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1.
The properties of OH megamaser galaxies in the x-ray and radio ranges are discussed. Based on a sample of OH megamaser galaxies it is shown that the x-ray emission and the width of the OH radio line are closely related. The line width is also related to the radio emission from megamasers, but it depends only weakly on the infrared emission and this relationship is statistically less significant. The OH line width and the radio and x-ray emissions depend on the central mass of megamasers. There is a weak correlation between the radio and x-ray emissions owing to multiple scattering of synchrotron photons and bursts from the galactic nucleus. These results indicate that an active nucleus can be dominant in OH megamaser galaxies.__________Translated from Astrofizika, Vol. 48, No. 3, pp. 421–430 (August 2005).  相似文献   

2.
The properties of OH megamaser galaxies in the x-ray region are discussed. Observational data from the XMM-Newton x-ray satellite are presented for three megamasers, IRAS 01418+1651, IRAS 11010+4107, and IRAS 13218+0552. Based on a sample of OH megamaser galaxies it is shown that the x-ray and OH emission are closely coupled. Megamaser emission also correlates with the column density of the medium and the OH emissivity increases as the square of the column density. The results of this study indicate that in OH megamaser galaxies an active nucleus, x-ray heating of molecules, and saturation of the maser emission can play an important role. In some megamasers, active star formation may be the dominant source. __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 171–182 (May 2007).  相似文献   

3.
Radio observations with the VLA-A radio telescope of 30 OH megamaser galaxies at a frequency of 1.49 GHz are discussed. Radio emission was detected from all 30 of these galaxies. Radio emission was detected from 5 of the 30 objects for the first time. Important results were obtained for 12 galaxies that had previously been little studied in the radio continuum. Additional data at 1.49 GHz were obtained for the remaining 13 objects. The core component of the continuum radio emission predominates in the OH megamaser galaxies.Translated from Astrofizika, Vol. 48, No. 1, pp. 125–138 (February 2005).  相似文献   

4.
The properties of a sample of extragalactic H2O maser sources over a wide spectral range are discussed. Based on a sample of 81 maser galaxies it is shown that mega- and kilomasers have completely different properties. In particular, for megamasers the strongest observed relationships are between the parameters of the H2O line and the mass of the galactic nucleus, while the parameters of the line are uncorrelated with the x-ray, infrared, and radio emission. A weak correlation between megamaser emission and the surface (column) density of hydrogen is observed. As for kilomasers, their H2O luminosity depends weakly on the x-ray emission, although in the case of soft x rays this dependence is significant. The H2O luminosity of kilomasers is moderately correlated with the infrared and radio continuum luminosities, but the line parameters are independent of the mass of the nucleus and the surface density of hydrogen.  相似文献   

5.
We have used the Australia Telescope Compact Array (ATCA) to search for 6.7-GHz methanol maser emission towards 87 galaxies. We chose the target sources using several criteria, including far-IR luminosities and the presence of known OH megamasers. In addition, we searched for methanol masers in the nearby starburst galaxy NGC 253, making a full spectral-line synthesis image. No emission was detected in any of the galaxies, with detection limits ranging from 25 to 75 mJy. This is surprising, given the close association of OH and methanol masers in Galactic star formation regions, and significantly constrains models of OH megamaser emission. This absence of maser emission may be a result of low methanol abundances in molecular clouds in starburst galaxies.  相似文献   

6.
An analysis of a sample of OH megamaser galaxies is presented. It is shown that the dependence of LOH on LFIR (far infrared) is not quadratic, as previously assumed, but closer to linear. In megamaser galaxies, LC (radio continuum) LFIR1. Analysis of the data also shows that as the OH emission line width decreases, the absolute values of the pumping efficiency and maser amplification coefficient increase. The radio luminosity of the central component in these galaxies increases with a decrease in the ratio LFIR/LC, whereas the FIR luminosity remains constant. These results will, in all probability, force a reexamination of the questions of pumping and maser emission mechanisms in megamaser galaxies.Translated fromAstrofizika, Vol. 39, No. 3, pp. 417–429, July–September, 1996.  相似文献   

7.
自从首次发现河外星系OH超脉泽以来，30多年(特别是近10年)中对河外星系OH超脉泽的观测和研究取得了极大的进展。到目前为止已发现106个河外星系OH超脉泽，其中包括59个较高红移的源。对河外星系OH超脉泽的观测和研究，是探测和研究其所成协的活动星系核、星暴星系的中央源和拱核盘的有效工具。主要评述对河外星系OH超脉泽的搜索、观测和理论研究现状。  相似文献   

8.
The properties of OH megamaser galaxies are analyzed. Using the linear dependence of L OH on L FIR and the luminosity function for IR galaxies, the expected number of megamasers is estimated. From observational data at many frequencies (from radio waves to x rays), the spectral energy distributions (SEDs) of 16 objects have been plotted and studied. The SEDs of megamasers have the same form from the radio to the x ray range. Considerable emission is observed in the 3 μm range, which evidently indicates the presence of red giants and supergiants in these objects. Possible reasons for the departure of the slope of the dependence of L OH on L FIR from unity are considered. The assumption that collisional pumping may play an important role in the inversion of ground levels of the OH molecule and the saturated gain mechanism in megamasers is confirmed. Translated from Astrofizika, Vol. 42, No. 1, pp. 23–36, January–March, 1999.  相似文献   

9.
OH megamaser emission is known to be associated with the most central 100 parsecs of ultra-luminous infrared galaxies (ULIRGs). The masers are probing dense concentrations of gas, which presumably have accumulated during the merger event forming the ULIRG. Here we summarize the results from primarily high resolution observations of the 18 cm OH lines in a few OH megamaser galaxies. The maser emission is commonly distributed in disks or tori, but there is also some evidence for other components such as outflows. The appearance of the observed emission strongly depends on the observing resolution, and new theoretical modeling has made important steps toward understanding the observed emission. The radio continuum in OH megamaser galaxies is generally starburst related, and detailed studies of the continuum could perhaps be used to date the merger.  相似文献   

10.
The expected x-ray luminosity of megamaser OH galaxies lies between 22.5 and 24.5 erg s-1 Hz-1, with an average of 23.6 erg s-1 Hz-1. This range of luminosities is typical of galaxies with active nuclei and galaxies with active star formation. X-ray heating ( X 10-22-10-18 erg s-1) and collisional pumping may be responsible for the maser emission in megamaser galaxies.  相似文献   

11.
We have produced radio maps, using the Australia Telescope Compact Array, of the central regions of six southern type 2 Seyfert galaxies (NGC 1365, 4945, 6221, 6810, 7582 and Circinus) with circumnuclear star formation, to estimate the relative contribution of star formation activity compared to activity from the active galactic nucleus (AGN). The radio morphologies range from extended diffuse structures to compact nuclear emission, with no evidence, even in the relatively compact sources, for synchrotron self-absorption. In each case the radio to far-infrared (FIR) ratio has a value consistent with star formation, and in all but one case the radio to [Fe  II ] ratio is also consistent with star formation. We derive supernova rates and conclude that, despite the presence of a Seyfert nucleus in these galaxies, the radio, FIR and [Fe  II ] line emissions are dominated by processes associated with the circumnuclear star formation (i.e. supernova remnants and H  II regions) rather than with the AGN.  相似文献   

12.
Results of radio observations of luminous and ultraluminous infrared galaxies are discussed. The declining or flattening of the radio spectra of compact and (in some cases) extended sources found using interplanetary scintillation observations at 102 MHz is accounted for by absorption in thermal plasma, in agreement with the observed brightness of optical emission lines. It is argued that a region of violent star formation occupies the area of a molecular disc 1 kpc in size. The discrepancy between the linear sizes of the compact radio sources and the star forming regions is discussed.  相似文献   

13.
We discuss the detection of redshifted line and continuum emission at radio wavelengths using a Square Kilometer Array (SKA), specifically from low-excitation rotational molecular line transitions of CO and HCN (molecular lines), the recombination radiation from atomic transitions in almost-ionized hydrogen (radio recombination lines; RRLs), OH and H2O maser lines, as well as from synchrotron and free–free continuum radiation and HI 21-cm line radiation. The detection of radio lines with the SKA offers the prospect to determine the redshifts and thus exact luminosities for some of the most distant and optically faint star-forming galaxies and active galactic nuclei, even those galaxies that are either deeply enshrouded in interstellar dust or shining prior to the end of reionization. Moreover, it provides an opportunity to study the astrophysical conditions and resolved morphologies of the most active regions in galaxies during the most active phase of star formation at redshift z 2. A sufficiently powerful and adaptable SKA correlator will enable wide-field three-dimensional redshift surveys at chosen specific high redshifts, and will allow new probes of the evolution of large-scale structure (LSS) in the distribution of galaxies. The detection of molecular line radiation favours pushing the operating frequencies of SKA up to at least 26 GHz, and ideally to 40 GHz, while very high redshift maser emissions requires access to about 100 MHz. To search for LSS the widest possible instantaneous field of view would be advantageous.  相似文献   

14.
We have observed the largest optical spectra sample of 97 blue compact galaxies. Stellar population properties of 74 star-forming BCGs of them were derived by comparing the equivalent widths of strong absorption features and continuum colors, using a method of empirical population synthesis based on star cluster sample. The results indicate that blue compact galaxies are typically age-composite stellar system, the continuum flux fractions at 5870Å due to old stellar components and young stellar components are both important for most of the galaxies. The stellar populations of blue compact galaxies present a variety of characteristics, and the contribution from different age and metallicity components is different. The star formation episodes are usually short, some galaxies maybe undergoing their first global episode of star formation, while for the most sample galaxies, older stars contribute to at most half the optical emission. Our results suggest that BCGs are old galaxies, in which star formation occurs in short intense burst separated by long quiescent phases.  相似文献   

15.
Many galaxies are thought to contain massive black holes, with masses in excess of ten million solar masses, at their centres and warped circumnu-clear toruses. The best evidence comes from observing gas or masers rotating rapidly within a circumnuclear torus surrounding a central body. Here we report on the first MERLIN observations of line emission from the OH megamaser toward IRAS 10173+0828. The position of peak flux contours of the OH megamaser is consistent with that of the continuum in IRAS 10173+0828. This means that the OH megamaser is a diffuse unsaturated maser which could amplify the diffuse 18 cm continuum emission with an amplification factor of order unity.  相似文献   

16.
We identify eight   z > 1  radio sources undetected at 850 μm but robustly detected at 70 μm, confirming that they represent ultraluminous infrared galaxies (ULIRGs) with hotter dust temperatures  (〈 T d〉= 52 ± 10 K)  than submillimetre galaxies (SMGs) at similar luminosities and redshifts. These galaxies share many properties with SMGs: ultraviolet spectra consistent with starbursts, high stellar masses and radio luminosities. We can attribute their radio emission to star formation since high-resolution Multi-Element Radio Linked Interferometer Network (MERLIN) radio maps show extended emission regions (with characteristic radii of 2–3 kpc), which are unlikely to be generated by active galactic nucleus (AGN) activity. These observations provide the first direct confirmation of hot, dusty ULIRGs which are missed by current submillimetre surveys. They have significant implications for future observations from the Herschel Space Observatory and Submillimetre Common-User Bolometer Array 2 (SCUBA2), which will select high-redshift luminous galaxies with less selection biases.  相似文献   

17.
We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC 045080 (or 1300+0144). PGC 045080 is a moderately distant galaxy having a highly inclined optical disc and massive H  i gas content. Radio continuum observations of the galaxy were carried out at 320, 610 MHz and 1.4 GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disc at all three frequencies. At 1.4 GHz and 610 MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with active galactic nucleus (AGN) activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the Hα flux and radio continuum at 1.4 GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC 045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centres can host significant AGN activity. We also mapped the H  i gas disc and velocity field in PGC 045080. The H  i disc extends well beyond the optical disc and appears warped. In the H  i intensity maps, the disc appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disc but is fairly uniform in the other half. We derived the H  i rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of ∼190 km s−1.  相似文献   

18.
俞志尧 《天文学报》2002,43(4):347-352
利用66个OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系,得到log L(OH)=1.71log L(IR)-17.67,即L(OH)α[L(IR)]1。71.这个结果介于Baan所得到的L(OH)α[L(IR)]2和Kandalian所得到的L(OH)α[L(IR)]1.38的结果之间.由于统计时所取的样本数最多,因此结果更能反映实际情况.进一步,可把这66个OH megamaser分为两类;第一类为L(OH)<102L(?)的小光度OH megamaser,小光度OH megamaser包含了14个OH megamaser;第二类为L(OH)≥102L的大光度OH megamaser,大光度OH megamaser包含了52个OHmegamaser.研究结果表明,小光度OH megamaser的光度和它们的宿主星系的红外光度之间相关关系为L(OH)α[L(IR)]1.43,与Kandalia所得到的结果相接近.大光度OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系为L(OH)α[L(IR)]2,与Baan所得到的结果相一致.  相似文献   

19.
Images of neutral hydrogen 21 cm absorption and radio continuum emission at 1.4 GHz from Mrk 273 were made using the Very Long Baseline Array and Very Large Array. These images reveal a gas disk associated with the northern nuclear region with a diameter 0&farcs;5 (370 pc) at an inclination angle of 53 degrees. The radio continuum emission is composed of a diffuse component plus a number of compact sources. This morphology resembles those of nearby, lower luminosity starburst galaxies. These images provide strong support for the hypothesis that the luminosity of the northern source is dominated by an extreme compact starburst. The H i 21 cm absorption shows an east-west gradient in velocity of 450 km s-1 across 0&farcs;3 (220 pc), which implies an enclosed mass of 2x109 M middle dot in circle, comparable to the molecular gas mass. The brightest of the compact sources may indicate radio emission from an active nucleus, but this source contributes only 3.8% to the total flux density of the northern nuclear regions. The H i 21 cm absorption toward the southeast radio nucleus suggests infall at 200 km s-1 on scales 相似文献   

20.
The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L 20cm > 1023 W Hz−1) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L 20cm ∼ 1022 W Hz−1) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters.  相似文献   

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