Star Formation in Galaxies Along the Hubble Sequence

Kennicutt, Robert C.

doi:10.1146/annurev.astro.36.1.189

Cited by 5,896 publications

(4,320 citation statements)

References 180 publications

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“…To determine the effective Lyα escape fraction, we first convert this limit to a nominal SFR by assuming a factor 8.7 flux ratio between Lyα and Hα, and a standard conversion between Hα and the star-formation rate 34 , but assuming a Chabrier IMF 11 , as used throughout the paper. This corresponds to a detection limit for the nominal Lyα SFR <0.7 M ⊙ yr -1 (corrected for lensing).…”

Section: Emission Line Flux Detection Limitsmentioning

confidence: 99%

A dusty, normal galaxy in the epoch of reionization

Watson

Christensen

Knudsen

et al. 2015

Nature

382

409

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Candidates for the modest galaxies that formed most of the stars in the early universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-UV imaging 1 . But it has proved difficult for existing spectrographs to characterise them in the UV 2,3,4 . The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant UV-selected galaxy detected in dust emission is only at z = 3.2 5 , and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at this early epoch 6,7,8 . Here we report thermal dust emission from an archetypal early universe starforming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5±0.2 from a spectroscopic detection of the Lyα break. A1689-zD1 is representative of the star-forming population during reionisation 9 , with a total star-formation rate of about 12 M ⊙ yr -1 . The galaxy is highly evolved: it has a large stellar mass, and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7, in spite of the very short time since they first appeared.As part of a programme to investigate galaxies at z > 7 with the X-shooter spectrograph on the Very Large Telescope, we observed the candidate high-redshift galaxy, A1689-zD1, behind the lensing galaxy cluster, Abell 1689 (Fig. 1). The source was originally identified 10 as a candidate z > 7 system from deep imaging with the Hubble and Spitzer Space Telescopes. Suggested to be at z = 7.6±0.4 from photometry fitting, it is gravitationally magnified by a factor of 9.3 by the galaxy cluster 10 , and though intrinsically faint, because of the gravitational amplification, is one of the brightest candidate z > 7 galaxies known. The X-shooter observations were carried out on several nights between March 2010 and March 2012 with a total time of 16 hours on target.The galaxy continuum is detected and can be seen in the binned spectrum (Fig. 2). The Lya cutoff is at 1035±24 nm and defines the redshift, z = 7.5±0.2. It is thus one of the most distant galaxies known to date to be confirmed via spectroscopy, and the only galaxy at z > 7 where the redshift is determined from spectroscopy of its stellar continuum. The spectral slope is blue; using a power-law fit, F λ ∝ λ -β , β = 2.0 ± 0.1. The flux break is sharp, and greater than a factor of ten in depth. In addition, no line emission is detected, ruling out a different redshift solution for the galaxy. Line emission is excluded to lensing-corrected depths of 3×10 -19 erg cm -2 s -1 (3σ) in the absence of sky emission lines, making this by far the deepest intrinsic spectrum published of a reionization era object, highlighting the difficulty of obtaining UV redshifts for objects at this epoch that are not strongly domin...

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Section: Emission Line Flux Detection Limitsmentioning

confidence: 99%

A dusty, normal galaxy in the epoch of reionization

Watson

Christensen

Knudsen

et al. 2015

Nature

382

409

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“…We use a pressure law to model star formation (Schaye & Dalla Vecchia 2008), which is designed to yield results consistent with the Schmidt-Kennicutt law (Schmidt 1959;Kennicutt 1998). The threshold density above which stars form is set to n = 10 cm −3 .…”

Section: Star Formationmentioning

confidence: 99%

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

Paardekooper

Khochfar

Vecchia

2015

Monthly Notices of the Royal Astronomical Society

250

280

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Proto-galaxies forming in low-mass dark matter haloes are thought to provide the majority of ionizing photons needed to reionize the Universe, due to their high escape fractions of ionizing photons. We study how the escape fraction in high-redshift galaxies relates to the physical properties of the halo in which the galaxies form, by computing escape fractions in more than 75000 haloes between redshifts 27 and 6 that were extracted from the First Billion Years project, high-resolution cosmological hydrodynamics simulations of galaxy formation. We find that the main constraint on the escape fraction is the gas column density in a radius of 10 pc around the stellar populations, causing a strong mass dependence of the escape fraction. The lower potential well in haloes with M 200 10 8 M results in low column densities that can be penetrated by radiation from young stars (age < 5 Myr). In haloes with M 200 10 8 M supernova feedback is important, but only ∼ 30% of the haloes in this mass range have an escape fraction higher than 1%. We find a large range of escape fractions in haloes with similar properties, caused by different distributions of the dense gas in the halo. This makes it very hard to predict the escape fraction on the basis of halo properties and results in a highly anisotropic escape fraction. The strong mass dependence, the large spread and the large anisotropy of the escape fraction may strongly affect the topology of reionization and is something current models of cosmic reionization should strive to take into account.

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“…Thus the EW(Hα) criterion is not optional. A better starburst indicator is probably the birthrate parameter, b [69,140]. It is defined as the ratio between the present SFR and the mean past SFR: b = SFR <SFR> .…”

Section: Starburstsmentioning

confidence: 99%

Star Forming Dwarf Galaxies

Bergvall¹

2011

Astrophysics and Space Science Proceedings

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Star forming dwarf galaxies (SFDGs) have a high gas content and low metallicities, reminiscent of the basic entities in hierarchical galaxy formation scenarios. In the young universe they probably also played a major role in the cosmic reionization. Their abundant presence in the local volume and their youthful character make them ideal objects for detailed studies of the initial stellar mass function (IMF), fundamental star formation processes and its feedback to the interstellar medium. Occasionally we witness SFDGs involved in extreme starbursts, giving rise to strongly elevated production of super star clusters and global superwinds, mechanisms yet to be explored in more detail. SFDGs is the initial state of all dwarf galaxies and the relation to the environment provides us with a key to how different types of dwarf galaxies are emerging. In this review we will put the emphasis on the exotic starburst phase, as it seems less important for present day galaxy evolution but perhaps fundamental in the initial phase of galaxy formation.

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Star Formation in Galaxies Along the Hubble Sequence

Cited by 5,896 publications

References 180 publications

A dusty, normal galaxy in the epoch of reionization

A dusty, normal galaxy in the epoch of reionization

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

Star Forming Dwarf Galaxies

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