197 research outputs found
Synthetic extinction maps around intermediate-mass black holes in Galactic globular clusters
During the last decades, much effort has been devoted to explain the
discrepancy between the amount of intracluster medium (ICM) estimated from
stellar evolution theories and that emerging from observations in globular
clusters (GCs). One possible scenario is the accretion of this medium by an
intermediate-mass black hole (IMBH) at the centre of the cluster. In this work,
we aim at modelling the cluster colour-excess profile as a tracer of the ICM
density, both with and without an IMBH. Comparing the profiles with
observations allows us to test the existence of IMBHs and their possible role
in the cleansing of the ICM. We derive the intracluster density profiles from
hydrodynamical models of accretion onto a central IMBH in a GC and we determine
the corresponding dust density. This model is applied to a list of 25 Galactic
GCs. We find that central IMBHs decrease the ICM by several orders of
magnitude. In a subset of 9 clusters, the absence of the black hole combined
with a low intracluster medium temperature would be at odds with present gas
mass content estimations. As a result, we conclude that IMBHs are an effective
cleansing mechanism of the ICM of GCs. We construct synthetic extinction maps
for M 62 and {\omega} Cen, two clusters in the small subset of 9 with observed
2D extinction maps. We find that under reasonable assumptions regarding the
model parameters, if the gas temperature in M 62 is close to 8000 K, an IMBH
needs to be invoked. Further ICM observations regarding both the gas and dust
in GCs could help to settle this issue.Comment: Accepted for publication in MNRAS.11 pages, 7 figure
Agujeros negros astrofísicos
De acuerdo a la Teoría General de la Relatividad, los agujeros negros pueden describirse través de solamente tres parámetros físicos: su masa, su momento angular (que indica su estado de rotación), y su carga eléctrica. Claramente la masa es el parámetro principal, ya que ella produce el campo gravitatorio responsable de la existencia misma de los agujeros negros. La masa de un agujero negro puede en principio tomar cualquier valor, aunque un límite inferior para la misma viene dado por la escala de Planck, en la que los efectos cuánticos de la gravedad se hacen perceptibles. Dicha masa corresponde a apenas unas decenas de microgramos, por lo que los agujeros negros con masas de este orden se denominan microagujeros negros. Éstos constituyen una predicción interesante de las modernas teorías sobre la gravitación, sin embargo, no trataremos sobre ellos en este artículo, ya que estamos interesados en agujeros negros detectables en el dominio de la Astrofísica.
En el área de la Astrofísica esperamos, en cambio, encontrar agujeros negros de masas comparables a las de los planetas, las estrellas, o las galaxias. Dos clases de agujeros negros astrofísicos han sido predichos: los agujeros negros de masa estelar, y los agujeros negros supermasivos. En ambos casos, existen observaciones que proveen evidencia de su existencia. Como su nombre lo indica, los primeros tienen masas comparables a las de las estrellas y se forman en ciertas etapas de la evolución de las mismas. Los últimos, por su parte, se observan en el centro de las galaxias, y sus masas son millones de veces mayores a las estelares. Existe actualmente un debate en la comunidad astrofísica, acerca de la existencia de una tercera clase de agujeros negros: los agujeros negros de masa intermedia. Éstos tendrían masas de cientos a miles de veces mayores a la del Sol, y su existencia podría resolver algunos misterios sin develar. Este artículo pretende dar una introducción general a los agujeros negros astrofísicos, haciendo énfasis en las características y procesos que permiten su detección
Stellar feedback from HMXBs in cosmological hydrodynamical simulations
We explored the role of X-ray binaries composed by a black hole and a massive
stellar companion (BHXs) as sources of kinetic feedback by using hydrodynamical
cosmological simulations. Following previous results, our BHX model selects low
metal-poor stars () as possible progenitors. The model that
better reproduces observations assumes that a fraction of
low-metallicity black holes are in binary systems which produce BHXs. These
sources are estimated to deposit erg of kinetic energy per
event. With these parameters and in the simulated volume, we find that the
energy injected by BHXs represents of the total energy released by
SNII and BHX events at redshift and then decreases rapidly as baryons
get chemically enriched. Haloes with virial masses smaller than (or K) are the most directly affected
ones by BHX feedback. These haloes host galaxies with stellar masses in the
range M. Our results show that BHX feedback is able to
keep the interstellar medium warm, without removing a significant gas fraction,
in agreement with previous analytical calculations. Consequently, the
stellar-to-dark matter mass ratio is better reproduced at high redshift. Our
model also predicts a stronger evolution of the number of galaxies as a
function of the stellar mass with redshift when BHX feedback is considered.
These findings support previous claims that the BHXs could be an effective
source of feedback in early stages of galaxy evolution.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Unveiling the nature of IGR J16283-4838
Context. One of the most striking discoveries of the INTEGRAL observatory is
the existence of a previously unknown population of X-ray sources in the inner
arms of the Galaxy. The investigations of the optical/NIR counterparts of some
of them have provided evidence that they are highly absorbed high mass X-ray
binaries hosting supergiants. Aims. We aim to identify the optical/NIR
counterpart of one of the newly discovered INTEGRAL sources, IGR J16283-4838,
and determine the nature of this system. Methods. We present optical and NIR
observations of the field of IGR J16283-4838, and use the astrometry and
photometry of the sources within it to identify its counterpart. We obtain its
NIR spectrum, and its optical/NIR spectral energy distribution by means of
broadband photometry. We search for the intrinsic polarization of its light,
and its short and long-term photometric variability. Results. We demonstrate
that this source is a highly absorbed HMXB located beyond the Galactic center,
and that it may be surrounded by a variable circumstellar medium.Comment: 6 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Structural and functional characterization of a cold-adapted stand-alone TPM domain reveals a relationship between dynamics and phosphatase activity
The TPM domain constitutes a family of recently characterized protein domains that are present in most living organisms. Although some progress has been made in understanding the cellular role of TPM-containing proteins, the relationship between structure and function is not clear yet. We have recently solved the solution and crystal structure of one TPM domain (BA42) from the Antarctic bacterium Bizionia argentinensis. In this work, we demonstrate that BA42 has phosphoric-monoester hydrolase activity. The activity of BA42 is strictly dependent on the binding of divalent metals and retains nearly 70% of the maximum at 4 °C, a typical characteristic of cold-adapted enzymes. From HSQC, 15 N relaxation measurements, and molecular dynamics studies, we determine that the flexibility of the crossing loops was associated to the protein activity. Thermal unfolding experiments showed that the local increment in flexibility of Mg2+ -bound BA42, when compared with Ca2+ -bound BA42, is associated to a decrease in global protein stability. Finally, through mutagenesis experiments, we unambiguously demonstrate that the region comprising the metal-binding site participates in the catalytic mechanism. The results shown here contribute to the understanding of the relationship between structure and function of this new family of TPM domains providing important cues on the regulatory role of Mg2+ and Ca2+ and the molecular mechanism underlying enzyme activity at low temperatures.Fil: Pellizza, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Smal, Clara. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Ithuralde, Raúl Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Turjanski, Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Cicero, Daniel Oscar. Universita Tor Vergata; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Aran, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentin
Metallicity dependence of HMXB populations
High-mass X-ray binaries (HMXBs) might have contributed a non-negligible
fraction of the energy feedback to the interstellar and intergalactic media at
high redshift, becoming important sources for the heating and ionization
history of the Universe. However, the importance of this contribution depends
on the hypothesized increase in the number of HMXBs formed in low-metallicity
galaxies and in their luminosities. In this work we test the aforementioned
hypothesis, and quantify the metallicity dependence of HMXB population
properties. We compile from the literature a large set of data on the sizes and
X-ray luminosities of HMXB populations in nearby galaxies with known
metallicities and star formation rates. We use Bayesian inference to fit simple
Monte Carlo models that describe the metallicity dependence of the size and
luminosity of the HMXB populations. We find that HMXBs are typically ten times
more numerous per unit star formation rate in low-metallicity galaxies (12 +
log(O/H) < 8, namely < 20% solar) than in solar-metallicity galaxies. The
metallicity dependence of the luminosity of HMXBs is small compared to that of
the population size. Our results support the hypothesis that HMXBs are more
numerous in low-metallicity galaxies, implying the need to investigate the
feedback in the form of X-rays and energetic mass outflows of these high-energy
sources during cosmic dawn.Comment: 9 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Non-parametric morphologies of mergers in the Illustris simulation
Indexación: Web of Science; ScopusWe study non-parametric morphologies of mergers events in a cosmological context, using the Illustris project. We produce mock g-band images comparable to observational surveys from the publicly available Illustris simulation idealized mock images at z = 0. We then measure non-parametric indicators: asymmetry, Gini, M-20, clumpiness, and concentration for a set of galaxies with M-* > 10(10) M circle dot. We correlate these automatic statistics with the recent merger history of galaxies and with the presence of close companions. Our main contribution is to assess in a cosmological framework, the empirically derived non-parametric demarcation line and average time- scales used to determine the merger rate observationally. We found that 98 per cent of galaxies above the demarcation line have a close companion or have experienced a recent merger event. On average, merger signatures obtained from the G-M-20 criterion anti- correlate clearly with the elapsing time to the last merger event. We also find that the asymmetry correlates with galaxy pair separation and relative velocity, exhibiting the larger enhancements for those systems with pair separations d < 50 h(-1) kpc and relative velocities V < 350 km s(-1). We find that the G-M-20 is most sensitive to recent mergers (similar to 0.14 Gyr) and to ongoing mergers with stellar mass ratios greater than 0.1. For this indicator, we compute a merger average observability time-scale of similar to 0.2 Gyr, in agreement with previous results and demonstrate that the morphologically derived merger rate recovers the intrinsic total merger rate of the simulation and the merger rate as a function of stellar mass.https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stw278
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