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首页> 外文期刊>The Astrophysical journal >HOT DUST AND POLYCYCLIC AROMATIC HYDROCARBON EMISSION AT LOW METALLICITY: A SPITZER SURVEY OF LOCAL GROUP AND OTHER NEARBY DWARF GALAXIES
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HOT DUST AND POLYCYCLIC AROMATIC HYDROCARBON EMISSION AT LOW METALLICITY: A SPITZER SURVEY OF LOCAL GROUP AND OTHER NEARBY DWARF GALAXIES

机译：低金属度下的热尘和多环芳烃排放：局部群和其他附近矮星系的斯皮策调查

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摘要

We present Spitzer 4.5 and 8.0 μm imaging of 15 Local Group and nearby dwarf galaxies. We find that the diffuse 8 μm emission is spatially correlated with regions of active star formation. Our sample spans a range of > 1 dex in nebular metallicity and 3 orders of magnitude in current star formation rate, allowing us to examine the dependence of emission from hot dust and PAHs on these parameters. We detect prominent diffuse 8 μm emission from the four most luminous galaxies in the sample (IC 1613, IC 5152, NGC 55, and NGC 3109) and only very low surface brightness emission from four others (DDO 216, Sextans A, Sextans B, and WLM). These are the first spatially resolved images of diffuse 8 μm emission from such low-metallicity objects [12 + log (O/H) ～ 7.5]. We observe correlations of this emission with the current star formation rate and the nebular metallicity of these galaxies. However, we also see evidence suggesting that other processes may also have a significant effect on the generation of this emission. These systems all have evidence for old and intermediate-age star formation; thus, the lack of diffuse 8 μm emission cannot be attributed to low galaxy ages. Also, winds cannot explain the paucity of this emission, since high-resolution imaging of the neutral gas in these objects shows no evidence of blowout. We propose that the lack of diffuse 8 μm emission in low-metallicity systems may be due to the destruction of dust grains by supernova shocks, assuming a long timescale to regrow dust. It is likely that the observed weak emission is at least partly due to a general absence of dust (including PAHs), in agreement with their low metallicities.
机译：我们介绍了15个本地群和附近的矮星系的Spitzer 4.5和8.0μm成像。我们发现，漫射8μm发射与活动恒星形成区域在空间上相关。我们的样本的星状金属性跨度范围大于1 dex，当前恒星形成率的范围大于3个数量级，这使我们能够检查热尘埃和PAHs的发射对这些参数的依赖性。我们检测到样品中四个最发光的星系（IC 1613，IC 5152，NGC 55和NGC 3109）的显着漫反射8μm发射，而其他四个（DDO 216，Sextans A，Sextans B，和WLM）。这些是从这种低金属性物体中扩散出的8μm发射的第一个空间分辨图像[12 + log（O / H）〜7.5]。我们观察到这种发射与当前星系形成率和这些星系的星云金属度的相关性。但是，我们也看到证据表明其他过程也可能对该排放的产生产生重大影响。这些系统都具有形成中老年恒星的证据。因此，缺乏漫射的8μm发射不能归因于低星系年龄。同样，风也不能解释这种排放的不足，因为在这些物体中对中性气体进行的高分辨率成像没有显示出井喷的迹象。我们建议在低金属系统中缺乏弥漫性的8μm发射，这可能是由于超新星冲击导致了尘粒的破坏，假设有较长的再生时间。观察到的微弱排放至少部分是由于普遍缺乏粉尘（包括多环芳烃）及其低金属性所致。

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