A census of the Carina Nebula - II. Energy budget and global properties of the nebulosity

Abstract

The first paper in this series took a direct census of energy input from the known OB stars in the Carina Nebula, and in this paper we study the global properties of the surrounding nebulosity. This detailed comparison may prove useful for interpreting observations of extragalactic giant H ii regions and ultraluminous infrared (IR) galaxies. We find that the total IR luminosity of Carina is about 1.2 × 107 L⊙, accounting for only about 50–60 per cent of the known stellar luminosity from Paper I. Similarly, the ionizing photon luminosity derived from the integrated radio continuum is about 7 × 1050 s−1, accounting for ∼75 per cent of the expected Lyman continuum from known OB stars. The total kinetic energy of the nebula is about 8 × 1051 erg, or ∼30 per cent of the mechanical energy from stellar winds over the lifetime of the nebula, so there is no need to invoke a supernova (SN) explosion based on energetics. Warm dust grains residing in the H ii region interior dominate emission at 10–30 μm, but cooler grains at 30–40 K dominate the IR luminosity and indicate a likely gas mass of ∼106 M⊙. We find an excellent correlation between the radio continuum and 20–25 μm emission, consistent with the idea that the ∼80‐K grain population is heated by trapped Lyα photons. Similarly, we find a near perfect correlation between the far‐IR optical depth map of cool grains and 8.6‐μm hydrocarbon emission, indicating that most of the nebular mass resides as atomic gas in photodissociation regions and not in dense molecular clouds. Synchronized star formation around the periphery of Carina provides a strong case that star formation here was indeed triggered by stellar winds and ultraviolet radiation. This second generation appears to involve a cascade toward preferentially intermediate‐ and low‐mass stars, but this may soon change when η Carinae and its siblings explode. If the current reservoir of atomic and molecular gas can be tapped at that time, massive star formation may be rejuvenated around the periphery of Carina much as if it were a young version of Gould's Belt. Furthermore, when these multiple SNe occur, the triggered second generation will be pelted repeatedly with SN ejecta bearing short‐lived radioactive nuclides. Carina may therefore represent the most observable analogue to the cradle of our own Solar system.

Herschelfar-infrared observations of the Carina Nebula complex

“…The SED modeling of Smith & Brooks (2007), who used a combination of three discrete blackbody curves with temperatures of 35 K, 80 K, and 220 K suggested a total (dust + gas) mass of ≈962 000 M , slightly higher but still well consistent with our result of ≤890 000 M . The SED model of Salatino et al (2012), which was based on a single temperature component with T = 34.5 K, yielded a total dust + gas mass of ≈950 000 M .…”

“…We constructed the spectral energy distribution (SED) of the above described 1 • radius region (which includes the entire CNC, but excludes the clouds around Gum 31) in the following way: first, we extracted the total fluxes in this region from our Herschel maps and found values of 844 500 Jy in the 70 μm band, 847 200 Jy in the 160 μm band, 374 700 Jy in the 250 μm band, 156 000 Jy in the 350 μm band, and 56 000 Jy in the 500 μm band. For fluxes at shorter wavelengths, we use the MSX and IRAS fluxes in the 8−100 μm range listed in Table 1 in Smith & Brooks (2007), which were derived for a very similar area 7 . Finally, we also added the FIR and mm-band fluxes determined in the recent study by Salatino et al (2012), who also considered the same area as Smith & Brooks (2007).…”

“…For fluxes at shorter wavelengths, we use the MSX and IRAS fluxes in the 8−100 μm range listed in Table 1 in Smith & Brooks (2007), which were derived for a very similar area 7 . Finally, we also added the FIR and mm-band fluxes determined in the recent study by Salatino et al (2012), who also considered the same area as Smith & Brooks (2007). The resulting global SED of the CNC is shown in Fig.…”

“…The CNC contains large amounts of gas and dust clouds, with an estimated total mass in the range 350 000−670 000 M based on CO radio maps (e.g. Grabelsky et al 1988;Yonekura et al 2005;Smith & Brooks 2007). The very strong radiative and wind feedback from the massive stars has already dispersed much of the original cloud mass in the central region, and drives a large expanding superbubble, extending over ∼80 pc (corresponding to ∼2 • ).…”

The isolated neutron star candidate 2XMM J104608.7-594306

“…We note that, in this case, position and velocity are not expected to be correlated. The gas mass in the Carina Nebula is ∼10 6 M (Smith & Brooks 2007) which, for a typical H ii region size of ∼100 pc, implies an average density of ∼10 cm −3 . In fact, as reported by Mizutani et al (2002), two distinct electron density components are detected in a 30 pc area centered on the Carina I and II H ii regions: a high-density (n e ∼ 100−350 cm −3 ) component and an extended low-density (n e < ∼ 100 cm −3 ) component detectable over the entire mapped region.…”