504 research outputs found
Hierarchical build-up of galactic bulges and the merging rate of supermassive binary black holes
The hierarchical build-up of galactic bulges should lead to the build-up of
present-day supermassive black holes by a mixture of gas accretion and merging
of supermassive black holes. The tight relation between black hole mass and
stellar velocity dispersion is thereby a strong argument that the supermassive
black holes in merging galactic bulges do indeed merge. Otherwise the ejection
of supermassive black holes by gravitational slingshot would lead to excessive
scatter in this relation. At high redshift the coalescence of massive black
hole binaries is likely to be driven by the accretion of gas in the major
mergers signposted by optically bright QSO activity. If massive black holes
only form efficiently by direct collapse of gas in deep galactic potential
wells with v_c > 100 km/s as postulated in the model of Kauffmann & Haehnelt
(2000) LISA expects to see event rates from the merging of massive binary black
holes of about 0.1-1 yr^{-1} spread over the redshift range 0 < z < 5. If,
however, the hierarchical build-up of supermassive black holes extends to
pre-galactic structures with significantly shallower potential wells event
rates may be as high as 10-100 yr^{-1} and will be dominated by events from
redshift z > 5.Comment: 8 pages, 4 postscript figures. Proceedings of the 4th International
LISA Symposium, Penn State University, 19-24 July 2002, ed. L S Fin
A Unified Model for the Evolution of Galaxies and Quasars
We incorporate a simple scheme for the growth of supermassive black holes
into semi-analytic models that follow the formation and evolution of galaxies
in a cold dark matter dominated Universe. We assume that supermassive black
holes are formed and fuelled during major mergers. If two galaxies of
comparable mass merge, their central black holes coalesce and a few percent of
the gas in the merger remnant is accreted by the new black hole over a
timescale of a few times 10^7 years. With these simple assumptions, our model
not only fits many aspects of the observed evolution of galaxies, but also
reproduces quantitatively the observed relation between bulge luminosity and
black hole mass in nearby galaxies, the strong evolution of the quasar
population with redshift and the relation between the luminosities of nearby
quasars and those of their host galaxies. The strong decline in the number
density of quasars from z=2 to z=0 is due to the combination of three effects:
i) a decrease in the merging rate, ii) a decrease in the amount of cold gas
available to fuel black holes, and iii) an increase in the timescale for gas
accretion. In a LCDM cosmology the predicted decline in the total content of
cold gas in galaxies is consistent with that inferred from observations of
damped Lyman-alpha systems. Our results strongly suggest that the evolution of
supermassive black holes, quasars and starbursts is inextricably linked to the
hierarchical build-up of galaxies.Comment: 30 pages, Latex, 18 figures included, submitted to MNRA
Lensing Induced Cluster Signatures in Cosmic Microwave Background
We show that clusters of galaxies induce step-like wiggles on top of the
cosmic microwave background (CMB). The direction of the wiggle is parallel to
the large scale gradient of CMB allowing one to isolate the effect from other
small scale fluctuations. The effect is sensitive to the deflection angle
rather than its derivative (shear or magnification) and is thus tracing outer
parts of the cluster with higher sensitivity than some other methods. A typical
amplitude of the effect is where
is the velocity dispersion of the cluster and several
signals extend out to a fraction of a degree. We derive the expressions for the
temperature profile for several simple parameterized cluster models and
identify some degeneracies between parameters. Finally, we discuss how to
separate this signal from other imprints on CMB using custom designed filters.
Detection of this effect is within reach of the next generation of small scale
CMB telescopes and could provide information about the cluster density profile
beyond the virial radius.Comment: 10 pages, 3 figures, submitted to Ap
The impact of galactic winds from LBGs on the Intergalactic Medium
An excess of sight-lines close to Lyman-break galaxies (LBGs) with little or
no absorption in QSO absorption spectra has been reported and has been
interpreted as the effect of galactic winds on the Intergalactic Medium. We use
here numerical simulations to investigate the flux probability function close
to plausible sites of LBGs. We show that the flux distribution near our LBGs in
the simulation depends strongly on redshift, and is very sensitive to the
averaging procedure. We show that a model without galactic winds and a model
with a wind bubble size of 0.5Mpc/h (comoving) are equally consistent with the
new determination of the conditional flux distribution by Adelberger et al.
(2005). Models with the larger bubble sizes suggested by the previous
observations of Adelberger et al. (2003) based on a much smaller sample at
higher redshift are not consistent with the new data. We therefore argue that
the volume filling factor of galactic winds driven by LBGs may be much smaller
than previously thought, and that most of the metals responsible for the metal
absorption associated with the low column density Lya forest are unlikely to
have been ejected by LBGs.Comment: 5 pages, 3 figure
The AGN-starburst connection, Galactic superwinds, and M_BH - sigma
Recent observations of young galaxies at redshifts z ~ 3 have revealed
simultaneous AGN and starburst activity, as well as galaxy-wide superwinds. I
show that there is probably a close connection between these phenomena by
extending an earlier treatment of the M_BH - sigma relation (King, 2003). As
the black hole grows, an outflow drives a shell into the surrounding gas. This
stalls after a dynamical time at a size determined by the hole's current mass
and thereafter grows on the Salpeter timescale. The gas trapped inside this
bubble cools and forms stars and is recycled as accretion and outflow. The
consequent high metallicity agrees with that commonly observed in AGN
accretion. Once the hole reaches a critical mass this region attains a size
such that the gas can no longer cool efficiently. The resulting energy-driven
flow expels the remaining gas as a superwind, fixing both the M_BH - sigma
relation and the total stellar bulge mass at values in good agreement with
observation. Black hole growth thus produces starbursts and ultimately a
superwind.Comment: ApJ, in press, 4 page
Retaining Black Holes with Very Large Recoil Velocities
Recent numerical simulations of binary black hole mergers show the
possibility of producing very large recoil velocities (> 3000 km/s). Kicks of
this magnitude should be sufficient to eject the final black hole from
virtually any galactic potential. This result has been seen as a potential
contradiction with observations of supermassive black holes residing in the
centers of most galaxies in the local universe. Using an extremely simplified
merger tree model, we show that, even in the limit of very large ejection
probability, after a small number of merger generations there should still be
an appreciable fraction (>50%) of galaxies with supermassive black holes today.
We go on to argue that the inclusion of more realistic physics ingredients in
the merger model should systematically increase this retention fraction,
helping to resolve a potential conflict between theory and observation. Lastly,
we develop a more realistic Monte Carlo model to confirm the qualitative
arguments and estimate occupation fractions as a function of the central
galactic velocity dispersion.Comment: 6 pages, 3 figures; Comments welcom
The power spectrum of the flux distribution in the Lyman-alpha forest of a Large sample of UVES QSO Absorption Spectra (LUQAS)
The flux power spectra of the Lyman-alpha forest from a sample of 27 QSOs
taken with the high resolution echelle spectrograph UVES on VLT are presented.
We find a similar fluctuation amplitude at the peak of the ``3D'' flux power
spectrum at k ~ 0.03 (km/sec)^(-1) as the study by Croft et al. (2002), in the
same redshift range. The amplitude of the flux power spectrum increases with
decreasing redshift if corrected for the increase in the mean flux level as
expected if the evolution of the flux power spectrum is sensitive to the
gravitational growth of matter density fluctuations. This is in agreement with
the findings of McDonald et al. (2000) at larger redshift. The logarithmic
slope of the "3D" flux power spectrum, P_F(k), at large scales k < 0.03
(km/sec)^(-1), is 1.4 +- 0.3, i.e. 0.3 shallower than that found by Croft et
al. (2002) but consistent within the errors.Comment: 18 pages, 9 PS figures, 6 tables. Note that the k-values of the 1D
flux power spectrum had been erroneously shifted by half a bin size (in log
k) in the previous version. All the other results are unaffected. New tables
can be found at http://www.ast.cam.ac.uk/~rtnigm/luqas.ht
X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin
We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus
cluster, for which van den Bosch et al. have recently claimed the presence of
an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF
of the stars in the stellar bulge is extremely bottom heavy. The X-rays
originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded
in a 1 keV thermal minicorona which has a half-light radius of about 360 pc,
typical of many early-type galaxies in rich clusters of galaxies. If Bondi
accretion operated onto the UMBH from the minicorona with a radiative
efficiency of 10 per cent, then the object would appear as a quasar with
luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The
accretion flow must be highly radiatively inefficient, similar to past results
on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any
significant growth at the present epoch. We note that there are 3 UMBH
candidates in the Perseus cluster and that the inferred present mean mass
density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the
estimated mean mass density of all black holes. We speculate on the implied
growth of UMBH and their hosts, and discuss the possibiity that extreme AGN
feedback could make all UMBH host galaxies have low stellar masses at redshifts
around 3. Only those which end up at the centres of groups and clusters later
accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277
and the other Perseus core UMBH, NGC1270, have not however been able to gather
more stars or gas owing to their rapid orbital motion in the cluster core.Comment: 5 pages, 4 figures, MNRAS in pres
The X-ray Spectrum of the z=6.30 QSO SDSS J1030+0524
We present a deep XMM-Newton observation of the z=6.30 QSO SDSS J1030+0524,
the second most distant quasar currently known. The data contain sufficient
counts for spectral analysis, demonstrating the ability of XMM-Newton to
measure X-ray spectral shapes of z~6 QSOs with integration times >100ks. The
X-ray spectrum is well fit by a power law with index Gamma=2.12 +/- 0.11, an
optical-X-ray spectral slope of a_{ox}=-1.80, and no absorption excess to the
Galactic value, though our data are also consistent with a power law index in
the range 2.02 < Gamma < 2.5 and excess absorption in the range 0 < N_H(cm^-2)
< 8x10^22. There is also a possible detection (2 sigma) of FeKa emission. The
X-ray properties of this QSO are, overall, similar to those of lower-redshift
radio-quiet QSOs. This is consistent with the statement that the X-ray
properties of radio-quiet QSOs show no evolution over 0<z<6.3. Combined with
previous results, this QSO appears indistinguishable in any way from lower
redshift QSOs, indicating that QSOs comparable to those seen locally existed
less than one Gyr after the Big Bang.Comment: ApJ Letters, accepte
Measuring the Mach number of the Universe via the Sunyaev-Zeldovich effect
We introduce a new statistic to measure more accurately the cosmic sound
speed of clusters of galaxies at different redshifts. This statistic is
evaluated by cross-correlating cosmic microwave background (CMB) fluctuations
caused by the Sunyaev-Zel'dovich effect from observed clusters of galaxies with
their redshifts. When clusters are distributed in redshift bins of narrow
width, one could measure the mean squared cluster peculiar velocity with an
error \sigma_{C_S^2}\lsim (300{\rm km/s})^2. This can be done around z>0.3 with
clusters of flux above 200 mJy which will be detected by PLANCK, coupled with
high resolution microwave images to eliminate the cosmological part of the CMB
fluctuations. The latter can be achieved with observations by the planned ALMA
array or the NSF South Pole telescope and other surveys. By measuring the
cosmic sound speed and the bulk flow in, e.g., 4 spheres of ~ 100h^{-1}Mpc at
z=0.3, we could have a direct measurement of the matter density
0.21<\Omega_m<0.47 at 95 % confidence level.Comment: Ap.J.Letters, submitte
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