259 research outputs found
Population statistics of intermediate mass black holes in dwarf galaxies using the NewHorizon simulation
While it is well established that supermassive black holes (SMBHs) co-evolve
with their host galaxy, it is currently less clear how lower mass black holes,
so-called intermediate mass black holes (IMBHs), evolve within their dwarf
galaxy hosts. In this paper, we present results on the evolution of a large
sample of IMBHs from the NewHorizon simulation. We show that occupation
fractions of IMBHs in dwarf galaxies are at least 50 percent for galaxies with
stellar masses down to 1E6 Msun, but BH growth is very limited in dwarf
galaxies. In NewHorizon, IMBH growth is somewhat more efficient at high
redshift z = 3 but in general IMBH do not grow significantly until their host
galaxy leaves the dwarf regime. As a result, NewHorizon under-predicts observed
AGN luminosity function and AGN fractions. We show that the difficulties of
IMBH to remain attached to the centres of their host galaxies plays an
important role in limiting their mass growth, and that this dynamic evolution
away from galactic centres becomes stronger at lower redshift.Comment: 15 pages, submitted to MNRA
The role of mergers and interactions in driving the evolution of dwarf galaxies over cosmic time
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record is available online at: https://doi.org/10.1093/mnras/staa3443Dwarf galaxies (Mâ < 109 Mâ) are key drivers of mass assembly in high-mass galaxies, but relatively little is understood about the assembly of dwarf galaxies themselves. Using the NEWHORIZON cosmological simulation (âŒ40 pc spatial resolution), we investigate how mergers and fly-bys drive the mass assembly and structural evolution of around 1000 field and group dwarfs up to z = 0.5. We find that, while dwarf galaxies often exhibit disturbed morphologies (5 and 20 per cent are disturbed at z = 1 and z = 3 respectively), only a small proportion of the morphological disturbances seen in dwarf galaxies are driven by mergers at any redshift (for 109 Mâ, mergers drive under 20 per cent morphological disturbances). They are instead primarily the result of interactions that do not end in a merger (e.g. fly-bys). Given the large fraction of apparently morphologically disturbed dwarf galaxies which are not, in fact, merging, this finding is particularly important to future studies identifying dwarf mergers and post-mergers morphologically at intermediate and high redshifts. Dwarfs typically undergo one major and one minor merger between z = 5 and z = 0.5, accounting for 10 per cent of their total stellar mass. Mergers can also drive moderate star formation enhancements at lower redshifts (3 or 4 times at z = 1), but this accounts for only a few per cent of stellar mass in the dwarf regime given their infrequency. Non-merger interactions drive significantly smaller star formation enhancements (around two times), but their preponderance relative to mergers means they account for around 10 per cent of stellar mass formed in the dwarf regime.Peer reviewe
The formation of cores in galaxies across cosmic time - the existence of cores is not in tension with the ÎCDM paradigm
© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/The 'core-cusp' problem is considered a key challenge to the ÎCDM paradigm. Haloes in dark matter only simulations exhibit 'cuspy' profiles, where density continuously increases towards the centre. However, the dark matter profiles of many observed galaxies (particularly in the dwarf regime) deviate strongly from this prediction, with much flatter central regions ('cores'). We use NewHorizon (NH), a hydrodynamical cosmological simulation, to investigate core formation, using a statistically significant number of galaxies in a cosmological volume. Haloes containing galaxies in the upper (Mâ â„ 1010.2 Mâ) and lower (Mâ †108 Mâ) ends of the stellar mass distribution contain cusps. However, Haloes containing galaxies with intermediate (108 Mâ †Mâ †1010.2 Mâ) stellar masses are generally cored, with typical halo masses between 1010.2 Mâ and 1011.5 Mâ. Cores form through supernova-driven gas removal from halo centres, which alters the central gravitational potential, inducing dark matter to migrate to larger radii. While all massive (Mâ â„ 109.5 Mâ) galaxies undergo a cored-phase, in some cases cores can be removed and cusps reformed. This happens if a galaxy undergoes sustained star formation at high redshift, which results in stars (which, unlike the gas, cannot be removed by baryonic feedback) dominating the central gravitational potential. After cosmic star formation peaks, the number of cores, and the mass of the Haloes they are formed in, remain constant, indicating that cores are being routinely formed over cosmic time after a threshold halo mass is reached. The existence of cores is, therefore, not in tension with the standard paradigm.Peer reviewe
The Horizon-AGN simulation: evolution of galaxy properties over cosmic time
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We compare the predictions of Horizon-AGN, a hydro-dynamical cosmological simulation that uses an adaptive mesh refinement code, to observational data in the redshift range 0 < z < 6. We study the reproduction, by the simulation, of quantities that trace the aggregate stellar-mass growth of galaxies over cosmic time: luminosity and stellar-mass functions, the star formation main sequence, rest-frame UV-optical-near infrared colours and the cosmic star-formation history. We show that Horizon-AGN, which is not tuned to reproduce the local Universe, produces good overall agreement with these quantities, from the present day to the epoch when the Universe was 5% of its current age. By comparison to Horizon-noAGN, a twin simulation without AGN feedback, we quantify how feedback from black holes is likely to help shape galaxy stellar-mass growth in the redshift range 0 < z < 6, particularly in the most massive galaxies. Our results demonstrate that Horizon-AGN successfully captures the evolutionary trends of observed galaxies over the lifetime of the Universe, making it an excellent tool for studying the processes that drive galaxy evolution and making predictions for the next generation of galaxy surveys.Peer reviewedFinal Published versio
Noncommutative Solitonic Black Hole
We investigate solitonic black hole solutions in three dimensional
noncommutative spacetime. We do this in gravity with negative cosmological
constant coupled to a scalar field. Noncommutativity is realized with the Moyal
product which is expanded up to first order in the noncommutativity parameter
in two spatial directions. With numerical simulation we study the effect of
noncommutativity by increasing the value of the noncommutativity parameter
starting from commutative solutions. We find that even a regular soliton
solution in the commutative case becomes a black hole solution when the
noncommutativity parameter reaches a certain value.Comment: 11 pages, 5 figures, LaTeX format, appendix added, minor correction
Bogomolnyi Bound with a Cosmological Constant
Bogomolnyi-type bound is constructed for the topological solitons in O(3)
nonlinear model coupled to gravity with a negative cosmological
constant. Spacetimes made by self-dual solutions form a class of G\"{o}del-type
universe. In the limit of a spinless massive point particle, the obtained
stationary metric does not violate the causality and it is a new point particle
solution different from the known static hyperboloid and black hole. We also
showed that static Nielsen-Olesen vortices saturate Bogomolnyi-type bound only
when the cosmological constant vanishes.Comment: 11 pages, RevTe
Constraining stellar assembly and AGN feedback at the peak epoch of star formation
We study stellar assembly and feedback from active galactic nuclei (AGN)
around the epoch of peak star formation (1<z<2), by comparing hydrodynamic
simulations to rest-frame UV-optical galaxy colours from the Wide Field Camera
3 (WFC3) Early-Release Science (ERS) Programme. Our Adaptive Mesh Refinement
simulations include metal-dependent radiative cooling, star formation, kinetic
outflows due to supernova explosions, and feedback from supermassive black
holes. Our model assumes that when gas accretes onto black holes, a fraction of
the energy is used to form either thermal winds or sub-relativistic
momentum-imparting collimated jets, depending on the accretion rate. We find
that the predicted rest-frame UV-optical colours of galaxies in the model that
includes AGN feedback is in broad agreement with the observed colours of the
WFC3 ERS sample at 1<z<2. The predicted number of massive galaxies also matches
well with observations in this redshift range. However, the massive galaxies
are predicted to show higher levels of residual star formation activity than
the observational estimates, suggesting the need for further suppression of
star formation without significantly altering the stellar mass function. We
discuss possible improvements, involving faster stellar assembly through
enhanced star formation during galaxy mergers while star formation at the peak
epoch is still modulated by the AGN feedback.Comment: 6 pages, 4 figures, accepted for publication in MNRAS Letter
Global Vortex and Black Cosmic String
We study global vortices coupled to (2+1) dimensional gravity with negative
cosmological constant. We found nonsingular vortex solutions in -theory
with a broken U(1) symmetry, of which the spacetimes do not involve physical
curvature singularity. When the magnitude of negative cosmological constant is
larger than a critical value at a given symmetry breaking scale, the spacetime
structure is a regular hyperbola, however it becomes a charged black hole when
the magnitude of cosmological constant is less than the critical value. We
explain through duality transformation the reason why static global vortex
which is electrically neutral forms black hole with electric charge. Under the
present experimental bound of the cosmological constant, implications on
cosmology as a straight black cosmic string is also discussed in comparison
with global U(1) cosmic string in the spacetime of the zero cosmological
constant.Comment: 35 pages, Late
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