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Register a new userPKS2250-41: a case study for triggering
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Added by
Katherine J. Inskip
Publication date
2008
fields
Physics
and research's language is
English
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We present the results of a multiwavelength study of the z = 0.31 radio source PKS2250-41. Integral field unit and long-slit spectroscopy obtained using VIMOS and FORS1 on the VLT, and archival HST optical imaging observations are used to study the morphology, kinematics and ionisation state of the extended emission line region (EELR) surrounding this source, and also a companion galaxy at a similar redshift. Near-infrared imaging observations obtained using the NTT are used to analyse the underlying galaxy morphologies. The EELR displays a complex variety of different gas kinematics and ionization states, consistent with a mixture of radio source shocks and AGN photoionization. The radio galaxy is likely to lie within a group environment, and is plausibly undergoing interactions with one or more other objects. The disk-like galaxy to the northeast of the radio source lies at a similar redshift to the radio galaxy itself, and has its major axis position angle aligned with the filamentary continuum and line emission extending outwards from the radio galaxy. This filamentary structure is most plausibly interpreted as a tidal structure associated with an interaction involving the radio source host galaxy and the aligned companion galaxy to the north-east; this encounter may have potentially triggered the current epoch of radio source activity. Overall, PKS2250-41 displays some of the best evidence that radio source activity can be triggered in this manner. [abridged]
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We present high resolution, long-slit spectra of the jet-cloud interaction in the powerful southern radio galaxy PKS2250-41. We have resolved the emission lines into two main kinematic components: a broad component (FWHM geq 900 km/s) and a narrow component (FWHM leq 150 km/s). While the broad component is characterized by a low ionization level (with particular ly weak HeII$lambda$4686 emission) and is spatially associated with the radio lobe, the narrow component is characterized by a higher ionization level and extends well beyond the radio lobe. Crucially, we measure a higher electron temperature for the broad component (T sim 30,000 K) than for the narrow component (T sim 15,000 K). The general line ratios and physical conditions of the two components are consistent with a model in which the broad component r epresents gas cooling behind the shock front driven by the radio jets, while the narrow component represents the AGN- or shock-photoionized precursor gas. However, uncertainties remain about the gas acceleration mechanism behind the shock front: unless the radio components are expanding unusually fast in this source, it is likely that entrainment of the warm clouds in the hot post-shock wind or radio plasma is required. The similarities between the kinematic properties of PKS2250-41 and some high redshift radio galaxies suggest that the ambient and the shocked gas have also been resolved in the more distant objects. Given the evidence that the emission line processes are affected by the interactions between the radio and the optical structures, care must be taken when interpreting the UV spectra of high redshift radio galaxies.
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