Embedded star formation in the extended narrow line region of Centaurus A: Extreme mixing observed by MUSE

Santoro, Francesco; Oonk, J. B. R.; Morganti, Raffaella; Oosterloo, Thomas; Tadhunter, C. N.

doi:10.1051/0004-6361/201628353

Cited by 40 publications

(43 citation statements)

References 33 publications

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“…We find a similar situation in many blue compact dwarfs, which show recent clustered star formation even in very isolated locations after a long period of quiescence (Fuse et al 2012). We also mention the possibility of "jet-induced star formation" that has been discussed, for example to explain the existence of a young stellar population near Centaurus A at a galactocentric distance of 15 kpc (Mould et al 2000;Santoro et al 2016;Salomé et al 2016). In that case the age of SH2 would indicate the epoch of the last nuclear activity in NGC1316.…”

Section: Possible Formation and Evolution Of Sh2supporting

confidence: 77%

The globular cluster system of NGC 1316

Richtler

Hilker

Puzia

et al. 2017

A&A

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Context. The light of the merger remnant NGC 1316 (Fornax A) is dominated by old and intermediate-age stars. The only sign of current star formation in this big galaxy is the HII region SH2, an isolated star cluster complex with a ring-like morphology and an estimated age of 0.1 Gyr at a galactocentric distance of about 35 kpc. A nearby intermediate-age globular cluster, surrounded by weak line emission and a few more young star clusters, is kinematically associated. The origin of this complex is enigmatic. Aims. We want to investigate the nature of this star cluster complex. The nebular emission lines permit a metallicity determination which can discriminate between a dwarf galaxy or other possible precursors. Methods. We used the Integrated Field Unit (IFU) of the VIMOS instrument at the Very Large Telescope of the European Southern Observatory in high dispersion mode to study the morphology, kinematics, and metallicity employing line maps, velocity maps, and line diagnostics of a few characteristic spectra. Results. The line ratios of different spectra vary, indicating highly structured HII regions, but define a locus of uniform metallicity. The strong-line diagnostic diagrams and empirical calibrations point to a nearly solar or even super-solar oxygen abundance. The velocity dispersion of the gas is highest in the region offset from the bright clusters. Star formation may be active on a low level. There is evidence for a large-scale disk-like structure in the region of SH2, which would make the similar radial velocity of the nearby globular cluster easier to understand. Conclusions. The high metallicity does not fit to a dwarf galaxy as progenitor. We favour the scenario of a free-floating gaseous complex having its origin in the merger 2 Gyr ago. Over a long period the densities increased secularly until finally the threshold for star formation was reached. SH2 illustrates how massive star clusters can form outside starbursts and without a considerable field population.

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Section: Possible Formation and Evolution Of Sh2supporting

confidence: 77%

The globular cluster system of NGC 1316

Richtler

Hilker

Puzia

et al. 2017

A&A

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“…The structures covered by the MUSE field of views are mostly excited by energy injection from the radio jet or shocks. The small inclusion excited by star formation claimed by Santoro et al (2016) is spatially coincident with one CO structure.…”

Section: Excitation Of the Cloudsmentioning

confidence: 65%

“…a well-defined knotty filament and a more diffuse structure, as highlighted by optical excitation lines (VIMOS and MUSE;Santoro et al 2015a,b;Hamer et al 2015). Recently Santoro et al (2016) identified a star-forming cloud in the MUSE data that contains several HII regions. Some of these regions are currently forming stars, whereas star formation seems to have recently stopped in the others.…”

Section: Introductionmentioning

confidence: 99%

Inefficient jet-induced star formation in Centaurus A

Salomé

Miville-Deschênes

et al. 2017

A&A

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NGC 5128 (Centaurus A) is one of the best targets to study AGN feedback in the local Universe. At 13.5 kpc from the galaxy, optical filaments with recent star formation lie along the radio jet direction. This region is a testbed for positive feedback, here through jet-induced star formation. Atacama Pathfinder EXperiment (APEX) observations have revealed strong CO emission in star-forming regions and in regions with no detected tracers of star formation activity. In cases where star formation is observed, this activity appears to be inefficient compared to the Kennicutt-Schmidt relation. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map the 12 CO(1-0) emission all along the filaments of NGC 5128 at a resolution of 1.3 ∼ 23.8 pc. We find that the CO emission is clumpy and is distributed in two main structures: (i) the Horseshoe complex, located outside the HI cloud, where gas is mostly excited by shocks and where no star formation is observed, and (ii) the Vertical filament, located at the edge of the HI shell, which is a region of moderate star formation. We identified 140 molecular clouds using a clustering method applied to the CO data cube. A statistical study reveals that these clouds have very similar physical properties, such as size, velocity dispersion, and mass, as in the inner Milky Way. However, the range of radius available with the present ALMA observations does not enable us to investigate whether or not the clouds follow the Larson relation. The large virial parameter α vir of the clouds suggests that gravity is not dominant and clouds are not gravitationally unstable. Finally, the total energy injection in the northern filaments of Centaurus A is of the same order as in the inner part of the Milky Way. The strong CO emission detected in the northern filaments is an indication that the energy injected by the jet acts positively in the formation of dense molecular gas. The relatively high virial parameter of the molecular clouds suggests that the injected kinetic energy is too strong for star formation to be efficient. This is particularly the case in the horseshoe complex, where the virial parameter is the largest and where strong CO is detected with no associated star formation. This is the first evidence of AGN positive feedback in the sense of forming molecular gas through shocks, associated with low star formation efficiency due to turbulence injection by the interaction with the radio jet.

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“…The MUSE data reveal three morphologically and kinematically distinct components in the ionised gas, which are thought to correspond to different stages in the jet-cloud interaction. The data also show that, overall, the ionisation of the gas is due to ionising photons from the AGN, but that locally star formation also plays a role (Santoro et al 2016). Interestingly, the rate at which the available gas reservoir is turned into stars is low, possibly connected to increased turbulence powered by injection Table 1) on the GALEX FUV image of the outer filament (Neff et al 2015).…”

Section: Special Region: the Outer Filamentmentioning

confidence: 79%

The missing link: Tracing molecular gas in the outer filament of Centaurus A

Morganti

Oosterloo

Oonk

et al. 2016

A&A

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We report the detection, using observations of the CO(2−1) line performed with the Atacama Pathfinder EXperiment (APEX), of molecular gas in the region of the outer filament of Centaurus A, a complex region known to show various signatures of an interaction between the radio jet, an H i cloud, and ionised gas filaments. We detect CO(2−1) at all observed locations, which were selected to represent regions with very different physical conditions. The H 2 masses of the detections range between 0.2 × 10 6 and 1.1 × 10 6 M , for conservative choices of the CO to H 2 conversion factor. Surprisingly, the stronger detections are not coincident with the H i cloud, but instead are in the region of the ionised filaments. We also find variations in the widths of the CO(2−1) lines throughout the region, with broader lines in the region of the ionised gas, i.e. where the jet-cloud interaction is strongest, and with narrow profiles in the H i cloud. This may indicate that the molecular gas in the region of the ionised gas has the momentum of the jet-cloud interaction encoded in it, in the same way as the ionised gas does. These molecular clouds may therefore be the result of very efficient cooling of the down-stream gas photo-or shock-ionised by the interaction. On the other hand, the molecular clouds with narrower profiles, which are closer to or inside the H i cloud, could be pre-existing cold H 2 cores which manage to survive the effects of the passing jet.

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Embedded star formation in the extended narrow line region of Centaurus A: Extreme mixing observed by MUSE

Cited by 40 publications

References 33 publications

The globular cluster system of NGC 1316

The globular cluster system of NGC 1316

Inefficient jet-induced star formation in Centaurus A

The missing link: Tracing molecular gas in the outer filament of Centaurus A

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