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J/A+A/608/A98       APEX spectra of Centaurus A                 (Salome+, 2017)

Inefficient jet-induced star formation in Centaurus A. High resolution ALMA observations of the northern filaments. Salome Q., Salome P., Miville-Deschenes M.-A., Combes F., Hamer S. <Astron. Astrophys. 608, A98 (2017)> =2017A&A...608A..98S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, radio ; Radio lines Keywords: methods: data analysis - galaxies: individual: Centaurus A - galaxies: evolution - galaxies: interactions - galaxies: star formation - radio lines: galaxies Abstract: NGC 5128 (Centaurus A) is one of the best targets to study AGN feedback in the local Universe. At 13.5kpc 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 12CO(1-0) emission all along the filaments of NGC 5128 at a resolution of 1.3"∼23.8pc. 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 αvir 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. Description: Catalogue of the molecular clouds (140) extracted from the ALMA data. See section 2 for the details. Table of the properties of the molecular clouds. The velocities are relative to Centaurus A (vLSR∼545 km/s). This is the extended version of table A.1. Objects: ---------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------- 13 25 27.62 -43 01 08.8 Cen A = NGC 5128 ---------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file catalog.dat 174 140 Catalogue of the molecular clouds extracted from the ALMA data (from catalogue.fits) catalog.fits 2880 7 Fits version of the catalog clumppro.dat 44 140 Properties of the molecular cloud
See also: J/A+A/595/A65 : APEX spectra of Centaurus A (Salome+, 2016) Byte-by-byte Description of file: catalog.dat
Bytes Format Units Label Explanations
1- 3 I3 --- ID [1/144] Clump sequential number (ID) 5- 13 F9.5 deg RAdeg Right ascension (J2000) (RA) 15- 23 E9.4 deg e_RAdeg rms uncertainty on RAdeg (dRA) 25- 34 F10.5 deg DEdeg Declination (J2000) (Dec) 36- 44 E9.4 deg e_DEdeg rms uncertainty on DEdeg (dDec) 46- 53 F8.4 deg PA Position angle (ANGLE) 55- 57 I3 --- Npix Number of pixels on the sky (NPIXELS) 59- 66 F8.3 km/s Vcent Centroid velocity relative to Cen A (VLSR∼545km/s) (VCENT) 68- 75 F8.5 km/s sigma Veloctiy dispersion (SIGV) 77- 84 F8.6 SCODv Total integrated emission of the cloud (SCODV) 86- 94 E9.4 LCO CO luminosity (LCO) 96-104 E9.4 Msun Mass Hydrogen molecular mass (MASS) 106-116 E11.6 deg+2 Area Angular area (AREA_DEG2) 118-128 E11.6 pc+2 Areapc2 Linear area (AREA_PC2) 130-138 E9.4 deg Major Major axis(LMAX) 140-148 E9.4 deg Minor Minor axis (LMIN) 150-156 F7.4 pc Radius Radius used in the paper (RADIUS) 158-164 F7.4 deg Reff Effective radius from Clumpfind (R_EFF) 166-174 F9.5 Msun/pc+2 SigmaH2 Hydrogen molecular surface density (SIGMA_H2)
Byte-by-byte Description of file: clumppro.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Clump [1/144] Clump sequential number 5- 9 F5.2 pc Radius Radius used in the paper 11- 15 F5.3 SCODv Total integrated emission of the cloud 17- 23 F7.2 km/s vcent Centroid velocity relative to Cen A (VLSR∼545km/s) 25- 29 F5.2 km/s sigma Velocity dispersion 31- 37 E7.3 Msun MH2 Hydrogen molecular mass 39- 44 F6.2 Msun/pc2 SigmaH2 Hydrogen molecular surface density
Acknowledgements: Quentin Salome, quentin.salome(at)
(End) Quentin Salome [IAS, France], Patricia Vannier [CDS] 15-Nov-2017
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