INVERSE COMPTON X-RAY HALOS AROUND HIGH- z RADIO GALAXIES: A FEEDBACK MECHANISM POWERED BY FAR-INFRARED STARBURSTS OR THE COSMIC MICROWAVE BACKGROUND? (original) (raw)
Related papers
2012
We report the detection of extended X-ray emission around two powerful high-z radio galaxies (HzRGs) at z~3.6 (4C03.24 & 4C19.71) and use these to investigate the origin of extended, Inverse Compton (IC) powered X-ray halos at high z. The halos have X-ray luminosities of Lx~3e44 erg/s and sizes of ~60kpc. Their morphologies are broadly similar to the ~60-kpc long radio lobes around these galaxies suggesting they are formed from IC scattering by relativistic electrons in the radio lobes, of either CMB or FIR photons from the dust-obscured starbursts in these galaxies. These observations double the number of z>3 HzRGs with X-ray detected IC halos. We compare the IC X-ray to radio luminosity ratios for these new detections to the two previously detected z~3.8 HzRGs. Given the similar redshifts, we would expect comparable X-ray IC luminosities if CMB mm photons are the seed field for the IC emission. Instead the two z~3.6 HzRGs, which are ~4x fainter in the FIR, also have ~4x fainter X-ray IC emission. Including a further six z>2 radio sources with IC X-ray halos from the literature, we suggest that in the more compact (lobe sizes <100-200kpc), majority of radio sources, the bulk of the IC emission may be driven by scattering of locally produced FIR photons from luminous, dust-obscured starbursts within these galaxies, rather than CMB photons. The resulting X-ray emission can ionise the gas on ~100-200-kpc scales around these systems and thus form their extended Ly-alpha emission line halos. The starburst and AGN activity in these galaxies are thus combining to produce an effective and wide-spread "feedback" process, acting on the long-term gas reservoir for the galaxy. If episodic radio activity and co-eval starbursts are common in massive, high-z galaxies, then this IC-feedback mechanism may affect the star-formation histories of massive galaxies. [Abridged]
The Astrophysical Journal, 1999
The infrared-luminous galaxy NGC 3256 is a classic example of a merger-induced nuclear starburst system. We find here that it is the most X-ray-luminous star-forming galaxy yet detected (L 0.5−10 keV = 1.6 × 10 42 ergs s −1 ). Long-slit optical spectroscopy and a deep, high-resolution ROSAT X-ray image show that the starburst is driving a "superwind" which accounts for ∼ 20% of the observed soft X-ray emission. Analysis of X-ray spectral data from ASCA indicates this gas has a characteristic temperature of kT ≈ 0.3 keV. Our model for the broadband X-ray emission of NGC 3256 contains two additional components: a warm thermal plasma (kT ≈ 0.8 keV) associated with the central starburst, and a hard power-law component with an energy index of α X ≈ 0.7. We discuss the energy budget for the two thermal plasmas and find that the input of mechanical energy from the starburst is more than sufficient to sustain the observed level of emission. We also examine possible origins for the power-law component, concluding that neither a buried AGN nor the expected population of high-mass X-ray binaries can account for this emission. Inverse-Compton scattering, involving the galaxy's copious flux of infrared photons and the relativistic electrons produced by supernovae, is likely to make a substantial contribution to the hard X-ray flux. Such a model is consistent with the observed radio and IR fluxes and the radio and X-ray spectral indices. We explore the role of X-ray-luminous starbursts in the production of the cosmic X-ray background radiation. The number counts and spectral index distribution of the faint radio source population, thought to be dominated by star-forming galaxies, suggest that a significant fraction of the hard X-ray background could arise from starbursts at moderate redshift.
Monthly Notices of the Royal Astronomical Society, 2012
X-ray selected galaxy group samples are usually generated by searching for extended Xray sources that reflect the thermal radiation of the intragroup medium. On the other hand, large radio galaxies that regularly occupy galaxy groups also emit in the X-ray window, and their contribution to X-ray selected group samples is still not well understood. In order to investigate their relative importance, we have carried out a systematic search for non-thermal extended X-ray sources in the COSMOS field. Based on the morphological coincidence of X-ray and radio extensions, out of 60 radio galaxies, and ∼ 300 extended X-ray sources, we find only one candidate where the observed extended X-ray emission arises from nonthermal processes related to radio galaxies. We present a detailed analysis of this source, and its environment. Our results yield that external Inverse Compton emission of the lobes is the dominant process that generates the observed X-ray emission of our extended X-ray candidate, with a minor contribution from the gas of the galaxy group hosting the radio galaxy. Finally, we show that finding only one potential candidate in the COSMOS field (in a redshift range 0 < z < 6 and with radio luminosity between 10 25 and 10 30 W/Hz) is consistent with expected X-ray-counts arising from synchrotron lobes. This implies that these sources are not a prominent source of contamination in samples of X-ray selected clusters/groups, but they could potentially dominate the z > 1 cluster counts at the bright end (S X > 7 · 10 −15 erg s −1 cm 2 ).
Extended X-ray emission in radio galaxies: 3C 305
2010
A key issue of the star formation process is its independence from the environmental conditions. In particular, it is not clear whether star formation in the outer Galaxy occurs in the same way as in the inner Galaxy. We present preliminary results of the analysis of a ∼ 440Ks ACIS-Chandra observation of NGC1893, a young cluster (∼ 3−4Myrs), far away from the Galactic Center with the aim to study star formation in the outer region of the Galaxy and investigate the coronal properties of the cluster stars. We detect more than 1000 X-ray sources, most of which are likely cluster members. We present also a preliminary analysis of X-ray variability of the cluster stars.
Far infrared and radio emission in dusty starburst galaxies
Arxiv preprint astro-ph/0206029, 2002
We revisit the nature of the far infrared (FIR)/Radio correlation by means of the most recent models for star forming galaxies, focusing in particular on the case of obscured starbursts. We model the IR emission with our population synthesis code, GRASIL (Silva et al. 1998). As for the radio emission, we revisit the simple model of . We find that a tight FIR/Radio correlation is natural when the synchrotron mechanism dominates over the inverse Compton, and the electrons cooling time is shorter than the fading time of the supernova (SN) rate. Observations indicate that both these conditions are met in star forming galaxies, from normal spirals to obscured starbursts. However, since the radio non thermal (NT) emission is delayed, deviations are expected both in the early phases of a starburst, when the radio thermal component dominates, and in the poststarburst phase, when the bulk of the NT component originates from less massive stars. We show that this delay allows the analysis of obscured starbursts with a time resolution of a few tens of Myrs, unreachable with other star formation (SF) indicators. We suggest to complement the analysis of the deviations from the FIR/Radio correlation with the radio slope (q-Radio slope diagram) to obtain characteristic parameters of the burst, e.g. its intensity, age and fading time scale. The analysis of a sample of compact ULIRGs shows that they are intense but transient starbursts, to which one should not apply usual SF indicators devised for constant SF rates. We also discuss the possibility of using the q-radio slope diagram to asses the presence of obscured AGN. A firm prediction of the models is an apparent radio excess during the post-starburst phase, which seems to be typical of a class of star forming galaxies in rich cluster cores. Finally we discuss how deviations from the correlation, due to the evolutionary status of the starburst, affect the technique of photometric redshift determination widely used for the high-z sources.
Radio-Excess IRAS Galaxies. IV. Optical Spectroscopy
The Astronomical Journal, 2006
This is the fourth in our series of papers discussing the nature of radio-excess galaxies, which have radio emission associated with an active nucleus but which do not fit into the traditional categories of either radio-loud or radio-quiet active galaxies. In this paper, we present optical spectra of our sample of FIR-luminous radio-excess galaxies. Optical emission line ratio diagnostics are used to determine the dominant source of the ionizing radiation. We find that radio excess is an excellent indicator of the presence of an active nucleus. The radio-excess sample contains a much higher fraction of AGN than samples selected on FIR luminosity alone, or using other criteria such as warm FIR colors. Several objects have ambiguous classifications and are likely to be composite objects with mixed excitation. The type of optical spectrum appears to be associated with the radio-loudness: our results suggest that radio-loud objects may be more 'pure' AGN than radio-intermediate objects. We find strong evidence for interaction between the radio plasma and the surrounding gas. Broad, structured optical emission lines are observed and a relative blueshift is measured between the [O III] λ5007 and Hα lines in several sources. Jet energy fluxes are inferred from the [O III] λ5007 luminosities using a shock model for the interaction between the radio jet and the line-emitting gas. The jet energy fluxes of the radioexcess objects are lower than in powerful radio sources, consistent with our previous results. We conclude that the jets of radio-intermediate sources are intrinsically weaker than those in sources with more powerful radio emission. A significant fraction of the sample spectra show post-starburst stellar continuum, with A-star absorption lines. Post-starburst stellar populations are consistent with the large fraction of merging or disturbed host galaxies in the sample. The ages of the radio sources are significantly less than those of A stars indicating that, if the radio sources are associated with merging activity, there is a delay between the interaction and the initiation of the radio activity.
Extended X-Ray Emission around FR II Radio Galaxies: Hot Spots, Lobes, and Galaxy Clusters
The Astrophysical Journal Supplement Series, 2021
We present a systematic analysis of the extended X-ray emission discovered around 35 FR II radio galaxies from the revised Third Cambridge Catalog (3CR) Chandra Snapshot Survey with redshifts between 0.05 and 0.9. We aimed to (i) test for the presence of extended X-ray emission around FR II radio galaxies, (ii) investigate whether the extended emission origin is due to inverse Compton (IC) scattering of seed photons arising from the cosmic microwave background (CMB) or thermal emission from an intracluster medium (ICM), and (iii) test the impact of this extended emission on hot-spot detection. We investigated the nature of the extended X-ray emission by studying its morphology and compared our results with low-frequency radio observations (i.e., ∼150 MHz) in the TGSS and LOFAR archives, as well as with optical images from Pan-STARRS. In addition, we optimized a search for X-ray counterparts of hot spots in 3CR FR II radio galaxies. We found statistically significant extended emissio...
EXTENDED X-RAY EMISSION IN RADIO GALAXIES: THE PECULIAR CASE OF 3C 305
The Astrophysical Journal, 2009
Extended X-ray structures are common in Active Galactic Nuclei (AGNs). Here we present the first case of a Compact Steep Spectrum (CSS) radio galaxy, 3C 305, in which the X-ray radiation appears to be associated with the optical emission line region, dominated by the [O III]5007. On the basis of a morphological study, performed using the comparison between the X-rays, the optical and the radio band, we argue that the high energy emission has a thermal nature and it is not directly linked to the radio jet and hotspots of this source. Finally, we discuss the origin of the extended X-ray structure connected with the optical emission line region following two different interpretations: as due to the interaction between matter outflows and shock-heated environment gas, or as due to gas photoionized by nuclear emission.