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.

Self-regulated star formation in galaxies via momentum input from massive stars

Abstract: Feedback from massive stars is believed to play a critical role in shaping the galaxy mass function, the structure of the interstellar medium (ISM) and the low efficiency of star formation, but the exact form of the feedback is uncertain. In this paper, the first in a series, we present and test a novel numerical implementation of stellar feedback resulting from momentum imparted to the ISM by radiation, supernovae and stellar winds. We employ a realistic cooling function, and find that a large fraction of the gas cools to ≲100 K, so that the ISM becomes highly inhomogeneous. Despite this, our simulated galaxies reach an approximate steady state, in which gas gravitationally collapses to form giant ‘molecular’ clouds (GMCs), dense clumps and stars; subsequently, stellar feedback disperses the GMCs, repopulating the diffuse ISM. This collapse and dispersal cycle is seen in models of Small Magellanic Cloud (SMC)-like dwarfs, the Milky Way and z∼ 2 clumpy disc analogues. The simulated global star formation efficiencies are consistent with the observed Kennicutt–Schmidt relation. Moreover, the star formation rates are nearly independent of the numerically imposed high-density star formation efficiency, density threshold and density scaling. This is a consequence of the fact that, in our simulations, star formation is regulated by stellar feedback limiting the amount of very dense gas available for forming stars. In contrast, in simulations without stellar feedback, i.e. under the action of only gravity and gravitationally induced turbulence, the ISM experiences runaway collapse to very high densities. In these simulations without feedback, the global star formation rates exceed observed galactic star formation rates by 1–2 orders of magnitude, demonstrating that stellar feedback is crucial to the regulation of star formation in galaxies.

The Star-formation Mass Sequence out to z=2.5

Abstract: We study the star formation rate (SFR) - stellar mass (M*) relation in a self-consistent manner from 0 10 at 1 < z < 1.5), 2) red star-forming galaxies with low levels of dust obscuration and low specific SFRs (11%), and 3) dusty, blue star-forming galaxies with high specific SFRs (7%). The remaining 28% comprises quiescent galaxies. Galaxies on the "normal" star formation sequence show strong trends of increasing dust attenuation with stellar mass and a decreasing specific SFR, with an observed scatter of 0.25 dex (0.17 dex intrinsic scatter). The dusty, blue galaxies reside in the upper envelope of the star formation sequence with remarkably similar spectral shapes at all masses, suggesting that the same physical process is dominating the stellar light. The red, low-dust star-forming galaxies may be in the process of shutting off and migrating to the quiescent population.

High-Resolution Submillimeter Constraints on Circumstellar Disk Structure

Abstract: We present a high spatial resolution submillimeter continuum survey of 24 circumstellar disks in the Taurus-Auriga and Ophiuchus-Scorpius star formation regions using the SMA. In the context of a simple model, we use broadband spectral energy distributions and submillimeter visibilities to derive constraints on some basic parameters that describe the structure of these disks. For the typical disk in the sample we infer a radial surface density distribution Σr r-p with a median p ≈ 0.5, although consideration of the systematic effects of some of our assumptions suggest that steeper distributions with p ≈ 1 are more reasonable. The distribution of the outer radii of these disks shows a distinct peak at Rd ≈ 200 AU, with only a few cases where the disk emission is completely unresolved. Based on these disk structure measurements, the mass accretion rates, and the typical spectral and spatial distributions of submillimeter emission, we show that the observations are in good agreement with similarity solutions for steady accretion disks that have a viscosity parameter α ≈ 0.01. We provide new estimates of the spectral dependence of the disk opacity κν νβ with a mean β ≈ 1.0, corrected for optically thick emission. This typical value of β is consistent with model predictions for the collisional growth of solids to millimeter-size scales in the outer disk. Although direct constraints on planet formation in these disks are not currently available, the extrapolated density distributions inferred here are substantially shallower than those calculated based on the solar system or extrasolar planets and typically used in planet formation models. It is possible that we are substantially underestimating disk densities due to an incomplete submillimeter opacity prescription.

Massive stars embedded in molecular clouds - Their population and distribution in the galaxy

Abstract: A new method for identifying massive stars inside molecular clouds is described which makes use of their characteristic FIR flux density distribution. A two-color selection criterion has been developed and carefully calibrated using stars which are known to be embedded in molecular clouds. When applied to the sensitive IRAS all-sky survey, a direct measure of the total number and distribution of embedded massive stars in the Galaxy is obtained. A lower limit is derived on the current O star formation rate in the Galaxy, the contribution O stars make to the FIR luminosity of the Galaxy is estimated, and it is shown that the number of IRAS sources found is consistent with a Galactic supernova rate of about one every 25 yrs.