Metallicity Inhomogeneities in Local Star-Forming Galaxies as a Sign of Recent Metal-Poor Gas Accretion

Alméida, J. Sánchez; Morales-Luis, A. B.; Muñoz–Tuñón, C.; Elmegreen, D. M.; Elmegreen, Bruce G.; Méndez-Abreu, J.

doi:10.1088/0004-637x/783/1/45

Cited by 77 publications

(43 citation statements)

References 91 publications

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“…Sánchez studied their morphological and dynamical properties and suggested that XMPs with tadpole morphologies are in early stages of their disk assembly. In this scenario, a massive accretion of external metal-poor gas feeds the starburst, leading to large inhomogeneities or gradients of metallicity from head to tail (Sánchez Almeida et al 2014), closely resembling recent findings at higher redshift (e.g., Cresci et al 2010;Queyrel et al 2012;Troncoso et al 2014). Future studies of very metal-poor EELGs using high-quality 3D spectroscopy will be used to test this scenario.…”

Section: Discovery Of Extremely Metal-poor Eelgssupporting

confidence: 66%

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

Amorín

Pérez-Montero

Contini

et al. 2015

A&A

102

113

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Context. The study of large and representative samples of low-metallicity star-forming galaxies at different cosmic epochs is of great interest to the detailed understanding of the assembly history and evolution of low-mass galaxies. Aims. We present a thorough characterization of a large sample of 183 extreme emission-line galaxies (EELGs) at redshift 0.11 ≤ z ≤ 0.93 selected from the 20k zCOSMOS bright survey because of their unusually large emission line equivalent widths. Methods. We use multiwavelength COSMOS photometry, HST-ACS I-band imaging, and optical zCOSMOS spectroscopy to derive the main global properties of star-forming EELGs, such as sizes, stellar masses, star formation rates (SFR), and reliable oxygen abundances using both "direct" and "strong-line" methods. Results. The EELGs are extremely compact (r 50 ∼ 1.3 kpc), low-mass (M * ∼ 10 7 −10 10 M ) galaxies forming stars at unusually high specific star formation rates (sSFR ≡ SFR/M up to 10 −7 yr −1 ) compared to main sequence star-forming galaxies of the same stellar mass and redshift. At rest-frame UV wavelengths, the EELGs are luminous and show high surface brightness and include strong Lyα emitters, as revealed by GALEX spectroscopy. We show that zCOSMOS EELGs are high-ionization, low-metallicity systems, with median 12+ log(O/H) = 8.16 ± 0.21 (0.2 Z ) including a handful of extremely metal-deficient (<0.1 Z ) EELGs. While ∼80% of the EELGs show non-axisymmetric morphologies, including clumpy and cometary or tadpole galaxies, we find that ∼29% of them show additional low-surface-brightness features, which strongly suggests recent or ongoing interactions. As star-forming dwarfs in the local Universe, EELGs are most often found in relative isolation. While only very few EELGs belong to compact groups, almost one third of them are found in spectroscopically confirmed loose pairs or triplets. Conclusions. The zCOSMOS EELGs are galaxies caught in a transient and probably early period of their evolution, where they are efficiently building up a significant fraction of their present-day stellar mass in an ongoing, galaxy-wide starburst. Therefore, the EELGs constitute an ideal benchmark for comparison studies between low-and high-redshift low-mass star-forming galaxies.

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Section: Discovery Of Extremely Metal-poor Eelgssupporting

confidence: 66%

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

Amorín

Pérez-Montero

Contini

et al. 2015

A&A

102

113

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“…Sánchez interpret this observation as an episode of gas accretion onto the tadpole head. Localized metallicity drops associated with starforming regions have also been observed in other objects, including gamma ray burst host galaxies (Levesque et al 2011;Thöne et al 2014), BCDs (Izotov et al 2009;Werk et al 2010;Sánchez Almeida et al 2014) and dwarf irregular galaxies (Haurberg et al 2013). Variations of metallicity among HII regions located at the same galactrocentric distance are not unusual even in large nearby spirals (Bresolin et al 2012;Li et al 2013); some of these variations could come from localized accretion events.…”

Section: Metallicity Inhomogeneities and Inverted Gradientsmentioning

confidence: 70%

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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“…The models proposed by Tassis et al (2008) introduce a critical density threshold for the activation of star-formation, without requiring outflows to reduce the star formation efficiency and the metal content. Finally, the observed MZR can be explained assuming accretion of metal-poor gas along filaments from the cosmic web (cold-flows) (e.g., Dalcanton et al 2004;Ceverino et al 2015;Sánchez Almeida et al 2014b), for which also indirect evidences have been found in recent observations (Sánchez Almeida et al 2015).…”

Section: Introductionmentioning

confidence: 86%

Characterization of star-forming dwarf galaxies at 0.1 ≲z ≲ 0.9 in VUDS: probing the low-mass end of the mass-metallicity relation

Calabró

Amorín

Fontana

et al. 2017

A&A

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Context. The study of statistically significant samples of star-forming dwarf galaxies (SFDGs) at different cosmic epochs is essential for the detailed understanding of galaxy assembly and chemical evolution. However, the main properties of this large population of galaxies at intermediate redshift are still poorly known. Aims. We present the discovery and spectrophotometric characterization of a large sample of 164 faint (i AB ∼ 23-25 mag) SFDGs at redshift 0.13 ≤ z ≤ 0.88 selected by the presence of bright optical emission lines in the VIMOS Ultra Deep Survey (VUDS). We investigate their integrated physical properties and ionization conditions, which are used to discuss the low-mass end of the mass-metallicity relation (MZR) and other key scaling relations. Methods. We use optical VUDS spectra in the COSMOS, VVDS-02h, and ECDF-S fields, as well as deep multi-wavelength photometry that includes HST-ACS F814W imaging, to derive stellar masses, extinction-corrected star-formation rates (SFR), and gas-phase metallicities of SFDGs. For the latter, we use the direct method and a T e -consistent approach based on the comparison of a set of observed emission lines ratios with the predictions of detailed photoionization models. Results. The VUDS SFDGs are compact (median r e ∼ 1.2 kpc), low-mass (M * ∼ 10 7 -10 9 M ) galaxies with a wide range of starformation rates (SFR(Hα) ∼ 10 −3 -10 1 M /yr) and morphologies. Overall, they show a broad range of subsolar metallicities (12 + log(O/H) = 7.26-8.7; 0.04 < ∼ Z/Z < ∼ 1). Nearly half of the sample are extreme emission-line galaxies (EELGs) characterized by high equivalent widths and emission line ratios indicative of higher excitation and ionization conditions. The MZR of SFDGs shows a flatter slope compared to previous studies of galaxies in the same mass range and redshift. We find the scatter of the MZR is partly explained in the low mass range by varying specific SFRs and gas fractions amongst the galaxies in our sample. In agreement with recent studies, we find the subclass of EELGs to be systematically offset to lower metallicity compared to SFDGs at a given stellar mass and SFR, suggesting a younger starburst phase. Compared with simple chemical evolution models we find that most SFDGs do not follow the predictions of a "closed-box" model, but those from a gas-regulating model in which gas flows are considered. While strong stellar feedback may produce large-scale outflows favoring the cessation of vigorous star formation and promoting the removal of metals, younger and more metal-poor dwarfs may have recently accreted large amounts of fresh, very metal-poor gas, that is used to fuel current star formation.

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Metallicity Inhomogeneities in Local Star-Forming Galaxies as a Sign of Recent Metal-Poor Gas Accretion

Cited by 77 publications

References 91 publications

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

Star formation sustained by gas accretion

Characterization of star-forming dwarf galaxies at 0.1 ≲z ≲ 0.9 in VUDS: probing the low-mass end of the mass-metallicity relation

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