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 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:
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RA (2000) DE Designation(s)
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13 25 27.62 -43 01 08.8 Cen A = NGC 5128
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File Summary:
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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
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See also:
J/A+A/595/A65 : APEX spectra of Centaurus A (Salome+, 2016)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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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 Jy.km/s SCODv Total integrated emission of the cloud
(SCODV)
86- 94 E9.4 K.km/s.pc2 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)
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Acknowledgements:
Quentin Salome, quentin.salome(at)ias.u-psud.fr
(End) Quentin Salome [IAS, France], Patricia Vannier [CDS] 15-Nov-2017