Two physical regimes for the giant H ii regions and giant molecular clouds in the Antennae galaxies

Abstract

We have combined observations of the Antennae galaxies from the radio interferometer ALMA (Atacama Large Millimeter/submillimeter Array) and from the optical interferometer GHαFaS (Galaxy Hα Fabry-Perot System). The two sets of observations have comparable angular and spectral resolutions, enabling us to identify 142 giant molecular clouds (GMCs) and 303 Hii regions. We have measured, and compared, their basic physical properties (radius, velocity dispersion, luminosity). For the Hii regions, we find two physical regimes, one for masses > 10 5.4 M ⊙ of ionized gas, where the gas density increases with gas mass, the other for masses < 10 5.4 M ⊙ of ionized gas, where the gas density decreases with gas mass. For the GMCs, we find, in contrast to previous studies in other galaxies over a generally lower mass range of clouds, that the gas surface density increases with the radius, hinting at two regimes for these clouds if we consider both sources of data. We also find that the GMC mass function has a break at 10 6.7 M ⊙ . Using the velocity dispersion measurements, we claim that the difference between the regimes is the nature of the dominant binding force. For the regions in the lower mass range, the dominant force is the external pressure, while in the higher mass range it is the internal gravity of the clouds. In the regime where gravity is dominant, the star formation rate, derived from the dust-corrected Hα luminosity, increases super-linearly with the velocity dispersion, and the gas density increases with the gas mass.

Lyman-continuum leakage as dominant source of diffuse ionized gas in the Antennae galaxy

“…3) show strong Hα emission in the disks of the merging galaxies. This is highlighted in panel (a) by the light gray contours and corresponds to the well-known structures detected in previous narrow-band (Whitmore et al 1999;Mengel et al 2005) and Fabry-Perot (Amram et al 1992;Zaragoza-Cardiel et al 2014) observations of the Antennae. However, in the much deeper MUSE data, we also detect faint Hα emission around the central merger, out to the edge of the field covered by the MUSE data.…”

“…To derive the luminosity, we used the reddening-corrected fluxes, computed using the Balmer decrement, and assumed a distance of 22 Mpc (Schweizer et al 2008). For comparison, we plot the LF derived from the table of H ii regions based on GHαFaS Fabry-Perot observations, publicly released by Zaragoza-Cardiel et al (2014) who used the same distance. It is apparent that we detect more regions in the luminosity range log 10 L(Hα) = 36 .…”

“…An important missing piece of information would be a spectroscopic optical mapping of the whole system, ideally at high spatial and spectral resolution, and covering as much of the optical spectral range as possible. Data taken with the GHαFaS instrument presented by Zaragoza-Cardiel et al (2014) were a first step in this direction. They cover the main body of both galaxies at very good spectral resolution (8 km s −1 ).…”

Mass Functions of Giant Molecular Clouds and Young Star Clusters in Six Nearby Galaxies

“…• Antennae: A catalog of 142 GMCs was published by Zaragoza-Cardiel et al (2014), based on ALMA CO(3-2) observations from the ALMA science verification program and project 2011.0.00876.S (PI: B. Whitmore). They assume a value for the CO-to-H 2 (α CO ) conversion factor of 4.8 M (K km s −1 pc 2 ) −1 , and a line ratio between CO(3-2) and CO(1-0) of 1.8.…”

Physical properties of superbubbles in the Antennae galaxies

“…There are also studies of the molecular gas and dust, and their relation to the star clusters (Wilson et al 2000;Nikola et al 1998;Gao et al 2001;Zhu, Seaquist, & Kuno 2003;Wilson et al 2003). In a recent publication (Zaragoza-Cardiel et al 2014) the authors of the present paper have compared the mass functions and the density distributions of the molecular and ionized gas clouds, showing that for both gas phases there are two populations, divided at a critical mass which is comparable for the HII region population and that of the molecular clouds.…”