Intergalactic medium 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 Lyα from the circum-QSO medium (CQM) of QSO HS1549+19 at redshift z = 2.843. Extensive extended emission is detected from the CQM, consistent with fluorescent and pumped Lyα produced by the ionizing and Lyα 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 theQSO. 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(H i) ~ 10¹²-10¹⁵ cm^-2, and the line center optical depth is also low (typically τ₀ < 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 = 12.5 ± 0.5) and the total (log M_tot = 13.3 ± 0.5). We can also calculate a kinematic mass from the total line profile (2 × 10¹³M), 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.