Ultra-diffuse Galaxies as Extreme Star-forming Environments. II. Star Formation and Pressure Balance in H i-rich UDGs
Ultra-diffuse Galaxies as Extreme Star-forming Environments. II. Star Formation and Pressure Balance in H i-rich UDGs
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DOI：
10.3847/1538-4357/ac9673
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发表时间：
2022-09
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影响因子：
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通讯作者：
Erin Kado-Fong;Chang-Goo Kim;J. Greene;Lachlan Lancaster
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作者：
Erin Kado-Fong;Chang-Goo Kim;J. Greene;Lachlan Lancaster
除了占据矮星系群的极端弥散尾部之外，超弥散星系（UDG）本身也是研究极端低密度环境中星星形成的关键实验室。在本系列的第二篇论文中，我们比较了空间分辨的星星形成活动的22个H i选择的UDG和21个“正常”矮星系在120 Mpc的预测内的压力调节，反馈调制（PRFM）理论的星星形成。为此，我们采用了联合光谱能量分布拟合方法，使我们能够估计星星形成率和恒星质量表面密度的紫外光学成像。我们发现，PRFM框架成功地扩展到UDG政权，虽然在我们的样本中的UDG显示出异常低的星星形成率表面密度鉴于其H i含量，这种低星星形成效率可以自然地解释的扩散结构的UDG。事实上，在PRFM框架下，UDG样本中的中平面压力和星星形成之间的关系不仅与“正常”矮参考样本吻合良好，而且与更大质量星系的测量结果吻合良好。我们的研究结果表明，尽管它们的低星星形成效率，富氢UDG不需要形成恒星在一个异国情调的方式。我们还发现，UDG可能是H2穷人相比，甚至整个侏儒人口。
In addition to occupying the extreme, diffuse tail of the dwarf galaxy population, ultra-diffuse galaxies (UDGs) are themselves a key laboratory in which to study star formation in extreme low-density environments. In the second paper of this series, we compare the spatially resolved star formation activity of 22 H i-selected UDGs and 21 “normal” dwarf galaxies within 120 Mpc to predictions within the pressure-regulated, feedback-modulated (PRFM) theory of star formation. To do so, we employ a joint spectral energy distribution fitting method that allows us to estimate star formation rate and stellar mass surface density from UV-optical imaging. We find that the PRFM framework extends successfully to the UDG regime—although the UDGs in our sample show unusually low star formation rate surface densities given their H i content, this low star formation efficiency can be naturally explained by the diffuse structure of the UDGs. In fact, when cast in the PRFM framework, the relationship between midplane pressure and star formation in the UDG sample is in good agreement not only with the “normal” dwarf reference sample, but also with measurements from more massive galaxies. Our results suggest that despite their low star formation efficiencies, the H i-rich UDGs need not be forming stars in an exotic manner. We also find that the UDGs are likely H2 poor compared even to the overall dwarf population.