解析 COSMOS 場中瀰塵恆星形成星系的特徵與演化

Abstract

宇宙時間內星系中塵埃特性的測量可以有效約束星系形成理論。近期研究顯示，在固定恆星質量的情況下，位於"Cosmic noon"(z ∼ 2)的星系塵埃質量比本 地宇宙中的高出約一個數量級，暗示早期宇宙中塵埃形成效率的劇烈變化。然而，這些研究往往在關鍵的遠紅外波段深度或重要信息如氣相金屬度上缺乏足夠的深入研究，可能導致偏頗結果或無法得出明確解釋。基於新創建的 super-deblended 目錄，該目錄包括最新的超深 SCUBA-2 450 和 850 微米數據，我們選擇了 41 個 主序星系，這些星系在至少三個遠紅外波段中均有顯著觀測，並且其光譜紅移和 氣相金屬度測量數據可在 Keck/MOSFIRE 和 VLT/KMOS 的檔案數據中找到。採用修正黑體(MBB)光譜能量分佈(SED)擬合，我們確定了塵埃的質量和溫度。樣本被分成三個紅移區間(z=0.9、1.5 和 2.4)以研究演化趨勢。我們的結果證實，具有較高恆星質量的星系具有較高的塵埃質量，並且氣相金屬豐度與塵埃質量之間存在正相關。儘管氣相金屬豐度與塵埃對恆星質量比例(D/M∗)之間沒有統計上顯著的相關性，高紅移樣本中的 D/M∗ 仍顯示約為 z ∼ 0 樣本的 3.3 倍。我們還確認了高紅移星系在給定恆星質量和金屬豐度時擁有顯著較高的塵埃質量。通過根據主序星系已知的相關性推斷氣體質量，我們發現從 z ∼ 0 到 z ∼ 2 的星系均遵循塵埃對氣體比和金屬豐度之間的相同相關性。因此，我們將高紅移星系中顯著較高的塵埃質量歸因於較高的氣體比例。

Measurements of dust properties in galaxies across cosmic time can help put valuable constraints on galaxy formation theories. Recent studies have shown that at a fixed stellar mass, galaxies at cosmic noon (z ∼ 2) have about one order of magnitude higher dust mass than those in the local Universe, suggesting a drastic change in dust formation efficiency in the early Universe. However, these studies often lack sufficient depths in the critical far-infrared wavebands or key information such as gas-phase metallicity, leading to potentially biased results or inconclusive explanations. Based on a newly created super-deblended catalogue that includes the latest ultra-deep SCUBA-2 450 and 850 μm data, we select 41 main-sequence galaxies that are significantly detected in at least three far-infrared bands, and their spectroscopic redshifts and gas-phase metallicity measurements are available in the archival data of Keck/MOSFIRE and VLT/KMOS. Employing modified blackbody (MBB) spectral energy distribution (SED) fitting, dust masses and temperatures were determined. The sample was divided into three redshift bins (z=0.9, 1.5, and 2.4) to study evolutionary trends. Our results confirm that sources with higher stellar masses have higher dust masses, and a positive correlation exists between gas-phase metallicity and dust mass. Despite no statistically significant correlation between metallicity and the dust-to-stellar mass ratio (D/M∗), D/M∗ ratios in higher redshift samples are shown approximately 3.3 times larger than those at z ∼ 0. We also confirm that higher redshift galaxies have significantly higher dust masses at given stellar masses and metallicity. By inferring gas masses from the known correlations for the main sequence galaxies, we find that galaxies from local to z ∼ 2 all follow the same correlation between dust-to-gas ratios and metallicity. As a result, we attribute the significantly higher dust masses at higher redshifts to higher gas fractions.