We present the results of a 5-8 micron spectral analysis performed on the largest sample of local ultraluminous infrared galaxies (ULIRGs) selected so far, consisting of 164 objects up to a redshift of ~0.35. The unprecedented sensitivity of the Infrared Spectrograph onboard Spitzer allowed us to develop an effective diagnostic method to disentangle the active galactic nucleus (AGN) and starburst (SB) contribution to this class of objects. The intrinsic bolometric corrections are estimated for both the components, in order to obtain the relative AGN/SB contribution to the total luminosity of each source. Our main results are the following: 1) The AGN detection rate among local ULIRGs amounts up to 70 per cent, with 113/164 convincing detections within our sample, while the global AGN/SB power balance is ~1/3. 2) A general agreement is found with optical classification; however, among the objects with no spectral signatures of nuclear activity, our IR diagnostics find a subclass of elusive, highly obscured AGN. 3) We analyse the correlation between nuclear activity and IR luminosity, recovering the well-known trend of growing AGN significance as a function of the overall energy output of the system: the average AGN contribution rises from ~10 to ~60 per cent across the ULIRG luminosity range. 4) We confirm that the AGN content is larger in compact systems, but the link between activity and evolutionary stage is rather loose. 5) By analysing a control sample of IR-luminous galaxies around z ~ 1, we find evidence for only minor changes with redshift of the large-scale spectral properties of the AGN and SB components. This underlines the potential of our method as a straightforward and quantitative AGN/SB diagnostic tool for ULIRG-like systems at high redshift as well.
We present radio observations of ultraluminous infrared galaxies (ULIRGs) using the Giant Metrewave Radio Telescope (GMRT) and combine them with archival multi-frequency observations to understand whether ULIRGs are the progenitors of the powerful radio loud galaxies in the local Universe. ULIRGs are characterized by large infrared luminosities ($L_{IR}>$10$^{12}$L$\odot$), large dust masses ($\sim10^{8}M_{\odot}$) and vigorous star formation (star formation rates $\sim$10-100 $M_{\odot}~$yr$^{-1}$). Studies show that they represent the end stages of mergers of gas-rich spiral galaxies. Their …
Star-Formation in the Ultraluminous Infrared Galaxy F00183-7111
我们报道了用澳大利亚望远镜紧凑阵列探测到F00183-7111中的分子CO(1-0)气体,F00183-7111是已知的最极端的超亮红外星系之一。我们从CO(1-0)线测量到F00183-7111的红移为0.3292,并估计00183中分子气体的质量为1 $\times$ 10 $^{10}$ M $_{\odot}$。我们发现F00183-7111主要是由活动星系核提供动力的,只有$\sim$总光度的14%是由恒星形成贡献的(SFR $\sim$ 220 M $_{\odot}$ yr $^{-1}$)。我们还提供了F00183-7111的光学图像,它显示了向东的延伸。我们使用无线电连续观测在这个扩展中搜索恒星形成,但没有检测到任何。这表明恒星的形成可能主要是核的。这些观测结果为一个模型提供了额外的支持,在这个模型中,ULIRGs的无线电发射是由恒星形成的强烈爆发和嵌入其核心的无线电大声活动星系核提供动力的,两者都是由富含气体的星系合并引发的。
This paper is the second in a series aimed at examining the gaseous environments of z$\le$0.3 quasars and ultraluminous infrared galaxies (ULIRGs) as a function of AGN/host galaxy properties across the merger sequence. This second paper focuses on the Ly$α$ emission and O VI and N V absorption features, tracers of highly ionized gas outflows, in ULIRGs observed with HST/COS. Ly$α$ emission is detected in 15 out of 19 ULIRGs, and 12 of the 14 clear Ly$α$ detections show emission with blueshifted velocity centroids and/or wings. The equivalent widths of the Ly$α$ emission increase with increasin…
A Chandra observation of the ultraluminous infrared galaxy IRAS 19254--7245 (the Superantennae): X-ray emission from the Compton-thick AGN and the diffuse starburst
我们提出了一个IRAS 19254- 7245的{ \it Chandra}观测,它是一个邻近的ULIRG,也被称为{ \it the Superantennas}。高空间分辨率的{ \it钱德拉}使我们能够解开第一次从嵌入康普顿厚的活动星系核的弥漫星暴辐射。活动星系核的2-10 keV辐射谱符合平坦的幂律($Γ=1.3$)和类He的Fe K $α$谱线,EW $\sim$ 1.5 keV,与以前的观测结果一致。Fe K $α$谱线轮廓可以被解析为中性6.4 keV谱线和电离6.7 keV(类He)或6.9 keV(类H)谱线的混合。与以前的{ \it XMM-Newton}和{ \it suzaku}观测相比,检测到了变化,证明了铁谱线发射的紧凑尺寸。我们拟合的光谱的星系尺度扩展发射不包括活动星系核和其他亮点源的软热分量与kT~0.8 keV。扩展辐射的亮度比活动星系核的亮度低一个数量级。扩展辐射的基本物理和结构性质与星暴驱动的星系风完全一致(不需要AGN的反馈)。在南核以南8 \arcsec处检测到候选超亮X射线源。如果发射是各向同性的,并且与超天线有关,那么这个离核点源的0.3-10 keV光度为~ $6\times 10^{40}$ erg s $^{-1}$。