arXiv subjects

R. Amorín

Publications and source records attributed to R. Amorín.

At least 37 records · Page 2Linked to original sources

arXiv2024

The evolution of the SFR and Sigma-SFR of galaxies in cosmic morning (4 < z < 10)

The galaxy integrated star-formation rate (SFR) surface density ($Σ_{\rm SFR}$) has been proposed as a valuable diagnostic of the mass accumulation in galaxies as being more tightly related to the physics of star-formation (SF) and stellar feedback than other SF indicators. In this paper, we assemble a statistical sample of 230 galaxies observed with JWST in the GLASS and CEERS spectroscopic surveys to estimate Balmer line based dust attenuations and SFRs, and UV rest-frame effective radii. We study the evolution of galaxy SFR and $Σ_{\rm SFR}$ in the first 1.5 Billion years of our Universe, finding that $Σ_{\rm SFR}$ is mildly increasing with redshift with a linear slope of $0.16 \pm 0.06$. We also explore the dependence of SFR and $Σ_{\rm SFR}$ on stellar mass, showing that a SF 'Main-Sequence' and a $Σ_{\rm SFR}$ `Main-Sequence' are in place out to z=10, with a similar slope compared to the same relations at lower redshifts. We find that the specific SFR (sSFR) and $Σ_{\rm SFR}$ are correlated with the [OIII]5007/[OII]3727 ratio and with indirect estimates of the escape fraction of Lyman continuum photons, hence they likely play an important role in the evolution of ionization conditions and in the escape of ionizing radiation. We also search for spectral outflow signatures in a subset of galaxies observed at high resolution, finding an outflow incidence of $2/11$ ($=20\%^{32\%}_{9\%}$) at $z<6$, but no evidence at $z>6$ ($<26\%$). Finally, we find a positive correlation between A$_V$ and $Σ_{\rm SFR}$, and a flat trend as a function of sSFR, indicating that there is no evidence of a drop of A$_V$ in extremely star-forming galaxies between z=4 and 10. This might be at odds with a dust-clearing outflow scenario, which might instead take place at redshifts $z\geq 10$, as suggested by some theoretical models.

astro-ph.GA↗

arXiv2024

A $Li$ne $Me$asuring library for large and complex spectroscopic data sets: Implementation of a virtual observatory for JWST spectra

The upcoming generation of telescopes, instruments, and surveys is poised to usher in an unprecedented "Big Data" era in the field of astronomy. Within this context, even seemingly modest tasks such as spectral line analyses could become increasingly challenging for astronomers. In this paper, we announce the release of ${\rm L{\small I}M{\small E}}$. This package is tailored for multidisciplinary observations with long-slit and integral field spectroscopy (IFS) support. ${\rm L{\small I}M{\small E}}$ functions encompass the reading of observational files, detecting lines, conditioned line fitting, and the plotting and storage of results. Most importantly, these measurements are structured to support the subsequent chemical and kinematic analyses. To reduce the coding effort required from users, we introduced a notation system for atomic transitions that is accessible to humans and machine-readable. Along with this system, we present an extensive database of line bands, spanning from the ultraviolet to the infrared wavelength range. Additionally, we propose a model designed to train machine learning algorithms in line detection. ${\rm L{\small I}M{\small E}}$ features a comprehensive online documentation, which details the command attributes and includes several tutorials. These tutorials range from measuring a single line to analyzing an entire IFS data cube. This library functions and measurements are showcased in an online virtual observatory. The data in this interactive website come from the JWST NIRSpec observations of the CEERs survey. In this regard, ${\rm L{\small I}M{\small E}}$ offers improvements related to the dissemination and accessibility of astronomical spectra.

astro-ph.IM↗

arXiv2023

A MUSE/VLT spatially resolved study of the emission structure of Green Pea galaxies

Green Pea galaxies are remarkable for their intense star formation and serve as a window into the early universe. In our study, we used integral field spectroscopy to examine 24 of these galaxies in the optical spectrum. We focused on the interaction between their ionized interstellar medium and the star formation processes within them. Our research generated spatial maps of emission lines and other properties like ionization structures and chemical conditions. These maps showed that areas with higher levels of excitation are usually located where starbursts are occurring. Continuum maps displayed more intricate structures than emission line maps and hinted at low brightness ionized gas in the galaxies' outer regions. We also analyzed integrated spectra from selected areas within these galaxies to derive physical properties like electron densities and temperatures. In some galaxies, we were able to determine metallicity levels. Our observations revealed the presence of high-ionizing lines in three galaxies, two of which had extremely high rates of star formation. Our findings provide valuable insights into the properties and star-forming processes in Green Pea galaxies, contributing to our broader understanding of galactic evolution in the early universe.

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arXiv2023

New insight on the nature of cosmic reionizers from the CEERS survey

The Epoch of Reionization (EoR) began when galaxies grew in abundance and luminosity, so their escaping Lyman continuum (LyC) radiation started ionizing the surrounding neutral intergalactic medium (IGM). Despite significant recent progress, the nature and role of cosmic reionizers are still unclear: in order to define them, it would be necessary to directly measure their LyC escape fraction ($f_{esc}$). However, this is impossible during the EoR due to the opacity of the IGM. Consequently, many efforts at low and intermediate redshift have been made to determine measurable indirect indicators in high-redshift galaxies so that their $f_{esc}$ can be predicted. This work presents the analysis of the indirect indicators of 62 spectroscopically confirmed star-forming galaxies at $6 \leq z \leq 9$ from the Cosmic Evolution Early Release Science (CEERS) survey, combined with 12 sources with public data from other JWST-ERS campaigns. From the NIRCam and NIRSpec observations, we measured their physical and spectroscopic properties. We discovered that on average $6<z<9$ star-forming galaxies are compact in the rest-frame UV ($r_e \sim $ 0.4 kpc), are blue sources (UV-$β$ slope $\sim $ -2.17), and have a predicted $f_{esc}$ of about 0.13. A comparison of our results to models and predictions as well as an estimation of the ionizing budget suggests that low-mass galaxies with UV magnitudes fainter than $M_{1500} = -18$ that we currently do not characterize with JWST observations probably played a key role in the process of reionization.

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arXiv2023

Ionized gas kinematics and chemical abundances of low-mass star-forming galaxies at $z\sim 3$

We selected 35 low-mass SFGs (7.9 1000Å and EW(CIII])>5Å, closely resembling those now seen in EoR galaxies with JWST. We find low gas-phase metallicities 12+log(O/H)~7.5-8.5 and C/O abundances from 23%-128% solar, with no apparent increasing trend with metallicity. From our [OIII]4959,5007 profile modeling, we find that 65% of our sample shows an outflow component, which is shifted relative to the ionized gas systemic velocity, with mean $v_{max}$~280 km/s which correlates with the $Σ_{SFR}$. We find that the mass-loading factor $μ$ of our sample is typically lower than in more massive galaxies from literature but higher than in typical local dwarf galaxies. In the stellar mass range covered, we find that $μ$ increases with $Σ_{SFR}$ thus suggesting that for a given stellar mass, denser starbursts in low-mass galaxies produce stronger outflows. Our results complement the picture drawn by similar studies at lower redshift, suggesting that the removal of ionized gas in low-mass SFGs driven by stellar feedback is regulated by their stellar mass and by the strength and concentration of their star formation, i.e. $Σ_{\rm SFR}$.

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arXiv2023

The VANDELS survey: the ionizing properties of star-forming galaxies at $3 \leq z \leq 5$ using deep rest-frame ultraviolet spectroscopy

To better understand the ionizing properties of galaxies in the EoR, we investigate deep, rest-frame ultraviolet (UV) spectra of $\simeq 500$ star-forming galaxies at $3 \leq z \leq 5$ selected from the public ESO-VANDELS spectroscopic survey. The absolute ionizing photon escape fraction ($f_{\rm esc}^{\rm abs}$) is derived by combining absorption line measurements with estimates of the UV attenuation. The ionizing production efficiency ($ξ_{ion}$) is calculated by fitting the far-UV (FUV) stellar continuum of the VANDELS galaxies. We find that the $f_{\rm esc}^{\rm abs}$ and $ξ_{ion}$ parameters increase towards low-mass, blue UV-continuum slopes and strong Ly$α$ emitting galaxies, and both are just slightly higher-than-average for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters (LCEs) and selected Lyman Alpha Emitters (LAEs) show systematically higher $ξ_{ion}$ ($\log ξ_{ion}$ (Hz\erg) $\approx 25.38, 25.41$) than non-LCEs and non-LAEs ($\log ξ_{ion}$ (Hz\erg) $\approx 25.18, 25.14$) at similar UV magnitudes. This indicates very young underlying stellar populations ($\approx 10~{\rm Myr}$) at relatively low metallicities ($\approx 0.2~{\rm Z_{\odot}}$). The FUV non-ionizing spectra of potential LCEs is characterized by very blue UV slopes ($\leq -2$), enhanced Ly$α$ emission ($\leq -25$A), strong UV nebular lines (e.g., high CIV1550/CIII]1908 $\geq 0.75$ ratios), and weak absorption lines ($\leq 1$A). The latter suggests the existence of low gas-column-density channels in the interstellar medium which enables the escape of ionizing photons. By comparing our VANDELS results against other surveys in the literature, our findings imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass and dustless galaxies.

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arXiv2023

Insights into the reionization epoch from cosmic-noon-CIV emitters in the VANDELS survey

Recently, intense emission from nebular C III] and C IV emission lines have been observed in galaxies in the epoch of reionization ($z>6$) and have been proposed as the prime way of measuring their redshift and studying their stellar populations. These galaxies might represent the best examples of cosmic reionizers, as suggested by recent low-z observations of Lyman Continuum emitting galaxies, but it is hard to directly study the production and escape of ionizing photons at such high redshifts. The ESO spectroscopic public survey VANDELS offers the unique opportunity to find rare examples of such galaxies at cosmic noon ($z\sim 3$), thanks to the ultra deep observations available. We have selected a sample of 39 galaxies showing C IV emission, whose origin (after a careful comparison to photoionization models) can be ascribed to star formation and not to AGN. By using a multi-wavelength approach, we determine their physical properties including metallicity and ionization parameter and compare them to the properties of the parent population to understand what are the ingredients that could characterize the analogs of the cosmic reionizers. We find that C IV emitters are galaxies with high photons production efficiency and there are strong indications that they might have also large escape fraction: given the visibility of C IV in the epoch of reionization this could become the best tool to pinpoint the cosmic reioinzers.

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arXiv2022

Spatially-resolved properties of the ionized gas in the HII galaxy J084220+115000

We present a spatially resolved spectroscopic study for the metal poor HII galaxy J084220+115000 using MEGARA Integral Field Unit observations at the Gran Telescopio Canarias. We estimated the gas metallicity using the direct method for oxygen, nitrogen and helium and found a mean value of 12+$\log$(O/H)=$8.03\pm$0.06, and integrated electron density and temperature of $\sim161$ cm$^{-3}$ and $\sim15400$ K, respectively. The metallicity distribution shows a large range of $Δ$(O/H) = 0.72 dex between the minimum and maximum (7.69$\pm$0.06 and 8.42$\pm$0.05) values, unusual in a dwarf star-forming galaxy. We derived an integrated $\log$(N/O) ratio of $-1.51\pm0.05$ and found that both N/O and O/H correspond to a primary production of metals. Spatially resolved maps indicate that the gas appears to be photoionized by massive stars according to the diagnostic line ratios. Between the possible mechanisms to explain the starburst activity and the large variation of oxygen abundance in this galaxy, our data support a possible scenario where we are witnessing an ongoing interaction triggering multiple star-forming regions localized in two dominant clumps.

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arXiv2022

Strong C IV emission from star-forming galaxies: a case for high Lyman continuum photon escape

Finding reliable indicators of Lyman continuum (LyC) photon leakage from galaxies is essential in order to infer their escape fraction in the epoch of reionisation, where direct measurements of LyC flux are impossible. To this end, here we investigate whether strong C IV $λλ1548,1550$ emission in the rest-frame UV spectra of galaxies traces conditions ripe for ample production and escape of LyC photons. We compile a sample of 19 star-forming galaxies in the redshift range $z=3.1-4.6$ from the VANDELS survey that exhibit strong C IV emission, producing a stacked spectrum where all major rest-UV emission lines are clearly detected. Best-fitting spectral energy distribution models containing both stellar and nebular emission suggest the need for low stellar metallicities ($Z=0.1-0.2\,Z_\odot$), young stellar ages ($\log(\rm{age/yr}) = 6.1-6.5$), a high ionisation parameter ($\log U = -2$) and little to no dust attenuation ($E(B-V)=0.00-0.01$). However, these models are unable to fully reproduce the observed C IV and He II line strengths. We find that the Ly$α$ line in the stacked spectrum is strong and peaks close to the systemic velocity, features that are indicative of significant LyC photon leakage along the line-of-sight. The covering fractions of low-ionisation interstellar absorption lines are also low implying LyC escape fraction in the range $\approx 0.05-0.30$, with signatures of outflowing gas. Finally, C IV/C III] ratios of >0.75 for a subset of individual galaxies with reliable detections of both lines are also consistent with physical conditions that enable significant LyC leakage. Overall, we report that multiple spectroscopic indicators of LyC leakage are present in the stacked spectrum of strong C IV emitting galaxies, potentially making C IV an important tracer of LyC photon escape at $z>6$.

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arXiv2022

Properties of the interstellar medium in star-forming galaxies at redshifts 2 < z < 5 from the VANDELS survey

Gaseous flows inside and outside galaxies are key to understanding galaxy evolution, as they regulate their star formation activity across cosmic time. We study the ISM kinematics of 330 CIII or HeII emitters, using far-UV ISM absorption lines detected in the VANDELS spectra. These galaxies span a broad range of stellar masses M$_\ast$ from $10^8$ to $10^{11}$ M$_\odot$, and SFRs from 1 to 500 M$_\odot$/yr, in the redshift range between 2 and 5. We find that the bulk ISM velocity v$_{ism}$ is globally in outflow, with v$_{ism}$ of -60 $\pm$ 10 km/s for low ionization gas traced by SiII 1260 Angstrom, CII 1334, SiII 1526, and AlII 1670, and v$_{ism}$ of -160 $\pm$ 30 and -170 $\pm$ 30 km/s for higher ionization gas traced respectively by AlIII 1854-1862 and SiIV 1393-1402. Interestingly, BPASS models are able to better reproduce the stellar continuum around the SiIV doublet than other stellar population templates. For individual galaxies, $34\%$ of the sample has a positive ISM velocity shift, almost double the fraction reported at lower redshifts. Comparing v$_{ism}$ to the host galaxies properties, we find no significant correlations with M$_\ast$ or SFR, and only a marginally significant dependence (at $\sim 2σ$) on morphology-related parameters, with slightly higher velocities in galaxies of smaller size (probed by the equivalent radius), higher concentration, and higher SFR surface density. The outflows are consistent with models of accelerating, momentum-driven winds, with densities decreasing towards the outskirts. Our moderately lower ISM velocities compared to those found in similar studies at lower redshifts suggest that inflows and internal turbulence might play an increased role at $z>2$. We estimate mass outflow rates comparable to the SFRs of the galaxies, and an average escape velocity of 625 km/s, suggesting that most of the ISM will remain bound to the galaxy halo.

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arXiv2022

The ionizing properties of two bright Ly$α$ emitters in the BDF reionized bubble at z=7

We investigate the ionizing properties of the pair of bright Ly$α$ emitting galaxies BDF521 and BDF2195 at z=7.012 in order to constrain their contribution to the formation of the BDF "reionized bubble". We obtain constraints on UV emission lines (CIV$λ1548$ doublet, HeII$λ1640$, OIII]$λ1660$ doublet, and CIII]$λ1909$ doublet) from deep VLT-XSHOOTER observations and compare them to those available for other high-redshift objects, and to models with mixed stellar and AGN emission. We use this spectroscopic information together with the photometry available in the field to constrain the physical properties of the two objects using the spectro-photometric fitting code BEAGLE. We do not detect any significant emission at the expected position of UV lines, with 3$σ$ upper limits of EW$\lesssim$2-7 AA rest-frame. We find that the two objects have lower CIII] emission than expected on the basis of the correlation between the Ly$α$ and CIII] EWs. The EW limits on CIV and HeII emission exclude pure AGN templates at $\sim2-3σ$ significance, and only models with a $\lesssim$40% AGN contribution are compatible with the observations. The two objects are found to be relatively young ($\sim$20-30 Myrs) and metal-poor ($\lesssim 0.3 Z_{\odot}$) with stellar masses of a few $10^9M_{\odot}$. Their production rate of hydrogen ionizing photons per intrinsic UV luminosity is log($ξ_{ion}^*$/Hz erg$^{-1}$)=25.02-25.26, consistent with values typically found in high-redshift galaxies, but more than twice lower than values measured in $z>$7 galaxies with strong CIII] and/or optical line emission ($\simeq$25.6-25.7). The two BDF emitters have no evidence of higher than average ionizing capabilities and are not capable of reionizing their surroundings by their own means under realistic assumptions on the escape fraction of ionizing photons. (abridged)

astro-ph.GA↗

arXiv2022

The VANDELS survey: a measurement of the average Lyman-continuum escape fraction of star-forming galaxies at z=3.5

We present a study designed to measure the average LyC escape fraction ($\langle f_{\rm esc}\rangle$) of star-forming galaxies at z=3.5. We assemble a sample of 148 galaxies from the VANDELS survey at $3.35\leq z_{\rm spec}\leq3.95$, selected to minimize line-of-sight contamination of their photometry. For this sample, we use ultra-deep, ground-based, $U-$band imaging and HST $V-$band imaging to robustly measure the distribution of $\mathcal{R_{\rm obs}}$ $=(L_{\rm LyC}/L_{\rm UV})_{\rm obs}$. We then model the distribution as a function of $\langle f_{\rm esc}\rangle$, carefully accounting for attenuation by dust, and the IGM (and CGM). A maximum likelihood fit to the $\mathcal{R_{\rm obs}}$ distribution returns a best-fitting value of $\langle f_{\rm esc}\rangle =0.07\pm0.02$, a result confirmed using an alternative Bayesian inference technique (both exclude $\langle f_{\rm esc}\rangle=0.0$ at $> 3σ$). By splitting our sample in two, we find evidence that $\langle f_{\rm esc}\rangle$ is positively correlated with Ly$α$ equivalent width, with high and low sub-samples returning best fits of $\langle f_{\rm esc}\rangle=0.12^{+0.06}_{-0.04}$ and $\langle f_{\rm esc} \rangle=0.02^{+0.02}_{-0.01}$, respectively. In contrast, we find evidence that $\langle f_{\rm esc}\rangle$ is anti-correlated with intrinsic UV luminosity and UV dust attenuation; with low UV luminosity and dust attenuation sub-samples returning best fits in the range $0.10 \leq \langle f_{\rm esc}\rangle \leq 0.22$. We do not find evidence for a clear correlation between $f_{\rm esc}$ and galaxy stellar mass, suggesting it is not a primary indicator of leakage. Although larger samples are needed to further explore these trends, they suggest that it is entirely plausible that the low dust and metallicity galaxies found at z > 6 will display the $\langle f_{\rm esc}\rangle\geq0.1$ required to drive reionization.

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arXiv2022

The VIMOS Ultra Deep Survey: The reversal of the star-formation rate $-$ density relation at $2 < z < 5$

Utilizing spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS), new observations from Keck/DEIMOS, and publicly available observations of large samples of star-forming galaxies, we report here on the relationship between the star formation rate (SFR) and the local environment ($δ_{gal}$) of galaxies in the early universe ($2<z<5$). Unlike what is observed at lower redshifts ($z<2$), we observe a definite, nearly monotonic increase in the average SFR with increasing galaxy overdensity over more than an order of magnitude in $δ_{gal}$. The robustness of this trend is quantified by accounting for both uncertainties in our measurements and galaxy populations that are either underrepresented or not present in our sample and find that the trend remains significant under all circumstances. This trend appears to be primarily driven by the fractional increase of galaxies in high density environments that are more massive in their stellar content and are forming stars at a higher rate than their less massive counterparts. We find that, even after stellar mass effects are accounted for, there remains a weak but significant SFR-$δ_{gal}$ trend in our sample implying that additional environmentally-related processes are helping to drive this trend. We also find clear evidence that the average SFR of galaxies in the densest environments increases with increasing redshift. These results lend themselves to a picture in which massive gas-rich galaxies coalesce into proto-cluster environments at $z\sim3$, interact with other galaxies or with a forming large-scale medium, subsequently using or losing most of their gas in the process, and begin to seed the nascent red sequence that is present in clusters at slightly lower redshifts.

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arXiv2022

No strong dependence of Lyman continuum leakage on physical properties of star-forming galaxies at $\mathbf{3.1 \lesssim z \lesssim 3.5}$

We present Lyman continuum (LyC) radiation escape fraction $f_{\rm{esc}}$ measurements for 183 spectroscopically confirmed star-forming galaxies in the redshift range $3.11 < z < 3.53$ in the \textit{Chandra} Deep Field South. We use ground-based imaging to measure $f_{\rm{esc}}$, and use ground- and space-based photometry to derive galaxy physical properties using spectral energy distribution (SED) fitting. We additionally derive [O III]+H$β$ equivalent widths (that fall in the observed K band) by including nebular emission in the SED fitting. After removing foreground contaminants, we report the discovery of 11 new candidate LyC leakers, with absolute LyC escape fractions, $f_{\rm{esc}}$ in the range $0.14-0.85$. From non-detections, we place $1σ$ upper limits of $f_{\rm{esc}}<0.12$, where the Lyman-break selected galaxies have $f_{\rm{esc}} < 0.11$ and `blindly' discovered galaxies with no prior photometric selection have $f_{\rm{esc}}<0.13$. We find a slightly higher $1σ$ limit of $f_{\rm{esc}}<0.20$ for extreme emission line galaxies with rest-frame [O III]+H$β$ equivalent widths $>300$A. For candidate LyC leakers, we find a weak negative correlation between $f_{\rm{esc}}$ and galaxy stellar masses, no correlation between $f_{\rm{esc}}$ specific star-formation rates (sSFRs) and a positive correlation between $f_{\rm{esc}}$ and EW$_0$([O III]+H$β$). The weak/no correlations between stellar mass and sSFRs may be explained by misaligned viewing angles and/or non-coincident timescales of starburst activity and periods of high $f_{\rm{esc}}$. Alternatively, escaping radiation may predominantly occur in highly localised star-forming regions, or $f_{\rm{esc}}$ measurements may be impacted by stochasticity of the intervening neutral medium, obscuring any global trends with galaxy properties. These hypotheses have important consequences for models of reionisation.

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arXiv2021

The VANDELS survey: global properties of CIII]$λ$1908Å emitting star-forming galaxies at z$\sim$3

We study the mean properties of a large representative sample of 217 galaxies showing CIII] emission at $2<z<4$, selected from a parent sample of $\sim$750 main-sequence star-forming galaxies in the VANDELS survey. These CIII] emitters have a broad range of UV luminosities, thus allowing a detailed stacking analysis to characterize their stellar mass, star formation rate (SFR) and stellar metallicity, as a function of the UV emission line ratios, EWs, and the carbon-to-oxygen (C/O) abundance ratio. Reliable CIII] detections represent $\sim$30% of the parent sample. Extreme CIII] emitters (EW(CIII])$\gtrsim$8Å) are exceedingly rare ($\sim$3%) in VANDELS. The UV line ratios of the sample suggest no ionization source other than massive stars. Stacks with larger EW(CIII]) show larger EW(Ly$α$) and lower metallicity, but not all CIII] emitters are Ly$α$ emitters. The stellar metallicities of CIII] emitters are not significantly different from that of the parent sample, increasing from $\sim$10% to $\sim$40% solar for stellar masses $\log$(M$_{\star}$/M$_{\odot})\sim$9-10.5. The stellar mass-metallicity relation of the CIII] emitters is consistent with previous works showing strong evolution from $z=0$ to $z\sim3$. The C/O abundances of the sample range 35%-150% solar, with a noticeable increase with FUV luminosity and a smooth decrease with the CIII] EW. We discuss the CIII] emitters in the C/O-Fe/H and the C/O-O/H planes and find they follow stellar and nebular abundance trends consistent with those of Milky Way halo and thick disc stars and local HII galaxies, respectively. A qualitative agreement is also found with chemical evolution models, which suggests that CIII] emitters at $z\sim$3 are experiencing an active phase of chemical enrichment.

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arXiv2021

New insights on the nebular emission, ionizing radiation and low metallicity of Green Peas from advanced modelling

Low-metallicity, compact starburst galaxies referred to as Green Peas (GPs) provide a unique window to study galactic evolution across cosmic epochs. In this work, we present new deep optical spectra for three GPs from OSIRIS at the 10m Gran Telescopio Canarias (GTC), which are studied using a state-of-the-art methodology. A stellar population synthesis is conducted with 1098 spectral templates. The methodology succeeds at characterising stellar populations from 0.5 Myrs to 10 Gyrs. The light distribution shows a large red excess from a single population with $log\left(age\right) > 8.5yr$ in the GP sample analysed. This points towards an incomplete characterisation of the gas luminosity, whose continuum already accounts between $7.4\%$ and $27.6\%$ in the galaxy sample. The emission spectra are fitted with the largest Bayesian chemical model consisting of a electron temperature, a electron density, the logarithmic extinction coefficient and eleven ionic species under the direct method paradigm. Additionally, building on previous work, we propose a neural networks sampler to constrain the effective temperature and ionization parameter of each source from photoionization model grids. Finally, we combine both methodologies into a 16-dimensional model, which for the first time, simultaneously explores the direct method and photoionization parameter spaces. Both techniques consistently indicate a low metallicity gas, $7.76<12+log\left(\frac{O}{H}\right)<8.04$, ionized by strong radiation fields, in agreement with previous works.

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arXiv2021

Extreme Emission-Line Galaxies in SDSS. I. Empirical and model-based calibrations of chemical abundances

Local star-forming galaxies show properties that are thought to differ from galaxies in the early Universe. Among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the Local Universe. A sample of 1969 Extreme Emission Line Galaxies (EELGs) at a redshift 0 < z < 0.49, selected from the Sloan Digital Sky Survey (SDSS) to be local analogues of high-redshift galaxies, was used to analyze their most prominent emission lines and to derive total oxygen abundances and nitrogen-to-oxygen ratios following the direct method in the ranges 7.7 < 12+log(O/H) < 8.6 and -1.8 < log(N/O) < -0.8. They allow us to obtain new empirically calibrated strong-line methods and to evaluate other recipes based on photoionization models that can be later used for a chemical analysis of actively star-forming galaxies in very early stages of galaxy evolution. Our new relations are in agreement with others found for smaller samples of objects at higher redshifts. When compared with other relations calibrated in the local Universe, they differ when the employed strong-line ratio depends on the hardness of the ionizing radiation, such as O32 or Ne3O2, but they do not when the main dependence is on the ionization parameter, such as S23. In the case of strong-line ratios depending on [NII] lines, the derivation of O/H becomes very uncertain due to the very high N/O values derived in this sample, above all in the low-metallicity regime. Finally, we adapt the bayesian-like code HII-Chi-mistry for the conditions found in this kind of galaxies and we prove that it can be used to derive within errors both O/H and N/O, in consistency with the direct method .

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arXiv2021

Measuring Chemical Abundances with Infrared Nebular Lines: HII-Chi-mistry-IR

We provide a new method to derive heavy element abundances based on the unique suite of nebular lines in the mid- to far-infrared (IR) range. Using grids of photo-ionisation models that cover a wide range in O/H and N/O abundances, and ionisation parameter, our code HII-Chi-mistry-IR (HCm-IR) provides model-based abundances based on extinction free and temperature insensitive tracers, two significant advantages over optical diagnostics. The code is probed using a sample of 56 galaxies observed with $Spitzer$ and $Herschel$ covering a wide range in metallicity, $7.2 \lesssim 12+\log(O/H) \lesssim 8.9$. The IR model-based metallicities obtained are robust within a scatter of 0.03 dex when the hydrogen recombination lines, which are typically faint transitions in the IR range, are not available. When compared to the optical abundances obtained with the direct method, model-based methods, and strong-line calibrations, HCm-IR estimates show a typical dispersion of ~0.2 dex, in line with previous studies comparing IR and optical abundances, a do not introduce a noticeable systematic above $12+\log(O/H) \gtrsim 7.6$. This accuracy can be achieved using the lines [SIV]$_{10.5 μm}$, [SIII]$_{18.7,33.5 μm}$, [NeIII]$_{15.6 μm}$ and [NeII]$_{12.8 μm}$. Additionally, HCm-IR provides an independent N/O measurement when the [OIII]$_{52,88 μm}$ and [NIII]$_{57 μm}$ transitions are measured, and therefore the derived abundances in this case do not rely on particular assumptions in the N/O ratio. Large uncertainties (~0.4 dex) may affect the abundance determinations of galaxies at sub- or over-solar metallicities when a solar-like N/O ratio is adopted. Finally, the code has been applied to 8 galaxies located at $1.8 < z < 7.5$ with ground-based detections of far-IR lines redshifted in the submm range, revealing solar-like N/O and O/H abundances in agreement with recent studies.

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