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Astron. Astrophys. 328, 483-492

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Imaging the nuclear environment of NGC 1365
with the Hubble Space Telescope*

Helmuth Kristen1, Steven Jörsäter1, Per Olof Lindblad1, and Alec Boksenberg2

1Stockholm Observatory, S-13336 Saltsjöbaden, Sweden
2Royal Greenwich Observatory, Madingley Road, Cambridge CB3 OEZ, UK

Received 5 February 1996 / Accepted 5 August 1997


The region surrounding the active nucleus of the barred spiral galaxy NGC 1365 is observed in the [O III] $\lambda 5007$ line and neighbouring continuum using the Faint Object Camera (FOC) aboard the Hubble Space Telescope (HST). In the continuum light numerous bright ''super star clusters'' (SSCs) are seen in the nuclear region. They tend to fall on an elongated ring around the nucleus and contribute about 20 % of the total continuum flux in this wavelength regime. Without applying any extinction correction the brightest SSCs have an absolute luminosity $M_{\rm
B}=-14\hbox{$.\!\!^{\rm m}$}1 \pm 0\hbox{$.\!\!^{\rm m}$}3$ and are very compact with radii $R \mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaystyle ... . Complementary ground-based spectroscopy gives an extinction estimate $A_{\rm B} = 2\hbox{$.\!\!^{\rm m}$}5 \pm 0\hbox{$.\!\!^{\rm m}$}5$ towards these regions, indicating a true luminosity $M_{\rm B} = -16\hbox{$.\!\!^{\rm m}$}6 \pm 0\hbox{$.\!\!^{\rm m}$}6$.

The bright compact radio source NGC 1365:A is found to coincide spatially with one of the SSCs. We conclude that it is a ''radio supernova''.

The HST observations resolve the inner structure of the conical outflow previously seen in the [O III] $\lambda 5007$ line in ground-based observations, and reveal a complicated structure of individual emission-line clouds, some of which gather in larger agglomerations. The total luminosity in the [O III] line amounts to $L_{\rm [OIII]} \simeq 3.7\times
10^{40} {\rm erg s^{-1}}$ where about $40 \%$ is emitted by the clouds.

Key words: stars: supernovae: general - galaxies: individual: NGC 1365 - galaxies: nuclei - galaxies: Seyfert - galaxies: star clusters

*Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555, and observations at the European Southern Observatory (ESO), La Silla, Chile.

Send offprint requests to: Helmuth Kristen (helmuth@astro.su.se)

© European Southern Observatory (ESO) 1997

Online publication: November 24, 1997
Last change: March 26, 1998