arXiv subjects

K. Z. Arellano-Córdova

Publications and source records attributed to K. Z. Arellano-Córdova.

30 records · Page 2Linked to original sources

arXiv2024

The JWST-PRIMAL Legacy Survey. A JWST/NIRSpec reference sample for the physical properties and Lyman-$α$ absorption and emission of $\sim 500$ galaxies at $z=5.5-13.4$

One of the surprising early findings with JWST has been the discovery of a strong "roll-over" or a softening of the absorption edge of Ly$α$ in a large number of galaxies at ($z\gtrsim 6$), in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as damped Ly$α$ absorption (DLA) wings from high column densities of neutral atomic hydrogen (HI), signifying major gas accretion events in the formation of these galaxies. To explore this new phenomenon systematically, we assemble the JWST/NIRSpec PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 494 galaxies at $z=5.5-13.4$. We characterize this benchmark sample in full and spectroscopically derive the galaxy redshifts, metallicities, star-formation rates, and ultraviolet slopes. We define a new diagnostic, the Ly$α$ damping parameter $D_{\rm Lyα}$ to measure and quantify the Ly$α$ emission strength, HI fraction in the IGM, or local HI column density for each source. The JWST-PRIMAL survey is based on the spectroscopic DAWN JWST Archive (DJA-Spec). All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. The fraction of strong galaxy DLAs are found to be in the range $65-95\%$ at $z>5.5$. The fraction of strong Ly$α$ emitters (LAEs) is found to increase with decreasing redshift, in qualitative agreement with previous observational results, and are predominantly associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine HI gas accretion. [abridged]

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arXiv2023

Constraining stellar and orbital co-evolution through ensemble seismology of solar-like oscillators in binary systems -- A census of oscillating red-giants and main-sequence stars in Gaia DR3 binaries

Binary systems constitute a valuable astrophysics tool for testing our understanding of stellar structure and evolution. Systems containing a oscillating component are interesting as asteroseismology offers independent parameters for the oscillating component that aid the analysis. About 150 of such systems are known in the literature. To enlarge the sample of these benchmark objects, we crossmatch the Two-Body-Orbit Catalogue (TBO) of Gaia DR3, with catalogs of confirmed solar-like oscillators on the main-sequence and red-giant phase from NASA Kepler and TESS. We obtain 954 new binary system candidates hosting solar-like oscillators, of which 45 and 909 stars are on the main sequence and red-giant, resp., including 2 new red giants in eclipsing systems. 918 oscillators in potentially long-periodic systems are reported. We increase the sample size of known solar-like oscillators in binary systems by an order of magnitude. We present the seismic properties of the full sample and conclude that the grand majority of the orbital elements in the TBO is physically reasonable. 82% of all TBO binary candidates with multiple times with APOGEE are confirmed from radial-velocity measurement. However, we suggest that due to instrumental noise of the TESS satellite the seismically inferred masses and radii of stars with $ν_\textrm{max}$$\lesssim$30$μ$Hz could be significantly overestimated. For 146 giants the seismically inferred evolutionary state has been determined and shows clear differences in their distribution in the orbital parameters, which are accounted the accumulative effect of the equilibrium tide acting in these evolved binary systems. For other 146 systems hosting oscillating stars values for the orbital inclination were found in the TBO. From testing the TBO on the SB9 catalogue, we obtain a completeness factor of 1/3.

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arXiv2023

Density biases and temperature relations for DESIRED HII regions

We present a first study based on the analysis of the DEep Spectra of Ionized REgions Database (DESIRED). This is a compilation of 190 high signal-to-noise ratio optical spectra of HII regions and other photoionized nebulae, mostly observed with 8-10m telescopes and containing $\sim$29380 emission lines. We find that the electron density --$n_{\rm e}$-- of the objects is underestimated when [SII] $\lambda6731/\lambda6716$ and/or [OII] $\lambda3726/\lambda3729$ are the only density indicators available. This is produced by the non-linear density dependence of the indicators in the presence of density inhomogeneities. The average underestimate is $\sim 300$ cm$^{-3}$ in extragalactic HII regions, introducing systematic overestimates of $T_{\rm e}$([OII]) and $T_{\rm e}$([SII]) compared to $T_{\rm e}$([NII]). The high-sensitivity of [OII] $λ\lambda7319+20+30+31/λ\lambda3726+29$ and [SII] $λ\lambda4069+76/λ\lambda6716+31$ to density makes them more suitable for the diagnosis of the presence of high-density clumps. If $T_{\rm e}$([NII]) is adopted, the density underestimate has a small impact in the ionic abundances derived from optical spectra, being limited to up to $\sim$0.1 dex when auroral [SII] and/or [OII] lines are used. However, these density effects are critical for the analysis of infrared fine structure lines, such as those observed by the JWST in local star forming regions, implying strong underestimates of the ionic abundances. We present temperature relations between $T_{\rm e}$([OIII]), $T_{\rm e}$([ArIII]), $T_{\rm e}$([SIII]) and $T_{\rm e}$([NII]) for the extragalactic HII regions. We confirm a non-linear dependence between $T_{\rm e}$([OIII])-$T_{\rm e}$([NII]) due to a more rapid increase of $T_{\rm e}$([OIII]) at lower metallicities.

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arXiv2022

About Metallicity Variations in the Local Galactic Interstellar Medium

In this paper we discuss and confront recent results on metallicity variations in the local interstellar medium, obtained from observations of HII regions and neutral clouds of the Galactic thin disk, and compare them with recent high-quality metallicity determinations of other tracers of the chemical composition of the interstellar medium as B-type stars, classical Cepheids and young clusters. We find that the metallicity variations obtained for these last kinds of objects are consistent with each other and with that obtained for HII regions but significantly smaller than those obtained for neutral clouds. We also discuss the presence of a large population of low-metallicity clouds as the possible origin for large metallicity variations in the local Galactic thin disk. We find that such hypothesis does not seem compatible with: (a) what is predicted by theoretical studies of gas mixing in galactic disks, and (b) the models and observations on the metallicity of high-velocity clouds and its evolution as they mix with the surrounding medium in their fall onto the Galactic plane. We conclude that that most of the evidence favors that the chemical composition of the interstellar medium in the solar neighborhood is highly homogeneous.

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arXiv2021

Gradients of chemical abundances in the Milky Way from HII regions: distances derived from Gaia EDR3 parallaxes and temperature inhomogeneities

We present a reassessment of the radial abundance gradients of He, C, N, O, Ne, S, Cl, and Ar in the Milky Way using the deep optical spectra of 42 HII regions presented in Arellano-Córdova et al. (2020, 2021) and Méndez-Delgado et al. (2020) exploring the impact of: (1) new distance determinations based on Gaia EDR3 parallaxes and (2) the use of Peimbert's temperature fluctuations paradigm ($t ^ 2> 0$) for deriving ionic abundances. We find that distances based on Gaia EDR3 data are more consistent with kinematic ones based on Galactic rotation curves calibrated with radio parallaxes, which give less dispersion and uncertainties than those calibrated with spectrophotometric stellar distances. The distances based on the Gaia parallaxes --DR2 or EDR3-- eliminate the internal flattening observed in previous determinations of the Galactic gradients at smaller distances than $\sim 7$ kpc. Abundances and gradients determined assuming $ t ^ 2> 0 $ -- not only for O but also for the rest of elements -- are not affected by the abundance discrepancy problem and give elemental abundances much consistent with the solar ones for most elements. We find that our radial abundance gradient of He is consistent with the most accurate estimates of the primordial He abundance. We do not find evidence of azimuthal variations in the chemical abundances of our sample. Moreover, the small dispersion in the O gradient -- indicator of metallicity in photoionized regions -- indicate that the gas of the HII regions is well mixed in the sampled areas of the Galaxy.

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arXiv2021

Photoionized Herbig-Haro objects in the Orion Nebula through deep high-spectral resolution spectroscopy II: HH204

We analyze the physical conditions, chemical composition and other properties of the photoionized Herbig-Haro object HH~204 through Very Large Telescope (VLT) echelle spectroscopy and Hubble Space Telescope (\textit{HST}) imaging. We kinematically isolate the high-velocity emission of HH~204 from the emission of the background nebula and study the sub-arcsecond distribution of physical conditions and ionic abundances across the HH object. We find that low and intermediate-ionization emission arises exclusively from gas at photoionization equilibrium temperatures, whereas the weak high-ionization emission from HH~204 shows a significant contribution from higher temperature shock-excited gas. We derive separately the ionic abundances of HH~204, the emission of the Orion Nebula and the fainter Diffuse Blue Layer.In HH~204, the O$^{+}$ abundance determined from Collisional Excited Lines (CELs) matches the one based on Recombination Lines (RLs), while the O$^{2+}$ abundance is very low, so that the oxygen abundance discrepancy is zero. The ionic abundances of Ni and Fe in HH~204 have similar ionization and depletion patterns, with total abundances that are a factor of 3.5 higher than in the rest of the Orion Nebula due to dust destruction in the bowshock. We show that a failure to resolve the kinematic components in our spectra would lead to significant error in the determination of chemical abundances (for instance, 40\% underestimate of O), mainly due to incorrect estimation of the electron density.

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arXiv2021

Photoionized Herbig-Haro objects in the Orion Nebula through deep high-spectral resolution spectroscopy I: HH529II and III

We present the analysis of physical conditions, chemical composition and kinematic properties of two bow shocks -HH529 II and HH529 III- of the fully photoionized Herbig-Haro object HH 529 in the Orion Nebula. The data were obtained with the Ultraviolet and Visual Echelle Spectrograph at the 8.2m Very Large Telescope and 20 years of Hubble Space Telescope imaging. We separate the emission of the high-velocity components of HH529 II and III from the nebular one, determining $n_{\rm e}$ and $T_{\rm e}$ in all components through multiple diagnostics, including some based on recombination lines (RLs). We derive ionic abundances of several ions, based on collisionally excited lines (CELs) and RLs. We find a good agreement between the predictions of the temperature fluctuation paradigm ($t^2$) and the abundance discrepancy factor (ADF) in the main emission of the Orion Nebula. However, $t^2$ can not account for the higher ADF found in HH 529 II and III. We estimate a 6% of Fe in the gas-phase of the Orion Nebula, while this value increases to 14% in HH 529 II and between 10% and 25% in HH 529 III. We find that such increase is probably due to the destruction of dust grains in the bow shocks. We find an overabundance of C, O, Ne, S, Cl and Ar of about 0.1 dex in HH 529 II-III that might be related to the inclusion of H-deficient material from the source of the HH 529 flow. We determine the proper motions of HH 529 finding multiple discrete features. We estimate a flow angle with respect to the sky plane of $58\pm 4^{\circ}$ for HH 529.

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arXiv2020

The Te[N II]-Te[O III] temperature relation in H II regions and the reliability of strong-line methods

We use a sample of 154 observations of 124 H II regions that have measurements of both Te[O III] and Te[N II], compiled from the literature, to explore the behaviour of the Te[O III]-Te[N II] temperature relation. We confirm that the relation depends on the degree of ionization and present a new set of relations for two different ranges of this parameter. We study the effects introduced by our temperature relations and four other available relations in the calculation of oxygen and nitrogen abundances. We find that our relations improve slightly on the results obtained with the previous ones. We also use a sample of 26 deep, high-resolution spectra to estimate the contribution of blending to the intensity of the temperature-sensitive line [O III] $\lambda4363$, and we derive a relation to correct Te[O III] for this effect. With our sample of 154 spectra, we analyse the reliability of the R, S, O3N2, N2, ONS, and C strong-line methods by comparing the metallicity obtained with these methods with the one implied by the direct method. We find that the strong-line methods introduce differences that reach ~ 0.2 dex or more, and that these differences depend on O/H, N/O, and the degree of ionization.

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arXiv2020

Helium abundances and its radial gradient from the spectra of HII regions and ring nebulae of the Milky Way

We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 $\text{H}\thinspace \text{II}$ regions and ring nebulae surrounding massive O stars. We revise the Galactocentric distances of the objects considering {\it Gaia} DR2 parallaxes and determine the physical conditions and the ionic abundance of He$^{+}$ in a homogeneous way, using between 3 and 10 $\text{He}\thinspace \text{I}$ recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ICF(He) schemes. The slope of the gradient is always negative and weakly dependent on the ICF(He) scheme, especially when only the objects with log($η$) $<$ 0.9 are considered. The slope values go from $-$0.0078 to $-$0.0044 dex kpc$^{-1}$, consistent with the predictions of chemical evolution models of the Milky Way and chemodynamical simulations of disc galaxies. Finally, we estimate the abundance deviations of He, O and N in a sample of ring nebulae around Galactic WR stars, finding a quite similar He overabundance of about +0.24 $\pm$ 0.11 dex in three stellar ejecta ring nebulae.

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arXiv2019

The radial abundance gradients of O, Ne, S and Cl of the Milky Way

We present preliminary results of the O, Ne, S and Cl abundance gradients of the Milky Way. We analyze in a homogenous way the physical conditions and chemical abundances of a sample of 35 H II regions with deep spectra observed mainly with the GTC and VLT telescopes. The sample covers a range in Galactocentric distances from 5 to 17 kpc. We reanalyze the O abundance gradient, obtaining a similar complex shape than previously reported in the literature. We calculate the Cl abundance gradient including a significantly larger number of objects than in previous works. Our results show a gradient for Cl/H of -0.034 dex kpc^-1 and a dispersion around the gradient of 0.14 dex. We obtain values for the Ne/H and S/H abundance gradients with slopes of -0.038 dex kpc^-1 and -0.046 dex kpc^-1, respectively, with dispersions around the gradient higher than 0.25 dex. We also report the values for the slopes of the Cl/O, Ne/O and S/O abundance ratio gradients, which show dispersions around the gradient up to 0.4 dex. Such high dispersion although may be interpreted as indications of chemical inhomogeneities in the Galactic ISM, it might be also an artifact produced by the selected ionization correction factor.

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arXiv2019

Galactic abundance gradients from deep spectra of HII regions

We present some results of an ongoing project devoted to reassess the radial abundance gradients in the disc of the MilkyWay based on deep spectroscopy of Hii regions. The data have been taken with large aperture telescopes, mainly with the GTC and VLT. The sample contains about 35 objects located at Galactocentric distances from 5 to 17 kpc. We determine the electron temperature for all nebulae, allowing the precise calculation of chemical abundances. In this paper, we present and discuss results mostly concerning the radial gradients of O, N and C.

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arXiv2015

The oxygen abundance gradient in M81 and the robustness of abundance determinations in H II regions

We study the sensitivity of the methods available for abundance determinations in H II regions to potential observational problems. We compare the dispersions they introduce around the oxygen and nitrogen abundance gradients when applied to five different sets of spectra of H II regions in the galaxy M81. Our sample contains 116 H II regions with galactocentric distances of 3 to 33 kpc, including 48 regions observed by us with the OSIRIS long-slit spectrograph at the 10.4-m Gran Telescopio Canarias telescope. The direct method can be applied to 31 regions, where we can get estimates of the electron temperature. The different methods imply oxygen abundance gradients with slopes of -0.010 to -0.002 dex kpc-1, and dispersions in the range 0.06-0.25 dex. The direct method produces the shallowest slope and the largest dispersion, illustrating the difficulty of obtaining good estimates of the electron temperature. Three of the strong-line methods, C, ONS, and N2, are remarkably robust, with dispersions of ~ 0.06 dex, and slopes in the range -0.008 to -0.006 dex kpc-1. The robustness of each method can be directly related to its sensitivity to the line intensity ratios that are more difficult to measure properly. Since the results of the N2 method depend strongly on the N/O abundance ratio and on the ionization parameter, we recommend the use of the C and ONS methods when no temperature estimates are available or when they have poor quality, although the behaviour of these methods when confronted with regions that have different properties and different values of N/O should be explored.

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