Abundances of Metal-rich H II Regions in M51
Abundances of Metal-rich H II Regions in M51
复制标题
DOI：
10.1086/424377
复制
发表时间：
2004-07
期刊：
影响因子：
--
通讯作者：
F. Bresolin;D. Garnett;Robert C. Kennicutt Jr.
中科院分区：
文献类型：
--
作者：
F. Bresolin;D. Garnett;Robert C. Kennicutt Jr.
我们用凯克望远镜和低分辨率成像光谱仪获得了旋涡星系M51中H Ⅱ区的多目标光谱。对于10个物体，我们已经检测到极光线[N II] λ5755，而[S III] λ6312已经在其中7个物体中测量到。这使我们能够测量气体的电子温度，并获得氧，硫和氮的丰度为10 H II区域。与先前对M51中少数H II区域的光电离模型和强线丰度指示器的预期相反，大多数物体的O/H丰度低于太阳值，其中金属最丰富的H II区域P203和CCM 72的log（O/H）= -3.16 [~1.4（O/H）<$]和log（O/H）= -3.29 [~1.0（O/H）<$]，分别减少的O/H的因素高达2或3相对于以前的间接测定具有重要的后果，为校准的经验丰度指标，如R23，在丰度和激发范围内发现的旋涡星系的中心区域。因此，这些星系中的丰度梯度可能比使用这种经验校准确定的丰度梯度要平坦得多。H Ⅱ区的电子温度范围为（0.19-1.04）R 0，表明M51的丰度梯度较浅：-0.02 ± 0.01 dex kpc-1。发现S/O丰度比与以前在其他旋涡星系中测定的值相似，log（S/O）= 1.6。因此，我们没有发现证据的变化，在高氧丰度的恒星初始质量函数或核合成。测得过量的氮，log（N/O）为-0.6。我们的新的丰度的基础上，我们修改了M51的有效产量，现在发现是几乎4倍低于以前的估计，我们讨论了这一结果的背景下，在星系盘的化学演化。沃尔夫-拉叶星的特征（4660 <$m的蓝色凸起和5696 <$m的C III线）在M51的大量H II区域中被探测到，C III λ5696线优先出现在中心，最富金属的物体中。
We have obtained multiobject spectroscopy of H II regions in the spiral galaxy M51 with the Keck I telescope and the Low Resolution Imaging Spectrometer. For 10 objects we have detected the auroral line [N II] λ5755, while [S III] λ6312 has been measured in seven of these. This has allowed us to measure the electron temperature of the gas and to derive oxygen, sulfur, and nitrogen abundances for the 10 H II regions. Contrary to expectations from previous photoionization models of a few H II regions in M51 and from strong-line abundance indicators, the O/H abundance is below the solar value for most objects, with the most metal-rich H II regions, P203 and CCM 72, having log(O/H) = -3.16 [~1.4(O/H)☉] and log(O/H) = -3.29 [~1.0 (O/H)☉], respectively. The reduction of O/H by factors of up to 2 or 3 with respect to previous indirect determinations has important consequences for the calibration of empirical abundance indicators, such as R23, in the abundance and excitation range found in the central regions of spiral galaxies. The abundance gradients in these galaxies can therefore be considerably flatter than those determined by using such empirical calibrations. The H II regions with a measured electron temperature span the range (0.19-1.04) R0 in galactocentric radius and indicate a shallow abundance gradient for M51: -0.02 ± 0.01 dex kpc-1. The S/O abundance ratio is found to be similar to previous determinations of its value in other spiral galaxies, log(S/O) ≈ -1.6. Therefore, we find no evidence for a variation in massive-star initial mass function or nucleosynthesis at high oxygen abundance. An overabundance of nitrogen is measured, with log(N/O) ≃ -0.6. On the basis of our new abundances, we revise the effective yield for M51, now found to be almost 4 times lower than previous estimates, and we discuss this result in the context of chemical evolution in galactic disks. Features from Wolf-Rayet stars (the blue bump at 4660 Å and the C III line at 5696 Å) are detected in a large number of H II regions in M51, with the C III λ5696 line found preferentially in the central, most metal-rich objects.