AI 中文总结
该研究结合eROSITA全天巡天与多波段目录，在低红移星系样本中选X射线AGN目录，探究特定吸积率分布等，识别众多低质量星系中的X射线AGN，借助贝叶斯框架约束分布，发现相关效应及断点，为黑洞占据分数设下限，突出AGN增长细微观点。
AI 中文摘要
将深度广域X射线巡天与多波段目录相结合，有助于深入了解低红移下罕见的、高吸积活动星系核（AGN）和低质量星系，后者可能是早期宇宙中首批星系的本地类似物。我们利用四波段eROSITA全天巡天，在低红移星系的高完备样本中，包括低质量星系（logM*/Msol<10），选出最大的X射线AGN目录。我们探究它们的特定吸积率分布，λ_SAR，以及不同λ_SAR阈值之上的累积AGN分数。我们的母样本由约535万个从遗产巡天DR10中选出的星系组成，其z波段通量亮于20等，红移0.03<z<0.2。我们特别强调对样本的详细表征，包括估计无偏物理星系属性，以及对X射线孔径测光和宿主星系关联进行严格清理和验证。我们在低质量星系中识别出874个X射线AGN，其中大多数是新发现的X射线发射体。借助贝叶斯框架，利用所有母样本星系的X射线信息，我们在广泛的λ_SAR范围内约束特定吸积率分布，p(logλ_SAR | M*, z)，并发现二阶质量依赖效应。我们在高λ_SAR处检测到一个断点，可能表明爱丁顿极限、自调节黑洞增长。对λ_SAR>10^-3之上的p(logλ_SAR | M*, z)积分，我们发现低质量星系的累积AGN分数约为1%，为该区域的黑洞占据分数设定了一个坚实的下限。总体而言，我们的特定吸积率分布，采样至尚未探索的低质量区域，突出了AGN增长和吸积历史中更细微、质量依赖的观点，这在未来建模中必须予以考虑。
英文摘要
Combining deep, wide-area X-ray surveys with multi-wavelength catalogues provides insights into rare, highly-accreting AGN and low-mass galaxies at low redshift, the latter potentially representing local analogues of the first galaxies in the early Universe. We use the four-pass eROSITA All Sky Survey to select the largest catalogue of X-ray AGN in a highly complete sample of low-redshift galaxies, including low-mass (logM*/Msol<10) ones. We probe their distribution of specific accretion rates, $λ$_SAR, and the cumulative AGN fraction above varying $λ$_SAR thresholds. Our parent sample consists of ~5.35 million galaxies selected from the Legacy Survey DR10 with z-band fluxes brighter than 20 mag and redshifts 0.03<z<0.2. We place particular emphasis on the detailed characterisation of our sample, including estimating unbiased physical galaxy properties and rigorous cleaning and validation of the X-ray aperture photometry and host-galaxy associations. We identify 874 X-ray AGN in low-mass galaxies, most of them newly discovered as X-ray emitters. Thanks to a Bayesian framework that makes use of the X-ray information from all parent sample galaxies, we constrain the specific accretion rate distribution, p(log$λ$_SAR | M*, z), across a wide range of $λ$_SAR and uncover second-order mass-dependent effects. We detect a break at high $λ$_SAR, possibly indicating Eddington-limited, self-regulated black hole growth. Integrating p(log$λ$_SAR | M*, z) above $λ$_SAR>10^-3, we find a cumulative AGN fraction of ~1% for low-mass galaxies, placing a firm lower limit on the black hole occupation fraction in this regime. Overall, our specific accretion rate distributions, sampling down to the as-of-yet unexplored low-mass regime, highlight a more nuanced, mass-dependent view of AGN growth and accretion history that must be taken into account in future modelling.
Comments27 pages, 20 figures; accepted for publication in A&A
