176 research outputs found
Extensions around z=2 QSOs
Based on an R-band imaging survey of 6 high redshift (z~2) and high
luminosity (M<-28mag) QSOs, we report the detection of extensions in two
radio-quiet and one radio-loud QSO. The extensions are most likely due to the
host galaxies of these QSOs, with luminosities of at least 3-7 per cent of the
QSO luminosity. The most likely values for the luminosity of the host galaxies
lie in the range $6-18 per cent of the QSO luminosity.Comment: uuencoded compressed postscript. The preprint is also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Multicolour imaging of z= 2 QSO hosts
We present multicolour images of the hosts of three z=2 QSOs previously
detected in R-band by our group. The luminosities, colours and sizes of the
hosts overlap with those of actively star-forming galaxies in the nearby
Universe. Radial profiles over the outer resolved areas roughly follow de
Vaucouleur or exponential disk laws. These properties give support to the host
galaxy interpretation of the extended light around QSOs at high-redshift. The
rest-frame UV colours and upper limits derived for the rest-frame UV-optical
colours are inconsistent with the hypothesis of a scattered halo of light from
the active nucleus by a simple optically-thin scattering process produced by
dust or hot electrons. If the UV light is indeed stellar, star formation rates
of hundreds of solar masses per year are implied, an order of magnitude larger
than field galaxies at similar redshifts and above. This might indicate that
the QSO phenomenon (at least the high-luminosity one) is preferentially
acompanied by enhanced galactic activity at high-redshifts.Comment: Accepted to be published in MNRAS. 11 pages, Latex, uses mn macros,
also available at http://www.mpa-garching.mpg.de/~itzia
Adaptive Optics observations of LBQS 0108+0028: K-band detection of the host galaxy of a radio-quiet QSO at z=2
We report the first unambiguous detection of the host galaxy of a normal
radio-quiet QSO at high-redshift in K-band. The luminosity of the host
comprises about 35% of the total K-band luminosity. Assuming the average colour
of QSOs at z=2, the host would be about 5 to 6 mag brighter than an unevolved
L* galaxy placed at z=2, and 3 to 4 mag brighter than a passively evolved L*
galaxy at the same redshift. The luminosity of the host galaxy of the QSO would
thus overlap with the highest found in radio-loud QSOs and radio-galaxies at
the same redshift.Comment: Accepted to be published in MNRAS. 4 pages, 2 postscript figures.
Also available at http://www.mpa-garching.mpg.de/~itzia
QSO hosts and environments at z=0.9 to 4.2: JHK images with adaptive optics
We have observed nine QSOs with redshifts 0.85 to 4.16 at near-IR wavelengths
with the adaptive optics bonnette of the Canada-France-Hawaii telescope.
Exposure times ranged from 1500 to 24000s (mostly near 7000s) in J, H, or K
bands, with pixels 0.035 arcsec on the sky. The FWHM of the co-added images at
the location of the quasars are typically 0.16 arcsec. Including another QSO
published previously, we find associated QSO structure in at least eight of ten
objects, including the QSO at z = 4.16. The structures seen in all cases
include long faint features which appear to be tidal tails. In four cases we
have also resolved the QSO host galaxy, but find them to be smooth and
symmetrical: future PSF removal may expand this result. Including one object
previously reported, of the nine objects with more extended structure, five are
radio-loud, and all but one of these appear to be in a dense small group of
compact galaxy companions. The radio-quiet objects do not occupy the same dense
environments, as seen in the NIR. In this small sample we do not find any
apparent trends of these properties with redshift, over the range 0.8 < z <
2.4. The colors of the host galaxies and companions are consistent with young
stellar populations at the QSO redshift. Our observations suggest that adaptive
optic observations in the visible region will exhibit luminous signatures of
the substantial star-formation activity that must be occurring.Comment: 22 pages including 10 tables, plus 11 figures. To appear in A
The host galaxies of z=2 radio-quiet QSOs
Based on an R-band imaging survey of high-redshift (z \approx 2) QSOs with the 4.2m WHT, we report the detection of extensions to the nuclear PSFs of two radio-quiet and one radio-loud QSO. The extensions are most likely host galaxies, with luminosities of at least 3-7\% of the QSO luminosity. The most likely values for the luminosities lie in the range 6-18\% of the QSO luminosity (R \sim 19.8-20.9~mag). Our observations show that, if the extensions we have detected are indeed galaxies, extraordinary massive and luminous galaxies are not only characteristic of radio-loud objects, but of QSOs as an entire class
AzTEC Millimetre Survey of the COSMOS Field - II. Source Count Overdensity and Correlations with Large-Scale Structure
We report an over-density of bright sub-millimetre galaxies (SMGs) in the
0.15 sq. deg. AzTEC/COSMOS survey and a spatial correlation between the SMGs
and the optical-IR galaxy density at z <~ 1.1. This portion of the COSMOS field
shows a ~ 3-sigma over-density of robust SMG detections when compared to a
background, or "blankfield", population model that is consistent with SMG
surveys of fields with no extragalactic bias. The SMG over-density is most
significant in the number of very bright detections (14 sources with measured
fluxes S(1.1mm) > 6 mJy), which is entirely incompatible with sample variance
within our adopted blank-field number densities and infers an over-density
significance of >> 4. We find that the over-density and spatial correlation to
optical-IR galaxy density are most consistent with lensing of a background SMG
population by foreground mass structures along the line of sight, rather than
physical association of the SMGs with the z <~ 1.1 galaxies/clusters. The SMG
positions are only weakly correlated with weak-lensing maps, suggesting that
the dominant sources of correlation are individual galaxies and the more
tenuous structures in the region and not the massive and compact clusters.
These results highlight the important roles cosmic variance and large-scale
structure can play in the study of SMGs.Comment: 12 pages, 11 figures, 2 tables, accepted for publication in MNRA
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