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arXiv 2411.02002astro-ph.GA
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利用uGMRT研究7个近邻大星系的射电连续晕

Radio Continuum Halos of 7 Nearby Large Galaxies using uGMRT

Souvik Manna, Subhashis Roy, Tapas Baug

备注：
17 pages, Accepted for publication in ApJ
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AI总结：

本研究利用uGMRT对7个近邻大星系开展0.3-0.5 GHz深度射电观测，首次发现2个中等倾角星系的弥散辐射，证实多类星系射电晕尺度更大，还测得晕区谱指数陡化至约-1.5。

摘要：

我们展示了使用升级后的巨型米波射电望远镜（upgraded Giant Metrewave Radio Telescope，uGMRT）0.3-0.5 GHz接收机对7个近邻大星系进行深度射电观测的结果，观测角分辨率约为10角秒。本次观测达到的灵敏度范围约为15至50微央/波束，比此前在这些频率下的观测灵敏度低约3-4倍。对于2个具有中等倾角的星系（NGC3344和NGC3627），我们首次观测到了显著的弥散辐射。在4个近侧向星系——NGC3623、NGC4096、NGC4594和NGC4631中，我们在0.4 GHz天图中探测到的垂直方向射电晕，比约1.5 GHz频率下的观测结果显著更大。对于这4个星系，沿星系盘方向也探测到了显著更大的晕结构。在NGC3623和NGC4594中，我们还探测到了此前未被发现的拉长射电盘。我们还展示了NGC3344和NGC3623在1.3 GHz下的新uGMRT图像，以及NGC3627在1.5 GHz下的新甚大阵（VLA）图像。我们对不同截线上的流量密度拟合了指数函数，发现0.4 GHz uGMRT图像中的分布比约1.5 GHz的高频图像显著更宽。利用0.144 GHz、0.4 GHz和约1.5 GHz的天图，我们制作了7个样本星系的谱指数天图，发现星系晕区域的谱指数陡化至约-1.5的数值。

英文摘要：

We present the results of deep radio observations of 7 nearby large galaxies observed using the upgraded Giant Metrewave Radio Telescope (uGMRT) 0.3-0.5 GHz receivers with an angular resolution of $\sim$10 arcsec. The achieved sensitivities of these observations range from $\approx$15 to 50 $μ$Jy/beam which is $\approx$3-4 factor lower than the previous observations at these frequencies. For 2 galaxies (NGC3344 and NGC3627) with moderate inclination angles, significant diffuse emissions are seen for the first time. Detected radio halos in the vertical direction are significantly larger in our 0.4 GHz maps than compared to the observations at $\sim$1.5 GHz for 4 nearly edge-on galaxies - NGC3623, NGC4096, NGC4594, and NGC4631. For these 4 galaxies, significantly larger halos are also detected along the galaxy disk. For NGC3623 and NGC4594, we could detect elongated radio disks which was not seen before. We also present new uGMRT images of NGC3344 and NGC3623 at 1.3 GHz and a new VLA image of NGC3627 at 1.5 GHz. We fitted an exponential function to the flux densities along different cross-cuts and found a significantly wider distribution at 0.4 GHz uGMRT images than compared to the high-frequency images at $\sim$1.5 GHz. Using maps at 0.144, 0.4, and $\sim$1.5 GHz, we made spectral index maps of the 7 sample galaxies and found steepening of the spectrum up to a value of $\sim$ -1.5 in the halo regions of the galaxies.

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