Cold dust in the giant barred galaxy NGC 1365

Abstract

Constraining the physcial properties of dust requires observations at submm wavelengths. This will provide important insight into the gas content of galaxies. We mapped NGC 1365 at 870 μm with LABOCA, the Large APEX Bolometer Camera, allowing us to probe the central mass concentration as well as the rate at which the gas flows to the center. We obtained the dust physical properties both globally and locally for different locations in the galaxy. A 20 K modified black body represents about 98% of the total dust content of the galaxy, the rest can be represented by a warmer dust component of 40 K. The bar exhibits an east-west asymmetry in the dust distribution: The eastern bar is heavier than the western bar by more than a factor of 4. Integrating the dust spectral energy distribution, we derived a total infrared luminosity, L_(TIR), of 9.8 × 10^(10) L⊙, leading to a dust-enshrouded star formation rate of SFRTIR ≃ 16.7 M⊙ yr^(-1) in NGC 1365. We derived the gas mass from the measurements of the dust emission, resulting in a CO-to-H_2 conversion factor of X_(CO) ≃ 1.2 × 10^(20) mol cm^(-2) (K km s^(-1))^(-1) in the central disk, including the bar. Taking into account the metallicity variation, the central gas mass concentration is only ≃20% at R < 40″ (3.6 kpc). On the other hand, the timescale on which the gas flows into the center, ≃300 Myr, is relatively short. This indicates that the current central mass in NGC 1365 is evolving fast because of the strong bar.