Excess Radio Emission Research Articles

Radio Identifications of Markarian Galaxies and the Correlation between Radio and Far-Infrared Properties

By checking DSS optical images and NVSS radio images, 782 Markarian galaxies were identified to be NVSS radio sources. A comparison of the radio luminosity at 1.4 GHz and the far-infrared (FIR) luminosity for 468 ``normal galaxies shows a tight correlation. Most of the Seyfert galaxies and quasars follow the radio-FIR relation deduced from the ``normal galaxy sample, but with a somewhat larger scatter. A total 167 Markarian galaxies, comprising 100 ``normal galaxies, 66 Seyfert galaxies and one quasar, have either excess radio emission or much lower FIR spectral index α (25μm, 60μm). These galaxies may be classified as ``AGN-powered. For ``normal galaxies, the average q value (defined as the log ratio between FIR and radio luminosities) is 2.3. There seems a trend for q to slightly decrease with increasing radio luminosity. This may imply that the ongoing active star formation in galaxies with higher radio luminosities is more efficient in heating the cosmic-ray electrons.

Mixed-Morphology Pairs as a Breeding Ground for Active Nuclei

Mixed-morphology pairs offer a simplification of the interaction equation that involves a gas-rich fast rotator paired with a gas-poor slow rotator. In past low-resolution IRAS studies it was assumed that the bulk of the far-infrared (FIR) emission originated in the spiral component. However, our Infrared Space Observatory studies revealed a surprising number of early-type components with significant IR emission, some of which turned out to show active nuclei. This motivated us to look at the current statistics of active nuclei in mixed pairs using the radio-FIR continuum correlation as a diagnostic. We find a clear excess of early-type components with radio continuum emission and active nuclei. We suggest that they arise more often in mixed pairs via cross-fueling of gas from the spiral companion. This fuel is more efficiently channeled into the nucleus of the slow-rotating receptor. In a sample of 112 mixed-morphology pairs from the Karachentsev catalog, we find that about 25%–30% of detected mixed pairs show a displacement from the radio-FIR relation defined by normal star-forming galaxies. The latter objects show excess radio continuum emission, while others extend the relation to unusually high radio and FIR flux levels. Many of the outliers or extreme emitters involve an early-type component with an active nucleus. The paired E/S0 galaxies in the sample exhibit a significant excess detection fraction and a marginal excess luminosity distribution compared to those of isolated unpaired E/S0 galaxies.

Radio Properties of Infrared‐Selected Galaxies in theIRAS2 Jy Sample

The radio counterparts to the IRAS Redshift Survey galaxies are identified in the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the IR flux-limited (S60 μm ≥ 2 Jy) complete sample of 1809 galaxies lists accurate radio positions, redshifts, and 1.4 GHz radio and IRAS fluxes. This sample is 6 times larger in size and 5 times deeper in redshift coverage (to z ≈ 0.15) than those used in earlier studies of the radio and far-IR (FIR) properties of galaxies in the local volume. The well-known radio-FIR correlation is obeyed by the overwhelming majority (≥98%) of the IR-selected galaxies, and the radio AGNs identified by their excess radio emission constitute only about 1% of the sample, independent of the IR luminosity. These FIR-selected galaxies can account for the entire population of late-type field galaxies in the local volume, and their radio continuum may be used directly to infer the extinction-free star formation rate in most cases. Both the 1.4 GHz radio and 60 μm IR luminosity functions are reasonably well described by linear sums of two Schechter functions, one representing normal, late-type field galaxies and the other representing starbursts and other luminous IR galaxies. The integrated FIR luminosity density for the local volume is (4.8 ± 0.5) × 107 L☉ Mpc-3, less than 10% of which is contributed by the luminous IR galaxies with LFIR ≥ 1011 L☉. The inferred extinction-free star formation density for the local volume is 0.015 ± 0.005 M☉ yr-1 Mpc-3.

Radio Loud Far-Infrared Galaxies

AbstractWe present the first results of a multiwavelength study of IRAS galaxies with excess radio emission. The sample was selected by cross-correlating the IRAS Faint Source Survey (for |b| ≥ 50°) and the Point Source Catalogue (for 10° < |b| < 50°) with the Texas radio survey. Recent optical (imaging and spectroscopic) and radio (VLA) observations are discussed. These observations will be used to investigate possible connections between radio galaxy activity, star formation and galaxy interactions.

Ex-Cess Radio Emission from Close Pairs of Galaxies

view Abstract Citations (126) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Excess Radio Emission from Close Pairs of Galaxies Stocke, John T. Abstract Statistics from a radio continuum survey of approximately 600 galaxy spairs [Stocke, Tifft, and Kaftan-Kassim (1978). Astron. J. 83, 322] show sthat close pairs are radio sources at more than twice the number than smore widely spaced pairs. This correlation holds both for ellipticals sand for spirals. A detailed consideration of possible selection effects sshows that these do not bias the results. Further investigation of the sgalaxy pairs and other radio samples generalize the above correlation to sone between radio sources and the local galaxy density. Such a srelationship suggests that radio sources are triggered by mass stransferral between galaxies during close encounters. Publication: The Astronomical Journal Pub Date: April 1978 DOI: 10.1086/112210 Bibcode: 1978AJ.....83..348S full text sources ADS |