IGM Emission Observations with the Cosmic Web Imager: I. The Circum-QSO
  Medium of QSO 1549+19, and Evidence for a Filamentary Gas Inflow
  The Palomar Cosmic Web Imager (PCWI), an integral field spectrograph designed
to detect and map low surface brightness emission, has obtained imaging
spectroscopic maps of Ly-alpha from the circum-QSO medium (CQM) of QSO
HS1549+19 at redshift of 2.843. Extensive extended emission is detected from
the CQM, consistent with fluorescent and pumped Ly-alpha produced by the
ionizing and Ly-alpha continuum of the QSO. Many features present in PCWI
spectral images match those detected in narrow-band images. Filamentary
structures with narrow line profiles are detected in several cases as long as
250-400 kpc. One of these is centered at a velocity redshifted with respect to
the systemic velocity, and displays a spatially collimated and kinematically
cold line profile increasing in velocity width approaching the QSO. This
suggests that the filament gas is infalling onto the QSO, perhaps in a cold
accretion flow. Because of the strong ionizing flux, the neutral column density
is low, typically N(HI) is roughly 10E12-10E15/square-cm, and the line center
optical depth is also low (typically tau0 is less than 10), insufficient to
display well-separated double peak emission characteristic of higher line
optical depths. With a simple ionization and cloud model we can very roughly
estimate the total gas mass (log M(gas) equal to 12.5 +/- 0.5) and the total
mass (log M(tot) equal to 13.3+/- 0.5). We can also calculate a kinematic mass
from the total line profile (2x10E13 M(sun)), which agrees with the mass
estimated from the gas emission. The intensity-binned spectrum of the CQM shows
a progression in kinematic properties consistent with heirarchical structure
formation.
