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.

The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators

Abstract: Spitzer data at 24, 70, and 160 μm and ground-based Hα images are analyzed for a sample of 189 nearby star-forming and starburst galaxies to investigate whether reliable star formation rate (SFR) indicators can be defined using the monochromatic infrared dust emission centered at 70 and 160 μm. We compare recently published recipes for SFR measures using combinations of the 24 μm and observed Hα luminosities with those using 24 μm luminosity alone. From these comparisons, we derive a reference SFR indicator for use in our analysis. Linear correlations between SFR and the 70 μm and 160 μm luminosity are found for L(70) ≳ 1.4 × 10^(42) erg s^(–1) and L(160) ≳ 2 × 10^(42) erg s^(–1), corresponding to SFR ≳ 0.1-0.3 M_☉ yr^(–1), and calibrations of SFRs based on L(70) and L(160) are proposed. Below those two luminosity limits, the relation between SFR and 70 μm (160 μm) luminosity is nonlinear and SFR calibrations become problematic. A more important limitation is the dispersion of the data around the mean trend, which increases for increasing wavelength. The scatter of the 70 μm (160 μm) data around the mean is about 25% (factor ~2) larger than the scatter of the 24 μm data. We interpret this increasing dispersion as an effect of the increasing contribution to the infrared emission of dust heated by stellar populations not associated with the current star formation. Thus, the 70 (160) μm luminosity can be reliably used to trace SFRs in large galaxy samples, but will be of limited utility for individual objects, with the exception of infrared-dominated galaxies. The nonlinear relation between SFR and the 70 and 160 μm emission at faint galaxy luminosities suggests a variety of mechanisms affecting the infrared emission for decreasing luminosity, such as increasing transparency of the interstellar medium, decreasing effective dust temperature, and decreasing filling factor of star-forming regions across the galaxy. In all cases, the calibrations hold for galaxies with oxygen abundance higher than roughly 12 +log(O/H) ~ 8.1. At lower metallicity, the infrared luminosity no longer reliably traces the SFR because galaxies are less dusty and more transparent.

Two Bright Submillimeter Galaxies in a z = 4.05 Protocluster in Goods-North, and Accurate Radio-Infrared Photometric Redshifts

Abstract: We present the serendipitous discovery of molecular gas CO emission lines with the IRAM Plateau de Bure interferometer coincident with two luminous submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey North field (GOODS-N). The identification of the millimeter emission lines as CO[4-3] at z = 4.05 is based on the optical and near-IR photometric redshifts, radio-infrared photometric redshifts and Keck+DEIMOS optical spectroscopy. These two galaxies include the brightest submillimeter source in the field (GN20; S850µm = 20.3mJy, zCO = 4.055 ± 0.001) and its companion (GN20.2; S850µm = 9.9mJy, zCO = 4.051 ± 0.003). These are among the most distant submillimeter-selected galaxies reliably identified through CO emission and also some of the most luminous known. GN20.2 has a possible additional counterpart and a luminous AGN inside its primary counterpart revealed in the radio. Continuum emission of 0.3mJy at 3.3mm (0.65mm in the rest frame) is detected at 5� for GN20, the first dust continuum detection in an SMG at such long wavelength, unveiling a spectral energy distribution that is similar to local ultra luminous infrared galaxies. In terms of CO to bolometric luminosities, stella r mass and star formation rates (SFRs), these newly discovered z > 4 SMGs are similar to z ∼ 2 − 3 SMGs studied to date. These z ∼ 4 SMGs have much higher specific SFRs than typical B-band dropout Lyman break galaxi es at the same redshift. The stellar mass-SFR correlation for normal galaxies does not seem to evolve much further, between z ∼ 2 and z ∼ 4. A significant z = 4.05 spectroscopic redshift spike is observed in GOODS-N, and a strong spatial overdensity of B-band dropouts and IRAC selected z > 3.5 galaxies appears to be centered on the GN20 and GN20.2 galaxies. This suggests a proto-cluster structure with total mass ∼ 10 14 M⊙. Using photometry at mid-IR (24µm), submm (850µm) and radio (20cm) wavelengths, we show that reliable photometric redshifts (�z/(1+ z) ∼ 0.1) can be derived for SMGs over 1 < ∼ z < ∼ 4. This new photometric redshift technique has been used to provide a first estimate of the space density of 3.5 < z < 6 hyper-luminous starburst galaxies, and to show that they both contribute substantially to the SFR density at early epochs and that they can account for the presence of old galaxies at z ∼ 2 − 3. Many of these high-redshift starbursts will be within rea ch of Herschel. We find that the

Pre-Main-Sequence Binary Stars

Abstract: The observational study of pre-main-sequence (PMS) binary stars is in many ways a very young field; most PMS binaries known today were discovered in the past decade. Nonetheless, T Tauri stars have been under study for more than a half century, and the serendipitous discovery of visual pairs has always been a by-product of their observation (e.g. Joy & Van Biesbroeck 1944). The acceleration of discovery in recent years has at least two stimuli, one technical and one sociological. First, the frequency of binaries among main-sequence solar-type stars peaks at semimajor axes of order 50 AU, projecting to less than 0.5" at the distance of the nearest star-forming regions. The requisite high­ angular-resolution techniques (and near-infrared detectors) have only recently permitted the major surveys for PMS binaries now coming to fruition. Second, and equally important, the formation and early evolution of binaries has attracted increasing attention from those studying star formation. This can perhaps be attributed to both a growing confidence in our general picture for single-star formation (e.g. Shu et a1 1987) and recognition that however correct our theories of single-star formation may be, the usual product of a star-formation event is a multiple-star system. Until recently, the primary observational constraint on the mechanisms of binary formation and early evolution have been provided by main-sequence (MS) binaries in the solar vicinity, acting as a surrogate for the zero-age-main­ sequence (ZAMS) binary population. As the ultimate product of the binary formation process, ZAMS binaries do supply essential constraints. However,

A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution

Abstract: We have carried out a large set of N-body simulations studying the effect of residual-gas expulsion on the survival rate, and final properties of star clusters. We have varied the star formation efficiency (SFE), gas expulsion time-scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. The complete data of these simulations are made available on the internet.

Massive star formation in 100,000 years from turbulent and pressurized molecular clouds

Abstract: Massive stars (with mass m* > 8 solar masses M⊙) are fundamental to the evolution of galaxies, because they produce heavy elements, inject energy into the interstellar medium, and possibly regulate the star formation rate. The individual star formation time, t*f, determines the accretion rate of the star; the value of the former quantity is currently uncertain by many orders of magnitude1,2,3,4,5,6, leading to other astrophysical questions. For example, the variation of t*f with stellar mass dictates whether massive stars can form simultaneously with low-mass stars in clusters. Here we show that t*f is determined by the conditions in the star's natal cloud, and is typically ∼105 yr. The corresponding mass accretion rate depends on the pressure within the cloud—which we relate to the gas surface density—and on both the instantaneous and final stellar masses. Characteristic accretion rates are sufficient to overcome radiation pressure from ∼100M⊙ protostars, while simultaneously driving intense bipolar gas outflows. The weak dependence of t*f on the final mass of the star allows high- and low-mass star formation to occur nearly simultaneously in clusters.