Miguel Pereira Santaella

Abstract:

The detection of several radio-loud narrow-line Seyfert 1 (NLS1) galaxies by the Fermi Gamma-Ray Space Telescope hints at the existence of a rare, new class of γ -ray emitting active galactic nuclei with low black hole masses. Like flat spectrum radio quasars (FSRQs), their γ -ray emission is thought to be produced via the external Compton mechanism whereby relativistic jet electrons upscatter a photon field external to the jet, e.g. from the accretion disc, broad line region (BLR), and dusty torus, to higher energies. Here we study the origin of the γ -ray emission in the lowest-redshift candidate among the currently known γ -ray emitting NLS1s, 1H 0323+342, and take a new approach. We observationally constrain the external photon field using quasi-simultaneous near-infrared, optical, and X-ray spectroscopy. Applying a one-zone leptonic jet model, we simulate the range of jet parameters for which this photon field, when Compton scattered to higher energies, can explain the γ -ray emission. We find that the site of the γ -ray emission lies well within the BLR and that the seed photons mainly originate from the accretion disc. The jet power that we determine, 1.0 × 1045 erg s−1, is approximately half the accretion disc luminosity. We show that this object is not simply a low-mass FSRQ, its jet is intrinsically less powerful than predicted by scaling a typical FSRQ jet by black hole mass and accretion rate. That γ -ray-emitting NLS1s appear to host underpowered jets may go some way to explaining why so few have been detected to date.

Abstract:

In an earlier paper we modelled the far-infrared emission from a star-forming galaxy using the photoionization code CLOUDY and presented metallicity sensitive diagnostics based on farinfrared fine structure line ratios. Here, we focus on the applicability of the [OIII] 88μm/[N II] 122 μm line ratio as a gas-phase metallicity indicator in high-redshift submillimetre luminous galaxies. The [O III] 88μm/[N II] 122 μm ratio is strongly dependent on the ionization parameter (which is related to the total number of ionizing photons) and on the gas electron density. We demonstrate how the ratio of 88/122 μm continuum flux measurements can provide a reasonable estimate of the ionization parameter, while the availability of the [NII] 205 μm line can constrain the electron density. Using the [OIII] 88μm/[N II] 122 μm line ratios from a sample of nearby normal and star-forming galaxies, we measure their gas-phase metallicities and find that their mass-metallicity relation is consistent with the one derived using optical emission lines. Using new, previously unpublished, Herschel spectroscopic observations of key far-infrared fine structure lines of the z ~ 3 galaxy HLSW-01 and additional published measurements of far-infrared fine structure lines of high-z submillimetre luminous galaxies, we derive gas-phasemetallicities using their [OIII] 88μm/[N II] 122 μmline ratio.We find that themetallicities of these z~3 submm-luminous galaxies are consistent with solarmetallicities and that they appear to follow the mass-metallicity relation expected for z ~ 3 systems.