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Star formation

About: Star formation is a research topic. Over the lifetime, 37405 publications have been published within this topic receiving 1808161 citations. The topic is also known as: astrogenesis.


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Journal ArticleDOI
TL;DR: The GAIA astrometric mission has recently been approved as one of the next two ''cornerstones'' of ESA's science programme, with a launch datetarget of not later than mid-2012 as discussed by the authors.
Abstract: The GAIA astrometric mission has recently been approved as one of thenext two ``cornerstones'' of ESA's science programme, with a launch datetarget of not later than mid-2012. GAIA will provide positional andradial velocity measurements with the accuracies needed to produce astereoscopic and kinematic census of about one billion stars throughoutour Galaxy (and into the Local Group), amounting to about 1 percent ofthe Galactic stellar population. GAIA's main scientific goal is toclarify the origin and history of our Galaxy, from a quantitative censusof the stellar populations. It will advance questions such as when thestars in our Galaxy formed, when and how it was assembled, and itsdistribution of dark matter. The survey aims for completeness to V=20mag, with accuracies of about 10 mu as at 15 mag. Combined withastrophysical information for each star, provided by on-boardmulti-colour photometry and (limited) spectroscopy, these data will havethe precision necessary to quantify the early formation, and subsequentdynamical, chemical and star formation evolution of our Galaxy.Additional products include detection and orbital classification of tensof thousands of extra-Solar planetary systems, and a comprehensivesurvey of some 105-106 minor bodies in our SolarSystem, through galaxies in the nearby Universe, to some 500 000 distantquasars. It will provide a number of stringent new tests of generalrelativity and cosmology. The complete satellite system was evaluated aspart of a detailed technology study, including a detailed payloaddesign, corresponding accuracy assesments, and results from a prototypedata reduction development. (Less)

1,281 citations

Journal ArticleDOI
TL;DR: In this article, the authors used a sample of galaxies drawn from the Sloan Digital Sky Survey to study how structure, star formation and nuclear activity depend on local density and on stellar mass.
Abstract: We use a complete sample of galaxies drawn from the Sloan Digital Sky Survey to study how structure, star formation and nuclear activity depend on local density and on stellar mass. Local density is estimated by counting galaxies above a fixed absolute magnitude limit within cylinders 2 Mpc in projected radius and ±500 km s -1 in depth. The stellar mass distribution of galaxies shifts by almost a factor of two towards higher masses between low-and high-density regions. At fixed stellar mass both star formation and nuclear activity depend strongly on local density, while structural parameters such as size and concentration are almost independent of it. Only for low-mass galaxies (M * 1-Gyr) time-scales. Since structure does not depend on environment for galaxies with masses greater than 3 x 10 10 M ○. , the trends in recent SFH, dust and nuclear activity in these systems cannot be driven by processes that alter structure, for example mergers or harassment. The SFH-density correlation is strongest for small-scale estimates of local density. We see no evidence that star formation history depends on environment more than 1 Mpc from a galaxy. Finally, we highlight a striking similarity between the changes in the galaxy population as a function of density and as a function of redshift. We use mock catalogues derived from N-body simulations to explain how this may be understood.

1,270 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the power of spectral synthesis as a means to estimate the physical properties of galaxies, including stellar mass, velocity dispersion, extinction, and emission lines.
Abstract: The study of stellar populations in galaxies is entering a new era with the availability of large and high-quality data bases of both observed galactic spectra and state-of-the-art evolutionary synthesis models. In this paper we investigate the power of spectral synthesis as a means to estimate the physical properties of galaxies. Spectral synthesis is nothing more than the decomposition of an observed spectrum in terms of a superposition of a base of simple stellar populations of various ages and metallicities, producing as output the star formation and chemical histories of a galaxy, its extinction and velocity dispersion. Our implementation of this method uses the recent models of Bruzual & Charlot and observed spectra in the 3650–8000 A range. The reliability of this approach is studied by three different means: (1) simulations, (2) comparison with previous work based on a different technique, and (3) analysis of the consistency of results obtained for a sample of galaxies from the Sloan Digital Sky Survey (SDSS). We find that spectral synthesis provides reliable physical parameters as long as one does not attempt a very detailed description of the star formation and chemical histories. Robust and physically interesting parameters are obtained by combining the (individually uncertain) strengths of each simple stellar population in the base. In particular, we show that, besides providing excellent fits to observed galaxy spectra, this method is able to recover useful information on the distributions of stellar ages and, more importantly, stellar metallicities. Stellar masses, velocity dispersion and extinction are also found to be accurately retrieved for realistic signal-to-noise ratios. We apply this synthesis method to a volume-limited sample of 50 362 galaxies from the SDSS Data Release 2, producing a catalogue of stellar population properties. Emission lines are also studied, their measurement being performed after subtracting the computed starlight spectrum from the observed one. A comparison with recent estimates of both observed and physical properties of these galaxies obtained by other groups shows good qualitative and quantitative agreement, despite substantial differences in the methods of analysis. The confidence in the present method is further strengthened by several empirical and astrophysically reasonable correlations between synthesis results and independent quantities. For instance, we report the existence of strong correlations between stellar and nebular metallicities, stellar and nebular extinctions, mean stellar age and equivalent width of Hα and 4000-A break, and between stellar mass and velocity dispersion.

1,265 citations

Journal ArticleDOI
TL;DR: The cooling time in the dense gas within 50-300 kpc of the central galaxy in most clusters is found from X-ray images to be less than about 1010 yr as discussed by the authors.
Abstract: The cooling time in the dense gas within 50 – 300 kpc of the central galaxy in most clusters is found from X-ray images to be less than about 1010 yr. The weight of the overlying gas then causes a net inflow which is called a cooling flow. X-ray spectra confirm that the gas is cooling and loses at least 90 per cent of its thermal energy. The rate at which the gas cools ranges from ~ 10 – 500 M⊙ yr−1 . The soft X-ray absorption now discovered in cooling flows suggests that the cooled gas accumulates as very cold, small, gas clouds. Any large-scale star formation must be biased to low mass objects, except in the centres of some flows where some massive star may form, possibly from larger clouds assembled from cloud collisions and aggregation.

1,264 citations

Journal ArticleDOI
TL;DR: In this article, the authors summarize the current empirical knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as well as among populations of Pre-Main Sequence stars, and embedded protostars.
Abstract: Stellar multiplicity is an ubiquitous outcome of the star formation process Characterizing the frequency and main characteristics of multiple systems and their dependencies on primary mass and environment is therefore a powerful tool to probe this process While early attempts were fraught with selection biases and limited completeness, instrumentation breakthroughs in the last two decades now enable robust analyses In this review, we summarize our current empirical knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as well as among populations of Pre-Main Sequence stars and embedded protostars Clear trends as a function of both primary mass and stellar evolutionary stage are identified that will serve as a comparison basis for numerical and analytical models of star formation

1,261 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023742
20221,675
20211,238
20201,489
20191,497
20181,530