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1.
High-resolution far-infrared observations of a large area of the star-forming complex RCW 106 obtained using the TIFR 1-m balloon-borne telescope are presented. Intensity maps have been obtained simultaneously in two bands centred around 150 and 210 μm. Intensity maps have also been obtained in the four IRAS bands using HIRES-processed IRAS data. From the 150- and 210-μm maps, reliable maps of dust temperature and optical depth have been generated. The star formation in this complex has occurred in five linear sub-clumps. Using the map at 210 μm, which has a spatial resolution superior to that of IRAS at 100 μm, 23 sources have been identified. The spectral energy distribution (SED) and luminosity of these sources have been determined using the associations with the IRAS maps. The luminosity distribution of these sources has been obtained. Assuming these embedded sources to be zero-age main-sequence stars and using the mass–luminosity relation for these, the power-law slope of the initial mass function is found to be −1.73±0.5 . This index for this very young complex is about the same as that for more evolved complexes and clusters. Radiation transfer calculations in spherically symmetric geometry have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR and the IRAS bands. From this, the r −2 density distribution in the envelopes is ruled out. Finally, a correlation is seen between the luminosity of embedded sources and the computed dust masses of the envelopes.  相似文献   

2.
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.  相似文献   

3.
As dust emission in the far infrared (FIR) is a characteristic property of planetary nebulae we searched the Infrared Astronomical Satellite (IRAS) point-source catalogue for confirmatory evidence on the two new possible planetary nebulae S 68 and 248 - 5 identified by Fesen, Gull & Heckathorn (1983) and the high-excitation planetary nebula 76 + 36 detected by Sanduleak (1983). We identify the nebulae 248 - 5 and 76 + 36 with IRAS sources 07404 - 3240 and 17125 + 4919, respectively and have determined their dust temperature, total FIR emission and optical depth. We also set a lower limit ranging in value from 1.2 × 10-6 to 3.7 × 10-5 forM dust /M bd of the nebula 248 - 5 depending on whether its grain material is silicate or graphite. S 68 could not be identified with an IRAS source.  相似文献   

4.
We have analysed the near-infrared (NIR) and far-infrared (FIR) colours of MASH I and MASH II (the Macquarie/AAO/Strasbourg surveys) planetary nebulae (PNe), using data deriving from the Two-Micron All-Sky Survey and Infrared Astronomical Satellite . We were able to identify ∼5 per cent of the sources in the NIR, and a slightly larger fraction (∼12 per cent) in the FIR. It is concluded that whilst the NIR colours of these nebulae are consistent with those of less evolved (and higher surface brightness) PNe, their FIR colours are markedly different. This disparity is likely to arise as a result of an evolution in dust temperatures, in their line emission characteristics, and in the relative contributions of the 8.6 and 11.3 μm polycyclic aromatic hydrocarbon emission features. A rump of ∼9 per cent of the detected sources have values  log[ F (25 μm)/ F (60 μm)]  which are lower than can be explained in terms of normal nebular evolution, however. If these are comparable in nature to the undetected PNe, then this would argue that ∼1 in 10 of MASH I and II nebulae may represent galactic H  ii regions, Stromgren spheres, symbiotic nebulae or other unrelated categories of source.  相似文献   

5.
Embedded Young Stellar Objects (YSO) in dense interstellar clouds are treated self-consistently to understand their spectral energy distributions (SED). Radiative transfer calculations in spherical geometry involving the dust as well as the gas component, have been carried out to explain observations covering a wide spectral range encompassing near-infrared to radio continuum wavelengths. Various geometric and physical details of the YSOs are determined from this modelling scheme. In order to assess the effectiveness of this self-consistent scheme, three young Galactic star forming regions associated with IRAS 18314-0720, 18355-0532 and 18316-0602 have been modelled as test cases. They cover a large range of luminosity (≈ 40). The modelling of their SEDs has led to information about various details of these sources, e.g. embedded energy source, cloud structure and size, density distribution, composition and abundance of dust grains etc. In all three cases, the best fit model corresponds to the uniform density distribution. Two types of dust have been considered, viz., Draine & Lee (DL) and the Mezger, Mathis & Panagia (MMP). Models with MMP type dust explain the dust continuum and radio continuum emission from IRAS 18314-0720 and 18355-0532 self-consistently. These models predict much lower intensities for the fine structure lines of ionized heavy elements, than those observed for IRAS 18314-0720 and 18355-0532. This discrepancy has been resolved by invoking clumpiness in the interstellar medium. For IRAS 18316-0602, the model with DL type dust grains is preferred.  相似文献   

6.
Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0) and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these molecular lines are free from dust extinction.  相似文献   

7.
We present new observations of the molecular gas distribution in the merging system Arp 299. The first observation set was obtained with the Canada–France–Hawaii Telescope near-IR camera Redeye and the second set comes from the IRAM Plateau de Bure interferometer (combined with short spacings observed at the IRAM 30 m Telescope). In the near IR, H2 ν=1→0 S(1) and Brγ line maps are globally identical: there is bright emission not only at the two galaxy nuclei but also in numerous extranuclear star forming regions. Moreover, there is weaker emission localized in filaments between and around the two nuclei. These filaments correspond to a dust lane observed in optical images from HST. 12CO(1→0), 13CO(1→0) and HCN(1→0) maps are also presented. The structure of the12CO(1→0) map is very close to the NIR observations: the same bright galaxy nuclei and star-forming regions, the same filaments, but half of the total flux is found in weak extended emission. Strong HCN emission is observed in the nucleus A indicating the presence of a large amount of dense gas. Nucleus B1 is weak in 12CO(1→0) emission while nucleus A and star-forming regions C-C′ show more normal 13CO/12CO ratios. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
We present ISOPHOT observations of eight interstellar regions in the 60–200 μm wavelength range. The regions belong to mostly quiescent high-latitude clouds and have optical extinction peaks from   AV ∼1–6 mag  . From the 150- and 200-μm emission, we derived colour temperatures for the classical big grain component which show a clear trend of decreasing temperature with increasing 200-μm emission. The 200-μm emission per unit   AV   , however, does not drop at lower temperatures. This fact can be interpreted in terms of an increased far-infrared (FIR) emissivity of the big grains. We developed a two-component model including warm dust with the temperature of the diffuse interstellar medium (ISM) of   T = 17.5 K  , and cold dust with   T = 13.5 K  and FIR emissivity increased by a factor of >4. A mixture of the two components can reproduce the observed colour variations and the ratios   I 200/ AV   and  τ200/ AV   . The relative abundance of small grains with respect to the big grains shows significant variations from region to region at low column densities. However, in lines of sight of higher column density, our data indicate the disappearance of small grains, perhaps a signature of adsorption/coagulation of dust. The larger size and porous structure could also explain the increased FIR emissivity. Our results from eight independent regions suggest that these grains might be ubiquitous in the galactic ISM.  相似文献   

9.
We report the astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high s 1090 K above the ground state. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km s-1) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containing compact H II regions and strong infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.  相似文献   

10.
We present 450- and 800-μm images, made with the James Clerk Maxwell Telescope, of the NGC 2024 molecular ridge. The seven previously known compact cores, FIR1–7, have been detected, and FIR5 has been resolved into a compact object and an associated extended source to the east. The estimated masses of the dense cores vary between 1.6 and 5.1 M⊙ per 14-arcsec beam, assuming a dust temperature of 30 K and a dust opacity of κ800 μm = 0.002 m2 kg−1. A spectral index map made from the 450- and 800-μm images shows spatial variations, with the spectral index, α ( F ν ∝ να), being systematically lower towards the dense cores. We interpret this as evidence for a lower value of the frequency dependence of the dust opacity, β, towards the denser cores relative to the surrounding molecular material. This may indicate that grain growth is occurring in the cores, prior to planetesimal formation. By comparing the high-resolution 450-μm image with interferometer maps of the integrated CS(2–1) emission, the previously reported discrepancy between dust continuum emission and molecular line emission is found to be very localized. Depletion and temperature variations are discussed as possible explanations.  相似文献   

11.
We report ISO LWS observations towards the star-forming regions W49N, W3(OH) and Sgr B2M in LWS04 mode (high-resolution Fabry–Perot scans). Possible far-infrared laser emission was detected in a water line at 133.55 μm towards W49N, but the spectral resolution was inadequate to establish firmly the nature of the emission. An additional water line was marginally detected in absorption at the 3 σ level, also towards W49N, at 169.74 μm. No OH lines were detected towards Sgr B2M or W3(OH) at either 134.83 or 135.95 μm, either in emission or in absorption.  相似文献   

12.
This is a statistical study of galaxies with a UV excess. A sample of 702 Kazarian galaxies (KG) is used. The KGs are identified with objects from the MAPS, IRAS FSC, IRAS PSC, and NVSS catalogs. The O and E magnitudes are known for more than 92% of the KGs. It is shown that the KG sample is complete up to 16m.0 in the blue and to 16m.5 in the red. More than 36% of the KGs are identified with infrared (IR) sources at wavelengths of 12, 25, 60, and 100 m. Calculations of the far IR (FIR) luminosities show that 4% of the KGs are strong FIR emitters (LFIR ≥ 1011 L⊙). More than 32% of the KGs have been identified as radio sources at a frequency of 1.4 GHz. A determination of the radio luminosities shows that the sample of KGs with known radial velocities include one powerful, LR ≥ 1025 W/Hz, radio object (Kaz 273) which is a BL Lac object. A close correlation (r=0.93) is bound between the FIR and radio luminosities for galaxies with a UV excess. An examination of the relationship between the FIR and radio luminosities for galaxies in different spectral classes shows that the correlation coefficient is higher (r=0.99) and the slope of the fit curve is larger (a=1.18) for Seyfert galaxies. Calculations of the logarithm of the ratio of the FIR and radio fluxes indicate that the sample includes 4 KGs with a radio excess, while there are none with an IR excess. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 369–379 (August 2007).  相似文献   

13.
The galactic and Extragalactic photodissociation regions are primarily heated by photoelectrons ejected from the surface of interstellar dust grains by Far-ultraviolet (FUV) photons. But there is no direct mechanism to measure the photoelectric heating efficiency. To understand the role of dust grains in processing the Interstellar Radiation Field (ISRF) and heating the gas, we compare the intensities I CII, I CO and I FIR for (2 P 3/2→2 P 1/2) & (J = 1→ 0) line emission of CII & CO at 158 μm & 2.6 mm and integrated far-infrared from number of photodissociation regions, HII regions, planetary nebulae, reflection nebulae and high latitude translucent clouds (HLCs). It is found that I CII is linearly correlated with I FIR. In the cold medium where cloud is exposed to weak radiations temperature is low and most of the cooling is due to [CII] emissions. As a result the ratio of I CII/I FIR provide indirect method to evaluate the photoelectric heating efficiency. For the neutral cold medium it is evaluated to be ∼0.028. The FUV radiation field G 0 are estimated through the model calculation of I CII and I CO for different galactic and photodissociation regions. The intensity of FIR radiation I FIR are well represented as 1.23×10−4 G 0(ergs cm−2 s−1 sr−1) almost same as estimated for HLCs by Ingalls et al (2002). Hydrogen density for each source has also been estimated.  相似文献   

14.
Using HST/ACS images in four bands F435W, F606W, F775W and F850LP, we identify optical counterparts to the X-ray sources in the Chandra Deep Field South in the GOODS South field. A detailed study has been made of these sources to study their morphological types. We use methods like decomposition of galaxy luminosity profiles, color maps and visual inspection of 192 galaxies which are identified as possible optical counterparts of Chandra X-ray sources in the CDFS-GOODS field. We find that most moderate luminosity AGN hosts are bulge dominated in the redshift range (z≈0.4–1.3), but not merging/interacting galaxies. This implies probable fueling of the moderate luminosity AGN by mechanisms other than those merger driven.  相似文献   

15.
We have theoretically studied the influence of a far-infrared radiation (FIR) field from Hπ region on the cooling by C and O atoms, C+ ion and CO molecule in a photodissociation region, and a molecular cloud associated with Hπ region (hereinafter referred as HI region) at low temperatures (T k≤200 K). Comparisons have been made for cooling with and without FIR for two extreme abundances (10−4 and 10−7) of the mentioned species for temperatures ranging between 10 and 200K and an hydrogen particle density range 10 cm−3≤n o≤ 107 cm3. The cooling by the species with low line-splitting (CI, Cπ and CO) is significantly influenced by the radiation field for temperaturesT k < 100 K while the effect of radiation field on cooling by OI is significant even at higher temperatures (T k > 100 K). The effect of FIR field on the cooling of CO from low rotational transitions is negligibly small, whereas it is considerable for higher transitions. In general, the cooling terms related to the short-wavelength transitions are more affected by FIR than those related to longer wavelengths. It is also demonstrated here that in the determination of thermal structure of an HI region the dust grains play an important role in the heating of gas only through photoelectron emission following irradiation by far-ultraviolet (FUV) radiation, as the infrared radiation from the dust is too small to have substantial effect on the cooling. It is found that in the Hπ /HI interface the FIR field from grains in the Hπ region is not capable of modifying the temperature of the warmest regions but does so in the inner part where the temperature is low enough.  相似文献   

16.
Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars (R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584, [S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and [S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than ∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar extinctions are suggested to be responsible for this difference  相似文献   

17.
Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2–18.5 μm infrared (IR) spectrophotometric and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = Tcolor/TBB ≥ 1.7, the peak of the 10 μm silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity) of the grains was ≥ 0.4 at a scattering angles, θ ≥ 135° This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

18.
SANTOS-SANZ  P.  SABALISCK  N.  KIDGER  M. R.  LICANDRO  J.  SERRA-RICART  M.  BELLOT RUBIO  L. R.  CASAS  R.  GOMEZ  A.  SANCHEZ PORTERO  J.  OSIP  D. 《Earth, Moon, and Planets》1997,78(1-3):235-241
We present a comparison between images of comet C/1995 O1 (Hale-Bopp) obtained from 12 March to 9 May 1997, with two telescopes of the Observatorio del Teide (IAC, Tenerife, Spain) in visible (Johnson-V filter) and three near-infrared narrowband filters (Brγ (2.166 μm), CO (2.295 μm), and Kcon (2.260 μm)). No significant differences are observed between the images in the three near-infrared bands suggesting that any CO emission is very weak, or produced by an extended flat source. We do not find evidence for the existence of an additional infrared component due to emission by warm dust, or to dust grains of diverse composition and/or size. Visible and infrared images of the same rotational phase look almost identical, supporting the view that the observed jets and shells are mainly dust structures. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
Radio and optical images of early-type galaxies with dust lanes have been analyzed in order to investigate the characteristics of the radio emission and to compare it with their properties at other frequencies. Except three galaxies, the remaining sources of our sample have diffuse radio emission, which does not extend beyond the stellar disk. The radio structures are small and weak (linear sizes in the range 2–10 kpc and radio powers in the range 5×1020–5×1021W Hz–1). Our preliminary results show that in a minority of cases (the most powerful radio sources) radio emission originates in the associated galactic nuclei, where a massive black hole is harboured. On the contrary, in the less powerful among our radio galaxies, sources originating from stellar phenomena may play and important role. We have classified the galaxies with respect to the dust lane morphology, comparing it with the radio emission. The sample is too small in order to reach firm conclusions, but the lack of radio sources in early-type galaxies with dust lanes along the galaxy minor axis seems to suggest that the accretion of material does not reach the conditions necessary to trigger nuclear activity.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

20.
The local correlation between far-infrared (FIR) emission and radio-continuum (RC) emission for the Small Magellanic Cloud (SMC) is investigated over scales from 3 kpc to 0.01 kpc. Here, we report good FIR/RC correlation down to ～15 pc. The reciprocal slope of the FIR/RC emission correlation (RC/FIR) in the SMC is shown to be greatest in the most active star forming regions with a power law slope of ～1.14 indicating that the RC emission increases faster than the FIR emission. The slope of the other regions and the SMC are much flatter and in the range of 0.63–0.85. The slopes tend to follow the thermal fractions of the regions which range from 0.5 to 0.95. The thermal fraction of the RC emission alone can provide the expected FIR/RC correlation. The results are consistent with a common source for ultraviolet (UV) photons heating dust and Cosmic Ray electrons (CRe?s) diffusing away from the star forming regions. Since the CRe?s appear to escape the SMC so readily, the results here may not provide support for coupling between the local gas density and the magnetic field intensity.  相似文献   

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