[Paper Review] Searching for the main powering outflow objects in Cepheus A East

Luis A. Zapata, Manuel Fernández-López+3 more|arXiv (Cornell University)|May 17, 2013

Astrophysics and Star Formation Studies3 citations

TL;DR

This study uses high-resolution (sub)millimeter SMA observations to identify multiple east-west molecular outflows in Cepheus A East, revealing that the outflows are powered by young massive protostars HW2, HW3c, and HW3d. It confirms a precessing jet from HW2 with five periodic ejections every ~10°, and links the bright HH 168/X-ray object to shocks from the HW3c-driven outflow.

ABSTRACT

We present (sub)millimeter line and continuum observations in a mosaicing mode of the massive star forming region Cepheus A East made with the Submillimeter Array (SMA). Our mosaic covers a total area of about 3$'$ $ imes$ 12$'$ centered in the HW 2/3 region. For the first time, this observational study encloses a high angular resolution ($\sim$ 3$''$) together with a large scale mapping of Cepheus A East. We report compact and high velocity $^{12}$CO(2-1) emission associated with the multiple east-west bright H$_2$ condensations present in the region. Blueshifted and redshifted gas emission is found towards the east as well as west of HW 2/3. The observations suggest the presence of multiple large-scale east-west outflows that seems to be powered at smaller scales by radio sources associated with the young stars HW2, HW3c and HW3d. A kinematical study of part of the data suggests that the molecular outflow powered by HW2 is precesing with time as recently reported. Our data reveal five periodic ejections of material separated approximately every 10$^\circ$ as projected in the plane of the sky. The most recent ejections appear to move toward the plane of the sky. An energetic explosive event as the one that occurred in Orion BN/KL or DR21 does not explain the kinematics, and the dynamical times of the multiple ejections found here. The continuum observations only revealed a strong millimeter source associated with the HW 2/3 region. High angular resolution observations allow us to resolve this extended dusty object in only two compact sources (with spatial sizes of approximately 300 AU) associated with HW2 and HW3c. Finally, the bright optical/X-Ray HH 168 -- GDD37 object might be produced by strong shocks related with the outflow from HW3c.

Motivation & Objective

• To identify the primary powering sources of large-scale molecular outflows in the massive star-forming region Cepheus A East.
• To resolve the kinematical and morphological complexity of outflows with multiple orientations and velocities.
• To determine whether precession or explosive events explain the observed outflow structures.
• To investigate the connection between radio sources, molecular outflows, and Herbig-Haro objects like HH 168.
• To assess the role of circumstellar disks and compact millimeter sources in driving outflows.

Proposed method

• Conducted (sub)millimeter line and continuum observations using the Submillimeter Array (SMA) in mosaicing mode over a 3′ × 12′ area centered on the HW2/3 region.
• Achieved high angular resolution (~3″) to resolve compact structures and trace high-velocity molecular gas in 12 CO(2-1) transitions.
• Mapped blueshifted and redshifted CO emission to identify bipolar outflows and determine their kinematics and spatial extent.
• Analyzed proper motions and radial velocities to infer precession and ejection periodicity in the outflow from HW2.
• Correlated millimeter continuum emission with radio sources to identify compact dusty protostellar components.
• Compared morphological and kinematical features with known Herbig-Haro objects (e.g., HH 168) to assess shock excitation mechanisms.

Experimental results

Research questions

• RQ1 What are the primary sources powering the large-scale east-west molecular outflows in Cepheus A East?
• RQ2 Is the observed precession in the HW2-driven outflow consistent with periodic ejections, and what is the ejection cadence?
• RQ3 Can the kinematics of the multiple outflows be explained by a single explosive event, or do they require sustained episodic ejection?
• RQ4 What is the nature of the compact millimeter continuum sources associated with HW2 and HW3c, and how do they relate to circumstellar disks?
• RQ5 Is the HH 168/X-ray object energized by the outflow from HW3c, and what evidence supports this connection?

Key findings

• Compact, high-velocity 12 CO(2-1) emission is detected toward multiple east-west H2 bow shocks, indicating active outflows in both directions from HW2.
• Three large-scale east-west molecular outflows are identified, with blueshifted and redshifted components extending up to ±65 km s⁻¹, powered by radio sources associated with HW2, HW3c, and HW3d.
• The outflow from HW2 exhibits precession, with five periodic ejections separated by approximately 10° in position angle, suggesting episodic jet activity.
• The dynamical times and kinematics of the multiple ejections rule out a single explosive event like those in Orion BN/KL or DR21.
• Millimeter continuum observations resolve the extended dusty object in the HW2/3 region into two compact sources (~300 AU) associated with HW2 and HW3c, likely tracing circumstellar disks.
• The HH 168/X-ray object is strongly linked to the blueshifted side of the outflow from HW3c, likely due to strong shocks with the ambient molecular cloud.