arXiv subjects

Hiroyuki Hirashita

Publications and source records attributed to Hiroyuki Hirashita.

At least 19 recordsLinked to original sources

arXiv2026

Ion-Neutral Drift Velocity as a Diagnostic of Dust Growth and Magnetic Field in Star-Forming Environments

Recent observations have revealed that the ion-neutral drift velocity in star-forming molecular clouds and dense cores is on the order of 100 m s^-1. Theoretical studies have shown that, in ambipolar diffusion, the process responsible for the differential motion between ions and neutrals, the dust size distribution has a significant impact on the magnetic resistivities. In this study, we perform simulations to investigate how dust growth through accretion and coagulation affects the ion-neutral drift velocity in molecular clouds and cores. We find that, on core scales, both dust growth and a magnetic field strength of 200 microgauss are required to reproduce the observed drift velocity. We suggest that measurements of ion-neutral drift velocity, particularly on core scales, may serve as a new diagnostic to constrain the dust size distribution and magnetic field strength in such environments.

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arXiv2024

CO-to-H$_2$ conversion factor and grain size distribution through the analysis of $α_\mathrm{CO}$-$q_\mathrm{PAH}$ relation

The CO-to-H$_2$ conversion factor ($α_\mathrm{CO}$) is expected to vary with dust abundance and grain size distribution through the efficiency of shielding gas from CO-dissociation radiation. We present a comprehensive analysis of $α_\mathrm{CO}$ and grain size distribution for nearby galaxies, using the PAH fraction ($q_\mathrm{PAH}$) as an observable proxy of grain size distribution. We adopt the resolved observations at 2-kpc resolution in 42 nearby galaxies, where $α_\mathrm{CO}$ is derived from measured metallicity and surface densities of dust and HI assuming a fixed dust-to-metals ratio. We use an analytical model for the evolution of H$_2$ and CO, in which the evolution of grain size distribution is controlled by the dense gas fraction ($η$). We find that the observed level of $q_\mathrm{PAH}$ is consistent with the diffuse-gas-dominated model ($η=0.2$) where dust shattering is more efficient. Meanwhile, the slight decreasing trend of observed $q_\mathrm{PAH}$ with metallicity is more consistent with high-$η$ predictions, likely due to the more efficient loss of PAHs by coagulation. We discuss how grain size distribution (indicated by $q_\mathrm{PAH}$) and metallicity impact $α_\mathrm{CO}$; we however did not obtain conclusive evidence that the grain size distribution affects $α_\mathrm{CO}$. Observations and model predictions show similar anti-correlation between $α_\mathrm{CO}$ and 12+log(O/H). Meanwhile, there is a considerable difference in how resolved $α_\mathrm{CO}$ behaves with $q_\mathrm{PAH}$. The observed $α_\mathrm{CO}$ has a positive correlation with $q_\mathrm{PAH}$, while the model-predicted $α_\mathrm{CO}$ does not have a definite correlation with $q_\mathrm{PAH}$. This difference is likely due to the limitation of one-zone treatment in the model.

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arXiv2024

JWST MIRI and NIRCam observations of NGC 891 and its circumgalactic medium

We present new JWST observations of the nearby, prototypical edge-on, spiral galaxy NGC 891. The northern half of the disk was observed with NIRCam in its F150W and F277W filters. Absorption is clearly visible in the mid-plane of the F150W image, along with vertical dusty plumes that closely resemble the ones seen in the optical. A $\sim 10 \times 3~{\rm kpc}^2$ area of the lower circumgalactic medium (CGM) was mapped with MIRI F770W at 12 pc scales. Thanks to the sensitivity and resolution of JWST, we detect dust emission out to $\sim 4$ kpc from the disk, in the form of filaments, arcs, and super-bubbles. Some of these filaments can be traced back to regions with recent star formation activity, suggesting that feedback-driven galactic winds play an important role in regulating baryonic cycling. The presence of dust at these altitudes raises questions about the transport mechanisms at play and suggests that small dust grains are able to survive for several tens of million years after having been ejected by galactic winds in the disk-halo interface. We lay out several scenarios that could explain this emission: dust grains may be shielded in the outer layers of cool dense clouds expelled from the galaxy disk, and/or the emission comes from the mixing layers around these cool clumps where material from the hot gas is able to cool down and mix with these cool cloudlets. This first set of data and upcoming spectroscopy will be very helpful to understand the survival of dust grains in energetic environments, and their contribution to recycling baryonic material in the mid-plane of galaxies.

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arXiv2024

Accurate Simultaneous Constraints on the Dust Mass, Temperature and Emissivity Index of a Galaxy at Redshift 7.31

We present new multi-frequency ALMA continuum observations of the massive [$\log_{10}(M_\star/M_\odot) = 10.3_{-0.2}^{+0.1}$], UV-luminous [$M_\mathrm{UV} = -21.7 \pm 0.2$] $z=7.31$ galaxy REBELS-25 in Bands 3, 4, 5, and 9. Combining the new observations with previously-taken data in Bands 6 and 8, we cover the dust continuum emission of the galaxy in six distinct bands -- spanning rest-frame $50-350\,μ$m -- enabling simultaneous constraints on its dust mass ($M_\mathrm{dust}$), temperature ($T_\mathrm{dust}$) and emissivity index ($β_\mathrm{IR}$) via modified blackbody fitting. Given a fiducial model of optically thin emission, we infer a cold dust temperature of $T_\mathrm{dust} = 32_{-6}^{+9}\,$K and a high dust mass of $\log_{10}(M_\mathrm{dust}/M_\odot) = 8.2_{-0.4}^{+0.6}$, and moderately optically thick dust does not significantly alter these estimates. If we assume dust production is solely through supernovae (SNe), the inferred dust yield would be high, $y = 0.7_{-0.4}^{+2.3}\,M_\odot$ per SN. Consequently, we argue grain growth in the interstellar medium of REBELS-25 also contributes to its dust build-up. This is supported by the steep dust emissivity index $β_\mathrm{IR} = 2.5 \pm 0.4$ we measure for REBELS-25, as well as by its high stellar mass, dense interstellar medium, and metal-rich nature. Our results suggest that constraining the dust emissivity indices of high-redshift galaxies is important not only to mitigate systematic uncertainties in their dust masses and obscured star formation rates, but also to assess if dust properties evolve across cosmic time. We present an efficient observing setup to do so with ALMA, combining observations of the peak and Rayleigh-Jeans tail of the dust emission.

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arXiv2024

Observational signatures of the dust size evolution in isolated galaxy simulations

We aim to provide observational signatures of the dust size evolution in the ISM. In particular, we explore indicators of the polycyclic aromatic hydrocarbon (PAH) mass fraction ($q_{PAH}$), defined as the mass fraction of PAHs relative to total dust grains. In addition, we validate our dust evolution model by comparing the observational signatures from our simulations to observations. We used the hydrodynamic simulation code, GADGET4-OSAKA to model the dust properties of Milky Way-like and NGC 628-like galaxies representing star-forming galaxies. This code incorporates the evolution of grain size distributions driven by dust production and interstellar processing. Furthermore, we performed post-processing dust radiative transfer with SKIRT based on the simulations to predict the observational properties. We find that the intensity ratio between 8 um and 24 um is correlated with $q_{PAH}$ and can be used as an indicator of PAH mass fraction. However, this ratio is influenced by the radiation field. We suggest the 8 um-to-total infrared intensity ratio ($νI_ν(8 μm)/I$(TIR)) as another indicator, since it is tightly correlated with $q_{PAH}$. Furthermore, we explored the spatially resolved $q_{PAH}$ in the simulated Milky Way-like galaxy using $νI_ν(8 μm)/I$(TIR). We find that the spatially resolved $q_{PAH}$ increases with metallicity at metallicity at Z<0.2 Zsun due to the interplay between accretion and shattering while it decreases at Z>0.2 Zsun because of coagulation. Finally, we compared the above indicators in the NGC 628-like simulation with those observed in NGC 628 by recent observations. Consequently, we find that our simulation underestimates the PAH mass fraction throughout the entire galaxy by a factor of $\sim 8$ on average. This could be due to the efficient loss of PAHs by coagulation in our model.

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arXiv2024

Evolution of grain size distribution in the circum-galactic medium

In order to theoretically understand dust properties in the circum-galactic medium (CGM), we construct a dust evolution model that incorporates the evolution of grain size distribution. We treat each of the galaxy and the CGM as a one-zone object, and consider the mass exchange between them. We take into account dust production and interstellar dust processing for the galaxy based on our previous models, and newly incorporate sputtering in the hot phase and shattering in the cool phase for the CGM. We find that shattering increases the dust destruction (sputtering) efficiency in the CGM. The functional shape of the grain size distribution in the CGM evolves following that in the galaxy, but it is sensitive to the balance between sputtering and shattering in the CGM. For an observational test, we discuss the wavelength dependence of the reddening in the CGM traced by background quasar colors, arguing that, in order to explain the observed reddening level, a rapid inflow from the CGM to the galaxy is favored because of quick dust/metal enrichment. Small grain production by shattering in the CGM also helps to explain the rise of dust extinction toward short wavelengths.

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arXiv2024

Dust enrichment in the circum-galactic medium

To understand the origin of dust in the circum-galactic medium (CGM), we develop a dust enrichment model. We describe each of the central galaxy and its CGM as a single zone, and consider the mass exchange between them through galactic inflows and outflows. We calculate the evolution of the gas, metal, and dust masses in the galaxy and the CGM. In the galaxy, we include stellar dust production and interstellar dust processing following our previous models. The dust in the galaxy is transported to the CGM via galactic outflows, and it is further processed by dust destruction (sputtering) in the CGM. We parameterize the time-scale or efficiency of each process and investigate the effect on the dust abundance in the CGM. We find that the resulting dust mass is sensitive to the dust destruction in the CGM, and the dust supply from galactic outflows, both of which directly regulate the dust abundance in the CGM. The inflow time-scale also affects the dust abundance in the CGM because it determines the gas mass evolution (thus, the star formation history) in the galaxy. The dust abundance in the CGM, however, is insensitive to stellar dust formation in the galaxy at later epochs because the dust production is dominated by dust growth in the interstellar medium. We also find that the resulting dust mass in the CGM is consistent with the value derived from a large sample of SDSS galaxies.

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arXiv2023

Submillimetre galaxies as laboratories for dust grain coagulation

Coagulation in the dense interstellar medium (ISM) is an important process that determines the size of the largest grains. We use submillimetre galaxies (SMGs) as laboratories of grain coagulation, since some of them host the densest ISM on a galactic scale among various populations of galaxies known. We examine how large the grains can be in such dense environments based on the mean ISM density estimated from the observed typical dust mass density in SMGs. We also consider local density enhancement based on a model of supersonic turbulence, which is expected from strong stellar feedback. In the unlimited coagulation model, in which we do not impose any coagulation threshold velocity, grains as large as $\sim 30~μ$m can form under the observationally estimated mean gas density if the Mach number of turbulence is $\mathcal{M}\gtrsim 3$. We exclude this possibility since the observed emissivity index $β\simeq 2$ in the far infrared (FIR) indicates that such large grains cannot actively form in SMGs. This means that coagulation does not proceed in an unlimited way: 30-$μ$m grains should have velocities larger than the coagulation threshold. If we use a coagulation threshold (upper limit) grain velocity ($\sim 0.08$ km s$^{-1}$) taken from a theoretical study, grains likely grow only up to $μ$m size, which is small enough not to affect the FIR emissivity index. The above results indicate that SMGs can be used to constrain the physical processes relevant to coagulation.

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arXiv2023

Effects of dust grain size distribution on the abundances of CO and H$_2$ in galaxy evolution

We model the effect of grain size distribution in a galaxy on the evolution of CO and H$_2$ abundances. The formation and dissociation of CO and H$_2$ in typical dense clouds are modelled in a manner consistent with the grain size distribution. The evolution of grain size distribution is calculated based on our previous model, which treats the galaxy as a one-zone object but includes various dust processing mechanisms in the interstellar medium (ISM). We find that typical dense clouds become fully molecular (H$_2$) when the dust surface area increases by shattering while an increase of dust abundance by dust growth in the ISM is necessary for a significant rise of the CO abundance. Accordingly, the metallicity dependence of the CO-to-H$_2$ conversion factor, $X_\mathrm{CO}$, is predominantly driven by dust growth. We also examine the effect of grain size distribution in the galaxy by changing the dense gas fraction, which controls the balance between coagulation and shattering, clarifying that the difference in the grain size distribution significantly affects $X_\mathrm{CO}$ even if the dust-to-gas ratio is the same. The star formation time-scale, which controls the speed of metal enrichment also affects the metallicity at which the CO abundance rapidly increases (or $X_\mathrm{CO}$ drops). We also propose dust-based formulae for $X_\mathrm{CO}$, which need further tests for establishing their usefulness.

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arXiv2023

Kpc-scale properties of dust temperature in terms of dust mass and star formation activity

We investigate how the dust temperature is affected by local environmental quantities, especially dust surface density ($Σ_\mathrm{dust}$), dust-to-gas ratio (D/G) and interstellar radiation field. We compile multi-wavelength observations in 46 nearby galaxies, uniformly processed with a common physical resolution of $2~$kpc. A physical dust model is used to fit the infrared dust emission spectral energy distribution (SED) observed with WISE and Herschel. The star formation rate (SFR) is traced with GALEX ultraviolet data corrected by WISE infrared. We find that the dust temperature correlates well with the SFR surface density ($Σ_{\rm SFR}$), which traces the radiation from young stars. The dust temperature decreases with increasing D/G at fixed $Σ_{\rm SFR}$ as expected from stronger dust shielding at high D/G, when $Σ_\mathrm{SFR}$ is higher than $\sim 2\times 10^{-3}~\rm M_\odot~yr^{-1}~kpc^{-2}$. These measurements are in good agreement with the dust temperature predicted by our proposed analytical model. Below this range of $Σ_\mathrm{SFR}$, the observed dust temperature is higher than the model prediction and is only weakly dependent on D/G, which is possibly due to the dust heating from old stellar population or the variation of SFR within the past $10^{10}~$yr. Overall, the dust temperature as a function of $Σ_\mathrm{SFR}$ and $Σ_\mathrm{dust}$ predicted by our analytical model is consistent with observations. We also notice that at fixed gas surface density, $Σ_{\rm SFR}$ tends to increase with D/G, i.e. we can empirically modify the Kennicutt-Schmidt law with a dependence on D/G to better match observations.

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arXiv2022

Effects of dust sources on dust attenuation properties in IllustrisTNG galaxies at $z\sim 7$

Dust emission from high-redshift galaxies gives us a clue to the origin and evolution of dust in the early Universe. Previous studies have shown that different sources of dust (stellar dust production and dust growth in dense clouds) predict different ultraviolet (UV) extinction curves for galaxies at $z\sim 7$ but that the observed attenuation curves depend strongly on the geometry of dust and star distributions. Thus, we perform radiative transfer calculations under the dust-stars geometries computed by a cosmological hydrodynamic simulation (IllustrisTNG). This serves to investigate the dust attenuation curves predicted from `realistic' geometries. We choose objects with stellar mass and star formation rate appropriate for Lyman break galaxies at $z\sim 7$. We find that the attenuation curves are very different from the original extinction curves in most of the galaxies. This makes it difficult to constrain the dominant dust sources from the observed attenuation curves. We further include infrared dust emission in the analysis and plot the infrared excess (IRX)-UV spectral slope ($β$) diagram. We find that different sources of dust cause different IRX-$β$ relations for the simulated galaxies. In particular, if dust growth is the main source of dust, a variation of dust-to-metal ratio causes a more extended sequence with smaller IRX in the IRX-$β$ diagram. Thus, the comprehensive analysis of the abundances of dust and metals, the UV slope, and the dust emission could provide a clue to the dominant dust sources in the Universe.

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arXiv2022

Evolution of grain size distribution with enhanced abundance of small carbonaceous grains in galactic environments

We propose an updated dust evolution model that focuses on the grain size distribution in a galaxy. We treat the galaxy as a one-zone object and include five main processes (stellar dust production, dust destruction in supernova shocks, grain growth by accretion and coagulation, and grain disruption by shattering). In this paper, we improve the predictions related to small carbonaceous grains, which are responsible for the 2175 Å bump in the extinction curve and the polycyclic aromatic hydrocarbon (PAH) emission features in the dust emission spectral energy distribution (SED), both of which were underpredicted in our previous model. In the new model, we hypothesize that small carbonaceous grains are not involved in interstellar processing. This avoids small carbonaceous grains being lost by coagulation. We find that this hypothetical model shows a much better match to the Milky Way (MW) extinction curve and dust emission SED than the previous one. The following two additional modifications further make the fit to the MW dust emission SED better: (i) The chemical enrichment model is adjusted to give a nearly solar metallicity in the present epoch, and the fraction of metals available for dust growth is limited to half. (ii) Aromatization for small carbonaceous grains is efficient, so that the aromatic fraction is unity at grain radii $\lesssim 20$ Å. As a consequence of our modelling, we succeed in obtaining a dust evolution model that explains the MW extinction curve and dust emission SED at the same time.

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arXiv2022

Cosmic evolution of grain size distribution in galaxies using the $ν^2$GC semi-analytic model

We investigate the cosmological evolution of interstellar dust with a semi-analytical galaxy formation model ($ν^2$GC), focusing on the evolution of grain size distribution. The model predicts the statistical properties of dust mass and grain size distribution in galaxies across cosmic history. We confirm that the model reproduces the relation between dust-to-gas ratio and metallicity in the local Universe, and that the grain size distributions of the Milky Way (MW)-like sample become similar to the so-called MRN distribution that reproduces the observed MW extinction curve. Our model, however, tends to overpredict the dust mass function at the massive end at redshift $z\lesssim 0.8$ while it reproduces the abundance of dusty galaxies at higher redshifts. We also examine the correlation between grain size distribution and galaxy properties (metallicity, specific star formation rate, gas fraction, and stellar mass), and observe a clear trend of large-grain-dominated, small-grain-dominated, and MRN-like grain size distributions from unevolved to evolved stages. As a consequence, the extinction curve shapes are flat, steep, and intermediate (MW-like) from the unevolved to evolved phases. At a fixed metallicity, the grain size distribution tends to have larger fractions of small grains at lower redshift; accordingly, the extinction curve tends to be steeper at lower redshift. We also predict that supersolar-metallicity objects at high redshift have flat extinction curves with weak 2175 Åbump strength.

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arXiv2022

Compact dust emission in a gravitationally lensed massive quiescent galaxy at z = 2.15 revealed in ~130 pc-resolution observations by ALMA

We present new observations of MRG-M2129, a quiescent galaxy at z = 2.15 with the Atacama Large Millimeter/submillimeter Array (ALMA). With the combination of the gravitational lensing effect by the foreground cluster and the angular resolution provided by ALMA, our data reveal 1.2 mm continuum emission at $\sim130$ pc angular resolution. Compact dust continuum is detected at 7.9 $σ$ in the target but displaced from its stellar peak position by $62 \pm 38$ mas, or $\sim169 \pm 105$ pc in the source plane. We find considerably high dust-to-stellar mass ratio, $4 \times 10^{-4}$. From non-detection of the [C i] 3P2 -> 3P1 line, we then derive $3 σ$ upper limits on the molecular gas-to-dust mass ratio $δ_\mathrm{GDR} < 60$ and the molecular gas-to-stellar mass ratio fH2 < 2.3%. The derived $δ_\mathrm{GDR}$ is $>2\times$ smaller than the typical value assumed for quiescent galaxies in the literature. Our study supports that there exists a broad range of $δ_\mathrm{GDR}$ and urges submillimeter follow-up observations of quenching/recently quenched galaxies at similar redshifts. Based on the derived low $δ_\mathrm{GDR}$ and other observed dust properties, we argue that the central black hole is still active and regulates star formation in the system. Our study exhibits a rare case of a gravitationally lensed type 2 QSO harbored by a quiescent galaxy.

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arXiv2022

Analytic models of dust temperature in high-redshift galaxies

We investigate physical reasons for high dust temperatures ($T_\mathrm{dust}\gtrsim 40$ K) observed in some high-redshift ($z>5$) galaxies using analytic models. We consider two models that can be treated analytically: the radiative transfer (RT) model, {where a broad distribution of values for $T_\mathrm{dust}$ is considered}, and the one-tempearture (one-$T$) model, which assumes {uniform $T_\mathrm{dust}$}. These two extremes {serve to bracket the most realistic scenario}. We adopt the Kennicutt--Schmidt (KS) law to relate stellar radiation field to gas surface density, and vary the dust-to-gas ratio. As a consequence, our model is capable of predicting the relation between the surface density of star formation rate ($Σ_\mathrm{SFR}$) or dust mass ($Σ_\mathrm{dust}$) and $T_\mathrm{dust}$. We show that the high $T_\mathrm{dust}$ observed at $z\gtrsim 5$ favour low dust-to-gas ratios ($\lesssim 10^{-3}$). An enhanced star formation compared with the KS law gives an alternative explanation for the high $T_\mathrm{dust}$. The dust temperatures are similar between the two (RT and one-$T$) models as long as we use ALMA Bands 6--8. We also examine the relation among $Σ_\mathrm{SFR}$, $Σ_\mathrm{dust}$ and $T_\mathrm{dust}$ without assuming the KS law, and confirm the consistency with the actual observational data at $z>5$. In the one-$T$ model, we also examine a clumpy dust distribution, which predicts lower $T_\mathrm{dust}$ because of the leakage of stellar radiation. This enhances the requirement of low dust abundance or high star formation efficiency to explain the observed high $T_\mathrm{dust}$.

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arXiv2022

Dissecting Nearby Galaxies with piXedfit: II. Spatially Resolved Scaling Relations Among Stars, Dust, and Gas

We study spatially resolved scaling relations among stars, dust, and gas in ten nearby spiral galaxies. In a preceding paper Abdurro'uf et al. (2022), we have derived spatially resolved properties of the stellar population and dust by panchromatic spectral energy distribution (SED) fitting using piXedfit. Now, we investigate resolved star formation ($Σ_{\rm H_{2}}$--$Σ_{\rm SFR}$--$Σ_{*}$) and dust scaling relations. While the relations with all sub-galactic regions of the galaxies are reasonably tight ($σ\lesssim 0.3$ dex), we find that most of the scaling relations exhibit galaxy-to-galaxy variations in normalization and shape. Only two relations of $Σ_{\rm dust}$--$Σ_{\rm gas}$ and $Σ_{\rm dust}$--$Σ_{\rm H_{2}}$ do not show noticeable galaxy-to-galaxy variations among our sample galaxies. We further investigate correlations among the scaling relations. We find significant correlations among the normalization of the $Σ_{\rm H_{2}}$--$Σ_{\rm SFR}$--$Σ_{*}$ relations, which suggest that galaxies with higher levels of resolved $\text{H}_{2}$ fraction ($f_{\rm H_{2}}$) tend to have higher levels of resolved star formation efficiency (SFE) and specific star formation rate (sSFR). We also observe that galaxies with higher levels of resolved dust-to-stellar mass ratios tend to have higher levels of resolved sSFR, SFE, and $f_{\rm H_{2}}$. Moreover, we find that galaxies with higher global sSFR and less compact morphology tend to have higher levels of the resolved sSFR, SFE, and $f_{\rm H_{2}}$, which can explain the variations in the normalization of the $Σ_{\rm H_{2}}$--$Σ_{\rm SFR}$--$Σ_{*}$ relationships. Overall, we observe indications of the contributions of both global and local factors in governing the star formation process in galaxies.

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arXiv2022

Dust diffusion in SPH simulations of an isolated galaxy

We compute the evolution of the grain size distribution (GSD) in a suite of numerical simulations of an isolated Milky-Way-like galaxy using the $N$-body/smoothed-particle-hydrodynamics code {\sc Gadget-4}. The full GSD is sampled on a logarithmically spaced grid with 30 bins, and its evolution is calculated self-consistently with the hydrodynamical and chemical evolution of the galaxy using a state-of-the-art star formation and feedback model. In previous versions of this model, the GSD tended to be slightly biased towards larger grains and the extinction curve had a tendency to be flatter than the observations. This work addresses these issues by considering the diffusion of dust and metals through turbulence on subgrid scales and introducing a multi-phase subgrid model that enables a smoother transition from diffuse to dense gas. We show that diffusion can significantly enhance the production of small grains and improve the agreement with the observed dust extinction curve in the Milky Way.

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arXiv2022

The co-evolution of molecular hydrogen and the grain size distribution in an isolated galaxy

Understanding the evolution of dust and molecular hydrogen (H$_2$) is a critical aspect of galaxy evolution, as they affect star formation and the spectral energy distribution of galaxies. We use the $N$-body/smoothed-particle-hydrodynamics code {\sc Gadget-4} to compute the evolution of dust and H$_2$ in a suite of numerical simulations of an isolated Milky-Way-like galaxy. The evolution of the full grain size distribution (GSD) is solved by sampling the grain size on a logarithmically spaced grid with 30 bins. The evolution of a primordial chemistry network with twelve species is solved consistently with the hydrodynamic evolution of the system, including star formation, metal and energy ejections from stars into the interstellar medium through supernova feedback and stellar winds. The formation model for H$_2$ considers the GSD and photo-dissociation through the UV radiation of young stars. We identify the processes needed for producing a sizeable amount of H$_2$, verify that the resulting star formation law in the later stages of galaxy evolution is consistent with observations of local spirals, and show that our model manages to produce a galactic molecular gas fraction in line with observations of Milky-Way-like galaxies. We stress the importance of the co-evolution of the GSD and H$_2$, as models assuming a fixed MRN shape for the GSD overestimate the production of H$_2$ in regimes where the dust abundance is dominated by large grains and underestimate it in the regime where the dust is dominated by small grains, both of which are realized in simulations of dust evolution.

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