28 research outputs found
Black hole clustering and duty cycles in the Illustris simulation
We use the high-resolution cosmological simulation Illustris to investigate the clustering of supermassive black holes across cosmic time, the link between black hole clustering and host halo masses, and the implications for black hole duty cycles. Our predicted black hole correlation length and bias match the observational data very well across the full redshift range probed. Black hole clustering is strongly luminosity dependent on small, 1-halo scales, with some moderate dependence on larger scales of a few Mpc at intermediate redshifts. We find black hole clustering to evolve only weakly with redshift, initially following the behaviour of their hosts. However, below z ~ 2 black hole clustering increases faster than that of their hosts, which leads to a significant overestimate of the clustering-predicted host halo mass. The full distribution of host halo masses is very wide, including a low-mass tail extending up to an order of magnitude below the naive prediction for minimum host mass. Our black hole duty cycles, duty, follow a power-law dependence on black hole mass and decrease with redshift, and we provide accurate analytic fits to these. The increase in clustering amplitude at late times, however, means that duty cycle estimates based on black hole clustering can overestimate duty substantially, by more than two orders of magnitude. We find the best agreement when the minimum host mass is assumed to be 10Mā, which provides an accurate measure across all redshifts and luminosity ranges probed by our simulation.CD and DS acknowledge support by the ERC starting grant 638707 āBlack holes and their host galaxies: co-evolution across cosmic timeā. DS further acknowledges support from the STFC. Simulations were run on the Harvard Odyssey and CfA/ITC clusters, the Ranger and Stampede supercomputers at the Texas Advanced Computing Center as part of XSEDE, the Kraken supercomputer at Oak Ridge National Laboratory as part of XSEDE, the CURIE supercomputer at CEA/France as part of PRACE project RA0844 and the SuperMUC computer at the Leibniz Computing Center, as part of project pr85je
The Formation of Galaxies Hosting z~6 Quasars
We investigate the formation and properties of galaxies hosting z~6 quasars,
in the gigaparsec scale cosmological hydrodynamical simulation: MassiveBlack,
which includes a self-consistent model for star formation, black hole accretion
and associated feedback. We show that the MassiveBlack reproduces current
estimates of the galaxy stellar mass function z=5, 6. We find that quasar hosts
in the simulation are compact gas rich systems with high star formations rates
of SFR ~ 100-1000 Msun/yr consistent with observed properties of Sloan quasar
hosts in the redshift range 5.5 < z < 6.5. We show that the star-forming gas in
these galaxies predominantly originates from high density cold streams which
are able to penetrate the halo and grow the galaxy at the center. MassiveBlack
predicts a deviation from the local Mbh-sigma and Mbh-Mstar relation implying
that black holes are relatively more massive for a given stellar host at these
redshifts.Comment: 12 pages, 8 figure
The Halo Occupation Distribution of Black Holes: Dependence on Mass
We investigate the halo occupation distribution (HOD) of black holes within a
hydrodynamic cosmological simulation that directly follows black hole growth.
Similar to the HOD of galaxies/subhalos, we find that the black hole occupation
number can be described by the form N_BH proportional to 1+ (M_Host)^alpha
where alpha evolves mildly with redshift indicating that a given mass halo
(M_Host) at low redshift tends to host fewer BHs than at high redshift (as
expected as a result of galaxy and BH mergers). We further divide the
occupation number into contributions from black holes residing in central and
satellite galaxies within a halo. The distribution of M_BH within halos tends
to consist of a single massive BH (distributed about a peak mass strongly
correlated with M_Host), and a collection of relatively low-mass secondary BHs,
with weaker correlation with M_Host. We also examine the spatial distribution
of BHs within their host halos, and find they typically follow a power-law
radial distribution (i.e. much more centrally concentrated than the subhalo
distribution). Finally, we characterize the host mass for which BH growth is
feedback dominated (e.g. star formation quenched). We show that halos with
M_Host > 3 * 10^12 M_sun have primary BHs that are feedback dominated by z~3
with lower mass halos becoming increasingly more affected at lower redshift.Comment: 10 pages, 7 figures, submitted to MNRA
Growth and anisotropy of ionization fronts near high redshift quasars in the MassiveBlack simulation
We use radiative transfer to study the growth of ionized regions around the
brightest, z=8 quasars in a large cosmological hydrodynamic simulation that
includes black hole growth and feedback (the MassiveBlack simulation). We find
that in the presence of the quasar s the comoving HII bubble radii reach 10
Mpc/h after 20 My while with the stellar component alone the HII bubbles are
smaller by at least an order of magnitude. Our calculations show that several
features are not captured within an analytical growth model of Stromgren
spheres. The X-ray photons from hard quasar spectra drive a smooth transition
from fully neutral to partially neutral in the ionization front. However the
transition from partially neutral to fully ionized is significantly more
complex. We measure the distance to the edge of bubbles as a function of angle
and use the standard deviation of these distances as a diagnostic of the
isotropy of ionized regions. We find that the overlapping of nearby ionized
regions from clustered halos not only increases the anisotropy, but also is the
main mechanism which allows the outer radius to grow. We therefore predict that
quasar ionized bubbles at this early stage in the reionization process should
be both significantly larger and more irregularly shaped than bubbles around
star forming galaxies. Before the star formation rate increases and the
Universe fully reionizes, quasar bubbles will form the most striking and
recognizable features in 21cm maps.Comment: 11 pages, 10 figures. Updated after referee repor
Infrared-Faint Radio Sources: A Cosmological View - AGN Number Counts, the Cosmic X-Ray Background and SMBH Formation
Context. Infrared Faint Radio Sources (IFRS) are extragalactic emitters
clearly detected at radio wavelengths but barely detected or undetected at
optical and infrared wavelengths, with 5 sigma sensitivities as low as 1 uJy.
Aims. Recent SED-modelling and analysis of their radio properties shows that
IFRS are consistent with a population of (potentially extremely obscured)
high-redshift AGN at 3<z<6. We demonstrate some astrophysical implications of
this population and compare them to predictions from models of galaxy evolution
and structure formation.
Methods. We compiled a list of IFRS from four deep extragalactic surveys and
extrapolated the IFRS number density to a survey-independent value of (30.8 +-
15.0) per square degree. We computed the IFRS contribution to the total number
of AGN in the Universe to account for the Cosmic X-ray Background. By
estimating the black hole mass contained in IFRS, we present conclusions for
the SMBH mass density in the early universe and compare it to relevant
simulations of structure formation after the Big Bang.
Results. The number density of AGN derived from the IFRS density was found to
be about 310 deg^-2, which is equivalent to a SMBH mass density of the order of
10^3 M_sun Mpc^-3 in the redshift range 3<z<6. This produces an X-ray flux of 9
10^-16 W m^-2 deg^-2 in the 0.5-2.0 keV band and 3 10^-15 W m^-2 deg^-2 in the
2.0-10 keV band, in agreement with the missing unresolved components of the
Cosmic X-ray Background. Concerning the problem of SMBH formation after the Big
Bang we find evidence for a scenario involving both halo gas accretion and
major mergers.Comment: 8 pages, 4 figures, accepted for publication in A&
The confinement of star-forming galaxies into a main sequence through episodes of gas compaction, depletion and replenishment
Using cosmological simulations, we address the properties of high-redshift star-forming galaxies (SFGs) across their main sequence (MS) in the plane of star formation rate (SFR) versus stellar mass. We relate them to the evolution of galaxies through phases of gas compaction, depletion, possible replenishment, and eventual quenching. We find that the high-SFR galaxies in the upper envelope of the MS are compact, with high gas fractions and short depletion times (`blue nuggets'), while the lower SFR galaxies in the lower envelope have lower central gas densities, lower gas fractions, and longer depletion times, consistent with observed gradients across the MS. Stellar-structure gradients are negligible. The SFGs oscillate about the MS ridge on time-scales 0.4tHubble (similar to 1 Gyr at z similar to 3). The propagation upwards is due to gas compaction, triggered, e.g. by mergers, counter-rotating streams, and/or violent disc instabilities. The downturn at the upper envelope is due to central gas depletion by peak star formation and outflows while inflow from the shrunken gas disc is suppressed. An upturn at the lower envelope can occur once the extended disc has been replenished by fresh gas and a new compaction can be triggered, namely as long as the replenishment time is shorter than the depletion time. The mechanisms of gas compaction, depletion, and replenishment confine the SFGs to the narrow (+/- 0.3 dex) MS. Full quenching occurs in massive haloes (M,1, > 1011 5 Me) and/or at low redshifts (z < 3), where the replenishment time is long compared to the depletion time, explaining the observed bending down of the MS at the massive end
Evolution of density profiles in high-z galaxies: compaction and quenching inside-out
Using cosmological simulations, we address the interplay between structure and star formation in high-redshift galaxies via the evolution of surface density profiles. Our sample consists of 26 galaxies evolving in the redshift range z = 7- 1, spanning the stellar mass range (0.2-6.4) x 10(10) M-circle dot at z = 2. We recover the main trends by stacking the profiles in accordance to their evolution phases. Following a wet compaction event that typically occurs when the stellar mass is similar to 10(9.5) M-circle dot at z similar to 2-4, the gas develops a cusp inside the effective radius, associated with a peak in star formation rate (SFR). The SFR peak and the associated feedback, in the absence of further gas inflow to the centre, marks the onset of gas depletion from the central 1 kpc, leading to quenching of the central SFR. An extended, star-forming ring that forms by fresh gas during the central quenching process shows as a rising specific SFR (sSFR) profile, which is interpreted as inside-out quenching. Before quenching, the stellar density profile grows self-similarly, maintaining its log-log shape because the sSFR is similar at all radii. During the quenching process, the stellar density saturates to a constant value, especially in the inner 1 kpc. The stellar mass and SFR profiles deduced from observations show very similar shapes, consistent with the scenario of wet compaction leading to inside-out quenching and the subsequent saturation of a dense stellar core. We predict a cuspy gas profile during the blue nugget phase, and a gas-depleted core, sometimes surrounded by a ring, in the post-blue nugget phase
The Demographics of Broad Line Quasars in the Mass-Luminosity Plane II. Black Hole Mass and Eddington Ratio Functions
We employ a flexible Bayesian technique to estimate the black hole mass and
Eddington ratio functions for Type 1 (i.e., broad line) quasars from a
uniformly-selected data set of ~58,000 quasars from the SDSS DR7. We find that
the SDSS becomes significantly incomplete at M_{BH} < 3 x 10^8 M_{Sun} or L /
L_{Edd} < 0.07, and that the number densities of Type 1 quasars continue to
increase down to these limits. Both the mass and Eddington ratio functions show
evidence of downsizing, with the most massive and highest Eddington ratio black
holes experiencing Type 1 quasar phases first, although the Eddington ratio
number densities are flat at z < 2. We estimate the maximum Eddington ratio of
Type 1 quasars in the observable Universe to be L / L_{Edd} ~ 3. Consistent
with our results in Paper I, we do not find statistical evidence for a
so-called "sub-Eddington boundary" in the mass-luminosity plane of broad line
quasars, and demonstrate that such an apparent boundary in the observed
distribution can be caused by selection effect and errors in virial BH mass
estimates. Based on the typical Eddington ratio in a given mass bin, we
estimate typical growth times for the black holes in Type 1 quasars and find
that they are typically comparable to or longer than the age of the universe,
implying an earlier phase of accelerated (i.e., with higher Eddington ratios)
and possibly obscured growth. The large masses probed by our sample imply that
most of our black holes reside in what are locally early type galaxies, and we
interpret our results within the context of models of self-regulated black hole
growth.Comment: Submitted to ApJ, 25 pages (emulateapj), 15 figures; revised to match
accepted version with primary changes to the introduction and discussion,
replaced Fig 1
Resolving discs and mergers in z ā¼ 2 heavily reddened quasars and their companion galaxies with ALMA
We present sub-arcsecond resolution Atacama Large Millimeter Array imaging of the CO(3ā2) emission in two z ā¼ 2.5 heavily reddened quasars (HRQs) ā ULASJ1234+0907 and ULASJ2315+0143 ā and their companion galaxies. Dynamical modelling of the resolved velocity fields enables us to constrain the molecular gas morphologies and host galaxy masses. Combining the new data with extensive multiwavelength observations, we are able to study the relative kinematics of different molecular emission lines, the molecular gas fractions, and the locations of the quasars on the MBHāMgal relation. Despite having similar black hole properties, the two HRQs display markedly different host galaxy properties and local environments. J1234 has a very massive host ā Mdyn ā¼ 5 Ć 1011 Mā and two companion galaxies that are similarly massive located within 200 kpc of the quasar. The molecular gas fraction is low (ā¼6 per cent). The significant ongoing star formation in the host galaxy is entirely obscured at rest-frame ultraviolet (UV) and optical wavelengths. J2315 is resolved into a close-separation major merger (Īr = 15 kpc; Īv = 170 kmāsā1) with a ā¼1:2 mass ratio. The total dynamical mass is estimated to be ā²1011 Mā and the molecular gas fraction is high (>45 per cent). A new HSC image of the galaxy shows unobscured UV-luminous star-forming regions co-incident with the extended reservoir of cold molecular gas in the merger. We use the outputs from the Illustris simulations to track the growth of such massive black holes from z ā¼ 6 to the present day. While J1234 is consistent with the simulated z ā¼ 2 relation, J2315 has a black hole that is overmassive relative to its host galaxy