Universität zu Köln

Bellocchi, E., Martin-Pintado, J., Guesten, R., Requena-Torres, M. A., Harris, A., van der Werf, P. P., Israel, F. P., Weiss, A., Kramer, C., Garcia-Burillo, S. and Stutzki, J. (2020). The multi-phase ISM in the nearby composite AGN-SB galaxy NGC 4945: large-scale (parsecs) mechanical heating. Astron. Astrophys., 642. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Understanding the dominant heating mechanism in the nuclei of galaxies is crucial to understanding star formation in starbursts (SBs), active galactic nuclei (AGN) phenomena, and the relationship between star formation and AGN activity in galaxies. Analysis of the carbon monoxide ((CO)-C-12) rotational ladder versus the infrared continuum emission (hereafter, (CO)-C-12/IR) in galaxies with different types of activity reveals important differences between them.Aims. We aim to carry out a comprehensive study of the nearby composite AGN-SB galaxy, NGC 4945, using spectroscopic and photometric data from the Herschel satellite. In particular, we want to characterize the thermal structure in this galaxy using a multi-transition analysis of the spatial distribution of the (CO)-C-12 emission at different spatial scales. We also want to establish the dominant heating mechanism at work in the inner region of this object at smaller spatial scales (less than or similar to 200 pc).Methods. We present far-infrared (FIR) and sub-millimeter (sub-mm) (CO)-C-12 line maps and single spectra (from J(up) = 3 to 20) using the Heterodyne Instrument for the Far Infrared (HIFI), the Photoconductor Array Camera and Spectrometer (PACS), and the Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, and the Atacama Pathfinder EXperiment (APEX). We combined the (CO)-C-12/IR flux ratios and the local thermodynamic equilibrium (LTE) analysis of the (CO)-C-12 images to derive the thermal structure of the interstellar medium (ISM) for spatial scales raging from less than or similar to 200 pc to 2 kpc. In addition, we also present single spectra of low- ((CO)-C-12, (CO)-C-13 and [CI]) and high-density (HCN, HNC, HCO+, CS and CH) molecular gas tracers obtained with APEX and HIFI applying LTE and non-LTE (NLTE) analyses. Furthermore, the spectral energy distribution of the continuum emission from the FIR to sub-mm wavelengths is also presented.Results. From the NLTE analysis of the low- and high-density tracers, we derive gas volume densities (10(3)-10(6) cm(-3)) for NGC 4945 that are similar to those found in other galaxies with different types of activity. From the (CO)-C-12 analysis we find a clear trend in the distribution of the derived temperatures and the (CO)-C-12/IR ratios. It is remarkable that at intermediate scales (360 pc-1 kpc, or 19 ''-57 '') we see large temperatures in the direction of the X-ray outflow while at smaller scales (less than or similar to 200 pc-360 pc, or similar to 9 ''-19 ''), the highest temperature, derived from the high-J lines, is not found toward the nucleus but toward the galaxy plane. The thermal structure derived from the (CO)-C-12 multi-transition analysis suggests that mechanical heating, like shocks or turbulence, dominates the heating of the ISM in the nucleus of NGC4945 located beyond 100 pc (greater than or similar to 5 '') from the center of the galaxy. This result is further supported by published models, which are able to reproduce the emission observed at high-J (PACS) (CO)-C-12 transitions when mechanical heating mechanisms are included. Shocks and/or turbulence are likely produced by the barred potential and the outflow observed in X-rays.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Bellocchi, E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Martin-Pintado, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Guesten, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Requena-Torres, M. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Harris, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED van der Werf, P. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Israel, F. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Weiss, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kramer, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Garcia-Burillo, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutzki, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-314836
DOI:	10.1051/0004-6361/202037782
Journal or Publication Title:	Astron. Astrophys.
Volume:	642
Date:	2020
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language MOLECULAR GAS; SEYFERT-GALAXY; MASER EMISSION; STAR-FORMATION; STARBURST; SPECTROSCOPY; SUBMILLIMETER; NUCLEUS; MILLIMETER; RESOLUTION Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/31483