias. However, due to the increased sensitivity, two new pointing-correlated systematic errors have emerged, and we introduced a new map-domain PCA filter to suppress these errors. Subtracting only five out of 256 PCA modes, we find that the standard deviation of the cleaned maps decreases by 67% on large angular scales, and after applying this filter, the maps appear consistent with instrumental noise. Combining all of these improvements, we find that each hour of raw Season 2 observations yields on average 3.2 times more cleaned data compared to the ES analysis. Combining this with the increase in raw observational hours, the effective amount of data available for high-level analysis is a factor of eight higher than in the ES analysis. The resulting maps have reached an uncertainty of 25–50 μK per voxel, providing by far the strongest constraints on cosmological CO line emission published to date.

The Carbon monOxide Mapping Array Project (COMAP) Pathfinder survey continues to demonstrate the feasibility of line-intensity mapping using high-redshift carbon monoxide (CO) line emission traced at cosmological scales. The latest COMAP Pathfinder power spectrum analysis is based on observations through the end of Season 2, covering the first three years of Pathfinder operations. We use our latest constraints on the CO(1–0) line-intensity power spectrum atz~ 3 to update corresponding constraints on the cosmological clustering of CO line emission and thus the cosmic molecular gas content at a key epoch of galaxy assembly. We first mirror the COMAP Early Science interpretation, considering how Season 2 results translate to limits on the shot noise power of CO fluctuations and the bias of CO emission as a tracer of the underlying dark matter distribution. The COMAP Season 2 results place the most stringent limits on the CO tracer bias to date, at ⟨T b⟩ < 4.8 μK, which translates to a molecular gas density upper limit ofρ_H2< 1.6 × 10⁸M_⊙Mpc⁻³atz~ 3 given additional model assumptions. These limits narrow the model space significantly compared to previous CO line-intensity mapping results while maintaining consistency with small-volume interferometric surveys of resolved line candidates. The results also express a weak preference for CO emission models used to guide fiducial forecasts from COMAP Early Science, including our data-driven priors. We also consider directly constraining a model of the halo–CO connection, and show qualitative hints of capturing the total contribution of faint CO emitters through the improved sensitivity of COMAP data. With continued observations and matching improvements in analysis, the COMAP Pathfinder remains on track for a detection of cosmological clustering of CO emission.

We present updated constraints on the cosmological 3D power spectrum of carbon monoxide CO(1–0) emission in the redshift range 2.4–3.4. The constraints are derived from the two first seasons of Carbon monOxide Mapping Array Project (COMAP) Pathfinder line intensity mapping observations aiming to trace star formation during the epoch of galaxy assembly. These results improve on the previous Early Science results through both increased data volume and an improved data processing methodology. On the methodological side, we now perform cross-correlations between groups of detectors (“feed groups”), as opposed to cross-correlations between single feeds, and this new feed group pseudo power spectrum (FGPXS) is constructed to be more robust against systematic effects. In terms of data volume, the effective mapping speed is significantly increased due to an improved observational strategy as well as a better data selection methodology. The updated spherically and field-averaged FGPXS,C^~(k), is consistent with zero, at a probability-to-exceed of around 34%, with an excess of 2.7σin the most sensitive bin. Our power spectrum estimate is about an order of magnitude more sensitive in our six deepest bins across 0.09 Mpc⁻¹<k< 0.73 Mpc⁻¹, compared to the feed-feed pseudo power spectrum (FPXS) of COMAP ES. Each of these bins individually constrains the CO power spectrum tok P_CO(k) < 2400–4900 μK²Mpc²at 95% confidence. To monitor potential contamination from residual systematic effects, we analyzed a set of 312 difference-map null tests and found that these are consistent with the instrumental noise prediction. In sum, these results provide the strongest direct constraints on the cosmological 3D CO(1–0) power spectrum published to date.

We present a new upper limit on the cosmic molecular gas density at z = 2.4–3.4 obtained using the first year of observations from the CO Mapping Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 243 quasars selected from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) catalog, yielding a 95% upper limit for flux from CO(1–0) line emission of 0.129 Jy km s⁻¹. Depending on the balance of the emission between the quasar host and its environment, this value can be interpreted as an average CO line luminosity L CO ′ of eBOSS quasars of ≤1.26 × 10¹¹ K km pc² s⁻¹, or an average molecular gas density ρ H 2 in regions of the Universe containing a quasar of ≤1.52 × 10⁸ M _⊙ cMpc⁻³. The L CO ′ upper limit falls among CO line luminosities obtained from individually targeted quasars in the COMAP redshift range, and the ρ H 2 value is comparable to upper limits obtained from other line intensity mapping (LIM) surveys and their joint analyses. Further, we forecast the values obtainable with the COMAP/eBOSS stack after the full 5 yr COMAP Pathfinder survey. We predict that a detection is probable with this method, depending on the CO properties of the quasar sample. Based on the achieved sensitivity, we believe that this technique of stacking LIM data on the positions of traditional galaxy or quasar catalogs is extremely promising, both as a technique for investigating large galaxy catalogs efficiently at high redshift and as a technique for bolstering the sensitivity of LIM experiments, even with a fraction of their total expected survey data.

We report observations of the ground state transitions of ¹²CO, ¹³CO, C¹⁸O, HCN, and HCO⁺ at 88–115 GHz in the inner region of the nearby galaxy IC 342. These data were obtained with the 16 pixel spectroscopic focal plane array Argus on the 100 m Robert C. Byrd Green Bank Telescope (GBT) at 6″–9″ resolution. In the nuclear bar region, the intensity distributions of ¹²CO(1–0) and ¹³CO(1–0) emission trace moderate densities, and differ from the dense gas distributions sampled in C¹⁸O(1–0), HCN(1–0), and HCO⁺(1–0). We observe a constant HCN(1–0)-to-HCO⁺(1–0) ratio of 1.2 ± 0.1 across the whole ∼1 kpc bar. This indicates that the HCN(1–0) and HCO⁺(1–0) lines have intermediate optical depth, and that the corresponding n H 2 of the gas producing the emission is of order 10^4.5−6 cm⁻³. We show that HCO⁺(1–0) is thermalized and HCN(1–0) is close to thermalization. The very tight correlation between the HCN(1–0) and HCO⁺(1–0) intensities across the 1 kpc bar suggests that this ratio is more sensitive to the relative abundance of the two species than to the gas density. We confirm an angular offset (∼10″) between the spatial distribution of molecular gas and the star formation sites. Finally, we find a breakdown of the L _IR– L HCN correlation at high spatial resolution due to the effect of incomplete sampling of star-forming regions by HCN emission in IC 342. The scatter of the L _IR– L HCN relation decreases as the spatial scale increases from 10″ to 30″ (170–510 pc), and is comparable to the scatter of the global relation at a scale of 340 pc.