J/MNRAS/475/5179 Spatially offset AGN cand. in CLASS survey (Skipper+, 2018) ================================================================================ Spatially offset AGN candidates in the CLASS survey. Skipper C.J., Browne I.W.A. =2018MNRAS.475.5179S (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Active gal. nuclei ; Positional data ; Redshifts Keywords: galaxies: active - galaxies: interactions - galaxies: nuclei Abstract: Prompted by a recent claim by Barrows et al. that X-ray active galactic nuclei (AGNs) are often found significantly offset from the centres of their host galaxies, we have looked for examples of compact radio sources that are offset from the optical centroids of nearby (z<0.2) galaxies. We have selected a sample of 345 galaxies from the Sloan Digital Sky Survey (SDSS) galaxy catalogue, which have nearby compact radio sources listed in the Cosmic-Lens All Sky Survey (CLASS) catalogue. We find only three matches ~0.87 per cent of the sample) with offsets greater than 600 milliarcsec (mas), which is considerably fewer than we would have expected from the Barrows et al. X-ray survey. We fit our histogram of offsets with a Rayleigh distribution with {sigma}=60.5mas, but find that there is an excess of objects with separations greater than ~150mas. Assuming that this excess represents AGNs with real offsets, we place an upper limit of ~17 per cent on the fraction of offset AGNs in our radio-selected sample. We select 38 objects with offsets greater than 150mas, and find they have some diverse properties: Some are well known, such as Mrk 273 and Arp 220, some have dust lanes, which may have affected the optical astrometry, and a few are strong new candidates for offset AGNs. Description: Our sample was constructed from the SDSS galaxy catalogue by cross matching sources with the z<0.2 OSSY catalogue (Oh et al., 2011ApJS..195...13O), and the CLASS catalogue (Myers et al., 2003MNRAS.341....1M, Browne et al., 2003MNRAS.341...13B, Cat. VIII/72) of compact radio sources. Our sample comprised 374 galaxies. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 257 345 *The high-offset galaxies -------------------------------------------------------------------------------- Note on table1.dat: galaxies identified as AGNs, and with the closest matched CLASS source offset by an angle of at least 150mas, and with a flux density of at least 8mJy. -------------------------------------------------------------------------------- See also: VIII/72 : CLASS survey of radio sources (Myers+, 2003) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 24 A24 --- SDSS SDSS catalog ID (SDSS JHHMMSS.ss+DDMMSS.s) 26- 43 I18 --- OSSY OSSY catalog ID 45- 57 F13.9 deg RAdeg OSSY right ascension (J2000) 59- 70 F12.9 deg DEdeg OSSY declination (J2000) 72- 84 E13.7 --- z Redshift of galaxy from OSSY catalog 86-145 A60 --- OName Other common galaxy names (i.e. NGC, Messier, UGC, IC, Markarian catalog IDs) 147-153 A7 --- Sy/LINER [SEYFERT LINER] Seyfert or LINER, based upon the line strengths from the OSSY catalog 155-171 A17 --- CLASS CLASS catalog ID (GB6JHHMMSS+DDMMSS) 173-185 F13.9 deg RANdeg Right ascension (J2000) of nearest CLASS source to galaxy position 187-198 F12.9 deg DENdeg Declination (J2000) of nearest CLASS source to galaxy position 200-207 F8.3 mas OffsetN Offset between galaxy position and nearest CLASS source 209-213 F5.1 mJy FluxN Flux density at 8.46GHz of nearest CLASS source 215-228 F14.10 deg RABdeg ? Right ascension (J2000) of brightest CLASS source (1) 230-242 F13.10 deg DEBdeg ? Declination (J2000) of brightest CLASS source (1) 244-251 F8.3 mas OffsetB ? Offset between galaxy position and brightest CLASS source (1) 253-257 F5.1 mJy FluxB ? Flux density at 8.46GHz of brightest CLASS source (1) -------------------------------------------------------------------------------- Note (1): The brightest CLASS source is usually the nearest to the galaxy position, and in these instances the last four columns are unpopulated. These four columns are only populated if there is a brighter CLASS detection within the central bulge of the host galaxy, but further from the recorded galaxy position. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Patricia Vannier [CDS] 08-Apr-2021