Stars Were Born in Significantly Denser Regions in the Early Universe

Shirazi, Maryam; Brinchmann, Jarle; Rahmati, Alireza

doi:10.1088/0004-637x/787/2/120

Cited by 85 publications

(120 citation statements)

References 71 publications

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“…We further explored how different physical conditions in the H II regions can affect the emission line strenght and thus the IRAC colors, using CLOUDY. In particular, since it has been suggested that high-redshift starforming regions might be characterized by more extreme conditions (e.g., Nakajima & Ouchi 2014;Shirazi et al 2014;Nakajima et al 2016), we assume a harder ionization field q log cm s 9.0 1 = -( ) and a higher density n=1000 cm . The results relevant to the present case are shown in the left panel of Figure 7, a thorough investigation of the ISM conditions will be presented in a forthcoming paper (S. De Barros et al 2017, in preparation).…”

Section: Implications On the Escape Fractionmentioning

confidence: 99%

Optical Line Emission from z ∼ 6.8 Sources with Deep Constraints on Lyα Visibility

Castellano

Pentericci

Fontana

et al. 2017

ApJ

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IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document VersionPublisher's PDF, also known as Version of record Publication date: 2017Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Castellano, M., Pentericci, L., Fontana, A., Vanzella, E., Merlin, E., De Barros, S., ... Yan, H. (2017). Optical Line Emission from z similar to 6.8 Sources with Deep Constraints on Ly alpha Visibility. The Astrophysical Journal, 839(2), [73]. https://doi.org/10.3847/1538-4357/aa696e Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. AbstractWe analyze a sample of z-dropout galaxies in the CANDELS GOODS South and UDS fields that have been targeted by a dedicated spectroscopic campaign aimed at detecting their Lyα line. Deep IRAC observations at 3.6 and 4.5 μm are used to determine the strength of optical emission lines affecting these bands at z∼6.5-6.9 in order to (1) investigate possible physical differences between Lyα emitting and non-emitting sources; (2) constrain the escape fraction of ionizing photons; and (3) Å,suggesting different physical conditions of the H II regions with respect to Lyα-emitting ones, or a larger f esc . The latter case is consistent with a combined evolution of f esc and theneutral hydrogen fraction as anexplanation of the lack of bright Lyα emission at z>6. A lower limit on the specific star formation rate, SSFR>9.1 Gyr −1 for M M 2 10 star 9=´ galaxies at these redshifts can be derived from the spectroscopically confirmed sample.

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Section: Implications On the Escape Fractionmentioning

confidence: 99%

Optical Line Emission from z ∼ 6.8 Sources with Deep Constraints on Lyα Visibility

Castellano

Pentericci

Fontana

et al. 2017

ApJ

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“…Brinchmann et al (2008) and Shirazi et al (2014) suggest that higher electron densities and a larger escape fraction of H-ionizing photons may be responsible for the larger ionization parameter. On the other hand, Steidel et al (2014) suggest that a high effective temperature in the massive stellar population, possibly from stellar rotation and/or binaries may be responsible for the large ionization parameters.…”

Section: The Ionization State Of the Gasmentioning

confidence: 99%

“…These elevated line ratios may indicate a major change in the ionized gas or star formation properties as a function of time. Many possible causes for this offset have been proposed, including a larger ionization parameter (e.g., Brinchmann et al 2008;Kewley et al 2013b;Shirazi et al 2014), a harder ionizing radiation field (Stanway et al 2014;Steidel et al 2014), a higher ISM pressure (density; Shirazi et al 2014), a contribution from an active galactic nucleus (AGN; Groves et al 2006;Wright et al 2010;Trump et al 2011), and contamination by shocks from galactic outflows (Förster Schreiber et al 2014;Newman et al 2014). Sample selection is likely to play a large role in the relative importance of each of these factors (Juneau et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Z-FIRE: ISM PROPERTIES OF THEz= 2.095 COSMOS CLUSTER

Kewley

Yuan

Nanayakkara

et al. 2016

ApJ

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We investigate the ISM properties of 13 star-forming galaxies within thez 2 COSMOS cluster. We show that the cluster members have [N II]/Hα and [O III]/Hβ emission-line ratios similar toz 2 field galaxies, yet systematically different emission-line ratios (by ∼0.17 dex) from the majority of local star-forming galaxies. We find no statistically significant difference in the [N II]/Hα and [O III]/Hβ line ratios or ISM pressures among thẽ z 2 cluster galaxies and field galaxies at the same redshift. We show that our cluster galaxies have significantly larger ionization parameters (by up to an order of magnitude) than local star-forming galaxies. We hypothesize that these high ionization parameters may be associated with large specific star formation rates (SFRs; i.e., a large SFR per unit stellar mass). If this hypothesis is correct, then this relationship would have important implications for the geometry and/or the mass of stars contained within individual star clusters as a function of redshift.

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“…Possible culprits include increased electron densities (Shirazi et al 2014), harder ionizing radiation fields (Kewley et al 2013;Steidel et al 2014), a larger ionization parameter (Brinchmann et al 2008;Kewley et al 2015a), increased AGN contributions (Trump et al 2011;Förster Schreiber et al 2014), shocks (Kewley et al 2013), or a combination thereof.…”

Section: Introductionmentioning

confidence: 99%

THE RELATION BETWEEN [ O III ] / H β AND SPECIFIC STAR FORMATION RATE IN GALAXIES AT z ∼ 2

Dickey

Dokkum

Oesch

et al. 2016

ApJL

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Recent surveys have identified a seemingly ubiquitous population of galaxies with elevated [O III]/Hβ emission line ratios at z > 1, although the nature of this phenomenon continues to be debated. The [O III]/Hβ line ratio is of interest because it is a main component of the standard diagnostic tools used to differentiate between active galactic nuclei and star-forming galaxies as well as the gas-phase metallicity indicators O 23 and R 23 . Here, we investigate the primary driver of increased [O III]/Hβ ratios by median-stacking rest-frame optical spectra for a sample of starforming galaxies in the 3D-HST survey in the redshift range z ∼ 1.4-2.2. Using N = 4220 star-forming galaxies, we stack the data in bins of mass and specific star formation rates (sSFRs), respectively. After accounting for stellar Balmer absorption, we measure [O III]λ5007 Å/Hβ down to M ∼ 10 9.2 M e and sSFR ∼ 10 −9.6 yr −1 , greater than an order of magnitude lower than previous work at similar redshifts. We find an offset of 0.59 ± 0.05 dex between the median ratios at z ∼ 2 and z ∼ 0 at fixed stellar mass, in agreement with existing studies. However, with respect to sSFR, the z ∼ 2 stacks all lie within 1σ of the median SDSS ratios, with an average offset of only −0.06 ± 0.05. We find that the excitation properties of galaxies are tightly correlated with their sSFR at both z ∼ 2 and z ∼ 0, with a relation that appears to be roughly constant over the last 10 Gyr of cosmic time.

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Stars Were Born in Significantly Denser Regions in the Early Universe

Cited by 85 publications

References 71 publications

Optical Line Emission from z ∼ 6.8 Sources with Deep Constraints on Lyα Visibility

Optical Line Emission from z ∼ 6.8 Sources with Deep Constraints on Lyα Visibility

Z-FIRE: ISM PROPERTIES OF THEz= 2.095 COSMOS CLUSTER

THE RELATION BETWEEN [ O III ] / H β AND SPECIFIC STAR FORMATION RATE IN GALAXIES AT z ∼ 2

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