The X-ray view of giga-hertz peaked spectrum radio galaxies (original) (raw)
Related papers
Modelling the broad‐band spectra of X‐ray emitting GPS galaxies
Astronomische Nachrichten, 2009
The study of the broad‐band emission of GHz‐Peaked‐Spectrum (GPS) radio galaxies is a powerful tool to investigate the physical processes taking place in the central, kpc‐sized region of their active hosts, where the jets propagate and the lobes expand, interacting with the surrounding interstellar medium (ISM). We recently developed a new dynamical‐radiative model to describe the evolution of the GPS phenomenon (Stawarz et al. 2008): as the relativistic jets propagate through the ISM, gradually engulfing narrow‐line emitting gas clouds along their way, the electron population of the expanding lobes evolves, emitting synchrotron light, as well as inverse‐Compton radiation via up‐scattering of the photon fields from the host galaxy and its active nucleus. The model, which successfully reproduces the key features of the GPS radio sources as a class, provides a description of the evolution of their spectral energy distribution (SED) with the lobes' expansion, predicting significant...
The Astrophysical Journal, 2010
In a dynamical-radiative model we recently developed to describe the physics of compact, GHz-Peaked-Spectrum (GPS) sources, the relativistic jets propagate across the inner, kpc-sized region of the host galaxy, while the electron population of the expanding lobes evolves and emits synchrotron and inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the expanding lobes, and photoionized by the active nucleus, are responsible for the radio spectral turnover through free-free absorption (FFA) of the synchrotron photons. The model provides a description of the evolution of the GPS spectral energy distribution (SED) with the source expansion, predicting significant and complex high-energy emission, from the X-ray to the γ-ray frequency domain. Here, we test this model with the broad-band SEDs of a sample of eleven X-ray emitting GPS galaxies with Compact-Symmetric-Object (CSO) morphology, and show that: (i) the shape of the radio continuum at frequencies lower than the spectral turnover is indeed well accounted for by the FFA mechanism; (ii) the observed X-ray spectra can be interpreted as non-thermal radiation produced via IC scattering of the local radiation fields off the lobe particles, providing a viable alternative to the thermal, accretion-disk dominated scenario. We also show that the relation between the hydrogen column densities derived from the X-ray (N H) and radio (N HI) data of the sources is suggestive of a positive correlation, which, if confirmed by future observations, would provide further support to our scenario of high-energy emitting lobes.
The radio properties of a complete, X-ray selected sample of nearby, massive elliptical galaxies
Monthly Notices of the Royal Astronomical Society, 2010
We investigate the radio properties of a complete sample of nearby, massive, X-ray bright elliptical and S0 galaxies. Our sample contains 18 galaxies with ROSAT All-Sky Survey Xray fluxes F X, 0.1−2.4 keV > 3 × 10 −12 erg s −1 cm −2 , within a distance of 100 Mpc. For these galaxies, we have complete (18/18) VLA radio and Chandra X-ray coverage. Nuclear radio emission is detected from 17/18 of the galaxies. Ten of the galaxies exhibit extended radio emission; of these ten, all but one also exhibit clear evidence of interaction of the radio source with the surrounding, X-ray emitting gas. Among the seven galaxies with unresolved radio sources, one has clear, and one has small, cavity-like features in the Chandra X-ray images; a third has a disturbed X-ray morphology. Using a radio luminosity limit equivalent to L 1.4 GHz > 10 23 W Hz −1 to calculate the radio-loud fraction, we find that this misses the majority of the radio detected galaxies in the sample. We determine integrated radio-to-X-ray flux ratios for the galaxies, GR X , which are shown to span a large range (factor of 100). We calculate the mass-weighted cooling times within 1 kpc, and find hints for an anticorrelation with the radio luminosity. We also calculate limits on k/f , where k is the ratio of the total particle energy to that of relativistic electrons radiating in the range 10 MHz-10 GHz and f is the volume filling factor of the plasma in the cavity. The k/f distribution is also broad, reflecting previous results for larger galaxy clusters. Lowering the X-ray flux limit, at the expense of less complete VLA and Chandra coverage, increases the size of our sample to 42 galaxies. Nuclear radio activity is detected in at least 34/42 of this extended sample.
2002
We investigate the nature of the luminous X-ray source population detected in a (72 ks) Chandra ACIS-S observation of NGC 4038/39, the Antennae galaxies. We derive the average X-ray spectral properties of sources in different luminosity ranges, and we correlate the X-ray positions with radio, IR, and optical (HST) data. The X-ray sources are predominantly associated with young stellar clusters, indicating that they belong to the young stellar population. Based on both their co-added X-ray spectrum, and on the lack of associated radio emission, we conclude that the Ultra Luminous X-ray sources (ULXs), with L X ≥ 10 39 ergs s −1 , are not young compact Supernova Remnants (SNR), but accretion binaries. While their spectrum is consistent with those of ULXs studied in nearby galaxies, and interpreted as the counterparts of intermediate mass black-holes (M> 10 − 1000 M ⊙ ), comparison with the position of star-clusters suggests that some of the ULXs may be runaway binaries, thus suggesting lower-mass binary systems. The co-added spectrum of the sources in the 3 × 10 38 − 10 39 erg s −1 luminosity range is consistent with those of Galactic black-hole candidates. These sources are also on average displaced from neighboring star clusters. The softer spectrum of the less luminous sources suggests the presence of SNRs or of hot interstellar medium (ISM) in the Chandra source extraction area. Comparison with HI and CO observations shows that most sources are detected in the outskirts of large concentrations of gas. The absorbing columns inferred from these observations would indeed absorb X-rays up to 5 keV, so there may be several hidden X-ray sources. Associated with these obscured regions we find 6 sources with heavily absorbed X-ray spectra and absorption-corrected luminosities in the ULX range. We detect the nuclei of both galaxies with luminosities in the 10 39 ergs s −1 range and soft, possibly thermal, X-ray spectra.
1997
Recent studies of the cosmic X-ray background (XRB) have suggested the possible existence of a population of relatively faint sources with hard X-ray spectra; however, the emission mechanism remains unclear. If the hard X-ray emission is from the radiatively inefficient, advection-dominated accretion flows (ADAFs) around massive black holes in galactic nuclei, X-ray luminosity and radio luminosity satisfy the approximate relation LR ∼ 7 × 10 (ν/15GHz)(M/10M⊙)(Lx/10 erg s) erg s where LR = νLν is the radio luminosity at frequency ν, M is the mass of the accreting black hole, and 10 <∼ Lx <∼ 10 erg s is the 2-10 keV X-ray luminosity. These sources are characterized by inverted radio spectra Iν ∝ ν . For example, an ADAF X-ray source with luminosity Lx ∼ 10 erg s has a nuclear radio luminosity of ∼ 4×10(M/3×10M⊙) erg s −1 at ∼ 20 GHz and if at a distance of ∼ 10(M/3 × 10M⊙) 1/2 Mpc would be detected as a ∼ 1mJy point radio source. High frequency (∼ 20GHz), high angular resolution...
Monthly Notices of the Royal Astronomical Society, 2016
We present radio active galactic nuclei (AGN) luminosity functions over the redshift range 0.005 < z < 0.75. The sample from which the luminosity functions are constructed is an optical spectroscopic survey of radio galaxies, identified from matched Faint Images of the Radio Sky at Twenty-cm survey (FIRST) sources and Sloan Digital Sky Survey images. The radio AGN are separated into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs) using the optical spectra. We derive radio luminosity functions for LERGs and HERGs separately in the three redshift bins (0.005 < z < 0.3, 0.3 < z < 0.5 and 0.5 < z < 0.75). The radio luminosity functions can be well described by a double power law. Assuming this double power-law shape the LERG population displays little or no evolution over this redshift range evolving as ∼(1 + z) 0.06 +0.17 −0.18 assuming pure density evolution or ∼(1 + z) 0.46 +0.22 −0.24 assuming pure luminosity evolution. In contrast, the HERG population evolves more rapidly, best fitted by ∼(1 + z) 2.93 +0.46 −0.47 assuming a double power-law shape and pure density evolution. If a pure luminosity model is assumed, the best-fitting HERG evolution is parametrized by ∼(1 + z) 7.41 +0.79 −1.33. The characteristic break in the radio luminosity function occurs at a significantly higher power (1 dex) for the HERG population in comparison to the LERGs. This is consistent with the two populations representing fundamentally different accretion modes.
The Phoenix Deep Survey: X-ray properties of faint radio sources
Monthly Notices of the Royal Astronomical Society, 2003
In this paper we use a 50 ks XMM-Newton pointing overlapping with the Phoenix Deep Survey, a homogeneous radio survey reaching µJy sensitivities, to explore the X-ray properties and the evolution of star-forming galaxies. Multiwavelength UV, optical and near-infrared photometric data are available for this field and are used to estimate photometric redshifts and spectral types for all radio sources brighter than R = 21.5 mag (total of 82). Faint radio galaxies with R < 21.5 mag and spiral galaxy SEDs (total of 34) are then segregated into two redshift bins with a median of z = 0.240 (total of 19) and 0.455 (total of 15) respectively. Stacking analysis for both the 0.5-2 keV and 2-8 keV bands is performed on the two subsamples. A high confidence level signal (> 3.5σ) is detected in the 0.5-2 keV band corresponding to a mean flux of ≈ 3 × 10 −16 erg s −1 cm −2 for both subsamples. This flux translates to mean luminosities of ≈ 5 × 10 40 and ≈ 1.5 × 10 41 erg s −1 for the z = 0.240 and 0.455 subsamples respectively. Only a marginally significant signal (2.6σ) is detected in the 2-8 keV band for the z = 0.455 subsample. This may indicate hardening of the mean X-ray properties of sub-mJy sources at higher redshifts and/or higher luminosities. Alternatively, this may be due to contamination of the z = 0.455 subsample by a small number of obscured AGNs. On the basis of the observed optical and X-ray properties of the faint radio sample we argue that the stacked signal above is dominated by starformation with the AGN contamination being minimal. The mean X-ray-to-optical flux ratio and the mean X-ray luminosity of the two subsamples are found to be higher than optically selected spirals and similar to starbursts. We also find that the mean Xray and radio luminosities of the faint radio sources studied here are consistent with the L X − L 1.4 correlation of local star-forming galaxies. Moreover, the X-ray emissivity of sub-mJy sources to z ≈ 0.3 is estimated and is found to be elevated compared to local H II galaxies. The observed increase is consistent with X-ray luminosity evolution of the form ≈ (1 + z) 3 . Assuming that our sample is indeed dominated by star-forming galaxies this is direct evidence for evolution of such systems at X-ray wavelengths. Using an empirical X-ray luminosity to star-formation rate (SFR) conversion factor we estimate a global SFR density at z ≈ 0.3 of 0.029 ± 0.007M ⊙ yr −1 Mpc −3 . This is found to be in fair agreement with previous results based on galaxy samples selected at different wavelengths.
Monthly Notices of the Royal Astronomical Society, 2016
We present radio active galactic nuclei (AGN) luminosity functions over the redshift range 0.005 < z < 0.75. The sample from which the luminosity functions are constructed is an optical spectroscopic survey of radio galaxies, identified from matched Faint Images of the Radio Sky at Twenty-cm survey (FIRST) sources and Sloan Digital Sky Survey images. The radio AGN are separated into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs) using the optical spectra. We derive radio luminosity functions for LERGs and HERGs separately in the three redshift bins (0.005 < z < 0.3, 0.3 < z < 0.5 and 0.5 < z < 0.75). The radio luminosity functions can be well described by a double power law. Assuming this double power-law shape the LERG population displays little or no evolution over this redshift range evolving as ∼(1 + z) 0.06 +0.17 −0.18 assuming pure density evolution or ∼(1 + z) 0.46 +0.22 −0.24 assuming pure luminosity evolution. In contrast, the HERG population evolves more rapidly, best fitted by ∼(1 + z) 2.93 +0.46 −0.47 assuming a double power-law shape and pure density evolution. If a pure luminosity model is assumed, the best-fitting HERG evolution is parametrized by ∼(1 + z) 7.41 +0.79 −1.33. The characteristic break in the radio luminosity function occurs at a significantly higher power (1 dex) for the HERG population in comparison to the LERGs. This is consistent with the two populations representing fundamentally different accretion modes.
ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum radio galaxies
Astronomy and Astrophysics
We present results from observations obtained with ISOPHOT, on board the ISO satellite, of a representative sample of seventeen CSS/GPS radio galaxies and of a control sample of sixteen extended radio galaxies spanning similar ranges in redshift (0.2 <= z <= 0.8) and radio luminosity (P_2.7 GHz >= 10^26 W/Hz). The observations have been performed at lambda = 60, 90, 174 and 200 microns. Seven of the CSS/GPS sources have detections >= 3 sigma at one or more wavelengths, one of which is detected at >= 5 sigma. By co-adding the data we have obtained average flux densities at the four wavelengths. We found no evidence that the FIR luminosities of the CSS/GPS sources are significantly different from those of the extended objects and therefore there is not any support for CSS/GPS sources being objects "frustrated" by an abnormally dense ambient medium. The two samples were then combined, providing FIR information on a new sample of radio galaxies at intermediate r...