18 research outputs found
Testing primordial non-Gaussianities on galactic scales at high redshift
Primordial non-Gaussianities provide an important test of inflationary
models. Although the Planck CMB experiment has produced strong limits on
non-Gaussianity on scales of clusters, there is still room for considerable
non-Gaussianity on galactic scales. We have tested the effect of local
non-Gaussianity on the high redshift galaxy population by running five
cosmological N-body simulations down to z=6.5. For these simulations, we adopt
the same initial phases, and either Gaussian or scale-dependent non-Gaussian
primordial fluctuations, all consistent with the constraints set by Planck on
clusters scales. We then assign stellar masses to each halo using the halo -
stellar mass empirical relation of Behroozi et al. (2013). Our simulations with
non-Gaussian initial conditions produce halo mass functions that show clear
departures from those obtained from the analogous simulations with Gaussian
initial conditions at z>~10. We observe a >0.3 dex enhancement of the low-end
of the halo mass function, which leads to a similar effect on the galaxy
stellar mass function, which should be testable with future galaxy surveys at
z>10. As cosmic reionization is thought to be driven by dwarf galaxies at high
redshift, our findings may have implications for the reionization history of
the Universe.Comment: 6 pages, 3 figures, 1 table, MNRAS (Letters) in pres
Decoupling the rotation of stars and gas - II. The link between black hole activity and simulated IFU kinematics in IllustrisTNG
Funding: UK Science and Technology Funding Council ( STFC) via an PhD studentship (grant number ST/N504427/1) (CD).We study the relationship between supermassive black hole (BH) feedback, BH luminosity and the kinematics of stars and gas for galaxies inIllustrisTNG. We use galaxies with mock MaNGA observations to identify kinematic misalignment at z = 0 (difference in rotation of stars and gas), for which we follow the evolutionary history of BH activity and gas properties over the last 8 Gyrs. Misaligned low mass galaxies (Mstel 1010.2M⊙) with misalignment typically have similar BH luminosities, show lower gas fractions, and have typically lower gas phase metallicity over the last 8 Gyrs in comparison to the high mass aligned.Publisher PDFPeer reviewe
Black hole formation and growth with non-Gaussian primordial density perturbations
Quasars powered by massive black holes (BHs) with mass estimates above a
billion solar masses have been identified at redshift 6 and beyond. The
existence of such BHs requires almost continuous growth at the Eddington limit
for their whole lifetime, of order of one billion years. In this paper, we
explore the possibility that positively skewed scale-dependent non-Gaussian
primordial fluctuations may ease the assembly of massive BHs. In particular,
they produce more low-mass halos at high redshift, thus altering the production
of metals and ultra-violet flux, believed to be important factors in BH
formation. Additionally, a higher number of progenitors and of nearly
equal-mass halo mergers would boost the mass increase provided by BH-BH mergers
and merger-driven accretion. We use a set of two cosmological simulations, with
either Gaussian or scale-dependent non-Gaussian primordial fluctuations to
perform a proof-of-concept experiment to estimate how BH formation and growth
are altered. We estimate the BH number density and the fraction of halos where
BHs form, for both simulations and for two popular scenarios of BH formation
(remnants of the first generation of stars and direct collapse in the absence
of metals and molecular hydrogen). We find that the fractions of halos where
BHs form are almost identical, but that non-Gaussian primordial perturbations
increase the total number density of BHs for the both BH formation scenarios.
We also evolve BHs using merger trees extracted from the simulations and find
that non-Gaussianities increase both the BH masses and the number of the most
massive BHs.Comment: 11 pages, 10 figures, MNRAS accepte
Linking galaxy structural properties and star formation activity to black hole activity with IllustrisTNG
We study the connection between active galactic nuclei (AGN) and their host
galaxies through cosmic time in the large-scale cosmological IllustrisTNG
simulations. We first compare BH properties, i.e. the hard X-ray BH luminosity
function, AGN galaxy occupation fraction, and distribution of Eddington ratios,
to available observational constraints. The simulations produce a population of
BHs in good agreement with observations, but we note an excess of faint AGN in
hard X-ray (L_x ~ 10^{43-44} erg/s), and a lower number of bright AGN
(L_x>10^{44} erg/s), a conclusion that varies quantitatively but not
qualitatively with BH luminosity estimation method. The lower Eddington ratios
of the 10^{9} Msun BHs compared to observations suggest that AGN feedback may
be too efficient in this regime. We study galaxy star formation activity and
structural properties, and design sample-dependent criteria to identify
different galaxy types (star-forming/quiescent, extended/compact) that we apply
both to the simulations and observations from the candels fields. We analyze
how the simulated and observed galaxies populate the specific star formation
rate - stellar mass surface density diagram. A large fraction of the z=0
M_{star}>10^{11} Msun quiescent galaxies first experienced a compaction phase
(i.e. reduction of galaxy size) while still forming stars, and then a quenching
event. We measure the dependence of AGN fraction on galaxies' locations in this
diagram. After correcting the simulations with a redshift and AGN
luminosity-dependent model for AGN obscuration, we find good qualitative and
quantitative agreement with observations. The AGN fraction is the highest among
compact star-forming galaxies (16-20% at z~1.5-2), and the lowest among compact
quiescent galaxies (6-10% at z~1.5-2).Comment: 35 pages, 22 figures, accepted for publication in MNRA
The relationship between black hole mass and galaxy properties: Examining the black hole feedback model in IllustrisTNG
Supermassive black hole feedback is thought to be responsible for the lack of
star formation, or quiescence, in a significant fraction of galaxies. We
explore how observable correlations between the specific star formation rate
(sSFR), stellar mass (M), and black hole mass (M) are
sensitive to the physics of black hole feedback in a galaxy formation model. We
use the IllustrisTNG simulation suite, specifically the TNG100 simulation and
ten model variations that alter the parameters of the black hole model.
Focusing on central galaxies at with M
M, we find that the sSFR of galaxies in IllustrisTNG decreases once
the energy from black hole kinetic winds at low accretion rates becomes larger
than the gravitational binding energy of gas within the galaxy stellar radius.
This occurs at a particular M threshold above which galaxies are
found to sharply transition from being mostly star-forming to mostly quiescent.
As a result of this behavior, the fraction of quiescent galaxies as a function
of M is sensitive to both the normalization of the
M-M relation and the M threshold for
quiescence in IllustrisTNG. Finally, we compare these model results to
observations of 91 central galaxies with dynamical M measurements
with the caveat that this sample is not representative of the whole galaxy
population. While IllustrisTNG reproduces the observed trend that quiescent
galaxies host more massive black holes, the observations exhibit a broader
scatter in M at a given M and show a smoother decline
in sSFR with M.Comment: 20 pages, submitted to MNRA
Cosmic voids::a novel probe to shed light on our Universe
Cosmic voids, the less dense patches of the Universe, are promising laboratories to extract cosmological information. Thanks to their unique low density character, voids are extremely sensitive to diffuse components such as neutrinos and dark energy, and represent ideal environments to study modifications of gravity, where the effects of such modifications are expected to be more prominent. Robust void-related observables, including for example redshift-space distortions (RSD) and weak lensing around voids, are a promising way to chase and test new physics. Cosmological analysis of the large-scale structure of the Universe predominantly relies on the high density regions. Current and upcoming surveys are designed to optimize the extraction of cosmological information from these zones, but leave voids under-exploited. A dense, large area spectroscopic survey with imaging capabilities is ideal to exploit the power of voids fully. Besides helping illuminate the nature of dark energy, modified gravity, and neutrinos, this survey will give access to a detailed map of under-dense regions, providing an unprecedented opportunity to observe and study a so far under-explored galaxy population
Overview of the Advanced X-ray Imaging Satellite (AXIS)
The Advanced X-ray Imaging Satellite (AXIS) is a Probe-class concept that will build on the legacy of the Chandra X-ray Observatory by providing low-background, arcsecond-resolution imaging in the 0.3-10 keV band across a 450 arcminute 2 field of view, with an order of magnitude improvement in sensitivity. AXIS utilizes breakthroughs in the construction of lightweight segmented X-ray optics using single-crystal silicon, and developments in the fabrication of large-format, small-pixel, high readout rate CCD detectors with good spectral resolution, allowing a robust and cost-effective design. Further, AXIS will be responsive to target-of-opportunity alerts and, with onboard transient detection, will be a powerful facility for studying the time-varying X-ray universe, following on from the legacy of the Neil Gehrels (Swift) X-ray observatory that revolutionized studies of the transient X-ray Universe. In this paper, we present an overview of AXIS, highlighting the prime science objectives driving the AXIS concept and how the observatory design will achieve these objectives
Formation of supermassive black holes
International audienceSupermassive black holes (BHs) harboured in the center of galaxies have been confirmed with the discovery of Sagittarius A* in the center of our galaxy, the Milky Way. Recent surveys indicate that BHs of millions of solar masses are common in most local galaxies, but also that some local galaxies could be lacking BHs (e.g. NGC205, M33), or at least hosting low-mass BHs of few thousands solar masses. Conversely, massive BHs under their most luminous form are called quasars, and their luminosity can be up to hundred times the luminosity of an entire galaxy. We observe these quasars in the very early Universe, less than a billion years after the Big Bang. BH formation models therefore need to explain both the low-mass BHs that are observed in low-mass galaxies today, but also the prodigious quasars we see in the early Universe.BH formation is still puzzling today, and many questions need to be addressed: How are BHs created in the early Universe? What is their initial mass? How many BHs grow efficiently? What is the occurrence of BH formation in high redshift galaxies? What is the minimum galaxy mass to host a BH? We have used cosmological hydrodynamical simulations to capture BH formation in the context of galaxy formation and evolution. Simulations offer the advantage of following in time the evolution of galaxies, and the processes related to them, such as star formation, metal enrichment, feedback of supernovae and BHs. We have particularly focused our studies on the three main BH formation models: Pop III remnant, stellar cluster, and direct collapse models
Formation de trous noirs supermassifs
Supermassive black holes (BHs) harboured in the center of galaxies have been confirmed with the discovery of Sagittarius A* in the center of our galaxy, the Milky Way. Recent surveys indicate that BHs of millions of solar masses are common in most local galaxies, but also that some local galaxies could be lacking BHs (e.g. NGC205, M33), or at least hosting low-mass BHs of few thousands solar masses. Conversely, massive BHs under their most luminous form are called quasars, and their luminosity can be up to hundred times the luminosity of an entire galaxy. We observe these quasars in the very early Universe, less than a billion years after the Big Bang. BH formation models therefore need to explain both the low-mass BHs that are observed in low-mass galaxies today, but also the prodigious quasars we see in the early Universe.BH formation is still puzzling today, and many questions need to be addressed: How are BHs created in the early Universe? What is their initial mass? How many BHs grow efficiently? What is the occurrence of BH formation in high redshift galaxies? What is the minimum galaxy mass to host a BH? We have used cosmological hydrodynamical simulations to capture BH formation in the context of galaxy formation and evolution. Simulations offer the advantage of following in time the evolution of galaxies, and the processes related to them, such as star formation, metal enrichment, feedback of supernovae and BHs. We have particularly focused our studies on the three main BH formation models: Pop III remnant, stellar cluster, and direct collapse models.Des trous noirs supermassifs (TNs) de plusieurs millions de masses solaires occupent le centre de la plupart des galaxies proches. La découverte du TN Sagittarius A* au centre de notre galaxie, La Voie lactée, l'a confirmé. Pour autant, certaines galaxies semblent dépourvues de TNs (par exemple NGC205, M33), ou alors ne posséder un TN que de quelques milliers de masses solaires. D'autre part, des TNs dans leur forme la plus lumineuse, appelés quasars, dont la luminosité est plus importante que des centaines de fois celle d'une galaxie toute entière, ont été observés à très grand décalage spectral, lorsque l'Univers n'était alors âgé que d'un milliard d'années. Les modèles de formation des TNs doivent expliquer à la fois l'existence des TNs de faibles masses observés aujourd'hui dans les galaxies de faibles masses, mais aussi leur prodigieux homologues quasars dans l'Univers jeune. La formation des TNs pose encore de nos jours de nombreuses questions: comment se forment les TNs au début de l'histoire de l'Univers? Quelle est leur masse initiale? Quelle est la masse minimale d'une galaxie pour posséder un TN? Pour répondre à ces questions et pour étudier la formation des TNs dans le contexte de l'évolution des galaxies, nous avons utilisé des simulations hydrodynamiques cosmologiques, qui offrent l'avantage de suivre l'évolution temporelle de nombreux processus comme la formation stellaire, l'enrichissement en métaux, les mécanismes de rétroactions des TNs et des supernovae. J'ai particulièrement dirigé mes recherches sur les trois principaux modèles de formation des TNs à partir du reliquat des premières étoiles, d'amas d'étoiles, ou encore par effondrement direct