The Role of Nuclear Starbursts in Luminous Infrared Seyfert 2 Galaxies

We present HST (WFPC2 and FOC) images and UV GHRS spectraplus ground-based optical spectra of four Luminous Infrared Galaxies (LIRGs) that have Seyfert 2nuclei (Mrk 477, NGC 7130, NGC 5135 and IC 3639). The data provide direct evidence of the existence of a central nuclearstarburst that dominates the UV and optical light and are dusty and compact. The bolometricluminosity ( 10¹⁰ L) of these starbursts is similar to the estimated bolometric luminosities of their obscured Seyfert 1 nuclei, and thus they contributein the same amount to the overall energetics of these galaxies. An extended work based on ground-based optical spectra of the 20 brightest nuclei known indicate that at least 40%of the Seyfert 2 galaxies harbor a nuclear starburst. The eight Seyfert 2 nuclei thatharbor a starburst are strong IR emitters. This suggests that nuclear starbursts can make a significant contribution or even dominate the UV and optical light of LIRGs.     

Radio AGNs among Luminous Infrared Galaxies

An analysis of radio and FIR emission in over 1500IRAS selected galaxies produces a good linear correlationbetween radio and FIR luminosity, indicating that star formationin normal field galaxies dominates the infrared luminosityin the local volume. Galaxies with clear radio-excess (definedas having at least5 times larger radio flux over expected from FIR) are identified as hosting a radio AGN, and they account for onlyabout 1% of the whole sample. This fraction increases to 10% among themore luminous galaxies with L _1.4GHz 10²³ W Hz^-1 (equivalently L _60m 10¹¹ L), however. The characteristic mid-IR excess of a Seyfert nucleus is ubiquitously present amongthe radio-excess objects, suggesting that mid-IR excess isa robust tracer of an AGN despite the high mid-IR opacity.We conclude that about 30% of the luminous infrared galaxies(L _60m 10¹¹ L) host an AGN based on themid-IR excess, and about 40% of the mid-IR excess AGNs alsohost a radio AGN. A VLA imaging survey of a distance limited sample of IR luminousgalaxies has revealed the presence of 100 kpc scale giant radioplumes in 3 out of 9 cases (Mrk 231, Mrk 273, NGC 6240). Theirlarge spatial extent, energetics, and presence of a powerful AGN in each case suggests that an AGN is the power source. Such plumesare not detected in other ultraluminous infrared galaxies which lack clear evidence for an AGN, such as Arp 220.     

Continuum Evn and Merlin Observations of Ultra Luminous Infrared Galaxies

Radio imaging of ULIR galaxies is ideal to explore the connection between the starburst and the AGN phenomenon since it is unaffected by dust obscuration, and provides the required high angular resolution to distinguish between an AGN and starburst emission. We have made combined 18 cm radio continuum, EVN and MERLIN observations of 13 ULIRGs that have the parsec and deci-parsec scale resolution necessary to distinguish between an AGN and supernovae remnants at the centres of these galaxies, and assess the contribution of each to the total energy distribution. Images of three galaxies are presented here.     

The Role of Starbursts in the Evolution of Galaxies

We have determined, for the first time, the nitrogen-to-oxygen abundance ratio (N/O) for a large sample of starburst nucleus galaxies (SBNGs) and compared it to the values observed in normal spiral galaxies. The N/O ratios in SBNGs are ∼ 0.2 dex higher than in normal HII regions observed in the discs of late-type spirals, but are comparable to the values found in the bulges of normal early-type spirals. The variation of the N/O ratio as a function of metallicity follows a primary + secondary relation, but the increase in nitrogen does not appear as a continuous process. Assuming that nitrogen is produced by intermediate-mass stars, we show that our observations are consistent with a model in which the bulk of the nitrogen was formed during past sequences of bursts of star formation which have probably started 2 or 3 Gyr in the past. What we observe, therefore, could be the main production of nitrogen in the bulges of these galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

The clustering properties of Luminous Red Galaxies

By cluster analysis, we study the clustering properties of Luminous Red Galaxies (LRGs) and compare them with those of Main galaxies. We find that the clustering properties of Luminous Red Galaxies is different from those of Main galaxies, and that LRGs cluster mainly in form of close double and multiple galaxies, galaxy groups. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Building Blocks of the most Luminous Galaxies

Nearby luminous galaxies serve as templates to gain insight into the building blocks of the most luminous galaxies in the distant universe. In this conference I have shown that the most luminous galaxies in the Local Universe are mergers of evolved gas-rich galaxies that radiate the bulk of their energy in the mid and far-infrared. The most important implication for future studies on the formation of galaxies at early cosmological timescales is that they will appear as luminous sub-millimeter sources. This revised version was published online in September 2006 with corrections to the Cover Date.     

A Catalog of Luminous Infrared Galaxies in the IRAS Survey and Second Data Release of SDSS

We selected a sample of luminous infrared galaxies by cross-identification of the Faint Source Catalogue (FSC) and Point Source Catalogue (PSC) of the IRAS Survey with the Second Data Release of the SDSS. The size of our sample is 1267 for FSC and 427 for PSC by using the 2σ significance level cross-section. The "likelihood ratio" method is used to estimate the individual's reliability and for defining two more reliable subsamples (908 for FSC and 356 for PSC). A catalog of infrared, optical and radio data is compiled and will be used in further work. Some statistical results show that luminous infrared galaxies are quite different from ultra-luminous infrared galaxies. The AGN fractions of galaxies at different infrared luminosities and the radio-infrared correlations are consistent with the previous studies.     

High Resolution Radio Observations of Luminous IR Galaxies

High resolution radio observations provide a unique tool for investigation ofultraluminous infrared galaxies, due to the combination of high angularresolution and source transparency available at centimeter wavelengths. Thetypical angular size of the IR emitting region in the most luminous systems isof order 0.1 arcsec, while dust absorption appears to obscure this region fromdirect view at wavelengths shorter than 100 microns. Radio observationswith VLBI and MERLIN are revealing compact radio structures indicative of bothstarburst and AGN activity in these systems. Additional observations arerequired to clarify relationships between radio structures and the energygeneration mechanisms, and to realize the full potential of radio interferometryfor ULIRG studies.     

Ultraluminous Infrared Galaxies: Far-Infrared Highlights

We discuss two significant recent developments in the far-IRwith relevance to the study of Ultraluminous Infrared Galaxies(ULIRGs). The first of these is the discovery of an isotropiccosmological infrared background radiation (CIB). This has beendetected in observations by two different instruments (FIRAS (Puget etal. 1996, Hauser et al. 1998) and DIRBE (Fixsen et al. 1998)) aboardthe COBE satellite, with consistent results. The second concernsobservations with the ISO satellite at 175m. Several groups haveconducted deep surveys with ISO at its most sensitive, longwavelength, 175m. If one assumes that the CIB is a coaddition ofdiscrete sources, it is entirely possible that deep long wavelengthobservations with ISO can detect these objects (Guiderdoni et al.1997). Several groups have undertaken such observations (eg. Puget etal. 1998, Kawara et al. 1998), and it would appear that a large numberof faint far-IR sources have been found. For the FIRBACK survey, whichis discussed in detail, covering about 4 sq. deg. to 175m fluxlimits of 100mJy, we are detecting 100 sources persq. deg., which amounts to about 10% of the CIB. The presence of theCIB at these flux levels, and its apparent origin as the integratedflux from numerous point sources, suggests that dust obscuration playsan important role in the early universe. We speculate that the sourcescontributing to the CIB may be a population of ULIRG-like objects atmoderate to high redshift.     

Quasi-periodical features in the distribution of Luminous Red Galaxies

A statistical analysis of radial distributions of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS DR7) catalogue within an interval 0.16≤z≤0.47 is carried out. We found that the radial distribution of ～ 106,000 LRGs incorporates a few quasi-periodical components relatively to a variable η, dimensionless line-of-sight comoving distance calculated for the ΛCDM cosmological model. The most significant peaks of the power spectra are obtained for two close periodicities corresponding to the spatial comoving scales (135±12) h^?1?Mpc and (101±6) h^?1?Mpc. The latter one is dominant and consistent with the characteristic scale of the baryon acoustic oscillations. We analyse also the radial distributions of two other selected LRG samples: ～33,400 bright LRGs (?23.2<M≤?21.8) and ～60,300 all LRGs within a rectangle region on the sky, and show differences of the quasi-periodical features characteristic for different samples. Being confirmed the results would allow to give preference of the spatial against temporal models which could explain the quasi-periodicities discussed here. As a caveat we show that estimations of the significance levels of the peaks strongly depend on a smoothed radial function (trend) as well as characteristics of random fluctuations.     

AGN Lifetimes in UV-selected Galaxies:A Clue to Supermassive Black Hole-galaxy Coevolution

The coevolution between supermassive black holes(SMBHs)and their host galaxies has been proposed for more than a decade,albeit with little direct evidence about...     

具有尘带的椭圆星系的红外辐射特性

IRAS在12,25,60和100μm的巡天,给我们提供了研究各类星系红外辐射特性的可能。为了研究具有尘带的E和SO星系的红外辐射特性,我们利用了E.Sadler给出的完备的E和SO星系表。在该星系表中共列出248个夭体,其中38个被证记为IRAS点源,且又有确切的60和100μm的流量值。在这38个天体中有6个被列在K.Ebneter和B.Balik最新发表的具有全带的椭圆星系表中。我们以这6个星系作为具有尘带的E和SO星系的样本,其它32个没有尘带的E和SO星系即作为对照样本。为了讨论具有尘带的椭圆星系的红外辐射特性,我们利用非参数Mann-Whitney检验,对这两个样本的LIR和FIR/FB的分布作了讨论,结果是在对于置信度α=0.05的水平上,我们不能拒绝另一假设:这两个样本的LIR和FIR/FB的分布是相同的。对于同时具有25,60和100μm确切流量的E和SO星系我们讨论了它们的双色图,结果发现,不具尘带的E和SO星系都处于Rowan-Robinson.et al所指出的正常星系区,而一些具有尘和带的ESO星系,则远离这一区域,它们是LINER和SEYFERT星系。     

ISO Spectroscopy of Ultraluminous Infrared Galaxies

Spectroscopy from the Infrared Space Observatory ISO has for the first timeprovided the sensitivity to exploit the diagnostic power ofmid-infrared fine structure lines and PAH features for the study ofultraluminous infrared galaxies (L_IR >10¹² L ). We report on observations obtainedwith SWS, ISOPHOT-S, and the CVF option of ISOCAM. From both fine structure lines and PAH features, we find that the majority of ULIRGs is predominantlypowered by star formation. Our total sample of about 75 ULIRGs allows tosearch for trends within the class of ULIRGs: The fraction of AGNs increaseswith luminosity above 3 × 10¹²L but there is no obvioustrend for ULIRGs to be more AGN-like with more advanced merger phase.     

光学亮星系大尺度分布中的多级结构

本文在Wen等人工作的基础上,对CfA红移巡天样本中银道以北和以南天区中星系的大尺度分布分别进行了分维计算并比较其所得结果。分析表明,这两个区域内星系的大尺度分布存在显著差异。说明CfA样本还不能构成代表宇宙大尺度结构的好样本。另一方面,两个区域中样本分析结果又存在着一些明显的共同点:它们都表现出明显的多级分形特征。结合对IRAS星系红移巡天样本和星系分立小天区红移巡天样本的分析结果。我们认为,多级分形很可能是宇宙大尺度结构的一个普遍和重要的特征。本文对这一特征的含义也作了简略的讨论。     

Infrared Imaging of Perpendicular Nested Bars in Spiral Galaxies with the Infrared Camera at the Carlos Sánchez Telescope

Images are presented of some of the galaxies in the sample of the BARS `International Time Project' in the near-infrared JHK _s bands, obtained with the Infra-Red Camera at the 1.5 m Carlos Sánchez Telescope, Teide Observatory, between 1996 and 1998. We discuss the scientific importance of imaging galaxies in the near-infrared bands and recent and future developments concerning the Infra-Red Camera. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Origin of Infrared Emission from the Infrared Luminous Galaxy NGC 4418

We present a study of the origin of infrared (IR) emission in the optically normal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features and continua in the range of 3600-8000 A from the Sloan Digital Sky Survey into a set of simple stellar populations, we derive the stellar properties for the nuclear region of NGC 4418. We compare the observed infrared luminosity with the one derived from the starburst model, and find that star-forming activity contributes only 7% to the total IR emission, that as the IR emission region is spatially very compact, the most possible source for the greater part of the IR emission is a deeply embedded AGN, though an AGN component is found to be unnecessary for fitting the optical spectrum.     

The AGN Feedback in Compact Galaxies: On the Impact of a More Massive Central Black Hole

We conduct high-resolution hydrodynamical simulations using the MACER framework to investigate the interplay between the interstellar medium,active galactic nuclei(AGN) feedback and black hole(BH) feeding in a massive compact galaxy,with an emphasis on the impact of different central BH masses.We find that with a more massive central BH,high-speed outflows are more prominent,and the gas fraction in the compact galaxy is reduced.Due to the lower gas density and higher gas temperature,the compact ...     

The Environmental Dependence of the Stellar Velocity Dispersion of Active Galactic Nucleus (AGN) Host Galaxies and Dependence of the Clustering Properties of AGN Host Galaxies on the Stellar Velocity Dispersion

Astrophysics - We use two volume-limited active galactic nucleus (AGN) host galaxy samples constructed by Deng &amp; Wen [47], and explore the environmental dependence of the stellar velocity...