Bibcode
van der Werf, P. P.; Rosenberg, M.; Schaerer, D.; Martín-Hernández, N. L.; Brandl, B. R.
Bibliographical reference
Astronomy and Astrophysics, Volume 543, id.A61, 16 pp.
Advertised on:
7
2012
Journal
Citations
17
Refereed citations
16
Description
Aims: Approximately 20% of all spiral galaxies display starburst
activity in nuclear rings of a few hundred parsecs in diameter. It is
our main aim to investigate how the starburst ignites and propagates
within the ring, leading to the formation of massive stellar clusters.
Methods: We observed the ring galaxy NGC 7552 with the
mid-infrared (MIR) instrument VISIR at an angular resolution of 0.3
arcsec - 0.4 arcsec and with the near-infrared (NIR) integral-field
spectrograph SINFONI on the VLT, and complement these observations with
data from ISO and Spitzer. Results: The starburst ring is clearly
detected at MIR wavelengths at the location of the dust-extincted, dark
ring seen in HST observations. This "ring", however, is a rather complex
annular region of more than 100 parsec width. We find a large fraction
of diffuse [Ne ii] and PAH emission in the central region that is not
associated with the MIR peaks on spatial scales of ~30 pc. We do not
detect MIR emission from the nucleus of NGC 7552, which is very
prominent at optical and NIR continuum wavelengths. However, we have
identified nine unresolved MIR peaks within the ring. The average
extinction of these peaks is AV = 7.4 and their total
infrared luminosity is LIR = 2.1 × 1010
L&sun;. The properties of these peaks are typical for
MIR-selected massive clusters found in other galaxies. The ages of the
MIR-selected clusters are in the range of 5.9 ± 0.3 Myr. The age
spread among the clusters of 0.8 Myr is small compared to the travel
time of ~5.6 Myr for half an orbit within the starburst ring. We find no
strong evidence for a scenario where the continuous inflow of gas leads
to the ongoing formation of massive clusters at the contact points
between galactic bar and starburst ring. Instead, it appears more likely
that the gas density build up more gradually over larger ring segments,
and that the local physical conditions govern cluster formation. We note
that the fundamental limitation on the accurate derivation of cluster
age, mass and initial mass function slope is the lack of higher angular
resolution. Resolving the highly embedded, massive clusters requires
milli-arcsecond resolution at infrared wavelengths, which will be
provided by the next generation of instruments on extremely large
telescopes (ELTs).
SINFONI data cubes are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/543/A61