ALMA CO and VLT/SINFONI H₂observations of the Antennae overlap region: mass and energy dissipation

Abstract

We present an analysis of super-giant molecular complexes (SGMCs) in the overlap region of the Antennae galaxy merger, based on ALMA CO(3−2) interferometry and VLT/SINFONI imaging spectroscopy of H 2 1−0 S(1) at angular resolutions of 0.9 and 0.7 , respectively. All but one SGMC have multiple velocity components offset from each other by up to 150 km s −1 . H 2 line emission is found in all SGMCs and the kinematics of H 2 and CO are well matched. H 2 /CO line ratios vary by up to a factor of 10 among SGMCs and different velocity components of the same SGMCs. We also identify the CO counterpart of a bright, compact source of near-IR H 2 line emission, which shows no Brγ, and was first identified with SINFONI. This source has the highest H 2 /CO line ratio, and coincides with the steepest CO velocity gradient of the entire overlap region. With a size of 50 pc and a virial mass of a few 10 7 M it is perhaps a pre-cluster cloud that has not yet formed significant numbers of massive stars. We present observational evidence that the H 2 emission is powered by shocks, and demonstrate how the H 2 1−0 S(1) and the CO(3−2) lines can be used as tracers of energy dissipation and gas mass, respectively. The variations in the H 2 /CO line ratio may indicate that the SGMCs are dissipating their turbulent kinetic energy at different rates. The compact source could represent a short (∼1 Myr) evolutionary stage in the early formation of super-star clusters.

Alma Observations of the Antennae Galaxies. I. A New Window on a Prototypical Merger

“…For this reason, the designation for this region is Stage 1 (protocluster). Herrera et al (2012) find a high H2/CO line ratio in this region, supporting the interpretation as a protocluster. See Johnson et al (2014) for a more detailed discussion of the Firecracker.…”

“…The SV CO(2-1) data revealed a previously unidentified molecular gas arm (Espada et al 2012), and the SV CO(3-2) data were able to resolve molecular structures at a level not previously possible (Herrera et al 2012). In particular, Herrera et al (2011Herrera et al ( , 2012 note the presence of a luminous and compact CO source in the "overlap" region of the Antennae that has strong H 2 emission associated with it, and they hypothesize that it may be a progenitor to a super star cluster. The new Cycle 0 ALMA observations reported here, with ≈0.…”

The Scaling Relations and Star Formation Laws of Mini-Starburst Complexes

“…These processes are supported by externally induced pressure such as shocks, galactic disk gravitational instability or colliding flow (Vazquez-Semadeni et al 1996;Bonnell et al 2013). Therefore, mini-starburst MCCs are often found at highly dynamics regions such as the overlapping regions in Antennae galaxy (Herrera et al 2012;Fukui et al 2014) or at the end of the Galactic Bar (Nguyen Luong et al 2011b). Simulation of molecular cloud evolution in a galaxy also agrees with this view by showing that MCCs are concentrated mostly in the Bar or spiral arms, and have high SFR (Fujimoto et al 2014).…”

“…They are the birthplaces of massive OB stars and Young Massive Clusters (YMCs), thus are important in maintaining the chemical, energy, and mass balance of hosting galaxies (Bressert et al 2012). This is especially true for starburst galaxies such as the Antennae merger system, which undergoes starburst events and contains many YMCs and mini-starburst MCCs (Herrera et al 2012;Whitmore et al 2014).…”

Maser observations with new instruments

“…Eight science verification datasets and one datum have now been released. Several publications based on Science Verification data have been published, though none has yet dealt with maser science (Herrera et al 2012, Oberg et al 2012). The datasets released so far include:…”