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Register a new userA Unified Catalog of Radio Objects Detected by NVSS, FIRST, WENSS, GB6, and SDSS
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(Abridged) We construct a catalog of radio sources detected by the GB6 (6 cm), FIRST and NVSS (20 cm), and WENSS (92 cm) radio surveys, and the SDSS optical survey. The 2.7 million entries in the publicly-available master catalog are comprised of the closest three FIRST to NVSS matches (within 30 arcsec) and vice-versa, and unmatched sources from each survey. Entries are supplemented by data from the other radio and optical surveys, where available. We perform data analysis a ~3000 deg^2 region of sky where the surveys overlap, which contains 140,000 NVSS-FIRST sources, of which 64,000 are detected by WENSS and 12,000 by GB6. About one third of each sample is detected by SDSS. An automated classification method based on 20 cm fluxes defines three radio morphology classes: complex, resolved, and compact. Radio color-magnitude- morphology diagrams for these classes show structure suggestive of strong underlying physical correlations. Complex and resolved sources tend to have a steep spectral slope (alpha ~ -0.8) that is nearly constant from 6 to 92 cm, while the compact class contains a significant number of flat-spectrum (alpha ~ 0) sources. In the optically-detected sample, quasars dominate the flat-spectrum compact sources while steep-spectrum and resolved objects contain substantial numbers of both quasars and galaxies. Differential radio counts of quasars and galaxies are similar at bright flux levels (>100 mJy at 20 cm), while at fainter levels the quasar counts are significantly reduced below galaxy counts. The optically-undetected sample is strongly biased toward steep-spectrum sources. In samples of quasars and galaxies with SDSS spectra, we find that radio properties such as spectral slope, morphology, and radio loudness are correlated with optical color and luminosity.
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We discuss the panchromatic properties of 99,088 galaxies selected from the SDSS Data Release 1 spectroscopic sample (a flux-limited sample for 1360 deg^2). These galaxies are positionally matched to sources detected by ROSAT, GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS. We find strong correlations between the detection fraction at other wavelengths and optical properties such as flux, colors, and emission-line strengths. Using GALEX, SDSS, and 2MASS data, we construct the UV-IR broad-band spectral energy distributions for various types of galaxies, and find that they form a nearly one-parameter family. For example, based on SDSS u- and r-band data, supplemented with redshift, the K-band 2MASS magnitudes can be predicted with an rms scatter of only 0.2 mag. When a dust content estimate determined from SDSS data by Kauffmann et al. (2003) is also utilized, this scatter decreases to 0.1 mag. We demonstrate that this dust content is indeed higher for galaxies detected by IRAS and that it can be used to predict measured IRAS 60 micron flux density within a factor of two using only SDSS data. We also show that the position of a galaxy in the emission-line-based Baldwin-Phillips-Terlevich diagram is correlated with the optical light concentration index and u-r color determined from the SDSS broad-band imaging data, and discuss changes in the morphology of this diagram induced by requiring detections at other wavelengths. We study the IR-radio correlation and find evidence that its slope may be different for AGN and star-forming galaxies and related to the H_alpha/H_beta line strength ratio.
Context: In 6 years of operation, INTEGRAL/ISGRI revealed more than 500 sources. Many of these sources are variable. Taking into account that nearly half of INTEGRAL/ISGRI sources are new and many of them are still unidentified, the variability properties of the sources can serve as additional parameters that may help to classify and identify the unknown sources. Aims: In order to study the variability properties of the sources detected by INTEGRAL/ISGRI we develop a method to quantify the variability of a source. We describe here our techniques and compile a catalog of the sources that fit our criteria of variability. Methods: We use the natural time binning of INTEGRAL observations called Science Window ($approx 2000$ seconds) and test the hypothesis that the detected sources are constant using a $chi^2$ all-sky map in three energy bands (20-40, 40-100, 100-200 keV). We calculate an intrinsic variance of the flux in individual pixels and use it to define the fractional variability of a source. The method is sensitive to the source variability on time scales of one Science Window and higher. We concentrate only on the sources which were already reported to be detected by INTEGRAL. Results: We present a catalog of 202 sources which are found to be significantly variable. For the catalog sources we give the measure of variability and fluxes with corresponding errors in 20-40, 40-100, 100-200 keV energy bands, and we present some statistics about the population of variable sources. The description of the physical properties of the variable sources will be given in a forthcoming paper.
With the aim of exploring the properties of the class of FR0 radio galaxies, we selected a sample of 108 compact radio sources, called FR0CAT, by combining observations from the NVSS, FIRST, and SDSS surveys. The catalog includes sources with z$leq 0.05$, with a radio size $lesssim$ 5 kpc, and with an optical spectrum characteristic of low-excitation galaxies. Their 1.4-GHz radio luminosities range $10^{38} lesssim u L_{1.4} lesssim 10^{40}$ erg/s. The FR0CAT hosts are mostly (86%) luminous ($-21 gtrsim M_r gtrsim -23$) red early-type galaxies with black hole masses $10^8 lesssim M_{rm BH} lesssim 10^9 M_odot$: similar to the hosts of FRI radio galaxies, but they are on average a factor $sim$1.6 less massive. The number density of FR0CAT sources is $sim$5 times higher than that of FRIs, and thus they represent the dominant population of radio sources in the local Universe. Different scenarios are considered to account for the smaller sizes and larger abundance of FR0s with respect to FRIs. An age-size scenario that considers FR0s as young radio galaxies that will all eventually evolve into extended radio sources cannot be reconciled with the large space density of FR0s. However, the radio activity recurrence, with the duration of the active phase covering a wide range of values and with short active periods strongly favored with respect to longer ones, might account for their large density number. Alternatively, the jet properties of FR0s might be intrinsically different from those of the FRIs, the former class having lower bulk Lorentz factors, possibly due to lower black hole spins. Our study indicates that FR0s and FRI/IIs can be interpreted as two extremes of a continuous population of radio sources that is characterized by a broad distribution of sizes and luminosities of their extended radio emission, but shares a single class of host galaxies.
We built a catalog of 219 FRI radio galaxies (FRIs), called FRICAT, selected from a published sample and obtained by combining observations from the NVSS, FIRST, and SDSS surveys. We included in the catalog the sources with an edge-darkened radio morphology, redshift $leq 0.15$, and extending (at the sensitivity of the FIRST images) to a radius $r$ larger than 30 kpc from the center of the host. We also selected an additional sample (sFRICAT) of 14 smaller (10 $<r<$ 30 kpc) FRIs, limiting to $z<0.05$. The hosts of the FRICAT sources are all luminous ($-21 gtrsim M_r gtrsim -24$), red early-type galaxies with black hole masses in the range $10^8 lesssim M_{rm BH} lesssim 3times10^9 M_odot$; the spectroscopic classification based on the optical emission line ratios indicates that they are all low excitation galaxies. Sources in the FRICAT are then indistinguishable from the FRIs belonging to the Third Cambridge Catalogue of Radio Sources (3C) on the basis of their optical properties. Conversely, while the 3C-FRIs show a strong positive trend between radio and [OIII] emission line luminosity, these two quantities are unrelated in the FRICAT sources; at a given line luminosity, they show radio luminosities spanning about two orders of magnitude and extending to much lower ratios between radio and line power than 3C-FRIs. Our main conclusion is that the 3C-FRIs just represent the tip of the iceberg of a much larger and diverse population of FRIs.
We discuss the optical and radio properties of 30,000 FIRST sources positionally associated with an SDSS source in 1230 deg$^2$ of sky. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r=21 are optically resolved. We estimate an upper limit of 5% for the fraction of quasars with broad-band optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux -- optical flux plane supports the existence of the quasar radio-dichotomy; 8% of all quasars with i<18.5 are radio-loud and this fraction seems independent of redshift and optical luminosity. The radio-loud quasars have a redder median color by 0.08 mag, and a 3 times larger fraction of objects with red colors. FIRST galaxies represent 5% of all SDSS galaxies with r<17.5, and 1% for r<20, and are dominated by red galaxies. Magnitude and redshift limited samples show that radio galaxies have a different optical luminosity distribution than non-radio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions, and resulting selection effects, are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux, and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies (abridged).
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