Modelo de Correlación de Pearson: la efectividad de programas de reinserción

The HH80–81 jet

At a distance of 1.7kpc (Rodriguez et al. 1980) the infrared source IRAS 18162– 2048 (G010.8411–02.5919 in this work) is the powering object of the Herbig-Haro objects HH80 and HH81. A study by Marti et al. (1993) using VLA observa- tions at 1.5, 5, 8 and 15 GHz revealed a multitude of radio knots separated by an average of ∼ 1400 au, with IRAS 18162–2048 ( Lbol ∼ 2 × 104L⊙) at their

geometric centre. A central, elongated source with a derived spectral index of α = 0.2 ± 0.1 and centred on the infrared source, was suggested to represent a biconical, ionised jet in keeping with the models of Reynolds (1986). The radio lobes were interpreted to represent working surfaces upon which the neutral jet acted upon, with spectral indices of α = −0.3 ± 0.1 for the lobes HH80, HH81 and HH80 North. Furthermore, the jet was shown to be highly collimated, with

an opening angle of ∼ 1◦_{. Careful analysis of the radio lobe positions along the}

jet’s axis, showed a sinusoidal path indicating a precession in the outflow axis with a period of 5500 years. Proper motions in the lobes ranging from 600 to 1400 kms−1 _{were found in a later work combining observations over a time period}

of 4 years (Marti et al. 1995). Compared to other ionised jets in the literature, this example is one of the most extended, with a distance between the terminal shocks of HH80 North and HH80 of 5.1pc.

A later study by Carrasco-Gonz´alez et al. (2010a) observed polarised, syn- chrotron emission in the radio lobes close (∼ 0.5 pc) to the jet’s launching point. Inferred magnetic field lines ran parallel to the jet’s outflow axis, a configuration expected of a helical, magnetic field confining the flow of the ionised material at its centre. This represents the only occurrence of this type of observation for ionised jets around MYSOs.

Cepheus A HW2

Located in the cloud complex, Cepheus OB3, Cepheus A hosts a great deal of star formation activity (see Rodriguez et al. 1994, and references therein). Obser- vations between 1.5 and 43 GHz with the VLA (Rodriguez et al. 1994) towards Cepheus A HW2, showed an elongated (θP.A. ∼ 40◦) structure in the maps of radio

flux, with an asymmetric tail to the south west (interpreted to be shock ionisation as a result of the jet’s interaction with surrounding material). A spectral index of α = 0.69±0.06 and power-law constant for the variation of major axis length with frequency of γ = −0.57 ± 0.02 were inferred. These values are close to the typical values expected of a non-confined, biconical jet (α ∼ 0.6, γ ∼ −0.7; Reynolds 1986). The jet’s elongation axis corresponded well to a HCO+_{molecular outflow’s}

red/blue (south west/north east respectively) axis (G´omez et al. 1999), while barely resolved SiO emission tentatively showed elongation perpendicular to the outflow direction. More up to date observations with the Sub-Millimeter Array (SMA) (Patel et al. 2005) conclusively identified a dusty disc with an inclination angle of 62 ± 10◦_{, radius of 330AU and mass between 1 and 8 M}

⊙(protostellar

mass was inferred to be 15 M⊙) whose major axis lay perpendicular to the jet.

This represented the first bona fide example of a jet-disc system in a high-mass protostellar case. Multi-epoch observations constrained the proper motions of the outer radio lobes to ∼ 480 km s−1 _{and inferred an asymmetric, episodic style}

of ejection in the jet (Curiel et al. 2006).

IRAS 16547–4247

Using ATCA radio observations (Garay et al. 2003) an ionised jet system was identified with a familiar central component/outer lobe structure in association with the infrared source IRAS 16547–4247 ( Lbol = 1.9 ×104L⊙). Spectral indices

were found to be 0.49 ± 0.12, −0.33 ± 0.04 and −0.61 ± 0.26 for the central component, southern lobe and northern lobe respectively. The position angle of the outflow axis was deduced to be 161◦_{, with a scale between outer lobes}

of 0.28 pc(for a distance of 2.7 kpc). Mass loss rates in the jet of ˙_{M ∼ 8 ×} 10−6_M

⊙yr−1 were derived, significantly exceeding the low mass case of 10−7 −

10−9_M

⊙yr−1. A set of observations with a noise ∼ 2.5 times lower than the first

set (Rodr´ıguez et al. 2005), detected many more radio lobes associated to the jet. These two complementary datasets show how deep radio observations should be used to reveal the full extent of ionised material emanating from the phenomena forming the subject of this thesis.

Further observations performed at different epochs over 2.68 years showed no (> 4σ) proper motions in the outer lobes of the jet, which also displayed a large precession in its outflow axis of 0.08◦_yr−1_{(Rodr´ıguez et al. 2008). The lack of any}

motions indicated that the outer radio lobes were the result of shock-ionisation along working surfaces where jet material collided with ambient material.

Most recently, ALMA 0.85mm observations detected a dusty, compact (1620 au× 1450 au) component coincident with IRAS 16547 − 4247, oriented at a position angle of 115 ± 5◦_{. Concurrent line observations of high-excitation temperature}

transitions of both CH3OH and CH3SH, showed that at smaller scales (<1000 au),

a compact, rotating structure whose major axis was perpendicular to that of the ionised jet was present, and from Keplerian arguments was inferred to be in rotation around a central mass of 20 M⊙(Zapata et al. 2015).

IRAS 16562–3959

Although not as extensively studied as the other examples of ionised jets reviewed here, the radio free-free emission associated to this target proves morphologically interesting. Radio observations are comprised of a thermal (α = 0.85 ± 0.15) central component centred on the infrared source ( Lbol = 7 × 104L⊙) and 4

aligned radio lobes with flat spectral indices (α ∼ −0.1) symmetrically arranged either side (Guzm´an et al. 2010), similar to other examples. The inferred mass loss rate was ˙_{M ∼ 2 × 10}−6_M

⊙yr−1, and proper motions in the inner/outer radio

lobes were extrapolated to determine terminal velocities in the jet of ∼ 360 and ∼ 280kms−1_{, for eastern and western components respectively. A quadrupolar}

morphology of CO(6→5) and CO(7→6) was observed by Guzm´an et al. (2011), suggesting the presence of two molecular outflows, one aligned with the radio jet

( ˙P = 3.0 × 10−2_M

⊙km s−1 yr−1) and another oriented in the N-S direction. In

this thesis the designation, G345.4938+01.4677, is adopted for this object.

Two previous radio surveys

Guzm´an et al. (2012) surveyed 7 out of 33 potential high mass young stellar object (HMYSO) candidates for ionised jets, in the southern hemisphere. Criteria used to select the sample were a positive radio spectral index, large bolometric luminosity ( Lbol > 2 × 104L⊙) of which most lies in the infrared (due to dust

extinction), an association with a luminous IRAS source and an under-luminosity in the radio compared to that expected from an optically-thin Hii region. These potential jet-harbouring YSOs were consequently followed up by ATCA radio observations at 1.4, 2.4, 4.8, and 8.6 GHz whose respective resolutions were 7′′_,

4′′_{, 2}′′_{, and 1}′′_.

Following radio observations, spectral index calculations and consideration of other wavelength observations, 2 out of the 33 candidates were definitively iden- tified as MYSOs with ionised jets; G337.4032–00.4037 and G345.4938+01.4677. Another five of the sample were categorised as either HCHii or UCHii regions based on their physical sizes and emission measures (size < 0.03 pc, EM> 108_{pc cm}−6 _{for HCHii; size < 0.1 pc, EM> 10}6_{pc cm}−6 _{for UCHii). On the ba-}

sis that 37.5 %, 37.5 % and 25 % of the observed objects were categorised as jets (including G343.1261–00.0623), HCHii regions and UCHii regions respectively, it was inferred that the ‘jet-stage’ of a forming massive star lasts ∼ 4 × 104_yr.

Another survey by Moscadelli et al. (2016) aimed to detect collimated outflow activity using a combination of multi-epoch, VLBI observations of water/methanol masers and high-sensitivity (σ ∼ 10 µJy) JVLA continuum observations (C, Ku

and K bands). A distance-limited (D < 9 kpc) sample of 40 high-mass star form- ing regions were selected from the BeSSeL maser survey under the criteria that they were radio weak (< 50 mJy), compact (θmaj < 1′′), possessed a bolometric

luminosity corresponding to ZAMS types B3 - O7 and possessed 10, or more, bright (> 1 Jy) maser spots (to map the outflow kinematics effectively). Of these 40 regions a sub-sample of 11 were reported upon. Five of the objects were cat- egorised as collimated, ionised jets on the basis of radio continuum morphology, spectral index and maser spatial and 3D velocity distribution. The other six were complex in the relationship of these two aspects and no definitive conclusions were drawn about them. Two of the five jets showed associated non-thermal emission in lobes spatially distinct from, but definitely associated to, the central, thermal jet.