FIRST SPECTROSCOPIC EVIDENCE FOR HIGH IONIZATION STATE AND LOW OXYGEN ABUNDANCE IN Lyα EMITTERS,

Nakajima, Kengo; Ouchi, Masami; Shimasaku, Kazuhiro; Hashimoto, T.; Ono, Yoshiyasu; Lee, Janice

doi:10.1088/0004-637x/769/1/3

Cited by 132 publications

(196 citation statements)

References 133 publications

(224 reference statements)

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“…Their EW(Hα)/EW(Lyα) ratios (∼14) are instead comparable with some high-excitation LAEs at higher redshift (e.g., z ∼ 2 Finkelstein et al 2011;Nakajima et al 2013). Compared with model predictions (e.g., Schaerer 2003), these EW(Hα)/EW(Lyα) ratios are in good agreement with tracks for instantaneous burst models with young ages (∼10 7 yr) and low metallicities (see Nakajima et al 2013, their Fig. 10), probably superposed with a more constant (e.g., exponentially declining) underlying star formation history (e.g., Amorín et al 2012a).…”

Section: Lyman-alpha Emission In Eelgsmentioning

confidence: 72%

“…Comparing their Lyα and Hα equivalent widths (EW(Hα) = 320−580 Å), these galaxies are among those with larger EW(Hα) low-z LAEs in the catalog of Cowie et al (2010). Their EW(Hα)/EW(Lyα) ratios (∼14) are instead comparable with some high-excitation LAEs at higher redshift (e.g., z ∼ 2 Finkelstein et al 2011;Nakajima et al 2013). Compared with model predictions (e.g., Schaerer 2003), these EW(Hα)/EW(Lyα) ratios are in good agreement with tracks for instantaneous burst models with young ages (∼10 7 yr) and low metallicities (see Nakajima et al 2013, their Fig.…”

Section: Lyman-alpha Emission In Eelgsmentioning

confidence: 93%

“…Cowie et al (2011) have shown that ∼75% of low-z LAEs have EW(Hα) > 100 Å, while only ∼30% of UV-continuum selected galaxies with EW(Hα) > 100 Å are LAEs. Moreover, recent studies have found evidence for high-ionization state and low metallicities in LAEs out to z > ∼ 2 (Xia et al 2012;Nakajima et al 2013, see also Cassata et al 2013, for HeII λ1640 detection in LAEs). These two properties are an imprint of green peas (Amorín et al 2012a;Jaskot & Oey 2013) and EELGs in general (see Fig.…”

Section: Lyman-alpha Emission In Eelgsmentioning

confidence: 93%

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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: Lyman-alpha Emission In Eelgsmentioning

confidence: 72%

Section: Lyman-alpha Emission In Eelgsmentioning

confidence: 93%

Section: Lyman-alpha Emission In Eelgsmentioning

confidence: 93%

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Extreme emission-line galaxies out toz~ 1 in zCOSMOS

Amorín

Pérez-Montero

Contini

et al. 2015

A&A

102

113

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“…This makes physical conditions in the star forming regions in Mrk 22 similar to those in the extreme star forming galaxies. Nakajima et al (2013) and Nakajima (2013) indicated that these extreme conditions can be produced in several ways such as density bounded HII regions, very high ionization parameters due to presence of hard ionizing sources, and low metallicity. The presence of WR stars in Mrk 22 and in some GP galaxies indicates high ionization parameter in these galaxies.…”

Section: Comparison With Extreme Star-forming Galaxies At Higher Redhmentioning

confidence: 99%

Tidal interaction, star formation and chemical evolution in blue compact dwarf galaxy Mrk 22

Paswan¹,

Omar²,

Jaiswal³

2017

Monthly Notices of the Royal Astronomical Society

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The optical spectroscopic and radio interferometric HI 21 cm-line observations of the blue compact dwarf galaxy Mrk 22 are presented. The Wolf-Rayet (WR) emission line features corresponding to high ionization lines of HeII λ4686 and CIV λ5808 from young massive stars are detected. The ages of two prominent star forming regions in the galaxy are estimated as ∼10 Myr and ∼ 4 Myr. The galaxy has non-thermal radio deficiency, which also indicates a young star-burst and lack of supernovae events from the current star formation activities, consistent with the detection of WR emission lines features. A significant N/O enrichment is seen in the fainter star forming region. The gas-phase metallicities [12 + log(O/H)] for the bright and faint regions are estimated as 7.98±0.07 and 7.46±0.09 respectively. The galaxy has a large diffuse HI envelop. The HI images reveal disturbed gas kinematics and HI clouds outside the optical extent of the galaxy, indicating recent tidal interaction or merger in the system. The results strongly indicate that Mrk 22 is undergoing a chemical and morphological evolution due to ongoing star formation, most likely triggered by a merger.

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“…Large enough statistics is needed to confirm this idea. The galaxies with very low metallicity share many properties of Lyα emitting galaxies and Ly-break galaxies (Prochaska et al 2003;Nakajima et al 2013;Shirazi et al 2014;Shapley et al 2015). Thanks to the fact that XMDs can be excellent local proxies for their high-z counterparts.…”

Section: Introductionmentioning

confidence: 99%

New candidates for extremely metal-poor emission-line galaxies in the SDSS/BOSS DR10

Гусева

Izotov

Fricke

et al. 2015

A&A

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We present a spectroscopic study of eight extremely low-metallicity candidate emission-line galaxies with oxygen abundances possibly below 12 + log O/H = 7.35. These galaxies were selected from data release 10 of the Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey (SDSS/BOSS DR10). We will call these extremely metal-deficient (XMD) galaxies. The electron temperaturesensitive emission line [O iii] λ4363 is detected in three galaxies and marginally detected in two galaxies, allowing for abundance determination by a "direct" method. Because of large uncertainties in the [O iii]λ4363 Å line fluxes, we also calculated oxygen abundance in these galaxies together with the remaining three galaxies using a strong-line semi-empirical method. This method gives oxygen abundances higher than 7.35 for three galaxies with detected [O iii]λ4363 Å line and lower than 7.35 for the remaining five objects of the sample. The newly-discovered galaxies represent excellent targets for follow-up spectroscopic observations with the largest telescopes to improve the oxygen abundance determination and to increase the number of these very rare low-metallicity objects. The extreme location of the most massive and luminous XMD galaxies and XMD candidates in the stellar mass-metallicity diagram implies that these galaxies may be genuine young objects. With stellar masses of up to ∼10 7 -10 8 M , the galaxies are not chemically enriched and strongly deviate to lower metallicity as compared to the relation obtained for a large sample of low-redshift, star-forming galaxies.

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FIRST SPECTROSCOPIC EVIDENCE FOR HIGH IONIZATION STATE AND LOW OXYGEN ABUNDANCE IN Lyα EMITTERS,

Cited by 132 publications

References 133 publications

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

Tidal interaction, star formation and chemical evolution in blue compact dwarf galaxy Mrk 22

New candidates for extremely metal-poor emission-line galaxies in the SDSS/BOSS DR10

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