High Resolution CO Imaging Research Articles

Source Structure and Molecular Gas Properties from High-resolution CO Imaging of SPT-selected Dusty Star-forming Galaxies

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of high-J CO lines ($J_\mathrm{up}=6$, 7, 8) and associated dust continuum towards five strongly lensed, dusty, star-forming galaxies (DSFGs) at redshift $z = 2.7$-5.7. These galaxies, discovered in the South Pole Telescope survey, are observed at $0.2''$-$0.4''$ resolution with ALMA. Our high-resolution imaging coupled with the lensing magnification provides a measurement of the structure and kinematics of molecular gas in the background galaxies with spatial resolutions down to kiloparsec scales. We derive visibility-based lens models for each galaxy, accurately reproducing observations of four of the galaxies. Of these four targets, three show clear velocity gradients, of which two are likely rotating disks. We find that the reconstructed region of CO emission is less concentrated than the region emitting dust continuum even for the moderate-excitation CO lines, similar to what has been seen in the literature for lower-excitation transitions. We find that the lensing magnification of a given source can vary by 20-50% across the line profile, between the continuum and line, and between different CO transitions. We apply Large Velocity Gradient (LVG) modeling using apparent and intrinsic line ratios between lower-J and high-J CO lines. Ignoring these magnification variations can bias the estimate of physical properties of interstellar medium of the galaxies. The magnitude of the bias varies from galaxy to galaxy and is not necessarily predictable without high resolution observations.

High-resolution CO images of the Galactic central molecular zone

Abstract We performed Nyquist-sampled mapping observations of the central molecular zone of our Galaxy in the J = 1–0 lines of CO, 13CO, and C18O using the 45 m telescope at the Nobeyama Radio Observatory. The newly obtained data sets were an improvement by a factor of four in spatial resolution of the CO data previously obtained with the same telescope 22 years ago, providing the highest angular resolution CO atlas of this special area of the Galaxy. The data cover the area: −0${^{\circ}_{.}}$8 ≤ l ≤ +1${^{\circ}_{.}}$4 and −0${^{\circ}_{.}}$35 ≤ b ≤ +0${^{\circ}_{.}}$35 with a 15″ beamwidth. Total intensity ratios for CO J = 3–2/J = 1–0, 13CO/CO J = 1–0 and C18O/13CO J = 1–0, are 0.70 ± 0.06, 0.12 ± 0.01, and 0.14 ± 0.01, respectively. The high-resolution CO images show the fine structure of the molecular gas and enable us to identify a number of compact clouds with broad velocity widths, i.e., high-velocity compact clouds. We conducted a detailed comparison of our CO J = 1–0 data with the CO J = 3–2 data obtained with the James Clerk Maxwell Telescope to derive the distribution and kinematics of the highly excited gas. Three, out of four, of the previously identified high CO J = 3–2/J = 1–0 ratio areas at l = +1${^{\circ}_{.}}$3, 0${^{\circ}_{.}}$0, and −0${^{\circ}_{.}}$4 were confirmed with a higher spatial resolution. In addition to these, we identified several very compact, high CO J = 3–2/J = 1–0 spots with broad velocity widths for the first time. These are candidates for accelerated gas in the vicinity of invisible, point-like massive objects.

Star Formation Efficiency per Free-fall Time in nearby Galaxies

Abstract We estimate the star formation efficiency per gravitational free-fall time, , from observations of nearby galaxies with resolution matched to the typical size of a giant molecular cloud. This quantity, , is theoretically important but so far has only been measured for Milky Way clouds or inferred indirectly in a few other galaxies. Using new, high-resolution CO imaging from the Physics at High Angular Resolution in nearby Galaxies-Atacama Large Millimeter Array (PHANGS-ALMA) survey, we estimate the gravitational free-fall time at 60–120 pc resolution, and contrast this with the local molecular gas depletion time in order to estimate . Assuming a constant thickness of the molecular gas layer (H = 100 pc) across the whole sample, the median value of in our sample is 0.7%. We find a mild scale dependence, with higher measured at coarser resolution. Individual galaxies show different values of , with the median ranging from 0.3% to 2.6%. We find the highest in our lowest-mass targets, reflecting both long free-fall times and short depletion times, though we caution that both measurements are subject to biases in low-mass galaxies. We estimate the key systematic uncertainties, and show the dominant uncertainty to be the estimated line-of-sight (LOS) depth through the molecular gas layer and the choice of star formation tracers.

High Resolution CO Imaging of a Cometary Globule in the Helix Nebula

We report high resolution CO (1–0) line imaging of a prominent cometary globule in the Helix Nebula. The results confirm earlier observations (Huggins et al. 1992) that globules consist of dense condensations of neutral gas embedded in the ionized nebula, and they provide new constraints on the structure and kinematics of the gas.

A Large‐Scale CO Survey of the Galactic Center

We present high-resolution CO images of the Galactic center region taken with the 2 × 2 focal-plane array receiver mounted on the 45 m telescope of Nobeyama Radio Observatory. We have collected about 44,00012C16O (J = 1-0) spectra and over 13,00013C16O (J = 1-0) spectra with a 34'' (1.4 pc) grid spacing. The 12CO mapping area is roughly -15 ≤ l ≤ +34 and -06 ≤ b ≤ +06, which covers almost the full extent of the molecular gas concentration in the Galactic center. These CO images demonstrate extremely complex distribution and kinematics of molecular gas in the Galactic center. While its large-scale behavior can be attributed to the well-known coherent features, bright CO emission arises from a number of compact (d ≤ 10 pc) clouds with large velocity widths (ΔV ≥ 30 km s-1). The small-scale structure of molecular gas is characterized by filaments, arcs, and shells. The boisterous molecular gas kinematics there may be a result of violent release of kinetic energy by a number of supernova explosions and/or Wolf-Rayet stellar winds.

High-Resolution CO Imaging of the Molecular Disk around the Jets in [CLC]KjPn[/CLC] 8

We report high-resolution (25) CO J = 1-0 line imaging that confirms the presence of a molecular disk around the origin of the spectacular, 14'×4', episodic jets in the planetary nebula KjPn 8. The disk is 30'' in diameter, with an expansion velocity of ≈ 7 km s-1. The axis of the disk is aligned with the youngest and fastest (≈ 300 km s−1) of the bipolar jets, and there is evidence for interaction between the jets and the disk material. The inner 4'' of the disk are photoionized by the central star. The disk-jet system dominates the environment of this young nebula and should govern the morphology of KjPn 8 as it evolves to become fully ionized.

4.14. Molecular shell formation by supernova remnants in the Galactic center—what we learn from the case of W44

Recent high resolution CO images of the Galactic center (GC) molecular clouds reveal many arc and/or shell structures (Oka et al. 1997). A considerable fraction of them may most probably be formed by an interaction between supernova remnants (SNRs) and molecular clouds. Studies of such cases in less confused areas are needed to clarify this picture. The SNR W44 is a good place for examining the SNR induced shell formation scenario.

4.3. A large-scale CO imaging of the Galactic center by the Nobeyama 45-m telescope: shell statistics and star formation history

As a key program of the 45-m telescope at Nobeyama Radio Observatory, we have made high-resolution CO images of the Galactic center region with the 2×2 focal plane array receiver. The data consist of 44,000 12CO and 13,000 13CO spectra taken with 16″ beams spaced by 34″. The 12CO image covers roughly −1.5° ≤ l ≤ +3.4° and −0.6° ≤ b ≤ +0.6° (Oka et al. 1997b)