By virtue of its proximity, the Virgo Cluster is an ideal laboratory for us to test our understanding of the formation of structure in our Universe. In this spirit, we present a dynamical study of 33 gas-poor and 34 gas-rich Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo survey. Our final spectroscopic data set was acquired at the 3.5-m telescope at the Apache Point Observatory. Hα rotation curves for the gas-rich galaxies were modelled with a multi-parameter fit function from which various velocity measurements were inferred. Analog values were measured off of the observed rotation curves, but yielded noisier scaling relations, such as the luminosity-velocity relation (also known as the Tully-Fisher relation). Our best i-band Tully-Fisher relation has slope α=-7.2 ± 0.5 and intercept M_i(2.3)=-21.5 ± 1.1 mag, matching similar previous studies. Our study takes advantage of our own, as well as literature, data; we plan to continue expanding our compilation in order to build the largest Tully-Fisher relation for a cluster to date. Following extensive testing of the IDL routine pPXF, extended velocity dispersion profiles were extracted for our gas-poor galaxies. Considering the lack of a common standard for the measurement of a fiducial galaxy velocity dispersion in the literature, we have endeavoured to rectify this situation by determining the radius at which the measured velocity dispersion, coupled with the galaxy luminosity, yields the tightest Faber-Jackson relation. We found that radius to be 1.5 R_e, which exceeds the extent of most dispersion profiles in other works. The slope of our Faber-Jackson relation is α=-4.3 ± 0.2, which closely matches the virial value of 4. This analysis will soon be applied to a study of the Virgo Cluster Fundamental Plane. Rotation correction of our dispersion profiles will also permit the study of galaxies' velocity dispersion profile shapes in an attempt to refine our understanding of the overall manifold of galaxy structural parameters. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-12-22 19:09:06.192

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Remarkably, the central regions of galaxies are very important in shaping and influencing galaxies as a whole. As such, galaxy cores can be used for classification, to determine which processes may be important in galaxy formation and evolution. Past studies, for example, have found a dichotomy in the inner slopes of early-type galaxy surface brightness profiles. Using deprojections of the galaxies from the ACS Virgo and Fornax Cluster Surveys (ACSVCS/FCS), we show that, in fact, this dichotomy does not exist. Instead, we demonstrate that the brightest early-type galaxies tend to have central light deficits, a trend which gradually transitions to central light excesses – also known as compact stellar nuclei – as we go to fainter galaxies. This effect is quantified, and can be used to determine what evolutionary factors are important as we move along the galaxy luminosity function. The number of stellar nuclei that we observe is, in fact, an unexpected result emerging from the ACSVCS/FCS. Being three times more common than previously thought, they are present in the vast majority of intermediate and low-luminosity galaxies. Conversely, it has been known for over a decade that there is likely a supermassive black hole weighing millions to billions of solar masses at the center of virtually every galaxy of sufficient size. These black holes are known to follow scaling relations with their host galaxies. Using the ACSVCS, along with new kinematical data from long-slit spectroscopy, we measure the dynamical masses of 83 galaxies, and show that supermassive black holes and nuclei appear to fall along the same scaling relation with host mass. Both represent approximately 0.2% of their host’s mass, implying an important link between the two types of central massive objects. Finally, we extract elliptical isophotes and fit parameterized models to the surface brightness profiles of new Hubble Space Telescope imaging of the ACSVCS galaxies, observed in infrared and ultraviolet bandpasses. Taken together, the two surveys represent an unprecedented collection of isophotal and structural parameters of early-type galaxies, and will allow us to learn a great deal about the stellar populations and formation histories of galaxy cores. / Graduate

Das High Energy Stereoscopic System (H.E.S.S.) ist ein System von fünf atmosphärischen Cherenkov-Teleskopen (IACT) in Namibia. Die H.E.S.S. Teleskope sind empfindlich für sehr energiereiche (VHE) Gammastrahlen zwischen ~30 TeV und 100 TeV. Mit einer Entfernung von 16,5 Mpc ist Messier 87 (M87) eine der nächsten Radiogalaxien und beherbergt eines der massereichsten supermassiven Schwarzen Löcher, das Materie in einen Plasmastrahl relativistischer Teilchen emittiert. Der Strahl wird im Bereich des gesamten elektromagnetischen Spektrums beobachtet und untersucht. M87 befindet sich im Zentrum des Virgo-Galaxienhaufens, eines kühlen Galaxienhaufens, der von Gas gefüllt ist, das in der Nähe des Zentrums kälter und in den Außenbereichen des Galaxienhaufens heißer ist. Gemäß der Cooling Flow (CF) Theorie kühlt das Plasma in Cool Core (CC) Haufen am Rand des Haufens ab und sinkt nach innen, wodurch die Sternentstehungsrate im Zentrum erhöht wird. Optische Messungen des Virgo Galaxienhaufens scheinen diesem Modell jedoch zu widersprechen. Als Heizmechanismus wird der aktive galaktische Kern Rückkopplungsmechanismus vorgeschlagen, der die Abkühlung des ICM ausgleicht und dessen CF vermeidet. Die kosmische Strahlung des Jets interagiert mit der ICM und erzeugt neutrale Pionen, die in Gammastrahlen zerfallen und ein nicht variables und ausgedehntes Gammastrahlensignal erzeugen. Allerdings konnten keine Gammastrahlen-Beobachtungen mit dem Pionenzerfall in dem Galaxienhaufen in Verbindung gebracht werden. In dieser Studie der H.E.S.S. Beobachtungen des niedrigen Strahl-Aktivitätszustands von M87 haben keine signifikante Ausdehnung der Emissionsregion gezeigt, woraus eine 3σ Obergrenze von 0.016° ≈ 4.6 kpc abgeleitet wurde. Das Verhältnis des Drucks in kosmischer Strahlung zur thermischen Strahlung ist auf <0.36 im Zentralregion beschränkt. Diese abgeleitete Obergrenze nimmt einen Gleichgewichtszustand zwischen den Erwärmungs und den Kühlprozessen an. Die neue Generation von IACTs, das Cherenkov Telescope Array Observatory (CTAO), wird eine unvergleichbare Empfindlichkeit und Winkelauflösung bieten. Um die langfristige Verfügbarkeit der Teleskope sicherzustellen, wurde ein auf Schwingungsmessungen basierendes Strukturüberwachungssystem entwickelt und zwischen 2019 und 2020 in Berlin am Prototyp des mittelgrossen Teleskopes erfolgreich getestet. CTAO wird in der Lage sein die Gammastrahlung des Virgo Haufens zu untersuchen und sie laut Simulationen und dem Steady-State-Modell innerhalb von ~210 h zu detektieren. / The High Energy Stereoscopic System (H.E.S.S.) is an array of five Imaging Atmospheric Cherenkov Telescopes (IACTs) located in Namibia. The H.E.S.S. telescopes are sensitive to Very-High-Energy (VHE) gamma rays between ~30 TeV and ~100 TeV. At a distance of 16.5 Mpc Messier 87 (M87) is one of the closest radio-galaxies, hosting one of the most massive Super-Massive Black Hole, which accretes matter and launches an inclined jet of relativistic particles. The jet is detected and studied by radiation emitted through the entire electromagnetic spectrum. M87 is located at the very center of the Virgo galaxy cluster, a Cool Core (CC) cluster, characterized by an Intra-cluster Medium (ICM) that is colder close to the center and hotter towards the outskirts of the galaxy cluster. According to the Cooling Flow (CF) theory, the plasma in CC clusters cools in the outskirts of the cluster and falls inwards, increasing the star formation ratio in the region. However, optical measurements of the Virgo Cluster seem to contradict this model. The Active Galactic Nucleus (AGN) feedback mechanism is proposed as a heating mechanism, which counterbalances the cooling of the ICM and avoids its CF. The cosmic rays from the jet interact with the ICM producing neutral pions, which decay to gamma rays, forming a non-variable and extended gamma-ray signal. However, no gamma-ray observations could be associated with pion decay in galaxy clusters. In this work, deep H.E.S.S. observations of M87's low state are analyzed, and the results have shown no significant gamma-ray extension leading to a 3σ upper limit of 0.016° ≈ 4.6 kpc. The ratio of cosmic-ray pressure to thermal pressure XCR is constrained to < 0.36 at its maximum position, assuming a steady-state between the heating and the cooling processes. The new generation of IACTs, the Cherenkov Telescope Array Observatory (CTAO) will offer unprecedented sensitivity and angular resolution. To assure the long-term availability of the telescopes, a structure monitoring system based on vibration measurements was developed and successfully tested at the Medium-sized Telescope (MST) prototype between 2019 and 2020 in Berlin. CTAO should be able to probe the gamma-ray emission from the Virgo Cluster, and, according to simulations and to the steady-state model, significantly detect it after ≈ 210 h.