Knud Jahnke

Discovery of a bright quasar without a massive host galaxy

A quasar is thought to be powered by the infall of matter onto a supermassive black hole at the centre of a massive galaxy. Because the optical luminosity of quasars exceeds that of their host galaxy, disentangling the two components can be difficult. This led in the 1990s to the controversial claim of the discovery of ‘naked’ quasars. Since then, the connection between quasars and galaxies has been well established. Here we report the discovery of a quasar lying at the edge of a gas cloud, whose size is comparable to that of a small galaxy, but whose spectrum shows no evidence for stars. The gas in the cloud is excited by the quasar itself. If a host galaxy is present, it is at least six times fainter than would normally be expected for such a bright quasar. The quasar is interacting dynamically with a neighbouring galaxy, whose gas might be feeding the black hole.

On-axis spectroscopy of the z = 0.144 radio-loud quasar HE 1434-1600: an elliptical host with a highly ionized ISM

VLT on-axis optical spectroscopy of the

Euclid space mission: a cosmological challenge for the next 15 years

z=0.144

Two-Dimensional Modeling of AGN Host Galaxies

radio-loud quasar HExa01434-1600u2000is presented. The spatially resolved spectra of the host galaxy are deconvolved and separated from those of the central quasar in order to study the dynamics of the stars and gas as well as the physical conditions of the ISM. We find that the host of HExa01434-1600u2000is an elliptical galaxy that resides in a group of at least 5 member galaxies, and that most likely experienced a recent collision with its nearest companion. Compared with other quasar host galaxies, HExa01434-1600u2000has a highly ionized ISM. The ionization state corresponds to that of typical Seyferts, but the ionized regions are not distributed in a homogeneous way around the QSO, and are located preferentially several kiloparsecs away from it. While the stellar absorption lines do not show any significant velocity field, the gas emission lines do. The observed gas velocity field is hard to reconcile with dynamical models involving rotating disk, modified Hubble laws or power laws, that all require extreme central masses (

STAGES master catalog (Gray+, 2009)

M>10^{9}~M_{odot}

Short Title (Caldwell+, 2008)

) to provide only poor fit to the data. Power law models, which best fit the data, provide a total mass of M (<10xa0kpc)xa0= 9.2xa0

GALFIT result for GEMS galaxies (Haussler+, 2007)

times

Characterizing barred galaxies in the Abell 901/902 Supercluster from STAGES

10^{10}~M_{odot}

NEW HORIZONS IN ASTRONOMY: FRANK N. BASH SYMPOSIUM 2007

. We conclude that the recent interaction between HExa01434-1600u2000and its closest companion has strongly affected the gas velocity and ionization state, from the center of the galaxy to its most external parts.