37 research outputs found
HST imaging of redshift z>0.5 7C and 3C Quasars
We present preliminary results from HST imaging of radio-loud quasar hosts,
covering a ~x100 range in radio luminosity but in a narrow redshift range (0.5
to 0.65). The sample was selected from our new, spectroscopically complete 7C
survey and the 3CRR catalogue. Despite the very large radio luminosity range,
the host luminosities are only weakly correlated (if at all) with radio power,
perhaps reflecting a predominance of purely central engine processes in the
formation of radio jets, and hence perhaps also in the radio-loud/-quiet
dichotomy at these redshifts. The results also contradict naive expectations
from several quasar formation theories, but the host magnitudes support
radio-loud Unified Schemes.Comment: To appear in the Proceedings of the ESO/IAC Conference on 'Quasar
Hosts' - Tenerife 24-27 September 199
IRAS F10214+4724: the inner 100pc
We use new near-infrared spectroscopy and our published optical spectroscopy
of the gravitationally-lensed Seyfert-2 galaxy F10214+4724 to study both the
links between the starburst and AGN in this object and the properties of the
inner narrow-line clouds. The UV spectrum is consistent with a compact,
moderately- reddened starburst providing about half the UV light. Spectroscopy
of the Halpha /[NII] line blend has enabled us to distinguish emission from the
narrow-line region of the Seyfert-2 and a moderately-reddened emission line
region which we argue is associated with the starburst. Estimates of the star
formation rate from the UV continuum flux and the Halpha flux are broadly
consistent. We can explain the unusual emission line properties of F10214+4724
in terms of conventional models for nearby Seyfert-2 galaxies if lensing is
preferentially magnifying the side of the inner narrow-line region between the
AGN and the observer, and the other side is both less magnified and partially
obscured by the torus. The hydrogen densities of clouds in this region are high
enough to make the Balmer lines optically thick and to suppress forbidden
emission lines with low critical densities. We have deduced the column density
of both ionised and neutral gas in the narrow-line clouds, and the density of
the ionised gas. Using these we have been able to estimate the mass of the
inner narrow-line clouds to be ~ 1 solar mass, and show that the gas:dust ratio
NH/E(B-V) in these clouds must be ~1.3x10^{27}m^{-2}mag^{-1}, significantly
higher than in the Milky Way. The cloud properties are consistent with the
those of the warm absorbers seen in the X-ray spectra of Seyfert-1 galaxies.
Our results favour models in which narrow-line clouds start close to the
nucleus and flow out.Comment: 13 pages, 5 figures. Accepted by MNRA
Spectroscopic Evidence That the Extreme Properties of IRAS F10214+4724 are due to Gravitational Lensing
The extreme bolometric luminosity of IRAS F10214+4724, and in particular the
huge mass in molecular gas inferred from the CO line fluxes have led to
suggestions that this is a giant galaxy in the process of formation. An
arc-like structure and the closeness of a second object suggest, however, that
gravitational lensing may be responsible for its anomalously high luminosity
and mass. In this paper, we use an optical spectrum taken in conditions of
0.7-arcsec seeing to provide further evidence that F10214+4724 is a
gravitationally lensed system. We measure tentative redshifts of 0.896 and
0.899 for galaxies projected and arcsec from IRAS
F10214+4724 respectively. Identifying the former as the lensing galaxy we
obtain a mass:light ratio consistent with those derived for other lenses, and
find that its luminosity is consistent with the velocity dispersion deduced
from the radius of the Einstein ring. If lensed, our models suggest
magnification by a factor , and hence an intrinsic bolometric
luminosity for F10214+4724 similar to local ULIRGs.Comment: 5 pages, uuencoded compressed PostScript, 3 figures included.
Accepted for publication in MNRAS pink pages; submitted 1 May 199
A spectroscopic study of IRAS F10214+4724
The z=2.286 IRAS galaxy F10214+4724 remains one of the most luminous galaxies
in the Universe, despite its gravitational lens magnification. We present
optical and near-infrared spectra of F10214+4724, with clear evidence for three
distinct components: lines of width ~1000 km/s from a Seyfert-II nucleus; <~200
km/s lines which are likely to be associated with star formation; and a broad
~4000 km/s CIII] 1909ang emission line which is blue-shifted by ~1000 km/s with
respect to the Seyfert-II lines. Our study of the Seyfert-II component leads to
several new results, including: (i) From the double-peaked structure in the Ly
alpha line, and the lack of Ly beta, we argue that the Ly alpha photons have
emerged through a neutral column of N_H ~ 2.5 x 10^{25}/m^2, possibly located
within the AGN narrow-line region as argued in several high redshift
radiogalaxies. (ii) The resonant O VI 1032,1036ang doublet (previously
identified as Ly beta) is in an optically thick (1:1) ratio. At face value this
implies an an extreme density (n_e ~ 10^{17}/m^3) more typical of broad line
region clouds. However, we attribute this instead to the damping wings of Ly
beta from the resonant absorption. (iii) A tentative detection of HeII 1086
suggests little extinction in the rest-frame ultraviolet.Comment: Accepted for publication in MNRAS. Uses BoxedEPS (included
The Radio-Optical Correlation in Steep-Spectrum Quasars
Using complete samples of steep-spectrum quasars, we present evidence for a
correlation between radio and optical luminosity which is not caused by
selection effects, nor caused by an orientation dependence (such as
relativistic beaming), nor a byproduct of cosmic evolution. We argue that this
rules out models of jet formation in which there are no parameters in common
with the production of the optical continuum. This is arguably the most direct
evidence to date for a close link between accretion onto a black hole and the
fuelling of relativistic jets. The correlation also provides a natural
explanation for the presence of aligned optical/radio structures in only the
most radio luminous high-redshift galaxies.Comment: MNRAS in press. Uses BoxedEPS (included
A Submillimetre Survey of the Hubble Deep Field: Unveiling Dust-Enshrouded Star Formation in the Early Universe
The advent of sensitive sub-mm array cameras now allows a proper census of
dust-enshrouded massive star-formation in very distant galaxies, previously
hidden activity to which even the deepest optical images are insensitive. We
present the deepest sub-mm survey, taken with the SCUBA camera on the James
Clerk Maxwell Telescope (JCMT) and centred on the Hubble Deep Field (HDF). The
high source density on this image implies that the survey is confusion-limited
below a flux density of 2 mJy. However within the central 80 arcsec radius
independent analyses yield 5 reproducible sources with S(850um) > 2 mJy which
simulations indicate can be ascribed to individual galaxies. These data lead to
integral source counts which are completely inconsistent with a no evolution
model, whilst the combined brightness of the 5 most secure sources in our map
is sufficient to account for 30-50% of the previously unresolved sub-mm
background, and statistically the entire background is resolved at about the
0.3 mJy level. Four of the five brightest sources appear to be associated with
galaxies which lie in the redshift range 2 < z < 4. With the caveat that this
is a small sample of sources detected in a small survey area, these submm data
imply a star-formation density over this redshift range that is at least five
times higher than that inferred from the rest-frame ultraviolet output of HDF
galaxies.Comment: to appear in the proceedings of `The Birth of Galaxies', Xth
Rencontres de Blois, 4 pages, 1 postscript figure, uses blois.sty (included
Recommended from our members
Hyper Suprime-Camera Survey of the Akari NEP Wide Field
The extragalactic background suggests half the energy generated by stars was reprocessed into the infrared (IR) by dust. At z âŒ1.3, 90% of star formation is obscured by dust. To fully understand the cosmic star formation history, it is critical to investigate infrared emission. AKARI has made deep mid-IR observation using its continuous 9-band filters in the NEP field (5.4 deg2), using âŒ10% of the entire pointed observations available throughout its lifetime. However, there remain 11,000 AKARI infrared sources undetected with the previous CFHT/Megacam imaging (r âŒ25.9ABmag). Redshift and IR luminosity of these sources are unknown. These sources may contribute significantly to the cosmic star-formation rate density (CSFRD). For example, if they all lie at 1 z g, r, i, z, and y) using Hyper Suprime-Camera (HSC), which has 1.5 deg field of view in diameter on Subaru 8m telescope. This will provide photometric redshift information, and thereby IR luminosity for the previously-undetected 11,000 faint AKARI IR sources. Combined with AKARI's mid-IR AGN/SF diagnosis, and accurate mid-IR luminosity measurement, this will allow a complete census of cosmic star-formation/AGN accretion history obscured by dust
The quasar fraction in low-frequency selected complete samples and implications for unified schemes
Low-frequency radio surveys are ideal for selecting orientation-independent
samples of extragalactic sources because the sample members are selected by
virtue of their isotropic steep-spectrum extended emission. We use the new 7C
Redshift Survey along with the brighter 3CRR and 6C samples to investigate the
fraction of objects with observed broad emission lines - the `quasar fraction'
- as a function of redshift and of radio and narrow emission line luminosity.
We find that the quasar fraction is more strongly dependent upon luminosity
(both narrow line and radio) than it is on redshift. Above a narrow [OII]
emission line luminosity of log L_[OII] > 35 W (or radio luminosity log L_151 >
26.5 W/Hz/sr), the quasar fraction is virtually independent of redshift and
luminosity; this is consistent with a simple unified scheme with an obscuring
torus with a half-opening angle theta_trans approx 53 degrees. For objects with
less luminous narrow lines, the quasar fraction is lower. We show that this is
not due to the difficulty of detecting lower-luminosity broad emission lines in
a less luminous, but otherwise similar, quasar population. We discuss evidence
which supports at least two probable physical causes for the drop in quasar
fraction at low luminosity: (i) a gradual decrease in theta_trans and/or a
gradual increase in the fraction of lightly-reddened (0 < A(V) < 5)
lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a
distinct second population of low luminosity radio sources which, like M87,
lack a well-fed quasar nucleus and may well lack a thick obscuring torus.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Herschel*-ATLAS: deep HST/WFC3 imaging of strongly lensed submillimetre galaxies
We report on deep near-infrared observations obtained with the Wide Field Camera-3 (WFC3) onboard the Hubble Space Telescope (HST) of the first five confirmed gravitational lensing events discovered by the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We succeed in disentangling the background galaxy from the lens to gain separate photometry of the two components. The HST data allow us to significantly improve on previous constraints of the mass in stars of the lensed galaxy and to perform accurate lens modelling of these systems, as described in the accompanying paper by Dye et al. We fit the spectral energy distributions of the background sources from near-IR to millimetre wavelengths and use the magnification factors estimated by Dye et al. to derive the intrinsic properties of the lensed galaxies. We find these galaxies to have star-formations rates (SFR) ⌠400â2000 Mâ yrâ1, with âŒ(6â25) Ă 1010 Mâ of their baryonic mass already turned into stars. At these rates of star formation, all remaining molecular gas will be exhausted in less than âŒ100 Myr, reaching a final mass in stars of a few 1011âMâ. These galaxies are thus proto-ellipticals caught during their major episode of star formation, and observed at the peak epoch (z ⌠1.5â3) of the cosmic star formation history of the Universe