A NICMOS imaging study of high-z quasar host galaxies

Abstract

We present the first results from a major Hubble Space Telescope programme designed to investigate the cosmological evolution of quasar host galaxies from z ≃ 2 to the present day. Here we describe J and H-band NICMOS imaging of two quasar samples at redshifts of 0.9 and 1.9 respectively. Each sample contains equal numbers of radioloud and radio-quiet quasars, selected to lie within the same narrow range of optical absolute magnitude (−24 ≥ M V ≥ −25). Filter and target selection were designed to ensure that at each redshift the images sample the same part of the object's restframe spectrum, longwards of 4000Å where starlight from the host galaxy is relatively prominent, but avoiding potential contamination by [Oiii]λ5007 and Hα emission lines.At z ≃ 1 we have been able to establish host-galaxy luminosities and scalelengths with sufficient accuracy to demonstrate that the hosts of both radio-loud and radioquiet quasars lie on the same Kormendy relation described by 3CR radio galaxies at comparable redshift . Taken at face value the gap between the host luminosities of radio-loud and radio-quiet objects appears to have widened from only ≃ 0.4 mag. at z ≃ 0.2 to ≃ 1 mag. at z ≃ 1, a difference that cannot be due to emission-line contamination given the design of our study. However, within current uncertainties, simple passive stellar evolution is sufficient to link these galaxies with the elliptical hosts of low-redshift quasars of comparable nuclear output, implying that the hosts are virtually fully assembled by z ∼ 1.At z ≃ 2 the hosts have proved harder to characterise accurately, and for only two of the nine z ≃ 2 quasars observed has it proved possible to properly constrain the scalelength of the host galaxy. However, the data are of sufficient quality to yield hostgalaxy luminosities accurate to within a factor ≃ 2. At this redshift the luminosity gap between radio-loud and radio-quiet quasars appears to have widened further to ≃ 1.5 mag. Thus while the hosts of radio-loud quasars remain consistent with a formation epoch of z > 3, allowing for passive evolution implies that the hosts of radio-quiet quasars are ≃ 2 − 4 times less massive at z ≃ 2 than at z ≃ 0.2.If the relationship between black-hole and spheroid mass is unchanged out to redshift z ≃ 2, then our results rule out any model of quasar evolution which involves a substantial component of luminosity evolution (e.g. Kauffmann & Haehnelt 2000). Rather, this study indicates that at z ≃ 2 there is a substantial increase in the number density of active black holes, along with a moderate increase in the fueling efficiency of a typical observed quasar. The fact that this latter effect is not displayed by the radio-loud objects in our sample might be explained by a selection effect arising from the fact that powerful radio sources are only produced by the most massive black holes McLure & Dunlop 2000b).

Reaching the peak of the quasar spectral energy distribution – II. Exploring the accretion disc, dusty torus and host galaxy

“…From our fitted host galaxy model, we measure the luminosity in the V, R, and K bands, comparing these to the results Kukula et al (2001) and Ridgway et al (2001). In panels (a) and (c), we show the derived relations by each work (short dashed lines) together with a simple least squares regression line (dotted line) with 1σ error, estimated by drawing 1000 bootstraps from the literature sample.…”

The Co-Evolution of Galaxies and Black Holes: Current Status and Future Prospects

“…The investigations to date (Ridgway et al 2001;Kukula et al 2001;Peng et al 2006) have determined only the most basic properties (luminosity and size) of the host galaxies for relatively small samples. The images are not sensitive enough to detect large-scale lowsurface brightness tidal features while the inner regions are strongly contaminated by the QSO.…”

The XMM large scale structure survey: optical vs. X-ray classifications of active galactic nuclei and the unified scheme

“…Finally, we apply the corresponding k-correction for a typical elliptical galaxy (Coleman et al 1980), and we use the galaxy profile of Burkert et al (1993) in order to estimate the fraction of the total optical flux of the host galaxy which enters the slit. Making the reasonable assumption that the typical absolute magnitude of the host galaxy of radio quiet AGN is similar at z = 0.3 and at z = 1.5, (Kukula et al 2001, Fig. 7), we derive the following values:…”