Gas dynamics in the Galactic Centre

The inner parsec of the Milky Way hosts tens of Wolf-Rayet stars. Their strong mass outflows fill the region with hot plasma. A fraction of this gas is expected to be accreted by the central super-massive black hole, Sgr A*. The main goal of this work is to improve our understanding of the accretion onto Sgr A*. In this context, I am studying the impact of stellar wind interactions on the accretion. To do so, I am modelling unstable colliding wind systems. The hydrodynamic instabilities could generate cold, dense clumps in these systems which could end up being accreted. The clumps could provide the bulk of the accretion and cause its variability episodes. I am making use of both analytic and numerical adaptive mesh refinement (AMR) hydrodynamic tools to build my models.

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The figure on the left-hand side is a density map on the orbital plane of a colliding wind binary. Notice the unstable interaction in the stellar wind collision where clumps are formed. The figure on the right-hand side is a projected density map along the z-axis (representing the line-of-sight direction).The simulation is a model the known 30 Wolf-Rayet stars blowing winds while orbiting around Sgr A* (Calderón et al. in prep.).

The Galactic Centre source G2

In 2012, an enigmatic source was discovered traveling on a nearly radial orbit to the central super-massive black hole of our Galaxy, Sgr A*. Several groups have been monitoring the so-called G2 object since then, aiming to capture its interaction with Sgr A* as well as to understand its astrophysical nature. Since its discovery there has been an interesting debate regarding G2's nature. Specially, after the discovery of more objects with similar properties. In this context, I have studied the hypothesis that such objects were formed as the result of the stellar wind collisions, which are constantly taking place in the region. The analytic analysis and test-particle simulations showed that this scenario is not likely to occur. In general, stellar close encounters do not have the necessary characteristics for clump formation to take place (Calderón et al. 2016). Although massive stellar binaries are potential clump sources, the known systems (e.g. IRS 16SW) are not capable to create such massive clumps or place them on orbits like G2's (Calderón et al. 2018).


The figure is a sky-projection of G2 orbit plotted with 3σ errors (Plewa et al. 2017) shown as solid black lines. Part of the orbit of IRS 16SW is also shown as dashed blue line. Coloured symbols represent positions at different epochs: t = 1816 yr (yellow triangles), t = 1916 yr (green squares), t = 2016 (red circles). The big black dot at the origin represents Sgr A*.

Active galactic nuclei

It is well-understood that the active galactic nucleus (AGN) phase plays a crucial role in galaxy evolution. The growth of the central super-massive black holes and the quenching of the star formation is intimately related to the AGN activity. In this context, I have searched for direct evidence of AGN feedback in galaxies. I have studied the most powerful luminous infrared galaxies, the so-called Hyper-Luminous Infrared Galaxies (HLIRGs). Using Herschel/PACS data I have constrained molecular outflows through the 119 μm OH doublet. Specifically, I managed to detect the presence of a molecular outflow whose maximum velocity is about 1500 km/s. The analysis showed that this system is in general agreement with previous results on Ultra-luminous infrared galaxies and QSOs, whose outflow velocities do not seem to correlate with stellar masses or starburst luminosities (star formation rates). Instead, the galaxy outflow likely arises from an embedded active galactic nuclei. These results were published in Calderón et al. (2016b).

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Smoothed Herschel/PACS spectrum of the 119 μm doublet divided by its continuum. The blueshifted wing of the profile indicates the presence of a molecular outflow (Calderón et al. 2016b).

Clusters of galaxies

The largest structures in the universe are the clusters of galaxies. They are composed mainly by dark matter, intracluster gas and galaxies. In general, their centres host a fairly massive cD galaxy. Some of them show strong AGN activity imprinted in powerful kiloparsec-scale radio jets. Although it is common observing them relatively well-collimated, there are cases where they are significantly bent. These "wide-angle tail" (WAT) radio sources may be generated due to the interaction of the radio jets and the intracluster medium. In this context, I have studied the dynamics of the cluster of galaxies Abell 562 using Gemini/GMOS multi-object spectroscopy data. The results support the hypothesis that the WAT in Abell 562 may be explained by a cluster of galaxies merger that is taking place.

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VLA 1.4 GHz (left) and 8.4 GHz (right) maps of the WAT hosted by Abell 562 (Douglass et al., 2016, ApJ, 743, 199)