Triggered Star Formation in a Bright-Rimmed Cloud (Brc 5) of Ic 1805

Abstract

We report recent optical, near-infrared (NIR), and millimeter observations which have revealed some new features of the bright-rimmed cloud BRC 5 associated with W4. With slitless spectroscopy, we detected 17 Hα emission stars around the cloud; 4 are near the surface of the cloud, and 1 is toward IRAS 02252+6120. NIR photometry shows that the central Hα emission star, together with one bright infrared source, has large NIR excesses and Class I spectral energy distributions. These two Class I objects are associated with the 2.9 mm continuum peaks and with a bipolar outflow, and are in between two separate, elongated C 18 O(J = 1-0) cores. The C 18 O cores and the two Class I sources are aligned along a line at position angle ∼240 • , somewhat less than perpendicular to the direction of UV radiation from the OB stars. Most of the detected Hα emission stars, all T Tauri candidates, are located within ∼3 of the cloud on the exciting star side. An estimate of the age of the stars based on a color-magnitude diagram suggests that these T Tauri candidates have ages of ∼1 Myr or less, but are more evolved objects than the central young stellar objects. This age sequence suggests sequential star formation within the BRC 5 cloud. The 13 CO(J = 1-0) emission shows three elongated structures, which indicates the asymmetric structure toward the UV incident axis. We present our exploratory simulation results by using a smoothed particle hydrodynamic code that suggests that the asymmetrical BRC 5 structure could possibly result from the evolution of a preexisting prolate molecular cloud subject to radiation-driven implosion (RDI). Our best-fit prolate cloud has an initial mass of ∼400 M , an axial ratio of ∼1.7, and a semi-major axis of ∼1.6 pc, pointing away from the ionization flux by an angle of 15 • . The simulated cloud structure not only closely matches the observed asymmetric morphological structure of BRC 5, but also reveals the possibility of the development of two major cores at the head of BRC 5. For the first time, the possibility of forming two stars by an RDI mechanism in a BRC is investigated.

APEX CO observations towards the photodissociation region of RCW 120

“…Simulations of H II region expansion in a turbulent medium show the formation of pillars and cometary globules (Tremblin et al 2012), and the expansion in a fractal medium triggers the formation of stars by combining elements from C&C and RDI (Walch et al 2015). Several theoretical (Bertoldi 1989;Lefloch & Lazareff 1994;Miao et al 2006) and observational studies (Urquhart et al 2009; A&A 639, A93 (2020) Morgan et al 2009;Fukuda et al 2013) have analyzed the interaction between a clump and the H II region through the RDI process. This mechanism is associated with an high ionizing flux (Bisbas et al 2011), an elongated tail, an ionized boundary layer (IBL), and 8 µm emission.…”

Interaction between the H ii region and AFGL 333-Ridge: Implications for the star formation scenario

“…As the northern part of AFGL 333-Ridge is located between these two IRAS sources, Rivera-Ingraham SFO 05 at the northern end of AFGL 333-Ridge is the typical case of star formation triggered by radiation-driven implosion. A pre-existing condensation of about 400M ⊙ was compressed by the pressure of the ionizing radiation of W4 (Fukuda et al 2013). And the compact HII region G 134.2+0.8 lies at the interface between the AFGL 333-Ridge and W4.…”

Progresses and methods in research of infrared dust bubble

“…更多的这类 观测的统计可以参考Dale等人 [59] 于2015年的工作. 对于亮边云的观测, 例如, Sugitani课题组 [60][61][62][63][64][65][66] [20,67] , MIPS-GAL [21] , 2MASS [68] , IRAS [69] , NVSS [70] , BGPS 1) , ATLASGAL 2) , WISE [71,72] , MAGPIS 3) , Herschel 4) 等, 射电巡天设备或项目主要有MOPRA [73,74] , JCMT 5) , GRS [75] , KOSMA 和PMO 6) 等. [76,77] [78] 于2012年和Zavagno等人 [30] 于2010年 使用赫歇尔望远镜开展的尘泡相关研究工作, 结合 多个波段的连续谱数据可以更好的利用SED拟合计 算红外尘泡的尘埃温度和柱密度等物理参数.…”