Researchers

• Dra. Patricia Arévalo: Active galactic nuclei, black hole accretion.
• Dr. Cristian Barrera: Cosmology, relativistic effects in the large-scale structure, gravitation, modified gravity and dark energy models, numerical simulations.
• Dr. Graeme Candlish: Cosmology, gravitation, galaxy evolution, numerical simulations
• Dr. Eduardo Ibar: Observational cosmology. Galaxy formation and cosmic evolution of the interstellar medium.
• Dr. Juan Molina: Galaxy kinematics and dynamics. Galaxy formation and evolution. Star formation activity. High-redshift galaxies. Active galactic nuclei feedback.
• Dra. Verónica Motta: Cosmology, gravitational lensing, active galactic nuclei, and high-redshift galaxies.

Areas of research

Gravitational lensing [Contact: Verónica Motta]

A gravitational lens is produced when the light from a distant source is deviated by a massive object (e.g., a galaxy or a cluster of galaxies) that lies along the line of sight to the observer. Three properties make strong gravitational lensing an extremely useful tool in a wide variety of research fields. First, strong lensing observables (e.g. the relative positions between multiple images, flux ratios, and time delays) depend on the gravitational potential of the foreground lens (galaxy or cluster of galaxies) and its derivatives. Second, those observables also depend on the overall geometry of the Universe through the angular diameter distance between the observer, the deflector, and the source. Third, background sources appear magnified to the observer, sometimes by more than one order of magnitude.

Gravitational lensing can therefore be used to solve three important astrophysical problems: (a) understanding the spatial distribution of mass in galaxies at kiloparsecs and sub-kiloparsecs scales; (b) determining the overall shape, content, and kinematics of the Universe; and (c) studying the structure of galaxies, black holes, and active galactic nuclei that are too small or too faint to be resolved or detected by current instruments.

During these days, our group focuses on the following astrophysical problems and participates in the following collaborations:

• Vista Variables in the Via Lactea eXtended (VVVX) imaging survey dedicated to investigate the center of our galaxy in the near infrared. The detection of microlensing in stars in our galaxy’s bulge allows us to infer the mass of the lens (black holes, dwarf stars, planets) that would otherwise go undetectable.
• Time Delay Cosmography (TDCosmo) consist of five projects dedicated to high-precision measurement of the Hubble constant using time delay measurements in lensed quasars.The project combine two previous ones consisting in the search for new lenses (STRong-lensing Insights into the Dark Energy Survey, STRIDES) and the follow-up broad-band imaging campaigns (COSmological MOnitoring of GRAvItational Lenses, COSMOGRAIL). Highly accurate lens models are produced from images taken with HST and JWST.
• High resolution ALMA imaging towards bright submillimetre and strongly lensed galaxies to reveal the cold ISM and their internal properties at sub-kpc scales. Most galaxy samples are taken from previous low-resolution single-dish detections.
• VLT/4MOST CHileAN Cluster galaxy Evolution Survey (CHANCES) spectroscopic survey dedicated to study the evolution of galaxies in around 150 clusters. Strong and weak lensing effects will be used to investigate the composition of the lens as well as the structure of the background sources.
• VLT/4MOST Chilean AGN/Galaxy Evolution Survey (ChANGES) spectroscopic survey dedicated to study a large sample of AGNs to constrain their structure. Microlensing in lensed quasars will be used to investigate the structure of the accretion disk.

Current projects that fund our research include the Millenium Institute of Astrophysics (MAS) and a personal research grant Fondecyt Regular, all supported by the National Agency for Research and Development, ANID, Chile.

Active galactic nuclei [Contact: Patricia Arévalo]

We study the accretion flow feeding the central supermassive black hole in Active Galactic Nuclei (AGN). As this accretion disc is very small, we study it indirectly, through the information encoded in the variability of the light emitted, mainly in the optical bands. Lately we have exploited the fantastic and massive variability data sets provided by the Zwicky Transient Facility to study the behaviour of AGN with unprecedented precision. Combined with the ALeRCE machine learning classifier we are finding new populations of AGN and interesting events, such as AGN changing state from type II to type I, newborn AGN, Tidal Disruption Events and even more exotic transient events in the nuclei of galaxies. Some of our group’s recent publications are listed here.

We also use other surveys and proprietary data to constrain the accretion disc and its connection to the X-ray corona, dusty torus and relativistic jet. Check some of our papers here.

A good starting point to study AGN variability is by looking at the more vigorously varying X-ray emission. The X-rays in radio quiet AGN are produced by a so-called corona of hot electrons that can be related to the accretion flow. Here are some of our group’s papers that use the variability properties, sometimes combined with spectroscopic studies, to constrain the behaviour of the X-ray corona.

The X-ray emission can penetrate large column densities of dust and gas, so it can reveal AGN activity in even very deeply buried AGN. We use this fact to find and study obscured AGN and even track the reflection of the X-rays over the surrounding gas to constrain its distribution around the supermassive black holes.

Finally, AGN in galaxy clusters can affect the hot gas that fills these structures, on very large spatial scales. The imprint of this AGN feedback can be tracked in the perturbations of the X-ray emission of the intra-cluster medium. Although not our main topic of research nowadays, some older works can be found here.For the topic above, we developed the Mexican Hat filter to extract the pattern of perturbations in images with sharp edges and irregular holes produced by masked-out foreground stars. This method can also be applied in 1 or 3 dimensions, and has now become extremely useful to estimate the power spectrum of optical lightcurves, in particular those produced by the ZTF, that are inevitably affected by yearly gaps and irregular sampling. This method is very quick to calculate and is used by the ALeRCE light curve classifier. It provides one of the key features that for example distinguishes AGN from long period variable stars. We have also used it in recent papers to characterise the optical variability of thousands of AGN.Current projects that fund the AGN research include the Millennium Nucleus TITANS, the Millennium Institute for Astrophysics, and a personal research grant Fondecyt Regular, all supported by the National Agency for Research and Development, ANID, Chile.

Galaxy formation and evolution  [Contact: Eduardo Ibar]

Understanding how galaxies form and evolve as a function of cosmological time (z, redshift) is a key goal in modern astrophysics. Standard theoretical models address this problem in a framework assuming a Lambda-CDM cosmology, where the hierarchical gravitational growth of dark matter haloes trace the large-scale structure of the observed baryonic matter. This framework is governed by a set of differential equations that can be computationally solved by powerful modern computers.

Nevertheless, at galactic scales, the evolution is driven by dissipative non-linear processes far more complex than the theory could predict. It is at this point where observations of different kinds of galaxies, and clusters of galaxies, at all redshifts, become an essential ingredient to feed semi-analytical models of galaxy formation and evolution.

Remarkable progress in the study of galaxy formation has been made over the last decade, primarily through deep optical and near-IR observations. Although the cosmic history of star formation, and the build-up of stellar mass, have been well quantified as a function of galaxy mass and environment, through its peak at z ∼ 2 and back to the near-edge of cosmic reionization (z > 6), the mechanisms that shape such evolution and generate the variety of morphological classes that we observe in the local Universe are far from being constrained. While progress has been impressive, optical studies of galaxy formation are limited to the stellar and ionised gas emission, being plagued by uncertainties in the way in which photons are re-processed by the gas and dust particles. Studies at submillimeter wavelengths are required to probe deep into the earliest, dust-obscured phases of galaxy formation, to reveal the cool gas that constitutes the fuel for star formation in galaxies.

To understand the evolution of galaxies, it is necessary to tackle the physical mechanisms which could shut off their star formation. Our research group has endeavoured various campaigns for characterising the formation and evolution of galaxies as a function of redshift, mass and cosmic environment. These days, the most remarkable collaborations in which we are involved are:

• We have developed ALMA follow-up campaigns to characterise the cold gas and dust of galaxies selected from the largest extragalactic surveys taken by the Herschel Space Observatory, H-ATLAS and HerMES. These campaigns are under the name of VALES, a survey of main sequence and starburst galaxies up to z<0.35.
• The JWST Emitting Line Survey (JELS) is identifying hundreds of star forming galaxies over an area of almost 60 arcmin2 in the COSMOS field previously covered by the PRIMER survey. We are part of JELS and our research focuses (mainly) on the properties of the Paschen-alpha population at z~1.5. We also have an approved MUSE large program to reveal the optical spectra over the same area.
• ALMA observations for obtaining deep wide-field sub-millimeter imaging and spectroscopy in fields previously observed by the Hubble Space Telescope, including the HUDF and the Frontier Fields,
• VLT/4MOST CHileAN Cluster galaxy Evolution Survey (CHANCES) is a spectroscopic survey to obtain hundreds of thousand optical spectra and is dedicated to tackle the evolution of galaxies at the outskirts of nearly 150 clusters. The statistical properties of the galaxies that are part of these large structures are nowadays under investigation at radio and submillimetre wavelengths.

To develop these areas of research, we have available funding including the Millennium Nucleus for Galaxies (MINGAL) and personal Fondecyt Regular’s grant, all supported by the National Agency for Research and Development, ANID, Chile.

Cosmological Numerical Simulations [Contact: Cristian Barrera; Graeme Candlish]

Numerical simulations have developed over recent decades into a crucial tool for physics, astrophysics and cosmology. In particular, numerical simulations offer the only possibility to investigate the non-linear process of structure formation due to gravitational instability in the dark matter distribution in our Universe, as well as the complex interplay of this structure formation with the astrophysical processes that affect the visible (baryonic) material in our Universe (star formation, supernovae, AGN feedbacks). Such simulations furnish the theoretical predictions of our standard cosmological model, which may then be compared to the wide range of available data about galaxy clustering, galaxy evolution, weak and strong gravitational lensing, and other observables.

Furthermore, simulations provide a unique opportunity to investigate the consequences of theories that attempt to explain the still mysterious dark sector of our Universe (dark matter and dark energy). One example is the MOdified Newtonian Dynamics (MOND) paradigm which attempts to explain the phenomenological aspects of dark matter by means of a modification of the Newtonian gravitational force. The consequences of such a modification are profound and would impact all aspects of the evolution of our Universe, from cosmology to galaxy formation and evolution. Many researchers have proposed alternative models to explain dark energy, including modifications of Einstein’s theory of gravity — General Relativity — and the inclusion of new matter/energy components, such as a scalar field referred to as “quintessence”. Finally, there may be interactions within the dark sector that unite both dark matter and dark energy, giving rise to further interesting phenomenological consequences that may be examined in simulations and compared with observations.

Numerical simulations are a fairly recent addition to the extragalactic group at IFA, yet there are several lines of research to investigate non-standard cosmological models:

• Numerical investigations of cosmological structure formation: Dr. Graeme Candlish and Dr. Cristian Barrera work on cosmological N-body simulations to study the formation of structure in our Universe, primarily concentrating on the dark matter distribution, and considering relativistic corrections to the gravitational interaction as well as modified gravity theories.
• Semiclassical gravity: Dr. Graeme Candlish is currently working in numerical studies of semiclassical gravity, where the matter content of the Universe is treated quantum mechanically while the spacetime is treated classically, as in General Relativity. Such studies aim to quantify the backreaction effect of quantum dynamics on an evolving spacetime, which is relevant for the very early Universe, black hole formation and may potentially have consequences for the late-time evolution of the Universe.
• Dark energy/dark matter couplings: as stated earlier, it is entirely possible that the dark sector contains hidden surprises just waiting to be discovered. In this project, we are investigating the possible cosmological consequences of different types of couplings between dark energy and dark matter and their potential impacts at smaller scales.

Kinematics and Dynamics [Contact: Juan Molina]

The study of the kinematics and dynamics of galaxies has always been at the core of extragalactic research in modern astronomy. Over the last century, many efforts were made to understand the kinematics of the constituents of galaxies in different types of galaxies: a long-standing work that culminated with the discovery of the galactic flat rotation curves and the existence of dark matter. Nowadays, with the advent of the integral field spectroscopy (IFS) technique and very sensitive interferometers like ALMA, mapping the motions of gas and stars within galaxies has become the new standard. The NIRSpec integral field unit (IFU) at JWST is revolutionising our understanding of young galaxies and the physical processes that shaped early galaxy evolution. All future facilities, such as the Extremely Large Telescope (ELT) and the Giant Magellan Telescope (GMT), are incorporating IFUs in their design to study galaxy kinematics and dynamics in exquisite detail.

Using IFU instruments like MEGARA, MUSE, and NIRSpec-IFU, along with ALMA, our research mainly focuses on:

• Starting from an UV-selected galaxy sample, we are part of the ALPINE collaboration, targeting the gas and dust content in galaxies at z~4.5–5.5. Our publications can be found here. We are currently working on JWST NIRSpec follow up campaigns on a subsample of galaxies, in collaboration with the CRISTAL team.
• Matched VLT-IFU and ALMA imaging at a sub-arcsecond resolution of H-alpha emitting star-forming “normal” galaxies at z~2-3, the peak of the cosmic star-formation rate density (from HiZELS and KGES surveys). We are also targeting the total molecular gas content in these galaxies.
• The feedback exerted by mass-accreting super massive black holes (BHs) is widely accepted as the mediator mechanism of the BH-host galaxy coevolution. It is also a key ingredient in hydrodynamical simulations to reproduce the massive end of the galaxy population. By using IFUs and ALMA, we can map the active galactic nuclei (AGN) host galaxies with unprecedented detail. We focus on studying quasars, the most luminous of the active galaxies, to characterise AGN-driven multiphase outflows and their interplay with the surrounding ISM.
• One of the main processes that shape the interstellar medium (ISM) of galaxies is ongoing star formation activity. Starbursts offer ideal laboratories to study the physical mechanisms that control the properties of the ISM due to their intense star formation. In some ISM models, massive young stars transition rapidly into supernovae, injecting considerable amounts of energy into their ISM surroundings. This input energy counterbalances the gravitational collapse of the gas, further controlling the efficiency of star formation. In this project, we combine high-resolution IFU and ALMA data to test ISM models and understand the processes that drive star formation.