What is GalFid about?
GalFid is a series of seminars pertaining mainly to topics of galaxy evolution, through a mixture of contributions from Galactic Fidelity (GalFid) members and invited speakers from around the world. Our target audience are members of African institutions, but we also have (and are open to additional) attendees beyond the continent.
Our webinars are usually at 15:00 SAST on Wednesdays, although this is adjusted to take into account the timezone of our speakers. To access recordings of past talks, online textbooks, and the calendar -- and to receive GalFid notifications -- please register here.
His research interests are organised around three themes: (1) nuclei, bulges and their scaling relations (2) stellar migration in discs and (3) the interaction of baryons and dark matter halos. In all these efforts, a key target is the Milky Way Galaxy, which is the main target of the European Space Agency’s Gaia satellite. Victor primarily use the N-body+SPH code GASOLINE. He has also developed a made-to-measure code for the dynamical modelling of the Milky Way’s bar and bulge. Victor is a full member of the LSST collaboration and co-leading the Milky Way bulge sub-group. He is also interested in the comparison of simulations with observations, including using Hubble Space Telescope data.
The VO encompasses astronomy data, tools and services interoperating to provide an environment which allows for easy remote access to data archives and to analyse the data therein. They generally serve as data archives, data discovery tools, analysis tools and visualisation/ plotting tools. The VO is opening up new ways of exploiting the huge amount of data provided by the ever-growing number of ground-based and space facilities, as well as by computer simulations. The goal this tutorial is to expose the students (and even researchers) to VO tools and services (specifically, Aladin & TOPCAT) so that they can use them efficiently for their own research.Download Video Recording
Abstract, Slides and Video Recording
Abstract - N/ADownload Slides
I will give an overview of the subject of dark matter in spiral galaxies. 21-cm HI line observations are essential in the determination of "flat" rotation curves extending well beyond the optical image, which indicate the presence of dark matter in the outer parts of galaxies. Additional observations of stellar velocity dispersions at high spectral resolution are needed to break the so-called "degeneracy" in the mass modelling (i.e., the need to determine independently the mass-to-light ratio of the stellar components of a galaxy). Attempts to determine the shape of dark matter haloes are difficult, since there is a lot of extraplanar HI, in particular in active star forming galaxies. The suite of HI surveys, to be undertaken by SKA pathfinders and precursors, will help develop this field of research.
Understanding how galaxies form and evolve requires a detailed knowledge of how gas cycles in and around them, and how this connects to their properties (stellar mass, structure, star formation rate etc.) and large-scale environment. One important challenge for this field is that we still lack measurements of the cold hydrogen gas, which is the reservoir for future star formation, for large and unbiased samples of galaxies for which ancillary data on stellar and star formation properties are also available. While progress is being made, new facilities such as the Square Kilometre Array and its precursor telescopes promise to revolutionise this field, ushering a golden era for studies of cold gas in galaxies.
We are in the midst of the Golden Age of X-ray astronomy, which blasted into the mainstream of research with the launch of both NASA's Chandra X-ray Observatory and ESA's XMM-Newton in 2019. In combination with smaller, specialised missions, such as Swift and NuSTAR, X-ray observations have become indispensible for expanding the frontiers of knowledge throughout astrophysics, leading to major advances in our understanding of celestial sources from exo-planetary atmospheres to the most distant supermassive black holes (SMBHs) in the cores of active galaxies. Chandra's uniquely high spatial and spectral resolution have faclitated the deepest (7Ms) image of the X-ray sky, finding it to be dominated by active galaxies, and the highest quality X-ray spectra to date, revealing the dynamic, multi-component structure of the material close to the SMBH. Chandra and XMM-Newton follow-up of transients found by Swift, along with the higher energy X-ray spectra observed with NuSTAR in combination with the two general observatories, probe multiple aspects of active galaxies, the SMBHs located in their cores, and their effect on their environment. I will review key advances in our knowledge from these past 20 years of X-ray, and multi-wavelength observations of active galaxies.
Past research has shown that the energy released by accreting super massive black holes (SMBHs) and by intense star formation activity can undermine even the coldest and densest phase of the interstellar medium (ISM), namely the cold molecular gas, which represents the main fuel for star formation. Massive molecular outflows, with velocities approaching 1000 km/s, outflow mass-loss rates of 100s of MSun/yr and sizes of several kiloparsecs, have been observed in the host galaxies of powerful starbursts and quasars from redshift, z~0 up to z>6. Molecular outflows were initially considered a viable mechanism to provide quenching through ejection. However, observations are now showing that a cumulative effect of these outflows is the transportation of metal-enriched cold material to circumgalactic medium (CGM) scales, where most of the cold gas stalls without escaping the halo. As a results, molecular outflows may be the main players of the baryon cycle in and out of galaxies, by temporarily storing in the CGM the fuel for future star formation, which will be eventually re-accreted to the host galaxy. Therefore, molecular outflows may have a two-fold role in galaxy evolution: immediate quenching of star formation in the central kiloparsecs, and long-term feeding of the galaxy by injecting (cold) gas in the CGM.
Until the mid-70ties of the last century it was accepted knowledge that disk galaxies have very similar surface brightness with only moderate scatter around th mean value (the "Freeman Law"). While it was known already then, that dwarf galaxies can have lower central surface brightnesses, only from 1976 onward it became clear, that the Freeman Law is mostly due to a selection effect. New methods and the advent of the CCD detectors brought Low Surface Brightness galaxies into the limelight, as a parallel branch to the "normal" high surface brightness galaxies. Again, new methods, and large-scale optical/NIR surveys, as well as progress with deep, large area HI surveys now spurned a renewed interest in these galaxies, partly under the label of Ultra Diffuse Galaxies, a class label with very much overlaps with the low surface brightness and ultra low surface brightness galaxies found and studies around begin of the new Millennium. In the talk I will give a short historical review of LSB galaxy research, try to disentangle the different (and not so different) types of LSB galaxies and their properties, and discuss search methods for LSB galaxies. I then will discuss the importance of the LSB galaxies for our understanding of galaxy evolution and point at several open questions.
Slides currently unavailable Download Video Recording
The large-scale structure (LSS) of the universe is made by a network of groups and clusters of galaxies, extended filaments and voids (e.g. Peebles, 1980). According to the Lambda-Cold Dark Matter (LCDM) galaxy formation theory, the clusters of galaxies in the LSS are expected to grow over time by accreting smaller groups along filaments, driven by the effect of gravity generated by the total matter content (e.g. Bond & Szalay 1983). In the deep potential well at the cluster centre, the galaxies continue to undergo active mass assembly and, in this process, gravitational interactions and merging between systems of comparable mass and/or smaller objects play a fundamental role in defining the galaxies' morphology and the build-up of the stellar halos. This is an extended (≥ 100 kpc) and faint (μg ≥ 26 - 27 mag/arcsec^2) component made of stars stripped from satellite galaxies, in the form of streams and tidal tails, with multiple stellar components and complex kinematics (see Duc 2017, Mihos 2017 as reviews). During the infall of groups of galaxies to form the cluster, the material stripped from the galaxy outskirts builds up the intra-cluster light, ICL (De Lucia & Blaizot 2007; Puchwein et al. 2010; Cui et al. 2014). This is a diffuse and very faint component (μg ≥ 28 mag/arcsec^2) that grows over time with the mass assembly of the cluster, to which the relics of the interactions between galaxies (stellar streams and tidal tails) also contribute. In this framework, exploring the low surface brightness (LSB) universe is a crucial ingredient to map the mass assembly of galaxies at all scales (from galaxies to clusters) and in all environments (in the low-density groups of galaxies as well as in rich clusters), to constrain their formation within the LCDM paradigm. In this talk, I will review the main analysis of the the galaxy structure down to the LSB regime in different environments (i.e. clusters and groups of galaxies), by using deep and large-scale multi-band images and spectroscopic follow-up data. I will show the main results on the map the mass assembly processes by comparing a set of observables with those from theoretical predictions.
Galaxies begin their lives as disk galaxies, before merging in early-type or elliptical galaxies. Disk galaxies are fast rotating, and develop spiral structures, that are the result of density waves in general, gathering the matter, gas and stars, in arms that are the locations of enhanced star formation. We will describe how these spirals can develop, weaken or re-form. We will describe also the formation of bars, the main motor of galaxy evolution. About two thirds of spiral galaxies are barred today, but it was not the case in the past (at high redshift).
This lecture will present a snapshot of the emerging field of radio spectropolarimetry: that is, the detailed study of polarized radio waves and their variation over frequency. The polarization properties of cosmic objects can reveal the magnetic structure of distant (emitting) sources such as radio galaxies, as well as intervening objects along the line of sight including galaxies, clusters, and our Milky Way. I will introduce the observational tools that are being used in this field to get the most out of modern radio telescopes, and describe some of the key science questions that we are now trying to answer. I will conclude with a summary of the headline survey projects that are now planned (or beginning!) with SKA precursors, while looking ahead to the prospects for the SKA itself.
In this talk I will provide an overview of the science enabled by deep radio continuum surveys, focusing on the new perspectives that next generation radio telescopes offer to galaxy evolution studies, through the assessment of the cosmic history of star formation, and of the role played by AGN feedback in regulating galaxy growth.
The low-redshift Universe is an excellent place to study the physical processes that govern how galaxies form stars and evolve. Multiwavelength observations are crucial for providing a more complete overview of the processes at play in each galaxy. In this talk, I will begin by briefly introducing some of the key radiative processes that are commonly observed in galaxies and then provide an overview of how galaxies form stars and evolve in the nearby Universe using multiwavelength observations.
Low-mass galaxies are the most numerous type of extragalactic system at all epochs of the universe. The population of low-mass galaxies in the local volume allows unique astrophysical and cosmological perspectives that are unavailable in more distant or more massive systems. The ALFALFA blind extragalactic HI survey has cataloged tens of thousands of gas-rich galaxies in the local universe and has populated the faint end of the HI mass function with statistical confidence for the first time. In this talk I will present results from comprehensive follow-up observing campaigns designed to study the low-redshift, low mass, gas-rich population discovered by ALFALFA. The centerpiece of this effort is the Survey of HI in Extremely Low-mass Dwarfs (SHIELD), an ongoing multi-wavelength investigation of the properties of 82 extremely low-mass galaxies selected from the complete ALFALFA catalog. I will also discuss results from parallel ongoing observing programs that explore more exotic low-mass objects, including "ultra compact high velocity clouds" (HI clouds with structural parameters that match those of gas-bearing "mini-halos" if located within 1 Mpc), candidate "dark galaxies" (systems with extreme hydrogen mass to stellar light ratios), and targeted studies of individual sources of interest (including two of the most metal-poor galaxies known in the universe). Taken as a whole, these observing programs are furthering our understanding of the continuum of galaxy properties in the low-mass regime.
The interstellar medium of the Milky Way is our window to the universe. Analogous to the Earth's atmosphere, its properties determine what kind of information we receive from space via electromagnetic radiation. In recent years, the sensitivities of spaceborne receivers have come close to their quantum limits. Longer integration times do not reveal finer details because they are limited by the unrelated "foregrounds". In this talk I will discuss the dust and gas "foregrounds" of the Milky Way with a multi-frequency approach. The combination of far-infrared and soft X-ray observations allows to detect and quantify the conditions for phase transitions in the HI gas, the formation of CO and finally the amount of CO-dark molecular hydrogen.
Understanding the diversity of nearby galaxies within the cosmological framework that describes the large-scale structure and evolution of the universe is an important research driver in extragalactic astronomy. In that context, the properties of the smallest and faintest ("dwarf") galaxies, which are both hard to observe and susceptible to a variety of competing physical processes because of their shallow gravitational potential wells, are the most challenging to explain. In this talk, I will describe how atomic gas observations with current and future radio telescopes can constrain the origin of some of the most extreme dwarfs known today. I will first focus on how sensitive single-dish observations of ultra-diffuse galaxies are a powerful tool for measuring their structure and distinguishing between competing formation models. Then, I will describe how a widefield atomic gas survey soon to be undertaken with a new radio interferometer in the Australian outback will allow for the first spatially resolved populations studies of the smallest field dwarfs for comparison with cosmological predictions.
Although we see clear differences in the properties of galaxies that inhabit different environments, our understanding of the mechanisms that underpin this evolution is obfuscated by several factors. In this talk I will attempt to give a very broad overview of why disentangling internal and environmental processes, and their relative roles in the evolution of a typical galaxy, remain a challenge. Most importantly, I will discuss why HI is a particularly useful tool for studying how galaxies are influenced by their environment, and how ambitious surveys of the future can transform this landscape and help us form a coherent understanding of galaxy evolution.
In this talk I will give an overview of supernova remnant physics, including their phases of life and multiwavelength properties. I will discuss their important impacts on the interstellar medium, which dramatically affects star and planetary formation. I will also discuss the challenges of detecting Galactic SNRs, and how new wideband low-frequency radio surveys are helping to find this enigmatic population, which may be responsible for some of the highest-energy phenomena in our Galaxy.
The absorption lines seen in the spectra of distant luminous sources such as quasi-stellar objects (QSOs) and Gamma-ray bursts (GRBs) provide a powerful tool to determine the physical and chemical state of the different phases of interstellar and intergalactic medium. In this talk, we describe how absorption lines can be used to obtain a luminosity unbiased view of the galaxy evolution and obtain the most stringent constraints on the variations of fundamental constants of physics. In particular, we will focus on absorption lines associated with the neutral hydrogen, and advancements expected with the SKA precursor telescopes
Even though we have known about the existence of external galaxies for almost a century now the structure and evolution of galaxies is still an active field of research. Central to understanding the structure and especially the evolution of galaxies is the movement of the different components such as the gas and stars. In order to facilitate the kinematic analysis of spiral galaxies HI observations have been analysed for five decades now. This has led to the inference of Dark Matter as well as observational evidence for the ongoing accretion and stripping of gas in these galaxies. I will present how these discoveries came about, the current state of our understanding and open questions as well as a crucial tool in the analysis of these observations, the Tilted Ring Model.
Active galactic nuclei (AGNs) are among the most extreme and fascinating objects in the Universe. Powered by actively feeding supermassive black holes, they may shine thousands of times brighter than all the stars in an entire galaxy and are capable of dramatically altering their surroundings through AGN feedback. One of the most striking distinctions among AGN is the presence or absence of radio-emitting jets/lobes. Over millions of years, some radio jets manage to grow to scales of 100’s of kpc or more, extending far beyond the stellar light of their galaxies. It is widely accepted that these large-scale “grown-up” jets play a major role in the regulation of galaxy and SMBH growth by preventing hot halos of gas around galaxies from cooling and forming new stars. However, the impact of feedback by young, small-scale jets still confined within their galaxies remains unknown. Progress in this topic requires the development of new strategies for building up large samples of candidate young jets. In this talk, I will review our understanding of the connection between radio jets and galaxy evolution including the potential role of feedback driven by small-scale jets. I will present recent progress in identifying compact and potentially newborn jets in distant galaxies using multi-epoch radio survey data and discuss exciting prospects for new instruments in the next decade.
The realism of hydrodynamical simulations of the formation and evolution of populations of galaxies has improved considerably in recent years. I will try to give some insight into the reasons behind this success and will discuss some of the outstanding issues. I will present recent examples from the EAGLE project of ways in which we can use cosmological simulations to learn about galaxy formation.
Slides and Video Recording unavailable
Samuel Twum (SARAO/Rhodes), Dr. Sarah White (Rhodes), Prof. Gyula Józsa (SARAO/Rhodes), Dr. Kshitij Thorat (University of Pretoria/IDIA), Eric Kamau (Rhodes) and Shilpa Ranchod (University of Pretoria)