60 research outputs found
Observational constraints on the spin of the most massive black holes from radio observations
We use recent progress in simulating the production of magnetohydrodynamic jets around black holes to derive the cosmic spin history of the most massive black holes, with masses >~10^8 Msol. Assuming the jet efficiency depends on spin a, we can approximately reproduce the observed `radio loudness' of quasars and the local radio luminosity function. Using the X-ray luminosity function and the local mass function of supermassive black holes, SMBHs we can reproduce the individual radio luminosity functions of radio sources showing high- and low-excitation narrow emission lines. The data favour spin distributions that are bimodal, with one component around spin zero and the other close to maximal spin. In the low-excitation galaxies, the two components have similar amplitudes. For the high-excitation galaxies, the amplitude of the high-spin peak is typically much smaller than that of the low-spin peak. A bimodality should be seen in the radio loudness of quasars. We predict that the low-excitation galaxies are dominated by SMBHs with masses >~10^8 Msol, down to radio luminosity densities ~10^21 W Hz-1 sr-1 at 1.4~GHz. Our model is also able to predict the radio luminosity function at z=1, and predicts it to be dominated by high-excitation galaxies above luminosity densities >~10^26 W Hz-1 sr-1, in full agreement with the observations. From our parametrisation and using the best fitting jet efficiencies there is marginal evidence for evolution in spin: the mean spin increases slightly from ~0.25 at z=1 to ~0.35 at z=0, and the fraction of SMBHs with a>=0.5 increases from 0.16+-0.03 at z=1 to 0.24+-0.09 at z=0. Our results are in excellent agreement with the mean radiative efficiency of quasars, as well as recent cosmological simulations. We discuss the implications in terms of accretion and SMBH mergers, and galactic black holes (Abridged).</a
Ground-state 12CO emission and a resolved jet at 115 GHz (rest-frame) in the radio loud quasar 3C318
An analysis of 44 GHz VLA observations of the z = 1.574 radio-loud quasar
3C318 has revealed emission from the redshifted J = 1 - 0 transition of the CO
molecule and spatially resolved the 6.3 kpc radio jet associated with the
quasar at 115 GHz rest-frame. The continuum-subtracted line emitter is
spatially offset from the quasar nucleus by 0.33" (2.82 kpc in projection).
This spatial offset has a significance of >8-sigma and, together with a
previously published -400 km/s velocity offset measured in the J = 2 - 1 CO
line relative to the systemic redshift of the quasar, rules out a circumnuclear
starburst or molecular gas ring and suggests that the quasar host galaxy is
either undergoing a major merger with a gas-rich galaxy or is otherwise a
highly disrupted system. If the merger scenario is correct then the event may
be in its early stages, acting as the trigger for both the young radio jets in
the quasar and a starburst in the merging galaxy. The total molecular gas mass
in the spatially offset line emitter as measured from the ground-state CO line
M_H2 = 3.7 (+/-0.4) x 10^10 (alpha_CO/0.8) M_solar. Assuming that the
line-emitter can be modelled as a rotating disk, an inclination-dependent upper
limit is derived for its dynamical mass M_dyn sin^2(i) < 3.2 x 10^9 M_solar,
suggesting that for M_H2 to remain less than M_dyn the inclination angle must
be i < 16 degrees. The far infrared and CO luminosities of 246 extragalactic
systems are collated from the literature for comparison. The high molecular gas
content of 3C318 is consistent with that of the general population of high
redshift quasars and sub-millimetre galaxies.Comment: 10 pages, 4 figures, 2 tables (additional table to appear online as
supplementary material), accepted for publication in MNRA
High-redshift obscured quasars
Using mid-infrared and radio criteria, we select a sample of candidate z~2
obscured quasars. Optical spectroscopy confirms about half of these as type-2
quasars, and modelling the population suggests 50-80% of the quasars are
obscured. We find some flat radio spectrum type-2 quasars, and tentative
evidence for obscuration unrelated to the torus. Using a similar sample, we
also find evidence for a significant fraction of Compton-thick quasars.Comment: 4 pages, 1 figure. Conference proceedings to appear in "The Central
Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San
Francisco: ASP
Infrared and millimetre-wavelength evidence for cold accretion within a z = 2.83 Lyman-alpha blob
‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.13580.xThis paper discusses infrared and millimetre-wavelength observations of a Lyman alpha blob (LAB) discovered by Smith & Jarvis, a candidate for ionization by the cold accretion scenario discussed in Fardal et al. and Dijkstra et al. We have observed the counterpart galaxy at infrared wavelengths in deep observations with the Spitzer Space Telescope using the IRAC 3.6, 4.5, 5.8 and 8.0 mu m and MIPS 24 mu m bands, as well as using the Max-Planck Millimeter Bolometer (MAMBO-2) at a wavelength of 1.2 mm with the IRAM 30 m telescope. These observations probe the greater than or similar to 95 kpc Lyman alpha halo for the presence of obscured active galactic nucleus (AGN) components or the presence of a violent period of star formation invoked by other models of ionization for these mysterious objects. 24 mu m observations suggest that an obscured AGN would be insufficiently luminous to ionize the halo, and that the star formation rate within the halo may be as low as < 140 M-circle dot yr(-1) depending on the model spectral energy distribution (SED) used. This is reinforced by our observations at 1.2 mm using MAMBO-2, which yield an upper limit of star formation rate < 550 M-circle dot yr(-1) from our non-detection to a 3 sigma flux limit of 0.86 mJy beam(-1). Finding no evidence for either AGN or extensive star formation, we conclude that this halo is ionized by a cold accretion process. We derive model SEDs for the host galaxy, and use the Bruzual & Charlot and Maraston libraries to show that the galaxy is well described by composite stellar populations of total mass 3.42 +/- 0.13 x 10(11) or 4.35 +/- 0.16 x 10(11) M-circle dot depending on the model SEDs used.Peer reviewe
The stellar, molecular gas and dust content of the host galaxies of two z~2.8 dust obscured quasars
We present optical through radio observations of the host galaxies of two
dust obscured, luminous quasars selected in the mid-infrared, at z=2.62 and
z=2.99, including a search for CO emission. Our limits on the CO luminosities
are consistent with these objects having masses of molecular gas <~10^10 solar
masses, several times less than those of luminous submillimeter-detected
galaxies (SMGs) at comparable redshifts. Their near-infrared spectral energy
distributions, however, imply that these galaxies have high stellar masses
(~10^11-12 solar masses). The relatively small reservoirs of molecular gas and
low dust masses are consistent with them being relatively mature systems at
high-z.Comment: AJ, in pres
VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data
obtained with the Very Large Telescope and the Gran Telescopio Canarias of the
type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich
environment. It appears to be physically connected by a tidal bridge to another
galaxy at a projected distance of ~100 kpc, which suggests this is an
interacting system. Ionized gas is detected to a distance of at least ~133 kpc
from the nucleus. The nebula has a total extension of ~180 kpc. This is one of
the largest ionized nebulae ever detected associated with an active galaxy.
Based on the environmental properties, we propose that the origin of the nebula
is tidal debris from a galactic encounter, which could as well be the
triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that
giant, luminous ionized nebulae can exist associated with type 2 quasars of low
radio luminosities, contrary to expectations based on type 1 quasar studies.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letter
Evidence for a large fraction of Compton-thick quasars at high redshift
Using mid-infrared and radio selection criteria, we pre-select a sample of
candidate high-redshift type-2 quasars in the Subaru XMM-Newton Deep Field
(SXDF). To filter out starburst contaminants, we use a bayesian method to fit
the spectral energy distributions (SEDs) between 24-microns and B-band, obtain
photometric redshifts, and identify the best candidates for high-z type-2
quasars. This leaves us with 12 z_phot >= 1.7 type-2 quasar candidates in an
area ~0.8 deg^2, of which only two have secure X-ray detections. The two
detected sources have estimated column densities N_H~2 & 3x10^27 m^-2, i.e.
heavily obscured but Compton-thin quasars. Given the large bolometric
luminosities and redshifts of the undetected objects, the lack of X-ray
detections suggests extreme absorbing columns N_H >= 10^28 m^-2 are typical. We
have found evidence for a population of ``Compton-thick'' high-redshift type-2
quasars, at least comparable to, and probably larger than the type-1 quasar
population, although spectroscopic confirmation of their AGN nature is
important.Comment: 6 pages, 2 colour figures. Accepted by MNRAS. Full resolution version
and supplementary figures can be found at:
http://www.mpia.de/homes/martinez/publications.htm
A population of high-redshift type-2 quasars-II. Radio Properties
We present multi-frequency radio observations of a sample of z~2 obscured
(type-2) quasars in the Spitzer extragalactic First Look Survey area. We
combine the public data at 1.4 GHz, used in the selection of these sources,
with new observations at 610 MHz (GMRT) and at 4.9 GHz (VLA). We find the
sample includes sources with steep, flat and gigahertz-peaked spectra. There
are no strong correlations between the presence or absence of emission lines in
the optical spectra and the radio spectral properties of the sample. However,
there are no secure flat-spectrum type-2 quasars with narrow emission lines
which would be problematic for unified schemes. Most of the population have
straight radio spectra with spectral index alpha~1 as is expected for
developed, potentially FRI-like, jets in which continous injection of
relativistic electrons is accompanied by inverse-Compton losses against the
cosmic microwave background.Comment: 6 pages, 2 colour figures, submitted to MNRA
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