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Register a new userHST/STIS low dispersion spectroscopy of three Compact Steep Spectrum sources Evidence for jet-cloud interaction
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We present Hubble Space Telescope Imaging Spectrograph long-slit spectroscopy of the emission line nebulae in the compact steep spectrum radio sources 3C 67, 3C 277.1, and 3C 303.1. We derive BPT (Baldwin- Philips-Terlevich; Baldwin et al. 1981) diagnostic emission line ratios for the nebulae which are consistent with a mix of shock excitation and photoionization in the extended gas. In addition, line ratios indicative of lower ionization gas are found to be associated with higher gas velocities. The results are consistent with a picture in which these galaxy scale radio sources interact with dense clouds in the interstellar medium of the host galaxies, shocking the clouds thereby ionizing and accelerating them.
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We report first X-ray Chandra observations of a sample of seven low luminosity compact (LLC) sources. They belong to a class of young compact steep spectrum (CSS) radio sources. Four of them have been detected, the other three have upper limit estimations for X-ray flux, one CSS galaxy is associated with an X-ray cluster. We have used the new observations together with the observational data for known strong CSS and gigahertz-peaked spectrum (GPS) objects and large scale FRIs and FRIIs to study the relation between morphology, X-ray properties and excitation modes in radio-loud AGNs. We found that: (1) The low power objects fit well to the already established X-ray - radio luminosity correlation for AGNs and occupy the space among, weaker in the X-rays, FRI objects. (2) The high excitation galaxies (HEG) and low excitation galaxies (LEG) occupy distinct locus in the radio/X-ray luminosity plane, notwithstanding their evolutionary stage. This is in agreement with the postulated different origin of the X-ray emission in these two group of objects. (3) We have tested the AGN evolution models by comparing the radio/X-ray luminosity ratio with the size of the sources, and indirectly, with their age. We conclude that the division for two different X-ray emission modes, namely originate in the base of the relativistic jet (FRIs) or in the accretion disk (FRIIs) is already present among the younger compact AGNs. (4) Finally, we found that the CSS sources are less obscured than the more compact GPSs in X-rays. However, the anti-correlation between X-ray column density and radio size does not hold for the whole sample of GPS and CSS objects.
Compact steep-spectrum (CSS) and peaked spectrum (PS) radio sources are compact, powerful radio sources. The multi-frequency observational properties and current theories are reviewed with emphasis on developments since the earlier review of ODea (1998). There are three main hypotheses for the nature of PS and CSS sources. (1) The PS sources might be very young radio galaxies which will evolve into CSS sources on their way to becoming large radio galaxies. (2) The PS and CSS sources might be compact because they are confined (and enhanced in radio power) by interaction with dense gas in their environments. (3) Alternately, the PS sources might be transient or intermittent sources. Each of these hypotheses may apply to individual objects. The relative number in each population will have significant implications for the radio galaxy paradigm. Proper motion studies over long time baselines have helped determine hotspot speeds for over three dozen sources and establish that these are young objects. Multifrequency polarization observations have demonstrated that many CSS/PS sources are embedded in a dense interstellar medium and vigorously interacting with it. The detection of emission line gas aligned with the radio source, and blue-shifted HI absorption and [OIII] emission lines indicates that AGN feedback is present in these objects -- possibly driven by the radio source. CSS/PS sources with evidence of episodic AGN over a large range of time-scales have been discussed. The review closes with a discussion of open questions and prospects for the future.
We present optical spectroscopy of 62 objects selected from several samples of ultra steep spectrum (USS) radio sources. 46 of these are from our primary catalog, consisting of 669 sources with radio spectral indices alpha < -1.30 (S_nu ~ nu^alpha); this first spectroscopic sub-sample was selected on the basis of their faint optical and near-IR identifications. Most are identified as narrow-lined radio galaxies with redshifts ranging from z=0.25 to z=5.19. Ten objects are at z>3, nearly doubling the number of such sources known to date. Four of the USS radio sources are identified with quasars, of which at least three have very red spectral energy distributions. The source TN J0936-2242 is identified with an extremely red object (ERO, R-K>5); both it and a close companion are at z=1.479. The spectrum of the ERO closely resembles that of previously discovered radio galaxies at z~1.5. Five sources show continuum emission, but fail to show any clear emission or absorption features, despite integrations of ~1 h with the Keck telescope. We suggest that these objects could be (i) radio galaxies with faint emission lines in the ``redshift desert at 1.5 <~ z <~ 2.3, (ii) radio galaxies with an obscured AGN, which are dominated by a stellar continuum observed with insufficient S/N, or (iii) pulsars. Three radio sources identified with faint objects in the K-band images remain undetected in 50-90 min spectroscopic integrations with the Keck telescope, and are possible z>7 candidates.
We present Very Long Baseline Interferometry observations of a faint and low-luminosity ($L_{rm 1.4 GHz} < 10^{27}~mbox{W Hz}^{-1}$) Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sample. We select eight sources from deep radio observations that have radio spectra characteristic of a GPS or CSS source and an angular size of $theta lesssim 2$ arcsec, and detect six of them with the Australian Long Baseline Array. We determine their linear sizes, and model their radio spectra using Synchrotron Self Absorption (SSA) and Free Free Absorption (FFA) models. We derive statistical model ages, based on a fitted scaling relation, and spectral ages, based on the radio spectrum, which are generally consistent with the hypothesis that GPS and CSS sources are young and evolving. We resolve the morphology of one CSS source with a radio luminosity of $10^{25}~mbox{W Hz}^{-1}$, and find what appear to be two hotspots spanning 1.7 kpc. We find that our sources follow the turnover-linear size relation, and that both homogenous SSA and an inhomogeneous FFA model can account for the spectra with observable turnovers. All but one of the FFA models do not require a spectral break to account for the radio spectrum, while all but one of the alternative SSA and power law models do require a spectral break to account for the radio spectrum. We conclude that our low-luminosity sample is similar to brighter samples in terms of their spectral shape, turnover frequencies, linear sizes, and ages, but cannot test for a difference in morphology.
We apply the V/Vm test to a subsample of compact steep-spectrum sources from a complete sample of radio sources selected at 2.7 GHz. We find that the <V/Vm> has a value intermediate between those found for samples of extended steep-spectrum sources and those of compact flat-spectrum sources. If the sample is split into two further classes of sources having more steep and less steep spectra, the <V/Vm> values for these then tally roughly with those found for the extended steep-spectrum and compact flat-spectrum classes of sources. Implications of this result are discussed.
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