The Green Bank Ammonia Survey: Data Release 2

TL;DR

The Green Bank Ammonia Survey DR2 delivers a final, publicly accessible suite of NH$_3$ (1,1), (2,2), and (3,3) maps plus carbon-chain tracers across Gould Belt clouds, using forward modeling of hyperfine structure to derive $v_{ m LSR}$, $oldsymbol{ extsigma}$, $T_K$, $T_{ m ex}$, and $N( m NH_3)$ at high angular resolution. By coupling NH$_3$ fits with dust-derived $N( m H_2)$ maps, the work derives molecular abundances, core properties via dendrogram cross-matching, and virial parameters to assess gravitational binding. The study finds no universal threshold for subsonic non-thermal motions, but a widespread presence of coherent, subsonic pockets that correlate with mean kinetic temperature and feedback influences; it also reveals regionally varying chemistry, with notable HC$_5$N and HC$_7$N detections and a clear kinematic connection between extended streamers and larger gas reservoirs, exemplified in B1 Per-emb-2. Overall, DR2 advances the understanding of dense gas structure and chemistry in nearby star-forming regions and provides a rich data resource for studying core evolution, kinematics, and mass accretion processes.

Abstract

We present an overview of the final data release (DR2) from the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green Bank Telescope to map all Gould Belt star-forming regions with $A_\mathrm{V} \gtrsim 7$~mag visible from the northern hemisphere in emission from NH$_3$ and other key molecular tracers. This final release includes the data for all the regions observed: Heiles Cloud 2 and B18 in Taurus; Barnard 1, Barnard 1-E, IC348, NGC 1333, L1448, L1451, and Per7/34 in Perseus; L1688 and L1689 in Ophiuchus; Orion A (North and South) and Orion B in Orion; Cepheus, B59 in Pipe; Corona Australis (CrA) East and West; IC5146; and Serpens Aquila and MWC297 in Serpens. Similar to what was presented in GAS DR1, we find that the NH$_3$ emission and dust continuum emission from Herschel correspond closely. We find that the NH$_3$ emission is generally extended beyond the typical 0.1 pc length scales of dense cores, and we find that the transition between coherent core and turbulent cloud is a common result. This shows that the regions of coherence are common throughout different star forming regions, with a substantial fraction of the high column density regions displaying subsonic non-thermal velocity dispersions. We produce maps of the gas kinematics, temperature, and NH$_3$ column densities through forward modeling of the hyperfine structure of the NH$_3$ (1,1) and (2,2) lines. We show that the NH$_3$ velocity dispersion, $σ_v$, and gas kinetic temperature, $T_{\rm kin}$, vary systematically between the regions included in this release, with an increase in both the mean value and spread of $σ_v$ and $T_{\rm kin}$ with increasing star formation activity. The data presented in this paper are publicly available via \dataset[DOI: 10.11570/24.0091]{https://doi.org/10.11570/24.0091}.

Figures (11)

• Figure 1: Observed GAS regions in the western Perseus molecular cloud. The color scale shows $N(\ce{H2})$ derived from SED fitting of Herschel continuum maps Singh2022-Tau_Herschel. White contours highlight the extent of the GAS maps. Black contours show the integrated NH_3 (1,1) emission. The 32 GBT beam is shown at bottom left.
• Figure 2: Integrated intensity of NH_3 (1,1), C2S, HC_5N, and HC_7N emission toward Heiles Cloud 2 in Taurus. In all plots, grey contours follow the NH_3 (1,1) emission. The blue circle at lower left shows the GBT beam
• Figure 3: Fit parameter results for NH_3 (1,1) and (2,2) across all observed GAS regions. Regions are ordered by increasing mean $T_\mathrm{K}$ as measured by the hyperfine structure NH_3 fitting. Violin plots show the extrema, median, and mean values (horizontal lines) and the distribution of values within each region.
• Figure 4: KDE of velocity dispersion as a function of H2 column density for all regions covered. The red-dotted and black-dashed lines correspond to the expected velocity dispersion, $\sigma_v$, in the case of $\mathcal{M}_s$ equals 1 and 0.5, respectively, for the median $T_\mathrm{K}$ value of each region. In the case of B1E, Pipe Core40, and "All Regions," we assume a temperature of 10 K. Notice that since the regions are already sorted by the typical kinetic temperature, the horizontal lines have only a small variation between neighbouring panels.
• Figure 5: KDE of the effective radius and minimum column density of subsonic structures across all regions. In both cases, the distributions exhibit peaks (representative values) but span a wide range, indicating the absence of a universal value for these structures. Left: Distribution of the effective radius ($R_{\mathrm{eff}} = \sqrt{A/\pi}$) for all subsonic structures. It shows a peak at $\approx 0.05$ pc, with a pronounced tail extending up to 0.3 pc. Right: Distribution of the minimum H2 column density within subsonic structures. It shows a peak near $6\times 10^{21}$$\mathrm{cm}^{-2}$ and covers a broad range, spanning more than an order of magnitude.