Institute for Advanced Study Informal Astrophysics Seminar

Astronomers have exquisite observations of both galaxies (by directly imaging their stars) and of the intergalactic medium (in absorption spectra of background sources). While we know that the galactic baryons must have been accreted from the IGM, we currently have virtually no direct observations of the galaxy assembly process itself. Contrary to the classical picture of galaxy formation in which the accreting gas is shock-heated to the virial temperature of the halo before cooling, recent simulations show that most of the gas is instead accreted in cold streams, with temperatures T~10^4-10^5 K. At these temperatures, the accretion streams will radiate primarily in the Ly-alpha line and may be accessible to current observations. I will present new results combining cosmological hydrodynamical simulations with detailed Ly-alpha radiative transfer, including the expected Ly-alpha luminosities, spectra, and morphologies of the accretion streams. I will discuss whether these streams may have already been detected in the form of extended 'Ly-alpha blobs'.