Water vapour at high redshift: Arecibo monitoring of the megamaser in MG J0414+0534

Abstract

Aims. The study of water masers at cosmological distances would allow us to investigate the parsec-scale environment around powerful radio sources, to probe the physical conditions of the molecular gas in the inner parsecs of quasars, and to estimate their nuclear engine masses in the early universe. To derive this information, the nature of the maser source needs to be assessed through a detailed investigation of the observational characteristics of the line emission. This will determine whether the emission is from a jet-or diskmaser source. Methods. We monitored the maser line in the lensed quasar MG J0414+0534 at z = 2.64 with the 300-m Arecibo telescope for ∼15 months to detect possible additional maser components and to measure a potential velocity drift of the lines. In addition, we followed the maser and continuum emissions to reveal significant variations in their flux density and to determine whether correlation or time-lag exists between them. Results. The main maser line profile is complex and can be resolved into a number of broad features with line widths of 30-160 km s −1 . A new maser component was tentatively detected in October 2008, and is redshifted by 470 km s −1 compared to the systemic velocity of the quasar. The line width of the main maser feature increased by a factor of two between the discovery Effelsberg and EVLA observations and the first epoch of the Arecibo monitoring campaign. After correcting for the lens magnification, we find that the total H 2 O isotropic luminosity of the maser in MG J0414+0534 is now ∼30 000 L , making this source the most luminous ever discovered. Both the main line peak and continuum flux densities are surprisingly stable throughout the period of the observations. The integrated flux density instead shows significant variations on monthly time scales, possibly due to changes in the individual velocity components. We place an upper limit on the velocity drift of the peak of the line emission of 2 km s −1 yr −1 . Conclusions. The large line width of the main maser line and the absence of a clear triple-peak pattern in the maser spectrum of MG J0414+0534 favours the jet-maser scenario. However, the stability of the line and continuum emission, and the presence of the tentative new maser component, which is potentially identified as a high-velocity feature of a rotating disk, seems to partly contradict this interpretation. Sensitive monitoring on a longer time scale and VLBI observations are mandatory for drawing a definite conclusion.

Smoke on the water: CO and H2O in a circumnuclear disc around a quasar at redshift 2.64

“…The centre of the CO (11-10) profile also suggests a slightly redshifted systemic velocity. We note that the peaks in the 380 GHz H 2 O line profile are consistent with the blue and redshifted components of the 22 GHz H 2 O megamaser system reported by Castangia et al (2011) (shown with black crosses in Fig. 3), but with larger associated dispersions.…”

“…It has also been suggested that microlensing by stars in foreground lensing galaxies can result in significant (extrinsic) variability of lensed 22 GHz H 2 O megamasers at high redshift (Garsden, Lewis & Harvey-Smith 2011). The 15 month monitoring campaign of MG J0414+0534 with the Arecibo telescope that was reported by Castangia et al (2011) revealed variations in the isotropic line luminosity over this timescale, consistent with an AGN origin. They did not find significant evidence of a velocity drift, indicative of rotation of any maser regions in a pc-scale accretion disc.…”

“…The H 2 O line integrated over both A1 and A2 is shown in red, and the line from the peak of A1 is shown in green. The black crosses indicate the peak and FWHM of the 22 GHz H 2 O megamaser components from Castangia et al (2011). The H 2 O line profiles are smoothed with a boxcar kernel of width 5 channels (113 km s −1 ) and scaled by a factor of 4, for comparison.…”

Measuring Magnetic Fields Near and Far with the SKA via the Zeeman Effect

“…Megamasers have been detected in hundreds of galaxies at z ∼ 0.1, and, with the aid of lensing, as far away as z = 2.6 (Castangia et al 2011). Intrinsically compact both spatially (detectable down to micro-arcsec scales) and spectrally (sub-km s −1 ), they provide the best directly mappable tracers of high-resolution structure in the inner few hundred parsecs of active galaxies.…”

“…McClure-Griffiths et al (2006) detected H I self-absorption throughout the Riegel-Crutcher cloud, an 8 • -by-8 • region at the Galactic Center showing an incredible network of long, cold filaments. When the method of Chandrasekhar & Fermi (1953) is used to investigate stellar polarization measurements along these filaments, magnetic fields in excess of 30 µG are inferred. The H I absorption profile has a height of 100 K and a width of 3.5 km s −1 .…”