The importance of star formation intensity in Lyα escape from Green Pea galaxies and Lyman Break Galaxy Analogs.
KIM K., MALHOTRA S., RHOADS J.E., BUTLER N.R. and YANG H.
Abstract (from CDS):
We have studied ultraviolet images of 40 Green Pea galaxies and 15 local Lyman Break Galaxy Analogs to understand the relation between Lyα photon escape and central UV photometric properties. We measured star-formation intensity (SFI; star formation rate per unit area) from the central 250 pc region (S250pc) using Cosmic Origins Spectrograph near-ultraviolet images from the Hubble Space Telescope. The measured S250pc of our sample Green Peas ranges from 2.3-46 M☉ yr–1 kpc–2, with a geometric mean of 15 M☉ yr–1 kpc–2 and a standard deviation of 0.266 dex, forming a relatively narrow distribution. The Lyman Break Galaxy Analogs show a similarly narrow distribution of S250pc (0.271 dex), though with a larger mean of 28 M☉ yr–1 kpc–2. We show that while the Lyα equivalent width (EW(Lyα)) and the Lyα escape fraction (fesc^Lyα^) are not significantly correlated with the central SFI (S250pc), both are positively correlated with the ratio of surface brightness to galaxy stellar mass (S_250 pc/Mstar_), with correlation coefficients (p-values) of 0.702 (1 x 10–8) and 0.529 (5 x 10–4) with EW(Lyα) and fesc^Lyα^, respectively. These correlations suggest a scenario where intense central star formation can drive a galactic wind in galaxies with relatively shallow gravitational potential wells, thus clearing channels for the escape of Lyα photons.