▪ Abstract More than a decade ago the IRAS satellite opened the realm of external galaxies for studies in the 10 to 100 μm band and discovered emission from tens of thousands of normal and active galaxies With the 1995–1998 mission of the Infrared Space Observatory1, the next major steps in extragalactic infrared astronomy became possible: detailed imaging, spectroscopy, and spectrophotometry of many galaxies detected by IRAS, as well as deep surveys in the mid- and far-IR The spectroscopic data reveal a wealth of detail about the nature of the energy source(s) and about the physical conditions in galaxies ISO's surveys for the first time explore the infrared emission of distant, high-redshift galaxies ISO's main theme in extragalactic astronomy is the role of star formation in the activity and evolution of galaxies

Extragalactic Results from the Infrared Space Observatory

Magnetic fields are amplified as a consequence of galaxy formation and turbulence-driven dynamos. Galaxy mergers can potentially amplify the magnetic fields from their progenitors, making the magnetic fields dynamically important. However, the effect of mergers on magnetic fields is still poorly understood. We use thermal polarized emission observations to trace the magnetic fields in the molecular disk of the nearest radio active galaxy, Centaurus A, which is thought to be the remnant of a merger. Here, we detect that the magnetic field orientations in the plane of the sky are tightly following the $\sim3.0$ kpc-scale molecular warped disk. Our simple regular large-scale axisymmetric spiral magnetic field model can explain, to some extent, the averaged magnetic field orientations across the disk projected on the sky. Our observations also suggest the presence of small-scale turbulent fields, whose relative strength increases with velocity dispersion and column density. These results have strong implications for understanding the generation and role of magnetic fields in the formation of galaxies across cosmic time.

The Magnetic Field Across the Molecular Warped Disk of Centaurus A

Since Lick indices were introduced in 1994, they have been used as a source of observational data against which computer models of galaxy evolution have been compared.

However, as this thesis demonstrates, observed Lick indices lead to mathematical ill-conditioning: small variations in observations can lead to very large differences in population synthesis models attempting to recreate the observed values. As such, limited reliance should be placed on any results currently or historically in the literature purporting to give the star formation history of a galaxy, or group of galaxies, where this is deduced from Lick observations taken from a single instrument, without separate verification from at least one other source.

Within these limitations, this thesis also constrains the star formation histories of 21 nearby elliptical
galaxies, finding that they formed 13.26 +0.09 -0.06 Gyrs ago, that all mergers are dry, and that galactic winds are formed from AGN activity (rather than being supernovae-driven). This thesis also finds evidence to support the established galaxy-formation theory of “downsizing”.

An existing galactic model from the literature is examined and evaluated, and the reasons for it being unable to establish star formation histories of individual galaxies are ascertained. A brand-new model is designed, developed, tested and used with two separate data sets, corroborated for 10 galaxies by data from a third source, and compared to results from a Single Stellar Population model from the literature, to model the star formation histories of nearby elliptical galaxies.

Modelling the star formation histories of nearby elliptical galaxies


 One of the most protracted problems in astronomy has been understanding the evolution of galaxy morphology. Much discussion has surrounded how lenticular galaxies may form a bridging population between elliptical and spiral galaxies. However, with recourse to a galaxy’s central black hole mass, accretion-built spiral galaxies have emerged as the bridging population between low-mass lenticular galaxies and the dusty merger-built lenticular galaxies contiguous with elliptical galaxies and ‘brightest cluster galaxies’ in the black hole/galaxy mass diagram. Spiral galaxies, including the Milky Way, appear built from gas accretion and minor mergers onto what were initially lenticular galaxies. These connections are expressed as a new morphology sequence, dubbed the ‘Triangal’, which subsumes elements of the Hubble sequence and the van den Bergh trident and reveals the bridging nature of the often overlooked ellicular galaxies. Furthermore, a quadratic black hole/galaxy mass relation is found to describe ordinary elliptical galaxies. The relation is roughly parallel to the quadratic-like relations observed for the central spheroidal component of spiral galaxies, dust-rich lenticular galaxies, and old dust-poor lenticular galaxies. The brightest cluster galaxies are offset according to expectations from an additional major merger. The findings have implications for feedback from active galactic nuclei, mapping morphology into simulations, and predicting gravitational wave signals from colliding supermassive black holes. A new galaxy speciation model is presented. It disfavours the ‘monolithic collapse’ scenario for spiral, dusty lenticular, and elliptical galaxies. It reveals substantial orbital angular momentum in the Universe’s first galaxies and unites dwarf and ordinary ‘early-type’ galaxies.

/pdf/resequencing-the-hubble-sequence-and-the-quadratic-black-3aoxd33t.pdf

Resequencing the Hubble sequence and the quadratic (black hole mass)–(spheroid stellar mass) relation for elliptical galaxies

From the disk of normal galaxies to the nucleus of prototype active sources, we review the wealth of results and new understanding provided by recent infrared probes and, in particular, the four instruments on-board of ISO.

/pdf/a-mid-and-far-infrared-view-of-galaxies-1vc8xqfii1.pdf

A Mid and Far Infrared View of Galaxies

We report observations at mid-infrared and sub- millimeter wavelengths of Centaurus A (Cen A, NGC 5128), the giant elliptical galaxy that harbors the closest radio loud Ac- tive Galactic Nucleus (AGN) to Earth. The dust emission from the deep interior of Cen A reveals a bisymmetric structure with a diameter of 5 0 (5 kpc), centred at the AGN. This structure is remarkably similar to that of a barred spiral galaxy, with the bar lying in a plane that is tilted 18 from the line of sight. The true nature of the distribution of dust in the inner regions of Cen A is noticeably displaced from the more chaotic and widespread optical obscuration. The barred spiral is a quasi-stable structure formed at the center of the giant elliptical from the tidal debris of a gas-rich object(s) accreted in the past 10 9 years. The total size and mass of interstellar gas in the barred spiral at the center of Cen A is comparable to the small Local Group spiral galaxy Messier 33. The observation of this remarkable structure opens the more general question on whether the dusty hosts of giant radio galaxies like Cen A, are "symbiotic" galaxies composed of a barred spiral inside an elliptical, where the bar serves to funnel gas toward the AGN. ? Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with partici- pation of ISAS and NASA.

http://aa.springer.de/papers/9341003/2300667.pdf

A barred spiral at the centre of the giant elliptical radio galaxy centaurus a

We report observations at mid-infrared and sub-millimeter wavelengths of Centaurus A (CenA, NGC 5128), the giant elliptical galaxy that harbors the closest radio loud Active Galactic Nucleus (AGN) to Earth. The dust emission from the deep interior of CenA reveals a bisymmetric structure with a diameter of 5' (5 kpc), centred at the AGN. This structure is remarkably similar to that of a barred spiral galaxy, with the bar lying in a plane that is tilted ~18 degrees from the line of sight. The true nature of the distribution of dust in the inner regions of CenA is noticeably displaced from the more chaotic and widespread optical obscuration. The barred spiral is a quasi-stable structure formed at the center of the giant elliptical from the tidal debris of a gas-rich object(s) accreted in the past 10^9 years. The total size and mass of interstellar gas in the barred spiral at the center of CenA is comparable to the small Local Group spiral galaxy Messier 33. The observation of this remarkable structure opens the more general question on whether the dusty hosts of giant radio galaxies like CenA, are "symbiotic" galaxies composed of a barred spiral inside an elliptical, where the bar serves to funnel gas toward the AGN.

https://arxiv.org/pdf/astro-ph/9810419.pdf

A barred spiral at the centre of the giant elliptical radio galaxy Centaurus A

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A barred spiral at the centre of the giant elliptical radio galaxy centaurus a

A barred spiral at the centre of the giant elliptical radio galaxy Centaurus A