Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Michele Perna, Santiago Arribas, Isabella Lamperti, Miguel Pereira-Santaella, Lorenzo Ulivi
| Summary:
Arp 220 is the nearest ULIRG; it shows evidence of 100 pc-scale molecular
outflows likely connected with galaxy-scale outflows traced by ionised and
neutral gas. The two highly obscured nuclei of Arp 220 are the site of intense
star formation, with extreme star-formation rate surface densities (~ 10^3
Msun/yr/kpc2). Despite extensive investigations searching for AGN activity in
the Arp 220 nuclei, direct evidence remains elusive. We present JWST/NIRSpec
IFS observations covering the 0.9 – 5.1 um wavelength range of the innermost
(5”x4”, i.e. 1.8×1.5 kpc) regions of Arp 220. The primary goal is to
investigate the potential presence of AGN signatures in the nuclear regions by
analysing the spectra extracted from circular apertures of radius 55 pc
(0.15”) around each of the two nuclei. We identify ~ 70 ionised and ~ 50
molecular emission lines in the nuclear spectra of Arp 220; we use
recombination line ratios to measure optical extinctions in the range AV ~ 11 –
14 mag. High ionisation lines are not detected, except the [Mg IV] line at 4.49
um which we interpret as due to shocks rather than to AGN ionisation. We
identify broadening and multiple kinematic components in the HI and H2 lines
caused by outflows and shocks, with velocities up to ~ 550 km/s. Significantly
higher velocities (up to ~ 900 km/s) are detected in the off-nuclear regions;
however, they do not conclusively represent evidence for AGN activity. Even
with the unprecedented sensitivity of JWST/NIRSpec IFS, achieving an
unambiguous identification or exclusion of the presence of an AGN in the Arp
220 system remains challenging, because of its extreme dust obscuration.
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