题  目：Mid-infrared Spectroscopy and Multi-wavelength Study of Ultra-luminous Star-forming Galaxies at Redshift z ∼ 2

报告人：方官文 （中国科技大学）

摘  要：In this talk, we present a study of a sample of 14 MIPS 24um sources with 0.2<F(24um)<0.6 mJy in the EGS region with IRS spectroscopy. The IRS spectra of this sample confirms that redshifts of this sample are in a very narrow range around z~1.95(sigma=0.19), and have very strong PAH features at 7.7, 8.6, and 11.3um. The redshift distribution in our sample is very similar to that of the SB-dominated ULIRGs (z~2) studied in other literatures. We fit the multi-wavelength SEDs from U-band to 8um for objects in the sample, and obtained stellar masses of M>10^11 Msun, similar to stellar mass of DRGs, BzKs and SMGs. The total infrared luminosities for objects in this sample were converted using their 8um luminosities L(8 um), indicating that their star formation rate are in range of 410<SFR<1020 Msun/yr. The optical ACS imaging of this sample shows irregular and clumpy morphologies, and a few objects in the sample are so red that they are barely detected at F814W. Because an optical band probes the rest-frame UV band for this sample, we argue that the optical imaging of this sample is inconclusive in studying their morphologies due to their heavy patchy dust distribution. There are deep NIR imaging available in the field obtained in CANDELS, and 4 objects are detected in the HST F160W imaging. Their rest-frame optical morphologies are very diversified including string-like, extended/diffused, and even early type spiral morphologies, implying that there are different formation process for these galaxies. We also search for AGN signature in our sample using X-ray, radio, and MIR emission. Four objects out of 14 sources in the sample are detected in X-ray. The X-ray luminosities for EGS22 and EGS34 can be accounted for by their intensive star formation. EGS25 and EGS27 have higher L(2-10keV) that their star formation can produce, indicating that they harbor AGNs. The MIR study with the 8 and 15um  photometry of this sample shows that 3 X-ray sources have highest 4.5um luminosities and reddest [4.5]-[8.0] colors, consistent with their being AGN dominated. The radio-FIR ratios for this sample are very close to q=2.35 without showing strong radio excess from AGNs, except EGS9 which has q=1.66. Thus 25-30% of the sample show signatures of AGNs in X-ray, MIR or radio.

时  间：2011年12月8日（星期四）下午 14：00

地  点：（北京西路2号）紫台大楼楼 327教室

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