We present GBT-EDGE, a new CO(1-0) survey using the Green Bank Telescope to map 62 nearby (10-140 Mpc) galaxies spanning the star-forming main sequence (SFMS), green valley, and red sequence. The galaxy sample is selected from the CALIFA survey with integral field spectroscopy (IFS), which provides a representative census of local galactic environments. Combining the CO dataset with CALIFA's optical IFS measurements, we derive molecular gas masses, star formation rates (SFR), metallicities, and stellar mass densities to measure star formation efficiency (SFE) and investigate the physical drivers of galaxy quenching. We obtain a median molecular gas depletion time of 2.10^+2.35_-1.31, 6.90^+17.00_-3.67, and 127.7^+201.6_-113.4 Gyr for our sample of main sequence, green valley, and red galaxies, respectively, assuming a Galactic CO-to-H2 conversion factor. By applying various conversion factor prescriptions, we also confirm a systematic decrease of SFE with galaxy's offset below the SFMS, regardless of the adopted prescription. This suggests that the low SFR in some quenched galaxies is primarily driven by suppressed SFE rather than an absence of molecular gas. Our results provide evidence that galaxies below the main sequence can retain substantial molecular gas reservoirs comparable to star-forming galaxies, but they exhibit longer depletion times and form stars inefficiently, possibly due to the combined effects of low gas density and morphological quenching mechanisms.

We observed the gravitationally lensed (mu = 9.6 +/- 0.19) galaxy A1689-zD1 at z = 7.1 in bands 3, 6, and 8 of the Atacama Large Millimeter/submillimeter Array. These high-resolution observations (approximate to 200 pc) enabled us to separate the source into five components in the [C II] 158 mu m and [O III] 88 mu m emission lines within a projected distance of 2 kpc. Even though these components appear to vary strongly from one another in both their line, continuum, and optical characteristics, the assembly of components do not show ordered rotation and appear consistent with simulations of a galaxy system undergoing the process of assembly. The total dynamical mass of the galaxy (2 x 10(10) M-circle dot) is an order of magnitude larger than the spectrally estimated stellar mass, suggesting a near-complete optical obscuration of the bulk of the stellar component. Comparing the line ratios as well as the line properties to other properties such as the star formation rate, we find that A1689-zD1 is consistent with the relations derived from local star-forming galaxies. Even though A1689-zD1 lies on local star formation scaling relations and has a high dust and stellar mass estimate, the kinematics suggest it is in an early assembly stage, which could lead to it becoming a disk galaxy at a later stage.

After over three decades of unsuccessful attempts, we report the first detection of molecular gas emission in Malin 1, the largest spiral galaxy observed to date, and one of the most iconic giant low surface brightness galaxies. Using Atacama Large Millimeter/submillimeter Array, we detect significant 12CO (J = 1-0) emission in the galaxy's central region and tentatively identify CO emission across three regions on the disk. These observations allow for a better estimate of the H2 mass and molecular gas mass surface density, both of which are remarkably low given the galaxy's scale. By integrating data on its H i mass, we derive a very low molecular-to-atomic gas mass ratio. Overall, our results highlight the minimal presence of molecular gas in Malin 1, contrasting sharply with its extensive, homogeneous atomic gas reservoir. For the first time, we position Malin 1 on the Kennicutt-Schmidt diagram, where it falls below the main sequence for normal spirals, consistent with previous upper limits but now with more accurate figures. These findings are crucial for constraining our understanding of star formation processes in environments characterized by extremely low molecular gas densities and for refining models of galaxy formation, thereby improving predictions concerning the formation, evolution, and distribution of these giant, elusive galaxies.

We report observations of the ground state transitions of $^{12}$CO, $^{13}$CO C$^{18}$O, 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$^{\prime\prime}$ resolution. In the nuclear bar region, the intensity distributions of $^{12}$CO(1-0) and $^{13}$CO(1-0) emission trace moderate densities, and differ from the dense gas distributions sampled in C$^{18}$O(1-0), HCN(1-0), and HCO$^+$(1-0). We observe a constant HCN(1-0)-to-HCO$^+$(1-0) ratio of 1.2$\pm$0.1 across the whole $\sim$1 kpc bar. This indicates that HCN(1-0) and HCO$^+$(1-0) lines have intermediate optical depth, and that the corresponding $n_{\textrm{H}_2}$ of the gas producing the emission is of 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 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 the angular offset ($\sim$10$^{\prime\prime}$) between the spatial distribution of molecular gas and the star formation sites. Finally, we find a breakdown of the $L_\textrm{IR}$-$L_\textrm{HCN}$ 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 $L_\textrm{IR}$-$L_\textrm{HCN}$ relation decreases as the spatial scale increases from 10$^{\prime\prime}$~to 30$^{\prime\prime}$ (170-510~pc), and is comparable to the scatter of the global relation at the scale of 340 pc.

The internal velocity structure within dense gaseous cores plays a crucial role in providing the initial conditions for star formation in molecular clouds. However, the kinematic properties of dense gas at core scales ( 0.01 - 0.1 pc) has not been extensively characterized because of instrument limitations until the unique capabilities of GBT-Argus became available. The ongoing GBT-Argus Large Program, Dynamics in Star-forming Cores (DiSCo) thus aims to investigate the origin and distribution of angular momenta of star-forming cores. DiSCo will survey all starless cores and Class 0 protostellar cores in the Perseus molecular complex down to 0.01 pc scales with < 0.05 km/s velocity resolution using the dense gas tracer N_2H^+. Here, we present the first datasets from DiSCo toward the B1 and NGC 1333 regions in Perseus. Our results suggest that a dense core's internal velocity structure has little correlation with other core-scale properties, indicating these gas motions may be originated externally from cloud-scale turbulence. These first datasets also reaffirm the ability of GBT-Argus for studying dense core velocity structure and provided an empirical basis for future studies that address the angular momentum problem with a statistically broad sample.

We present the results of a James Webb Space Telescope NIRCam investigation into the young massive star cluster (YMC) population in the luminous infrared galaxy VV 114. We identify 374 compact YMC candidates with signal-to-noise ratios >= 3, 5, and 5 at F150W, F200W, and F356W, respectively. A direct comparison with our HST cluster catalog reveals that similar to 20% of these sources are undetected at optical wavelengths. Based on yggdrasil stellar population models, we identify 17 YMC candidates in our JWST imaging alone with F150W - F200W and F200W - F356W colors suggesting they are all very young, dusty (A(V) = 5-15), and massive (10(5.8) < M-circle dot < 10(6.1)). The discovery of these "hidden" sources, many of which are found in the "overlap" region between the two nuclei, quadruples the number of t < 3 Myr clusters and nearly doubles the number of t < 6 Myr clusters detected in VV 114. Now extending the cluster age distribution (dN d tau (sic) t(gamma)) to the youngest ages, we find a slope of gamma = -1.30 +/- 0.39 for 10(6) < tau(yr) < 10(7), which is consistent with the previously determined value from 10(7) < tau(yr) < 10(8.5), and confirms that VV 114 has a steep age distribution slope for all massive star clusters across the entire range of cluster ages observed. Finally, the consistency between our JWST-and HST-derived age distribution slopes indicates that the balance between cluster formation and destruction has not been significantly altered in VV 114 over the last 0.5 Gyr.

Astronomical observations in the molecule rich 3-mm window using large reflector antennas provide a unique view of the Universe. To efficiently carry out these observations gravitational and thermal deformations have to be corrected. Terrestrial laser scanners have been used to measure the deformations in large reflector antennas due to gravity, but have not yet been used for measuring thermal deformations. In this work, we investigate the use of a terrestrial laser scanner to measure thermal deformations on the primary reflector of the Green Bank Telescope (GBT). Our method involves the use of differential measurements to reduce the systematic effects of the terrestrial laser scanner. We use the active surface of the primary reflector of the GBT to validate our method and explore its limitations. We find that when using differential measurements it is possible to accurately measure deformations corresponding to different Zernike polynomials down to an amplitude of 60  m. The difference between the amplitudes of known deformations and those measured are m when the wind speed is  m s . From these differences we estimate that it should be possible to bring the surface error of the GBT down to m. This suggests that using a commercial off-the-shelf terrestrial laser scanner it is possible to measure deformations induced by thermal gradients on a large parabolic reflector.

We report on results from GBT/ARGUS 12 CO(1-0) observations for the giant low surface brightness galaxy Malin 1, which allow us to determine an upper limit for its CO mass, and hence its molecular gas mass and molecular gas mass surface density Σ H 2 . Although we performed very deep observations through 17 hr on-source integration time, reaching a noise level of ∼0.2 mK ( T A * ) with a corresponding extended source CO limit (3 σ ) of 0.09 K km s −1 , 19 times more sensitive than previous works, we do not detect the 12 CO(1-0) emission line. However, the observations allow us to estimate an upper limit (3 σ ) for the CO mass of about 7.4 × 10 9 M ⊙ for the extended emission, and 1.4 × 10 8 M ⊙ for the central part of the galaxy. With these figures we conclude that the molecular gas surface density is lower than 0.3 M ⊙ pc −2 , and the corresponding molecular to atomic gas mass ratio is lower than 0.13. The evidence suggests quite different physical conditions for the interstellar medium in Malin 1 compared to that of normal, high surface brightness spirals. This, in one way to another, keeps an usual molecular gas tracer as CO hidden from our observations, in spite of the diverse stellar and structural properties of Malin 1 observed by several authors since more than 30 yr.

Starburst galaxies at redshifts z~2 to 4 are among the most intensely star-forming galaxies in the universe. The way they accrete their gas to form stars at such high rates is still a controversial issue. We have detected the CH+(1-0) line in emission and/or in absorption in all the gravitationally lensed starburst galaxies observed so far with ALMA in this redshift range. The unique spectroscopic and chemical properties of CH+ allow its rotational transition to highlight the sites of dissipation of mechanical energy. Whilst the absorption lines reveal highly turbulent reservoirs of low-density molecular gas extending far out of the galaxies, the broad emission lines with widths up to a few thousands of km/s, arise in myriad molecular shocks powered by the feedback of star formation and possibly active galactic nuclei. The CH+(1-0) lines therefore probe the sites of prodigious energy releases, mainly stored in turbulent reservoirs before being radiated away. These turbulent reservoirs act as extended buffers of mass and energy over timescales of a few tens to hundreds of Myr. Their mass supply involves multi-phasic gas inflows from galaxy mergers and/or cold stream accretion, as supported by Keck/KCWI Lyα observations of one of these starburst galaxies.

Dense cores are the final place where turbulence is dissipated. It has been proposed from theoretical arguments that the non-thermal velocity dispersion should be narrower both for molecular ions (compared to neutrals) and for transitions with higher critical densities. To test these hypotheses, we compare the velocity dispersion of N_2H^+ (1–0) (n_ crit = 6×10^4 cm^-3) and NH_3(n_crit=2×10^3cm^-3), in the dense core Barnard 5. We analyse well resolved and high signal-to-noise observations of NH_3 (1,1) and (2,2) obtained with combining GBT and VLA data, and N_2H^+ (1–0) obtained with GBT Argus, which present a similar morphology. systematically higher than that of the neutral by 20%. The derived sonic Mach number, ℳ_s = σ_ NT/c_s, has peak values ℳ_s, N_2H^+ = 0.59 and ℳ_s, NH_3 = 0.48 for N_2H^+ and NH_3, respectively. magnetic field even deep within the dense core is still oscillating, as it is in the turbulent region outside the core. The ions should be more strongly dynamically coupled to this oscillating field than the neutrals, thus accounting for their broader linewidth. If corroborated by further observations, this finding would shed additional light on the transition to quiescence in dense cores.

Dense cores are the final place where turbulence is dissipated. It has been proposed from theoretical arguments that the nonthermal velocity dispersion should be narrower both for molecular ions (compared to neutrals) and for transitions with higher critical densities. To test these hypotheses, we compare the velocity dispersion of N2H+ (1-0) (n(crit) = 6 x 10(4) cm(-3)) and NH3 (n(crit) = 2 x 10(3) cm(-3)), in the dense core Barnard 5. We analyze well-resolved and high signal-to-noise observations of NH3 (1,1) and (2,2) obtained with combining Robert C. Byrd Green Bank Telescope (GBT) and Very Large Array (VLA) data, and N2H+ (1-0) obtained with GBT Argus, which present a similar morphology. Surprisingly, the nonthermal velocity dispersion of the ion is systematically higher than that of the neutral by 20%. The derived sonic Mach number, M-s = sigma(NT)/c(s), has peak values M-s,M-N2H+ = 0.59 and M-s,M- NH3 = 0.48 for N2H+ and NH3, respectively. This observed difference may indicate that the magnetic field even deep within the dense core is still oscillating, as it is in the turbulent region outside the core. The ions should be more strongly dynamically coupled to this oscillating field than the neutrals, thus accounting for their broader line width. If corroborated by further observations, this finding would shed additional light on the transition to quiescence in dense cores.

Aims. Radio observing efficiency can be improved by calibrating and reducing the observations in total power mode rather than in frequency, beam, or position-switching modes.Methods. We selected a sample of spectra obtained from the Institut de Radio-Astronomie Millimétrique (IRAM) 30-m telescope and the Green Bank Telescope (GBT) to test the feasibility of the method. Given that modern front-end amplifiers for the GBT and direct Local Oscillator injection for the 30 m telescope provide smooth pass bands that are a few tens of megahertz in width, the spectra from standard observations can be cleaned (baseline removal) separately and then co-added directly when the lines are narrow enough (a few km s−1), instead of performing the traditional ON minus OFF data reduction. This technique works for frequency-switched observations as well as for position- and beam-switched observations when the ON and OFF data are saved separately.Results. The method works best when the lines are narrow enough and not too numerous so that a secure baseline removal can be achieved. A signal-to-noise ratio improvement of a factor of √2 is found in most cases, consistent with theoretical expectations.Conclusions. By keeping the traditional observing mode, the fallback solution of the standard reduction technique is still available in cases of suboptimal baseline behavior, sky instability, or wide lines, and to confirm the line intensities. These techniques of total-power-mode reduction can be applied to any radio telescope with stable baselines as long as they record and deliver the ONs and OFFs separately, as is the case for the GBT.