Multiple-line study of molecular gas in spiral galaxy NGC 2903

Authors : Selçuk TOPAL

Pages : 706-720

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Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :Multiple molecular lines with radiative transfer modeling are a powerful tool to probe the physics of starforming gas in galaxies. We investigate the gas properties in the center of spiral galaxy NGC 2903 using low- J CO lines, i.e. 12 COinsert ignore into journalissuearticles values(1-0);, 12 COinsert ignore into journalissuearticles values(2-1);, 12 COinsert ignore into journalissuearticles values(3-2);, 13 COinsert ignore into journalissuearticles values(1-0);, and HCNinsert ignore into journalissuearticles values(1-0);. We apply a nonlocal thermodynamic equilibrium radiative transfer code to derive beam-averaged molecular gas properties. We use two methods insert ignore into journalissuearticles values(i.e. X 2 minimization and likelihood); to define the best model representing the observed line ratios best. The line ratio diagnostics suggest that CO gas in the center of NGC 2903 is thinner and the dense gas fraction is similar compared to that of spirals, starbursts, and early-type galaxies insert ignore into journalissuearticles values(ETGs);, while the gas in the center of the galaxy is warmer than that of ETGs and colder than that of starbursts. Based on the best-fitting model results, we find that the beam-averaged gas kinetic temperature is T K = 20 K, H 2 volume number density is loginsert ignore into journalissuearticles values( n insert ignore into journalissuearticles values(H 2 );); = 4.2 cm -3 , and CO column number density is loginsert ignore into journalissuearticles values( N insert ignore into journalissuearticles values(CO);); = 19.0 cm -2 in the center of NGC 2903. Both methods, i.e. the line ratio diagnostics and modeling, indicate an ISM in the center of NGC 2903 having intermediate temperature and star formation activity insert ignore into journalissuearticles values(also supported by star formation rates);, thinner CO gas with similar dense gas fraction, and higher H2 volume number density compared to that of spirals, ETGs, and starbursts.
Keywords : Molecular gas, star formation, galaxies, spirals, early types, starbursts