Stellar Population Models Research Articles

Carbon and Iron Deficiencies in Quiescent Galaxies at z = 1–3 from JWST-SUSPENSE: Implications for the Formation Histories of Massive Galaxies

Abstract We present the stellar metallicities and multielement abundances (C, Mg, Si, Ca, Ti, Cr, and Fe) of 15 massive (log M/M ⊙ = 10.2–11.2) quiescent galaxies at z = 1–3, derived from ultradeep JWST-SUSPENSE spectra. Compared to quiescent galaxies at z ∼ 0, these galaxies exhibit a deficiency of 0.26 ± 0.04 dex in [C/H], 0.16 ± 0.03 dex in [Fe/H], and 0.07 ± 0.04 dex in [Mg/H], implying rapid formation and quenching before significant enrichment from asymptotic giant branch stars and Type Ia supernovae. Additionally, we find that galaxies forming at higher redshift consistently show higher [Mg/Fe] and lower [Fe/H] and [Mg/H], regardless of their observed redshift. The evolution in [Fe/H] and [C/H] is therefore primarily driven by lower-redshift samples naturally including galaxies with longer star formation timescales. In contrast, the lower [Mg/H] likely reflects earlier-forming galaxies expelling larger gas reservoirs during their quenching phase. Consequently, the mass–metallicity relation, primarily reflecting [Mg/H], is somewhat lower at z = 1–3 compared to the lower-redshift relation. Finally, we compare our results to standard stellar population modeling approaches employing solar abundance patterns and nonparametric star formation histories (using Prospector). Our simple stellar population (SSP)-equivalent ages agree with the mass-weighted ages from Prospector, while the metallicities disagree significantly. Nonetheless, the metallicities better reflect [Fe/H] than total [Z/H]. We also find that the star formation timescales inferred from elemental abundances are significantly shorter than those from Prospector, and we discuss the resulting implications for the early formation of massive galaxies.

Extragalactic globular cluster near-infrared spectroscopy

Many recent studies have pointed out significant discrepancies between observations and models of stellar populations in the near-infrared (NIR). With current and future observing facilities being focused in this wavelength range, properly assessing and solving these issues is of utmost importance. Here, we present the first application of the extragalactic globular cluster (GC) near-infrared spectroscopy survey, and present evidence that these GCs reveal an age zero-point problem of stellar population synthesis (SPS) models. This problem has already been identified in the optical range for the GCs of the Milky Way. Such an issue arises when derived GC spectroscopic ages appear older than the Universe itself. We extend this discussion for the first time to the NIR, specifically using the Paβ line at 1.28 microns. We focus on the GCs of the nearby Centaurus A galaxy using their NIR spectra. This work broadens our understanding of the age zero-point problem and emphasises the necessity to revisit and refine SPS models, especially in the NIR domain.

Parameters of star formation regions in galaxies NGC 3963 and NGC 7292

Results of a study of physical parameters of stellar population in star formation regions in galaxies with signs of peculiarity NGC 3963 and NGC 7292 are presented. The study was carried out based on the analysis of photometric (UBVRI bands), Hα and spectroscopic data obtained by the authors, using evolutionary models of stellar population. Among 157 star formation regions identified in galaxies, the young stellar population mass estimates were obtained for 16 of them and the age estimates were obtained for 15 ones. The age of star formation regions clearly correlates with the presence of emission in the Hα line: H II regions in galaxies are younger than 6–8 Myr, and the regions without gas emission are older. The studied objects are included in the version 3 of our catalogue of photometric, physical and chemical parameters of star formation regions, which includes 1667 objects in 21 galaxies. Key aspects of the used technique to estimate the physical parameters and different relations between observational and physical parameters of the young stellar population in star formation regions are discussed.

Initial Mass Functions of Young Stellar Clusters from the Gemini Spectroscopic Survey of Nearby Galaxies. I. Young Massive Clusters in the Antennae Galaxies

The stellar initial mass function (IMF) is a key parameter to understand the star formation process and the integrated properties of stellar populations in remote galaxies. We present a spectroscopic study of young massive clusters (YMCs) in the starburst galaxies NGC 4038/9. The integrated spectra of seven YMCs obtained with GMOS-S attached to the 8.1 m Gemini South telescope reveal the spectral features associated with stellar ages and the underlying IMFs. We constrain the ages of the YMCs using the absorption lines and strong emission bands from Wolf–Rayet stars. The internal reddening is also estimated from the strength of the Na i D absorption lines. Based on these constraints, the observed spectra are matched with the synthetic spectra generated from a simple stellar population model. Several parameters of the clusters including age, reddening, cluster mass, and the underlying IMF are derived from the spectral matching. The ages of the YMCs range from 2.5 to 6.5 Myr, and these clusters contain stellar masses ranging from 1.6 × 105 M ☉ to 7.9 × 107 M ☉. The underlying IMFs appear to differ from the universal form of the Salpeter/Kroupa IMF. Interestingly, massive clusters tend to have the bottom-heavy IMFs, although the masses of some clusters are overestimated due to the crowding effect. Based on this, our results suggest that the universal form of the IMF is not always valid when analyzing integrated light from unresolved stellar systems. However, further study with a larger sample size is required to reach a definite conclusion.

Comparing E-MOSAICS predictions of high-redshift proto-globular clusters with JWST observations in lensed galaxies

ABSTRACT High-resolution imaging and strong gravitational lensing of high-redshift galaxies have enabled the detection of compact sources with properties similar to nearby massive star clusters. Often found to be very young, these sources may be globular clusters detected in their earliest stages. In this work, we compare predictions of high-redshift ($z \sim 1$–10) star cluster properties from the E-MOSAICS simulation of galaxy and star cluster formation with those of the star cluster candidates in strongly lensed galaxies from JWST and Hubble Space Telescope (HST) imaging. We select galaxies in the simulation that match the luminosities of the majority of lensed galaxies with star cluster candidates observed with JWST. We find that the luminosities, ages, and masses of the brightest star cluster candidates in the high-redshift galaxies are consistent with the E-MOSAICS model. In particular, the brightest cluster ages are in excellent agreement. The results suggest that star clusters in both low- and high-redshift galaxies may form via common mechanisms. However, the brightest clusters in the lensed galaxies tend to be $\approx 1$–$1.5 \, \rm {mag}$ brighter and $\approx 0.5$ dex more massive than the median E-MOSAICS predictions. We discuss the large number of effects that could explain the discrepancy, including simulation and observational limitations, stellar population models, cluster detection biases, and nuclear star clusters. Understanding these limitations would enable stronger tests of globular cluster formation models.

Testing the Accuracy of Spectral Energy Distribution Modeling Techniques Using the NIHAO-SKIRT-Catalog

We use simulated galaxy observations from the NIHAO-SKIRT-Catalog to test the accuracy of spectral energy distribution (SED) modeling techniques. SED modeling is an essential tool for inferring star formation histories from nearby galaxy observations but is fraught with difficulty due to our incomplete understanding of stellar populations, chemical enrichment processes, and the nonlinear, geometry-dependent effects of dust. The NIHAO-SKIRT-Catalog uses hydrodynamic simulations and radiative transfer to produce SEDs from the ultraviolet (UV) through the infrared (IR), accounting for dust. We use the commonly used Prospector software to perform inference on these SEDs and compare the inferred stellar masses and star formation rates (SFRs) to the known values in the simulation. We match the stellar population models to isolate the effects of differences in the star formation history, the chemical evolution history, and the dust. For the high-mass NIHAO galaxies (>109.5 M ⊙), we find that model mismatches lead to inferred SFRs that are on average underestimated by a factor of 2 when fit to UV through IR photometry, and a factor of 3 when fit to UV through optical photometry. These biases lead to significant inaccuracies in the resulting specific SFR–mass relations, with UV through optical fits showing particularly strong deviations from the true relation of the simulated galaxies. In the context of massive existing and upcoming photometric surveys, these results highlight that star formation history inference from photometry may remain imprecise and inaccurate and that there is a pressing need for more realistic testing of existing techniques.

Correction to: sMILES SSPs: a library of semi-empirical MILES stellar population models with variable [α/Fe] abundances

Correction to: sMILES SSPs: a library of semi-empirical MILES stellar population models with variable [α/Fe] abundances

The Sunburst Arc with JWST

We report the detection of a population of Wolf-Rayet (WR) stars in the Sunburst Arc, a strongly gravitationally lensed galaxy at redshift z = 2.37. As the brightest known lensed galaxy, the Sunburst Arc has become an important cosmic laboratory for studying star and cluster formation, Lyman α (Lyα) radiative transfer, and Lyman continuum (LyC) escape. Here, we present the first results of JWST/NIRSpec IFU observations of the Sunburst Arc, focusing on a stacked spectrum of the 12-fold imaged Sunburst LyC-emitting (LCE) cluster. In agreement with previous studies, we find that the Sunburst LCE cluster is a very massive, compact star cluster with Mdyn = (9 ± 1)×106 M⊙. Our age estimate of 4.2–4.5 Myr is much larger than the crossing time of tcross = 183 ± 9 kyr, indicating that the cluster is dynamically evolved and consistent with it being gravitationally bound. We find a significant nitrogen enhancement of the low ionization state interstellar medium (ISM), with log(N/O) = − 0.74 ± 0.09, which is ≈0.8 dex above typical values for H II regions of a similar metallicity in the local Universe. We find broad stellar emission complexes around He IIλ4686 and C IVλ5808 with associated nitrogen emission; this is the first time WR signatures have been directly observed at redshifts above ∼0.5. The strength of the WR signatures cannot be reproduced by stellar population models that only include single-star evolution. While models with binary evolution better match the WR features, they still struggle to reproduce the nitrogen-enhanced WR features. JWST reveals the Sunburst LCE cluster to be a highly ionized proto-globular cluster with low oxygen abundance and extreme nitrogen enhancement that hosts a population of WR stars, likely including a previously suggested population of very massive stars (VMSs), which together are rapidly enriching the surrounding medium.

Observations of Extremely Metal-poor O Stars: Weak Winds and Constraints for Evolution Models

Metal-poor massive stars drive the evolution of low-mass galaxies, both locally and at high redshift. However, quantifying the feedback they impart to their local surroundings remains uncertain because models of stellar evolution, mass loss, and ionizing spectra are unconstrained by observations below 20% solar metallicity (Z ⊙). We present new Keck Cosmic Web Imager optical spectroscopy of three O-type stars in the nearby dwarf galaxies Leo P, Sextans A, and WLM, which have gas-phase oxygen abundances of 3%–14% Z ⊙. To characterize their fundamental stellar properties and radiation-driven winds, we fit PoWR atmosphere models to the optical spectra simultaneously with Hubble Space Telescope far-ultraviolet (FUV) spectra and multiwavelength photometry. We find that all three stars have effective temperatures consistent with their spectral types and surface gravities typical of main-sequence dwarf stars. Yet, the combination of those inferred parameters and luminosity for the two lower-Z stars is not reproduced by stellar evolution models, even those that include rotation or binary interactions. The scenario of multiple-star systems is difficult to reconcile with all available data, suggesting that these observations pose a challenge to current evolution models. We highlight the importance of validating the relationship between stellar mass, temperature, and luminosity at very low Z for accurate estimates of ionizing photon production and spectral hardness. Finally, all three stars’ FUV wind profiles reveal low mass-loss rates and terminal wind velocities in tension with expectations from widely adopted radiation-driven wind models. These results provide empirical benchmarks for future development of mass-loss and evolution models for metal-poor stellar populations.

GOALS-JWST: Constraining the Emergence Timescale for Massive Star Clusters in NGC 3256

We present the results of a James Webb Space Telescope NIRCam and NIRSpec investigation into the young massive star cluster (YMC) population of NGC 3256, the most cluster-rich luminous infrared galaxy in the Great Observatories All Sky LIRG Survey. We detect 3061 compact YMC candidates with a signal-to-noise ratio ≥3 at F150W, F200W, and F335M. Based on yggdrasil stellar population models, we identify 116/3061 sources with F150W – F200W > 0.47 and F200W – F355M > −1.37 colors, suggesting that they are young (t ≤ 5 Myr), dusty (A V = 5−15), and massive (M ⊙ > 105). This increases the sample of dust-enshrouded YMCs detected in this system by an order of magnitude relative to previous Hubble Space Telescope studies. With NIRSpec integral field unit pointings centered on the northern and southern nucleus, we extract the Paα and 3.3 μm polycyclic aromatic hydrocarbon (PAH) equivalent widths for eight bright and isolated YMCs. Variations in both the F200W – F335M color and 3.3 μm PAH emission with the Paα line strength suggest a rapid dust clearing (<3−4 Myr) for the emerging YMCs in the nuclei of NGC 3256. Finally, with both the age and dust emission accurately measured, we use yggdrasil to derive the color excess (E(B − V)) for all eight YMCs. We demonstrate that YMCs with strong 3.3 μm PAH emission (F200W – F335M > 0) correspond to sources with E(B − V) > 3, which are typically missed in UV-optical studies. This underscores the importance of deep near-infrared imaging for finding and characterizing these very young and dust-embedded sources.

A new perspective on the stellar mass-metallicity relation of quiescent galaxies from the LEGA-C survey

We investigated the stellar mass-metallicity relation (MZR) using a sample of 637 quiescent galaxies with 10.4 ≤ log(M*/M⊙) &lt; 11.7 selected from the LEGA-C survey at 0.6 ≤ z ≤ 1. We derived mass-weighted stellar metallicities using full-spectral fitting. We find that while lower-mass galaxies are both metal-rich and metal-poor, there are no metal-poor galaxies at high masses, and that metallicity is bounded at low values by a mass-dependent lower limit. This lower limit increases with mass, empirically defining a MEtallicity-Mass Exclusion (MEME) zone. We find that the spectral index MgFe ≡ √Mgb × Fe4383, a proxy for the stellar metallicity, also shows a mass-dependent lower limit resembling the MEME relation. Crucially, MgFe is independent of stellar population models and fitting methods. By constructing the metallicity enrichment histories, we find that, after the first gigayear, the star formation history of galaxies has a mild impact on the observed metallicity distribution. Finally, from the average formation times, we find that galaxies populate differently the metallicity-mass plane at different cosmic times, and that the MEME limit is recovered by galaxies that formed at z ≥ 3. Our work suggests that the stellar metallicity of quiescent galaxies is bounded by a lower limit which increases with the stellar mass. On the other hand, low-mass galaxies can have metallicities as high as galaxies ∼1 dex more massive. This suggests that, at log(M*/M⊙)≥10.4, rather than lower-mass galaxies being systematically less metallic, the observed MZR might be a consequence of the lack of massive metal-poor galaxies.

JWST Observations of Starbursts: Massive Star Clusters in the Central Starburst of M82

We present a near-infrared (NIR) candidate star cluster catalog for the central kiloparsec of M82 based on new JWST NIRCam images. We identify star cluster candidates using the F250M filter, finding 1357 star cluster candidates with stellar masses >104 M ⊙. Compared to previous optical catalogs, nearly all (87%) of the candidates we identify are new. The star cluster candidates have a median intrinsic cluster radius of ≈1 pc and stellar masses up to 106 M ⊙. By comparing the color–color diagram to dust-free yggdrasil stellar population models, we estimate that the star cluster candidates have A V ∼ 3−24 mag, corresponding to A 2.5μm ∼ 0.3−2.1 mag. There is still appreciable dust extinction toward these clusters into the NIR. We measure the stellar masses of the star cluster candidates, assuming ages of 0 and 8 Myr. The slope of the resulting cluster mass function is β = 1.9 ± 0.2, in excellent agreement with studies of star clusters in other galaxies.

Validating full-spectrum fitting with a synthetic integral-field spectroscopic observation of the milky way

Abstract Ongoing deep IFS observations of disk galaxies provide opportunities for comparison with the Milky Way (MW) to understand galaxy evolution. However, such comparisons are marred by many challenges such as selection effects, differences in observations and methodology, and proper validation of full-spectrum fitting methods. In this study, we present a novel code GalCraft to address these challenges by generating mock IFS data cubes of the MW using simple stellar population models and a mock MW stellar catalog derived from E-Galaxia. We use the widely adopted full-spectrum fitting code pPXF to investigate the ability to recover kinematics and stellar populations for an edge-on mock MW IFS observation. We confirm that differences in kinematics, mean age, [M/H], and [α/Fe] between thin and thick disks can be distinguished. However, the age distribution is overestimated in the ranges between 2 − 4 and 12 − 14 Gyr compared to the expected values. This is likely due to the age spacing and degeneracy of SSP templates. We find systematic offsets in the recovered kinematics due to insufficient spectral resolution and the variation of line-of-sight velocity distribution with age and [M/H]. With future higher resolution and multi-[α/Fe] SSP templates, GalCraft will be useful to validate key signatures such as [α/Fe]-[M/H] distribution at different R and |z| and potentially infer radial migration and kinematic heating efficiency to study detailed chemodynamical evolution of MW-like galaxies.

Physical properties of strong 1 &lt; z &lt; 3 Balmer and Paschen line emitters observed with JWST

Context. The ultraviolet continuum traces young stars while the near-infrared unveils older stellar populations and dust-obscured regions. Balmer emission lines provide insights into gas properties and young stellar objects but are highly affected by dust attenuation. The near-infrared Paschen lines suffer less dust attenuation and can be used to measure star formation rates (SFRs) in star-forming regions obscured by dust clouds. Aims. We present a new way of combining spectro-photometric data in order to test the robustness of the SFRs and stellar mass estimates of star-forming sources observed with JWST. We also aim to quantify the amount of differential attenuation between the interstellar medium and the birth clouds with the use of Paschen emission lines. Methods. We select 13 sources between redshifts 1 and 3 observed with HST, JWST/NIRCam and NIRSpec based on the availability of at least one Balmer and one Paschen line with S/N ≥ 5. With a newly developed version of CIGALE, we fit their hydrogen line equivalent widths (EWs) and photometric data. We assess the impacts of the removal of spectroscopic data by comparing the quality of the fits of the spectro-photometric data to those with photometric data only. We compare the single (BC03) vs binary (BPASS) stellar population models in the fitting process of spectro-photometric data. We derive the differential attenuation and explore different attenuation recipes by fitting spectro-photometric data with BC03. For each stellar model and for each input dataset (with and without EWs), we quantify the deviation on the SFRs and stellar masses from the “standard” choice. Results. The combination of spectro-photometric data provides robust constraints on the physical properties of galaxies, with a significant reduction in the uncertainties compared to using only photometric data. On average, the SFRs are overestimated and the stellar masses are underestimated when EWs are not included as input data. We find a major contribution of the Hα emission line to the broadband photometric measurements of our sources, and a trend of increasing contribution with specific SFR. Using the BPASS models has a significant impact on the derived SFRs and stellar masses, with SFRs being higher by an average of 0.13 dex and stellar masses being lower by an average of 0.18 dex compared to BC03. We show that a flexible attenuation recipe provides more accurate estimates of the dust attenuation parameters, especially the differential attenuation. Finally, we reconstruct the total effective attenuation curves of the most dust-obscured galaxies in our sample.

Mg/Fe] and variable initial mass function: Revision of [α/Fe] for massive galaxies

Observations of nearby massive galaxies have revealed that they are older and richer in metals and magnesium than their low-mass counterparts. In particular, the overabundance of magnesium compared to iron, [Mg/Fe], is interpreted to reflect the short star formation history that the current massive galaxies underwent early in the Universe. We present a systematic revision of the [Mg/Fe] – velocity dispersion (σ) relation based on stacked spectra of early-type galaxies with a high signal-to-noise ratio from the Sloan Digital Sky Survey. Using the penalized pixel-fitting (pPXF) method and the MILES single stellar population models, we fit a wide optical wavelength range to measure the net α-abundance. The combination of pPXF and α-enhanced MILES models incorrectly leads to an apparently decreasing trend of [α/Fe] with velocity dispersion. We interpret this result as a consequence of variations in the individual abundances of the different α-elements. This warrants caution for a naive use of full spectral fitting algorithms paired with stellar population models that do not take individual elemental abundance variations into account, especially when deriving averaged quantities such as the mean [α/Fe] of a stellar population. In addition, and based on line-strength measurements, we quantify the impact of a non-universal initial mass function on the recovered abundance pattern of galaxies. In particular, we find that a simultaneous fit of the slope of the initial mass function and the [Mg/Fe] results in a shallower [Mg/Fe]–σ relation. Therefore, our results suggest that star formation in massive galaxies lasted longer than what has been reported previously, although it still occurred significantly faster than in the solar neighbourhood.

Age of Massive Galaxies at Redshift 8

Recent James Webb Space Telescope data analyses have shown that massive red galaxies existed at redshifts z ≳ 6, a discovery that is difficult to understand in the context of standard cosmology (ΛCDM). Here, we analyze these observations more deeply, by fitting a stellar population model to the optical and near-infrared photometric data. These fits include a main stellar population in addition to a residual younger population and with the same extinction for both (a lower extinction for the younger population is unphysical). Extra stellar populations or the inclusion of an active galactic nucleus component do not significantly improve the fits. These galaxies are being viewed at very high redshifts, with an average 〈z〉 ≈ 8.2, when the ΛCDM Universe was only ≈600 Myr old. This result conflicts with the inferred ages of these galaxies, however, which were on average between 0.9 and 2.4 Gyr old within a 95% confidence level. Given the sequence of star formation and galaxy assembly in the standard model, these galaxies should instead be even younger than 290 Myr on average, for which our analysis assigns a probability of only <3 × 10−4 (≳3.6σ tension). This outcome may indicate the need to consider nonstandard cosmologies. Nevertheless, our conclusions result from several approximations in stellar astrophysics and extinction, so they should be taken with a grain of salt. Further research is necessary to corroborate the possible existence of galaxies older than the ΛCDM Universe at their observed redshifts.

The nature of diffuse ionized gas in star-forming galaxies

ABSTRACT We present an analysis of the diffuse ionized gas (DIG) in a high-resolution simulation of an isolated Milky Way-like galaxy, incorporating on-the-fly radiative transfer and non-equilibrium thermochemistry. We utilize the Monte-Carlo radiative transfer code colt to self-consistently obtain ionization states and line emission in post-processing. We find a clear bimodal distribution in the electron densities of ionized gas ($n_{\rm e}$), allowing us to define a threshold of $n_{\rm e}=10\, \mathrm{cm}^{-3}$ to differentiate DIG from ${\rm H\, {\small II}}$ regions. The DIG is primarily ionized by stars aged 5 – 25 Myr, which become exposed directly to low-density gas after ${\rm H\, {\small II}}$ regions have been cleared. Leakage from recently formed stars ($\lt 5$ Myr) is only moderately important for DIG ionization. We forward model local observations and validate our simulated DIG against observed line ratios in [${\rm S\, {\small II}}$]/H$\alpha$, [${\rm N\, {\small II}}$]/H$\alpha$, [${\rm O\, {\small I}}$]/H$\alpha$, and [${\rm O\, {\small III}}$]/H$\beta$ against $\Sigma _{\rm H\alpha }$. The mock observations not only reproduce observed correlations, but also demonstrate that such trends are related to an increasing temperature and hardening ionizing radiation field with decreasing $n_{\rm e}$. The hardening of radiation within the DIG is caused by the gradual transition of the dominant ionizing source with decreasing $n_{\rm e}$ from 0 to 25 Myr stars, which have progressively harder intrinsic ionizing spectra primarily due to the extended Wolf–Rayet phase caused by binary interactions. Consequently, the DIG line ratio trends can be attributed to ongoing star formation, rather than secondary ionization sources, and therefore present a potent test for stellar feedback and stellar population models.

No Top-heavy Stellar Initial Mass Function Needed: The Ionizing Radiation of GS9422 Can Be Powered by a Mixture of an Active Galactic Nucleus and Stars

JWST is producing high-quality rest-frame optical and UV spectra of faint galaxies at z > 4 for the first time, challenging models of galaxy and stellar populations. One galaxy recently observed at z = 5.943, GS9422, has nebular line and UV continuum emission that appears to require a high ionizing photon production efficiency. This has been explained with an exotic stellar initial mass function (IMF; Cameron et al. 2023a), 10–30x more top-heavy than a Salpeter IMF. Here we suggest an alternate explanation to this exotic IMF. We use a new flexible neural net emulator for CLOUDY, Cue, to infer the shape of the ionizing spectrum directly from the observed emission line fluxes. By describing the ionizing spectrum with a piecewise power law, Cue is agnostic to the source of the ionizing photons. Cue finds that the ionizing radiation from GS9422 can be approximated by a double power law characterized by QHeIIQH=−1.5 , which can be interpreted as a combination of young, metal-poor stars and a low-luminosity active galactic nucleus with F ν ∝ λ 2 in a 65%/35% ratio. This suggests a significantly lower nebular continuum contribution to the observed UV flux (24%) than a top-heavy IMF (≳80%), and hence, necessitates a damped Lyα absorber to explain the continuum turnover bluewards of ∼1400 Å. While current data cannot rule out either scenario, given the immense impact the proposed top-heavy IMF would have on models of galaxy formation, it is important to propose viable alternative explanations and to further investigate the nature of peculiar high-z nebular emitters.

Understanding stellar populations in thin and thick discs of edge-on galaxies with MUSE – I. The case of the reignited S0 galaxy ESO 544-27

ABSTRACT Edge-on galaxies act as the best laboratories to understand the origin of thin and thick discs in galaxies. Measurement of spatially resolved stellar population properties in such galaxies, particularly age, metallicity, and [α/Fe], are crucial to understanding the formation and evolution of disc galaxies. Such measurements are made possible from stellar population model fits to deep integral field spectroscopic (IFU) observations of resolved galaxies. We utilize archival MUSE IFU observations of the edge-on galaxy ESO 544-27 to uncover the formation history of its thin and thick discs through its stellar populations. We find the thin disc of the galaxy is dominated by an old (&amp;gt;9 Gyr) low [α/Fe] metal-rich stellar population. Its outer thick disc is dominated by an old (&amp;gt;9 Gyr) high [α/Fe] metal-rich component that should have formed with higher star formation efficiency than the Milky Way thick disc. We thus find [α/Fe] dichotomy in ESO 544-27 with its thin and thick discs dominated by low and high [α/Fe] stellar populations, respectively. However, we also find a metal-rich younger (&amp;lt;2 Gyr old) stellar population in ESO 544-27. The galaxy was nearly quenched until its star formation was reignited recently first in the outer and inner thick disc (∼1 Gyr ago) and then in the thin disc (∼600 Myr ago). We thus find that both the low [α/Fe] thin and high [α/Fe] thick discs of ESO 544-27 are inhabited primarily by similarly old metal-rich stellar populations, a contrast to that of other galaxies with known thin and thick disc stellar population properties.

The miniJPAS survey: Evolution of luminosity and stellar mass functions of galaxies up to z~0.7

We aim to develop a robust methodology for constraining the luminosity and stellar mass functions (LMFs) of galaxies by solely using photometric measurements from multi-filter imaging surveys. We test the potential of these techniques for determining the evolution of these functions up to $z 0.7$ in the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS), which will image thousands of square degrees in the northern hemisphere with an unprecedented photometric system that includes $54$ narrow band filters. As J-PAS is still an ongoing survey, we used the miniJPAS dataset (a stripe of $1$ deg$^2$ dictated according to the J-PAS strategy) for determining the LMFs of galaxies at $0.05 z 0.7$. Stellar mass and $B$-band luminosity for each of the miniJPAS galaxies are constrained using an updated version of our fitting code for spectral energy distribution, MUlti-Filter FITting (MUFFIT), whose values are based on non-parametric composite stellar population models and the probability distribution functions of the miniJPAS photometric redshifts. Galaxies are classified according to their star formation activity through the stellar mass versus rest-frame colour diagram corrected for extinction (MCDE) and we assign a probability to each source of being a quiescent or star-forming galaxy. Different stellar mass and luminosity completeness limits are set and parametrised as a function of redshift, for setting the limitations of our flux-limited sample ($r_ SDSS 22$) for the determination of the miniJPAS LMFs. The miniJPAS LMFs are parametrised according to Schechter-like functions via a novel maximum likelihood method accounting for uncertainties, degeneracies, probabilities, completeness, and priors. Overall, our results point to a smooth evolution with redshift ($0.05 z 0.7$) of the miniJPAS LMFs, which is in agreement with previous studies. The LMF evolution of star-forming galaxies mainly involve the bright and massive ends of these functions, whereas the LMFs of quiescent galaxies also exhibit a non-negligible evolution in their faint and less massive ends. The cosmic evolution of the global $B$-band luminosity density decreases by $ 0.1$ dex from $z=0.7$ to $0.05$; whereas for quiescent galaxies, this quantity roughly remains constant. In contrast, the stellar mass density increases by $ dex in the same redshift range, where the evolution is mainly driven by quiescent galaxies, owing to an overall increase in the number of this type of galaxy. In turn, this covers the majority and most massive galaxies, namely, $60$--$100$&lt;!PCT!&gt; of galaxies at $ (M_