scholarly journals Probing cosmic dawn with emission lines: predicting infrared and nebular line emission for ALMA and JWST

2019 ◽  
Vol 487 (4) ◽  
pp. 5902-5921 ◽  
Author(s):  
Harley Katz ◽  
Thomas P Galligan ◽  
Taysun Kimm ◽  
Joakim Rosdahl ◽  
Martin G Haehnelt ◽  
...  
Keyword(s):  
High Redshift ◽  
Formation Rate ◽  
Line Emission ◽  
Emission Lines ◽  
Strong Line ◽  
Radiation Hydrodynamics ◽  
High Redshift Galaxies ◽  
Physical Conditions ◽  
Velocity Gradients ◽  
Ionization Parameter

ABSTRACT Infrared and nebular lines provide some of our best probes of the physics regulating the properties of the interstellar medium (ISM) at high redshift. However, interpreting the physical conditions of high-redshift galaxies directly from emission lines remains complicated due to inhomogeneities in temperature, density, metallicity, ionization parameter, and spectral hardness. We present a new suite of cosmological, radiation-hydrodynamics simulations, each centred on a massive Lyman-break galaxy that resolves such properties in an inhomogeneous ISM. Many of the simulated systems exhibit transient but well-defined gaseous discs that appear as velocity gradients in [C ii] 157.6 $\mu$m emission. Spatial and spectral offsets between [C ii] 157.6 $\mu$m and [O iii] 88.33 $\mu$m are common, but not ubiquitous, as each line probes a different phase of the ISM. These systems fall on the local [C ii]–SFR relation, consistent with newer observations that question previously observed [C ii] 157.6 $\mu$m deficits. Our galaxies are consistent with the nebular line properties of observed z ∼ 2–3 galaxies and reproduce offsets on the BPT and mass-excitation diagrams compared to local galaxies due to higher star formation rate (SFR), excitation, and specific-SFR, as well as harder spectra from young, metal-poor binaries. We predict that local calibrations between H α and [O ii] 3727$\, \mathring{\rm A}$ luminosity and galaxy SFR apply up to z > 10, as do the local relations between certain strong line diagnostics (R23 and [O iii] 5007$\, \mathring{\rm A}$/H β) and galaxy metallicity. Our new simulations are well suited to interpret the observations of line emission from current (ALMA and HST) and upcoming facilities (JWST and ngVLA).

scholarly journals The MOSDEF survey: direct-method metallicities and ISM conditions at z ∼ 1.5–3.5

2019 ◽  
Vol 491 (1) ◽  
pp. 1427-1455 ◽  
Author(s):  
Ryan L Sanders ◽  
Alice E Shapley ◽  
Naveen A Reddy ◽  
Mariska Kriek ◽  
Brian Siana ◽  
...  
Keyword(s):  
Star Formation Rate ◽  
Direct Method ◽  
High Redshift ◽  
Formation Rate ◽  
Strong Line ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Rapid Formation ◽  
Binary Evolution ◽  
Ionization Parameter

ABSTRACT We present detections of [O iii] λ4363 and direct-method metallicities for star-forming galaxies at z = 1.7–3.6. We combine new measurements from the MOSFIRE Deep Evolution Field (MOSDEF) survey with literature sources to construct a sample of 18 galaxies with direct-method metallicities at z > 1, spanning 7.5 < 12+log(O/H) < 8.2 and log(M*/M⊙) = 7–10. We find that strong-line calibrations based on local analogues of high-redshift galaxies reliably reproduce the metallicity of the z > 1 sample on average. We construct the first mass–metallicity relation at z > 1 based purely on direct-method O/H, finding a slope that is consistent with strong-line results. Direct-method O/H evolves by ≲0.1 dex at fixed M* and star formation rate from z ∼ 0 to 2.2. We employ photoionization models to constrain the ionization parameter and ionizing spectrum in the high-redshift sample. Stellar models with supersolar O/Fe and binary evolution of massive stars are required to reproduce the observed strong-line ratios. We find that the z > 1 sample falls on the z ∼ 0 relation between ionization parameter and O/H, suggesting no evolution of this relation from z ∼ 0 to z ∼ 2. These results suggest that the offset of the strong-line ratios of this sample from local excitation sequences is driven primarily by a harder ionizing spectrum at fixed nebular metallicity compared to what is typical at z ∼ 0, naturally explained by supersolar O/Fe at high redshift caused by rapid formation time-scales. Given the extreme nature of our z > 1 sample, the implications for representative z ∼ 2 galaxy samples at ∼1010 M⊙ are unclear, but similarities to z > 6 galaxies suggest that these conclusions can be extended to galaxies in the epoch of reionization.

scholarly journals The mass–metallicity and the fundamental metallicity relation revisited on a fully Te-based abundance scale for galaxies

2019 ◽  
Vol 491 (1) ◽  
pp. 944-964 ◽  
Author(s):  
Mirko Curti ◽  
Filippo Mannucci ◽  
Giovanni Cresci ◽  
Roberto Maiolino
Keyword(s):  
High Redshift ◽  
Formation Rate ◽  
Cosmic Time ◽  
Stellar Mass ◽  
Strong Line ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Theoretical Predictions ◽  
Galaxy Population ◽  
Good Agreement

ABSTRACT The relationships between stellar mass, gas-phase metallicity and star-formation rate (i.e. the mass–metallicity, MZR, and the fundamental metallicity relation, FMR) in the local Universe are revisited by fully anchoring the metallicity determination for SDSS galaxies on the Te abundance scale defined exploiting the strong-line metallicity calibrations presented by Curti et al. Self-consistent metallicity measurements allow a more unbiased assessment of the scaling relations involving M, Z and SFR, which provide powerful constraints for the chemical evolution models. We parametrize the MZR with a new functional form that allows us to better characterize the turnover mass. The slope and saturation metallicity are in good agreement with previous determinations of the MZR based on the Te method, while showing significantly lower normalization compared to those based on photoionization models. The Z–SFR dependence at fixed stellar mass is also investigated, being particularly evident for highly star-forming galaxies, where the scatter in metallicity is reduced up to a factor of ${\sim}30{{\ \rm per\ cent}}$. A new parametrization of the FMR is given by explicitly introducing the SFR dependence of the turnover mass into the MZR. The residual scatter in metallicity for the global galaxy population around the new FMR is 0.054 dex. The new FMR presented in this work represents a useful local benchmark to compare theoretical predictions and observational studies (of both local and high-redshift galaxies) whose metallicity measurements are tied to the abundance scale defined by the Te method, hence allowing proper assessment of its evolution with cosmic time.

scholarly journals Predicting FIR lines from simulated galaxies

2020 ◽  
Vol 496 (4) ◽  
pp. 5160-5175 ◽  
Author(s):  
Alessandro Lupi ◽  
Andrea Pallottini ◽  
Andrea Ferrara ◽  
Stefano Bovino ◽  
Stefano Carniani ◽  
...  
Keyword(s):  
State Of The Art ◽  
High Redshift ◽  
Line Emission ◽  
Far Infrared ◽  
Emission Lines ◽  
Cosmological Simulations ◽  
High Redshift Galaxies ◽  
Emission Models ◽  
Excellent Tool ◽  
Non Equilibrium

ABSTRACT Far-infrared (FIR) emission lines are a powerful tool to investigate the properties of the interstellar medium, especially in high-redshift galaxies, where ALMA observations have provided unprecedented information. Interpreting such data with state-of-the-art cosmological simulations post-processed with cloudy, has provided insights on the internal structure and gas dynamics of these systems. However, no detailed investigation of the consistency and uncertainties of this kind of analysis has been performed to date. Here, we compare different approaches to estimate FIR line emission from state-of-the-art cosmological simulations, either with cloudy or with on-the-fly non-equilibrium chemistry. We find that [C ii]158μ predictions are robust to the model variations we explored. [O i] emission lines, that typically trace colder and denser gas relative to [C ii]158μ, are instead model dependent, as these lines are strongly affected by the thermodynamic state of the gas and non-equilibrium photoionization effects. For the same reasons, [O i] lines represent an excellent tool to constrain emission models, hence future observations targeting these lines will be crucial.

scholarly journals An analytic model for [O iii] fine structure emission from high redshift galaxies

2020 ◽  
Vol 499 (3) ◽  
pp. 3417-3433 ◽  
Author(s):  
Shengqi Yang ◽  
Adam Lidz
Keyword(s):  
Fine Structure ◽  
High Redshift ◽  
Formation Rate ◽  
Line Emission ◽  
Relative Volume ◽  
H Ii Regions ◽  
Analytic Model ◽  
Free Electrons ◽  
High Redshift Galaxies ◽  
Better Than

ABSTRACT Recent ALMA measurements have revealed bright [O iii] 88 micron line emission from galaxies during the Epoch of Reionization (EoR) at redshifts as large as z ∼ 9. We introduce an analytic model to help interpret these and other upcoming [O iii] 88 micron measurements. Our approach sums over the emission from discrete Str$\ddot{\mathrm{o}}$mgren spheres and considers the total volume of ionized hydrogen in a galaxy of a given star-formation rate. We estimate the relative volume of doubly ionized oxygen and ionized hydrogen and its dependence on the spectrum of ionizing photons. We then calculate the level populations of O iii ions in different fine-structure states for H ii regions of specified parameters. In this simple model, a galaxy’s [O iii] 88 μm luminosity is determined by the typical number density of free electrons in H ii regions (ne), the average metallicity of these regions (Z), the rate of hydrogen ionizing photons emitted (QH i), and the shape of the ionizing spectrum. We cross-check our model by comparing it with detailed cloudy calculations, and find that it works to better than 15${{\ \rm per\ cent}}$ accuracy across a broad range of parameter space. Applying our model to existing ALMA data at z ∼ 6–9, we derive lower bounds on the gas metallicity and upper bounds on the gas density in the H ii regions of these galaxies. These limits vary considerably from galaxy to galaxy, with the tightest bounds indicating Z ≳ 0.5Z⊙ and nH ≲ 50 cm−3 at 2 − σ confidence.

scholarly journals UV emission line studies of NGC-low redshift Seyfert Galaxies, LINERS and HII regions

2017 ◽  
Vol 16 (1) ◽  
pp. 25-43
Author(s):  
Vedavathi P ◽  
Vijayakumar H Doddamani
Keyword(s):  
Emission Line ◽  
Spectral Data ◽  
High Redshift ◽  
Line Emission ◽  
Seyfert Galaxies ◽  
Uv Spectra ◽  
Active Galaxies ◽  
Emission Lines ◽  
Strong Line ◽  
Continuum Source

Active galaxies as a special class of galaxies are characterized by very strong and broad emission lines. The strong emission lines such as Lyα, NV, Si IV, C IV, and Mg II observed in the UV spectra of Seyfert galaxies and quasars can be used to probe the physical conditions of the gas in the BLR regions surrounding the central accretion discs of these most luminous and exotic objects. In the standard model of broad line emission regions for active galaxies it is assumed that the broad permitted lines are emitted by the photo-ionization of a large number of spherically distributed optically thick clouds which are in Keplerian motion surrounding a central continuum source. However, issues related to variability time-scales, delays in the light curves and BLR sizes etc., remain unexplained consistent with observations.  In this paper, a study of emission line properties 9 objects satisfying good SNR (> 5.0) out of 98 NGC (catalogued) IUE observed low redshift active galaxies (z ≤ 0.017) is presented. The International Ultraviolet Explorer (IUE) satellite launched in 1978 by NASA has made low redshift UV spectroscopic observations of many different kinds of UV sources including active galaxies till 1996 and the flux calibrated spectral data of almost all observations have been hosted in NED-IUE database. In the present studies, IUE spectral data of a complete sample of NGC-catalogued active galaxies has been undertaken to understand the emission line properties of low luminosity and low z active galaxies. We find that the emission lines such as Lyα, N V, Si IV, O III], C III], C IV, and Mg II are observed as strong and broad lines in the spectra of only 9 objects owing to the criterion of S/N ≥ 5.0 adopted for the spectral analysis. The Lyα has not been found to be a strong line unlike in high z Seyfert galaxies and quasars observed by IUE satellite. C IV and Mg II lines are observed to be stronger lines in all the nine objects consistent with their usual presence in the remaining (~ 400) active galaxies observed by the IUE satellite. These observations are indicative of different physical and geometrical conditions in the BLR regions surrounding the central accretion disk compared to the intermediate and high redshift Seyfert galaxies and quasars.

scholarly journals The [CII] 158 μm line emission in high-redshift galaxies

2018 ◽  
Vol 609 ◽  
pp. A130 ◽  
Author(s):  
G. Lagache ◽  
M. Cousin ◽  
M. Chatzikos
Keyword(s):  
Galaxy Evolution ◽  
High Redshift ◽  
Formation Rate ◽  
Line Emission ◽  
Interstellar Gas ◽  
Structure Transition ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Crucial Component ◽  
Redshift Galaxies

Gas is a crucial component of galaxies, providing the fuel to form stars, and it is impossible to understand the evolution of galaxies without knowing their gas properties. The [CII] fine structure transition at 158 μm is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through metre wavelengths, almost unaffected by attenuation. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a star formation rate (SFR) indicator at z ≥ 4. In this paper, we have used a semi-analytical model of galaxy evolution (G.A.S.) combined with the photoionisation code CLOUDY to predict the [CII] luminosity of a large number of galaxies (25 000 at z ≃ 5) at 4 ≤ z ≤ 8. We assumed that the [CII]-line emission originates from photo-dominated regions. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We studied the L[CII ]–SFR and L[ CII ]–Zg relations and show that they do not strongly evolve with redshift from z = 4 and to z = 8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher SFRs but the correlations are very broad, with a scatter of about 0.5 and 0.8 dex for L[ CII ]–SFR and L[ CII ]–Zg, respectively. Our model reproduces the L[ CII ]–SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local L[ CII ]–SFR relations. Accordingly, the local observed L[ CII ]–SFR relation does not apply at high-z (z ≳ 5), even when CMB effects are ignored. Our model naturally produces the [CII] deficit (i.e. the decrease of L[ CII ]/LIR with LIR), which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of L[ CII] probed by the model (1 × 107–2 × 109 L⊙ at z = 6) with a slope α = −1. The slope is not evolving from z = 4 to z = 8 but the number density of [CII]-emitters decreases by a factor of 20×. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions.

scholarly journals A physical model for [C ii] line emission from galaxies

2019 ◽  
Vol 489 (1) ◽  
pp. 1-12 ◽  
Author(s):  
A Ferrara ◽  
L Vallini ◽  
A Pallottini ◽  
S Gallerani ◽  
S Carniani ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Brightness ◽  
Star Formation Rate ◽  
High Redshift ◽  
Formation Rate ◽  
Line Emission ◽  
Emission Lines ◽  
Additional Information ◽  
Low Metallicity ◽  
Local Relation

ABSTRACT A tight relation between the [C ii] 158 $\mu$m line luminosity and star formation rate is measured in local galaxies. At high redshift (z > 5), though, a much larger scatter is observed, with a considerable (15–20 per cent) fraction of the outliers being [C ii]-deficient. Moreover, the [C ii] surface brightness ($\Sigma_{\rm [C\, \small {II}]}$) of these sources is systematically lower than expected from the local relation. To clarify the origin of such [C ii]-deficiency, we have developed an analytical model that fits local [C ii] data and has been validated against radiative transfer simulations performed with cloudy. The model predicts an overall increase of $\Sigma_{\rm [C\, \small {II}]}$ with ΣSFR. However, for ΣSFR ${\gtrsim} 1 \, \mathrm{M}_\odot \,{\rm yr}^{-1}\,{\rm kpc}^{-2}$, $\Sigma_{\rm [C\, \small {II}]}$ saturates. We conclude that underluminous [C ii] systems can result from a combination of three factors: (a) large upward deviations from the Kennicutt–Schmidt relation (κs ≫ 1), parametrized by the ‘burstiness’ parameter κs; (b) low metallicity; (c) low gas density, at least for the most extreme sources (e.g. CR7). Observations of [C ii] emission alone cannot break the degeneracy among the above three parameters; this requires additional information coming from other emission lines (e.g. [O iii]88 $\mu$m, C iii]1909 Å, CO lines). Simple formulae are given to interpret available data for low- and high-z galaxies.

scholarly journals New methods for identifying Lyman continuum leakers and reionization-epoch analogues

2020 ◽  
Vol 498 (1) ◽  
pp. 164-180 ◽  
Author(s):  
Harley Katz ◽  
Dominika Ďurovčíková ◽  
Taysun Kimm ◽  
Joki Rosdahl ◽  
Jeremy Blaizot ◽  
...  
Keyword(s):  
Emission Line ◽  
Galaxy Formation ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Indirect Methods ◽  
High Redshift Galaxies ◽  
Lyman Continuum ◽  
The Universe ◽  
Ionization Parameter ◽  
Redshift Galaxies

ABSTRACT Identifying low-redshift galaxies that emit Lyman continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly ‘analogues’ of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at z ∼ 3 and z ∼ 0. We find that the simulated galaxies with high LyC escape fractions (fesc) often exhibit high O32 and populate the same regions of the R23–O32 plane as z ∼ 3 LyC leakers. However, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the O32–fesc plane. Based on emission line diagnostics and how they correlate with fesc, lower metallicity LyC leakers at z ∼ 3 appear to be good analogues of reionization-era galaxies. In contrast, local [S ii]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the S ii Baldwin–Phillips–Terlevich (BPT) diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using infrared and nebular emission lines. We show that our model using only [C ii]158 μm and [O iii]88 μm can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS 1149_JD1 at z = 9.1 is the most likely galaxy to be actively contributing to the reionization of the Universe.

scholarly journals Constraints on the production and escape of ionizing radiation from the emission-lines of metal-poor star-forming galaxies

2019 ◽  
Vol 15 (S352) ◽  
pp. 121-122
Author(s):  
A. Plat ◽  
S. Charlot ◽  
G. Bruzual ◽  
A. Feltre ◽  
A. Vidal-Garca ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Emission Line ◽  
Active Galactic Nuclei ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Emission Lines ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Radiative Shocks ◽  
Metal Poor Star

AbstractTo understand how the nature of the ionizing sources and the leakage of ionizing photons in high-redshift galaxies can be constrained from their emission-line spectra, we compare emission-line models of star-forming galaxies including leakage of ionizing radiation, active galactic nuclei (AGN) and radiative shocks, with observations of galaxies at various redshifts with properties expected to approach those of primeval galaxies.

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