Complex Radio Structure Research Articles

Identifying Host Galaxies of Extragalactic Radio Emission Structures using Machine Learning

This paper presents an automatic multi-band source cross-identification method based on deep learning to identify the hosts of extragalactic radio emission structures. The aim is to satisfy the increased demand for automatic radio source identification and analysis of large-scale survey data from next-generation radio facilities such as the Square Kilometre Array and the Next Generation Very Large Array. We demonstrate a 97% overall accuracy in distinguishing quasi-stellar objects, galaxies and stars using their optical morphologies plus their corresponding mid-infrared information by training and testing a convolutional neural network on Pan-STARRS imaging and WISE photometry. Compared with an expert-evaluated sample, we show that our approach has 95% accuracy at identifying the hosts of extended radio components. We also find that improving radio core localization, for instance by locating its geodesic center, could further increase the accuracy of locating the hosts of systems with a complex radio structure, such as C-shaped radio galaxies. The framework developed in this work can be used for analyzing data from future large-scale radio surveys.

Chandra View of the LINER-type Nucleus in the Radio-loud Galaxy CGCG 292–057: Ionized Iron Line and Jet–ISM Interactions

Abstract We present an analysis of the new, deep (94 ksec) Chandra ACIS-S observation of radio-loud active galaxy CGCG 292−057, characterized by a LINER-type nucleus and a complex radio structure that indicates intermittent jet activity. On the scale of the host galaxy bulge, we detected excess X-ray emission with a spectrum best fit by a thermal plasma model with a temperature of ∼0.8 keV. We argue that this excess emission results from compression and heating of the hot diffuse fraction of the interstellar medium displaced by the expanding inner, ∼20 kpc-scale lobes observed in this restarted radio galaxy. The nuclear X-ray spectrum of the target clearly displays an ionized iron line at ∼6.7 keV, and is best fitted with a phenomenological model consisting of a power-law (photon index ≃ 1.8) continuum absorbed by a relatively large amount of cold matter (hydrogen column density ≃0.7 × 1023 cm−2), and partly scattered (fraction ∼3%) by ionized gas, giving rise to a soft excess component and Kα line from iron ions. We demonstrate that the observed X-ray spectrum, particularly the equivalent width of Fe XXV Kα (of order 0.3 keV) can in principle, be explained in a scenario involving a Compton-thin gas located at the scale of the broad-lined region in this source and photoionized by nuclear illumination. We compare the general spectral properties of the CGCG 292−057 nucleus, with those of other nearby LINERs studied in X-rays.

NGC 326: X-shaped no more

ABSTRACT We present new 144-MHz Low-Frequency Array (LOFAR) observations of the prototypical ‘X-shaped’ radio galaxy NGC 326, which show that the formerly known wings of the radio lobes extend smoothly into a large-scale, complex radio structure. We argue that this structure is most likely the result of hydrodynamical effects in an ongoing group or cluster merger, for which pre-existing X-ray and optical data provide independent evidence. The large-scale radio structure is hard to explain purely in terms of jet reorientation due to the merger of binary black holes, a previously proposed explanation for the inner structure of NGC 326. For this reason, we suggest that the simplest model is one in which the merger-related hydrodynamical processes account for all the source structure, though we do not rule out the possibility that a black hole merger has occurred. Inference of the black hole–black hole merger rate from observations of X-shaped sources should be carried out with caution in the absence of deep, sensitive low-frequency observations. Some X-shaped sources may be signposts of cluster merger activity, and it would be useful to investigate the environments of these objects more generally.

Megaparsec-scale Radio Structure Associated with a Hybrid Blazar SBS B1646+499: Episodic Jet Activity with Precessing Axis

Abstract Here we report on the total-intensity 610 MHz Giant Meterwave Radio Telescope (GMRT) observations of the peculiar hybrid blazar SBS B1646+499, which merges the properties of BL Lacertae objects and flat-spectrum radio quasars. The complex radio structure of SBS B1646+499, emerging from the archival radio data and our new GMRT observations, consists of the megaparsec-scale elongated halo, the unilateral kiloparsec-scale jet, and the nuclear jet extending up to ∼20 pc from the compact core. The giant halo is characterized by a steep radio spectrum, indicative of the advanced aging of the electron population within the lobes. For the large-scale jet, we detected a spectral gradient along and across the outflow, and in particular spectral flattening of the radio continuum toward the jet edges, suggestive of the spine-boundary shear layer morphology. The nuclear jet displays superluminal knots emerging from the self-absorbed and variable radio core. We interpret all these findings in the framework of the model of an episodic jet activity with a precessing jet axis.

Chandra view on the active nucleus of CGCG 292–057: Jet-ISM interactions

AbstractWe present the analysis of the 93 ksec Chandra ACIS–S data for the galaxy CGCG 292–057 (z = 0.054), with complex radio structure indicative of the intermittent jet activity. In order to characterize precisely the spectrum of the unresolved low-luminosity active nucleus in the source, we performed detailed MARX/PSF simulations and studied the radial profile of the source region surface brightness. In this way, we have detected an additional X-ray component extending from a few up to ∼10 kpc from the unresolved core, which could be associated with the hot gaseous medium compressed and heated (up to 0.9 keV) by the expanding inner lobes of the radio galaxy. We modeled the X-ray spectrum of the unresolved nucleus assuming various emission models, including an absorbed power-law, a power-law plus thermal emission component, and a two-temperature thermal plasma. The best fit was however obtained assuming a power-law emission scattered by a hot ionized gas, giving rise to the 6.7 keV iron line.

Infalling groups and galaxy transformations in the cluster A2142

Context. Superclusters of galaxies provide dynamical environments for the study of the formation and evolution of structures in the cosmic web from galaxies, to the richest galaxy clusters, and superclusters themselves. Aims. We study galaxy populations and search for possible merging substructures in the rich galaxy cluster A2142 in the collapsing core of the supercluster SCl A2142, which may give rise to radio and X-ray structures in the cluster, and affect galaxy properties of this cluster. Methods. We used normal mixture modelling to select substructure of the cluster A2142. We compared alignments of the cluster, its brightest galaxies (hereafter BCGs), subclusters, and supercluster axes. The projected phase space (PPS) diagram and clustercentric distributions are used to analyse the dynamics of the cluster and study the distribution of various galaxy populations in the cluster and subclusters. Results. We find several infalling galaxy groups and subclusters. The cluster, supercluster, BCGs, and one infalling subcluster are all aligned. Their orientation is correlated with the alignment of the radio and X-ray haloes of the cluster. Galaxy populations in the main cluster and in the outskirts subclusters are different. Galaxies in the centre of the main cluster at the clustercentric distances 0.5 h−1 Mpc (Dc∕Rvir < 0.5, Rvir = 0.9 h−1 Mpc) have older stellar populations (with the median age of 10−11 Gyr) than galaxies at larger clustercentric distances. Star-forming and recently quenched galaxies are located mostly at the clustercentric distances Dc ≈ 1.8 h−1 Mpc, where subclusters fall into the cluster and the properties of galaxies change rapidly. In this region the median age of stellar populations of galaxies is about 2 Gyr. Galaxies in A2142 on average have higher stellar masses, lower star formation rates, and redder colours than galaxies in rich groups. The total mass in infalling groups and subclusters is M ≈ 6 × 1014 h−1 M⊙, that is approximately half of the mass of the cluster. This mass is sufficient for the mass growth of the cluster from redshift z = 0.5 (half-mass epoch) to the present. Conclusions. Our analysis suggests that the cluster A2142 has formed as a result of past and present mergers and infallen groups, predominantly along the supercluster axis. Mergers cause complex radio and X-ray structure of the cluster and affect the properties of galaxies in the cluster, especially at the boundaries of the cluster in the infall region. Explaining the differences between galaxy populations, mass, and richness of A2142, and other groups and clusters may lead to better insight about the formation and evolution of rich galaxy clusters.

Dynamical analysis of the complex radio structure in 3C 293: clues on a rapid jet realignment in X-shaped radio galaxies

Radio galaxies classified as X-shaped/winged, are characterised by two pairs of extended and misaligned lobes, which suggest a rapid realignment of the jet axis, for which a potential cause is still under debate. Here we analyse the complex radio structure of 3C 293 winged source hosted by the post-merger galaxy, which uniquely displays a significant asymmetry between the sizes of the two pairs of lobes, indicating that an episode of jet realignment took place only very recently. Based on all the available radio data for 3C 293, we have performed a detailed spectral modelling for the older and younger lobes in the system. In this way we derived the lobes' ages and jet energetics, which we then compared to the accretion power in the source. We found that the 200 kpc-scale outer lobes of 3C 293 are ~60 Myr old and that jet activity related to the formation of the outer lobes ceased within the last Myr. Meanwhile, the inner 4 kpc-scale lobes, tilted by ~40 deg with respect to the outer ones, are only about ~0.3 Myr old. The best model fits also return identical values of the jet power supplying the outer and the inner structures. This power is of the order of the maximum kinetic luminosity of a Blandford-Znajek jet for a given black hole mass and accretion rate, but only in the case of relatively low values of a black hole spin, a~0.2. The derived jet energetics and timescales, along with the presence of two optical nuclei in 3C 293, all provide a strong support to the Lense-Thirring precession model in which the supermassive black hole spin, and therefore the jet axis, flips rapidly owing to the interactions with the tilted accretion disk in a new tidal interaction episode of the merging process. We further speculate that, in general, X-shape radio morphology forms in post-merger systems that are rich in cold molecular gas, and only host slowly spinning supermassive black holes.

The radio structure of 3C 316, a galaxy with double-peaked narrow optical emission lines

The galaxy 3C\,316 is the brightest in the radio band among the optically-selected candidates exhibiting double-peaked narrow optical emission lines. Observations with the Very Large Array (VLA), Multi-Element Remotely Linked Interferometer Network (e-MERLIN), and the European VLBI Network (EVN) at 5\,GHz have been used to study the radio structure of the source in order to determine the nature of the nuclear components and to determine the presence of radio cores. The e-MERLIN image of 3C 316 reveals a collimated coherent east-west emission structure with a total extent of about 3 kpc. The EVN image shows seven discrete compact knots on an S-shaped line. However, none of these knots could be unambiguously identified as an AGN core. The observations suggest that the majority of the radio structure belongs to a powerful radio AGN, whose physical size and radio spectrum classify it as a compact steep-spectrum source. Given the complex radio structure with radio blobs and knots, the possibility of a kpc-separation dual AGN cannot be excluded if the secondary is either a naked core or radio quiet.

Detection of very-high-energyγ-ray emission from the vicinity of PSR B1706–44 and G 343.1–2.3 with H.E.S.S.

The gamma-ray pulsar PSR B1706-44 and the adjacent supernova remnant (SNR) candidate G343.1-2.3 were observed by H.E.S.S. during a dedicated observation campaign in 2007. As a result of this observation campaign, a new source of very-high-energy (VHE; E > 100 GeV) gamma-ray emission, HESS J1708-443, was detected with a statistical significance of 7 sigma, although no significant point-like emission was detected at the position of the energetic pulsar itself. In this paper, the morphological and spectral analyses of the newly-discovered TeV source are presented. The centroid of HESS J1708-443 is considerably offset from the pulsar and located near the apparent center of the SNR, at RA(J2000) = 17h08m11s +/- 17s and Dec(J2000) = -44d20' +/- 4'. The source is found to be significantly more extended than the H.E.S.S. point spread function (~0.1 deg), with an intrinsic Gaussian width of 0.29 deg +/- 0.04 deg. Its integral flux between 1 and 10 TeV is ~ 3.8 x 10^-12 ph cm^-2 s^-1, equivalent to 17% of the Crab Nebula flux in the same energy range. The measured energy spectrum is well-fit by a power law with a relatively hard photon index Gamma = 2.0 +/- 0.1 (stat) +/- 0.2 (sys). Additional multi-wavelength data, including 330 MHz VLA observations, were used to investigate the VHE gamma-ray source's possible associations with the pulsar wind nebula of PSR B1706-44 and/or with the complex radio structure of the partial shell-type SNR G343.1-2.3.

Multiwaveband polarimetric observations of NRAO 530 on parsec-scale

We report on multi-bands VLBA polarimetric observations of NRAO 530 in February 1997. Total intensity, EVPA distributions at all these frequencies are presented. Model fitting has been performed, from which the fitted southmost component A is confirmed as the core of the radio structure with relatively high brightness temperature and hard spectrum between 15 and 43 GHz in comparison with the central component B of dominant flux. The relatively high degree of polarization for the component A may arise from its complex radio structure, which is resolvable at 86 GHz. As a contrast, the component B shows a well fitted power-law spectrum with the spectral index of about -0.5, and a linear correlation between EVPAs and wavelength square with the observed RM of about -1062 rad m^{-2}, indicating its structural singleness. Assuming that the component B has a comparable degree of polarization without depolarization at these frequencies, the decrease in fractional polarization with wavelength mainly results from opacity and Faraday rotation, in which the opacity plays quite a large part of role. A spine-sheath like structure in fractional polarization is detected covering almost the whole emission region at 5 and 8 GHz. The linear polarization at 5 GHz shows 3 separate polarized emission regions with alternately aligned and orthogonal polarization vectors down the jet. The polarization goes to zero between the top two regions, with the highest polarization level occurring at the top and bottom. The 5 and 8 GHz images show EVPA changes across the width of the jet as well as along the jet. These complex polarimetric properties can be explained in terms of either the presence of a large helical magnetic field or tangled magnetic fields compressed and sheared down the jet.

THE DISCOVERY OF HOST GALAXY H I ABSORPTION IN CTA 21

We report the discovery of HI 21-cm absorption towards the well-studied GHz Peaked-Spectrum source CTA 21 (4C 16.09) using the Arecibo Telescope on 2009 September 20 and 21. Recently, the frequency band between 700 and 800 MHz was temporarily opened up to radio astronomy when US TV stations were mandated to switch from analog to digital transmissions, with new frequency allocations. The redshifted HI frequency for CTA 21 falls within this band. CTA 21 has a complex radio structure on a range of scales. The innermost prominent components are separated by ~12 mas while weak diffuse emission extends for up to ~300 mas. The HI absorption profile that we find has two main components, one narrow, the other wider and blue-shifted. The total HI column density is 7.9 x 10^20 cm^-2, assuming a covering factor of unity and a spin temperature of 100 K. This HI absorption confirms the recently determined optical redshift of this faint galaxy of z ~ 0.907. We discuss this new detection in the light of HI absorption studies towards compact radio sources, and also the possibility that CTA 21 may be exhibiting multiple cycles of nuclear activity. This new detection in CTA 21 is consistent with a strong trend for detection of HI absorption in radio galaxies with evidence of episodic nuclear/jet activity.

The radio-loud active nucleus in the “dark lens” galaxy J1218+2953

Context: There is a possibility that the optically unidentified radio source J1218+2953 may act as a gravitational lens, producing an optical arc ~4" away from the radio position. Until now, the nature of the lensing object has been uncertain since it is not detected in any waveband other than the radio. The estimated high mass-to-light ratio could even allow the total mass of this galaxy to be primarily in the form of dark matter. In this case, J1218+2953 could be the first known example of a "dark lens". Aims: We investigate the nature of J1218+2953 by means of high-resolution radio imaging observations to determine whether there is a radio-loud active galactic nucleus (AGN) in the position of the lensing object. Methods: We report on Very Long Baseline Interferometry (VLBI) observations with the European VLBI Network (EVN) at 1.6 and 5 GHz. Results: Our images, having angular resolutions of ~1 to ~10 milli-arcseconds (mas), reveal a rich and complex radio structure extending to almost 1". Based on its radio spectrum and structure, J1218+2953 can be classified as a compact steep-spectrum (CSS) source, and as a medium-size symmetric object (MSO). The object harbours an AGN. It is also found as an X-ray source in the XMM-Newton EPIC (European Photon Imaging Cameras) instrument serendipitous source catalogue. Conclusions: Rather than being a dark lens, J1218+2953 is most likely a massive, heavily obscured galaxy in which the nuclear activity is currently in an early evolutionary stage.

THE RADIO PROPERTIES AND MAGNETIC FIELD CONFIGURATION IN THE CRAB-LIKE PULSAR WIND NEBULA G54.1+0.3

We present a multifrequency radio investigation of the Crab-like pulsar wind nebula (PWN) G54.1+0.3 using the Very Large Array. The high resolution of the observations reveals that G54.1+0.3 has a complex radio structure which includes filamentary and loop-like structures that are magnetized, a diffuse extent similar to the associated diffuse X-ray emission. But the radio and X-ray structures in the central region differ strikingly, indicating that they trace very different forms of particle injection from the pulsar and/or particle acceleration in the nebula. No spectral index gradient is detected in the radio emission across the PWN, whereas the X-ray emission softens outward in the nebula. The extensive radio polarization allows us to image in detail the intrinsic magnetic field, which is well-ordered and reveals that a number of loop-like filaments are strongly magnetized. In addition, we determine that there are both radial and toroidal components to the magnetic field structure of the pulsar wind nebula. Strong mid-IR emission detected in Spitzer Space Telescope data is closely correlated with the radio emission arising from the southern edge of G54.1+0.3. In particular, the distributions of radio and X-ray emission compared with the mid-IR emission suggest that the PWN may be interacting with this interstellar cloud. This may be the first PWN where we are directly detecting its interplay with an interstellar cloud that has survived the impact of the supernova explosion associated with the pulsar's progenitor.

A Radio Study of the Seyfert Galaxy Markarian 6: Implications for Seyfert Life Cycles

We have carried out an extensive radio study with the Very Large Array on the Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the source. The radio emission occurs on three different spatial scales, from ~7.5 kpc bubbles to ~1.5 kpc bubbles lying nearly orthogonal to them and a ~1 kpc radio jet lying orthogonal to the kpc-scale bubble. To explain the complex morphology, we first consider a scenario in which the radio structures are the result of superwinds ejected by a nuclear starburst. However, recent Spitzer observations of Mrk 6 provide an upper limit to the star formation rate (SFR) of ~5.5 M_sun/yr, an estimate much lower than the SFR of ~33 M_sun/yr derived assuming that the bubbles are a result of starburst winds energized by supernovae explosions. Thus, a starburst alone cannot meet the energy requirements for the creation of the bubbles in Mrk 6. We show that a single plasmon model is energetically infeasible, and we argue that a jet-driven bubble model while energetically feasible does not produce the complex radio morphologies. Finally, we consider a model in which the complex radio structure is a result of an episodically-powered precessing jet that changes its orientation. This model is the most attractive as it can naturally explain the complex radio morphology, and is consistent with the energetics, the spectral index and the polarization structure. Radio emission in this scenario is a short-lived phenomenon in the lifetime of a Seyfert galaxy which results due to an accretion event.

The Infrared‐dominated Jet of 3C 401

We present a Hubble Space Telescope image of the FR II radio galaxy 3C 401, obtained at 1.6 μm with NICMOS, in which we identify the infrared counterpart of the brightest region of the radio jet. The jet has a complex radio structure and brightens where bending occurs, most likely as a result of relativistic beaming. We analyze archival data in the radio, optical, and X-ray bands, and we derive its spectral energy distribution. Unlike all of the previously known optical extragalactic jets, the jet in 3C 401 is not detected in the X-rays, even in a long 48 ks X-ray Chandra exposure, and the infrared emission dominates the overall spectral energy distribution (SED). We propose that the dominant radiation mechanism of this jet is synchrotron. The low X-ray emission is then caused by two different effects: (1) the lack of any strong external photon field and (2) the shape of the electron distribution. This affects the location of the synchrotron peak in the SED, resulting in a sharp cutoff at energies lower than the X-rays. Thus 3C 401 shows a new type of jet, with intermediate spectral properties between those of FR I galaxies, which are dominated by synchrotron emission up to X-ray energies, and FR II galaxies/QSOs, which show strong high-energy emission due to inverse Compton scattering of external photons. This might indicate the presence of a continuous in the properties of large-scale jets, analogous to the blazar sequence already proposed for subparsec-scale jets.

Evidence for X-ray obscuration in Type II quasar candidates from the Sloan Digital Sky Survey

Recently, Zakamska et al. selected 291 high-ionization narrow-emission-line active galactic nuclei (AGN) in the redshift range 0.3-0.83 from the Sloan Digital Sky Survey (SDSS) spectroscopic data. The sample includes both type 2 Seyfert galaxies and their higher-luminosity 'cousins', Type II quasar candidates. Here we present the results on the X-ray properties of 17 of these objects for which archival X-ray data (ROSAT and XMM-Newton) are available. Three sources have been significantly (≥6a) detected, one being the most radio-loud source of the sample; its X-ray emission, possibly enhanced by jet emission, is consistent with the absence of absorption. Another source has 6σ detection in the ROSAT All-Sky Survey (RASS), possibly complex radio structure, and no evidence for strong X-ray absorption. For the third X-ray detection, the XMM-Newton spectrum indicates a column density of N H = 1.26 +0.75 -0.51 x 10 22 cm -2 ; this result, coupled with the 2-10 keV luminosity of 4 × 10 44 erg s -1 , makes this source a genuine Type II quasar. Using the [O III] λ5007 line luminosities, we estimated the intrinsic X-ray power of the AGN and found that ≥47 per cent of the observed sample shows indications of X-ray absorption, with column densities ≥10 22 cm -2 . This provides further evidence that a considerable fraction are obscured quasars. Support for our conclusions also comes from the very recent analysis of RASS data performed by Zakamska et al., who found five additional lower-significance (2.1σ-3.6σ) X-ray matches.

The complex radio and X-ray structure in the nuclear regions of the active galaxy NGC 1365

ABSTRA C T We present a multiwavelength analysis of the prominent active galaxy NGC 1365, in particular looking at the radio and X-ray properties of the central regions of the galaxy. We analyse ROSAT (PSPC and HRI) observations of NGC 1365, and discuss recent ASCA results. In addition to a number of point sources in the vicinity of NGC 1365, we find a region of extended X-ray emission extending along the central bar of the galaxy, combined with an emission peak near the centre of the galaxy. This central X-ray emission is centred on the optical/radio nucleus, but is spatially extended. The X-ray spectrum can be well fitted by a thermal plasma model, with a temperature of kT a 0:6‐0:8 keV and a very low local absorbing column. The thermal spectrum is suggestive of starburst emission rather than emission from a central black hole. The ATCA radio observations show a number of hotspots, located in a ring around a weak radio nucleus. Synchrotron emission from electrons accelerated by supernovae and supernova remnants (SNRs) is the likely origin of these hotspots. The radio nucleus has a steep spectrum, indicative perhaps of an active galactic nucleus (AGN) or SNRs. The evidence for a jet emanating from the nucleus (as has been previously claimed) is at best marginal. The extent of the radio ring is comparable to that of the extended central X-ray source. We discuss the nature of the central activity in NGC 1365 in the light of these observations. The extended X-ray emission and the thermal spectra strongly suggest that at soft X-ray energies we are not seeing emission predominantly from a central black hole, although the presence of Fe K line emission at higher energies does suggest the presence of an AGN. Consequently, a black hole is probably not the dominant contributor to the energetics of the central regions of NGC 1365 at radio, optical or soft X-ray wavelengths. Activity associated with a starburst is likely the dominant explanation for the observed properties of NGC 1365.

Optical Properties of the Radio Source B2 0828+32

A small number of radio galaxies have two sets of classical double radio lobes with the radio axes aligned in different directions. Furthermore differences in the properties of the radio lobes such as the surface brightness and spectral index indicate that the two sets of double radio structure have different ages. The radio ejection axis has therefore changed direction with time. In the first two known radio galaxies of this type, 3C 315 and B2 0055+26, the host galaxy is a member of a close pair of ellipticals in a common optical envelope suggesting that the complex radio structure is caused by gravitational interaction.

VLA Observations of Strong IRAS Point Sources Associated with Compact H II Regions

view Abstract Citations (135) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA Observations of Strong IRAS Point Sources Associated with Compact H II Regions Garay, Guido ; Rodriguez, Luis F. ; Moran, James M. ; Churchwell, Ed Abstract We present multifrequency radio continuum observations made with the Very Large Array of a sample of 16 strong IRAS point sources associated with compact H II regions. Twelve sources were observed at 1.5, 4.9, and 15.0 GHz, with angular resolution of ∼15", 5", and 3", respectively. Three were observed at 1.5 and 4.9 GHz, and one at 1.5 GHz. The radio continuum brightness distribution was resolved for all sources. Nine objects show simple morphologies: core-halo (2), shell (3), cometary (3), and bipolar (1), consistent with their being excited by a single star. The remaining seven sources show complex radio structure. The average infrared luminosity of the complex sources is 3 times larger than that of the simple sources. The morphologies of the complex H II regions, which can be decomposed into multiple components, together with their large IR luminosities, suggest that these regions are excited by a cluster of stars. Furthermore, the observed infrared and radio properties suggest that the cluster contains only massive stars (0 and early B spectral types). About 70% of the individual regions of ionized gas have linear diameters between 0.1 and 1 pc and electron densities between 103 and 104 cm-3, corresponding to H II regions of class II in the classification scheme of Habing & Israel (1979). The electron densities and diameters follow a power-law relation of the form Ne ∝ D-1. For the sources showing simple morphologies, the ratio between the total infrared and Lyman-α luminosities ranges from 6 to 21. If single stars excite these simple H II regions, then the infrared excesses are fully accounted for by dust emission in large, cool envelopes heated by stellar photons longward of the Lyman continuum limit and by optical/near-infrared photons emitted by hot dust within the H II regions. The fraction of Lyman continuum photons absorbed by dust within the H II regions is typically 55%. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173396 Bibcode: 1993ApJ...418..368G Keywords: ISM: H II REGIONS; RADIO CONTINUUM: INTERSTELLAR full text sources ADS | data products SIMBAD (44)

Optical spectroscopy of 28 southern radio galaxies

The results of an optical spectroscopic survey of 28 southern radio galaxies including redshifts and descriptions of their spectra are presented. One of these objects is a quasar, while five of the remainder involve fields where more than one galaxy has been observed because of the complex radio structure or uncertain identification. A Fleurs synthesis telescope map at 21cm of PKS 0114 – 47 and a VLA map at 6cm of PKS 0843 – 33 are also presented and discussed.