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At least 127 records · Page 7
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DOE OSTI2024

A spatially resolved spectral analysis of giant radio galaxies with MeerKAT

ABSTRACT In this study we report the spatially resolved, wideband spectral properties of three giant radio galaxies (GRGs) in the COSMOS field: MGTC J095959.63+024608.6, MGTC J100016.84+015133.0, and MGTC J100022.85+031520.4. One of these galaxies, MGTC J100022.85+031520.4, is reported here for the first time, with a projected linear size of 1.29 Mpc at a redshift of 0.1034. Unlike the other two, it is associated with a brightest cluster galaxy (BCG), making it one of the few GRGs known to inhabit cluster environments. We examine the spectral age distributions of the three GRGs using new MeerKAT UHF-band (544–1088 MHz) observations, and L-band (900–1670 MHz) data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey. We test two models of spectral ageing, the Jaffe–Perola and Tribble models, using the Broadband Radio Astronomy Tools (brats) software, and find that they agree well with each other. We estimate the Tribble spectral age for MGTC J095959.63+024608.6 as 68 Myr, for MGTC J100016.84+015133.0 as 47 Myr, and for MGTC J100022.85+031520.4 as 67 Myr. We find significant disagreements between these spectral age estimates and the estimates of the dynamical ages of these GRGs, modelled in cluster and group environments. Our results highlight the need for additional processes that are not accounted for in either the dynamic age or the spectral age estimations.

Charlton, K. K. L. (ORCID:0000000229252047)↗
NASA NTRS1988

4C 40.36 - A radio galaxy at a redshift of 2.3

Long-slit spectroscopy of a faint extended optical object identified with the radio source 4C 40.36 is presented. Three emission lines are detected. Their wavelengths match those of C IV 1549 A, He II 1640 A, and semiforbidden C III 1909 A to within 0.5 percent for a redshift of z = 2.269. The extended continuum emission (20 kpc) together with the large equivalent widths (about 100 A) and narrow profiles (1500 km/s) of the emission lines, all show that 4C 40.36 is a galaxy with properties similar to those of other distant radio galaxies. The redshift of 4C 40.36, however, considerably exceeds that of the most distant radio galaxy (3C 326.1 at z = 1.825) known to date. 4C 40.36 is of additional interest as an excellent example of the recently discovered phenomenon of alignment between the optical and radio axes of powerful distant radio galaxies. The object was investigated as part of a survey of ultra-steep spectrum radio sources, and it is shown that the selection criteria used to discover 4C 40.36 result in a sample of objects having a relatively low dispersion of monochromatic radio luminosities.

Chambers, K. C.↗
NASA NTRS2017

Feeding and Feedback in the Powerful Radio Galaxy 3C 120

We present a spectral analysis of a 200-kilosecond observation of the broad-line radio galaxy 3C 120, performed with the high-energy transmission grating spectrometer on board the Chandra X-Ray Observatory. We find (i) a neutral absorption component intrinsic to the source with a column density of log N (sub H) equals 20.67 plus or minus 0.05 square centimeters; (ii) no evidence for a warm absorber (WA) with an upper limit on the column density of just log N (sub H) less than 19.7 square centimeters, assuming the typical ionization parameter log xi approximately equal to 2.5 ergs per second per centimeter; the WA may instead be replaced by (iii) a hot emitting gas with a temperature kT approximately equal to 0.7 kiloelectronvolts observed as soft X-ray emission from ionized Fe L-shell lines, which may originate from a kiloparsec-scale shocked bubble inflated by the active galactic nucleus (AGN) wind or jet with a shock velocity of about 1000 kilometers per second determined by the emission line width; (iv) a neutral Fe K alpha line and accompanying emission lines indicative of a Compton-thick cold reflector with a low reflection fraction R approximately equal to 0.2, suggesting a large opening angle of the torus; (v) a highly ionized Fe XXV emission feature indicative of photoionized gas with an ionization parameter log xi equal to 3.75 (sup plus 0.38) (sub minus 0.27) ergs per second per centimeter and a column density of log N (sub H) greater than 22 square centimeters localized within approximately 2 pc from the X-ray source; and (vi) possible signatures of a highly ionized disk wind. Together with previous evidence for intense molecular line emission, these results indicate that 3C 120 is likely a late-state merger undergoing strong AGN feedback.

black hole physics – galaxies: active – line: ↗
NASA NTRS2001

Multiple Spectral Components in Nearby Radio Galaxies

The purpose of this work was to study the complicated structures appearing in ROSAT PSPC observations of nearby radio galaxies through detailed spectroscopy using ASCA, and through combining spectroscopic and structural analyses. The galaxy studied in this work was NGC 6251, believed to have a composite structure based on our ROSAT PSPC analysis, with a strong, point-like, nonthermal core embedded in a weaker, group-scale, thermal halo. However, this simplest interpretation of the PSPC data (Birkinshaw & Worrall 1993; ApJ 412 568) is not unique. Other possibilities included strong thermal emission from the core, with an implied cooling flow. ASCA's spectroscopic capabilities were expected to resolve the ambiguity. When the ASCA data for NGC 6251 were received, we found (after resolving considerable difficulties with the calibration) that they are entirely consistent with a simple power-law interpretation, but that a strong intrinsic X-ray absorbing column is required in NGC 6251. This absorbing column can be identified with the neutral hydrogen found with the VLA (Birkinshaw & Worrall, 1994; BAAS, 25, 1432), and confirmed in a later, higher-resolution, VLA study.

Birkinshaw, M.↗
NASA NTRS1993

Nuclear activity and the environments of nearby radio galaxies

Much of our present understanding of galaxy evolution over a large redshift range is based on the study of samples selected on the basis of non-thermal radio emission. It is therefore necessary to understand the relationship between radio source activity and the host galaxy. Recent observations suggest that there is a connection between radio galaxy (RG) activity and radio galaxy evolution. For example, high-redshift RGs (z approx. greater than 0.7) show evidence for significant populations of young stars, and have optical continuum morphologies nearly always aligned with the radio axis (McCarthy et al. 1987; Chambers et al. 1987). This phenomenon is generally attributed to radio jet induced star formation (DeYoung 1989), but the lack of high S/N spectra of the galaxy continua, and recent detections of polarized light in a few objects make it hard to rule out other processes such as scattering or synchrotron radiation. A detailed study of the continuum light in the distant RGs is difficult as they are optically very faint. However, nearby RGs (z approx. less than 0.1) have bluer B-V colors than radio-quiet ellipticals, presumably due to the presence of young stellar populations (Smith and Heckman 1989) and several have extended UV continuum emitting regions along their radio axes (van Bruegel et al. 1985a, b, di Serego Alighieri et al. 1989), reminiscent of the alignment effect seen in the high redshift RGs. We have almost completed a continuum imaging survey of nearby (and therefore optically brighter), powerful RGs to study any possible relationships between the optical continuum light and radio source activity. In particular we are interested in (1) whether these lower redshift RGs shown any evidence of the alignment effect (in their rest-frame UV light) that is seen in the distant RGs, and (2) the effects that the radio source has on the environment of the host galaxy.

Dey, Arjun↗
NASA NTRS1994

Multiple X-ray emission components in low-power radio galaxies

We report x-ray observations of the first six sources observed with ROSAT in our study of low-power radio galaxies. Spatial and spectral measurements show that both resolved (thermal) and unresolved X-ray emission in a single source are typical, although the relative strength and size of the resolved component varies between objects. The unresolved X-ray component correlates well with the core radio emission and may be dominated by nonthermal emission associated with an inner radio jet.

Worrall, D. M.↗
NASA NTRS1997

The Nearest GHz Peaked-Spectrum Radio Galaxy, PKS 1718-649

In this paper we identify PKS 1718-649, at a distance of 56 Mpc (z = 0.014; H(sub o) = 75 km/s/Mpc, q(sub o) = 0), as the nearest GHz peaked-spectrum (GPS) radio galaxy, more than four times closer than any previously known. Extensive observations at radio wavelengths with the Australia Telescope Compact Array, the Southern Hemisphere VLBI Experiment array, and the Swedish-ESO Submillimetre Telescope have allowed us to determine the properties of the radio source: PKS 1718-649 consists of two compact sub-pc-scale components separated by approximately 2 pc, the overall radio polarization is low, and the radio spectrum is peaked near 3 GHz. Order-of-magnitude agreement between the quantitative model for GPS sources of Bicknell et al. and the radio data we present, as well as data at optical wavelengths from the literature, raises the interesting possibility that PKS 1718-649 may be frustrated in its development by the nuclear environment of its host galaxy, NGC 6328. The model of Bicknell et al. suggests free-free absorption as an explanation of the PKS 1718-649 radio spectrum. However, both free-free absorption and synchrotron self-absorption mechanisms are plausible for this source and both may contribute to the overall radio spectrum. PKS 1718-649 provides evidence to strengthen the speculative suggestion that GPS sources arise as a consequence of galaxy merger activity.

Tingay, S. J.↗
NASA NTRS2020

Extended X-ray emission from the z=4.26 radio galaxy 4C 63.20

We report on deep Chandra X-ray Telescope imaging observations of 4C 63.20, one of the few known radio galaxies at z > 3.5.The X-ray counterpart is resolved into a core plus two off-nuclear sources that (combined) account for close to 30 per cent of the total X-ray flux. Their morphology and orientation are consistent with a diffuse, lobe-like nature, albeit compact hotspots cannot be ruled out. The broad-band spectral energy distribution of 4C 63.20 can be reproduced with a jet model where the majority of the radio flux can be ascribed to synchrotron emission from the hotspots, whereas the (non-nuclear) X-ray emission is produced via inverse Compton (IC) off of cosmic microwave background (CMB) photons within the extended lobes. This scenario is broadly consistent with the expectation from highly magnetized lobes in a hotter CMB, and supports the view that IC/CMB may quench less extreme radio lobes at high redshifts.

Kate Napier↗
NASA NTRS1985

Strong Lyman-alpha emission in three distant radio galaxies

Very strong, narrow Lyman alpha emission (equivalent width approximately 1000 angstroms) has been discovered in the redshifted ultraviolet spectra of three radio galaxies having z between 1.62 and 1.82. The three are 3C 256, 3C 239, and 3C 241. It is noted that Lyman alpha will probably be a very useful redshift and classification determinant in future spectroscopic surveys of active galaxies at still greater distances.

Spinrad, H.↗
NASA NTRS2010

Chandra High Resolution Spectroscopy of the Circumnuclear Matter in the Broad Line Radio Galaxy, 3C 445

We present evidence for X-ray line emitting and absorbing gas in the nucleus of the Broad-Line Radio Galaxy (BLRG), 3C445. A 200 ks Chandra LETG observation of 3C 445 reveals the presence of several highly ionized emission lines in the soft X-ray spectrum, primarily from the He and H-like ions of O, Ne, Mg and Si. Radiative recombination emission is detected from O VII and O VIII, indicating that the emitting gas is photoionized. The He-like emission appears to be resolved into forbidden and intercombination line components, which implies a high density of greater than 10(sup 10) cm(sup -3), while the lines are velocity broadened with a mean width of 2600 km s(sup -1). The density and widths of the ionized lines indicate an origin of the gas on sub-parsec scales in the Broad Line Region (BLR). The X-ray continuum of 3C 445 is heavily obscured by a photoionized absorber of column density N(sub H) = 2 x 10(sup 23) cm(sup -2) and ionization parameter log xi = 1.4 erg cm s(sup -1). However the view of the X-ray line emission is unobscured, which requires the absorber to be located at radii well within any parsec scale molecular torus. Instead we suggest that the X-ray absorber in 3C 445 may be associated with an outflowing, but clumpy accretion disk wind, with an observed outflow velocity of approximately 10000 km s(sup -1).

Reeves, J. N.↗
NASA NTRS2016

The Complex Circumnuclear Environment of the Broad-Line Radio Galaxy 3C 390.3 Revealed by Chandra HETG

We present the first high spectral resolution X-ray observation of the broad-line radio galaxy 3C 390.3 obtained with the high-energy transmission grating spectrometer on board the Chandra X-ray Observatory. The spectrum shows complex emission and absorption features in both the soft X-rays and Fe K band. We detect emission and absorption lines in the energy range E = 700-1000 eV associated with ionized Fe L transitions (Fe XVIIXX). An emission line at the energy of E approximately equal to 6.4 keV consistent with the Fe K alpha is also observed. Our best-fit model requires at least three different components: (i) a hot emission component likely associated with the hot interstellar medium in this elliptical galaxy with temperature kT = 0.5 +/- 0.1 keV; (ii) a warm absorber with ionization parameter log Epislon = 2.3 +/- 0.5 erg s(exp 1) cm, column density logN(sub H) = 20.7 +/- 0.1 cm(exp -2), and outflow velocity v(sub out) less than 150 km s(exp -1); and (iii) a lowly ionized reflection component in the Fe K band likely associated with the optical broad-line region or the outer accretion disk. These evidences suggest the possibility that we are looking directly down the ionization cone of this active galaxy and that the central X-ray source only photoionizes along the unobscured cone. This is overall consistent with the angle-dependent unified picture of active galactic nuclei.

black hole physics↗
NASA NTRS2013

Gas Sloshing and Radio Galaxy Dynamics in the Core of the 3C 449 Group

We present results from a 140 ks Chandra/ACIS-S observation of the hot gas around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks Chandra observation of the group gas showed an unusual entropy distribution and a surface brightness edge in the gas that could be a strong shock around the inner radio lobes. In our deeper data we find no evidence for a temperature increase inside of the brightness edge, but a temperature decrease across part of the edge. This suggests that the edge is a "sloshing" cold front due to a merger within the last 1.3-1.6 Gyr. Both the northern and southern inner jets are bent slightly to the west in projection as they enter their respective lobes, suggesting that the sloshing core is moving to the east. The straight inner jet flares at approximately the position where it crosses the contact edge, suggesting that the jet is entraining and thermalizing some of the hot gas as it crosses the edge.We also detect filaments of X-ray emission around the southern inner radio jet and lobe which we attribute to low entropy entrained gas. The lobe flaring and gas entrainment were originally predicted in simulations of Loken et al. and are confirmed in our deep observation.

Lal, Dharam V.↗
NASA NTRS2000

Chandra Observations of the Nuclei of Radio Galaxies: 3C 295 and Hydra A

The angular resolution available with Chandra allows us to isolate the X-ray emission from the nucleus of many radio galaxies and obtain their spectra. As expected from unification schemes, spectra so far obtained can best be interpreted as heavily absorbed power laws. We present the spectral parameters so derived for 3C 295 and Hydra A and compare them to data obtained at other wavelengths.

Harris, D. E.↗
NASA NTRS1999

The Hyperluminous Infrared Quasar 3C 318 and Its Implications for Interpreting Sub-MM Detections of High-Redshift Radio Galaxies

We present near-infrared spectroscopy and imaging of the compact steep-spectrum radio source 3C 318 which shows it to be a quasar at redshift z = 1.574 (the z = 0.752 value previously reported is incorrect). 3C 318 is an IRAS, ISO and SCUBA source so its new redshift makes it the most intrinsically luminous far-infrared (FIR) source in the 3C catalogue (there is no evidence of strong gravitational lensing effects). Its bolometric luminosity greatly exceeds the 10(exp 13) solar luminosity level above which an object is said to be hyperluminous. Its spectral energy distribution (SED) requires that the quasar heats the dust responsible for the FIR flux, as is believed to be the case in other hyperluminous galaxies, and contributes (at the greater than 10% level) to the heating of the CIA dust responsible for the sub-mm emission. We cannot determine whether a starburst makes an important contribution to the heating of the coolest dust, so evidence for a high star-formation rate is circumstantial being based on the high dust, and hence gas, C-1 mass required by its sub-mm detection. We show that the current sub-mm and FIR data available for the highest-redshift radio galaxies are consistent with SEDs similar to that of 3C 318. This indicates that at least some of this population may be detected in the sub-mm because of dust heated by the quasar nucleus, and that interpreting sub-mm detection as evidence for very high (approx. less than 1000 solar mass/yr) star-formation rates may not always be valid. We show that the 3C318 quasar is slightly reddened (A(sub v) approx. = 0.5), the most likely cause of which is SMC-type dust in the host galaxy. If very distant radio galaxies are reddened in a similar way then we show that only slightly greater amounts of dust could obscure the quasars in these sources. We speculate that the low fraction of quasars amongst the very high redshift (z approx. greater than 3) objects in low-frequency radio-selected samples is the result of such obscuration. The highest-z objects might be preferentially obscured because like 3C318 they are inevitably observed very shortly after the jet-triggering event, or because their host galaxies are richer in dust and gas at earlier cosmic epochs, or because of some combination of these two effects.

Willott, Chris J.↗
NASA NTRS1977

On possible associations of quasi-stellar objects and radio galaxies with rich clusters of galaxies

A comparison of the cataloged coordinates of QSOs and of 3CR galaxies with those of Abell's rich clusters of galaxies yields the following results: (1) There is no statistically significant evidence that high-redshift QSOs lie preferentially close to Abell clusters. (2) There is no statistically significant evidence that low-redshift QSOs lie preferentially close to Abell clusters. (3) There is (as is well known) highly significant evidence that 3CR galaxies lie preferentially close to Abell clusters. (4) The distributions of angular separations between QSOs and clusters and between 3CR galaxies and clusters differ at statistically significant (but not highly significant) levels. In view of these results, a generic relationship between low-redshift QSOs and radio galaxies seems questionable. This result for the QSOs is also entirely consistent with the idea that they are 'local' objects with redshifts of noncosmological origin.

Roberts, D. H.↗