Sub-millimeter galaxies as progenitors of compact quiescent galaxies (1401.1510v1)

Abstract: Three billion years after the big bang (at redshift z=2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3<z<6). Simulations show that gas-rich major mergers can give rise to such starbursts which produce dense remnants. Sub-millimeter selected galaxies (SMGs) are prime examples of intense, gas-rich, starbursts. With a new, representative spectroscopic sample of compact quiescent galaxies at z=2 and a statistically well-understood sample of SMGs, we show that z=3-6 SMGs are consistent with being the progenitors of z=2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is 42 (+40/-29) Myr (consistent with independent estimates), which indicates that the bulk of stars in these massive galaxies were formed in a major, early surge of star-formation. These results suggests a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star-formation through their appearance as high stellar-density galaxy cores and to their ultimate fate as giant ellipticals.

• The paper establishes an evolutionary link by showing that intense starbursts in high-redshift SMGs lead to the formation of compact quiescent galaxies observed at z ≈ 2.
• It employs near-infrared spectroscopy and high-resolution imaging to measure stellar mass densities and size distributions that support this transformation.
• Consistent space densities and starburst durations reinforce the rapid transition from active star formation to quiescence in massive galaxies.

Sub-millimeter Galaxies as Progenitors of Compact Quiescent Galaxies

The paper presents an empirical investigation into the evolution of massive galaxies, proposing a link between high-redshift sub-millimeter galaxies (SMGs) and compact quiescent galaxies (cQGs) observed at redshift $z \approx 2$. Leveraging a new spectroscopic sample of SMGs and high-quality imaging data of compact quiescent galaxies, this paper elucidates the evolutionary pathway of massive galaxies approximately three billion years post-Big Bang.

Key Findings

1. Evolutionary Connection Between SMGs and cQGs: The SMG population, characterized by their intense starbursts at high redshifts ($z = 3 - 6$), is argued to evolve into the densely packed stellar remnants observed in cQGs at $z = 2$. This framework underscores an evolutionary trajectory initiated by significant star formation, potentially driven by gas-rich mergers, leading to subsequent quenching of star formation.
2. Stellar Mass Densities and Size Distributions: The paper measures stellar mass densities within SMGs and finds them comparable to those of cQGs, with densities exceeding those found in evolved ellipticals in the local universe by an order of magnitude. The analysis of distribution in sizes reveals similar compactness, strengthening the hypothesis of an evolutionary link.
3. Consistent Space Densities and Starburst Durations: The space densities of the SMGs and cQGs align under the assumption of a duty cycle of SMG starbursts lasting $42^{+40}_{-29}$ Myr, a duration supported by independent gas depletion and clustering analyses. This supports the assertion that a significant fraction of stellar content in these galaxies formed rapidly during initial starbursts.
4. Spectral and Structural Analyses: The paper employs near-infrared spectroscopy to robustly constrain the age and stellar population parameters of cQGs, complemented by spatial and structural analyses of SMGs via high-resolution imaging.

Implications

This research enhances the understanding of the formation of massive galaxies in the early universe. Identifying SMGs as precursors to cQGs provides a coherent evolutionary model linking large-scale star formation episodes to observed galaxy structures at $z = 2$. This connection has significant implications for the paper of galaxy formation and evolution, particularly regarding the mechanisms that quench star formation and transform starbursting systems into quiescent stellar assemblies.

Future Directions

Future research may focus on refining the evolutionary timeline and detailed mechanisms transitioning SMGs to cQGs. Enhanced datasets from upcoming astronomical instruments like the James Webb Space Telescope will allow for better resolution of high redshift galaxies, potentially identifying intermediate galaxy forms and confirming dynamical processes hypothesized in this paper. Additionally, deeper multi-wavelength surveys will be instrumental in further constraining the physical conditions within these galaxies, offering greater insight into the path from early star formation to quiescence.