Investigating the Influence of Radiative Feedback in Bright-Rimmed Cloud 44

TL;DR

This study investigates the impact of radiative feedback from massive stars on star formation in the bright-rimmed cloud BRC 44 by combining optical, near-infrared, mid-infrared, Gaia astrometry, and CO (J=1-0) data. A multi-faceted approach—YSO identification, CMD and SED analysis, NIR spectroscopy, and LTE CO modeling—reveals two YSO groups with distinct ages and spatial distributions, as well as an under-pressured molecular cloud relative to the ionized boundary, consistent with radiation-driven compression. The authors infer that radiative feedback has triggered new star formation via the RDI mechanism beginning around $0.7$ Myr ago, accompanied by rocket-like motion of YSOs away from the ionizing source. Overall, the work demonstrates how radiative feedback can both sculpt cloud morphology and promote subsequent star formation, with implications for star-formation efficiency in H II regions.

Abstract

Radiative feedback from massive stars plays a central role in the evolution of molecular clouds and the interstellar medium. This paper presents a multi-wavelength analysis of the bright-rimmed cloud, BRC 44, which is located at the periphery of the Hii region Sh2-145 and is excited by the massive stars in the region. We use a combination of archival and newly obtained infrared data, along with new optical observations, to provide a census of young stellar objects (YSOs) in the region and to estimate stellar parameters such as age, mass etc. The spatial distribution of YSOs visible in the optical wavelength suggests that they are distributed in separate clumps compared to the embedded YSOs and are relatively older. Near-Infrared (NIR) spectroscopy of four YSOs in this region using the TANSPEC mounted on the 3.6m Devasthal Optical Telescope (DOT) confirms their youth. From Spectral Energy Distribution (SED) fitting, most of the embedded YSO candidates are in their early stage of evolution, with the majority of them in their Class II and some in Class I stage. The relative proper motions of the YSOs with respect to the ionizing source are indicative of the rocket effect in the BRC. The 12CO, 13CO, and C18O observations with the Purple Mountain Observatory are used to trace the distribution of molecular gas in the region. A comparison of the cold molecular gas distribution with simple analytical model calculations shows that the cloud is in the compression stage, and massive stars may be influencing the formation of young embedded stars in the BRC region due to radiative feedback.

Figures (11)

• Figure 1: RGB image of the BRC 44 using Spitzer IRAC 3.6 $\mu$m (Blue), Spitzer IRAC 5.8 $\mu$m (Green), and Spitzer MIPS 24 $\mu$m(Red) data. The area observed using TIRCAM2 is shown using boxes.
• Figure 2: The $V$ vs ($V$-$I$) and $J$ vs ($J$-$H$) CMDs for the sources in the BRC 44 region obtained from the DFOT and 2MASS/TIRCAM2 data are plotted in the top and bottom panels, respectively. The inverted triangle markers represent optically visible YSOs identified using NIR and MIR data. Sources $S\_0$, $S\_1$, $S\_2$, and $S\_3$ are marked. Blue inverted triangle markers belong to Group 1 (defined in Section \ref{['identify_spitzer_app']}) optically visible YSOs. The brown vector indicates a reddening vector of $A_V = 21$. Note: $S\_0$ is not optically visible.
• Figure 3: Sample SEDs for the NIR spectroscopic targets. The bold line indicates the best fit with the lowest $\chi^{2}$ value. The light lines indicates fits that has $\chi^{2}$ value following $\chi^{2} - \chi^{2}_{model} < 3\times n_{data}$ criteria.
• Figure 4: Wavelength-calibrated normalized NIR spectra of the four sources. Note: Lines obtained for each source are in different wavelength ranges. Tanspec covers a larger wavelength range than as shown in figure (5500 to 25400 Å). We have only plotted regions where features are visible.
• Figure 5: $^{12}$CO contour map of the region. Velocity range is between -13 km s$^{-1}$ and -5 km s$^{-1}$. The contour levels are 11.1, 19.7, 28.2, 36.8, 45.3, 53.9, 62.5 K km s$^{-1}$. Beam size is shown in bottom right (50$^{\prime\prime}$).