To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure no-reply@cambridge.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Even though individual stars shine for a relatively long time, they are not eternal. Stars are born out of the gas and dust that exist within a galaxy (see the Chapter Opener); they then shine brightly on their own for a long time. Eventually, they die. Though we can directly observe only the outer layers of stars, we can deduce that the temperatures at their centers must be millions of kelvins. We can even figure out what it is deep down inside that makes them shine.
The light that reaches us from the stars and planets is only one type of radiation, a certain way in which energy moves through space. Radiation in this sense results from the continuous changes in electricity and magnetism at each point of space, so it is more formally known as electromagnetic radiation or electromagnetic waves.
The Sun, the Moon, and the stars rise every day in the eastern half of the sky and set in the western half. If you leave your camera on a tripod with the shutter open for a few minutes or hours in a dark place at night, you will photograph the “star trails” – the trails across the photograph left by the individual stars. In this chapter, we will discuss the phases of the Moon and planets, and how to find stars and planets in the sky. Stars twinkle; planets don’t twinkle as much (■ Fig. 4–1). We will also discuss the motions of the Sun, Moon, and planets, as well as of the stars in the sky.
Cosmology is the study of the structure and evolution of the Universe on its grandest scales (see the Chapter Opener). Some of the major issues studied by cosmologists include the Universe’s birth, age, size, geometry, and ultimate fate. We are also interested in the birth and evolution of galaxies, topics already discussed in Chapter 16.
We have already described the stars, which are important parts of any galaxy, and how they are born, live, and die. In this chapter, we discuss the gas and dust (small particles of matter) that are present to some extent throughout a galaxy. Substantial clouds of this gas and dust are called nebulae (the Latin plural; singular: nebula); “nebula” is Latin for “fog” or “mist.” New stars are born from such nebulae. We also discuss the overall structure of the Milky Way Galaxy and how, from our location inside it, we detect this structure.
Ancient peoples knew of five planets – Mercury, Venus, Mars, Jupiter, and Saturn. When we observe these planets in the sky, we join the people of long ago in noticing that the positions of the planets vary from night to night with respect to each other and with respect to the stars. In this chapter, we will discuss the motions of the planets, and you will learn how major figures in the history of astronomy explained these motions. These explanations have led to today’s conceptions of the Universe and of our place in it.
We have completed our grand tour of the Universe. We have seen stars and planets, matter between the stars, giant collections of stars called galaxies and clusters of galaxies, and very distant objects such as quasars with curved space lensing even farther objects. We have witnessed the evolution of stars, in some cases ending with spectacular explosions leaving compact remnants the size of a city but half a million times more massive than Earth. We have pondered the properties of still more bizarre objects, black holes. We have learned how our Universe began in a hot, compressed state and has been expanding ever since – seemingly faster and faster during the past five billion years, perhaps driven by a cosmic antigravity effect. We have explored the origins of the Universe, galaxies, stars, the chemical elements, planets, and ultimately life itself.
Through vertical resonances, bars can produce pseudo-bulges, within secular evolution. Bulges and pseudo-bulges have doubled their mass since z=1. The frequency of bulge-less galaxies at z=0 is difficult to explain, especially since clumpy galaxies at high z should create classical bulges in all galaxies. This issue is solved in modified gravity models. Bars and spirals in a galaxy disk, produce gravity torques that drive the gas to the center and fuel central star formation and nuclear activity. At 0.1-1kpc scale, observations of gravity torques show that only about one third of Seyfert galaxies experience molecular inflow and central fueling, while in most cases the gas is stalled in resonant rings. At 10-20pc scale, some galaxies have clearly revealed AGN fueling due to nuclear trailing spirals, influenced by the black hole potential. Thanks to ALMA, and angular resolution of up to 80mas, it is possible to reach the central black hole (BH) zone of influence, discover molecular tori, circum-nuclear disks misaligned with the galaxy, and the BH mass can be derived more directly from the kinematics.
We investigate the stellar and dynamical mass profiles of 32 brightest cluster galaxies (BCGs, MK = −25.7 to −27.8 mag) in massive clusters (0.05 < z < 0.30), and in particular the rising velocity dispersion profiles of 23 of these BCGs found in Loubser et al. (2018). We make comprehensive measurements of the Gauss-Hermite higher order velocity moments h3 and h4, and find positive central values for h4 for all the BCGs. We model the stellar and dynamical mass profiles of 25 of the BCGs using the Multi-Gaussian Expansion (MGE) and Jeans Anisotropic Method (JAM) for an axisymmetric case, deriving the stellar mass-to-light ratio (ϒ*DYN), and anisotropy (βz). We further explicitly add a dark matter halo mass component (MDM within r200) which we constrain from weak lensing results. In this proceedings, we summarise the study and show an example of the results.
Spatially resolved studies of galaxies in the high-redshift Universe have traditionally been reliant on data at rest-frame optical and UV wavelengths, which can be biased towards the least dust-obscured galaxies. For several years now, we have been able to resolve and probe the morphology of longer-wavelength emission from distant galaxies with ALMA, and a number of recent ALMA studies were presented at the IAU Symposium No. 352. These included our study of the resolved multi-wavelength emission of galaxies at z ∼ 2. As part of the SHiZELS collaboration, we are mapping the Hα emission line (from SINFONI/VLT), UV continuum (from HST), and the far-infrared (from ALMA) emission from a small sample of Hα-selected galaxies. In this proceedings paper, we showcase the high quality of our data, and the spectacular structures displayed by one of our most dusty sources. We also provide an overview of some highly complementary simulation-based work, using galaxies drawn from the FIRE-2 zoom-in cosmological hydrodynamical simulations. Using sophisticated radiative transfer techniques, we have derived predictions for the spatially-resolved emission of a sample of star-forming galaxies, from rest-frame far-ultraviolet to the far-infrared. For both observed and simulated galaxies, emission maps show striking differences with wavelength, with the same galaxy appearing clumpy and extended in the far-ultraviolet yet compact at far-infrared wavelengths.
The Galaxy Zoo project has provided quantitative visual morphologies for over a million galaxies, and has been part of a reinvigoration of interest in the morphologies of galaxies and what they reveal about galaxy evolution. Morphological information collected by GZ has shown itself to be a powerful tool for studying galaxy evolution, and GZ continues to collect classifications - currently serving imaging from DECaLS in its main site, and running a variety of related projects hosted by the Zooniverse; the citizen science platform which came out of the early success of GZ. I highlight some of the results from the last twelve years, with a particular emphasis on linking morphology and dynamics, look forward to future projects in the GZ family, and provide a quick start guide for how you can easily make use of citizen science techniques to analysis your own large and complex data sets.
I will review recent developments in the modeling of high-redshift galaxy spectra, focusing in particular on the rest-frame ultraviolet and optical emission from young stellar populations and the interstellar medium.