2014A&A...566A..15V


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.10CEST01:38:11

2014A&A...566A..15V - Astronomy and Astrophysics, volume 566A, 15-15 (2014/6-1)

The radio core structure of the luminous infrared galaxy NGC 4418. A young clustered starburst revealed ?

VARENIUS E., CONWAY J.E., MARTI-VIDAL I., AALTO S., BESWICK R., COSTAGLIOLA F. and KLOECKNER H.-R.

Abstract (from CDS):

The galaxy NGC4418 contains one of the most compact obscured nuclei within a luminous infrared galaxy (LIRG) in the nearby Universe. This nucleus contains a rich molecular gas environment and an unusually high ratio of infrared-to-radio luminosity (q-factor). The compact nucleus is powered by either a compact starburst or an active galactic nucleus (AGN). The aim of this study is to constrain the nature of the nuclear region (starburst or AGN) within NGC4418 via very-high-resolution radio imaging. Archival data from radio observations using the European Very Long Baseline Interferometry Network (EVN) and Multi-Element Radio Linked Interferometer Network (MERLIN) interferometers are imaged. Sizes and flux densities are obtained by fitting Gaussian intensity distributions to the image. The average spectral index of the compact radio emission is estimated from measurements at 1.4GHz and 5.0GHz. The nuclear structure of NGC4418 visible with EVN and MERLIN consists of eight compact (<49mas i.e. <8pc) features spread within a region of 250mas, i.e. 41pc. We derive an inverted spectral index α≥0.7 (Sν∝να) for the compact radio emission. Brightness temperatures >104.8K indicate that these compact features cannot be HII-regions. The complex morphology and inverted spectrum of the eight detected compact features is evidence against the hypothesis that an AGN alone is powering the nucleus of NGC4418. The compact features could be super star clusters with intense star formation, and their associated free-free absorption could then naturally explain both their inverted radio spectrum and the low radio-to-IR ratio of the nucleus. The required star formation area density is extreme, however, and close to the limit of what can be observed in a well-mixed thermal/non-thermal plasma produced by star formation, and is also close to the limit of what can be physically sustained.

Abstract Copyright:

Journal keyword(s): galaxies: Seyfert - galaxies: star formation - galaxies: individual: NGC 4418

Simbad objects: 13

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Number of rows : 13

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 M 77 GiP 02 42 40.771 -00 00 47.84 9.70 9.61 8.87 10.1 9.9 ~ 4093 2
2 7C 055201.39+394824.00 QSO 05 55 30.80561150 +39 48 49.1649664     18.0 17.5   ~ 466 2
3 M 82 IG 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 5336 6
4 NGC 3690 IG 11 28 31.326 +58 33 41.80   13.19 12.86     ~ 883 4
5 NGC 4261 LIN 12 19 23.2160630 +05 49 29.700024   13.92 12.87     ~ 1115 0
6 NGC 4355 Sy2 12 26 54.628 -00 52 39.51   14.21 13.37     ~ 405 2
7 3C 273 BLL 12 29 06.6996828061 +02 03 08.598846466   13.05 14.830 14.11   ~ 5320 1
8 4C -02.55 QSO 12 32 00.0157879377 -02 24 04.790684994   17.41 17.06 16.4   ~ 378 1
9 3C 286 Sy1 13 31 08.2885060664 +30 30 32.960825108   17.51 17.25     ~ 3716 1
10 QSO B1404+286 BLL 14 07 00.3933203928 +28 27 14.695133019   16.13 15.35 10.29   ~ 675 2
11 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2683 4
12 NGC 6240 Sy2 16 52 58.861 +02 24 03.55   14.31 13.37     ~ 1481 2
13 ESO 338-4 IG 19 27 58.338 -41 34 30.81   13.55 13.21 13.14 13.43 ~ 210 1

    Equat.    Gal    SGal    Ecl

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2020.07.10-01:38:11

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