G183: An outer galaxy filament feeding a massive protostar

Abstract

We present the first detailed multi-tracer observation of a 5-pc long outer Galaxy filament, G183, and the massive young stellar object (YSO) IRAS 05480+2545 associated with it. Using the IRAM 30-m telescope at lambda = 1.4 and 3 mm, we probed the molecular gas distribution at angular resolutions of ~12"-28" (0.1-0.3 pc at d = 2.1 kpc). The velocity-resolved C18O(1-0) observations conclusively show a main filament with a skeleton of ridges. The main filament is a 5 pc long velocity-coherent structure with a continuous and quiescent velocity field along its length up to the star-forming hub that accretes mass from the filament. The internal gas kinematics of most of the G183 filament is dominated by thermal motions (sigma_NT/cs~1) and large-scale velocity gradients arising due to outflows and accretion of matter in the massive YSO. The dispersion-size relation almost up to 1 pc is consistent with Larson's law, suggesting that the origin of the filament is a turbulence cascade. The massive YSO, S1, with no corresponding radio continuum detection is characterized as a high-mass protostellar object with a mass of 156 Msun and an M/L ratio of 0.04. We identify a kinematic signature of the accretion of material from the filament onto the YSO, S1. The rates of molecular gas accretion and entrainment in S1 are estimated to be 8.6 and 2.6 (in units of 10^-4 Msun/yr), respectively. In comparison to the inner Galaxy high-mass star-forming filaments forming massive stars, G183 has a lower column density; however, the accretion and outflow rates in S1 are similar. The detection of hydrocarbons such as CH3CN and HC3N indicates the presence of hot-core chemistry in S1. These results highlight the universality of physical processes involved in massive star formation across a range of Galactic environments.

Figures (19)

• Figure 1: Continuum images of the G183 region. Left WISE 12 $\mu$m . Middle Herschel/PACS at 70 $\mu$m . ( Right:) 250 $\mu$m SPIRE image (colour) with 350 $\mu$m SHARC image with a beam size of 85 as contours. Contour levels (Jy/beam) are 0.5, 2, 4, 6, 8, 10, 12 to 30 in steps of 8. Continuum sources at 70 and 160 $\mu$m shown as white open squares and triangles, respectively. Class 1 and Class 2 sources from GLIMPSE360 are shown as inverted red triangles and white asterisks. The location of the massive YSO S1 is also marked for reference.
• Figure 2: Integrated intensity maps in the 3 mm band observed with the IRAM 30m telescope towards the G183 region. The colour plot in each panel is the integrated emission of C$^{18}$O(1--0) and the contours correspond to molecular transitions, as is indicated above the panels in units of K km s$^{-1}$ with step sizes in brackets. Above each panel the contour levels are given to the right. The intensities are integrated between velocities of -12 to -2 km s$^{-1}$ , except for N$_2$H$^+$ (1--0), which is integrated between -22 to 0 km s$^{-1}$. In the top left panel, the region mapped at 1.4 mm is shown by the smaller box. Positions selected for further analysis are shown as '+' in the bottom right panel and marked as S1 (0$^{\prime\prime}$, 0$^{\prime\prime}$), S2(123$^{\prime\prime}$, -125$^{\prime\prime}$) and S3 (-15$^{\prime\prime}$,-96$^{\prime\prime}$). The solid curve drawn on the C$^{18}$O(1--0) map shows the direction in which the velocity analysis including the position-velocity diagram (Fig. \ref{['fig_pvdiags']}) was done. The HPBW is shown on the lower right.
• Figure 3: Integrated intensity maps of HC$_3$N and CH$_3$CN in the 3 mm band observed with the IRAM 30m telescope. Observations covered the region shown in Fig. \ref{['fig_g183_90GHz_1']} but emission in these lines was only detected in the inner region shown here. The colour plot in each panel is the integrated emission of C$^{18}$O(1--0) and contours correspond to molecular transitions as indicated above the panels. The intensities are integrated between velocities of -20 to 0 km s$^{-1}$. Contour levels in units of (K km s$^{-1}$) are indicated at the top of the panels. The HPBW is shown on the lower right.
• Figure 4: Integrated intensity maps at 1.4 mm observed with the IRAM 30m telescope towards the G183 region. The colour plot in each panel is the integrated emission of C$^{18}$O(2--1) and the contours correspond to molecular transitions, as is indicated above the panels. The intensities are integrated between velocities of -20 to 0 km s$^{-1}$. The HPBW is shown on the lower right.
• Figure 5: Position-velocity diagram for C$^{18}$O, $^{13}$CO(1--0) and CO, $^{13}$CO(2--1) emission along the cut shown in Fig. \ref{['fig_g183_90GHz_1']}. The dashed blue lines are drawn at -9 km s$^{-1}$ to guide the eye.