Diego Falcetagonçalves | Universidade de São Paulo (original) (raw)

Papers by Diego Falcetagonçalves

ABSTRACT In this work we performed a number of MHD numerical simulations of the ISM, for differen... more ABSTRACT In this work we performed a number of MHD numerical simulations of the ISM, for different Alfvenic and sonic Mach numbers. We used the data cubes to perform synthetic calculations of observable polarization and velocity dispersion maps. Based on these, we were able to study the statistics of polarization vectors and compare the obtained results with the different turbulent regimes.

The Astrophysical Journal

AIP Conference Proceedings, 2005

ABSTRACT

Proceedings of the International Astronomical Union, 2012

In this work we discuss the turbulent evolution of molecular clouds and the formation of dense st... more In this work we discuss the turbulent evolution of molecular clouds and the formation of dense structures within. Typically, the clumps evolution occurs apart from the secular evolution of the turbulent mother cloud due to its high density and large inertia. Despite of current theoretical assumptions we show, by means of numerical simulations, that the clump lifetimes are greater than previously thought by more than an order of magnitude. The presence of dense and long-lived clumps modifies the spectral line profiles of clouds, which are strongly related to the determination of Larson's relations. We address the main modifications of these if a realistic distribution of dense structures is taken into account.

Astrophysics and Space Science Proceedings, 2014

ABSTRACT Turbulence is ubiquitous in the ISM, from large (galactic) scales down to planet-sized e... more ABSTRACT Turbulence is ubiquitous in the ISM, from large (galactic) scales down to planet-sized eddies within pre-stellar accretion disks. The ISM turbulence is known to operate in the both ends of triggering star formation when occurring at molecular clouds, as well as quenching the process at HII regions. Its origin, however, is still controversial. Supernovae are generally accounted as the main source of the turbulent energy of the ISM. However, recent observations of stellar orbits and the gravitational potential of the Galaxy revealed a new possibility: ISM gas flows driven by the global galactic gravitational potential. In this work we provide the first numerical simulations of the dynamics of the diffuse and molecular ISM interacting with the gravitational potential wells of the Galaxy. These reveal the generation of arms and the triggering of turbulence at large scales ( > 100 pc). During the interactions, molecular clouds may be disrupted and dense cores be formed. We compare the statistics of the obtained turbulent media with the observations.

Astronomy & Astrophysics, 2007

Context. The dust component of the interstellar medium (ISM) has been extensively studied in past... more Context. The dust component of the interstellar medium (ISM) has been extensively studied in past decades. Late-type stars have been assumed as the main source of dust to the ISM, but recent observations show that supernova remnants may play a role in the ISM dust feedback. Aims. In this work, we study the importance of low and high mass stars, along with their evolutionary phase, in the ISM dust feedback process. We also determine the changes in the obtained results considering different mass distribution functions and star formation history. Methods. We describe a semi-empirical calculation of the relative importance of each star at each evolutionary phase in the dust ejection to the ISM. We compared the obtained results for two stellar mass distribution functions, the classic Salpeter initial mass function, and the current mass function. We used the evolutionary track models for each stellar mass and the empirical mass-loss rates and dust-togas ratio. Results. We show that the relative contribution of each stellar mass depends on the used distribution. Ejecta from massive stars represent the most important objects for the ISM dust replenishment using the Salpeter IMF. On the other hand, for the present mass function, low and intermediate mass stars are dominant. Conclusions. We confirm that late-type giant and supergiant stars dominate the ISM dust feedback in our Galaxy, but this may not the case for galaxies experiencing high star formation rates or at high redshifts. In those cases, SNe are dominant in the dust feedback process.

arXiv (Cornell University), Sep 4, 2013

We present an extensive analysis of the 850 µm polarization maps of the SCUPOL Catalog produced b... more We present an extensive analysis of the 850 µm polarization maps of the SCUPOL Catalog produced by Matthews et al. (2009), focusing exclusively on the molecular clouds and star-forming regions. For the sufficiently sampled regions, we characterize the depolarization properties and the turbulent-tomean magnetic field ratio of each region. Similar sets of parameters are calculated from 2D synthetic maps of dust emission polarization produced with 3D MHD numerical simulations scaled to the S106, OMC-2/3, W49 and DR21 molecular clouds polarization maps. For these specific regions the turbulent MHD regimes retrieved from the simulations, as described by the turbulent Alfvén and sonic Mach numbers, are consistent within a factor 1 to 2 with the values of the same turbulent regimes estimated from the analysis of Zeeman measurements data provided by Crutcher (1999). Constraints on the values of the inclination angle α of the mean magnetic field with respect to the LOS are also given. The values obtained from the comparison of the simulations with the SCUPOL data are consistent with the estimates made by use of two different observational methods provided by other authors. Our main conclusion is that simple ideal, isothermal and non-selfgraviting MHD simulations are sufficient to describe the large scale observed physical properties of the envelopes of this set of regions.

Symposium - International Astronomical Union, 2003

Massive binary star systems are not uncommon, and neither the supersonic collision of their winds... more Massive binary star systems are not uncommon, and neither the supersonic collision of their winds. In the present work we study these shocks and the further consequences on wind structure. The post-shock gas is a warm and high-density environment, which allows dust to form and grow. We show that this growth is fast, of just a few hours. An application to η Car shows that, probably, the decline of X-rays fluxes observed in its light curve is the consequence of its high absorption in periodic dust formation events, at periastron passage.

Mon Notic Roy Astron Soc, 2010

Mon Notic Roy Astron Soc, 2005

Monthly Notices of the Royal Astronomical Society, 2014

Turbulence is ubiquitous in the interstellar medium (ISM) of the Milky Way and other spiral galax... more Turbulence is ubiquitous in the interstellar medium (ISM) of the Milky Way and other spiral galaxies. The energy source for this turbulence has been much debated with many possible origins proposed. The universality of turbulence, its reported large-scale driving, and that it occurs also in starless molecular clouds, challenges models invoking any stellar source. A more general process is needed to explain the observations. In this work, we study the role of galactic spiral arms. This is accomplished by means of three-dimensional hydrodynamical simulations which follow the dynamical evolution of interstellar diffuse clouds (∼100 cm −3) interacting with the gravitational potential field of the spiral pattern. We find that the tidal effects of the arm's potential on the cloud result in internal vorticity, fragmentation and hydrodynamical instabilities. The triggered turbulence results in large-scale driving, on sizes of the ISM inhomogeneities, i.e. as large as ∼100 pc, and efficiencies in converting potential energy into turbulence in the range ∼10-25 per cent per arm crossing. This efficiency is much higher than those found in previous models. The statistics of the turbulence in our simulations are strikingly similar to the observed power spectrum and Larson scaling relations of molecular clouds and the general ISM. The dependence found from different models indicate that the ISM turbulence is mainly related to local spiral arm properties, such as its mass density and width. This correlation seems in agreement with recent high angular resolution observations of spiral galaxies, e.g. M51 and M33.

Proceedings of the International Astronomical Union, 2009

It is well known that the interstellar (ISM) and intergalactic (ICM) media are threaded by large ... more It is well known that the interstellar (ISM) and intergalactic (ICM) media are threaded by large scale magnetic fields. The understanding of its role on the dynamics of the media is, however, still in progress. For the ISM, magnetic fields may control or, at least, play a major role on the turbulence cascade leading to the star formation process. The ICM, on the other hand, is assumed to be thermally dominated but still the magnetic field may play an important role on the processes of acceleration and propagation of cosmic rays. In this work we provide a review of the latest theoretical results on the evolution of MHD turbulence under collisional and collisionless plasma approaches.

Revista mexicana de astronomía y astrofísica

� Carinae is a binary system formed by two massive stars, loosing mass through strong winds. The ... more � Carinae is a binary system formed by two massive stars, loosing mass through strong winds. The wind-wind interactions originate shocks that rise the plasma temperature to 106¿¿8 K, producing X-ray emission. Although the overall shape of the light curve can be explained and it is used to calculate the orbital eccentricity, the observed short quasi-periodic oscillations have not been explained yet. In our work we propose that these oscillations are produced by the nutation of the rotation axis of � Carinae, which is not be perpendicular to the orbital plane. Since in � Carinae, both the mass loss rate and the wind velocity are latitude dependent, the intensity of the emitted X-rays will be a function of the latitude at which the stellar surface intercepts the orbital plane. By assuming an angle of about 30� between the rotation axis and the perpendicular to the orbital plane, an nutation amplitude of about 5� and a nutation period of 22 days, we were able to reproduce very well the ...

Proceedings of the International Astronomical Union, 2010

Several galaxy clusters are known to present multiple and misaligned pairs of cavities seen in X-... more Several galaxy clusters are known to present multiple and misaligned pairs of cavities seen in X-rays, as well as twisted kiloparsec-scale jets at radio wavelengths. It suggests that the AGN precessing jets play a role in the formation of the misaligned bubbles. Also, X-ray spectra reveal that typically these systems are also able to supress cooling flows, predicted theoretically. The absence of cooling flows in galaxy clusters has been a mistery for many years since numerical simulations and analytical studies suggest that AGN jets are highly energetic, but are unable to redistribute it at all directions. We performed 3D hydrodynamical simulations of the interaction between a precessing AGN jet and the warm intracluster medium plasma, in which dynamics is coupled to a NFW dark matter gravitational potential. Radiative cooling has been taken into account and the cooling flow problem was studied. We found that precession is responsible for multiple pairs of bubbles, as observed. The ...

Proceedings of the International Astronomical Union, 2008

The Perseus Cluster (A426) is the brightest cluster of galaxies observed in X-rays in the sky and... more The Perseus Cluster (A426) is the brightest cluster of galaxies observed in X-rays in the sky and its giant central galaxy (NGC1275) hosts the extended double radio source 3C84. There is a spectacular H-alpha nebulosity surrounding NGC1275 with loops and filaments that are probably magnetized and extend over 100 kpc. The continuous blowing of bubbles leading to the propagation of shock fronts is also evident and more recently, outflow and infall velocities of several 1000 km/s have been detected associated to the surrounding filaments. We here present preliminary results of 2.5D MHD simulations of the Perseus cluster central region assuming that the production of the outflow structures and loops that arise from the surface of NGC1275 are due to turbulent injection triggered by recent star formation and SNe activity in the galaxy. This is in turn, probably induced by a continuous gas infall from the satellite galaxies around NGC1275. Our simulations which include both, the turbulent ...

Proceedings of the International Astronomical Union, 2006

When the winds of two massive stars orbiting each other collide, an interaction zone is created c... more When the winds of two massive stars orbiting each other collide, an interaction zone is created consisting of two shock fronts at both sides of a contact surface. During the cooling process, elements may recombine generating spectral lines. These lines may be Doppler shifted, as the gas stream flows over the interaction zone. To calculate the stream velocity projected into the line of sight we use a simplified conical geometry for the shock fronts and, to determine the synthetic line profile, we have to sum the amount of emitting gas elements with the same Doppler shifted velocity. We show that the stellar mass loss rates and wind velocities, and the orbital inclination and eccentricity, are the main parameters on this physical process. By comparing observational data to the synthetic line profiles it is possible to determine these parameters. We tested this process to Brey 22 WR binary system, and applied to the enigmatic object of η Carinae.

The Astrophysical Journal, 2014

The Astrophysical Journal, 2006