Faint Images Of The Radio Sky At Twenty-cm Research Articles

Search for hybrid morphology radio galaxies from the FIRST survey at 1400 MHz

ABSTRACT Hybrid Morphology Radio Sources (HyMoRS) are a very rare subclass of radio galaxies with apparent mixed FR morphology, i.e. these galaxies seem to have an FR-I structure on one side of the core and an FR-II structure on the other side of the core. We systematically searched for HyMoRS using Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-cm (FIRST) survey with 1400 MHz frequency and identified 33 candidate HyMoRS. Our finding significantly increased the known sample size of HyMoRS. HyMoRS may play an essential role in understanding the interaction of jets with the interstellar medium and the much-debated topic of the FR dichotomy. We identified optical counterparts for 29 sources in our catalogue. In our sample of sources, one source (J1106+1355) had quasar-like behaviour. Four sources were BRCLG (Brightest Cluster Galaxies) and six were LRG (Luminous Red Galaxies). We have estimated the spectral index and radio luminosity of HyMoRS in our catalogue, when possible. We found that J1136–0328 was the most luminous source in our sample (log L = 27.01 W Hz−1sr−1). It was also the farthest HyMoRS (with a redshift z = 0.82) in our sample. With the help of a large sample size of discovered sources, various statistical properties of detected galaxies were studied.

Infrared-radio relation in the local Universe

Context.The Square Kilometer Array (SKA) is expected to detect high-redshift galaxies with star formation rates (SFRs) up to two orders of magnitude lower thanHerschelsurveys and will thus boost the ability of radio astronomy to study extragalactic sources. The tight infrared-radio correlation offers the possibility of using radio emission as a dust-unobscured star formation diagnostic. However, the physics governing the link between radio emission and star formation is poorly understood, and recent studies have pointed to differences in the exact calibration required when radio is to be used as a star formation tracer.Aims.We improve the calibration of the relation of the local radio luminosity–SFR and to test whether there are nonlinearities in it.Methods.We used a sample ofHerschelAstrophysical Terahertz Large Area Survey (H-ATLAS) sources and investigated their radio luminosity, which was derived using the NRAO VLA Sky Survey (NVSS) and Faint Images of the Radio Sky at Twenty-cm (FIRST) maps. We stacked the bins of infrared luminosity and SFR and accounted for bins with no detections in the stacked images using survival analysis fitting. This approach was tested using Monte Carlo simulations.Results.After removing sources from the sample that have excess radio emission, which is indicative of nuclear radio activity, we found no deviations from linearity of the mean relations between radio luminosity and either SFR or infrared luminosity.Concluisions.We analyzed the link between radio emission and SFR or infrared luminosity using a local sample of star-forming galaxies without evidence of nuclear radio activity and found no deviations from linearity, although our data are also consistent with the small nonlinearity reported by some recent analyses. The normalizations of these relations are intermediate between those reported by earlier works.

Characterization of unresolved and unclassified sources detected in radio continuum surveys of the Galactic plane

ABSTRACT The continuum emission from 1 to 2 GHz of The H i/OH/Recombination line survey of the inner Milky Way (THOR) at ≲18 arcsec resolution covers ∼132 deg2 of the Galactic plane and detects 10 387 sources. Similarly, the first data release of the Global View of Star Formation in the Milky Way (GLOSTAR) survey covers ∼16 deg2 of the Galactic plane from 4 to 8 GHz at 18 arcsec resolution and detects 1575 sources. However, a large fraction of the unresolved discrete sources detected in these radio continuum surveys of the Galactic plane remain unclassified. Here, we study the Euclidean-normalized differential source counts of unclassified and unresolved sources detected in these surveys and compare them with simulated extragalactic radio source populations and previously established source counts. We find that the differential source counts for THOR and GLOSTAR surveys are in excellent agreement with both simulation and previous observations. We also estimate the angular two-point correlation function of unclassified and unresolved sources detected in THOR survey. We find a higher clustering amplitude in comparison with the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey up to the angular separation of 5°. The decrease in angular correlation with increasing flux cut and the excellent agreement of clustering pattern of sources above 1 mJy with high-z samples (z > 0.5) of the FIRST survey indicates that these sources might be high-z extragalactic compact objects. The similar pattern of one-point and two-point statistics of unclassified and compact sources with extragalactic surveys and simulations confirms the extragalactic origin of these sources.

Radio Galaxy Zoo: Knowledge Transfer Using Rotationally Invariant Self-organizing Maps

With the advent of large scale-surveys the manual analysis and classification of individual radio source morphologies is rendered impossible as existing approaches do not scale. The analysis of complex morphological features in the spatial domain is a particularly important task. Here, we discuss the challenges of transferring crowdsourced labels obtained from the Radio Galaxy Zoo project and introduce a proper transfer mechanism via quantile random forest regression. By using parallelized rotation and flipping invariant Kohonen-maps, image cubes of Radio Galaxy Zoo selected galaxies formed from the Faint Images of the Radio Sky at Twenty-cm (FIRST) radio continuum and the Wide-field Infrared Survey Explorer (WISE) infrared all-sky surveys are first projected down to a two-dimensional embedding in an unsupervised way. This embedding can be seen as a discretized space of shapes with the coordinates reflecting morphological features as expressed by the automatically derived prototypes. We find that these prototypes have reconstructed physically meaningful processes across two channel images at radio and infrared wavelengths in an unsupervised manner. In the second step, images are compared with those prototypes to create a heat map, which is the morphological fingerprint of each object and the basis for transferring the user generated labels. These heat maps have reduced the feature space by a factor of 248, and are able to be used as the basis for subsequent machine-learning (ML) methods. Using an ensemble of decision trees we achieve upwards of 85.7% and 80.7% accuracy when predicting the number of components and peaks in an image, respectively, using these heat maps. We also question the currently used discrete classification schema and introduce a continuous scale that better reflects the uncertainty in transition between two classes, caused by sensitivity and resolution limits.

Galaxy And Mass Assembly: the 1.4 GHz SFR indicator, SFR–M*relation and predictions for ASKAP–GAMA

We present a robust calibration of the 1.4GHz radio continuum star formation rate (SFR) using a combination of the Galaxy And Mass Assembly (GAMA) survey and the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey. We identify individually detected 1.4GHz GAMA-FIRST sources and use a late-type, non-AGN, volume-limited sample from GAMA to produce stellar mass-selected samples. The latter are then combined to produce FIRST-stacked images. This extends the robust parametrisation of the 1.4GHz-SFR relation to faint luminosities. For both the individually detected galaxies and our stacked samples, we compare 1.4GHz luminosity to SFRs derived from GAMA to determine a new 1.4GHz luminosity-to-SFR relation with well constrained slope and normalisation. For the first time, we produce the radio SFR-M* relation over 2 decades in stellar mass, and find that our new calibration is robust, and produces a SFR-M* relation which is consistent with all other GAMA SFR methods. Finally, using our new 1.4GHz luminosity-to-SFR calibration we make predictions for the number of star-forming GAMA sources which are likely to be detected in the upcoming ASKAP surveys, EMU and DINGO.

The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy

We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z = 0.8. The catalogue covers roughly 800 square degrees of sky, and provides optical identifications for 19,179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of i_mod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5,000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12,329 radio sources in the survey area, of which 10,856 have reliable redshifts. 85% of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15% are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83%) of LARGESS radio AGN at z < 0.8, with 12% being high-excitation radio galaxies (HERGs) and 5% radio-loud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disk.

Dark bubbles around high-redshift radio-loud active galactic nucleus

Abstract At redshift larger than 3 there is a disagreement between the number of blazars (whose jet is pointing at us) and the number of expected parents (whose jet is pointing elsewhere). Now we strengthen this claim because (i) the number of blazars identified within the Sloan Digital Sky Survey (SDSS)+Faint Images of the Radio Sky at Twenty-cm (FIRST) survey footprint increased, demanding a more numerous parent population, and (ii) the detected blazars have a radio flux large enough to be above the FIRST flux limit even if the jet is slightly misaligned. The foreseen number of these slightly misaligned jets, in principle detectable, is much larger than the radio-detected sources in the FIRST+SDSS survey (at redshift larger than 4). This argument is independent of the presence of an isotropic radio component, such as the hotspot or the radio lobe, and does not depend on the bulk Lorentz factor Γ. We propose a scenario that ascribes the lack of slightly misaligned sources to an overobscuration of the nucleus by a ‘bubble’ of dust, possibly typical of the first high-redshift quasars.

WHAT MAKES A RADIO-AGN TICK? TRIGGERING AND FEEDING OF ACTIVE GALAXIES WITH STRONG RADIO JETS

Although the link between activity in the nuclei of galaxy and galactic mergers has been under scrutinyfor several years, it is still unclear to what extent and for which populations of active galaxies merger-triggered activity is relevant. The environments of AGN allow an indirect probe of the past merger historyand future merger probability of these systems, su ering less from sensitivity issues when extended tohigher redshifts than traditional morphological studies of AGN host galaxies. Here we present results fromour investigation of the environment of radio selected sources out to a redshift z=2. We employ the rstdata release J-band catalog of the new near-IR Infrared Medium-Deep Survey (IMS), 1.4 GHz radio datafrom the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and a deep dedicated VLA survey ofthe VIMOS eld, covering a combined total of 20 sq. degrees. At a ux limit of the combined radio catalogof 0.1 mJy, we probe over 8 orders of magnitude of radio luminosity. Using the second closest neighbordensity parameters, we test whether active galaxies inhabit denser environments. We nd evidence for asub-population of radio-selected AGN that reside in signi cantly overdense environments at small scales,although we do not nd signi cant overdensities for the bulk of our sample. We show that radio-AGN inthe most underdense environments have vigorous ongoing star formation. We interpret these results interms of the triggering and fuelling mechanism of radio-AGN.Key words: galaxies: active { galaxies: jets { galaxies: star formation { galaxies: evolution1. THE TRIGGERING OF RADIO-AGNThe recent decades have revolutionized our understand-ing of how galaxies and the supermassive black holes attheir centers evolve (e.g., Springel et al. 2005, Hopkinset al. 2006). However, an ongoing debate concerns theway that active galactic nuclei (AGN) in galaxies aretriggered and sustained. The temporal coincidence ofthe peak of cosmic nuclear and star-formation activity(e.g., Richards et al. 2006, Aird et al. 2010), as well asthe predominantly very luminous AGN discovered be-yond our local universe, have led to the merger-drivenparadigm of AGN triggering (e.g., Sanders et al. 1988).However, with the advent of deeper extragalactic sur-veys this paradigm has come in question. Moderateluminosity X-ray AGN at intermediate redshifts werenot found to be preferentially associated with merg-ers (e.g., Cisternas et al. 2011), nor to inhabit denserenvironments than their non-active counterparts (e.g.,Karouzos et al. 2014a). While undoubtedly a fractionof AGN are triggered by mergers, the question still re-mains: how are di erent species of AGN triggered?Here we use the population of radio-AGN as a case studyto address this question. We present results about thehttp://pkas.kas.orgenvironments and host galaxy properties of radio-AGNthat help elucidate the di erent AGN feeding mecha-nisms within the broader context of galaxy evolution.2. THE SA22 FIELD AND THE RADIO-AGN WITHIN ITWe use data from the Infrared Medium-Deep Survey(IMS; see this proceedings) at J band and the Deep eX-tragalactic Survey (DXS; Lawrence et al. 2007). In ad-dition, we utilize radio data at 1.4 GHz from the FIRSTsurvey (Becker et al. 1995) and a deep VLA survey ofpart of SA22 (Chapman et al. 2004a). The combined ra-dio ux density limit of our sample is 0.1 mJy. Finally,we also employ the full coverage of the WISE telescope(Wright et al. 2010). In total we select 913 radio-AGNover the ˘ 20 deg

Galaxy and Mass Assembly: the evolution of bias in the radio source population to z∼1.5

We present a large-scale clustering analysis of radio galaxies in the Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-cm (FIRST) survey over the Galaxy And Mass Assembly (GAMA) survey area, limited to S1.4 GHz >1 mJy with spectroscopic and photometric redshift limits up to r < 19.8 and r < 22 mag, respectively. For the GAMA spectroscopic matches, we present the redshift-space and projected correlation functions, the latter of which yielding a correlation length r0 ~ 8.2 Mpc/h and linear bias of ~1.9 at z ~ 0.34. Furthermore, we use the angular two-point correlation function w({\theta}) to determine spatial clustering properties at higher redshifts. We find r0 to increase from ~6 to ~14 Mpc/h between z = 0.3 and z = 1.55, with the corresponding bias increasing from ~2 to ~10 over the same range. Our results are consistent with the bias prescription implemented in the SKADS simulations at low redshift, but exceed these predictions at z > 1. This is indicative of an increasing (rather than fixed) halo mass and/or AGN fraction at higher redshifts or a larger typical halo mass for the more abundant FRI sources.

AN EXAMINATION OF THE OPTICAL SUBSTRUCTURE OF GALAXY CLUSTERS HOSTING RADIO SOURCES

Using radio sources from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey, and optical counterparts in the Sloan Digital Sky Survey (SDSS), we have identified a large number of galaxy clusters. The radio sources within these clusters are driven by active galactic nuclei, and our cluster samples include clusters with bent, and straight, double-lobed radio sources. We also included a single-radio-component comparison sample. We examine these galaxy clusters for evidence of optical substructure, testing the possibility that bent double-lobed radio sources are formed as a result of large-scale cluster mergers. We use a suite of substructure analysis tools to determine the location and extent of substructure visible in the optical distribution of cluster galaxies, and compare the rates of substructure in clusters with different types of radio sources. We found no preference for significant substructure in clusters hosting bent double-lobed radio sources compared to those with other types of radio sources.

Mining the Herschel-Astrophysical Terahertz Large Area Survey: submillimetre-selected blazars in equatorial fields

The Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) provides an unprecedented opportunity to search for blazars at sub-mm wavelengths. We cross-matched the Faint Images of the Radio Sky at Twenty-cm (FIRST) radio source catalogue with the 11 655 sources brighter than 35 mJy at 500 μm in the ∼135 deg2 of the sky covered by the H-ATLAS equatorial fields at 9h and 15h, plus half of the field at 12h. We found that 379 of the H-ATLAS sources have a FIRST counterpart within 10 arcsec, including eight catalogued blazars (plus one known blazar that was found at the edge of one of the H-ATLAS maps). To search for additional blazar candidates we have devised new diagnostic diagrams and found that known blazars occupy a region of the log (S500 μm/S350 μm) versus log (S500 μm/S1.4 GHz) plane separated from that of sub-mm sources with radio emission powered by star formation, but shared with radio galaxies and steep-spectrum radio quasars. Using this diagnostic we have selected 12 further possible candidates that turn out to be scattered in the (r − z) versus (u − r) plane or in the Wide-Field Infrared Survey Explorer colour–colour diagram, where known blazars are concentrated in well defined strips. This suggests that the majority of them are not blazars. Based on an inspection of all the available photometric data, including unpublished VISTA Kilo-degree Infrared Galaxy survey photometry and new radio observations, we found that the spectral energy distributions (SEDs) of only one out of the 12 newly selected sources are compatible with being synchrotron dominated at least up to 500 μm, i.e. with being a blazar. Another object may consist of a faint blazar nucleus inside a bright star-forming galaxy. The possibility that some blazar hosts are endowed with active star formation is supported by our analysis of the SEDs of Planck Early Release Compact Source Catalogue blazars detected at both 545 and 857 GHz. The estimated rest-frame synchrotron peak frequencies of H-ATLAS blazars are in the range 11.5 ≤ log (νpeak, Hz) ≤ 13.7, implying that these objects are low synchrotron peak. Six of them also show evidence of an ultraviolet excess that can be attributed to emission from the accretion disc. Allowing for the possibility of misidentifications and of contamination of the 500 μm flux density by the dusty torus or by the host galaxy, we estimate that there are seven or eight pure synchrotron sources brighter than S500 μm = 35 mJy over the studied area, a result that sets important constraints on blazar evolutionary models.

Revealing a strongly reddened, faint active galactic nucleus population by stacking deep co-added images

More than half of the sources identified by recent radio sky surveys have not been detected by wide-field optical surveys. We present a study based on our co-added image stacking technique, in which our aim is to detect the optical emission from unresolved, isolated radio sources of the Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-cm (FIRST) survey that have no identified optical counterparts in the Sloan Digital Sky Survey (SDSS) Stripe 82 co-added data set. From the FIRST catalogue, 2116 such radio point sources were selected, and cut-out images, centred on the FIRST coordinates, were generated from the Stripe 82 images. The already co-added cut-outs were stacked once again to obtain images of high signal-to-noise ratio, in the hope that optical emission from the radio sources would become detectable. Multiple stacks were generated, based on the radio luminosity of the point sources. The resulting stacked images show central peaks similar to point sources. The peaks have very red colours with steep optical spectral energy distributions. We have found that the optical spectral index alpha_nu falls in the range -2.9 < alpha_nu < -2.2, depending only weakly on the radio flux. The total integration times of the stacks are between 270 and 300 h, and the corresponding 5 sigma detection limit is estimated to be about m_r = 26.6 mag. We argue that the detected light is mainly from the central regions of dust-reddened Type 1 active galactic nuclei. Dust-reddened quasars might represent an early phase of quasar evolution, and thus they can also give us an insight into the formation of massive galaxies. The data used in the paper are available on-line at http://www.vo.elte.hu/doublestacking.

DISCOVERY OF A RADIO-SELECTEDz∼ 6 QUASAR

We present the discovery of only the second radio-selected, z ~ 6 quasar. We identified SDSS J222843.54+011032.2 (z=5.95) by matching the optical detections of the deep Sloan Digital Sky Survey (SDSS) Stripe 82 with their radio counterparts in the Stripe82 VLA Survey. We also matched the Canadian-France-Hawaiian Telescope Legacy Survey Wide (CFHTLS Wide) with the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey but have yet to find any z ~ 6 quasars in this survey area. The discovered quasar is optically-faint, z = 22.3 and M_{1450} ~ -24.5, but radio-bright, with a flux density of f$_{1.4GHz, peak}$ = 0.31mJy and a radio-loudness of R ~ 1100 (where R = f_{5GHz}/f_{2500}). The i-z color of the discovered quasar places it outside the color selection criteria for existing optical surveys. We conclude by discussing the need for deeper wide-area radio surveys in the context of high-redshift quasars.

Radio galaxies in the 2SLAQ Luminous Red Galaxy Survey – I. The evolution of low-power radio galaxies to z∼ 0.7

Abstract We have combined optical data from the 2dF-SDSS (Sloan Digital Sky Survey) LRG (Luminous Red Galaxy) and QSO (quasi-stellar object) (2SLAQ) redshift survey with radio measurements from the 1.4 GHz VLA (Very Large Array) FIRST (Faint Images of the Radio Sky at Twenty-cm) and NVSS (NRAO VLA Sky Survey) surveys to identify a volume-limited sample of 391 radio galaxies at redshift 0.4 &amp;lt; z &amp;lt; 0.7. By determining an accurate radio luminosity function for luminous early-type galaxies in this redshift range, we can investigate the cosmic evolution of the radio-galaxy population over a wide range in radio luminosity. The low-power radio galaxies in our LRG sample (those with 1.4 GHz radio luminosities in the range 1024 to 1025 W Hz−1, corresponding to Fanaroff–Riley I (FR I) radio galaxies in the local Universe) undergo significant cosmic evolution over the redshift range 0 &amp;lt; z &amp;lt; 0.7, consistent with pure luminosity evolution of the form (1 +z)k, where k= 2.0 ± 0.3. Our results appear to rule out (at the 6–7σ level) models in which low-power radio galaxies undergo no cosmic evolution. The most powerful radio galaxies in our sample (with radio luminosities above 1026 W Hz−1) may undergo more rapid evolution over the same redshift range. The evolution seen in the low-power radio-galaxy population implies that the total energy input into massive early-type galaxies from active galactic nucleus (AGN) heating increases with redshift, and was at least 50 per cent higher at z∼ 0.55 (the median redshift of the 2SLAQ LRG sample) than in the local universe.

Isophotal shapes of elliptical/lenticular galaxies from the Sloan Digital Sky Survey

We revisit the shapes of isophotes for elliptical (E) and lenticular (S0) galaxies by studying 847 nearby early-type galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 4 (DR4) with velocity dispersions above 200 km s −1 . The IRAF task ELLIPSE was used to derive the deviations of the isophotes from pure ellipses (Fourier coefficients a 3/a and a 4/a), position angles (PAs) and ellipticities as a function of radius. We show the statistical distributions of the a 3/a and a 4/a parameters as a function of velocity dispersion, magnitude and colour. The a 4/a parameter is correlated with the ellipticity and absolute Petrosian magnitude of galaxies. No significant correlation was found between the a 4/a parameter with colour and velocity dispersion. A cross-correlation between the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and the SDSS data reveals a lack of powerful radio emitters in discy E/S0s, as previously found by Bender et al. We also find that boxy E/S0s favour denser environments while discy E/S0s favour more isolated environments. The median values of changes in the ellipticity and PA between one and one and a half Petrosian half-light radii in the isophotes are about −0.023 and 1. ◦ 61, respectively. The average change in the PA is much larger, about 4. 12, due to an extended tail. The change in ellipticity is weakly correlated with the ellipticity itself, with an increasing ellipticity for galaxies with higher ellipticity as the radius increases. The isophote parameters for the 847 galaxies are available online.

The soft X-ray properties of quasars in the Sloan Digital Sky Survey

We use the ROSAT All-Sky Survey (RASS) to study the soft X-ray properties of a homogeneous sample of 46 420 quasars selected from the third data release of the Sloan Digital Sky Survey (SDSS). Optical luminosities, both at rest frame 2500 angstrom (L-2500) and in [O III] (L-[O III]) span more than three orders of magnitude, while redshifts range over 0.1 < z < 5.4. We detect 3366 quasars directly in the observed 0.1-2.4 keV band. Subsamples of radio-loud quasars (RLQs) and radio-quiet quasars (RQQs) are obtained by cross-matching with the Faint Images of the Radio Sky at Twenty-cm (FIRST) catalogue. We study the distribution of X-ray luminosity as a function of optical luminosity, redshift and radio power using both individual detections and stacks of complete sets of similar quasars. At every optical luminosity and redshift log L-2keV is, to a good approximation, normally distributed with dispersion similar to 0.40, at least brightwards of the median X-ray luminosity. This median X-ray luminosity of quasars is a power law of optical luminosity with index similar to 0.53 for L-2500 and similar to 0.30 for L-[O III]. RLQs are systematically brighter than RQQs by about a factor of 2 at given optical luminosity. The zero-points of these relations increase systematically with redshift, possibly in different ways for RLQs and RQQs. Evolution is particularly strong at low redshift and if the optical luminosity is characterized by L-[O III]. At low redshift and at given L-[O III] the soft X-ray emission from type II active galactic nucleus (AGN) is more than 100 times weaker than that from type I AGN.

Evolving neural networks to identify bent-double galaxies in the FIRST survey

The FIRST (Faint Images of the Radio Sky at Twenty-cm) survey is an ambitious project scheduled to cover 10,000 square degrees of the northern and southern galactic caps. Until recently, astronomers associated with FIRST identified radio-emitting galaxies with a bent-double morphology through a visual inspection of images. Besides being subjective, prone to error and tedious, this manual approach is becoming increasingly infeasible: upon completion, FIRST will include almost a million galaxies. This paper describes the application of six methods of evolving neural networks (NNs) with genetic algorithms (GAs) to the identification of bent-double galaxies. The objective is to demonstrate that GAs can successfully address some common problems in the application of NNs to classification problems, such as training the networks, choosing appropriate network topologies, and selecting relevant features. We measured the overall accuracy of the networks using the arithmetic and geometric means of the accuracies on bent and non-bent galaxies. Most of the combinations of GAs and NNs perform equally well on our data, but using GAs to select feature subsets produces the best results, reaching accuracies of 90% using the arithmetic mean and 87% with the geometric mean. The networks found by the GAs were more accurate than hand-designed networks and decision trees.

Pulsars in FIRST Observations

We identified 16 pulsars from the Faint Images of the Radio Sky at Twenty-cm (FIRST) at 1.4 GHz. Their positions and total flux densities are extracted from the FIRST catalog. Comparing the source positions with those in the PSRcatalog, we obtained better determined positions of PSRs J1022+1001, J1518+4904, J1652+2651, and proper motion upper limits of another three pulsars PSRs J0751+1807, J1012+5307, J1640+2224. Proper motions of the other 10 pulsars are consistent with the values in the catalog.

The Optical, Infrared and Radio Properties of Extragalactic Sources Observed by SDSS, 2MASS and FIRST Surveys

AbstractWe positionally match sources observed by the Sloan Digital Sky Survey (SDSS), the Two Micron All Sky Survey (2MASS), and the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey. Practically all 2MASS sources are matched to an SDSS source within 2 arcsec; ~11% of them are optically resolved galaxies and the rest are dominated by stars. About 1/3 of FIRST sources are matched to an SDSS source within 2 arcsec; ~80% of these are galaxies and the rest are dominated by quasars. Based on these results, we project that by the completion of these surveys the matched samples will include about 107stars and 106galaxies observed by both SDSS and 2MASS, and about 250,000 galaxies and 50,000 quasars observed by both SDSS and FIRST. Here we present a preliminary analysis of the optical, infrared and radio properties for the extragalactic sources from the matched samples. In particular, we find that the fraction of quasars with stellar colors missed by the SDSS spectroscopic survey is probably not larger than ~10%, and that the optical colors of radio-loud quasars are ~0.05 mag. redder (with 4σ significance) than the colors of radio-quiet quasars.

Extended radio emission in BL Lac objects

We have observed 28 sources selected from the 1Jy sample of BL Lac objects [(Stickel et al. 1991)] with the Very Large Array (VLA) in A, B and D configurations at 1.36, 1.66 and 4.85 GHz, and/or with the Westerbork Synthesis Radio Telescope (WSRT) at 1.40 GHz. In this paper we present high sensitivity images at arcsecond resolution of the 18 objects showing extended structure in our images, and of another source from the FIRST (Faint Images of the Radio Sky at Twenty-cm) survey [(Becker et al. 1995).] In general our high sensitivity images reveal an amount of extended emission larger than previously reported. In some objects the luminosity of the extended structure is comparable with that of FR II radio sources. A future paper will be devoted to the interpretation of these results.