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Register a new userA novel approach to investigate chemical inhomogeneities in GRB host galaxies: The $Z_{rm abs} - Z_{rm emiss}$ relation
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Models of chemical enrichment and inhomogeneity in high-redshift galaxies are challenging to constrain observationally. In this work, we discuss a novel approach to probe chemical inhomogeneities within long Gamma-Ray Burst (GRB) host galaxies, by comparing the absorption metallicity, Z_abs, from the GRB afterglow (which probes the environment along the line of sight) with the emission-line metallicity, Z_emiss, measured via slit spectroscopy. Using the IllustrisTNG simulation, the theoretical relationship between these metallicity metrics is explored for a range of GRB formation models, varying the GRB progenitor metallicity threshold. For galaxies with fixed Z_emiss, the median value of Z_abs depends strongly on the GRB progenitor threshold metallicity, with Z_abs significantly lower than Z_emiss for high metallicity hosts. Conversely, at fixed Z_abs, the median value of Z_emiss depends primarily on the metallicity distribution of galaxies in IllustrisTNG and their chemical inhomogeneities, offering a GRB-model-independent way to constrain these processes observationally. Currently, only one host galaxy has data for both absorption and emission metallicities (GRB121014A). We re-analyse the emission spectrum and compare the inferred metallicity Z_emiss to a recent Bayesian determination of Z_abs, finding $log(Z_{rm emiss}/Z_{odot}) = log(Z_{rm abs}/Z_{odot}) +0.35^{+ 0.14}_{- 0.25}$, within ~2 standard deviations of predictions from the IllustrisTNG simulation. Future observations with the James Webb Space Telescope will be able to measure Z_emiss for 4 other GRB hosts with known Z_abs values, using ~2 hour observations. While small, the sample will provide preliminary constraints on the Z_abs-Z_emiss relation to test chemical enrichment schemes in cosmological simulations.
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We try to identify the nature of high redshift long Gamma-Ray Bursts (LGRBs) host galaxies by comparing the observed abundance ratios in the interstellar medium with detailed chemical evolution models accounting for the presence of dust. We compared measured abundance data from LGRB afterglow spectra to abundance patterns as predicted by our models for different galaxy types. We analysed in particular [X/Fe] abundance ratios (where X is C, N, O, Mg, Si, S, Ni, Zn) as functions of [Fe/H]. Different galaxies (irregulars, spirals, ellipticals) are, in fact, characterised by different star formation histories, which produce different [X/Fe] ratios (time-delay model). This allows us to identify the morphology of the hosts and to infer their age (i.e. the time elapsed from the beginning of star formation) at the time of the GRB events, as well as other important parameters. Relative to previous works, we use newer models in which we adopt updated stellar yields and prescriptions for dust production, accretion and destruction. We have considered a sample of seven LGRB host galaxies. Our results have suggested that two of them (GRB 050820, GRB 120815A) are ellipticals, two (GRB 081008, GRB 161023A) are spirals and three (GRB 050730, GRB 090926A, GRB 120327A) are irregulars. We also found that in some cases changing the initial mass function can give better agreement with the observed data. The calculated ages of the host galaxies span from the order of 10 Myr to little more than 1 Gyr.
We report the detection of HI 21 cm absorption from the $z=2.289$ damped Lyman-$alpha$ system (DLA) towards TXS 0311+430, with the Green Bank Telescope. The 21 cm absorption has a velocity spread (between nulls) of $sim 110$ km s$^{-1}$ and an integrated optical depth of $int tau {rm d}V = (0.818 pm 0.085)$ km s$^{-1}$. We also present new Giant Metrewave Radio Telescope 602 MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA HI column density of hi = $(2 pm 0.5) times 10^{20}$ cm, yields a spin temperature of $T_s = (138 pm 36)$ K, assuming a covering factor of unity. This is the first case of a low spin temperature ($< 350$ K) in a $z > 1$ DLA and is among the lowest ever measured in any DLA. Indeed, the $T_s$ measured for this DLA is similar to values measured in the Milky Way and local disk galaxies. We also determine a lower limit (Si/H) $gtrsim 1/3$ solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low redshift correlations, the low $T_s$, large 21 cm absorption width and high metallicity all suggest that the $z sim 2.289$ DLA is likely to arise in a massive, luminous disk galaxy.
The scatter (${rmsigma_{text{sSFR}}}$) of the specific star formation rates (sSFRs) of galaxies is a measure of the diversity in their star formation histories (SFHs) at a given mass. In this paper we employ the EAGLE simulations to study the dependence of the ${rm sigma_{text{sSFR}}}$ of galaxies on stellar mass (${rm M_{star}}$) through the ${rm sigma_{text{sSFR}}}$-${rm M_{star}}$ relation in $ {rm z sim 0-4}$. We find that the relation evolves with time, with the dispersion depending on both stellar mass and redshift. The models point to an evolving U-shape form for the ${rm sigma_{text{sSFR}}}$-${rm M_{star}}$ relation with the scatter being minimal at a characteristic mass $M^{star}$ of ${rm 10^{9.5}}$ ${rm M_{odot}}$ and increasing both at lower and higher masses. This implication is that the diversity of SFHs increases towards both at the low- and high-mass ends. We find that active galactic nuclei feedback is important for increasing the ${rm sigma_{text{sSFR}}}$ for high mass objects. On the other hand, we suggest that SNe feedback increases the ${rm sigma_{text{sSFR}}}$ of galaxies at the low-mass end. We also find that excluding galaxies that have experienced recent mergers does not significantly affect the ${rm sigma_{text{sSFR}}}$-${rm M_{star}}$ relation. Furthermore, we employ the combination of the EAGLE simulations with the radiative transfer code SKIRT to evaluate the effect of SFR/stellar mass diagnostics in the ${rm sigma_{text{sSFR}}}$-${rm M_{star}}$ relation and find that the ${rm SFR/M_{star}}$ methodologies (e.g. SED fitting, UV+IR, UV+IRX-$beta$) widely used in the literature to obtain intrinsic properties of galaxies have a large effect on the derived shape and normalization of the ${rm sigma_{text{sSFR}}}$-${rm M_{star}}$ relation.
ALMA observations of $z>6$ galaxies have revealed abnormally high [OIII]$_{rm 88mu m}$/[CII]$_{rm 158mu m}$ ratios and [CII] deficits compared to local galaxies. The origin of this behaviour is unknown. Numerous solutions have been proposed including differences in C and O abundance ratios, observational bias, and differences in ISM properties, including ionisation parameter, gas density, or PDR covering fraction. In order to elucidate the underlying physics that drives this high-redshift phenomenon, we employ SPHINX$^{20}$, a state-of-the-art, cosmological radiation-hydrodynamics simulation, that resolves detailed ISM properties of thousands of galaxies in the epoch of reionization. We find that the observed $z>6$ [OIII]-SFR and [CII]-SFR relations can only be reproduced when the C/O abundance ratio is $sim8times$ lower than Solar and the total metal production is $sim5.7times$ higher than that of a Kroupa IMF. This implies that high-redshift galaxies are potentially primarily enriched by low-metallicity core-collapse supernovae with a more top-heavy IMF. As AGB stars and type-Ia supernova begin to contribute to the galaxy metallicity, both the [CII]-SFR and [CII] luminosity functions are predicted to converge to observed values at $zsim4.5$. While we demonstrate that ionisation parameter, LyC escape fraction, and CMB attenuation all drive galaxies towards higher [OIII]/[CII], observed values at $z>6$ can only be reproduced with substantially lower C/O abundances compared to Solar. The combination of [CII] and [OIII] can be used to predict the values of ionisation parameter, ISM gas density, and LyC escape fraction. We provide estimates of these quantities for nine observed $z>6$ galaxies. Finally, we demonstrate that [OI]$_{rm 63mu m}$ can be used as a replacement for [CII] when [CII] is unobserved and argue that more observation time should be used to target [OI] at $z>6$.
[Abridged] We investigate the nature of the relations between black hole (BH) mass ($M_{rm BH}$) and the central velocity dispersion ($sigma$) and, for core-Sersic galaxies, the size of the depleted core ($R_{rm b}$). Our sample of 144 galaxies with dynamically determined $M_{rm BH}$ encompasses 24 core-Sersic galaxies, thought to be products of gas-poor mergers, and reliably identified based on high-resolution HST imaging. For core-Sersic galaxies -- i.e., combining normal-core ($R_{rm b} < 0.5 $ kpc) and large-core galaxies ($R_{rm b} gtrsim 0.5$ kpc), we find that $M_{rm BH}$ correlates remarkably well with $R_{rm b}$ such that $M_{rm BH} propto R_{rm b}^{1.20 pm 0.14}$ (rms scatter in log $M_{rm BH}$ of $Delta_{rm rms} sim 0.29$ dex), confirming previous works on the same galaxies except three new ones. Separating the sample into Sersic, normal-core and large-core galaxies, we find that Sersic and normal-core galaxies jointly define a single log-linear $M_{rm BH}-sigma$ relation $M_{rm BH} propto sigma^{ 4.88 pm 0.29}$ with $Delta_{rm rms} sim 0.47$ dex, however, at the high-mass end large-core galaxies (four with measured $M_{rm BH}$) are offset upward from this relation by ($2.5-4) times sigma_{rm s}$, explaining the previously reported steepening of the $M_{rm BH}-sigma$ relation for massive galaxies. Large-core spheroids have magnitudes $M_{V} le -23.50$ mag, half-light radii Re $>$ 10 kpc and are extremely massive $M_{*} ge 10^{12}M_{odot}$. Furthermore, these spheroids tend to host ultramassive BHs ($M_{rm BH} ge 10^{10}M_{odot}$) tightly connected with their $R_{rm b}$ rather than $sigma$. The less popular $M_{rm BH}-R_{rm b}$ relation exhibits $sim$ 62% less scatter in log $M_{rm BH}$ than the $M_{rm BH}- sigma$ relations.
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