Observations of star formation rates (SFRs) in galaxies provide vital clues to the physical nature of the Hubble sequence and are key probes of the evolutionary histories of galaxies. The focus of this review is on the broad patterns in the star formation properties of galaxies along the Hubble sequence and their implications for understanding galaxy evolution and the physical processes that drive the evolution. Star formation in the disks and nuclear regions of galaxies are reviewed separately, then discussed within a common interpretive framework. The diagnostic methods used to measure SFRs are also reviewed, and a self-consistent set of SFR calibrations is presented as an aid to workers in the field. One of the most recognizable features of galaxies along the Hubble sequence is the wide range in young stellar content and star formation activity. This variation in stellar content is part of the basis of the Hubble classification itself (Hubble 1926), and understanding its physical nature and origins is fundamental to understanding galaxy evolution in its broader context. This review deals with the global star formation properties of galaxies, the systematics of those properties along the Hubble sequence, and their implications for galactic evolution. I interpret “Hubble sequence” in this context very loosely, to encompass not only morphological type but other properties such as gas content, mass, bar structure, and dynamical environment, which can strongly influence the largescale star formation rate (SFR).

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Star formation in galaxies along the hubble sequence

Physics welcomes the idea that space contains energy whose gravitational effect approximates that of Einstein's cosmological constant, \ensuremath{\Lambda}; today the concept is termed dark energy or quintessence. Physics also suggests that dark energy could be dynamical, allowing for the arguably appealing picture of an evolving dark-energy density approaching its natural value, zero, and small now because the expanding universe is old. This would alleviate the classical problem of the curious energy scale of a millielectron volt associated with a constant \ensuremath{\Lambda}. Dark energy may have been detected by recent cosmological tests. These tests make a good scientific case for the context, in the relativistic Friedmann-Lema\^{\i}tre model, in which the gravitational inverse-square law is applied to the scales of cosmology. We have well-checked evidence that the mean mass density is not much more than one-quarter of the critical Einstein--de Sitter value. The case for detection of dark energy is not yet as convincing but still serious; we await more data, which may be derived from work in progress. Planned observations may detect the evolution of the dark-energy density; a positive result would be a considerable stimulus for attempts at understanding the microphysics of dark energy. This review presents the basic physics and astronomy of the subject, reviews the history of ideas, assesses the state of the observational evidence, and comments on recent developments in the search for a fundamental theory.

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The Cosmological Constant and Dark Energy

https://www.physics.rutgers.edu/grad/690/Padmanabhan-2003.pdf

Cosmological constant—the weight of the vacuum

▪ Abstract At luminosities above 1011 , infrared galaxies become the dominant population of extragalactic objects in the local Universe (z ≲ 0.3), being more numerous than optically selected starburst and Seyfert galaxies and quasi-stellar objects at comparable bolometric luminosity. The trigger for the intense infrared emission appears to be the strong interaction/merger of molecular gas-rich spirals, and the bulk of the infrared luminosity for all but the most luminous objects is due to dust heating from an intense starburst within giant molecular clouds. At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus. These ultraluminous infrared galaxies may represent an important stage in the formation of quasi-stellar objects and powerful radio galaxies. They may al...

/pdf/luminous-infrared-galaxies-zoi3y3hutv.pdf

Luminous infrared galaxies

We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star-formation rates are discussed, and updated prescriptions for calculating star-formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.

Star Formation in the Milky Way and Nearby Galaxies

We reconsider the relation between spiral and SO galaxies in the light of recent data on the colors and morphology of disk systems, and on the content of clusters at different redshifts. Star formation will strongly deplete the gas in most spirals in a fraction of the Hubble time, so we suggest that the gas in spirals has been replenished by infall from residual envelopes, probably including gas-rich companions and tidal debris. SO's may then be disk systems that lost their gas-rich envelopes at an early stage and consumed their remaining gas by star formation. This picture is consistent with the color of SO's if most of their star formation stopped at least a few gigayears ago, and it is consistent with their small disk-to-bulge ratios relative to spirals, since this is a direct result of the early truncation of star formation. Numerical simulations show that the gas envelopes of disk galaxies in clusters are largely stripped away when the clusters collapse, but star formation can continue in the spirals for several gigayears while their remaining disk gas is consumed. These results can explain the blue galaxies observed by Butcher and Oemler in two condensed clusters at zapprox.0.4: these clustersmore » are seen just before most of their galaxies run out of gas, so that star formation is still occurring in them but will soon die out, causing the spirals to evolve into SO's with normal present colors. A rapid evolution of the galaxy content of condensed clusters is predicted at moderate redshifts, ranging from a large fraction of blue galaxies at zapprox.0.4 to very few at zapprox.0.« less

The evolution of disk galaxies and the origin of S0 galaxies

Star formation rates in normal and peculiar galaxies

Models for chemical evolution and stellar abundances are used to test assumptions about the nucleosynthesis of various elements. For primary elements, the emphasis is on empirical evidence that carbon and iron, but not oxygen, are ejected in significant quantities by longer-lived stars than those proposed by Arnett for their entire nucleosynthesis, which all have lifetimes <2 x 10/sup 7/ years.

Stellar lifetimes and abundance ratios in chemical evolution.

Evolution of the stars and gas in galaxies.

Essentially everything of astronomical interest is either part of a galaxy, or from a galaxy, or otherwise relevant to the origin or evolution of galaxies. Diverse examples are that the isotropic composition of meteorites provides clues to the history of star formation billions of years ago, and cosmological tests for the deceleration of the Universe are strongly affected by changes in the luminosities of galaxies during the lookback time sampled. The aim of this article is to review some of the vital connections that galaxy evolution makes among many astronomical phenomena. The evolution of galaxies can be broadly divided into three areas: dynamical evolution, chemical evolution, and the evolution of photometric properties. Chemical and photometric evolution are the main topics of this review, and dynamical processes will be considered only where they directly affect the others. The article is intended to be self-contained for readers with a general knowledge of astronomy and astrophysics but with no special expertise on galaxies. Because the background and literature relevant to the evolution of stars and gas in galaxies are so extensive, complete coverage cannot be attempted. Instead, comprehensive reviews and recent papers are emphasized in the references; these include detailed works in closely related fields, such as galaxy formation and nucleosynthesis, that are treated very briefly here. The history of the subject has been discussed in several recent reviews (e.g. Sandage et al. 1975; Spinrad & Peimbert 1975; Trimble 1975; van den Bergh 1975), so here the emphasis will be on current ideas.

Beatrice M. Tinsley

Papers

The evolution of disk galaxies and the origin of S0 galaxies

Star formation rates in normal and peculiar galaxies

Stellar lifetimes and abundance ratios in chemical evolution.

Evolution of the stars and gas in galaxies.

Evolution of the stars and gas in galaxies.