Licentiate Seminar: Observations of neutral gas flows in nearby Lyman alpha emitting galaxies
by
Andreas Sandberg(Dept of Astronomy, Stockholm University)
→
Europe/Stockholm
FB55
FB55
Description
The Lyman alpha (Ly α) emission line has grown to become one of the most successful tools for finding galaxies at high redshift. At redshifts corresponding to the early cosmic times of reionization and primeval galaxy formation, the wavelength of Ly α still remains accessible with current instrumentation. Unfortunately, Ly α is a resonance line which undergoes a com- plicated radiative transfer process through the neutral gas inside galaxies which is still not fully understood. The precise distribution and kinematics of stars, gas and dust all seem to affect the amount of Ly α that eventually escapes the galaxy. Studies of nearby Ly α emitting galaxies are therefore an important key to understanding this process in detail.
From previous observations and simulations, it is evident that outflows of neutral gas can facilitate the escape of Ly α photons, as the Doppler effect shifts the frequency out of resonance. In this thesis, we present a study of two known Ly α emitters; Haro 11 and ESO 338-IG 04. We have attempted to measure the velocity of the neutral gas in front of the strongest Ly α emitting and absorbing regions by using the Na D absorption feature as a tracer. By utilizing an integral field unit, we acquire both high spectral and spatial information of our targets. This comprises the first detailed observational study of Na D as a tracer of neutral gas in connection with the Ly α radiative transfer process.
Our results are unexpected; we find no strong correlation between the velocity of neutral gas and Ly α escape, and low covering fractions of gas in all cases, also when Ly α is absorbed. We discuss the possible complications and limitations of Na D as a tracer of the neutral gas, and conclude that the Na D we measure represents only the densest clumps in the ISM. Although we probe structures on a scale of only a few hundred pc, it is likely that the complexity of Ly α emitting and absorbing structures continues on even smaller scales.