The candidate Seyfert 1-like objects found from ULIRGs in the Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey and 6dF Galaxy Survey

The infrared properties of ULIRGs in samples from the Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey and 6dF Galaxy Survey (SDSS-2dF-6dF Survey) and ULIRGs in the IRAS 1 Jy sample are compared. We find that the infrared properties are quite similar in both the far infrared and the near infrared for those two samples. By using the IRAS two-color diagram and the 2MASS two-color diagram we find that 24 sources in the SDSS-2dF-6dF Survey are candidate Seyfert 1-like sources indicative of strong AGN-dominant nature.     

The SCUBA Local Universe Galaxy Survey – II. 450-μm data: evidence for cold dust in bright IRAS galaxies

This is the second in a series of papers presenting results from the SCUBA Local Universe Galaxy Survey. In our first paper we provided 850-μm flux densities for 104 galaxies selected from the IRAS Bright Galaxy Sample and we found that the 60-, 100-μm ( IRAS ) and 850-μm (SCUBA) fluxes could be adequately fitted by emission from dust at a single temperature. In this paper we present 450-μm data for the galaxies. With the new data, the spectral energy distributions of the galaxies can no longer be fitted with an isothermal dust model – two temperature components are now required. Using our 450-μm data and fluxes from the literature, we find that the 450/850-μm flux ratio for the galaxies is remarkably constant, and this holds from objects in which the star formation rate is similar to our own Galaxy, to ultraluminous infrared galaxies (ULIRGs) such as Arp 220. The only possible explanation for this is if the dust emissivity index for all of the galaxies is ∼2 and the cold dust component has a similar temperature in all galaxies     . The 60-μm luminosities of the galaxies were found to depend on both the dust mass and the relative amount of energy in the warm component, with a tendency for the temperature effects to dominate at the highest L ₆₀. The dust masses estimated using the new temperatures are higher by a factor of ∼2 than those determined previously using a single temperature. This brings the gas-to-dust ratios of the IRAS galaxies into agreement with those of the Milky Way and other spiral galaxies which have been intensively studied in the submm.     

Infrared photometric study of type II quasars

For this paper, we collected almost all of the type II quasars so far discovered. Among them, 485 sources have photometric data at JHK bands, mainly from Two-Micron All-Sky Survey observations, 65 sources have IRAS photometric data in at least one of the three IRAS bands at 25, 60 and 100 μm and 15 sources have IRAS photometric data in all three IRAS bands. We find that in nearly half of all type II quasars, both the near- and far-infrared radiations are dominated by starlight or thermal reprocessing of starlight by dust in the underlying galaxy. The infrared radiation of the other group (slightly over half) is dominated by a non-thermal radiation in the near-infrared, and mostly in the far-infrared also (although there is a mixture particularly for the longer wavelengths). It is proposed that for the later group, hidden broad lines may exist in the infrared. On the basis of our and previous results, we also discuss the possibility that there are two distinct classes of type II quasars: 'true' type II quasars without a broad-line region and heavily obscured type I quasars, in full analogy with the case for type II Seyfert galaxies. No relationships can be found for either the near-infrared or the far-infrared colours and the redshift. Correlations between absolute magnitude in the near- and far-infrared with redshift are found, but could be due to a flux limit (Malmquist bias).     

Dense molecular gas in galactic nuclei

Summary The nuclear regions of many galaxies are not accessible at optical wavelengths and are devoid of HI, but contain large quantities of molecular gas and dust. With recent advances in instrumentation it is now possible to probe the kinematics and physical state of the cool dense interstellar medium, thus providing a new and important tool to investigate the circumnuclear gas in galaxies that are more active than our own. The scope of this review is to summarize results related to the subject with an emphasis on observational data. Sects. 1 and 2 present a general introduction, followed by a discussion of molecular mass estimates. In Sect. 3 correlations between nuclear and global galactic properties are discussed. Sects. 4 and 5 summarize observational results for nearby strongly interacting galaxies, properties of molecular bars and rings, and theoretical advances in modelling the data. The main part of the review (Sects. 6–8) describes the kinematics and the physical and chemical properties of the dense gas, including masers, and compares them with the nuclear region of the Galaxy. Molecular gas in distant galaxies and the evolution of active galaxies are discussed in Sect. 9. Some promising avenues for future research are outlined in Sect. 10.     

A new scheme of radiation transfer in HII regions including transient heating of grains

A new scheme of radiation transfer for understanding the infrared spectra of HII regions, has been developed. This scheme considers non-equilibrium processes (e.g. transient heating of the very small grains, VSG; and the polycyclic aromatic hydrocarbon, PAH) also, in addition to the equilibrium thermal emission from normal dust grains (BG). The spherically symmetric interstellar dust cloud is segmented into a large number of “onion skin” shells in order to implement the non-equilibrium processes. The scheme attempts to fit the observed SED originating from the dust component, by exploring the following parameters: (i) geometrical details of the dust cloud, (ii) PAH size and abundance, (iii) composition of normal grains (BG), (iv) radial distribution of all dust (BG, VSG & PAH). The scheme has been applied to a set of five compact H II regions (IRAS 18116 − 1646, 18162 − 2048, 19442 + 2427, 22308 + 5812, and 18434 - 0242) whose spectra are available with adequate spectral resolution. The best fit models and inferences about the parameters for these sources are presented.     

Zur zeitlichen Variation des Metallgehaltes in der Galaxis

The two oldest known open clusters, NGC 188 and M67, are observed to have a higher heavy-element abundance than the sun and the stars in the Hyades. This observation might be explained by assuming that these clusters were formed from unusually dusty and hence metal-rich interstellar clouds. Alternatively it may be supposed that the radiation pressure produced by stars in the spiral arms of the Galaxy ejected dust from high-latitude clouds. The calculations presented in this paper show that the loss of dust from such clouds might just be sufficient to produce a significant decrease in the mean heavy-element abundance of the interstellar gas. According to this picture, the first burst of star formation in the Galaxy led to a rapid increase in the interstellar heavy-element abundance. Subsequently, the metal abundance of the interstellar gas decreased due to the radiation pressure by young stars. The present rate of change of the heavy-element abundance in the Galaxy depends on the ratio of heavy-element production by stars to ejection of these elements by radiation pressure on dust grains. Since noble gases do not condense on grains, the neon abundance in the interstellar gas should be a monotonously increasing function of time. The observation that the neon abundance in the sun is much lower than that in young stars and nebulae lends some support to the suggestion that ejection of grains from the Galaxy effects the heavy-element abundance in the interstellar gas.     

Three components of 3–4 μm absorption bands

We present 2–4 μm spectra of six infrared sources for which the extinction is not purely interstellar, but is dominated by circumstellar or molecular cloud dust. In all cases the absorption bands differ from the interstellar case, though a component of the interstellar absorption is often present. We also present an improved absorption spectrum for the galactic centre source IRS 7, correcting spurious features in our previous spectrum. Three independent components can be identified: (i) The interstellar component, probably of organic origin, and itself not necessarily invariant; (ii) The symmetrical water ice feature at 3.06 μm, found most commonly in molecular clouds; (iii) A component at 3.53 μm possibly identified with solid formaldehyde grains, and seen only in molecular clouds because of its weakness. Other absorption components appear to be unrelated to those in the 3–4 μm region, most notably the 10 μm absorption found in oxygen-rich giants and the interstellar medium, and presumable inorganic in nature. Our observations include the first detection of water ice absorption in a source in the ρ Oph dark cloud. Biological materials provide the best fit to the interstellar case, but do not presently account for the distinct 3.53 μm component. We stress the need for further laboratory experiments using simpler organic materials.     

Cloudy circumstellar dust shells around young variable stars

A number of variable stars of the Orion population has been identified with IRAS point sources by us. This finding supports the conclusion that the prominent Algol-like minima in the lightcurves of these stars originate from obscurations by dust clouds in a circumstellar shell. The discussion of the existingUBVR data leads to the remarkable conclusion that the extinction properties of the grain populations contained in individual dust clouds moving in one and the same circumstellar shell are quite different.From the multicolour photometric data of the different Algol-like minima we derived individual values of the reddening parameterR = A _v /E(B - V). It covers a remarkable wide range of values from that one typical of the interstellar extinction law up to 7. In the case of SV Cep one of the grain populations produces a virtually neutral extinction. The large values ofR speak in favour of larger than normal (interstellar) dust grains, which may have grown by coagulation processes. The cloudy circumstellar dust shell provides a natural explanation for the observed infrared excess. The properties derived from the optical light variations are fully compatible with the properties deduced from the infrared radiation. The irregularity of the light variations indicates that many clouds are involved and may sometimes superimpose themselves.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

IRAS05391—0217和IRAS06572—0742源的热动性质

利用紫金山天文台青海观测站１３．７米射电望远镜对源ＩＲＡＳ０５３９１０２１７和ＩＲＡＳ０６５７２０７４２进行了１２ＣＯＪ＝１－０观测,获得了气体的相应参数;用ＩＲＡＳ及其他红外观测资料,获得了尘埃热结构;探讨了云中气体的热平衡．对于ＩＲＡＳ０５３９１０２１７中由远红外得出的Ｔｄ＜Ｔｋ的情形,考虑了几种可能的加热机制．光电加热对该云可能是比较重要的;激波可能是另一种加热途径．     

The link between SCUBA and Spitzer: cold galaxies at z≲ 1

We show that the far-IR properties of distant Luminous and UltraLuminous InfraRed Galaxies (LIRGs and ULIRGs, respectively) are on average divergent from analogous sources in the local Universe. Our analysis is based on Spitzer Multiband Imaging Photometer (MIPS) and Infrared Array Camera (IRAC) data of   L _IR > 10¹⁰ L_⊙, 70 μm  selected objects in the  0.1 < z < 2  redshift range and supported by a comparison with the IRAS Bright Galaxy Sample. The majority of the objects in our sample are described by spectral energy distributions (SEDs) which peak at longer wavelengths than local sources of equivalent total infrared luminosity. This shift in SED peak wavelength implies a noticeable change in the dust and/or star-forming properties from   z ∼ 0  to the early Universe, tending towards lower dust temperatures, indicative of strong evolution in the cold dust, 'cirrus', component. We show that these objects are potentially the missing link between the well-studied local IR-luminous galaxies, Spitzer IR populations and SCUBA sources – the   z < 1  counterparts of the cold   z > 1  SubMillimetre Galaxies (SMGs) discovered in blank-field submillimetre surveys. The Herschel Space Observatory is well placed to fully characterize the nature of these objects, as its coverage extends over a major part of the far-IR/sub-mm SED for a wide redshift range.     

The post-explosion shock propagation in the central region of our Galaxy

Immediate consequences of nuclear explosions on the structure and physical state of a galactic disk are considered in this paper. Explosions in the nucleus of a Galaxy generate strong shock waves which, when propagating onward heat and condensing the gas, form thin dense ring-like gaseous features behind it. Such rings and dense gaseous complexes have been observed in the central region of the Galaxy. These features have been treated here as the remnants of galactic shocks generated by nuclear explosions. We have estimated the time elapsed since the corresponding explosion, the energy released by explosion and the initial temperature and the velocity of the shock wave thus generated. The cooling of the gas heated by strong shocks has also been considered. The time taken by shock-heated gas to cool to its original temperature has been estimated to be of the order of 10⁵ to 10⁶ yr, according to the initial shock temperature which is about 9×10⁶ K or 6.4×10⁷ K. The rate of emission of energy and the total amount of energy dissipated away in the form of radiation in the cooling process, have been calculated for different values of initial shocktemperatures and also for different field intensities. The high-energy radiation emitted in the cooling process is suggested here as a source for the heating of dust grains, which ultimately are radiated in the infrared spectrum. Thus, a part of the infrared radiation, as measured by many authors, in the central region of the Galaxy, may originate ultimately from the cooling of the shock-heated gas there.     

Far-infrared emission from ring nebulae

Ring nebulae are known to form around stars like the Wolf-Rayet and the Of stars. The dust in these nebulae is heated by the central star and, therefore, provides a positive clue to the origin of the nebulae, complementing the optical techniques. A systematic search has been carried out to study the infra-red emission from these nebulae based on the IRAS data. The influence of the local interstellar material properties on the formation of nebular dust is studied.     

Infrared studies of X-ray sources

A detailed study of the infrared radiation from galactic X-ray sources indicates that the galactic bulge sources and X-ray binary sources have different infrared emission characteristics. The galactic bulge sources seem to show a power law dependence between the X-ray flux and the infrared flux emitted by the X-ray source. The results presented suggests that the infrared radiation in the galactic bulge sources is dominated by free-free radiation and, in the case of eclipsing binary sources, the black-body emission from the early-type companion star contributes significantly to the infrared radiation.     

Electrons in a closed galaxy model of cosmic rays

We consider the consistency of positrons and electrons with a propagation model in which the cosmic rays are stopped by nuclear collisions or energy losses before they can escape from the Galaxy (the closed-galaxy model). The fact that we find no inconsistency between the predictions and the data implies that the protons which produce the positrons by nuclear reactions could have their origin in a large number of distant sources, as opposed to the heavier nuclei which in this model come from a more limited set of sources. The closed-galaxy model predicts steep electron and positron spectra at high energies. None of these are inconsistent with present measurements; but future measurements of the spectrum of high-energy positrons could provide a definite test for the model. The closed-galaxy model also predicts that the interstellar electron intensity below a few GeV is larger than that implied by other models. The consequence of this result is that electron brems-strahlung is responsible for about 50% of the galactic gamma-ray emission at photon energies greater than 100 MeV.     

Cold Dust and Very Cold Excess Emission in the Galaxy

We provide insight in the origin of the far-IR to mm emission from galaxies by presenting a decomposition of the Galaxy emission where we separate the contributions from dust in the atomic gas and dust associated with quiescent molecular gas as a function of Galacto-centric distance. This decomposition leaves a puzzling very cold emission excess with a brightness independent of Galactic longitude that might be pointing at interstellar matter in the outer Galaxy not traced by H I nor CO emission. This revised version was published online in September 2006 with corrections to the Cover Date.     

On the lack of cold dust in IRAS P09104+4109 and IRAS F15307+3252: their spectral energy distributions and implications for finding dusty AGNs at high redshift

We present upper limits on the 850-μm and 450-μm fluxes of the warm hyperluminous (bolometric luminosity     galaxies IRAS P09104+4109     and IRAS F15307+3252     , derived from measurements using the SCUBA bolometer array on the James Clerk Maxwell Telescope. Hot luminous infrared sources like these are thought to differ from more normal cold ultraluminous infrared     galaxies in that they derive most of their bolometric luminosities from dusty active galactic nuclei (AGNs) as opposed to starbursts. Such hot, dusty AGNs at high redshift are thought to be responsible for much of the mass accretion of the Universe that is in turn responsible for the formation of the supermassive black holes seen in the centres of local galaxies. The galaxy IRAS P09104+4109 is also unusual in that it is a cD galaxy in the centre of a substantial cooling-flow cluster, not an isolated interacting galaxy like most ultraluminous infrared galaxies. Previously it was known to have large amounts of hot     dust from IRAS observations. We now show that the contribution of cold dust to the bolometric luminosity is less than 3 per cent. Most ultraluminous infrared galaxies possess large amounts of cold dust, and it is now known that some cooling-flow cluster cD galaxies do as well. Yet this object, which is an extreme example of both, does not have enough cold gas to contribute significantly to the bolometric luminosity. We outline physical reasons why this could have happened. We then provide a discussion of strategies for finding hot dusty AGNs, given the limitations on submillimetre surveys implied by this work.     

Diatoms on Earth, Comets, Europa and in Interstellar Space

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 Å, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of acosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.     

Galactic PeV neutrinos

The IceCube experiment has detected two neutrinos with energies between 1 and 10 PeV. They might have originated from Galactic or extragalactic sources of cosmic rays. In the present work we consider hadronic interactions of the diffuse very high energy cosmic rays with the interstellar matter within our Galaxy to explain the PeV neutrino events detected in IceCube. We also expect PeV gamma ray events along with the PeV neutrino events if the observed PeV neutrinos were produced within our Galaxy in hadronic interactions. PeV gamma rays are unlikely to reach us from sources outside our Galaxy due to pair production with cosmic background radiation fields. We suggest that in future with simultaneous detections of PeV gamma rays and neutrinos it would be possible to distinguish between Galactic and extragalactic origins of very high energy neutrinos.     

About the nature of IRAS 19075+0921

We use infrared data to further investigate the nature of IRAS 19075+0921. Our results indicate that IRAS 19075+0921 is heavily obscured by its thick, circumstellar envelope and possibly composed of two infrared sources all with late spectral types so that it presents a dual chemistry nature.     

Diatoms on earth,comets, europa and in interstellar space

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 », which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of a cosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.