Lx-SFR-Z Relationship in NGC 300

We examine the relationship between the integrated X-ray luminosity (LX) of high mass X-ray binaries (HMXBs), star formation rate (SFR), and metallicity (Z) on sub-galactic scales within the nearby star-forming galaxy NGC 300 using new and archival Chandra/ACIS-I observations in conjunction with Hubble ACS and WFC, GALEX FUV, and Spitzer 24 μm imaging. We use a Bayesian optimized inference code to identify sources as likely X-ray binaries (XRBs) based on their projected location within NGC 300, their X-ray spectral shape, long- and short-term X-ray variability, and multiwavelength properties, and we determine the most probable Z of each XRB based on the published metallicity gradient in NGC 300. The XRB candidates are sorted into subsamples based on galactocentric distance (a proxy for metallicity), and X-ray luminosity functions down to ~10^36 erg/s are obtained and modeled as a linear combination of high- and low-mass X-ray binary components. The LX-SFR-Z relationship for high-mass XRBs is significantly steeper than reported in previous studies. We propose that this steeper slope is the result of two factors: (1) the use of direct metallicity measurements from stars and auroral nebular emission compared to metallicities inferred from strong-line methods, and (2) the “washing out” of metallicity gradients and variations that occurs in galaxy-integrated studies.

本研究针对邻近恒星形成星系NGC 300的亚星系尺度，利用全新及存档的钱德拉/ACIS-I（Chandra/ACIS-I）观测数据，结合哈勃ACS与WFC（Hubble ACS and WFC）成像、GALEX远紫外（FUV）以及斯皮策24微米（Spitzer 24 μm）成像数据，探究了高质量X射线双星（high mass X-ray binaries, HMXBs）的积分X射线光度（LX）、恒星形成率（star formation rate, SFR）与金属丰度（Z）之间的关联。研究基于候选源在NGC 300内的投影位置、X射线光谱形态、长短时X射线变异性及多波段属性，采用贝叶斯优化推断代码将其识别为X射线双星（X-ray binaries, XRBs）候选体；并依据已发表的NGC 300金属丰度梯度，确定每个X射线双星候选体的最概然金属丰度。随后，本研究按星系心距（作为金属丰度的代理变量）将X射线双星候选体划分为子样本，构建并建模了低至~10^36 尔格每秒的X射线光度函数，该函数可表示为高质量与低质量X射线双星组分的线性组合。研究发现，高质量X射线双星的LX-SFR-Z关联斜率显著陡峭于既往研究报道的结果。我们提出该陡峭斜率源于两方面因素：(1) 本研究采用恒星与极光星云发射的直接金属丰度测量值，而非强线方法推导的金属丰度；(2) 星系整体研究所出现的金属丰度梯度与变化的"抹平效应"。