A near-infrared spectroscopic survey of massive jets towards extended green objects

Abstract

Context. Protostellar jets and outflows are the main outcome of the star formation process, and their analysis can provide us with major clues about the ejection and accretion history of young stellar objects (YSOs). Aims. We aim at deriving the main physical properties of massive jets from near-infrared (NIR) observations, comparing them to those of a large sample of jets from low-mass YSOs, and relating them to the main features of their driving sources. Methods. We present a NIR imaging (H 2 and K s ) and low-resolution spectroscopic (0.95−2.50 μm) survey of 18 massive jets towards GLIMPSE extended green objects (EGOs), driven by intermediate-and high-mass YSOs, which have bolometric luminosities (L bol ) between 4 × 10 2 and 1.3 × 10 5 L . Results. As in low-mass jets, H 2 is the primary NIR coolant, detected in all the analysed flows, whereas the most important ionic tracer is [Fe ii], detected in half of the sampled jets. Our analysis indicates that the emission lines originate from shocks at high temperatures and densities. No fluorescent emission is detected along the flows, regardless of the source bolometric luminosity. On average, the physical parameters of these massive jets (i.e. visual extinction, temperature, column density, mass, and luminosity) have higher values than those measured in their low-mass counterparts. The morphology of the H 2 flows is varied, mostly depending on the complex, dynamic, and inhomogeneous environment in which these massive jets form and propagate. All flows and jets in our sample are collimated, showing large precession angles. Additionally, the presence of both knots and jets suggests that the ejection process is continuous with burst episodes, as in low-mass YSOs. We compare the flow H 2 luminosity with the source bolometric luminosity confirming the tight correlation between these two quantities. Five sources, however, display a lower L H 2 /L bol efficiency, which might be related to YSO evolution. Most important, the inferred L H 2 vs. L bol relationship agrees well with the correlation between the momentum flux of the CO outflows and the bolometric luminosities of high-mass YSOs indicating that outflows from high-mass YSOs are momentum driven, as are their low-mass counterparts. We also derive a less stringent correlation between the inferred mass of the H 2 flows and L bol of the YSOs, indicating that the mass of the flow depends on the driving source mass. Conclusions. By comparing the physical properties of jets in the NIR, a continuity from low-to high-mass jets is identified. Massive jets appear as a scaled-up version of their low-mass counterparts in terms of their physical parameters and origin. Nevertheless, there are consistent differences such as a more variegated morphology and, on average, stronger shock conditions, which are likely due to the different environment in which high-mass stars form.

Trigonometric distance and proper motions of H 2 O maser bowshocks in AFGL 5142

“…Since outflow activity is expected to correlate with accretion activity (Caratti o Garatti et al 2015) the 10 4 year timescale of ejections could indicate alternating periods of accretion bursts and quiescence in AFGL 5142 MM1, consistent with timescales predicted for episodic accretion in low- (Stamatellos et al 2011) and high-mass stars (Meyer et al 2017). The short episodic ejection seen on a 10 year timescales (Section 3.4) would likely originate in the inner disk.…”

“…In disk-jet systems, ejection rates correlate with accretion rates (Corcoran & Ray 1998;Caratti o Garatti et al 2015) -thus the ejection history of an MYSO allows inference of its accretion history -which is itself unobservable in a practical sense due to the timescales involved. Accretion history, based on ejection history, can therefore be used to compare low-and high-mass star formation.…”

Tracing jet emission at the base of a high-mass YSO

“…Figure 2 shows the continuum-subtracted Brγ-line photocentre displacements (with the errorbars in polar coordinates), which were derived from the astrometric solution in the different (radial) velocity channels (colour coded). Both the inner rim, defined by the study of the NIR continuum (see Kraus et al 2010), and the known jet axis (see Caratti o Garatti et al 2015a), are shown as a black solid ellipse and red solid line, respectively. The red dashed ellipses indicate the uncertainty on the size of the inner rim (1.97 ± 0.37 mas; Kraus et al 2010).…”

“…Kraus et al 2010;Ilee et al 2013;Cesaroni et al 2014;Sanna et al 2015) with the parsec-scale jet and outflow emission being driven by the central accreting source (e.g. Sanna et al 2014;Caratti o Garatti et al 2015a). Moreover, compelling observational evidence for the accretion disc scenario has recently come from the detection of compact discs in Keplerian rotation (e.g.…”

“…Kraus et al 2010;Ilee et al 2013;Cesaroni et al 2014) and parsec-scale collimated jets driven by HMYSOs (e.g. Stecklum et al 2009;Varricatt et al 2010;Caratti o Garatti et al 2015a). …”