The ALMA Spectroscopic Survey in the HUDF: The Cosmic Dust and Gas Mass Densities in Galaxies up to $z\sim3$ (2002.08640v1)

Abstract: Using the deepest 1.2 mm continuum map to date in the Hubble Ultra Deep Field obtained as part of the ALMA Spectroscopic Survey (ASPECS) large program, we measure the cosmic density of dust and implied gas (H${2}+$H I) mass in galaxies as a function of look-back time. We do so by stacking the contribution from all $H$-band selected galaxies above a given stellar mass in distinct redshift bins, $\rho{\rm dust}(M_\ast>M,z)$ and $\rho_{\rm gas}(M_\ast>M,z)$. At all redshifts, $\rho_{\rm dust}(M_\ast>M,z)$ and $\rho_{\rm gas}(M_\ast>M,z)$ grow rapidly as $M$ decreases down to $10^{10}\,M_\odot$, but this growth slows down towards lower stellar masses. This flattening implies that at our stellar mass-completeness limits ($10^8\,M_\odot$ and $10^{8.9}\,M_\odot$ at $z\sim0.4$ and $z\sim3$), both quantities converge towards the total cosmic dust and gas mass densities in galaxies. The cosmic dust and gas mass densities increase at early cosmic time, peak around $z\sim2$, and decrease by a factor $\sim4$ and 7, compared to the density of dust and molecular gas in the local universe, respectively. The contribution of quiescent galaxies -- i.e., with little on-going star-formation -- to the cosmic dust and gas mass densities is minor ($\lesssim10\%$). The redshift evolution of the cosmic gas mass density resembles that of the star-formation rate density, as previously found by CO-based measurements. This confirms that galaxies have relatively constant star-formation efficiencies (within a factor $\sim2$) across cosmic time. Our results also imply that by $z\sim0$, a large fraction ($\sim90\%$) of dust formed in galaxies across cosmic time has been destroyed or ejected to the intergalactic medium.

• The paper demonstrates that dust and gas densities rapidly increase with decreasing stellar mass until 10^10 M☉, after which the growth slows.
• The paper shows that quiescent galaxies contribute less than 10% to cosmic dust and gas densities, emphasizing star-forming galaxies’ dominant role.
• The paper validates the dust-based approach by confirming that inferred gas densities align closely with CO-based molecular gas measurements.

An Expert Analysis of "The ALMA Spectroscopic Survey in the HUDF: The Cosmic Dust and Gas Mass Densities in Galaxies up to $z\sim3$"

This paper, authored by Magnelli et al., presents a detailed analysis of cosmic dust and gas mass densities in galaxies, particularly focusing on their evolution up to a redshift of $z\sim3$. The paper leverages data from the ALMA Spectroscopic Survey (ASPECS) conducted in the Hubble Ultra Deep Field (HUDF), utilizing the unprecedented depth of a 1.2 mm continuum map to investigate the dust and inferred gas content within galaxies across different epochs.

The research is executed with a stellar mass-complete galaxy sample, allowing the authors to capture a comprehensive picture of the cosmic dust and gas mass densities. The authors have developed an innovative stacking technique, integrating data from all known galaxies in the HUDF to collectively measure the dust and gas contributions across redshift bins. This methodology provides a robust framework for tracing cosmic density evolution and complements existing measurements obtained through CO line emission.

Key Findings and Results

1. Stellar Mass and Redshift Evolution: The stacking analysis revealed a rapid growth in $\rho_{\rm dust}(M_\ast>M,z)$ and $\rho_{\rm gas}(M_\ast>M,z)$ as stellar mass decreases, but this growth notably slows down below masses of $10^{10}M_\odot$. This suggests that the majority of cosmic dust and gas reside in galaxies above this threshold.
2. Minor Contribution from Quiescent Galaxies: Quiescent galaxies, identified via standard $UVJ$ selection, contribute insignificantly (<10%) to cosmic dust and gas densities, indicating that active star-forming galaxies predominantly harbor the dust and gas contents.
3. Agreement with CO-based Studies: The inferred gas densities align well with molecular gas densities from CO measurements, affirming that the dust-based approach is primarily tracing the molecular gas component in galaxies.
4. Redshift Trends: Both $\rho_{\rm dust}$ and $\rho_{\rm gas}$ showcase a similar trend with redshift, peaking around $z\sim2$ and diminishing towards $z\sim0$. However, the reduction in cosmic dust density is not as steep as in the case of gas, which decreases by a factor of $\sim7$ compared to the $\sim4$ factor seen in dust density.
5. Methodological Corroboration and Implications: The paper uses the star-forming galaxy stellar mass function and average dust-to-stellar and gas-to-stellar mass ratios to model the density evolution. This analysis demonstrates the decreasing dust and gas ratios from $z=3$ to present, implying a gradual decline in available star-forming material over cosmic time.

Implications for Galaxy Evolution

The results support models of galaxy evolution, positing that star formation efficiencies remain relatively constant over time, with the primary determinant of star formation being the availability of gas resources. The paper advocates for a gas regulator model of galaxy evolution, emphasizing consistent fresh gas supply as a key factor in maintaining star formation.

This work implies that significant dust production mechanisms, like contributions from supernovae (SNe) and Asymptotic Giant Branch (AGB) stars, are active, expressing a crucial link between stellar life cycles and cosmic dust content. The observed stagnation of dust density at $z<2$ suggests extensive dust destruction or ejection into intergalactic mediums, an important constraint on models for cosmic dust lifecycle and interstellar medium (ISM) processes.

Conclusion

Magnelli et al.'s paper provides a detailed and quantified foundation for understanding dust and gas evolution in galaxies, supporting theoretical models that link star formation with gas availability and ISM conditions. The combination of this observational approach with stellar mass functions furnishes valuable insights into the complex interplay of star formation and the baryonic matter cycle across cosmic history, bolstering the paradigm of gas-driven galaxy growth and evolution. Future research could potentially benefit from this methodology, further segregating molecular and atomic gas contributions and expanding observational constraints beyond the current redshift bounds.