Low Radio Luminosity Research Articles

Revision of the Properties of the GRS 1915+105 Jets: Clues from the Large‐Scale Structure

The jets of GRS 1915+105 carry a considerable energy away from the central source into the interstellar medium (ISM). The similarity of the jets of this source and jets in radio galaxies or radio-loud quasars suggests that we should detect large-scale, synchrotron-emitting radio structures surrounding GRS 1915+105. However, these large structures have not been found. We show that by adapting a model for the radio lobes of extragalactic jet sources we predict a radio surface brightness of the equivalent structures of GRS 1915+105 below the current detection limits. The model uses an energy transport rate of the jets averaged over the jet lifetime. This transport rate is found to be considerably lower than the power of the jets during the rare major ejection events. Thus, the lobes contain less energy than would be inferred from these events and produce a lower radio luminosity. The model also predicts a lifetime of the jets of order 106 yr and a gas density of the ISM in the vicinity of GRS 1915+105 of ~150 cm-3. The impact sites of the jets are identified with two IRAS regions with a flat radio spectrum located on either side of GRS 1915+105. Observations of molecular lines and dust emission from these objects are consistent with our interpretation. Distance estimates for the IRAS regions give 6.5 kpc, and our model implies that this is also the distance to GRS 1915+105. This low distance estimate in combination with the observed motions of jet ejections on small scales yields a jet velocity of about 0.7c and an angle of 53° of the jets to our line of sight.

The Boomerang: A Crushed and Re-born PWN?

We present new high radio frequency observations of the Boomerang pulsar wind nebula (PWN) made with the Effelsberg 100-m radio telescope. A comparison with low frequency data from the Canadian Galactic Plane Survey (CGPS; Taylor et al. 2003) reveals a change of the nebula's emission structure with frequency caused by a radial steepening of the radio spectrum above 5 GHz. We also find evidence that the reverse shock of the initial supernova shock wave has driven away or crushed the original PWN which might explain why the current nebula around the pulsar has such a low radio luminosity.

An increased estimate of the merger rate of double neutron stars from observations of a highly relativistic system

The merger of close binary systems containing two neutron stars should produce a burst of gravitational waves, as predicted by the theory of general relativity. A reliable estimate of the double-neutron-star merger rate in the Galaxy is crucial in order to predict whether current gravity wave detectors will be successful in detecting such bursts. Present estimates of this rate are rather low, because we know of only a few double-neutron-star binaries with merger times less than the age of the Universe. Here we report the discovery of a 22-ms pulsar, PSR J0737-3039, which is a member of a highly relativistic double-neutron-star binary with an orbital period of 2.4 hours. This system will merge in about 85 Myr, a time much shorter than for any other known neutron-star binary. Together with the relatively low radio luminosity of PSR J0737-3039, this timescale implies an order-of-magnitude increase in the predicted merger rate for double-neutron-star systems in our Galaxy (and in the rest of the Universe).

The hard X-ray view of the low-luminosity blazar in the radio galaxy NGC 6251

We present results from a BeppoSAX (July 2001) observation of the FR I radio galaxy NGC 6251, together with a re-analysis of archival ASCA (October 1994) and Chandra (September 2000) data. The weak detection above 10 keV and the lack of iron fluorescent K α emission lines in the BeppoSAX spectrum rule out that the bulk of the X-ray emission is due to an obscured Seyfert nucleus. The study of the multiwavelength spectral energy distribution suggests instead that X-rays probably originate as inverse-Compton of synchrotron seed photons in a relativistic jet, indicating that NGC 6251 hosts a low radio luminosity ($L_{{\rm 5 GHz}} \sim 10^{40}$ erg s -1 ) blazar. The BeppoSAX spectrum is flatter than in the earlier ASCA observation. This might be due to the emergence of a different spectral component during phases of lower X-ray flux. In this context, we discuss some possible explanations for the intense and mildly-ionized fluorescent iron line measured by ASCA.

Renewed Activity in the Radio Galaxy PKS B1545−321: Twin Edge‐brightened Beams within Diffuse Radio Lobes

Australia Telescope Compact Array images of the giant radio galaxy PKS B1545-321 show a pair of oppositely directed beams emerging from a radio core and ending in bright components that are symmetrically located on either side. These inner beams are embedded within edge-brightened outer lobes of lower surface brightness, and the bright ends of the inner beams are well recessed from the ends of the outer lobes. The inner beams and diffuse surrounding lobes share a common central core and radio axis. We propose that the observed inner beams are double lobes that have been created within relic outer lobes as a consequence of a restarting of the central activity; therefore, PKS B1545-321 is a rare opportunity for examining the development of restarted beams within a relic synchrotron plasma cocoon. The inner double representing the new episode has among the highest axial ratios found in typical edge-brightened radio galaxies. The low radio luminosity of the inner double, the narrow and constant transverse extent of its cocoon, and the relatively low brightness of the hot spots at its ends are consistent with the almost ballistic propagation expected for a beam that has a low density contrast and is advancing within a relatively light ambient medium.

The 2dF Galaxy Redshift Survey: the population of nearby radio galaxies at the 1-mJy level

We use redshift determinations and spectral analysis of galaxies in the 2dF Galaxy Redshift Survey to study the properties of local radio sources with $S\ge 1$ mJy. 557 objects drawn from the FIRST survey, corresponding to 2.3 per cent of the total radio sample, are found in the 2dFGRS cataloge within the area $9^h 48^m \simlt {\rm RA}({\rm 2000}) \simlt 14^h 32^m$ and $-2.77^\circ \simlt {\rm dec}({\rm 2000}) \simlt 2.25^\circ$, down to a magnitude limit $b_J= 19.45$. The excellent quality of 2dF spectra allows us to divide these sources into classes, according to their optical spectra. Radio galaxies (i.e. absorption systems, mainly belonging to the class of FR I sources, whose spectra may or may not show emission lines due to AGN activity) make up 63 per cent of the spectroscopic sample; they are characterized by relatively high radio-to-optical ratios, red colours and luminosities $10^{21}\simlt P_{1.4{\rm GHz}} W Hz^${-1}$ sr$^{-1}$ \simlt 10^{24}$. Actively star-forming galaxies instead contribute with 30 per cent to the total sample. These objects -- principally found at low redshifts ($z \simlt 0.1$) -- in general show low radio-to-optical ratios, blue colours and low radio luminosities. We also found 18 Seyfert 2 galaxies and 4 Seyfert 1's. Analysis of the local radio luminosity function shows that radio galaxies are well described by models that assume pure luminosity evolution, at least down to radio powers $P_{1.4{\rm GHz}}\simlt 10^{20.5} W Hz$^{-1}$ sr$^{-1}$ Late-type galaxies, whose relative contribution to the RLF is found to be lower than was predicted by previous work, present a luminosity function which is compatible with the IRAS galaxy LF, and therefore plausibly constitute the radio counterpart of the dusty spirals and starbursts that dominate the counts at 60 $\mu$m.

The Reddest Quasars

In a survey of quasar candidates selected by matching the Faint Images of the Radio Sky at Twenty cm (FIRST) and Two Micron All-Sky Survey catalogs, we have found two extraordinarily red quasars. FIRST J013435.7-093102 is a 1 Jy source at z = 2.216 and has B-K 10, while FIRST J073820.1+275045 is a 2.5 mJy source at z = 1.985 with B-K ≈ 8.4. FIRST J073820.1+275045 has strong absorption lines of Mg II and C IV in the rest frame of the quasar and is highly polarized in the rest-frame ultraviolet, strongly favoring the interpretation that its red spectral energy distribution is caused by dust reddening local to the quasar. FIRST J073820.1+275045 is thus one of the few low radio luminosity, highly dust-reddened quasars known. The available observational evidence for FIRST J013435.7-093102 leads us to conclude that it too is reddened by dust. We show that FIRST J013435.7-093102 is gravitationally lensed, increasing the number of known lensed, extremely dust-reddened quasars to at least three, including MG 0414-0534 and PKS 1830-211. We discuss the implications of whether these objects are reddened by dust in the host or lensing galaxies. If reddened by their local environment, then we estimate that between 10% and 20% of the radio-loud quasar population is reddened by dust in the host galaxy. The discovery of FIRST J073820.1+275045 and objects now emerging from X-ray surveys suggests the existence of an analogous radio-quiet red quasar population. Such objects would be entirely missed by standard radio or optical quasar surveys. If dust in the lensing galaxies is primarily responsible for the extreme redness of the lensed quasars, then an untold number of gravitationally lensed quasars are being overlooked.

Blazars from the CLASS Survey

AbstractThis paper presents preliminary results from the CLASS blazar sample; the aim is to study the cosmological properties of radio selected BL Lacs and their closest relatives, the other low radio luminosity flat spectrum sources.

Compact Radio Emission from Warm Infrared Galaxies

In this paper, we present a comparison between the optical spectroscopic data and the incidence of compact radio emission for a sample of 60 warm infrared galaxies. We find that 80% of optically classified active galactic nucleus (AGN)-type galaxies contain compact radio sources, while 37% of optically classified starburst galaxies contain compact radio sources. The compact radio luminosity shows a bimodal distribution, indicating two populations in our sample. The majority of the higher radio luminosity class (L > 104 L☉) are AGNs, while the majority of the lower radio luminosity class (L < 104 L☉) are starbursts. The compact radio emission in the starburst galaxies may be due to either obscured AGNs or complexes of extremely luminous supernovae such as that seen in Arp 220. The incidence of optically classified AGNs increases with increasing far-infrared (FIR) luminosity. Using FIR color-color diagrams, we find that globally the energetics of 92% of the galaxies in our sample are dominated by starburst activity, including 60% of galaxies that we find to contain AGNs on the basis of their optical classification. The remainder are energetically dominated by their AGNs in the infrared. For starburst galaxies, electron density increases with dust temperature, consistent with the merger model for infrared galaxies.

10.1146/annurev-astro-081710-102624

Radio galaxies were discovered and mapped in the 1950s. The optical spectra showed little or no nuclear continuum light. Some also revealed powerful high ionization emission lines, while others showed at most weak low-ionization emission lines. Quasars were found in the 1960s, and their spectra were dominated by powerful continuum radiation which was subsequently identified with optically thick thermal radiation from copious accretion flows, as well as high ionization narrow emission lines, and powerful broad permitted lines. By the 1980s, data from optical polarization and statistics of the radio properties required that many radio galaxies contain hidden quasar nuclei, hidden from the line of sight by dusty, roughly toroidal gas distributions. The radio galaxies with hidden quasars are referred to as thermal. Do all radio galaxies have powerful hidden quasars? We now know the answer using arguments based on radio, infrared, optical and X-ray properties. Near the top of the radio luminosity function, for FRII, GPS, and CSS galaxies, the answer is yes. Below the top of the radio luminosity function, many do not. At low radio luminosities, most do not. Instead these nonthermal weakly-accreting galaxies are powerful emitters of kinetic energy in the form of synchrotron jets. They generally have weak low-ionization lines. This applies to all types of radio galaxy, big FR II doubles, as well as the small young GigaHertz-Peaked-Spectrum and Compact Steep Spectrum sources. Only a few FR I sources are of the thermal type.

Radio--optical alignments in a low radio luminosity sample

We present an optically-based study of the alignment between the radio axes and the optical major axes of eight z approximately 0.7 radio galaxies in a 7C sample. The radio galaxies in this sample are approximately 20-times less radio luminous than 3C galaxies at the same redshift, and are significantly less radio-luminous than any other well-defined samples studied to date. Using Nordic Optical Telescope images taken in good seeing conditions at rest-frame wavelengths just longward of the 4000A break, we find a statistically significant alignment effect in the 7C sample. Furthermore, in two cases where the aligned components are well separated from the host we have been able to confirm spectroscopically that they are indeed at the same redshift as the radio galaxy. However, a quantitative analysis of the alignment in this sample and in a corresponding 3C sample from HST (Hubble Space Telescope) archival data indicates that the percentage of aligned flux may be lower and of smaller spatial scale in the 7C sample. Our study suggests that alignments on the 50-kpc scale are probably closely related to the radio luminosity, whereas those on the 15 kpc scale are not. We discuss these results in the context of popular models for the alignment effect.

Radio Properties of Magellanic Cloud SNRs

Supernova remnants in the Magellanic Clouds may have somewhat lower surface brightnesses at radio wavelengths than their counterparts in the Milky Way but otherwise they appear to be very similar. Balmer dominated SNRs have a lower radio luminosity than other shell remnants.

A Hidden Broad‐Line Region in the Weak Seyfert 2 Galaxy NGC 788

ABSTRACTWe have detected a broad Hα emission line in the polarized flux spectrum of the Seyfert 2 galaxy NGC 788, indicating that it contains an obscured Seyfert 1 nucleus. Although such features have been observed in ∼15 other Seyfert 2 galaxies, this example is unusual because it has a higher fraction of galaxy starlight in its spectrum, a lower average measured polarization, and a significantly lower radio luminosity than other hidden Seyfert 1 galaxies discovered to date. This demonstrates that polarized broad‐line regions can be detected in relatively weak classical Seyfert 2 galaxies and illustrates why well‐defined, reasonably complete spectropolarimetric surveys at Hα are necessary in order to assess whether or not all Seyfert 2 galaxies are obscured Seyfert 1 galaxies.

The radio pulsar Geminga

We report the results of our search for pulsed radio emission from Geminga carried out in 1992, 1993 and 1996–1997 at 102.5 MHz using the BSA radiotelescope of the Pushchino Radioastronomy Observatory. The Geminga radio pulsar (PSR J0633+1746) was detected in all three observation periods. With the best signal to noise ratio Geminga was detected in records taken in 1993, when the maximum passband of the radiotelescope was used for the searches. The main criterion for radio pulsar detection was the presence of records containing the dominant spectral line at the rotation frequency of the pulsar Ω = 4.22 Hz in the amplitude spectra. The method of averaging the amplitude spectra, obtained for many days in February–June 1993, was used for the determination of the mean flux density of the Geminga radio emission at 102.5 MHz.We report the main parameters of the pulsar PSR J0633 + 1746, obtained from our observations. The mean flux S102 = 8(−2+3)mJy. The average pulse profile is very wide and has a shape like in X-rays (Halpern and Holt, 1992 [Natur, 357, 222]). The profile width on the 0.5 level W0.5 ⋍ 120 ms, i.e. about 180°. The dispersion measure DM = 3.2±0.3 pc · cm−3. A timing analysis, which was performed for the best profiles, obtained from 1992 to 1997, yields values for the period P and derivative P, which are, within error limits, in agreement with the data published by Mayer-Hasselwander et al. (1994)[ApJ, 421, 276]. We discuss possible reasons for the extremely low radio luminosity of the Geminga pulsar.

Low-luminosity BL Lac Objects and Flat-spectrum Radio Galaxies

AbstractWe present first results from a new sample of low radio luminosity flat spectrum radio galaxies.

Low Luminosity Radio Galaxies

This review talk will deal almost exclusively with the radio aspects of low luminosity radio galaxies, as the other wavelength bands (optical, X, IR) are covered by others during this conference. By low radio luminosity we mean a radio power at 20 cm in the range 1019 to 1024,5 W Hz–1 (Hubble constant of 100, as throughout this talk). At the upper limit occurs the “break” in the radio luminosity (RLF) (Auriemma et al 1977) as well as the transition from Fanaroff -Riley type I to type II (Fanaroff &amp; Riley, 1974). This limitation to weak radio powers does not necessarily imply that such radio sources constitute a homogeneous class of objects; it has been shown by Wrobel &amp; Heeschen (1991) that a number of radio galaxies of very low luminosity have a ratio between far-infrared and radio emission similar to spiral galaxies and this might suggest that these objects are powered by star formation phenomena. Long baseline interferometry is able to pinpoint compact radio nuclei and therefore can distinguish starburst related radio sources from those powered by nuclear activity (see Slee et al 1994).

H0414 + 009 - an X-ray bright BL Lac with a radio tail in a distant cluster of galaxies

VLA observations of the X-ray selected BL Lac H0414 + 009 at 6, 20 and 90 cm show that it has a steep-spectrum (⁠|$\alpha \simeq 1; f_\nu \propto\nu^{-\alpha}$|⁠) radio tail. The tail extends ∼ 40 arcsec from the core, in a gentle curve. There is no evidence of extended emission on the opposite side of the core. This is by far the clearest example of a single-sided radio tail associated with a BL Lac source. The low radio luminosity (⁠|$1.6\times 10^{25} \text {W Hz}^{-1}$| at 20 cm for H0 = 50 km s−1 Mpc−1 and q0 = 1/2 at z = 0.287) and morphology of the extended emission strengthens the proposed association of BL Lacs with Fanaroff–Riley type I (FR I) radio sources. Deep V, R and I CCD images show that the BL Lac is located in a galaxy whose surface brightness and colours are best fitted by an elliptical model with absolute total magnitude Mv = − 23.53. The elliptical host galaxy is the brightest of a poor cluster. We confirm the recently published redshift (z = 0.287) for the BL Lac and find similar redshifts for five of the surrounding, faint galaxies, supporting the conclusion that the BL Lac and the cluster are physically associated and are not merely a chance super-position. We conclude, contrary to earlier suggestions, that BL Lacs do not avoid the cluster environment but are found in groups and clusters just as often as are normal radio galaxies, consistent with the hypothesis that BL Lacs are simply normal radio galaxies seen ‘end-on’. The appearance of the cluster is striking, containing a number of ‘twin’ galaxy pairs. It has been suggested that the pairs could be the result of gravitational lensing by a foreground cosmic string, but our observations do not support this hypothesis. We have analysed the cluster properties and present VRI CCD photometry for 108 galaxies fainter than the BL Lac host galaxy in the CCD images (1.1 × 1.2 Mpc2). In the Bautz–Morgan morphological classification scheme we classify this cluster as BM I. The cluster could be as rich as Abell class 0, however, the richness may be lower due to considerable uncertainties in the corrections for the field galaxy background and the small field of view of the CCD. We have searched deep EXOSAT images for evidence of extended X-ray emission from a hot intracluster medium, but find none. The upper limit to the luminosity of any cluster-type emission from 0414 + 009, however, is still rather high, |$L_\text x(2-10\text {keV})\le 4 \times 10^{37}\text W$|⁠, comparable with that of moderately X-ray luminous Abell clusters. If hot gas emitting at that luminosity does exist in the cluster, it could help explain the unusual structure of the radio source.

Fanaroff-Riley I galaxies as the parent population of BL Lacertae objects. II - Optical constraints

view Abstract Citations (77) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fanaroff-Riley I Galaxies as the Parent Population of BL Lacertae Objects. II. Optical Constraints Padovani, Paolo ; Urry, C. Megan Abstract As part of a continuing investigation of the hypothesis that BL Lacertae objects are low-luminosity radio galaxies with relativistic jets pointing along the line of sight, we consider the number density of these objects at optical wavelengths. There are no well-defined optical samples of BL Lacertae objects, but, using existing catalogs of active galactic nuclei, we obtain new estimates of the optical counts and luminosity function of BL Lacertae objects that are not inconsistent with the beaming hypothesis. Our calculations depend primarily on observed quantities, including the optical luminosity function of the assumed parent population, Fanaroff-Riley type I (FR I) galaxies. Although FR I galaxies have relatively low radio luminosities, they are bright optical galaxies and their luminosity function is very steep. We extend the formalism of Urry and Shafer for comparing beamed and parent populations to cases, such as the optical one, where galaxy light represents a substantial fraction of the total luminosity. The Lorentz factor of the optical jet is estimated to be roughly in the range 8 < γ_0_ < 20, larger than the X-ray value, γ_x_ ~ 3, found by Padovani and Urry. Since currently observed BL Lacertae objects already have luminosities below the predicted break in the luminosity function, itself a signature of beaming, a definite test of the beaming hypothesis does not depend on more sensitive surveys (in contrast to the X-ray case); it simply requires a sizable optically selected sample of BL Lacertae objects. Publication: The Astrophysical Journal Pub Date: February 1991 DOI: 10.1086/169701 Bibcode: 1991ApJ...368..373P Keywords: Bl Lacertae Objects; Galactic Structure; Radio Galaxies; Active Galactic Nuclei; Astronomical Catalogs; Astronomical Models; Luminosity; Astrophysics; BL LACERTAE OBJECTS; GALAXIES: JETS; GALAXIES: NUCLEI; RADIO SOURCES: GALAXIES full text sources ADS | Related Materials (2) Part 1: 1990ApJ...356...75P Part 3: 1991ApJ...382..501U

A phenomenological pulsar model

Particle injection energies and rates previously calculated for the stellar wind generation by rotating magnetized neutron stars are adopted. It is assumed that the ambient space-charge density being emitted to form this wind is bunched. These considerations immediately place the coherent radio frequency luminosity from such bunches near 10 to the 28th erg/s for typical pulsar parameters. A comparable amount of incoherent radiation is emitted for typical (1 second) pulsars. For very rapid pulsars, however, the latter component grows more rapidly than the available energy sources. The comparatively low radio luminosity of the Crab and Vela pulsars is attributed to both components being limited in the same ratio. The incoherent radiation essentially has a synchotron spectrum and extends to gamma-ray energies; consequently the small part of the total luminosity that is at optical wavelengths is unobservable. Assuming full coherence at all wavelengths short of a critical length gives a spectral index for the flux density of -8/3 at higher frequencies. The finite energy available from the injected particles would force the spectrum to roll over below about 100 MHz, although intrinsic morphological factors probably enter for any specific pulsar as well.

B0924 + 30 an unusual radio galaxy

THE radio source B0924 + 30 (ref. 1) has been studied as part of a systematic survey of radio galaxies of relatively low (< 1041 erg s−1) radio luminosity. The radio source is identified with a 14 mag elliptical galaxy with a redshift z = 0.0266 (refs 2 and 3). A 12-h observation of this radio source was made with the Westerbork Synthesis Radio Telescope4 at 1.4 GHz in September 1974, and Fig. 1 is a contour plot of the brightness distribution obtained. The resolution is 23″ in right ascension and 46″ in declination. The r.m.s. noise level in the map is 0.5 mJy. For a single 12-h observation the map is distorted by elliptical grating rings of semiaxis 10′×20′. The grating rings from many of the small diameter sources have been removed, but the distortion from the extended part of the radio galaxy remains and is the cause of the low level negative regions to the north and south of the galaxy. No correction for the primary beam attenuation, which reaches a factor of 2 at the edge of the map, has been applied. The position of the nucleus of the elliptical galaxy is RA = 09 h 24 min 55.1 s, dec. = 30°12′15″, and is indicated by the + in Fig. 1.