arXiv subjects

Rongjun Huang

Publications and source records attributed to Rongjun Huang.

4 recordsLinked to original sources

arXiv2026

MAUVE-MUSE: When Metallicity Follows or Fights Star Formation -- A Mass-Dependent Inversion in Virgo Galaxies

Although globally-integrated studies often find that, at fixed stellar mass, high star formation rate (SFR) galaxies are relatively metal-poor while lower-SFR systems are more metal-rich, the corresponding coupling between gas-phase metallicity ($Z_{\rm gas}$) and star formation on sub-galactic scales remains poorly constrained. In this study, we analyse 14 Virgo spirals from the MAUVE-MUSE survey to revisit the resolved mass-metallicity relation (rMZR) and its secondary dependence on SFR surface density ($\Sigma_\mathrm{SFR}$) at $\sim 100$\,pc scales. We construct co-spatial maps of stellar mass surface density ($\Sigma_*$), $\Sigma_\mathrm{SFR}$, and oxygen abundance. MAUVE-MUSE galaxies follow a standard rMZR, but when binned by $\Sigma_*$, we find a mass-dependent inversion in the $Z_\mathrm{gas}$-$\Sigma_\mathrm{SFR}$ relation using O3N2 calibrations: the standard anti-correlation is confined to low-$\Sigma_*$ bins, while high-$\Sigma_*$ regions show a positive correlation, inverting at $\log_{10}(\Sigma_*/M_\odot\,\mathrm{kpc}^{-2})\simeq 7.5$-8.0. Correlated and anti-correlated \ion{H}{ii} regions coexist within the same discs; the mass dependence emerges only when grouping spaxels by $\Sigma_*$. We develop a spatially resolved gas-regulator model showing this $Z_\mathrm{gas}$-$\Sigma_\mathrm{SFR}$ (anti-)correlation arises from competition between star-formation-driven and gas-supply-driven variability. This framework naturally extrapolates to the integrated scenario, providing a unified explanation for resolved and global relations. However, the presence and strength of the $Z_\mathrm{gas}$-$\Sigma_\mathrm{SFR}$ (anti-)correlation depend strongly on the metallicity indicator used, highlighting the challenge of disentangling physical secondary trends within metallicity scaling relations.

astro-ph.GA↗

arXiv2025

Quokka-based understanding of outflows (QED) -- IV. Limitations of H$\alpha$ as an outflow diagnostic

The presence of broad wings in the H$\alpha$ line is commonly used as a diagnostic of the presence and properties of galactic winds from star-forming galaxies. However, the accuracy of this approach has not been subjected to extensive testing. In this paper, we use high-resolution simulations of galactic wind launching to calibrate the extent to which broad H$\alpha$ wings can be used to infer the properties of galactic outflows. For this purpose, we analyse a series of high-resolution wind simulations from the QED suite spanning two orders of magnitude in star formation surface density ($\Sigma_\mathrm{SFR}$). We show that the broad component of H$\alpha$ emission correlates well with the wind mass flux at heights $\sim1$ kpc above the galactic plane, but that the correlation is poor at larger distances from the plane, and that even at 1 kpc the relationship between mass flux and surface brightness of broad H$\alpha$ is significantly sub-linear. The sub-linear scaling suggests that the electron column density in the wind increases systematically with outflow strength, and that the conventional assumption of constant electron density in the wind leads to a systematic overestimate of how steeply mass loading factors depend on $\Sigma_\mathrm{SFR}$. We provide empirical scaling relations that observers can apply to correct for this effect when converting H$\alpha$ measurements to mass outflow rates. Finally, we use synthetic observations of the density-diagnostic $[\mathrm{S_{II}}]\,\lambda\lambda6716,6731$ doublet to show that using this diagnostic only slightly improves estimates of wind outflow rates compared to the naive assumption of constant electron density, and performs significantly worse than the empirical correlation we provide.

astro-ph.GA↗

arXiv2024

Quokka-based understanding of outflows (QED) -- II. X-ray metallicity gradients as a signature of galactic wind metal loading

Supernova-driven galactic outflows play a vital but still poorly-understood role in galactic chemical evolution, and one of the largest uncertainties about them is the extent to which they consist of supernova ejecta that are unmixed, or only poorly-mixed, with the remainder of the interstellar medium (ISM). Simulations of wind launching make a range of predictions about the extent of mixing between the wind and the ISM, but thus far these have proven challenging to test observationally. In this study, we post-process high-resolution simulations of outflows from the QED simulation suite to generate synthetic X-ray spectra from galactic winds, which we then analyse using standard observational procedures, in order to search for detectable markers of wind mixing. Our synthetic observations reveal that partially-mixed winds show significant and detectable metallicity gradients when viewed edge-on, with metallicity decreasing away from the central galactic disc. We explore how this signature results from imperfect mixing and the extent to which measurements of it can be used to diagnose the level of mixing in winds. We determine the signal-to-noise ratio (SNR) requirements for such measurements to be reliable, and provide a simple quantitative model that can be used to connect metallicity gradients to mixing between the hot ($T>10^{6}$ K) and cold ($T<10^{4}$ K) phases in observations that reach the required SNR, providing a framework to interpret current and future observations.

astro-ph.GA↗

arXiv2023

Exploring the Intrinsic Scatter of the Star-Forming Galaxy Main Sequence at redshift 0.5 to 3.0

Previous studies have shown that the normalization and scatter of the galaxy 'main sequence' (MS), the relation between star formation rate (SFR) and stellar mass ($M_*$), evolves over cosmic time. However, such studies often rely on photometric redshifts and/or only rest-frame UV to near-IR data, which may underestimate the SFR and $M_*$ uncertainties. We use MAGPHYS+photo-z to fit the UV to radio spectral energy distributions of 12,380 galaxies in the COSMOS field at $0.5<z<3.0$ and self-consistently include photometric redshift uncertainties on the derived SFR and $M_*$. We quantify the effect on the observed MS scatter from (1) photometric redshift uncertainties (which are minor) and (2) fitting only rest-frame ultraviolet to near-infrared observations (which are severe). At fixed redshift and $M_*$, we find that the intrinsic MS scatter for our sample of galaxies is 1.4 to 2.6 times larger than the measurement uncertainty. The average intrinsic MS scatter has decreased by 0.1 dex from $z=0.5$ to $\sim2.0$. At low-$z$, the trend between the intrinsic MS scatter and $M_*$ follows a functional form similar to an inverse stellar mass-halo mass relation (SMHM; $M_*$/$M_{\rm halo}$ vs $M_*$), with a minimum in intrinsic MS scatter at log($M_*/M_{\odot})\sim10.25$ and larger scatter at both lower and higher $M_*$; while this distribution becomes flatter for high-$z$. The SMHM is thought to be a consequence of feedback effects and this similarity may suggest a link between galaxy feedback and the intrinsic MS scatter. These results favor a slight evolution in the intrinsic MS scatter with both redshift and mass.

astro-ph.GA↗