共查询到20条相似文献，搜索用时 343 毫秒
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D. J. Saikia C. Konar V. K. Kulkarni 《Monthly notices of the Royal Astronomical Society》2006,366(4):1391-1398
We report the discovery of a double–double radio galaxy (DDRG), J0041+3224, with the Giant Metrewave Radio Telescope (GMRT) and subsequent high-frequency observations with the Very Large Array (VLA). The inner and outer doubles are aligned within ∼4° and are reasonably collinear with the parent optical galaxy. The outer double has a steeper radio spectrum compared to the inner one. Using an estimated redshift of 0.45, the projected linear sizes of the outer and inner doubles are 969 and 171 kpc, respectively. The time-scale of interruption of jet activity has been estimated to be ∼20 Myr, similar to other known DDRGs. We have compiled a sample of known DDRGs, and have re-examined the inverse correlation between the ratio of the luminosities of the outer to the inner double and the size of the inner double, l in . Unlike the other DDRGs with l in ≳ 50 kpc , the inner double of J0041+3224 is marginally more luminous than the outer one. The two DDRGs with l in ≲ few kpc have a more luminous inner double than the outer one, possibly due to a higher efficiency of conversion of beam energy as the jets propagate through the dense interstellar medium. We have examined the symmetry parameters and found that the inner doubles appear to be more asymmetric in both its armlength and its flux density ratios compared to the outer doubles, although they appear marginally more collinear with the core than the outer double. We discuss briefly the possible implications of these trends. 相似文献
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C. Konar D. J. Saikia M. Jamrozy J. Machalski 《Monthly notices of the Royal Astronomical Society》2006,372(2):693-702
We present new radio observations at frequencies ranging from 240 to 4860 MHz of the well-known, double–double radio galaxy (DDRG), J1453+3308, using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). These observations enable us to determine the spectra of the inner and outer lobes over a large frequency range and demonstrate that while the spectrum of the outer lobes exhibits significant curvature, that of the inner lobes appears practically straight. The break frequency, and hence the inferred synchrotron age of the outer structure, determined from 16-arcsec strips transverse to the source axis, increases with distance from the heads of the lobes. The maximum spectral ages for the northern and southern lobes are ∼47 and 58 Myr, respectively. Because of the difference in the lengths of the lobes, these ages imply a mean separation velocity of the heads of the lobes from the emitting plasma of 0.036 c for both the northern and southern lobes. The synchrotron age of the inner double is about 2 Myr which implies an advance velocity of ∼0.1 c , but these values have large uncertainties because the spectrum is practically straight. 相似文献
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UV and optical emission lines from the z∼ 2.6 radio galaxy 0828+193: spatially resolved measurements
A. Humphrey F. Iwamuro M. Villar-Martín L. Binette R. Fosbury S. di Serego Alighieri 《Monthly notices of the Royal Astronomical Society》2007,382(4):1729-1737
We present an investigation into the spatial variation of the rest-frame ultraviolet (UV) and optical line and continuum emission along the radio axis of the z ∼ 2.6 radio galaxy 0828+193, using long-slit spectra from the Keck II and Subaru telescopes. Line brightnesses, line ratios and electron temperatures are examined, and their relationship with the arm-length asymmetry of the radio source is also investigated. We find that on the side of the nucleus with the shortest radio lobe, the gas covering factor is higher, and the ionization parameter is lower. The contrasts in environmental density required to explain the asymmetries in the line brightness and the radio arm-length asymmetries are in fair agreement with each other. These results add further weight to the conclusion of McCarthy, van Breugel & Kapahi – lobe distance asymmetries in powerful radio sources are the result of an asymmetry in the environmental density.
We also note that the brightness of both the UV and optical continuum emission shows a similar spatial asymmetry to that shown by the line emission. While the UV continuum asymmetry can be wholly explained by the expected asymmetry in the nebular continuum, the optical continuum asymmetry cannot. We argue that, at least at optical wavelengths, the starlight and/or the scattered light must also be strongly spatially asymmetric. 相似文献
We also note that the brightness of both the UV and optical continuum emission shows a similar spatial asymmetry to that shown by the line emission. While the UV continuum asymmetry can be wholly explained by the expected asymmetry in the nebular continuum, the optical continuum asymmetry cannot. We argue that, at least at optical wavelengths, the starlight and/or the scattered light must also be strongly spatially asymmetric. 相似文献
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TomasDahlén ClaesFransson MagnusNäslund 《Monthly notices of the Royal Astronomical Society》2002,330(1):167-183
Photometric redshifts are used to determine the rest-frame luminosity function (LF) of both early- and late-type galaxies to MB ∼−17.6 for the cluster Cl 1601+42 at z=0.54 . The total LF shows a steep faint-end slope α ∼−1.4 , indicating the existence of a population of numerous dwarf galaxies. Luminous galaxies, with MB ≲−19.5 are mostly red, early-type galaxies, with a LF best described by a Gaussian. Faint galaxies are predominantly blue, late-type galaxies, well fitted by a Schechter function with α ∼−1.7 . Compared with clusters at lower redshift, the steepening of the faint end starts at brighter magnitudes for Cl 1601+42, which may indicate a brightening of the present-day dwarf population relative to the giant population with increasing redshift. Early-type galaxies are centrally concentrated, and dominate the core region, implying that the radial gradient of early-type galaxies seen in local clusters is already established at z∼0.5 . Bright, late-type galaxies are rare, consistent with a decrease in star formation in field galaxies as they are accreted on to the cluster, while faint, blue galaxies are evenly distributed across the cluster, except for a depletion in the core region. The blue fraction is fB ∼0.15 , which is somewhat lower than the Butcher–Oemler average at z∼0.5 . The value of f B is found to increase with limiting magnitude and with radius from the centre. 相似文献
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A. C.Fabian C. S.Crawford K.Iwasawa 《Monthly notices of the Royal Astronomical Society》2002,331(4):L57-L59
We report a Chandra observation of the z =3.395 radio galaxy B2 0902+343. The unresolved X-ray source is centred on the active nucleus. The spectrum is well fitted by a flat power law of photon index of Γ∼1.1 with intrinsic absorption of 8×1022 cm-2 , and an intrinsic 2–10 keV luminosity of 3.3×1045 erg s-1 . More complex models that allow for a steeper spectral index cause the column density and intrinsic luminosity to increase. The data limit any thermal luminosity of the hot magnetized medium, assumed responsible for high Faraday rotation measures seen in the radio source, to less than ∼1045 erg s−1 . 相似文献
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Using simple stellar population synthesis, we model the bulge stellar contribution in the optical spectrum of a narrow-line Seyfert 1 galaxy, RE J1034+396. We find that its bulge stellar velocity dispersion is 67.7 ± 8 km s−1 . The supermassive black hole (SMBH) mass is about (1–4) × 106 M⊙ if it follows the well-known M BH –σ* relation found in quiescent galaxies. We also derive the SMBH mass from the Hβ second moment, which is consistent with that from its bulge stellar velocity dispersion. The SMBH mass of (1–4) × 106 M⊙ implies that the X-ray quasi-periodic oscillation (QPO) of RE J1034+396 can be scaled to a high-frequency QPO at 27–108 Hz found in Galactic black hole binaries with a 10-M⊙ black hole. With the mass distribution in different age stellar populations, we find that the mean specific star formation rate (SSFR) over the past 0.1 Gyr is 0.0163 ± 0.0011 Gyr−1 , the stellar mass in the logarithm is 10.155 ± 0.06 in units of solar mass and the current star formation rate is 0.23 ± 0.016 M⊙ yr−1 . For RE J1034+396, there is no relation between the Eddington ratio and the SSFR as suggested by Chen et al., despite a larger scatter in their relation. We also suggest that about 7.0 per cent of the total Hα luminosity and 50 per cent of the total [O ii ] luminosity come from the star formation process. 相似文献
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We present Very Large Array H i observations of the gas-rich, interacting spiral galaxies, NGC 1253/1253A (Arp 279). The larger of the two galaxies, NGC 1253, has a very pronounced H i ring and well-defined spiral structure. The velocity structure of the H i data shows a sudden change at the position of the spiral arms; we identify this change as evidence of a strong spiral shock and hence proceed to estimate the pattern speed, Ωp , of the spiral arms in NGC 1253. Assuming that the pattern speed is constant across the disc our derived value places the outer Lindblad resonance (OLR) at the position of the observed H i ring. As an accumulation of gas is expected at the OLR when this falls within the disc of a galaxy this agreement provides independent support for the derived value of Ωp . 相似文献
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X. Barcons F. J. Carrera M. T. Ceballos 《Monthly notices of the Royal Astronomical Society》2003,346(3):897-904
The bright type 1 Seyfert galaxy H1419+480 ( z ∼ 0.072) , whose X-ray colours from earlier HEAO-1 and ROSAT missions suggested a complex X-ray spectrum, has been observed with XMM–Newton . The EPIC spectrum above 2 keV is well fitted by a power law with photon index Γ= 1.84 ± 0.01 and an Fe Kα line of equivalent width ∼250 eV. At softer energies, a decrement with respect to this model extending from 0.5 to 1 keV is clearly detected. After trying a number of models, we find that the best fit corresponds to O vii absorption at the emission redshift, plus a 2σ detection of O viii absorption. A photoionized gas model fit yields log ξ∼ 1.15–1.30 (ξ in erg cm s−1 ) with N H ∼ 5 × 1021 cm−2 for solar abundances. We find that the ionized absorber was weaker or absent in an earlier ROSAT observation. An International Ultraviolet Explorer spectrum of this source obtained two decades before shows a variable (within a year) C iv absorber outflowing with a velocity ∼1800 km s−1 . We show that both X-ray and ultraviolet absorptions are consistent with arising in the same gas, with varying ionization. 相似文献
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We report two new XMM–Newton observations of PG1211+143 in 2007 December, again finding evidence for the fast outflow of highly ionized gas first detected in 2001. Stacking the new spectra with those from two earlier XMM–Newton observations reveals strong and broad emission lines of Fe xxv and O viii , indicating the fast outflow to be persistent and to have a large covering factor. This finding confirms a high mass rate for the ionized outflow in PG1211+143 and provides the first direct measurement of a wide angle, subrelativistic outflow from an active galactic nuclei (AGN) transporting mechanical energy with the potential to disrupt the growth of the host galaxy. We suggest PG1211+143 may be typical of an AGN in a rapid super-Eddington growth phase. 相似文献
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