2018A&A...615A.155H


Query : 2018A&A...615A.155H

2018A&A...615A.155H - Astronomy and Astrophysics, volume 615A, 155-155 (2018/7-1)

Molecular line emission in NGC 4945, imaged with ALMA.

HENKEL C., MUHLE S., BENDO G., JOZSA G.I.G., GONG Y., VITI S., AALTO S., COMBES F., GARCIA-BURILLO S., HUNT L.K., MANGUM J., MARTIN S., MULLER S., OTT J., VAN DER WERF P., MALAWI A.A., ISMAIL H., ALKHUJA E., ASIRI H.M., ALADRO R., ALVES F., AO Y., BAAN W.A., COSTAGLIOLA F., FULLER G., GREENE J., IMPELLIZZERI C.M.V., KAMALI F., KLESSEN R.S., MAUERSBERGER R., TANG X.D., TRISTRAM K., WANG M. and ZHANG J.S.

Abstract (from CDS):

NGC 4945 is one of the nearest (D~=3.8Mpc; 1''~=19pc) starburst galaxies. To investigate the structure, dynamics, and composition of the dense nuclear gas of this galaxy, ALMA band 3 (λ~=3-4 mm) observations were carried out with ~=2'' resolution. Three HCN and two HCO+ isotopologues, CS, C3H2, SiO, HCO, and CH3C2H were measured. Spectral line imaging demonstrates the presence of a rotating nuclear disk of projected size 10''x2'' reaching out to a galactocentric radius of r~=100pc 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'' (≥285pc) on opposite sides of the dynamical center. These are connected by a (deprojected) ~=0.6kpc 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≤100pc) with tilted rings provides a good fit by inferring a coplanar outflow reaching a characteristic deprojected velocity of ~=50km/s. All our molecular lines, with the notable exception of CH3 C2H, show significant absorption near the systemic velocity (~=571km/s), within the range ~=500-660km/s. Apparently, only molecular transitions with low critical H2 density (ncrit≤104cm–3) do not show absorption. The velocity field of the nuclear disk, derived from CH3 C2H, provides evidence for rigid rotation in the inner few arcseconds and a dynamical mass of Mtot=(2.1±0.2)x108M inside a galactocentric radius of 2.45" (~=45pc), 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" (~=30pc) 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 14N/15N~=200-450 is estimated. This range of values is much higher then previously reported on a tentative basis. Therefore, because 15N is less abundant than expected, the question for strong 15N enrichment by massive star ejecta in starbursts still remains to be settled.

Abstract Copyright: © ESO 2018

Journal keyword(s): galaxies: starburst - galaxies: structure - galaxies: ISM - nuclear reactions, nucleosynthesis, abundances - galaxies: individual: NGC4945 - radio lines: ISM

Simbad objects: 15

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Number of rows : 15
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NGC 253 SyG 00 47 33.134 -25 17 19.68   8.03   6.94 8.1 ~ 3148 2
2 M 33 GiG 01 33 50.8965749232 +30 39 36.630403128 6.17 6.27 5.72     ~ 5523 1
3 M 77 GiP 02 42 40.7091669408 -00 00 47.859690204 9.70 9.61 8.87 10.1 9.9 ~ 4348 2
4 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6367 1
5 QSO B1104-445 QSO 11 07 08.6939907024 -44 49 07.618243620   17.84 18.2 17.37   ~ 214 1
6 ICRF J124828.4-455947 QSO 12 48 28.4950346640 -45 59 47.176505592   17.24   22.76   ~ 33 1
7 Mrk 231 Sy1 12 56 14.2341182928 +56 52 25.238373852   14.68 13.84     ~ 1906 3
8 NGC 4945 Sy2 13 05 27.279 -49 28 04.44   9.31 14.40 7.55   ~ 1375 2
9 NAME Centaurus A Sy2 13 25 27.6039817176 -43 01 09.493008456   8.18 6.84 6.66   ~ 4262 3
10 M 51 GiP 13 29 52.698 +47 11 42.93   9.26 8.36 8.40   ~ 4098 4
11 NAME NGC 5236 Group GrG 13 37 06 -29 51.9           ~ 61 0
12 QSO B1424-41 QSO 14 27 56.2977548952 -42 06 19.437654096   18.48 17.7 16.30   ~ 432 1
13 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2835 4
14 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13080 0
15 NAME Local Group GrG ~ ~           ~ 7713 0

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2022.08.08-03:34:18

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