Dynamics of starbursting dwarf galaxies: I Zw 18

Lelli, Federico; Verheijen, Marc; Fraternali, Filippo; Sancisi, R.

doi:10.1051/0004-6361/201117867

Cited by 88 publications

(134 citation statements)

References 55 publications

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“…The HI image of the dwarf galaxy IZw18 in Fig. 5 is particularly illustrative (from Lelli et al 2012a). It shows large amounts of HI gas around the galaxy (M g /M ∼ 5) with a plume of different velocity directed towards the galaxy where a large starburst goes on at present (Fig.…”

Section: Neutral Gas Observationsmentioning

confidence: 96%

Star formation sustained by gas accretion

Alméida

Elmegreen

Muñoz–Tuñón

et al. 2014

Astron Astrophys Rev

183

130

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Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.

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Section: Neutral Gas Observationsmentioning

confidence: 96%

Star formation sustained by gas accretion

Alméida

Elmegreen

Muñoz–Tuñón

et al. 2014

Astron Astrophys Rev

183

130

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“…The origin of these lines (e.g., WR stars, H  region...) is unclear. (Lelli et al 2012). Table 4 also shows the radial velocities inferred from each species individually.…”

Section: Normalized Flux Observed Wavelength [å]mentioning

confidence: 99%

“…Furthermore, the red wing of Lyα is contaminated by nebular continuum emission (2-photon and Balmer continuum) arising in the H  region of I Zw 18 and by the N  λ1238, λ1240 wind lines from the ionizing stars in I Zw 18. Finally, the continuum level is uncertain, because Lyα A16, page 8 of 32 (2000); (3) Kunth et al (1994); (4) A03; (5) L04; (6) Brown et al (2002); (7) van Zee et al (1998); (8) Lelli et al (2012).…”

Section: Hydrogenmentioning

confidence: 99%

“…The H  spatial distribution observed by Lelli et al (2012) is particularly informative. The high-spatial resolution (2 beam) reveals that the NW region lies in a H  hole (see also Fig.…”

Section: Hydrogenmentioning

confidence: 99%

“…Images were downloaded from the Hubble Legacy Archive (http://hla.stsci.edu/) and later combined. The green contours show the H  column density distribution from Lelli et al (2012) with 2 resolution (beam size in the bottom left). Contours are drawn for 3 (dashed), 6, 9, 12, and 15 × 10 21 cm −2 .…”

Section: Introductionmentioning

confidence: 99%

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Chemical enrichment and physical conditions in I Zw 18

Lebouteiller

Heap

Hubený

et al. 2013

A&A

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Context. Low-metallicity star-forming dwarf galaxies are prime targets to understand the chemical enrichment of the interstellar medium. The H  region contains the bulk of the mass in blue compact dwarfs, and it provides important constraints on the dispersal and mixing of heavy elements released by successive star-formation episodes. The metallicity of the H  region is also a critical parameter to investigate the future star-formation history, as metals provide most of the gas cooling that will facilitate and sustain star formation. Aims. Our primary objective is to study the enrichment of the H  region and the interplay between star-formation history and metallicity evolution. Our secondary objective is to constrain the spatial-and time-scales over which the H  and H  regions are enriched, and the mass range of stars responsible for the heavy element production. Finally, we aim to examine the gas heating and cooling mechanisms in the H  region. Methods. We observed the most metal-poor star-forming galaxy in the Local Universe, I Zw 18, with the Cosmic Origin Spectrograph onboard Hubble. The abundances in the neutral gas are derived from far-ultraviolet absorption-lines (H , C , C *, N , O , ...) and are compared to the abundances in the H  region. Models are constructed to calculate the ionization structure and the thermal processes. We investigate the gas cooling in the H  region through physical diagnostics drawn from the fine-structure level of C + . Results. We find that H  region abundances are lower by a factor of ∼2 as compared to the H  region. There is no differential depletion on dust between the H  and H  region. Using sulfur as a metallicity tracer, we calculate a metallicity of 1/46 Z (vs. 1/31 Z in the H  region). From the study of the C/O, [O/Fe], and N/O abundance ratios, we propose that C, N, O, and Fe are mainly produced in massive stars. We argue that the H  envelope may contain pockets of pristine gas with a metallicity essentially null. Finally, we derive the physical conditions in the H  region by investigating the C * absorption line. The cooling rate derived from C * is consistent with collisions with H 0 atoms in the diffuse neutral gas. We calculate the star-formation rate from the C * cooling rate assuming that photoelectric effect on dust is the dominant gas heating mechanism. Our determination is in good agreement with the values in the literature if we assume a low dust-to-gas ratio (∼2000 times lower than the Milky Way value).

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Gas Accretion and Star Formation Rates

Alméida

2017

Gas Accretion Onto Galaxies

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Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star-formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star-formation that it induces. A number of observations pointing out the connection between metalpoor gas accretion and star-formation are analyzed, specifically, the short gas consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the socalled G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the α-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas.

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Dynamics of starbursting dwarf galaxies: I Zw 18

Cited by 88 publications

References 55 publications

Star formation sustained by gas accretion

Star formation sustained by gas accretion

Chemical enrichment and physical conditions in I Zw 18

Gas Accretion and Star Formation Rates

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