Radio-optical analysis of extended radio sources in the FLS field 2009 SA SKA Postgraduate Bursary Conference 4 th Annual Postgraduate Bursary Conference Author: Claudio Moises Paulo Supervisor: Prof. C. Cress Co-supervisor: Dr. R. Morganti and Dr. I. Prandoni

Aims The aim of this study is to understand the sub-mJy radio population, focussing on the multi-component sources. Such a study may give important clues on the relative contribution of radiative versus jet-driven feedback from AGN in models of galaxy formation.

IR Data The First Look Survey (FLS) was the first scientific program carried out by Spitzer Space Telescope. A small region of this field has been imaged very deeply, permitting the detection of cosmologically distant sources.

Radio Data ObservedArea Res.1Sigma Sources VLA (1.4 GHz)Condon et al. (2003) WSRT (1.4 GHz)Morganti et al. (2004)~114x GMRT (0.61 GHz)Garn et al. (2004)~45.8x Very useful is the availability of data at two radio frequencies, since different accreting regimes display different spectral signatures in the radio domain.

Redshift surveys of the extragalactic FLS targeting selected 24 μm and 1.4 GHz sources were made with: WIYN/HYDRA (Marleau et al. 2007) and the MMT/Hectospec fiber spectrograph (Papovich et al. 2006). Optical Data

Methods A cross-correlation between radio sources from VLA and GMRT catalogues with position offsets d<3” was done with the aim of studying the radio spectral properties of the sample.

Methods (Cont.) As a first step we extracted sub-images of multi-component sources from the VLA, GMRT and WSRT Mosaic Images. We visually inspected the source morphology to decide which GMRT components to sum up in order to get the same source structure as for the VLA. and then, we performed a preliminary classification of the radio source morphology in FR Class, Peculiar, Compact, etc. From VLA & GMRT fluxes at same resolution, we computed:

Methods (Cont.) Adopting a distance-only based criterion we cross-correlated our two frequency multi-component radio catalogue with the optical catalogues of Marleau et al. (2007) and Papovich et al. (2006), assuming d<6”. »Optical identification. Before the optical identification, we had to estimate the central position of multi-component sources using the source centroid, i.e. the flux-weighted average position of all the components (Prandoni et al. 2006). Radio and optical luminosity of all identified sources were calculated using their Redshift.

Methods (Cont.) In order to enhance our preliminary classifications, we made the overlay between radio and deep NOAO optical image of the FLS region.

Methods (Cont.)

Results After cross-correlating the VLA and GMRT data, we obtained a catalogue of 1573 radio component sources. From which we identified a sample of 164 sources which appeared to be part of multi-component systems. Sub-images of these were then produced. Visual inspection of the sub-images shows that at 0.61 GHz: We ended up with a radio catalogue of 107 sources, preliminarily classified according to their morphology as FR Class, Peculiar, Compact, etc. Total Sources Components1234

Results (Cont.) Lower power objects showing a variety of forms in which the highest brightness occurs near their centres, excluding their cores. Gray Scale: VLA. Its not so clear because they don't show the effect of primary beam correction as in the WSRT and GMRT. Red contour: GMRT. 3, 4.5, 6, 10, 20, 50 Cyan contour: WSRT. 6, 10, 20, 50 FR Class I

Results (Cont.) There are more powerful sources having their regions of highest surface brightness at the ends of a double-lobed structure. The Gray Scale and Contours are same as FRI image. FR Class II

Results (Cont.) Extended radio source located in cluster of galaxies (Mignano et al., 2008). The Gray Scale and Contours are same as FRI image. WSRT contours are very confusing because this source is locate on the edge of WSRT Mosaic Image. Wide angle tail source

Results (Cont.) As expected, the majority of multi-component sources are steep-spectrum sources. Note wider range of spectral indices for fainter sources: variety of accretion modes? Left: Radio Spectral index as a function of flux density for VLA. Right: Spectral index distribution for the same sources shown on the left. The vertical dashed line indicates the average spectral index value of the sample.

Results (Cont.) The cross-correlation between the 107 multi-component radio sources with Marleau et al. (2007) and Papovich et al. (2006) catalogues gave us 23 identifications, 18 of which have a redshift determination. To recover the missing redshifts we used the Nasa Extragalactic Database (NED).

Results (Cont.) Left: Position in the sky of optically identified multi-component radio sources. Right: Redshift distribution of the indentified sources.

Results (Cont.) The identified objects are spectroscopically classified as galaxies. Some of them are classified as star forming or starburst galaxies.

Results (Cont.) According to their radio power: FRIFRII Identified objects176 Power (W/Hz)< 24.5> 24.5

In the next 4 slides you will see a gallery of optically identified sources, ordered by radio power. Results (Cont.)

Results (Cont.) In order to enhance our preliminary classifications, we made the overlay between radio and deep NOAO optical image of the FLS region.

Results (Cont.) An example of an overlay of a radio and a deep optical image of the FLS region, related to one of the identified sources with z= (clearly an FRI).

Conclusions and future work I have presented an analysis of a sample of multi-component radio sources from the FLS region, obtained by cross-correlating the VLA and GMRT FLS catalogues. By visual inspection, we classified them as FRI/II, Peculiar, Compact, etc. Most sources have steep radio spectra as expected for multi-component radio sources, and all sources optically identified are spectroscopically classified as galaxies. Fainter multi-component sources show a wider range of spectral indices than brighter multicomponent sources, indicating a less homogenous population and possibly a wider variety of feedback mechanisms. The increased number of ultra-steep spectrum sources could be attributed to a larger population of higher-redshift galaxies. Further optical follow-up will allow a more complete census of the sub-mJy population and more information on AGN feedback from such sources.

References Condon et al. 2003, AJ, 125, Fanaroff B. L. & Riley J. M., 1974, MNRAS, 167, 31. Garn T., Alexander, 2004, MNRAS, 000,1-9. Marleau et al. 2007, ApJ, 663, 218. Mignano et al. 2008, A&A, Morganti et al. 2004, A&A 424, 371. Papovich et al. 2006, AJ, 132: Snellen & Best, 2001, MNRAS, 328,

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