27 research outputs found
The High Mass X-ray Binaries in star-forming galaxies
The high mass X-ray binaries (HMXBs) provide an exciting framework to
investigate the evolution of massive stars and the processes behind binary
evolution. HMXBs have shown to be good tracers of recent star formation in
galaxies and might be important feedback sources at early stages of the
Universe. Furthermore, HMXBs are likely the progenitors of gravitational wave
sources (BH--BH or BH--NS binaries that may merge producing gravitational
waves). In this work, we investigate the nature and properties of HMXB
population in star-forming galaxies. We combine the results from the population
synthesis model MOBSE (Giacobbo et al. 2018) together with galaxy catalogs from
EAGLE simulation (Schaye et al. 2015). Therefore, this method describes the
HMXBs within their host galaxies in a self-consistent way. We compute the X-ray
luminosity function (XLF) of HMXBs in star-forming galaxies, showing that this
methodology matches the main features of the observed XLF.Comment: 4 pages, 2 figures. To appear in Proc. IAUS 346: High-mass X-ray
binaries: illuminating the passage from massive binaries to merging compact
object
Alignment of the central galaxies with the environment
In this work, we combine ellipticity and major axis position angle
measurements from the Sloan Digital Sky Server Data Release 16 (SDSS DR16) with
the group finder algorithm of Rodriguez \& Merch\'an to determine the alignment
of the central galaxies with the surrounding structures and satellite galaxies
lying in their group. We use two independent methods: A modified version of the
two-point cross-correlation function and the angle between the central galaxy
orientation and the satellite galaxies relative position. The first method
allows us to study the inner and outer regions of the cluster, while the second
method provides information within the halos. Our results show that central
galaxies present anysotropy in the correlation function up to , which becomes 10\% stronger for the brightest ones
(). When we split the galaxy sample by colour, we find that
red central galaxies are the main contributors to this anisotropy. We also show
that this behaviour does not depend on the group mass or central galaxy
ellipticity. Finally, our results are in agreement with previous findings,
showing that the two-point cross-correlation function is a best tracer of the
galaxy alignments using all galaxies and not only those of the group to which
it belongs. In addition, this feature allows us to explore the behaviour of the
alignment on larger scales.Comment: 10 pages, 9 figures, sent to MNRA
Anisotropic correlation functions as tracers of central galaxy alignments in simulations
Motivated by observational results, we use IllustrisTNG hydrodynamical
numerical simulations to study the alignment of the central galaxies in groups
with the surrounding structures. This approach allows us to analyse galaxy and
group properties not available in observations. To perform this analysis, we
use a modified version of the two-point cross-correlation function and a
measure of the angle between the semi-major axes of the central galaxies and
the larger structures. Overall, our results reproduce observational ones, as we
find large-scale anisotropy, which is dominated by the red central galaxies. In
addition, the latter is noticeably more aligned with their group than the blue
ones. In contrast to the observations, we find a strong dependence of the
anisotropy on the central galaxy with mass, probably associated with the
inability of observational methods to determine them. This result allows us to
link the alignment to the process of halo assembly and the well-known
dependence of halo anisotropy on mass. When we include the dark matter
distribution in our analysis, we conclude that the galaxy alignment found in
simulations (and observations) can be explained by a combination of physical
processes at different scales: the central galaxy aligns with the dark matter
halo it inhabits, and this, in turn, aligns with the surrounding structures at
large scales.Comment: 9 pages, 11 figures, Accepted by MNRA
The cosmic merger rate density of compact objects: impact of star formation, metallicity, initial mass function and binary evolution
We evaluate the redshift distribution of binary black hole (BBH), black hole
- neutron star binary (BHNS) and binary neutron star (BNS) mergers, exploring
the main sources of uncertainty: star formation rate (SFR) density, metallicity
evolution, common envelope, mass transfer via Roche lobe overflow, natal kicks,
core-collapse supernova model and initial mass function. Among binary evolution
processes, uncertainties on common envelope ejection have a major impact: the
local merger rate density of BNSs varies from to
Gpc yr if we change the common envelope efficiency parameter from
to 0.5, while the local merger rates of BBHs and BHNSs vary
by a factor of . The BBH merger rate changes by one order of
magnitude, when uncertainties on metallicity evolution are taken
into account. In contrast, the BNS merger rate is almost insensitive to
metallicity. Hence, BNSs are the ideal test bed to put constraints on uncertain
binary evolution processes, such as common envelope and natal kicks. Only
models assuming values of and moderately low natal
kicks (depending on the ejected mass and the SN mechanism), result in a local
BNS merger rate density within the 90% credible interval inferred from the
second gravitational-wave transient catalogue.Comment: 14 pages, 12 figures, 2 tables, accepted for publication in MNRA
The galaxy size - halo mass scaling relations and clustering properties of central and satellite galaxies
In this work, we combine size and stellar mass measurements from the Sloan
Digital Sky Server (SDSS) with the group finder algorithm of Rodriguez \&
Merch\'an in order to determine the stellar and halo mass -- size relations of
central and satellite galaxies separately. We show that, while central and
satellite galaxies display similar stellar mass -- size relations, their halo
mass -- size relations differ significantly. As expected, more massive haloes
tend to host larger central galaxies. However, the size of satellite galaxies
depends only slightly on halo virial mass. We show that these results are
compatible with a remarkably simple model in which the size of central and
satellite galaxies scales as the cubic root of their host halo mass, with the
normalization for satellites being 30 \% smaller than that for central
galaxies, which can be attributed to tidal stripping. We further check that our
measurements are in excellent agreement with predictions from the IllustrisTNG
hydrodynamical simulation. In the second part of this paper, we analyse how the
clustering properties of central and satellite galaxies depend on their size.
We demonstrate that, independently of the stellar mass threshold adopted,
smaller galaxies are more tightly clustered than larger galaxies when either
the entire sample or only satellites are considered. The opposite trend is
observed on large scales when the size split is performed for the central
galaxies alone. Our results place significant constraints for halo-galaxy
connection models that link galaxy size with the properties of their hosting
haloes.Comment: 15 pages, 12 figures. Accepted for publication in MNRA
Impact of gas hardening on the population properties of hierarchical black hole mergers in AGN disks
Hierarchical black hole (BH) mergers in active galactic nuclei (AGNs) are
unique among formation channels of binary black holes (BBHs) because they are
likely associated with electromagnetic counterparts and can efficiently lead to
the mass growth of BHs. Here, we explore the impact of gas accretion and
migration traps on the evolution of BBHs in AGNs. We have developed a new fast
semi-analytic model, which allows us to explore the parameter space while
capturing the main physical processes involved. We find that effective exchange
of energy and angular momentum between the BBH and the surrounding gas
(hereafter, gas hardening) during inspiral greatly enhances the efficiency of
hierarchical mergers, leading to the formation of intermediate-mass BHs (up to
10.000 solar masses) and triggering spin alignment. Moreover, our models with
efficient gas hardening show both an anti-correlation between BBH mass ratio
and effective spin, and a correlation between primary BH mass and effective
spin. In contrast, if gas hardening is inefficient, the hierarchical merger
chain is already truncated after the first two or three generations. We compare
the BBH population in AGNs with other dynamical channels as well as isolated
binary evolution.Comment: 21 pages, 15 figures, submitted to A&A, comments welcom
New insights on binary black hole formation channels after GWTC-2: young star clusters versus isolated binaries
With the recent release of the second gravitational-wave transient catalogue
(GWTC-2), which introduced dozens of new detections, we are at a turning point
of gravitational wave astronomy, as we are now able to directly infer
constraints on the astrophysical population of compact objects. Here, we tackle
the burning issue of understanding the origin of binary black hole (BBH)
mergers. To this effect, we make use of state-of-the-art population synthesis
and N-body simulations, to represent two distinct formation channels: BBHs
formed in the field (isolated channel) and in young star clusters (dynamical
channel). We then use a Bayesian hierarchical approach to infer the
distribution of the mixing fraction , with () in the pure
dynamical (isolated) channel. %that controls the proportion of isolated and
dynamical BBHs. We explore the effects of additional hyper-parameters of the
model, such as the spread in metallicity and the parameter
, describing the distribution of spin magnitudes. We find
that the dynamical model is slightly favoured with a median value of ,
when and . Models with higher
spin magnitudes tend to strongly favour dynamically formed BBHs ( if
). Furthermore, we show that hyper-parameters
controlling the rates of the model, such as , have a large
impact on the inference of the mixing fraction, which rises from to
when we increase from 0.2 to 0.6, for a fixed value
of . Finally, our current set of observations is better
described by a combination of both formation channels, as a pure dynamical
scenario is excluded at the credible interval, except when the spin
magnitude is high.Comment: 13 pages, 10 figures, 2 tables, published in MNRA
Small-scale galaxy clustering in the eagle simulation
We study present-day galaxy clustering in the EAGLE cosmological hydrodynamical simulation. EAGLE’s galaxy formation parameters were calibrated to reproduce the redshift z = 0.1 galaxy stellar mass function, and the simulation also reproduces galaxy colours well. The simulation volume is too small to correctly sample large-scale fluctuations and we therefore concentrate on scales smaller than a few mega parsecs. We find very good agreement with observed clustering measurements from the Galaxy And Mass Assembly (GAMA) survey, when galaxies are binned by stellar mass, colour or luminosity. However, low-mass red galaxies are clustered too strongly, which is at least partly due to limited numerical resolution. Apart from this limitation, we conclude that EAGLE galaxies inhabit similar dark matter haloes as observed GAMA galaxies, and that the radial distribution of satellite galaxies, as a function of stellar mass and colour, is similar to that observed as well