[Paper Review] Dust depletion of of metals from local to distant galaxies II: Cosmic dust-to-metal ratio and dust composition

Christina Konstantopoulou, A. De+11 more|arXiv (Cornell University)|Oct 11, 2023

Astrophysics and Star Formation StudiesPhysics and Astronomy1 references3 citations

TL;DR

This study presents a novel method to estimate cosmic dust-to-metal (DTM) and dust-to-gas (DTG) ratios and dust composition across galaxies from the Milky Way to high-redshift damped Lyman-alpha absorbers (DLAs). It finds that DTM and DTG increase with metallicity and [Zn/Fe], indicating grain growth as the dominant dust production mechanism, with O, Fe, Si, Mg, C, S, Ni, and Al as primary dust contributors, and suggests stellar dust yields are only ~1% of metal yields.

ABSTRACT

The evolution of the cosmic dust content and the cycle between metals and dust in the interstellar medium (ISM) play a fundamental role in galaxy evolution. The chemical enrichment of the Universe can be traced through the evolution of the dust-to-metals ratio (DTM) and the dust-to-gas ratio (DTG) with metallicity. We use a novel method to determine mass estimates of the DTM, DTG and dust composition based on our previous measurements of the depletion of metals in different environments (the Milky Way, the Magellanic Clouds, and damped Lyman-$α$ absorbers, DLAs, toward quasars and towards gamma-ray bursts, GRBs), which were calculated from the relative abundances of metals in the ISM through absorption-line spectroscopy column densities observed mainly from VLT/UVES and X-shooter, and HST/STIS. We derive the dust extinction from the estimated dust depletion ($A_{V, m depl}$) and compare with the $A_{V}$ from extinction. We find that the DTM and DTG ratios increase with metallicity and with the dust tracer [Zn/Fe]. This suggests that grain growth in the ISM is a dominant process of dust production. The increasing trend of the DTM and DTG with metallicity is in good agreement with a dust production and evolution model. Our data suggest that the stellar dust yield is much lower than the metal yield and thus that the overall amount of dust in the warm neutral medium that is produced by stars is much lower. We find that $A_{V, m depl}$ is overall lower than $A_{V, m ext}$ for the Milky Way and a few Magellanic Clouds lines of sight, a discrepancy that is likely related to the presence of carbonaceous dust. We show that the main elements that contribute to the dust composition are, O, Fe, Si, Mg, C, S, Ni and Al for all the environments. Abundances at low dust regimes suggest the presence of pyroxene and metallic iron in dust.

Motivation & Objective

• To determine the cosmic dust-to-metal (DTM) and dust-to-gas (DTG) ratios across diverse galactic environments from the Milky Way to high-redshift DLAs.
• To investigate the role of grain growth in dust production by analyzing the dependence of DTM and DTG on metallicity and [Zn/Fe] abundance.
• To estimate the dust composition in terms of mass fractions contributed by individual elements (f_M_X) across different environments.
• To compare extinction derived from dust depletion (A_V,depl) with extinction measured from photometry (A_V,ext), identifying discrepancies linked to dust morphology.
• To assess the contribution of stellar dust yields relative to total metal yields, challenging previous estimates.

Proposed method

• Utilizes absorption-line spectroscopy from VLT/UVES, X-shooter, and HST/STIS to measure column densities of metals in the ISM, enabling calculation of elemental depletions.
• Applies a novel mass-based method to derive DTM and DTG ratios from observed depletions, assuming dust is formed from depleted elements.
• Estimates A_V,depl from the total depletion of elements, using the relation between depletion and extinction, and compares it with A_V,ext from photometric data.
• Computes dust mass fractions (f_M_X) for each element X by normalizing the mass of dust formed from X to the total dust mass.
• Analyzes trends in DTM and DTG with respect to metallicity ([M/H]_tot) and [Zn/Fe], using data from the Milky Way, Magellanic Clouds, and GRB- and quasar-DLAs.
• Tests consistency with hydrodynamical models of dust evolution, particularly those including grain growth in the ISM.

Figure 1 : (Top): Dust-to-metal ratio as a function of the dust tracer [Zn/Fe]. (Bottom): Dust-to-gas ratio as a function of [Zn/Fe]. The black triangles are for QSO-DLAs, the purple squares are for the LMC, the blue triangles are for the SMC, the orange diamonds for the GRB-DLAs and the green circl

Experimental results

Research questions

• RQ1 How does the dust-to-metal ratio (DTM) evolve with metallicity across galaxies from the Milky Way to high-redshift DLAs?
• RQ2 To what extent does grain growth in the ISM contribute to dust production, as indicated by the dependence of DTM and DTG on metallicity and [Zn/Fe]?
• RQ3 What is the composition of interstellar dust in terms of mass contributions from individual elements (e.g., O, Fe, Si, C) across different galactic environments?
• RQ4 Why is A_V,depl systematically lower than A_V,ext in some environments, such as the Milky Way and certain Magellanic Cloud lines of sight?
• RQ5 How do the inferred stellar dust yields compare to the total metal yields, and what does this imply for dust production mechanisms?

Key findings

• The dust-to-metal ratio (DTM) and dust-to-gas ratio (DTG) increase with metallicity and [Zn/Fe], supporting grain growth as the dominant dust production mechanism in the studied metallicity range (-2 ≤ [M/H]_tot ≤ 0.5) and redshift range (0.6 < z < 6.3).
• The stellar dust yield is estimated to be only about 1% of the total metal yield, indicating that stellar contributions to dust are significantly lower than previously assumed.
• A_V,depl is systematically lower than A_V,ext in the Milky Way and some Magellanic Cloud lines of sight, likely due to carbonaceous dust in dense, cold neutral gas clumps not fully captured by depletion-based extinction estimates.
• For most environments, A_V,depl and A_V,ext show good agreement, validating the method’s consistency across diverse ISM conditions.
• The main dust contributors by mass (f_M_X ≥ 1%) are O, Fe, Si, Mg, C, S, Ni, and Al, with Si, Mg, and C contributing approximately equally to the total dust mass.
• In low-dust environments such as quasar- and GRB-DLAs, the dust composition suggests the presence of pyroxene and metallic iron, indicating a different dust mineralogy at low metallicities.

Figure 2 : (Top): Dust-to-metal ratio as a function of the total dust-corrected gas metallicity [ M / $\rm{H}$ ] tot . (Bottom): Dust-to-gas ratio as a function of the total dust-corrected gas metallicity [ M / $\rm{H}$ ] tot . The symbols are the same as in Fig. 1 . For the Milky Way metallicities