* Astronomy

Quasar 3C249.1
The powerful and distant quasar 3C 249.1 has one of the largest extended emission-line regions (EELRs) known, extending out over tens of kiloparsecs of surrounding space. Astronomers Hai Fu and Alan Stockton of the Institute for Astronomy (University of Hawai'i) recently constructed velocity maps of the gas in the EELR around the quasar (which is at a redshift of z=0.31) using the Gemini Multi-Object Spectrograph's integral field unit (IFU) on Gemini North. Using diagnostic emission-line ratios, they were able to map the electron temperatures and densities of the extended emission gas and study the mechanisms exciting the gas.

The EELR of 3C 249.1 exhibits rather complex global kinematics. Its gas velocities range from -400 to +600 km/sec and some knots have velocity widths as broad as 600 km/sec (FWHM) and greater. The total mass of the EELR (derived from the Hβ luminosity and electron density) of the ionised gas is a staggering 10^9 Msun. Fu and Stockton estimate that the bulk of the kinetic energy associated with the EELR is about 2.5 x 10^57 ergs and the momentum of the moving gas represents about 10^50 dyne-second. A relatively short dynamical timescale of ~10 Myr is inferred for an average gas velocity of 500 km/sec
One process that could be speeding up the gases in the massive EELR is a superwind generated by supernovae. These stellar explosions would be expected in regions where sudden bursts of massive star formation had taken place earlier in the object's history. In the case of quasar 3C 249.1, a maximum star-formation rate (SFR) ~ 30 Msun per year can be derived from various luminosity indicators. However, the observed mass outflow is an order of magnitude larger than the expected mass injection rate from the many supernovae that would result if we had a SFR ~ 30 Msun per year. Hence a collective supernovae-driven flow is energetically insufficient.
Instead, the authors suggest a mechanism in which the EELR outflow is directly driven by the quasar. Radiation from the quasar can, they argue, couple to the surrounding gas via various processes such as electron scattering and photoionisation to accelerate the gas. The input momentum rate from radiation pressure is related to the mass accretion rate of the black hole. The accretion rate describes how much mass and how fast the central supermassive black hole is gobbling the surrounding stars and gas. In the case of 3C 249.1, a mass accretion rate of 2.5 Msun per year would be sufficient to inject enough momentum to the clouds in 10 Myr. Although this is an impressive rate, it is not unrealistic and thus a plausible explanation.

Read more


Title: Integral Field Spectroscopy of the Extended Emission-Line Region of 3C 249.1
Authors: Hai Fu, Alan Stockton (IfA Hawaii)
Comments: Accepted for publication in ApJ. 8 pages including 7 figures

We present Gemini Multiobject Spectrograph integral field spectroscopy of the extended emission-line region associated with quasar 3C 249.1. The kinematics of the ionised gas measured from the (O III) lambda 5007 line is rather complex and cannot be explained globally by a simple dynamical model, but some clouds can be modelled individually as having locally linear velocity gradients. The temperatures of the ionised gas appear uniform (varying from ~12000 to 15000 K), while the densities vary from a few tens to a few hundreds cm^-3. The emission mechanism of all of the emission clouds, as indicated by the line-ratio diagnostics, is consistent both with "shock + precursor" and pure photoionisation models. The total mass of the ionised gas is on the order of 10^9 M_Sun. We estimate the bulk kinetic energy and momentum of the extended emission-line region of 2.5*10^57 ergs and 10^50 dyne s, and a dynamical timescale of ~10 Myr. By comparing the injection rates of kinetic energy and momentum of different galactic wind models with the observation, we argue that the emission-line clouds are most likely a direct result from the feedback of the quasar. We also discuss the nature of the extended X-ray emission surrounding the quasar.

Read more (863kb, PDF)