The ALMA-QUARKS survey: Investigating Thermal Feedback of Massive Protostars in Hot Molecular Cores

Abstract

We identify a sample of 83 spatially resolved hot molecular cores (HMCs) in the QUARKS survey, aiming at investigating thermal feedback from massive stars. Using CH$_3$CN\,(12--11) line emission together with 1.3\,mm continuum data we derive the radial temperature, volume density and \ch3cn{} abundance profiles for the 83 HMCs. Based on the envelope temperature and density profiles, we compute the luminosities of the embedded massive protostars with \radmc{} radiation transfer model. The derived luminosities are comparable (within $\sim1$ dex) to the bolometric luminosities of their natal clumps and show strong correlations with several core-scale properties, including the HMC mass ($Log[ M_\mathrm{env}] = 1.01\,Log [L_\star] - 4.80$), the inner core radius (the flat radius of Plummer-like volume density profile) ($Log[a] = 0.46\,Log[L_\star] + 0.52$) and the central density $ (Log[n_c] = -0.55 Log[L_\star] +10.47) $. These empirical relations provide useful observational constraints for physical models of protostellar objects. Importantly, we find a strong positive correlation between the massive protostellar luminosity and the local thermal Jeans mass. The derived Jeans masses, $M_\mathrm{Jeans}$, exceed the HMC masses $M_\mathrm{env}$, with the average $M_\mathrm{Jeans}$ being two times larger than the average $M_\mathrm{env}$. This provides observational evidence that thermal feedback from massive protostars can effectively suppress further fragmentation of HMCs, thereby promoting massive star formation. In addition, the positive correlation between massive protostellar luminosity and natal clump mass suggests that more massive clumps preferentially host more luminous protostars, leading to stronger thermal feedback.

Figures (13)

• Figure 1: Overall workflow illustrating the calculation of most physical quantities in this paper; detailed procedures are provided in the main text.
• Figure 2: Example images for field I13134-6242 showing the spatial distribution of different parameters. The corresponding physical quantities are labeled in the upper-left corner of each panel. Upper panels: rotational temperature map (left panel) and CH$_3$CN column density map (right panel) produced by simultaneously fitting the multi-transitions of CH$_3$CN (12--11) pixel-by-pixel using spectuner. Lower-left panel: H$_2$ column density map derived from CH$_3$CN rotational temperature map and 1.3 mm continuum map. The cyan ellipse outlines the I13134-6242-HC1 structure identified by astrodendro. The synthesized beam is shown in the lower-left corner, and the scale bar is indicated in the lower-right corner. Lower-right panel: CH$_3$CN abundance map. The gray contours for the four panels represent the 1.3 mm continuum. The contour levels were plotted from 3$\sigma_{\mathrm{cont}}$ (1.5 mJy beam$^{-1}$) to 0.95 times the peak value, with 5 logarithmically spaced contours between these values. The similar images for the remaining sources are displayed in the complete figure set, which is available in the online journal.
• Figure 3: Representative example for the fitting results for the radial profile of different parameters. Upper-left and lower-left panels display the binned radial temperature profile derived from the CH$_3$CN rotational temperature map, but the different models (upper: Equation \ref{['eq: T_pow-law']}; lower: RADMC-3D model) are used to fit both in order to get different physical quantities. The upper-right panel and lower-right panel show the binned radial H$_2$ column density profile and CH$_3$CN abundance profile, which were derived from the H$_2$ column density map and CH$_3$CN abundance map shown in the lower-left and lower-right panels of Figure \ref{['fig:image_example']}, respectively. The data points used for the radial profile fit are shown in blue, while gray points are excluded from the model fits. The red solid lines show the best-fitted models. All physical parameters derived from the fits are shown in the legend of each panel. The inner unresolved region is shown as a grey-shaded area. The similar images for the remaining sources are displayed in the complete figure set, which is available in the online journal.
• Figure 4: The radial profiles of temperature (upper-left), CH$_3$CN abundance (upper-right), H$_2$ volume density (lower-left) and column density (lower-right) for all HMCs. The thin gray lines are the profiles for individual HMCs. The solid red lines present the averaged profile, and the dashed red line indicate the 1 $\sigma$ uncertainty ranges of the mean profiles. Note that we exclude the temperature profiles of I16348-4654-HC1 and I18056-1952-HC1, as their unusually high temperatures significantly deviate from those of the other HMCs and are likely unreliable. The average temperature, CH$_3$CN abundance and volume density profile can be fitted with Equation \ref{['eq: T_pow-law']}, \ref{['eq:abundance']} and \ref{['eq:volume density']}, respectively. The best-fit parameters are labeled in the corresponding panels.
• Figure 5: The histograms of the calculated parameters for all hot cores. The orange represents the dust-ff hot cores, and the blue represents the rest of the hot cores.