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1.
The cluster 3C 129 is classified as a rich cluster. An analysis of the properties of the cluster 3C 129 from ROSAT PSPC and HRI, Einstein IPC, and EXOSAT ME observations is presented. The mean temperature from a joint fit of the ROSAT PSPC and EXOSAT ME data is 5.5(±0.2) keV. The luminosity is 0.6×1044 erg s−1 in 0.2–2.4 keV and 2.7×1044 erg s−1 in 0.2–10 keV. We find a cooling flow with a rate of ∼84 M⊙ yr−1. The central gas density is 6×10−3 cm−3, and the ICM mass is 3.6×1013 M⊙. The total cluster mass is ∼5×1014 M⊙. The X-ray morphology shows an east–west elongation, which is evidence for a recent merger event. The radio source 3C 129.1 is located near the X-ray centre. Another cluster member galaxy (the radio galaxy 3C 129) is a prototype of head-tailed radio galaxies, and is located in the west part of the cluster. The tail points along the gradient of intracluster gas pressure. There are no significant point X-ray sources associated with the AGNs of the two radio galaxies.  相似文献   

2.
We present the results of Australia Telescope Compact Array (ATCA) H  i line and 20-cm radio continuum observations of the galaxy quartet NGC 6845. The H  i emission extends over all four galaxies but can only be associated clearly with the two spiral galaxies, NGC 6845A and B, which show signs of strong tidal interaction. We derive a total H  i mass of at least  1.8 × 1010 M⊙  , most of which is associated with NGC 6845A, the largest galaxy of the group. We investigate the tidal interaction between NGC 6845A and B by studying the kinematics of distinct H  i components and their relation to the known H  ii regions. No H  i emission is detected from the two lenticular galaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCA  J2001−4659  , was detected 4.4 arcmin NE from NGC 6845B and has an H  i mass of  ∼5 × 108 M⊙  . No H  i bridge is visible between the group and its newly detected companion. Extended 20-cm radio continuum emission is detected in NGC 6845A and B as well as in the tidal bridge between the two galaxies. We derive star formation rates of  15–40 M⊙ yr−1  .  相似文献   

3.
We study the origin of unresolved X-ray emission from the bulge of M31 based on archival Chandra and XMM–Newton observations. We demonstrate that three different components are present. (i) Broad-band emission from a large number of faint sources – mainly accreting white dwarfs and active binaries, associated with the old stellar population, similar to the Galactic ridge X-ray emission of the Milky Way. The X-ray to K -band luminosity ratios are compatible with those for the Milky Way and for M32; in the 2–10 keV band, the ratio is  (3.6 ± 0.2) × 1027 erg s−1 L−1⊙  . (ii) Soft emission from ionized gas with a temperature of about ∼300 eV and a mass of  ∼2 × 106 M⊙  . The gas distribution is significantly extended along the minor axis of the galaxy, suggesting that it may be outflowing in the direction perpendicular to the galactic disc. The mass and energy supply from evolved stars and Type Ia supernovae is sufficient to sustain the outflow. We also detect a shadow cast on the gas emission by spiral arms and the 10-kpc star-forming ring, confirming significant extent of the gas in the 'vertical' direction. (iii) Hard extended emission from spiral arms, most likely associated with young stellar objects and young stars located in the star-forming regions. The   L X/SFR  (star formation rate) ratio equals  ∼9 × 1038 (erg s−1)(M⊙ yr−1)−1  , which is about ∼1/3 of the high-mass X-ray binary contribution, determined earlier from Chandra observations of other nearby galaxies.  相似文献   

4.
We present high angular resolution MERLIN observations of the 18-cm OH maser and continuum emission associated with the active core of the ultraluminous infrared galaxy Markarian 273. The continuum emission comes from three distinct regions in the central arcsecond of the galaxy. The brightest region of emission has a double-peaked structure which is spatially coincident with similar structures observed at 6 cm and 2.2 μm. The peak of the OH maser emission is spatially coincident with the peak in the continuum. For the first time the maser emission is spatially resolved, allowing us to measure the gas motion within the central 100 pc of the galaxy. Maser emission is found in both the 1665- and 1667-MHz lines, with no systematic offset found in the spatial locations of the two lines. The brighter component of the maser emission shows ordered motion and is aligned along the axis of the double-peaked structure in the brightest continuum region. The gas motion enables us to estimate the central mass density to be 850±50 M⊙ pc−3, which corresponds to a total mass of ≈1.5×108 M⊙.  相似文献   

5.
Using MERLIN with 0.2-arcsec resolution we have observed neutral hydrogen absorption against the central region of the starburst galaxy NGC 3628. The central region resolves into ∼16 continuum components at 1.4 GHz. From comparison with published 15-GHz data, we infer that these components are supernova remnants, although three components may be consistent with a weak active galactic nucleus. Neutral hydrogen absorption is seen against the continuum emission with column densities ∼1022 cm−2. The absorption appears to be from two separate absorbing structures. Assuming a simple morphology, the main velocity structure can be attributed to a ring of neutral gas with a radius 130 pc rotating around a central starburst with a velocity gradient of 1270 km s−1 kpc−1. From simple assumptions, the mass interior to this ring is 0.9 × 109 M⊙. The second absorption structure may represent outflow from the starburst region or a large-scale galactic structure. Alternatively the absorption structure may be non-axisymmetric, such as a bar.  相似文献   

6.
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   

7.
We present a new determination of the local volume-averaged star formation rate from the 1.4-GHz luminosity function of star forming galaxies. Our sample, taken from the   B ≤12  Revised Shapley–Ames catalogue (231 normal spiral galaxies over an effective area of 7.1 sr) has ≃100 per cent complete radio detections and is insensitive to dust obscuration and cirrus contamination. After removal of known active galaxies, the best-fitting Schechter function has a faint-end slope of  −1.27±0.07  in agreement with the local H α luminosity function, characteristic luminosity   L ∗=(2.6±0.7)×1022 W Hz−1  and density   φ ∗=(4.8±1.1)×10−4 Mpc−3.  The inferred local radio luminosity density of  (1.73±0.37±0.03)×1019 W Hz−1 Mpc−3  (Poisson noise, large-scale structure fluctuations) implies a volume-averaged star formation rate ∼2 times larger than the Gallego et al. H α estimate, i.e.   ρ 1.4 GHz=(2.10±0.45±0.04)×10−2 M⊙ yr−1 Mpc−3  for a Salpeter initial mass function from  0.1–125 M⊙  and Hubble constant of 50 km s−1 Mpc−1. We demonstrate that the Balmer decrement is a highly unreliable extinction estimator, and argue that optical–ultraviolet (UV) star formation rates (SFRs) are easily underestimated, particularly at high redshift.  相似文献   

8.
We present results from two high-resolution hydrodynamical simulations of protocluster regions at   z ≃ 2.1  . The simulations have been compared to observational results for the so-called Spiderweb galaxy system, the core of a putative protocluster region at   z = 2.16  , found around a radio galaxy. The simulated regions have been chosen so as to form a poor cluster with   M 200≃ 1014  h −1 M⊙  (C1) and a rich cluster with   M 200≃ 2 × 1015  h −1 M⊙  (C2) at   z = 0  . The simulated protoclusters show evidence of ongoing assembly of a dominating central galaxy. The stellar mass of the brightest cluster galaxy of the C2 system is in excess with respect to observational estimates for the Spiderweb galaxy, with a total star formation rate which is also larger than indicated by observations. We find that the projected velocities of galaxies in the C2 cluster are consistent with observations, while those measured for the poorer cluster C1 are too low compared with the observed velocities. We argue that the Spiderweb complex resembles the high-redshift progenitor of a rich galaxy cluster. Our results indicate that the included supernovae feedback is not enough to suppress star formation in these systems, supporting the need of introducing active galactic nuclei feedback. According to our simulations, a diffuse atmosphere of hot gas in hydrostatic equilibrium should already be present at this redshift, and enriched at a level comparable to that of nearby galaxy clusters. The presence of this gas should be detectable with future deep X-ray observations.  相似文献   

9.
We report results of an 18-ks exposure with the ACIS instrument on Chandra of the powerful z =0.62 radio galaxy 3C 220.1. The X-ray emission separates into cluster gas of emission-weighted kT ∼5 keV , 0.7–12 keV luminosity (to a radius of 45 arcsec) of 5.6×1044 erg s−1 and unresolved emission (coincident with the radio core). While the extended X-ray emission is clearly thermal in nature, a straightforward cooling-flow model, even in conjunction with a point-source component, is a poor fit to the radial profile of the X-ray emission. This is despite the fact that the measured properties of the gas suggest a massive cooling flow of ∼130 M⊙ yr−1, and the data show weak evidence for a temperature gradient. The central unresolved X-ray emission has a power-law spectral energy index α ∼0.7 and 0.7–12 keV luminosity of 1045 erg s−1, and any intrinsic absorption is relatively small. The two-point spectrum of the core emission between radio and X-ray energies has α rx=0.75 . Since this is a flatter spectrum than seen in other sources where the X-ray emission is presumed to be radio-related, regions close to the active galactic nucleus (AGN) in this source may dominate the central X-ray output, as is believed to be the case for lobe-dominated quasars. Simple unification models would be challenged if this were found to be the case for a large fraction of high-power radio galaxies.  相似文献   

10.
The first spectroscopic census of active galactic nuclei (AGNs) associated with late-type galaxies in the Virgo cluster was carried out by observing 213 out of a complete set of 237 galaxies more massive than   M dyn > 108.5 M⊙  . Among them, 77 are classified as AGNs [including 21 transition objects, 47 low-ionization nuclear emission regions (LINERs) and nine Seyferts] and comprise 32 per cent of the late-type galaxies in Virgo. Due to spectroscopic incompleteness, at most 21 AGNs are missed in the survey, so that the fraction would increase up to 41 per cent. Using corollary near-infrared observations that enable us to estimate galaxy dynamical masses, it is found that AGNs are hosted exclusively in massive galaxies, i.e.   M dyn≳ 1010 M⊙  . Their frequency increases steeply with the dynamical mass from zero at   M dyn≈ 109.5 M⊙  to virtually 1 at   M dyn > 1011.5 M⊙  . These frequencies are consistent with those of low-luminosity AGNs found in the general field by the Sloan Digital Sky Survey. Massive galaxies that harbour AGNs commonly show conspicuous r -band star-like nuclear enhancements. Conversely, they often, but not necessarily, contain massive bulges. A few well-known AGNs (e.g. M61, M100, NGC 4535) are found in massive Sc galaxies with little or no bulge. The AGN fraction seems to be only marginally sensitive to galaxy environment. We infer the black hole masses using the known scaling relations of quiescent black holes. No black holes lighter than  ∼106 M⊙  are found active in our sample.  相似文献   

11.
We present 0.15-arcsec (25-pc) resolution MERLIN observations of neutral hydrogen absorption detected towards the nuclear region of the type 2 Seyfert galaxy NGC 5929. Absorption is detected only towards the north-eastern radio component with a column density of (6.5 ± 0.6) × 1021 cm−2. Based on comparison with an HST WFPC2 continuum image, we propose that the absorption is caused by a 1.5-arcsec structure of neutral gas and dust offset 0.3 arcsec south-east of the nucleus and running NE–SW. A separate cloud of dust is apparent 1.5 arcsec to the south-west of the nucleus in the HST image. A comparison of the centroid velocity (2358 ± 5 km s−1) and full width at half-maximum (43 ± 6 km s−1) of the absorbing gas with previous [O  III ] observations suggests that both the neutral and ionized gas are undergoing galactic rotation towards the observer in the north-east and away from the observer in the south-west. The main structure is consistent with an inclined ring of gas and dust encircling the active galactic nucleus (AGN); alternatively it may be a bar or inner spiral arm. We do not detect neutral hydrogen absorption or dust obscuration against the radio nucleus (column density < 3.1 × 1021 cm−2) expected by a torus of neutral gas and dust in unified models of AGNs for a type 2 Seyfert galaxy.  相似文献   

12.
We present millimetre photometry and submillimetre imaging of the central core and two hotspots in the radio lobes of the galaxy Cygnus A. For both hotspots and the central core, the synchrotron spectrum continues smoothly from the radio to a frequency of 677 GHz. The spectral index of the hotspots is constant over our frequency range, with a spectral index of α ≈ −1.0 ( S ν ∝ να), which is steeper than at lower frequencies and represents the emission from an aged population of electrons. The core is significantly flatter, with α = −0.6 ± 0.1, suggestive of an injected spectrum with no ageing, but some evidence for steepening exists at our highest observing frequency. Although IRAS data suggest the presence of dust in Cygnus A, our 450-μm data show no evidence of cold dust, therefore the dust component must have a temperature lying between 85 and 37 K, corresponding to dust masses of 1.4 × 106 and 1.0 × 108 M⊙ respectively.  相似文献   

13.
We present X-ray, broad-band optical and low-frequency radio observations of the bright type IIP supernova SN 2004et. The Chandra X-ray Observatory observed the supernova at three epochs, and the optical coverage spans a period of ∼470 d since explosion. The X-ray emission softens with time, and we characterize the X-ray luminosity evolution as   L X∝ t −0.4  . We use the observed X-ray luminosity to estimate a mass-loss rate for the progenitor star of  ∼2 × 10−6 M⊙ yr−1  . The optical light curve shows a pronounced plateau lasting for about 110 d. Temporal evolution of photospheric radius and colour temperature during the plateau phase is determined by making blackbody fits. We estimate the ejected mass of 56Ni to be  0.06 ± 0.03 M⊙  . Using the expressions of Litvinova & Nadëzhin we estimate an explosion energy of  (0.98 ± 0.25) × 1051 erg  . We also present a single epoch radio observation of SN 2004et. We compare this with the predictions of the model proposed by Chevalier, Fransson & Nymark. These multiwavelength studies suggest a main-sequence progenitor mass of  ∼20 M⊙  for SN 2004et.  相似文献   

14.
We compute two-point correlation functions and measure the shear signal due to galaxy–galaxy lensing for 80 000 optically identified and 5700 radio-loud active galactic nuclei (AGN) from Data Release 4 of the Sloan Digital Sky Survey. Halo occupation models are used to estimate halo masses and satellite fractions for these two types of AGN. The large sample size allows us to separate AGN according to the stellar mass of their host galaxies. We study how the halo masses of optical and radio AGN differ from those of the parent population at fixed   M *  . Halo masses deduced from clustering and from lensing agree satisfactorily. Radio AGN are found in more massive haloes than optical AGN: in our samples, their mean halo masses are  1.6 × 1013  and  8 × 1011  h −1 M⊙  , respectively. Optical AGN follow the same relation between stellar mass and halo mass as galaxies selected without regard to nuclear properties, but radio-loud AGN deviate significantly from this relation. The dark matter haloes of radio-loud AGN are about twice as massive as those of control galaxies of the same stellar mass. This boost is independent of radio luminosity, and persists even when our analysis is restricted to field galaxies. The large-scale gaseous environment of the galaxy clearly plays a crucial role in producing observable radio emission. The dark matter halo masses that we derive for the AGN in our two samples are in good agreement with recent models in which feedback from radio AGN becomes dominant in haloes where gas cools quasi-statically.  相似文献   

15.
NGC 3783 is a nearby SBa, type 1 Seyfert galaxy. We present H  i and radio continuum images of the galaxy made with the Australia Telescope Compact Array (ATCA). We find that NGC 3783 has an H  i mass of 8.4×109 M⊙, an H  i diameter of 1.9 D 0 ( D 0=37 kpc for h =0.5), and a nuclear depression in the H  i surface density. The H  i rotation curve is dominated by differential rotation, with little evidence of warping. The rotation curve suggests a mass-to-light ratio M L B =7.2 and a bar-pattern speed of 19±7 km s−1 kpc−1. The total mass of gas in the inner 50 arcsec is ≳10 per cent of the dynamical mass, and consistent with models that require significant gas content to fuel the Seyfert nucleus. There is no evidence that the nuclear activity in NGC 3783 is being stimulated by an interaction or merger: it may be a self-generated, perhaps bar-driven, process.  相似文献   

16.
We have used MERLIN to observe neutral hydrogen absorption against the central region of the ultraluminous infrared galaxy (ULIRG) galaxy Mrk 273 with an angular resolution of 0.2 arcsec. This represents a factor of 5 increase in resolution compared with previous work. Absorption has been resolved against two of three radio continuum components. A Hubble Space Telescope ( HST ) image reveals a complex central region composed of clumpy emission obscured by dust lanes. We find that the northern and south-eastern radio components are associated with two optical components. The alignment supports the idea that Mrk 273 has a double nucleus due to a recent galactic merger event.
Broad, strong and spatially varying absorption is seen against the northern radio component with a velocity gradient of 1990±50 km s−1 kpc−1. The absorption resolves into six discrete components with an average column density of 1.7×1022 atom cm−2. We propose that the absorption is due to a clumpy ring or disc of neutral gas of radius ∼250 pc rotating around a central starburst. In addition to the broad component, narrow absorption (<100 km s−1) is detected against the northern and south-eastern components. Absorption is not detected against the weak (2 mJy) south-western component. We propose that the narrow absorption is due to quiescent gas in a large-scale dust lane that coincides with these regions of narrow absorption.  相似文献   

17.
We examine the accretion and merger histories of central and satellite galaxies in a smoothed particle hydrodynamics (SPH) cosmological simulation that resolves galaxies down to  7 × 109 M⊙  . Most friends-of-friends haloes in the simulation have a distinct central galaxy, typically 2–5 times more massive than the most massive satellite. As expected, satellites have systematically higher assembly redshifts than central galaxies of the same baryonic mass, and satellites in more massive haloes form earlier. However, contrary to the simplest expectations, satellite galaxies continue to accrete gas and convert it to stars; the gas accretion declines steadily over a period of 0.5–1 Gyr after the satellite halo merges with a larger parent halo. Satellites in a cluster mass halo eventually begin to lose baryonic mass. Typically, satellites in our simulation are 0.1–0.2 mag bluer than in models that assume no gas accretion on to satellites after a halo merger. Since   z = 1  , 27 per cent of central galaxies (above  3 × 1010 M⊙  ) and 22 per cent of present-day satellite galaxies have merged with a smaller system above a 1:4 mass ratio; about half of the satellite mergers occurred after the galaxy became a satellite and half before. In effect, satellite galaxies can remain 'central' objects of halo substructures, with continuing accretion and mergers, making the transition in assembly histories and physical properties a gradual one. Implementing such a gradual transformation in semi-analytic models would improve their agreement with observed colour distributions of satellite galaxies in groups and with the observed colour dependence of galaxy clustering.  相似文献   

18.
We present a Chandra observation of the powerful radio galaxy 3C 294 showing clear evidence for a surrounding intracluster medium. At a redshift of 1.786 this is the most distant cluster of galaxies yet detected in X-rays. The radio core is detected as a point source, which has a spectrum consistent with a heavily absorbed power law, implying an intrinsic 2–10 keV luminosity of ∼1045 erg s−1. A small excess of emission is associated with the southern radio hotspots. The soft, diffuse emission from the intracluster medium is centred on the radio source. It has an hourglass shape in the north–south direction, extending to radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of this extended component is fitted by a thermal model with temperature ∼5 keV, or by gas cooling from above 7 keV at rates of ∼ 400–700 M⊙ yr−1. The rest-frame 0.3–10 keV luminosity of the cluster is ∼ 4.5×1044 erg s−1. The existence of such a cluster is consistent with a low-density universe.  相似文献   

19.
We have observed the   z =0.78  cluster MS 1137.5+6625 with the Ryle Telescope (RT) at 15 GHz. After subtraction of contaminating radio sources in the field, we find a Sunyaev–Zel'dovich flux decrement of  -421±60 μJy  on the ≈0.65 k λ baseline of the RT, spatially coincident with the optical and X-ray positions for the cluster core.
For a spherical King-profile cluster model, the best fit to our flux measurement has a core radius   θ C=20 arcsec  , consistent with previous X-ray observations, and a central temperature decrement  Δ T =650±92 μK  .
Using this model, we calculate that the cluster has a gas mass inside a     radius of  2.9×1013 M⊙  for an  Ω M =1  universe and  1.6×1013 M⊙  for  Ω M =0.3  ,  ΩΛ=0.7  . We compare this model with existing measurements of the total mass of the cluster, based on gravitational lensing, and estimate a gas fraction for MS 1137.5+6625 of ≈8 per cent.  相似文献   

20.
We present indications of rotation in the galaxy cluster A2107 by a method that searches for the maximum gradient in the velocity field in a flat disc-like model of a cluster. Galaxies from cumulative subsamples containing more and more distant members from the cluster centre are projected on to an axis passing through the centre and we apply a linear regression model on the projected distances x and the line-of-sight velocities V . The axis with the maximum linear correlation coefficient   r max= max[ r ( V , x )]  defines the direction of the maximum velocity gradient, and consequently it presents the major axis of the apparently elliptical cluster. Because the effects of rotation are subtle, we put strong emphasis on the estimation of the uncertainties of the results by implementing different bootstrap techniques. We have found that rotational effects are more strongly expressed at distances of 0.26–0.54 Mpc from the cluster centre. The total virial mass of the cluster is  (3.2 ± 0.6) × 1014 M⊙  , while the virial mass, corrected for rotation, is  (2.8 ± 0.5) × 1014 M⊙  .  相似文献   

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