Detection of the H92<i>α</i>recombination line from NGC 4945

Roy, A. L.; Oosterloo, Thomas; Goss, W. M.; Anantharamaiah, K. R.

doi:10.1051/0004-6361/200913926

Cited by 14 publications

(8 citation statements)

References 35 publications

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“…′′ 45 (≈45 pc) and with a rotation velocity of 140 km s −1 we obtain with equation (1) of Mauersberger et al (1996;η = 1) an enclosed mass of M 2.45 = 2.1 × 10 8 M ⊙ with an estimated error of 10%, in good agreement with Cunningham & Whiteoak (2005). For comparison, Roy et al (2010) obtain with the H92α line 3×10 7 M ⊙ for the mass inside a radius of 1 ′′ (≈19 pc). Furthermore, we note that the nuclear region is slightly lopsided: The center of the line connecting the two outer peaks of line width is located ≈1 .…”

Section: Inclinationssupporting

confidence: 80%

Molecular line emission in NGC 4945, imaged with ALMA

Henkel

Mühle

Bendo

et al. 2018

A&A

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NGC 4945 is one of the nearest (D≈3.8 Mpc; 1 ′′ ≈ 19 pc) starburst galaxies. To investigate structure, dynamics, and composition of its dense nuclear gas, ALMA band 3 (λ≈3-4 mm) observations were carried out with ≈2 ′′ resolution. Measured were three HCN and two HCO + isotopologues, CS, C3H2, SiO, HCO, and CH3C2H. Spectral line imaging demonstrates the presence of a rotating nuclear disk of projected size 10 ′′ ×2 ′′ reaching out to a galactocentric radius of r≈100 pc with position angle PA = 45 • ±2 • , inclination i = 75 • ±2 • and an unresolved bright central core of size < ∼ 2 ′′ . The continuum source, representing mostly free-free radiation from star forming regions, is more compact than the nuclear disk by a linear factor of two but shows the same position angle and is centered 0 . ′′ 39 ± 0 . ′′ 14 northeast of the nuclear accretion disk defined by H2O maser emission. Near the systemic velocity but outside the nuclear disk, both HCN J=1→0 and CS J=2→1 delineate molecular arms of length > ∼ 15 ′′ ( > ∼ 285 pc) on opposite sides of the dynamical center. These are connected by a (deprojected) ≈0.6 kpc sized molecular bridge, likely a dense gaseous bar seen almost ends-on, shifting gas from the front and back side into the nuclear disk. Modeling this nuclear disk located farther inside (r < ∼ 100 pc) with tilted rings provides a good fit by inferring a coplanar outflow reaching a characteristic deprojectd velocity of ≈50 km s −1 . All our molecular lines, with the notable exception of CH3C2H, show significant absorption near the systemic velocity (≈571 km s −1 ), within a range of ≈500 -660 km s −1 . Apparently, only molecular transitions with low critical H2-density (ncrit < ∼ 10 4 cm −3 ) do not show absorption. The velocity field of the nuclear disk, derived from CH3C2H, provides evidence for rigid rotation in the inner few arcseconds and a dynamical mass of Mtot = (2.1±0.2) × 10 8 M⊙ inside a galactocentric radius of 2 .′′ 45 (≈45 pc), with a significantly flattened rotation curve farther out. Velocity integrated line intensity maps with most pronounced absorption show molecular peak positions up to ≈1 .′′ 5 (≈30 pc) southwest of the continuum peak, presumably due to absorption, which appears to be most severe slightly northeast of the nuclear maser disk. A nitrogen isotope ratio of 14 N/ 15 N ≈ 200-450 is estimated. This range of values is much higher then previously reported on a tentative basis. Therefore, with 15 N being less abundant than expected, the question for strong 15 N enrichment by massive star ejecta in starbursts still remains to be settled.

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Section: Inclinationssupporting

confidence: 80%

Molecular line emission in NGC 4945, imaged with ALMA

Henkel

Mühle

Bendo

et al. 2018

A&A

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“…On the other hand, Bendo et al (2016) analyzed the continuum emission at 85.69 GHz ad the H42α emission line deriving comparable size (∼7 ×1.7 ) with those measured by previous works at similar frequencies and emission lines (Ott et al 2001;Cunningham & Whiteoak 2005;Roy et al 2010). They support the hypothesis that if the gas around the nucleus would be photoionized by the AGN they would expect to see a central peak excess in their exponential disk model (with scale length of 2.1 ).…”

Section: Dust Heatingsupporting

confidence: 72%

The multi-phase ISM in the nearby composite AGN-SB galaxy NGC 4945: large (parsecs) scale mechanical heating

Bellocchi,

Martín-Pintado,

Güsten

et al. 2020

Preprint

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Context. Understanding the dominant heating mechanism in the nuclei of galaxies is crucial to understand star formation in starbursts (SB), active galactic nuclei (AGN) phenomena and the relationship between the star formation and AGN activity in galaxies. The analysis of the carbon monoxide ( 12 CO) rotational ladder versus the infrared continuum emission (hereafter, 12 CO/IR) in galaxies with different type of activity have shown important differences between them. Aims. We aim at carrying 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 by a multi-transitions analysis of the spatial distribution of the 12 CO 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 ( 200 pc). Methods. We present far-infrared (FIR) and sub-millimeter (sub-mm) 12 CO line maps and single spectra (from Jup = 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 12 CO/IR flux ratios and the local thermodynamic equilibrium (LTE) analysis of the 12 CO images to derive the thermal structure of the Interstellar Medium (ISM) for spatial scales raging from 200 pc to 2 kpc. In addition, we also present single spectra of low ( 12 CO, 13 CO and [CI]) and high density (HCN, HNC, HCO + , CS and CH) molecular gas tracers obtained with APEX and HIFI applying LTE and non-LTE analyses. Furthermore, the Spectral Energy Distribution (SED) of the continuum emission from the far-IR to sub-mm wavelengths is also presented. Results. From the non-LTE analysis of the low and high density tracers we derive in NGC 4945 gas volume densities (10 3 -10 6 cm −3 ) similar to those found in other galaxies with different type of activity. From the 12 CO analysis we found clear trend in the distribution of the derived temperatures and the 12 CO/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 ( 200 pc-360 pc, or ∼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 12 CO 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 ( 5 ) from the center of the galaxy. This result is further supported by the Kazandjian et al. ( 2015) models, which are able to reproduce the emission observed at high-J (PACS) 12 CO transitions when mechanical heating mechanisms are included. Shocks and/or turbulence are likely produced by the barred potential and the ou...

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“…On the other hand, Bendo et al (2016) analyzed the continuum emission at 85.69 GHz and the H42α emission line deriving a comparable size (∼7 × 1.7 ) to those measured by previous works at similar frequencies and emission lines (Ott et al 2001;Cunningham & Whiteoak 2005;Roy et al 2010). Bendo et al (2016) support the hypothesis that if the gas around the nucleus were photoionized by the AGN then they would expect to see a central peak excess in their exponential disk model (with scale length of 2.1 ).…”

Section: Dust Heatingsupporting

confidence: 65%

The multi-phase ISM in the nearby composite AGN-SB galaxy NGC 4945: large-scale (parsecs) mechanical heating

Bellocchi

Martı́n-Pintado

Güsten

et al. 2020

A&A

View full text Add to dashboard Cite

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 (12CO) rotational ladder versus the infrared continuum emission (hereafter, 12CO/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 12CO 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 (≲200 pc). Methods. We present far-infrared (FIR) and sub-millimeter (sub-mm) 12CO line maps and single spectra (from Jup = 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 12CO/IR flux ratios and the local thermodynamic equilibrium (LTE) analysis of the 12CO images to derive the thermal structure of the interstellar medium (ISM) for spatial scales raging from ≲200 pc to 2 kpc. In addition, we also present single spectra of low- (12CO, 13CO 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 (103–106 cm−3) for NGC 4945 that are similar to those found in other galaxies with different types of activity. From the 12CO analysis we find a clear trend in the distribution of the derived temperatures and the 12CO/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 (≲200 pc–360 pc, or ∼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 12CO 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 (≳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) 12CO 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.

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Detection of the H92αrecombination line from NGC 4945

Cited by 14 publications

References 35 publications

Molecular line emission in NGC 4945, imaged with ALMA

Molecular line emission in NGC 4945, imaged with ALMA

The multi-phase ISM in the nearby composite AGN-SB galaxy NGC 4945: large (parsecs) scale mechanical heating

The multi-phase ISM in the nearby composite AGN-SB galaxy NGC 4945: large-scale (parsecs) mechanical heating

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