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The metal content of galaxies is a direct probe of the baryon cycle. A hallmark example is the relationship between a galaxy's stellar mass, star formation rate (SFR), and gas-phase metallicity: the fundamental metallicity relation (FMR). While low-redshift (⁠|$z\lesssim 4$|⁠) observational studies suggest that the FMR is redshift-invariant, recent high- zJWST data indicate deviations from the FMR established at low- z. In this study, we utilize the FMR to predict the evolution of the normalization of the mass–metallicity relation (MZR) using the cosmological simulations Illustris, IllustrisTNG, EAGLE, and SIMBA. Our findings demonstrate that a |$z = 0$| calibrated FMR struggles to predict the evolution in the MZR of each simulation. To quantify the divergence of the predictions, we introduce the concepts of a 'static' FMR, where the role of the SFR in setting the normalization of the MZR does not change with redshift, and a 'dynamic' FMR, where the role of SFR evolves over time. We find static FMRs in SIMBA and dynamic FMRs in Illustris, IllustrisTNG, and EAGLE. We suggest that the differences between these models likely points to the subtle differences in the implementation of the baryon cycle. Moreover, we echo recent JWST results at |$z \gt 4$| by finding significant offsets from the FMR in IllustrisTNG and EAGLE, suggesting that the observed FMR may have a similar dynamic trend as these simulations. Overall, our findings imply that the current FMR framework neglects important time variations of these simulations' baryon cycles. [ABSTRACT FROM AUTHOR]

We present the spatially resolved relationship between the dust-to-gas mass ratio (DGR) and gas-phase metallicity (⁠|$Z_{\rm gas}$| or 12 + log(O/H)) (i.e. DGR– |$Z_{\rm gas}$| relation) of 11 nearby galaxies with a large-metallicity range (1.5 dex of 12 + log(O/H)) at (sub-)kpc scales. We used the large field-of-view (⁠|$\gtrsim$| 3 arcmin) optical pseudo-Integral Field Spectroscopy data taken by the TYPHOON/Progressive Integral Step Method survey, covering the optical size of galaxies, combining them with multiwavelength data [far-ultrviolet (UV) to far-infrared (IR), CO, and H  i 21 cm radio]. A large scatter of DGR in the intermediate-metallicity galaxies (8.0 |$\lt $| 12 + log(O/H) |$\lt $| 8.3) is found, which is in line with dust evolution models, where grain growth begins to dominate the mechanism of dust mass accumulation. In the lowest metallicity galaxy of our sample, Sextans A (12 + log(O/H) |$\lt $| 7.6), the star-forming regions have significantly higher DGR values (by 0.5–2 dex) than the global estimates from literature at the same metallicity, but aligns with the DGR values from metal depletion method from damped Lyman alpha systems and high hydrogen gas density regions of Sextans A. Using dust evolution models with a Bayesian Monte Carlo Markov Chain approach suggests: (1) a high supernova dust yield and (2) a negligible amount of photofragmentation by UV radiation, although we note that our sample in the low-metallicity regime is limited to Sextans A. On the other hand, it is also possible that while metallicity influences DGR, gas density also plays a role, indicating an early onset of dust grain growth in the dust mass build-up process despite its low metallicity. [ABSTRACT FROM AUTHOR]

Most star formation in the local Universe occurs in spiral galaxies, but their origin remains an unanswered question. Various theories have been proposed to explain the development of spiral arms, each predicting different spatial distributions of the interstellar medium. This study maps the star formation rate (SFR) and gas-phase metallicity of nine spiral galaxies with the TYPHOON survey to test two dominating theories: density wave theory and dynamic spiral theory. We discuss the environmental effects on our galaxies, considering reported environments and merging events. Taking advantage of the large field of view covering the entire optical disc, we quantify the fluctuation of SFR and metallicity relative to the azimuthal distance from the spiral arms. We find higher SFR and metallicity in the trailing edge of NGC 1365 (by 0.117 and 0.068 dex, respectively) and NGC 1566 (by 0.119 and 0.037 dex, respectively), which is in line with density wave theory. NGC 2442 shows a different result with higher metallicity (0.093 dex) in the leading edge, possibly attributed to an ongoing merging. The other six spiral galaxies show no statistically significant offset in SFR or metallicity, consistent with dynamic spiral theory. We also compare the behaviour of metallicity inside and outside the corotation radius (CR) of NGC 1365 and NGC 1566. We find comparable metallicity fluctuations near and beyond the CR of NGC 1365, indicating gravitational perturbation. NGC 1566 shows the greatest fluctuation near the CR, in line with the analytic spiral arms. Our work highlights that a combination of mechanisms explains the origin of spiral features in the local Universe. [ABSTRACT FROM AUTHOR]

The scatter about the mass-metallicity relation (MZR) has a correlation with the star formation rate (SFR) of galaxies. The lack of evidence of evolution in correlated scatter at z ≲ 2.5 leads many to refer to the relationship between mass, metallicity, and SFR as the Fundamental Metallicity Relation (FMR). Yet, recent high-redshift (z > 3) JWST observations have challenged the fundamental (i.e. redshift-invariant) nature of the FMR. In this work, we show that the cosmological simulations Illustris, IllustrisTNG, and Evolution and Assembly of GaLaxies and their Environment (EAGLE) all predict MZRs that exhibit scatter with a secondary dependence on SFR up to z  = 8. We introduce the concept of a 'strong' FMR, where the strength of correlated scatter does not evolve with time, and a 'weak' FMR, where there is some time evolution. We find that each simulation analysed has a statistically significant weak FMR – there is non-negligible evolution in the strength of the correlation with SFR. Furthermore, we show that the scatter is reduced an additional ∼10–40 per cent at z ≳ 3 when using a weak FMR, compared to assuming a strong FMR. These results highlight the importance of avoiding coarse redshift binning when assessing the FMR. [ABSTRACT FROM AUTHOR]

The metal content of galaxies provides a window into their formation in the full context of the cosmic baryon cycle. In this study, we examine the relationship between stellar mass and stellar metallicity (MZ*R) in the hydrodynamic simulations Illustris, TNG, and EAGLE (Evolution and Assembly of GaLaxies and their Environment) to understand the global properties of stellar metallicities within the feedback paradigm employed by these simulations. Interestingly, we observe significant variations in the overall normalization and redshift evolution of the MZ*R across the three simulations. However, all simulations consistently demonstrate a tertiary dependence on the specific star formation rate (sSFR) of galaxies. This finding parallels the relationship seen in both simulations and observations between stellar mass, gas-phase metallicity, and some proxy of galaxy gas content (e.g. SFR, gas fraction, and atomic gas mass). Since we find this correlation exists in all three simulations, each employing a subgrid treatment of the dense, star-forming interstellar medium (ISM) to simulate smooth stellar feedback, we interpret this result as a fairly general feature of simulations of this kind. Furthermore, with a toy analytic model, we propose that the tertiary correlation in the stellar component is sensitive to the extent of the 'burstiness' of feedback within galaxies. [ABSTRACT FROM AUTHOR]

Galactic fountains driven by star formation result in a variety of kinematic structures such as ionized winds and thick gas discs, both of which manifest as complex emission-line profiles that can be parametrized by multiple Gaussian components. We use integral field spectroscopy from the SAMI Galaxy Survey to spectrally resolve these features, traced by broad |${\rm H}\alpha$| components, and distinguish them from the star-forming (SF) thin disc, traced by narrow components, in 3068 galaxies in the local Universe. Using a matched sample analysis technique, we demonstrate that the presence of complex emission-line profiles in SF galaxies is most strongly correlated with the global star formation rate (SFR) surface density of the host galaxy measured within 1 R e (⁠|$\Sigma _{{\rm SFR},\, R_{\rm e}}$|⁠), even when controlling for both observational biases, including inclination, amplitude-to-noise and angular scale, and sample biases in parameters such as stellar mass and SFR. Leveraging the spatially resolved nature of the data set, we determine that the presence of complex emission-line profiles within individual spaxels is driven not only by the local ΣSFR, but by the |$\Sigma _{{\rm SFR},\, R_{\rm e}}$| of the host galaxy. We also parametrize the clumpiness of the SFR within individual galaxies, and find that |$\Sigma _{{\rm SFR},\, R_{\rm e}}$| is a stronger predictor of the presence of complex emission-line profiles than clumpiness. We conclude that, with a careful treatment of observational effects, it is possible to identify structures traced by complex emission-line profiles, including winds and thick ionized gas discs, at the spatial and spectral resolution of SAMI using the Gaussian decomposition technique. [ABSTRACT FROM AUTHOR]

Spiral structures are important drivers of the secular evolution of disc galaxies, however, the origin of spiral arms and their effects on the development of galaxies remain mysterious. In this work, we present two three-armed spiral galaxies at z ∼ 0.3 in the Middle Age Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey. Taking advantage of the high spatial resolution (∼0.6 arcsec) of the Multi-Unit Spectroscopic Explorer (MUSE), we investigate the two-dimensional (2D) distributions of different spectral parameters: Hα, gas-phase metallicity, and D4000. We notice significant offsets in Hα (∼0.2 dex) and gas-phase metallicities (∼0.05 dex) among the spiral arms, downstream and upstream of MAGPI 1202197197 (SG 1202). This observational signature suggests the spiral structure in SG 1202 is consistent with arising from density wave theory. No azimuthal variation in Hα or gas-phase metallicities is observed in MAGPI 1204198199 (SG 1204), which can be attributed to the tighter spiral arms in SG 1204 than SG 1202, coming with stronger mixing effects in the disc. The absence of azimuthal D4000 variation in both galaxies suggests the stars at different ages are well mixed between the spiral arms and distributed around the disc regions. The different azimuthal distributions in Hα and D4000 highlight the importance of time-scales traced by various spectral parameters when studying 2D distributions in spiral galaxies. This work demonstrates the feasibility of constraining spiral structures by tracing interstellar medium (ISM) and stellar population at z ∼ 0.3, with a plan to expand the study to the full MAGPI survey. [ABSTRACT FROM AUTHOR]

Bars play an important role in mixing material in the inner regions of galaxies and stimulating radial migration. Previous observations have found evidence for the impact of a bar on metallicity gradients but the effect is still inconclusive. We use the TYPHOON/PrISM survey to investigate the metallicity gradients along and beyond the bar region across the entire star-forming disc of five nearby galaxies. Using emission line diagrams to identify star-forming spaxels, we recover the global metallicity gradients ranging from −0.0162 to −0.073 dex kpc−1 with evidence that the galactic bars act as an agent in affecting in situ star formation as well as the motions of gas and stars. We observe cases with a 'shallow-steep' metallicity radial profile, with evidence of the bar flattening the metallicity gradients inside the bar region (NGC 5068 and NGC 1566) and also note instances where the bar appears to drive a steeper metallicity gradient producing 'steep-shallow' metallicity profiles (NGC 1365 and NGC 1744). For NGC 2835, a 'steep-shallow' metallicity gradient break occurs at a distance ∼4 times the bar radius, which is more likely driven by gas accretion to the outskirt of the galaxy instead of the bar. The variation of metallicity gradients around the bar region traces the fluctuations of star formation rate surface density in NGC 1365, NGC 1566, and NGC 1744. A larger sample combined with hydrodynamical simulations is required to further explore the diversity, and the relative importance of different ISM mixing mechanisms on the gas-phase metallicity gradients in local galaxies. [ABSTRACT FROM AUTHOR]

We present radial gas-phase metallicity profiles, gradients, and break radii at redshift z  = 0–3 from the TNG50-1 star-forming galaxy population. These metallicity profiles are characterized by an emphasis on identifying the steep inner gradient and flat outer gradient. From this, the break radius, R break, is defined as the region where the transition occurs. We observe the break radius having a positive trend with mass that weakens with redshift. When normalized by the stellar half-mass radius, the break radius has a weaker relation with both mass and redshift. To test if our results are dependent on the resolution or adopted physics of TNG50-1, the same analysis is performed in TNG50-2 and Illustris-1. We find general agreement between each of the simulations in their qualitative trends; however, the adopted physics between TNG and Illustris differ and therefore the breaks, normalized by galaxy size, deviate by a factor of ∼2. In order to understand where the break comes from, we define two relevant time-scales: an enrichment time-scale and a radial gas mixing time-scale. We find that R break occurs where the gas mixing time-scale is ∼10 times as long as the enrichment time-scale in all three simulation runs, with some weak mass and redshift dependence. This implies that galactic discs can be thought of in two-parts: a star-forming inner disc with a steep gradient and a mixing-dominated outer disc with a flat gradient, with the break radius marking the region of transition between them. [ABSTRACT FROM AUTHOR]

This paper presents deep K-band spectroscopic observations of galaxies at z = 3 − 4 with composite photometric rest-frame H  β +[O  iii ] 5007 equivalent widths (EW0) > 600 Å, comparable to the EW of galaxies observed during the epoch of reionization (EoR, z > 6). The typical spectroscopic [O  iii ] 5007 EW0 and stellar mass of our targets is ∼700 Å and log (M */M⊙) = 8.98. By stacking the [O  iii ] 5007 emission profiles, we find evidence of a weak broad component with |$\rm F_{broad}/F_{narrow} \sim 0.2$| and velocity width σbroad ∼ 170 km s−1. The strength and velocity width of the broad component does not change significantly with stellar mass and [O  iii ] 5007 EW0 of the stacked sample. Assuming similar broad component profiles for [O  iii ] 5007 and Hα emission, we estimate a mass loading factor ∼0.2, similar to low stellar mass galaxies at z > 1 even if the star formation rates of our sample is 10 times higher. We hypothesize that either the multiphase nature of supernovae driven outflows or the suppression of winds in the extreme star-forming regime is responsible for the weak signature of outflows in the EoR analogues. [ABSTRACT FROM AUTHOR]

Understanding the nucleosynthetic origin of nitrogen and the evolution of the N/O ratio in the interstellar medium is crucial for a comprehensive picture of galaxy chemical evolution at high-redshift because most observational metallicity (O/H) estimates are implicitly dependent on the N/O ratio. The observed N/O at high-redshift shows an overall constancy with O/H, albeit with a large scatter. We show that these heretofore unexplained features can be explained by the pre-supernova wind yields from rotating massive stars (M≳10M⊙,ν/νcrit≳0.4). Our models naturally produce the observed N/O plateau, as well as the scatter at low O/H. We find the scatter to arise from varying star formation efficiency. However, the models that have supernovae dominated yields produce a poor fit to the observed N/O at low O/H. This peculiar abundance pattern at low O/H suggests that dwarf galaxies are most likely to be devoid of SNe yields and are primarily enriched by pre-supernova wind abundances. [ABSTRACT FROM AUTHOR]

We investigate the mean locally measured velocity dispersions of ionized gas (σgas) and stars (σ*) for 1090 galaxies with stellar masses |$\log \, (M_{\!\ast }/M_{\odot }) \ge 9.5$| from the SAMI Galaxy Survey. For star-forming galaxies, σ* tends to be larger than σgas, suggesting that stars are in general dynamically hotter than the ionized gas (asymmetric drift). The difference between σgas and σ* (Δσ) correlates with various galaxy properties. We establish that the strongest correlation of Δσ is with beam smearing, which inflates σgas more than σ*, introducing a dependence of Δσ on both the effective radius relative to the point spread function and velocity gradients. The second strongest correlation is with the contribution of active galactic nuclei (AGN) (or evolved stars) to the ionized gas emission, implying that the gas velocity dispersion is strongly affected by the power source. In contrast, using the velocity dispersion measured from integrated spectra (σap) results in less correlation between the aperture-based Δσ (Δσap) and the power source. This suggests that the AGN (or old stars) dynamically heat the gas without causing significant deviations from dynamical equilibrium. Although the variation of Δσap is much smaller than that of Δσ, a correlation between Δσap and gas velocity gradient is still detected, implying that there is a small bias in dynamical masses derived from stellar and ionized gas velocity dispersions. [ABSTRACT FROM AUTHOR]

We present the radial gas-phase, mass-weighted metallicity profiles and gradients of the TNG50 star-forming galaxy population measured at redshifts z = 0–3. We investigate the redshift evolution of gradients and examine relations between gradient (negative) steepness and galaxy properties. We find that TNG50 gradients are predominantly negative at all redshifts, although we observe significant diversity among these negative gradients. We determine that the gradients of all galaxies grow more negative with redshift at a roughly constant rate of approximately |$-0.02\ \mathrm{dex\, kpc^{-1}}/\Delta z$|⁠. This rate does not vary significantly with galaxy mass. We observe a weak negative correlation between gradient (negative) steepness and galaxy stellar mass at z < 2. However, when we normalize gradients by a characteristic radius defined by the galactic star formation distribution, we find that these normalized gradients do not vary significantly with either stellar mass or redshift. We place our results in the context of previous simulations and show that TNG50 high-redshift gradients are more negative than those of models featuring burstier feedback, which may further highlight high-redshift gradients as important discriminators of galaxy formation models. We also find that z = 0 and z = 0.5 TNG50 gradients are consistent with the gradients observed in galaxies at these redshifts, although the preference for flat gradients observed in redshift z ≳ 1 galaxies is not present in TNG50. If future JWST (James Webb Space Telescope) and ELT (Extremely Large Telescope) observations validate these flat gradients, it may indicate a need for simulation models to implement more powerful radial gas mixing within the ISM (interstellar medium), possibly via turbulence and/or stronger winds. [ABSTRACT FROM AUTHOR]

In this paper, we analyse the statistics of the 2D gas-phase oxygen abundance distributions of 100 nearby galaxies drawn from the Calar Alto Legacy Integral Field spectroscopy Area survey. After removing the large-scale radial metallicity gradient, we compute the two-point correlation functions of the resulting metallicity fluctuation maps. We detect correlations in the majority of our targets, which we show are significantly in excess of what is expected due to beam-smearing, and are robust against the choice of metallicity diagnostic. We show that the correlation functions are generally well-fit by the predictions of a simple model for stochastic metal injection coupled with diffusion, and from the model we show that, after accounting for the effects of both beam smearing and noise, the galaxies in our sample have characteristic correlation lengths of ∼1 kpc. Correlation lengths increase with both stellar mass and star formation rate, but show no significant variation with Hubble type, barredness, or merging state. We also find no evidence for a theoretically predicted relationship between gas velocity dispersion and correlation length, though this may be due to the small dynamic range in gas velocity dispersion across our sample. Our results suggest that measurements of 2D metallicity correlation functions can be a powerful tool for studying galaxy evolution. [ABSTRACT FROM AUTHOR]

We present a pixelized source reconstruction method applied on integral field spectroscopic observations of gravitationally lensed galaxies. We demonstrate the effectiveness of this method in a case study on the clumpy morphology of a z ∼ 2 lensed galaxy behind a group-scale lens. We use a Bayesian forward source modelling approach to reconstruct the surface brightness distribution of the source galaxy on a uniformly pixelized grid while accounting for the image point spread function. The pixelated approach is sensitive to clump sizes down to 100 pc and resolves smaller clump sizes with an improvement in the signal-to-noise ratio by almost a factor of 10 compared with more traditional ray-tracing approaches. [ABSTRACT FROM AUTHOR]

We measure the gas-phase metallicity gradients of 248 galaxies selected from Data Release 2 of the SAMI Galaxy Survey. We demonstrate that there are large systematic discrepancies between the metallicity gradients derived using common strong emission line metallicity diagnostics. We determine which pairs of diagnostics have Spearman's rank coefficients greater than 0.6 and provide linear conversions to allow the accurate comparison of metallicity gradients derived using different strong emission line diagnostics. For galaxies within the mass range 8.5 < log (M /M⊙) < 11.0, we find discrepancies of up to 0.11 dex/ R e between seven popular diagnostics in the metallicity gradient–mass relation. We find a suggestion of a break in the metallicity gradient–mass relation, where the slope shifts from negative to positive, occurs between 9.5 < log (M /M⊙) < 10.5 for the seven chosen diagnostics. Applying our conversions to the metallicity gradient–mass relation, we reduce the maximum dispersion from 0.11 dex/ R e to 0.02 dex/ R e. These conversions provide the most accurate method of converting metallicity gradients when key emission lines are unavailable. We find that diagnostics that share common sets of emission line ratios agree best, and that diagnostics calibrated through the electron temperature provide more consistent results compared to those calibrated through photoionization models. [ABSTRACT FROM AUTHOR]

Local examples of jet-induced star formation lend valuable insight into its significance in galaxy evolution and can provide important observational constraints for theoretical models of positive feedback. Using optical integral field spectroscopy, we present an analysis of the ISM conditions in Minkowski's object (z = 0.0189), a peculiar star-forming dwarf galaxy located in the path of a radio jet from the galaxy NGC 541. Full spectral fitting with ppxf indicates that Minkowski's object primarily consists of a young stellar population |$\sim \! 10\, \rm Myr$| old, confirming that the bulk of the object's stellar mass formed during a recent jet interaction. Minkowski's object exhibits line ratios largely consistent with star formation, although there is evidence for a low level (⁠|$\lesssim \! 15 \, \rm per \, cent$|⁠) of contamination from a non-stellar ionizing source. Strong-line diagnostics reveal a significant variation in the gas-phase metallicity within the object, with |$\log \left(\rm O / H \right) + 12$| varying by |$\sim \! 0.5\, \rm dex$|⁠ , which cannot be explained by in-situ star formation, an enriched outflow from the jet, or enrichment of gas in the stellar bridge between NGC 541 and NGC 545/547. We hypothesize that Minkowski's object either (i) was formed as a result of jet-induced star formation in pre-existing gas clumps in the stellar bridge, or (ii) is a gas-rich dwarf galaxy that is experiencing an elevation in its star formation rate due to a jet interaction, and will eventually redden and fade, becoming an ultradiffuse galaxy as it is processed by the cluster. [ABSTRACT FROM AUTHOR]

Metallicity gradients are important diagnostics of galaxy evolution, because they record the history of events such as mergers, gas inflow, and star formation. However, the accuracy with which gradients can be measured is limited by spatial resolution and noise, and hence, measurements need to be corrected for such effects. We use high-resolution (∼20 pc) simulation of a face-on Milky Way mass galaxy, coupled with photoionization models, to produce a suite of synthetic high-resolution integral field spectroscopy (IFS) datacubes. We then degrade the datacubes, with a range of realistic models for spatial resolution (2−16 beams per galaxy scale length) and noise, to investigate and quantify how well the input metallicity gradient can be recovered as a function of resolution and signal-to-noise ratio (SNR) with the intention to compare with modern IFS surveys like MaNGA and SAMI. Given appropriate propagation of uncertainties and pruning of low SNR pixels, we show that a resolution of 3–4 telescope beams per galaxy scale length is sufficient to recover the gradient to ∼10–20 per cent uncertainty. The uncertainty escalates to ∼60 per cent for lower resolution. Inclusion of the low SNR pixels causes the uncertainty in the inferred gradient to deteriorate. Our results can potentially inform future IFS surveys regarding the resolution and SNR required to achieve a desired accuracy in metallicity gradient measurements. [ABSTRACT FROM AUTHOR]

We study the physical mechanisms that cause the offset between low-redshift and high-redshift galaxies on the [O  iii ] λ5007/H β versus [N  ii ] λ6584/H α 'Baldwin, Phillips & Terlevich' (BPT) diagram using a sample of local analogues of high-redshift galaxies. These high-redshift analogue galaxies are selected from the Sloan Digital Sky Survey. Located in the same region on the BPT diagram as the ultraviolet selected galaxies at z ∼ 2, these high-redshift analogue galaxies provide an ideal local benchmark to study the offset between the local and high-redshift galaxies on the BPT diagram. We compare the nitrogen-to-oxygen ratio (N/O), the shape of the ionizing radiation field, and ionization parameters between the high-redshift analogues and a sample of local reference galaxies. The higher ionization parameter in the high-redshift analogues is the dominant physical mechanism driving the BPT offset from low- to high-redshift, particularly at high [N  ii ] λ6584/H α. Furthermore, the N/O ratio enhancement also plays a minor role to cause the BPT offset. However, the shape of the ionizing radiation field is unlikely to cause the BPT offset because the high-redshift analogues have a similar hard ionizing radiation field as local reference galaxies. This hard radiation field cannot be produced by the current standard stellar synthesis models. The stellar rotation and binarity may help solve the discrepancy. [ABSTRACT FROM AUTHOR]

In the optical spectra of galaxies, the separation of line emission from gas ionized by star formation and an active galactic nucleus (AGN), or by star formation and shocks, are very well-understood problems. However, separating line emission between AGN and shocks has proven difficult. With the aid of a new three-dimensional diagnostic diagram, we show the simultaneous separation of line emission from star formation, shocks, and AGN in NGC 1068, and quantify the ratio of star formation, shocks, and AGN in each spaxel. The AGN, shock, and star formation luminosity distributions across the galaxy accurately align with X-ray, radio, and CO(3–2) observations, respectively. Comparisons with previous separation methods show that the shocked emission heavily mixes with the AGN emission. We also show that if the H α flux is to be used as a star formation rate indicator, separating line emission from as many sources as possible should be attempted to ensure accurate results. [ABSTRACT FROM AUTHOR]

We review the use of emission lines for understanding galaxy evolution, focusing on excitation source, metallicity, ionization parameter, ISM pressure, and electron density. We discuss the physics, benefits, and caveats of emission line diagnostics, including the effects of theoretical model uncertainties, diffuse ionized gas, and sample selection bias. In anticipation of upcoming telescope facilities, we provide new self-consistent emission line diagnostic calibrations for complete spectral coverage from the UV to the IR. These diagnostics can be used in concert to understand how fundamental galaxy properties have changed across cosmic time. We conclude the following: ▪ The UV, optical, and IR contain complementary diagnostics that can probe the conditions within different nebular ionization zones. ▪ Accounting for complex density gradients and temperature profiles is critical for reliably estimating the fundamental properties of Hii regions and galaxies. ▪ Diffuse ionized gas can raise metallicity estimates, flatten metallicity gradients, and introduce scatter in ionization parameter measurements. ▪ New 3D emission line diagnostics successfully separate the contributions from star formation, AGN, and shocks using integral field spectroscopy. We summarize with a discussion of the challenges and major opportunities for emission line diagnostics in the coming years. [ABSTRACT FROM AUTHOR]

In the optical spectra of galaxies, methods for the separation of line emission arising from star formation and an additional hard component, such as shocks or active galactic nuclei (AGNs), is well-understood and possible with current diagnostics. However, such diagnostics fail when attempting to separate and define line emission which arises from shocked gas, and that arising from AGNs. We present a new three-dimensional diagnostic diagram for integral field unit data which can simultaneously separate the line emission amongst star formation, shocks, and AGNs within a galaxy. We show that regions we define as AGN-dominated correlate well with the hard X-ray distribution in our test case NGC 1068, as well as with known regions of AGN activity in NGC 1068. Similarly, spaxels defined as shock-dominated correlate strongly with regions of high-velocity dispersion within the galaxy. [ABSTRACT FROM AUTHOR]

We present spatially resolved analysis of a lensed galaxy, SDSS1958+5950 at |$z$| = 2.225, from the Cambridge Sloan Survey of Wide Arcs in the Sky. We use our new high-resolution imaging data to construct a robust lens model for the galaxy group at |$z$| = 0.214. We employ the updated lens model to combine the Integral Field Spectrographic observations on two highly distorted images of the lensed target. We adopt a forward-modelling approach to deconvolve the effects of point spread function from the combined source-plane reconstruction. The approach is adapted to the lens model magnification and enables a resolution of ∼170 pc in the galaxy-source plane. We propose an ongoing merger as the origin of the lensed system on the basis of its source-plane morphology, kinematics and rest-frame emission-line ratios. Using our novel technique of adaptive coadded source plane reconstruction, we are able to detect different components in the velocity gradient that were not seen in previous studies of this object, plausibly belonging to different components in the merging system. [ABSTRACT FROM AUTHOR]

We demonstrate a robust method of resolving the star formation and AGN contributions to emission lines using two very well known AGN systems: NGC 1365 and NGC 1068, using the high spatial resolution data from the TYPHOON/PrISM survey. We expand the previous method of calculating the AGN fraction by using theoretical-based model grids rather than empirical points. The high spatial resolution of the TYPHOON/PrISM observations shows evidence of both star formation and AGN activity occurring in the nuclei of the two galaxies. We rebin the data to the lower resolutions, typically found in other integral field spectroscopy surveys such as SAMI, MaNGA, and CALIFA. The results show that when rebinned from the native resolution of TYPHOON (<200 pc pixel−1) to 1 kpc pixel−1, the effects include an ∼3 kpc increase in the radius of measured AGN activity, and a factor of 2–7 increase in the detection of low surface brightness features such as shocks. All of this information is critical, because information on certain physical processes may be lost at varying resolutions. We make recommendations for analysing data at current IFU survey resolutions. [ABSTRACT FROM AUTHOR]

We present gas-phase metallicity and ionization parameter maps of 25 star-forming face-on spiral galaxies from the SAMI Galaxy Survey Data Release 1. Self-consistent metallicity and ionization parameter maps are calculated simultaneously through an iterative process to account for the interdependence of the strong emission line diagnostics involving ([O  ii ]+[O  iii ])/Hβ (R23) and [O  iii ]/[O  ii] (O32). The maps are created on a spaxel-by-spaxel basis because H  ii regions are not resolved at the SAMI spatial resolution. We combine the SAMI data with stellar mass, star formation rate (SFR), effective radius (R e), ellipticity, and position angles (PA) from the GAMA survey to analyse their relation to the metallicity and ionization parameter. We find a weak trend of steepening metallicity gradient with galaxy stellar mass, with values ranging from −0.03 to −0.20 dex/ R e. Only two galaxies show radial gradients in the ionization parameter. We find that the ionization parameter has no significant correlation with either SFR, sSFR (specific SFR), or metallicity. For several individual galaxies, we find the structure in the ionization parameter maps suggestive of spiral arm features. We find a typical ionization parameter range of 7.0 < log (q) < 7.8 for our galaxy sample with no significant overall structure. An ionization parameter range of this magnitude is large enough to caution the use of metallicity diagnostics that have not considered the effects of a varying ionization parameter distribution. [ABSTRACT FROM AUTHOR]

We investigate the evolution of the ionization parameter of star-forming galaxies using a high-redshift (z ~ 1.5) sample from the FMOS-COSMOS (Fibre Multi-Object Spectrograph- COSMic evOlution Survey) and matched low-redshift samples from the Sloan Digital Sky Survey. By constructing samples of low-redshift galaxies for which the stellar mass (M*), star formation rate (SFR), and specific star formation rate (sSFR) are matched to the high-redshift sample, we remove the effects of an evolution in these properties. We also account for the effect of metallicity by jointly constraining the metallicity and ionization parameter of each sample. We find an evolution in the ionization parameter for main-sequence, star-forming galaxies and show that this evolution is driven by the evolution of sSFR. By analysing the matched samples as well as a larger sample of z< 0.3, star-forming galaxies we show that high ionization parameters are directly linked to high sSFRs and are not simply the by-product of an evolution in metallicity. Our results are physically consistent with the definition of the ionization parameter, a measure of the hydrogen ionizing photon flux relative to the number density of hydrogen atoms. [ABSTRACT FROM AUTHOR]

We use the IllustrisTNG simulations to investigate the evolution of the mass–metallicity relation (MZR) for star-forming cluster galaxies as a function of the formation history of their cluster host. The simulations predict an enhancement in the gas-phase metallicities of star-forming cluster galaxies (109 < M* < 1010 M⊙ h−1) at z ≤ 1.0 in comparisons to field galaxies. This is qualitatively consistent with observations. We find that the metallicity enhancement of cluster galaxies appears prior to their infall into the central cluster potential, indicating for the first time a systematic 'chemical pre-processing' signature for infalling cluster galaxies. Namely, galaxies that will fall into a cluster by z = 0 show a ∼0.05 dex enhancement in the MZR compared to field galaxies at z ≤ 0.5. Based on the inflow rate of gas into cluster galaxies and its metallicity, we identify that the accretion of pre-enriched gas is the key driver of the chemical evolution of such galaxies, particularly in the stellar mass range (109 < M* < 1010 M⊙ h−1). We see signatures of an environmental dependence of the ambient/inflowing gas metallicity that extends well outside the nominal virial radius of clusters. Our results motivate future observations looking for pre-enrichment signatures in dense environments. [ABSTRACT FROM AUTHOR]

We present the ~800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on Hα emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/H β, [NII]/H α, [S II]/H α, and [O I]/H α line ratios. Using thesemaps, we examine the global and resolved starforming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main-sequence population has centrally concentrated star formation similar to late-type galaxies, while galaxies >3σ below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions. [ABSTRACT FROM AUTHOR]

The most rapidly evolving regions of galaxies often display complex optical spectra with emission lines excited by massive stars, shocks and accretion on to supermassive black holes. Standard calibrations (such as for the star formation rate) cannot be applied to such mixed spectra. In this paper, we isolate the contributions of star formation, shock excitation and active galactic nucleus (AGN) activity to the emission line luminosities of individual spatially resolved regions across the central 3 × 3 kpc2 region of the active barred spiral galaxy NGC 613. The star formation rate and AGN luminosity calculated from the decomposed emission line maps are in close agreement with independent estimates from data at other wavelengths. The star formation component traces the B-band stellar continuum emission, and the AGN component forms an ionization cone which is aligned with the nuclear radio jet. The optical line emission associated with shock excitation is cospatial with strong H2 and [Fe II] emission and with regions of high ionized gas velocity dispersion (σ ≳100 km s-1). The shock component also traces the outer boundary of the AGN ionization cone and may therefore be produced by outflowing material interacting with the surrounding interstellar medium. Our decomposition method makes it possible to determine the properties of star formation, shock excitation and AGN activity from optical spectra, without contamination from other ionization mechanisms. [ABSTRACT FROM AUTHOR]

Stars form in cold molecular clouds. However, molecular gas is difficult to observe because the most abundant molecule (H2) lacks a permanent dipole moment. Rotational transitions of CO are often used as a tracer of H2, but CO is much less abundant and the conversion from CO intensity to H2 mass is often highly uncertain. Here we present a new method for estimating the column density of cold molecular gas (Σgas) using optical spectroscopy. We utilize the spatially resolved Hα maps of flux and velocity dispersion from the Sydney-AAOMulti-object Integral field spectrograph (SAMI) Galaxy Survey. We derive maps of ègas by inverting the multi-freefall star formation relation, which connects the star formation rate surface density (ΣSFR) with Σgas and the turbulent Mach number (M). Based on the measured range of ΣSFR = 0.005-1.5MΣ yr-1 kpc-2 and M= 18-130, we predict Σgas = 7-200M⊚ pc-2 in the star-forming regions of our sample of 260 SAMI galaxies. These values are close to previously measured Σgas obtained directly with unresolved CO observations of similar galaxies at low redshift. We classify each galaxy in our sample as 'star-forming' (219) or 'composite/AGN/shock' (41), and find that in 'composite/AGN/shock' galaxies the average ΣSFR, M and Σgas are enhanced by factors of 2.0, 1.6 and 1.3, respectively, compared to star-forming galaxies. We compare our predictions of Σgas with those obtained by inverting the Kennicutt-Schmidt relation and find that our new method is a factor of 2 more accurate in predicting Σgas, with an average deviation of 32 per cent from the actual Σgas. [ABSTRACT FROM AUTHOR]

We use the ZFIRE (http://zfire.swinburne.edu.au) survey to investigate the high-mass slope of the initial mass function (IMF) for a mass-complete (log10(M*/M⊙) ~ 9.3) sample of 102 star-forming galaxies at z ~ 2 using their Hα equivalent widths (Hα EWs) and rest-frame optical colours. We compare dust-corrected Hα EW distributions with predictions of star formation histories (SFHs) from PEGASE.2 and STARBURST99 synthetic stellar population models. We find an excess of high Hα EWg alaxies that are up to 0.3-0.5 dex above the model-predicted Salpeter IMF locus and the Hα EW distribution is much broader (10-500 Å) than can easily be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though this discrepancy is somewhat alleviated when it is assumed that there is no relative attenuation difference between stars and nebular lines, the result is robust against observational biases, and no single IMF (i.e. non-Salpeter slope) can reproduce the data. We show using both spectral stacking and Monte Carlo simulations that starbursts cannot explain the EW distribution. We investigate other physical mechanisms including models with variations in stellar rotation, binary star evolution, metallicity and the IMF upper-mass cut-off. IMF variations and/or highly rotating extreme metal-poor stars (Z ~ 0.1 Z⊙) with binary interactions are the most plausible explanations for our data. If the IMF varies, then the highest Hα EWs would require very shallow slopes (Γ >-1.0) with no one slope able to reproduce the data. Thus, the IMF would have to vary stochastically. We conclude that the stellar populations at z ≳ 2 show distinct differences from local populations and there is no simple physical model to explain the large variation in Hα EWs at z ~ 2. [ABSTRACT FROM AUTHOR]