2000A&A...358...95T

Query : 2000A&A...358...95T

2000A&A...358...95T - Astronomy and Astrophysics, volume 35895-103 (2000/6-1)

Radio supernovae, supernova remnants and HII regions in NGC 2146 observed with MERLIN and the VLA.

TARCHI A., NEININGER N., GREVE A., KLEIN U., GARRINGTON S.T., MUXLOW T.W.B., PEDLAR A. and GLENDENNING B.E.

Abstract (from CDS):

We present a high-resolution 5-GHz radio continuum map of the starburst galaxy NGC 2146 made with MERLIN and the VLA (A-array), in a search of radio supernovae and supernova remnants expected to be already produced by the most massive stars in the starburst. At 5GHz, about 20 point sources were detected earlier by Glendenning & Kronberg (1986BAAS...18.1006G) in the central 800pc of NGC 2146. Our observations with higher sensitivity and resolution made with MERLIN and the VLA confirm the detection of 18 sources, and resolve 7 of them. Additional 1.6-GHz MERLIN observations disclose 9 sources coincident in position with those detected at 5GHz, which allows us to derive their spectral indices α1.65, (Sν~να). Only 3 sources have indices (α<0) consistent with synchrotron emission from supernova remnants or radio supernovae, while the others have very steep inverted spectra (α>0). We suggest that the sources with positive spectral index are optically thick ultra-compact and/or ultra-dense HII regions with high electron densities and high emission measures (EM>107cm–6.pc). Minimum energy requirements indicate that these regions may contain up to 1000 equivalent stars of type O6, comparable to the number of stars found in super starclusters. When compared with M 82, the galaxy NGC 2146 lacks however a large number of supernova remnants. We suggest that NGC 2146 is experiencing a burst of star formation stronger than that in M 82, but being in a younger phase. In this phase, only few stars have already exploded, whereas the others cause strong thermal emission from compact, optically thick ionized gas regions, around the young super starclusters. We may, however, not exclude an alternative scenario in which strong free-free absorption at 1.6GHz in foreground ionized gas with very high emission measures (EM>108cm–6.pc) hides a certain number of supernova remnants, thus rendering for some sources the observed inverted spectra.

Abstract Copyright: ∼

Journal keyword(s): ISM: HII regions - ISM: supernova remnants - galaxies: individual: NGC 2146 - galaxies: starburst - radio continuum: ISM

Nomenclature: Table 2: TNG SS.s+SS.s N=18.

Simbad objects: 29

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Number of rows : 29
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 NGC 1808 Sy2 05 07 42.343 -37 30 46.98 11.05 10.80 9.94 9.36 10.2 ~ 756 3
2 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 19090 0
3 7C 055201.39+394824.00 Bla 05 55 30.80561419 +39 48 49.1649683     18.30 17.5   ~ 527 2
4 NVSS J061024+780136 rG 06 10 24.27936963 +78 01 36.1956277           ~ 26 1
5 TNG 35.0+28.0 Rad 06 18 34.96 +78 21 28.0           ~ 1 0
6 TNG 35.3+30.9 Rad 06 18 35.32 +78 21 30.9           ~ 1 0
7 TNG 36.6+27.5 Rad 06 18 36.6 +78 21 28           ~ 2 0
8 TNG 36.8+24.0 Rad 06 18 36.8 +78 21 24           ~ 1 0
9 TNG 37.6+24.2 Rad 06 18 37.60 +78 21 24.0           ~ 3 0
10 TNG 37.7+23.7 Rad 06 18 37.7 +78 21 24           ~ 1 0
11 NGC 2146 AGN 06 18 37.710 +78 21 25.27 11.67 11.38 10.59     ~ 765 2
12 TNG 37.9+23.7 Rad 06 18 37.9 +78 21 24           ~ 1 0
13 TNG 38.1+26.1 Rad 06 18 38.1 +78 21 26           ~ 1 0
14 TNG 38.2+24.3 Rad 06 18 38.2 +78 21 24           ~ 1 0
15 TNG 38.4+23.8 Rad 06 18 38.4 +78 21 24           ~ 1 0
16 TNG 38.6+24.0 Rad 06 18 38.6 +78 21 24           ~ 2 0
17 TNG 38.9+22.5 Rad 06 18 38.90 +78 21 22.0           ~ 2 0
18 TNG 39.0+17.9 Rad 06 18 39.0 +78 21 18           ~ 1 0
19 TNG 39.2+20.7 Rad 06 18 39.2 +78 21 21           ~ 1 0
20 TNG 39.5+17.7 Rad 06 18 39.5 +78 21 18           ~ 1 0
21 TNG 40.2+18.1 Rad 06 18 40.2 +78 21 18           ~ 1 0
22 TNG 41.2+17.3 Rad 06 18 41.2 +78 21 17           ~ 1 0
23 TNG 41.4+15.0 Rad 06 18 41.40 +78 21 15.0           ~ 2 0
24 MCG-04-21-005 AGN 08 36 15.190 -26 24 33.66 12.04 11.93 11.45 11.09 12.3 ~ 600 3
25 M 82 AGN 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 6156 6
26 M 94 SyG 12 50 53.0737971432 +41 07 12.900884628 9.15 8.96 8.24 7.78   ~ 1476 2
27 NGC 5253 rG 13 39 55.990 -31 38 24.11 11.48 10.94 10.49 10.33 13.47 ~ 1421 4
28 Mrk 668 BLL 14 07 00.39441712 +28 27 14.6901341   16.13 15.35 10.29   ~ 826 3
29 NAME Cas A SNR 23 23 26.0 +58 48 41     14.30     ~ 3033 1

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