Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-04-06
Astrophys.J. 610 (2004) 201-212
Astronomy and Astrophysics
Astrophysics
36 pages, including 9 figures. Accepted for publication in Astrophys. J
Scientific paper
10.1086/421546
We have obtained high resolution Echelle spectra (R = 30,000-50,000) of the Na D absorption doublet (5890A, 5896A) for six dwarf starburst galaxies and two more luminous starbursts: M82 and NGC 1614. The absorption features were separated into multiple components and separated into stellar and interstellar parts based on kinematics. We find that three of the dwarfs show outflows, with an average blueshift of 27 km/s. This is small compared to the highest velocity components in NGC 1614 and M82 (blueshifted by 150 km/s and 91 km/s, respectively); these two brighter galaxies also show more complex absorption profiles than the dwarfs. None of the outflow speeds clearly exceed the escape velocity of the host galaxy. Sightlines in NGC 2363 and NGC4214 apparently intersect expanding shells. We compare the shocked gas velocity (v_NaD) to the ionized gas velocity (v_Halpha) and interpret the velocity difference as either a trapped ionization front (NGC 4214) or a leaky HII region (NGC 2363). The dwarfs show N(NaD) = 10^(11.8-13.7) cm^-2, while the Na D columns in M82 and NGC 1614 are 10^13.7 cm^-2 and 10^14.0 cm^-2, respectively. The mass of expelled gas is highly sensitive to outflow geometry, dust depletion, and ionization fraction, but with a simple shell model we estimate neutral outflow gas masses from ~10^6 M_solar to ~10^10 M_solar.
Martin Crystal L.
Schwartz Colleen M.
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