To study the vertical distribution of the earliest stages of star formation in galaxies, three edge-on spirals, NGC 891, NGC 3628, and IC 5052 observed by the Spitzer Space Telescope InfraRed Array Camera (IRAC) were examined for compact 8 micron cores using an unsharp mask technique; 173, 267, and 60 cores were distinguished, respectively. Color-color distributions suggest a mixture of PAHs and highly-extincted photospheric emission from young stars. The average V-band extinction is ~20 mag, equally divided between foreground and core. IRAC magnitudes for the clumps are converted to stellar masses assuming an age of 1 Myr, which is about equal to the ratio of the total core mass to the star formation rate in each galaxy. The extinction and stellar mass suggest an intrinsic core diameter of ~18 pc for 5% star formation efficiency. The half-thickness of the disk of 8 micron cores is 105 pc for NGC 891 and 74 pc for IC 5052, varying with radius by a factor of ~2. For NGC 3628, which is interacting, the half-thickness is 438 pc, but even with this interaction, the 8 micron disk is remarkably flat, suggesting vertical stability. Small scale structures like shingles or spirals are seen in the core positions. Very few of the 8 micron cores have optical counterparts.

中文翻译：

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观察星系中恒星形成的最早阶段：三个边缘盘中的 8 微米核心

为了研究星系中恒星形成最早阶段的垂直分布，使用斯皮策太空望远镜红外阵列相机 (IRAC) 观察到的三个边缘螺旋，NGC 891、NGC 3628 和 IC 5052 的紧凑 8 微米核心被检查一种不清晰的蒙版技术；分别区分了 173、267 和 60 个核心。颜色-颜色分布表明多环芳烃和年轻恒星高度消光的光球发射的混合物。平均 V 波段消光约为 20 mag，在前景和核心之间平均分配。假设年龄为 1 Myr，团块的 IRAC 星等被转换为恒星质量，这大约等于每个星系的总核心质量与恒星形成率的比率。消光和恒星质量表明，对于 5% 的恒星形成效率，固有核心直径约为 18 pc。NGC 891 的 8 微米内核圆盘的半厚为 105 pc，IC 5052 为 74 pc，随半径变化约 2 倍。对于相互作用的 NGC 3628，半厚为 438 pc，但即使有这种相互作用，8 微米的圆盘也非常平坦，表明垂直稳定性。在核心位置可以看到小规模的结构，如带状疱疹或螺旋状结构。8 微米核心中很少有光学对应物。