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

Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by Leitherer & Heckman. We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by Lejeune et al. Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 106—109 yr. We also show the spectral energy distributions which are used to compute colors and other quantities. The full data set is available for retrieval at a Web site, which allows users to run specific models with nonstandard parameters as well. We also make the source code available to the community.

https://iopscience.iop.org/article/10.1086/313233/pdf

Starburst99: Synthesis Models for Galaxies with Active Star Formation

Over the past two decades, an avalanche of data from multiwavelength imaging and spectroscopic surveys has revolutionized our view of galaxy formation and evolution. Here we review the range of complementary techniques and theoretical tools that allow astronomers to map the cosmic history of star formation, heavy element production, and reionization of the Universe from the cosmic "dark ages" to the present epoch. A consistent picture is emerging, whereby the star-formation rate density peaked approximately 3.5 Gyr after the Big Bang, at z~1.9, and declined exponentially at later times, with an e-folding timescale of 3.9 Gyr. Half of the stellar mass observed today was formed before a redshift z = 1.3. About 25% formed before the peak of the cosmic star-formation rate density, and another 25% formed after z = 0.7. Less than ~1% of today's stars formed during the epoch of reionization. Under the assumption of a universal initial mass function, the global stellar mass density inferred at any epoch matches reasonably well the time integral of all the preceding star-formation activity. The comoving rates of star formation and central black hole accretion follow a similar rise and fall, offering evidence for co-evolution of black holes and their host galaxies. The rise of the mean metallicity of the Universe to about 0.001 solar by z = 6, one Gyr after the Big Bang, appears to have been accompanied by the production of fewer than ten hydrogen Lyman-continuum photons per baryon, a rather tight budget for cosmological reionization.

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Cosmic Star-Formation History

▪ 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...

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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

Hubble Space Telescope ultraviolet (UV) images of nine starburst galaxies reveal them to be highly irregular, even after excluding compact sources (clusters and resolved stars). Most (7/9) are found to have a similar intrinsic effective surface brightnesses, suggesting that a negative feedback mechanism is setting an upper limit to the star formation rate per unit area. All starbursts in our sample contain UV bright star clusters indicating that cluster formation is an important mode of star formation in starbursts. On average about 20% of the UV luminosity comes from these clusters. The brightest clusters, or super star clusters (SSC), are preferentially found at the very heart of starbursts. The size of the nearest SSCs are consistent with those of Galactic globular clusters. The luminosity function of SSCs is well represented by a power law with a slope alpha ~ -2. There is a strong correlation between the far infrared excess and the UV spectral slope. The correlation is well modeled by a geometry where much of their dust is in a foreground screen near to the starburst, but not by a geometry of well mixed stars and dust.

Starbursts and Star Clusters in the Ultraviolet

Models for the integrated output of mass, momentum, and energy from a population of massive stars are presented. We computed an extensive grid of radiatively wind models for hot stars and derived scaling relations for the mass-loss rates and wind velocities as a function of stellar parameters, including the metal abundance. It is found that the mass-loss rate scales with metal abundance like M∞Z 0.8 . These wind models are combined with empirical stellar-wind data of other stellar types to obtain predictions for mass-loss rates and wind velocities in the entire upper Hertzsprung-Russell diagram

Deposition of Mass, Momentum, and Energy by Massive Stars into the Interstellar Medium

We report the results of a systematic study of the vacuum ultraviolet (λ 1150-2000 A) spectra of a sample of 45 starburst and related galaxies observed with the IUE satellite. These span broad ranges in metallicity (from 0.02 to 3 times solar), bolometric luminosity (~107-4 × 1011 L☉), and galaxy properties (e.g., including low-mass dwarf galaxies, normal disk galaxies, and massive galactic mergers). The projected size of the IUE spectroscopic aperture is typically 1 to several kpc and therefore usually encompasses the entire starburst and is similar to the aperture sizes used for spectroscopy of high-redshift galaxies. Our principal conclusion is that local starbursts occupy a very small fractional volume in the multidimensional manifold defined by such fundamental parameters as the extinction, metallicity, and vacuum-UV line strengths (both stellar and interstellar) of the starburst and the rotation speed (mass) and absolute magnitude of the starburst's "host" galaxy. More metal-rich starbursts are redder and more heavily extinguished in the UV, are more luminous, have stronger vacuum-UV lines, and occur in more massive and optically brighter host galaxies. We advocate using these local starbursts as a "training set" to learn how to interpret the rest frame UV spectra of star-forming galaxies at high redshift better, and we stress that the degree of similarity between local starbursts and high-redshift galaxies in this multidimensional parameter space can already be tested empirically. The results on local starbursts suggest that the high- redshift "Lyman Dropout" galaxies are typically highly reddened and extinguished by dust (by an average factor of 5-10 in the UV), may have moderately high metallicities (0.1-1 times solar?), are probably building galaxies with stellar surface-mass densities similar to present-day ellipticals, and may be suffering substantial losses of metal-enriched gas that can "pollute" the intergalactic medium.

Carmelle Robert

Papers

Starburst99: Synthesis Models for Galaxies with Active Star Formation

Starbursts and Star Clusters in the Ultraviolet

Starbursts and Star Clusters in the Ultraviolet

Deposition of Mass, Momentum, and Energy by Massive Stars into the Interstellar Medium

The Ultraviolet Spectroscopic Properties of Local Starbursts: Implications at High Redshift