Metallicity Of Galaxies Research Articles

The Mass Assembly History for Galaxies with MaNGA

How galaxies assemble masses through their own star formation or interaction with the external environment is still an important topic in the field of galaxy formation and evolution. We use Value Added Catalogs with galaxy features that are spatially and temporally resolved from Sloan Digital Sky Survey Data Release 17 to investigate the mass growth histories of early-type galaxies (ETGs) and late-type galaxies (LTGs). We find that the mass growth of ETGs is earlier than that of LTGs for massive galaxies (M * > 1010 M ⊙), while low-mass (M * ≤ 1010 M ⊙) ETGs have statistically similar mass assembly histories as low-mass LTGs. The stellar metallicity of all massive galaxies shows a negative gradient and basically does not change with time. However, in low-mass galaxies, the stellar metallicity gradient of elliptical galaxies is negative, and the stellar metallicity gradient of lenticular and spiral galaxies evolves from positive to negative. ETGs are not all in a high-density environment, but exhibit mass dependence. As the tidal strength increases, the star formation rate of low-mass ETGs rapidly decreases. These results support a picture where massive galaxies exhibit inside-out quenching mode, while low-mass galaxies show outside-in quenching mode. Environmental effects play an important role in regulating the mass assembly histories of low-mass ETGs.

CEERS Key Paper. VIII. Emission-line Ratios from NIRSpec and NIRCam Wide-Field Slitless Spectroscopy at z > 2

We use James Webb Space Telescope Near-Infrared Camera Wide Field Slitless Spectroscopy (NIRCam WFSS) and the Near-Infrared spectrograph (NIRSpec) in the Cosmic Evolution Early Release survey to measure rest-frame optical emission-line ratios of 155 galaxies at z > 2. The blind NIRCam grism observations include a sample of galaxies with bright emission lines that were not observed on the NIRSpec masks. We study the changes of the Hα, [O III]/Hβ, and [Ne III]/[O II] emission lines in terms of redshift by comparing to lower-redshift SDSS, CLEAR, and MOSDEF samples. We find a significant (>3σ) correlation between [O III]/Hβ with redshift, while [Ne III]/[O II] has a marginal (2σ) correlation with redshift. We compare [O III]/Hβ and [Ne III]/[O II] to stellar mass and Hβ SFR. We find that both emission-line ratios have a correlation with Hβ SFR and an anticorrelation with stellar mass across the redshifts 0 < z < 9. Comparison with MAPPINGS V models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-SFR galaxies. We additionally compare to IllustrisTNG predictions and find that they effectively describe the highest [O III]/Hβ ratios observed in our sample, without the need to invoke MAPPINGS models with significant shock ionization components.

Chemical evolution of local post-starburst galaxies: implications for the mass–metallicity relation

ABSTRACT We use the stellar fossil record to constrain the stellar metallicity evolution and star-formation histories of the post-starburst (PSB) regions within 45 local PSB galaxies from the MaNGA survey. The direct measurement of the regions’ stellar metallicity evolution is achieved by a new two-step metallicity model that allows for stellar metallicity to change at the peak of the starburst. We also employ a Gaussian process noise model that accounts for correlated errors introduced by the observational data reduction or inaccuracies in the models. We find that a majority of PSB regions (69 per cent at &amp;gt;1σ significance) increased in stellar metallicity during the recent starburst, with an average increase of 0.8 dex and a standard deviation of 0.4 dex. A much smaller fraction of PSBs are found to have remained constant (22 per cent) or declined in metallicity (9 per cent, average decrease 0.4 dex, standard deviation 0.3 dex). The pre-burst metallicities of the PSB galaxies are in good agreement with the mass–metallicity (MZ) relation of local star-forming galaxies. These results are consistent with hydrodynamic simulations, which suggest that mergers between gas-rich galaxies are the primary formation mechanism of local PSBs, and rapid metal recycling during the starburst outweighs the impact of dilution by any gas inflows. The final mass-weighted metallicities of the PSB galaxies are consistent with the MZ relation of local passive galaxies. Our results suggest that rapid quenching following a merger-driven starburst is entirely consistent with the observed gap between the stellar mass–metallicity relations of local star-forming and passive galaxies.

Stellar mass is not the best predictor of galaxy metallicity

Context. Interpreting the scaling relations followed by galaxies is a fundamental tool for assessing how well we understand galaxy formation and evolution. Several scaling relations involving the galaxy metallicity have been discovered through the years, the foremost of which is the scaling with stellar mass. This so-called mass–metallicity relation is thought to be fundamental and has been subject to many studies in the literature. Aims. We study the dependence of the gas-phase metallicity on many different galaxy properties to assess which of them determines the metallicity of a galaxy. Methods. We applied a random forest regressor algorithm on a sample of more than 3000 nearby galaxies from the SDSS-IV MaNGA survey. Using this machine-learning technique, we explored the effect of 148 parameters on the global oxygen abundance as an indicator of the gas metallicity. Results. M⋆/Re, as a proxy for the baryonic gravitational potential of the galaxy, is found to be the primary factor determining the average gas-phase metallicity of the galaxy (Zg). It outweighs stellar mass. A subsequent analysis provides the strongest dependence of Zg on M⋆/Re0.6. We argue that this parameter traces the total gravitational potential, and the exponent α ≃ 0.6 accounts for the inclusion of the dark matter component. Conclusions. Our results reveal the importance of the relation between the total gravitational potential of the galaxy and the gas metallicity. This relation is tighter and likely more primordial than the widely known mass–metallicity relation.

Understanding the universal dust attenuation scaling relation of star-forming galaxies

ABSTRACT Star-forming galaxies (SFGs) adhere to a surprisingly tight scaling relation of dust attenuation parametrized by the infrared excess (IRX≡ LIR/LUV), being jointly determined by the star formation rate (SFR), galaxy size (Re), metallicity (Z/Z⊙), and axial ratio (b/a). We examine how these galaxy parameters determine the effective dust attenuation and give rise to the universal IRX relation, utilizing a simple two-component star-dust geometry model in which dust in the dense and diffuse interstellar medium (ISM) follows exponential mass density profiles, connected with but not necessarily identical to the stellar mass profiles. Meanwhile, empirical relations are adopted to link galaxy properties, including the gas–star formation relation, the dust-to-stellar size relation, as well as the dust-to-gas ratio versus metallicity relation. By fitting a large sample of local SFGs with the model, we obtain the best-fitting model parameters as a function of metallicity, showing that the two-component geometry model is able to successfully reproduce the dependence of IRX on SFR, Re, b/a at given Z/Z⊙, as well as the dependence of power-law indices on metallicity. Moreover, we also retrieve constraints on the model geometry parameters, including the optical depth of birth clouds (BCs), BC-to-total dust mass fraction, BC covering factor of UV-emitting stars, and star-to-total dust disc radius ratio, which all evolve with galaxy metallicity. Finally, a consistent picture of how the star-dust geometry in SFGs evolves with galaxy metallicity is discussed.

The impact of gas accretion and AGN feedback on the scatter of the mass–metallicity relation

ABSTRACT The gas-phase metallicity of galaxies encodes important information about galaxy evolution processes, in particular star formation, feedback, outflows, and gas accretion, the relative importance of which can be extracted from systematic trends in the scatter of the mass–metallicity relation (MZR). Here, we use a sample of low-redshift (0.02 &amp;lt; z &amp;lt; 0.055) galaxies from SDSS to investigate the nature of the scatter around the MZR, the observables and physical processes causing it, and its dependence on galaxy mass. We use cold gas masses inferred from optical emission lines using the technique of Scholte &amp; Saintonge (2023) to confirm that at fixed stellar mass, metallicity and gas mass are anticorrelated, but only for galaxies up to M* = 1010.5 M⊙. In that mass regime, we find a link between the offset of a galaxy from the MZR and halo mass, using the amplitude of the two-point correlation function as a proxy for halo mass; at fixed stellar mass, the most gas-poor galaxies reside in the most massive haloes. This observation is consistent with changes in gas accretion rates onto galaxies as a function of halo mass, with environmental effects acting on satellite galaxies also contributing. At higher stellar masses, the scatter of the MZR does no longer correlate with gas or halo mass. Instead, there is some indication of a link with AGN activity, as expected from models and simulations that metallicity is set by the interplay between gas in- and outflows, star formation, and AGN feedback, shaping the MZR and its scatter.

The Impact of Patchy Reionization on Ultrafaint Dwarf Galaxies

We investigate how patchy reionization affects the star formation history (SFH) and stellar metallicity of ultrafaint dwarf galaxies (UFDs). Patchy reionization refers to varying ultraviolet background strengths depending on a galaxy’s environment. Recent observations highlight the significance of this effect on UFDs, as UFDs can have different SFHs depending on their relative position with respect to their host halo during the period of reionization. However, most cosmological hydrodynamic simulations do not consider environmental factors such as patchy reionization, and the effect of reionization is typically applied homogeneously. Using a novel approach to implement patchy reionization, we show how SFHs of simulated UFDs can change. Our cosmological hydrodynamic zoom-in simulations focus on UFD analogs with M vir ∼ 109 M ⊙, M * ≲ 105 M ⊙ at z = 0. We find that patchy reionization can weaken the effect of reionization by 2 orders of magnitude up to z = 3, enabling late star formation in half of the simulated UFDs, with quenching times ∼460 Myr later than those with homogeneous reionization. We also show that halo merger and mass assembly can affect the SFHs of simulated UFDs, in addition to patchy reionization. The average stellar iron-to-hydrogen ratio, [Fe/H], of the simulated UFDs with patchy reionization increases by 0.22–0.42 dex. Finally, our findings suggest that patchy reionization could be responsible for the extended SFHs of Magellanic UFDs compared to non-Magellanic UFDs.

From Halos to Galaxies. VII. The Connections between Stellar Mass Growth History, Quenching History, and Halo Assembly History for Central Galaxies

The assembly of galaxies over cosmic time is tightly connected to the assembly of their host dark matter halos. We investigate the stellar mass growth history and the chemical enrichment history of central galaxies in the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory. We find that the derived stellar metallicity of passive central galaxies is always higher than that of the star-forming ones. This stellar metallicity enhancement becomes progressively larger toward low-mass galaxies (at a given epoch) and earlier epochs (at a given stellar mass), which suggests strangulation as the primary mechanism for star formation quenching in central galaxies not only in the local Universe but also very likely at higher redshifts up to z ∼ 3. We show that at the same present-day stellar mass, passive central galaxies assembled half of their final stellar mass ∼2 Gyr earlier than star-forming central galaxies, which agrees well with the semi-analytic model. Exploring the semi-analytic model, we find that this is because passive central galaxies reside in, on average, more massive halos with a higher halo mass increase rate across cosmic time. As a consequence, passive central galaxies are assembled faster and also quenched earlier than their star-forming counterparts. While at the same present-day halo mass, different halo assembly history also produces a very different final stellar mass of the central galaxy within, and halos assembled earlier host more massive centrals with a higher quenched fraction, in particular around the “golden halo mass” at 1012 M ⊙. Our results call attention back to the dark matter halo as a key driver of galaxy evolution.

The metallicity dependence of the stellar initial mass function

ABSTRACT During star formation, dust plays the crucial role of coupling gas to stellar radiation fields, allowing radiation feedback to influence gas fragmentation and thus the stellar initial mass function (IMF). Variations in dust abundance therefore provide a potential avenue by which variation in galaxy metallicity might affect the IMF. In this paper, we present a series of radiation-magnetohydrodynamic simulations in which we vary the metallicity and thus the dust abundance from 1 per cent of solar to 3× solar, spanning the range from the lowest metallicity dwarfs to the most metal-rich early-type galaxies (ETGs) found in the local Universe. We design the simulations to keep all dimensionless parameters constant so that the interaction between feedback and star-forming environments of varying surface density and metallicity is the only factor capable of breaking the symmetry between the simulations and modifying the IMF, allowing us to isolate and understand the effects of each environmental parameter cleanly. We find that shifts in the IMF with varying metallicity at a fixed surface density are smaller than the shifts in varying surface density at a fixed surface metallicity. We also find that metallicity-induced IMF variations are too small to explain the mass-to-light ratio shifts seen in the ETGs. We therefore conclude that metallicity variations are much less important than variations in surface density in driving changes in the IMF and that the latter rather than the former are most likely responsible for the IMF variations found in ETGs.

The impact of supernova feedback on the mass–metallicity relations

ABSTRACT Metallicity is a fundamental physical property that strongly constrains galaxy formation and evolution. The formation of stars in galaxies is suppressed by the energy released from supernova explosions and can be enhanced by metal production. In order to understand the impact of this supernova feedback, we compare four different feedback methods, ejecting energy in thermal, kinetic, stochastic, and mechanical forms, into our self-consistent cosmological chemodynamical simulations. To minimize other uncertainties, we use the latest nucleosynthesis yields that can reproduce the observed elemental abundances of stars in the Milky Way. For each method, we predict the evolution of stellar and gas-phase metallicities as a function of galaxy mass, i.e. the mass–metallicity relations. We then find that the mechanical feedback can give the best match to a number of observations up to redshift z ∼ 3, although the predicted gas-phase metallicities seem to be higher than those observed at z ≳ 1. The feedback modelling can be further constrained by the metallicities in distant galaxies with the JWST and those of a large sample with ongoing and future spectroscopic surveys.

Evolution of the Mass–Metallicity Relation from Redshift z ≈ 8 to the Local Universe

A tight positive correlation between the stellar mass and the gas-phase metallicity of galaxies has been observed at low redshifts. The redshift evolution of this correlation can strongly constrain theories of galaxy evolution. The advent of JWST allows probing the mass–metallicity relation at redshifts far beyond what was previously accessible. Here we report the discovery of two emission line galaxies at redshifts 8.15 and 8.16 in JWST NIRCam imaging and NIRSpec spectroscopy of targets gravitationally lensed by the cluster RX J2129.4+0005. We measure their metallicities and stellar masses along with nine additional galaxies at 7.2 < z spec < 9.5 to report the first quantitative statistical inference of the mass–metallicity relation at z ≈ 8. We measure ∼0.9 dex evolution in the normalization of the mass–metallicity relation from z ≈ 8 to the local universe; at a fixed stellar mass, galaxies are 8 times less metal enriched at z ≈ 8 compared to the present day. Our inferred normalization is in agreement with the predictions of FIRE simulations. Our inferred slope of the mass–metallicity relation is similar to or slightly shallower than that predicted by FIRE or observed at lower redshifts. We compare the z ≈ 8 galaxies to extremely low-metallicity analog candidates in the local universe, finding that they are generally distinct from extreme emission line galaxies or “green peas,” but are similar in strong emission line ratios and metallicities to “blueberry galaxies.” Despite this similarity, at a fixed stellar mass, the z ≈ 8 galaxies have systematically lower metallicities compared to blueberry galaxies.

The star formation histories of quiescent ultra-diffuse galaxies and their dependence on environment and globular cluster richness

ABSTRACT We derive the stellar population parameters of 11 quiescent ultra-diffuse galaxies (UDGs) from Keck/KCWI data. We supplement these with 14 literature UDGs, creating the largest spectroscopic sample of UDGs to date (25). We find a strong relationship between their α-enhancement and their star formation histories: UDGs that formed on very short time-scales have elevated [Mg/Fe] abundance ratios, whereas those forming over extended periods present lower values. Those forming earlier and faster are overall found in high-density environments, being mostly early infalls into the cluster. No other strong trends are found with infall times. We analyse the stellar mass–metallicity, age–metallicity, and [Mg/Fe]–metallicity relations of the UDGs, comparing them to other types of low mass galaxies. Overall, UDGs scatter around the established stellar mass–metallicity relations of classical dwarfs. We find that GC-rich UDGs have intermediate-to-old ages, but previously reported trends of galaxy metallicity and GC richness are not reproduced with this spectroscopic sample due to the existence of GC-rich UDGs with elevated metallicities. In addition, we also find that a small fraction of UDGs could be ‘failed-galaxies’, supported by their GC richness, high alpha-abundance, fast formation time-scales and that they follow the mass–metallicity relation of z ∼2 galaxies. Finally, we also compare our observations to simulated UDGs. We caution that there is not a single simulation that can produce the diverse UDG properties simultaneously, in particular the low metallicity failed galaxy like UDGs.

The Mass–Metallicity Relation of Dwarf Galaxies at Cosmic Noon from JWST Observations

We present a study of the mass–metallicity relation (MZR) of 51 dwarf galaxies (M ⋆ ≈ 106.5–109.5 M ⊙) at z = 2–3 from the A2744 and SMACS J0723-3732 galaxy cluster fields. These dwarf galaxies are identified and confirmed by deep JWST/NIRISS imaging and slitless grism spectroscopic observations. By taking advantage of the superior performance of JWST and the gravitational lensing effect, we extend the previous MZR relation at z = 2–3 to a much lower-mass regime down by ≈2.5 orders of magnitude as compared with previous studies. We find that the MZR has a shallower slope at the low-mass end (M ⋆ < 109 M ⊙), with a slope turnover point of ≈109 M ⊙. This implies that the dominating feedback processes in dwarf galaxies may be different from that in massive galaxies. From z = 3, to z = 2, the metallicity of the dwarf galaxies is enhanced by ≈0.09 dex for a given stellar mass, consistent with the mild evolution found in galaxies with higher mass. Furthermore, we confirm the existence of a fundamental metallicity relation (FMR) between the gas-phase metallicity, stellar mass, and star formation rate in dwarf galaxies at z = 2–3. Our derived FMR, which has no significant redshift evolution, can be used as a benchmark to understand the origin of the anticorrelation between the star formation rate and metallicity of dwarf galaxies in the high-z Universe.

Stellar metallicity from optical and UV spectral indices: Test case for WEAVE-StePS

Context. The upcoming generation of optical spectrographs on four meter-class telescopes, with their huge multiplexing capabilities, excellent spectral resolution, and unprecedented wavelength coverage, will provide high-quality spectra for thousands of galaxies. These data will allow us to examine of the stellar population properties at intermediate redshift, an epoch that remains unexplored by large and deep surveys. Aims. We assess our capability to retrieve the mean stellar metallicity in galaxies at different redshifts and signal-to-noise ratios (S/N), while simultaneously exploiting the ultraviolet (UV) and optical rest-frame wavelength coverage. Methods. The work is based on a comprehensive library of spectral templates of stellar populations, covering a wide range of age and metallicity values and built assuming various star formation histories, to cover an observable parameter space with diverse chemical enrichment histories and dust attenuation. We took into account possible observational errors, simulating realistic observations of a large sample of galaxies carried out with WEAVE at the William Herschel Telescope at different redshifts and S/N values. We measured all the available and reliable indices on the simulated spectra and on the comparison library. We then adopted a Bayesian approach to compare the two sets of measurements in order to obtain the probability distribution of stellar metallicity with an accurate estimate of the uncertainties. Results. The analysis of the spectral indices has shown how some mid-UV indices, such as BL3580 and Fe3619, can provide reliable constraints on stellar metallicity, along with optical indicators. The analysis of the mock observations has shown that even at S/N = 10, the metallicity can be derived within 0.3 dex, in particular, for stellar populations older than 2 Gyr. The S/N value plays a crucial role in the uncertainty of the estimated metallicity and so, the differences between S/N = 10 and S/N = 30 are quite large, with uncertainties of ~0.15 dex in the latter case. On the contrary, moving from S/N = 30 to S/N = 50, the improvement on the uncertainty of the metallicity measurements is almost negligible. Our results are in good agreement with other theoretical and observational works in the literature and show how the UV indicators, coupled with classic optical ones, can be advantageous in constraining metallicities. Conclusions. We demonstrate that a good accuracy can be reached on the spectroscopic measurements of the stellar metallicity of galaxies at intermediate redshift, even at low S/N, when a large number of indices can be employed, including some UV indices. This is very promising for the upcoming surveys carried out with new, highly multiplexed, large-field spectrographs, such as StePS at the WEAVE and 4MOST, which will provide spectra of thousands of galaxies covering large spectral ranges (between 3600 and 9000 Å in the observed frame) at relatively high S/N (&gt;10 Å−1).

A Surprising Lack of Metallicity Evolution with Redshift in the Long Gamma-Ray Burst Host Galaxy Population

The number of long-duration gamma-ray burst (LGRB) host galaxies with measured metallicities and host masses has expanded sufficiently to investigate how the distributions of these properties change with redshift. Using the combined host galaxy metallicity sample from Graham & Fruchter and Krühler et al., we find a surprising lack of evolution in the LGRB metallicity distribution across different redshifts. In particular, the fraction of LGRB hosts with relatively high metallicity (12+log(O/H) ≥ 8.4) remains essentially constant out to z = 2.5. This result is at odds with the evolution in the mass–metallicity relation of typical galaxies, which become progressively more metal poor with increasing redshift. A similar result is found when converting the LGRB host galaxy mass distribution taken from the Swift GRB Host Galaxy Legacy Survey (SHOALS) sample to a corresponding metallicity distribution by applying a redshift-dependent mass–metallicity relation. The SHOALS sample is compiled using an unbiased selection function implying that the observed lack of evolution in the host galaxy high-metallicity distribution is not caused by selection effects. However, the LGRB host galaxy metallicities estimated from the stellar mass are typically a quarter dex higher at all redshifts than the metallicity we measure spectroscopically. This implies that using mass–metallicity relationships to estimate host metallicities will thus produce a substantial systematic bias.

A complete catalogue of broad-line AGNs and double-peaked emission lines from MaNGA integral-field spectroscopy of 10K galaxies: stellar population of AGNs, supermassive black holes, and dual AGNs

ABSTRACT We analyse the integral field spectroscopy data for the ≈10 000 galaxies in final data release of the MaNGA survey. We identify 188 galaxies for which the emission lines cannot be described by single Gaussian components. These galaxies can be classified into (1) 38 galaxies with broad $\rm H\alpha$ and [O iii] $\rm \lambda$5007 lines, (2) 101 galaxies with broad $\rm H\alpha$ lines but no broad [O iii] $\rm \lambda$5007 lines, and (3) 49 galaxies with double-peaked narrow emission lines. Most of the broad-line galaxies are classified as active galactic nuclei (AGNs) from their line ratios. The catalogue helps us further understand the AGN-galaxy coevolution through the stellar population of broad-line region host galaxies and the relation between broad lines’ properties and the host galaxies’ dynamical properties. The stellar population properties (including mass, age, and metallicity) of broad-line host galaxies suggest there is no significant difference between narrow-line Seyfert-2 galaxies and Type-1 AGNs with broad $\rm H\alpha$ lines. We use the broad-$\rm H\alpha$ line width and luminosity to estimate masses of black hole in these galaxies, and test the MBH–σe relation in Type-1 AGN host galaxies. Furthermore, we find three dual AGN candidates supported by radio images from the VLA FIRST survey. This sample may be useful for further studies on AGN activities and feedback processes.

The impact of environmental effects on active galactic nuclei: A decline in the incidence of ionized outflows

Active galactic nuclei (AGNs) have generally been considered to be less frequent in denser environments due to a lower number of galaxy-galaxy interactions and/or the removal of their gas-rich reservoirs by the dense intergalactic medium. However, recent observational and theoretical works suggest that the effect of ram-pressure stripping acting on galaxies in dense environments might reduce the angular momentum of their gas, causing it to infall towards the super massive black hole at their centre, activating the AGN phase. In this work we explore the connection between environment and nuclear activity by evaluating the variation in the incidence of ionized outflows, a common phenomenon associated with nuclear activity, in AGNs across different environments. We select a sample of approximately 3300 optical AGNs from the Sloan Digital Sky Survey Data Release 13, which we match with a group catalogue to identify galaxies in isolation or residing in groups. We further probe their environments through the projected distance to the central galaxy of the group or cluster and the projected surface density to the fifth neighbour (δ5). The presence of ionized outflows is determined through the modelling of the [O III] λ5007 emission line. We find that at lower masses (&lt; 1010.3 M⊙), the fraction of ionized outflows is significantly lower in satellite AGNs (∼7%) than in isolated (∼22%) AGNs, probably due to their different AGN luminosity, L[O III], in this stellar mass range. The fraction of outflows decreases at distances closer to the central galaxy of the group or cluster for all satellite AGNs; however, only the lower-mass ones (109 − 1010.3 M⊙) display a significant decline with δ5. Although this study does not include AGNs in the densest regions of galaxy clusters, our findings suggest that AGNs in dense environments accrete less gas than those in the field, potentially due to the removal of the gas reservoirs via stripping or starvation, leading to a negative connection between environment and AGN activity. Based on our results, we propose that the observed change in the incidence of outflows when moving towards denser regions of groups and clusters could contribute to the higher gas metallicities of cluster galaxies compared to field galaxies, especially at lower masses.

You Are What You Eat: The Circumgalactic Medium around BreakBRD Galaxies Has Low Mass and Angular Momentum

Observed breakBRD (“break bulges in red disks”) galaxies are a nearby sample of face-on disk galaxies with particularly centrally concentrated star formation: they have red disks but recent star formation in their centers as measured by the D n 4000 spectral index. In Kopenhafer et al., a comparable population of breakBRD analogs was identified in the TNG simulation, in which the central concentration of star formation was found to reflect a central concentration of dense, star-forming gas caused by a lack of dense gas in the galaxy outskirts. In this paper, we examine the circumgalactic medium of the central breakBRD analogs to determine if the extended halo gas also shows differences from that around comparison galaxies with comparable stellar mass. We examine the circumgalactic medium gas mass, specific angular momentum, and metallicity in these galaxy populations. We find less gas in the circumgalactic medium of breakBRD galaxies, and that the breakBRD circumgalactic medium is slightly more concentrated than that of comparable M * galaxies. In addition, we find that the angular momentum in the circumgalactic medium of breakBRD galaxies tends to be low for their stellar mass, and shows more misalignment to the angular momentum vector of the stellar disk. Finally, we find that the circumgalactic medium metallicity of breakBRD galaxies tends to be high for their stellar mass. Together with their low star formation rate, we argue that these circumgalactic medium properties indicate a small amount of disk feeding concentrated in the central regions and a lack of low-metallicity gas accretion from the intergalactic medium.

JWST/NIRSpec Measurements of the Relationships between Nebular Emission-line Ratios and Stellar Mass at z ∼ 3–6

We analyze the rest-optical emission-line ratios of star-forming galaxies at 2.7 ≤ z < 6.5 drawn from the Cosmic Evolution Early Release Science (CEERS) Survey and their relationships with stellar mass (M *). Our analysis includes both line ratios based on the [N ii] λ6583 feature ([N ii] λ6583/Hα, ([O iii] λ5007/Hβ)/([N ii] λ6583/Hα) (O3N2), and [N ii] λ6583/[O ii] λ3727) and those featuring α-elements ([O iii] λ5007/Hβ, [O iii] λ5007/[O ii] λ3727 (O32), ([O iii] λλ4959, 5007 + [O ii] λ3727)/Hβ (R23), and [Ne iii] λ3869/[O ii] λ3727). Given the typical flux levels of [N ii] λ6583 and [Ne iii] λ3869, which are undetected in the majority of individual CEERS galaxies at 2.7 ≤ z < 6.5, we construct composite spectra in bins of M * and redshift. Using these composite spectra, we compare the relationships between emission-line ratios and M * at 2.7 ≤ z < 6.5 with those observed at lower redshift. While there is significant evolution toward higher excitation (e.g., higher [O iii] λ5007/Hβ, O32, O3N2) and weaker nitrogen emission (e.g., lower [N ii] λ6583/Hα and [N ii] λ6583/[O ii] λ3727) between z ∼ 0 and z ∼ 3, we find in most cases that there is no significant evolution in the relationship between line ratio and M * beyond z ∼ 3. The [Ne iii] λ3869/[O ii] λ3727 ratio is anomalous in showing evidence for significant elevation at 4.0 ≤ z < 6.5 at fixed mass, relative to z ∼ 3.3. Collectively, however, our empirical results suggest no significant evolution in the mass–metallicity relationship at 2.7 ≤ z < 6.5. Representative galaxy samples and metallicity calibrations based on existing and upcoming JWST/NIRSpec observations will be required to translate these empirical scaling relations into ones tracing chemical enrichment and gas cycling and to distinguish among descriptions of feedback in galaxy formation simulations at z > 3.

FIREbox: simulating galaxies at high dynamic range in a cosmological volume

ABSTRACT We introduce a suite of cosmological volume simulations to study the evolution of galaxies as part of the Feedback in Realistic Environments project. FIREbox, the principal simulation of the present suite, provides a representative sample of galaxies (∼1000 galaxies with $M_{\rm star}\gt 10^8\, M_\odot$ at z = 0) at a resolution ($\Delta {}x\sim {}20\, {\rm pc}$ , $m_{\rm b}\sim {}6\times {}10^4\, M_\odot$ ) comparable to state-of-the-art galaxy zoom-in simulations. FIREbox captures the multiphase nature of the interstellar medium in a fully cosmological setting (L = 22.1 Mpc) thanks to its exceptionally high dynamic range (≳106) and the inclusion of multichannel stellar feedback. Here, we focus on validating the simulation predictions by comparing to observational data. We find that star formation rates, gas masses, and metallicities of simulated galaxies with $M_{\rm star}\lt 10^{10.5-11}\, M_\odot$ broadly agree with observations. These galaxy scaling relations extend to low masses ($M_{\rm star}\sim {}10^7\, M_\odot$ ) and follow a (broken) power-law relationship. Also reproduced are the evolution of the cosmic HI density and the HI column density distribution at z ∼ 0–5. At low z , FIREbox predicts a peak in the stellar-mass–halo-mass relation but also a higher abundance of massive galaxies and a higher cosmic star formation rate density than observed, showing that stellar feedback alone is insufficient to reproduce the properties of massive galaxies at late times. Given its high resolution and sample size, FIREbox offers a baseline prediction of galaxy formation theory in a ΛCDM Universe while also highlighting modelling challenges to be addressed in next-generation galaxy simulations.