ar X iv : a st ro - p h / 98 04 16 2 v 1 1 6 A pr 1 99 8 [ C II ] Emission From NGC 4038 / 39 ( The “ Antennae ” )

We present observations of NGC 4038/39 in the [C II] 158 µm fine structure line taken with the MPE/UCB Far-infrared Imaging Fabry-Perot Inter-ferometer (FIFI) on the KAO. A fully sampled map of the galaxy pair (without the tidal tails) at 55 ′′ resolution has been obtained. The [C II] emission line is detected from the entire galaxy pair and peaks at the interaction zone. The total [C II] luminosity of the Antennae is L [CII] = 3.7 × 10 8 L ⊙ , which is about 1% of the far-infrared luminosity observed with IRAS. The main part of the [C II] emission probably arises from photodissociation regions (PDRs), and a minor fraction may be emitted from H II regions. A small part of the [C II] emission comes from standard cold neutral medium (CNM); however , for high temperature (T ∼ 100 K) and high density (n H ∼ 200 cm −3) about one third of the observed [C II] emission may originate from CNM. From PDR models we derive densities of the order of ∼ 10 5 cm −3 and far-UV (FUV) intensities of 460χ • , 500χ • , and 240χ • for the PDRs in the interaction zone, NGC 4038, and NGC 4039, respectively. However, PDRs with densities of the order of ∼ 10 2 cm −3 and FUV intensities of the order of ∼ 100χ • could also explain the observed [C II] emission. The minimum masses in the [C II] emitting regions in the interaction zone and the nuclei are a few ×10 7 M ⊙. A comparison with single dish CO observations of the Antennae shows a [C II] to CO intensity ratio at the interaction zone a factor of 2.6 lower than usually observed in starburst galaxies, but still a factor of about 1.3 to 1.4 higher – 2 – than that at the nuclei of NGC 4038/39. Therefore, no global starburst is taking place in the Antennae. [C II] emission arising partly from confined starburst regions and partly from surrounding quiescent clouds could explain the observed [C II] radiation at the interaction zone and the nuclei, though the star formation activity toward the nuclei is lower. Accordingly there are small confined regions with high star formation activity in the interaction zone and with a lower star formation activity in the nuclei. This supports the high density and high FUV intensity for the …