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J/AJ/151/74   VLA/VLBA obscured radio-loud active galactic nuclei   (Yan+, 2016)

Invisible active galactic nuclei. II. Radio morphologies and five new H I 21cm absorption line detectors. Yan T., Stocke J.T., Darling J., Momjian E., Sharma S., Kanekar N. <Astron. J., 151, 74 (2016)> =2016AJ....151...74Y (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Radio continuum ; Redshifts ; Spectroscopy ; Morphology ; Interferometry Keywords: quasars: absorption lines - radio continuum: galaxies Abstract: This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Yan et al. 2012AJ....144..124Y. In this paper, we present both high-resolution radio continuum images for all of these sources and H I 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size <0.5" and flux densities >0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ∼three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H I 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral "window" (i.e., the percentage of H I 21 cm absorption-line detections could be as high as ∼90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H I detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H I absorption may well be present but is masked by the RFI. Future searches for highly redshifted H I and molecular absorption can easily find more distant CSOs among bright, "blank field" radio sources, but will be severely hampered by an inability to determine accurate spectroscopic redshifts due to their lack of rest-frame UV continuum. Description: The specific selection criteria for the sample presented in Yan et al. 2012AJ....144..124Y (Paper I) include the presence of an SDSS r-band optical counterpart within 1.5" of a bright (≥0.5 Jy) FIRST radio source position and characteristics of the optical counterpart that favor it being a late-type galaxy. Of the 82 objects originally selected (Paper I), 2 are nearby galaxies at z<0.05 (J1352+3126 and J1413-0312) and are excluded from our discussion in this paper. Except when archive data were available, we observed all the sources at 4.9 and 8.5 GHz using the VLA of NRAO in its most extended A-configuration (VLA-A; project # AY0052). Overall, we obtained data for 35 sources at both frequencies, 14 at 4.9 GHz only, and 8 at 8.5 GHz only. Our data were taken during 2007 June to August in the transitional period from VLA to Expanded VLA (EVLA; currently the Karl G. Jansky VLA). We used the VLBA to obtain 1.4 GHz images for sources that are unresolved or have compact components in VLA-A images (project # BY0020). Overall, 36 sources were observed in 2009 December and 2010 January. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 75 81 Observing Summary table2.dat 97 80 Summary of Radio Galaxy Properties table10.dat 98 80 Basic Observing Results table11.dat 79 123 VLA 4.9 GHz Gaussian Fit Results table12.dat 79 102 VLA 8.5 GHz Gaussian Fit Results table13.dat 79 76 VLBA 1.4 GHz Gaussian Fit Results
See also: VIII/60 : Interferometer phase calibration sources (Patnaik+ 1998) VIII/72 : CLASS survey of radio sources (Myers+, 2003) J/A+A/369/380 : CSS/GPS radio sources VLA observations (Fanti+, 2001) J/A+A/416/35 : Radio Emission from VLA FIRST Survey AGN (Wadadekar, 2004) J/ApJ/658/203 : VLBA imaging and polarimetry survey at 5GHz (Helmboldt+, 2007) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 10 A10 --- Name Object name (JHHMM+DDMM) 12- 23 A12 --- Radio Radio name 25- 35 A11 "date" Date4.9 Date of observation at 4.9 GHz 37- 38 I2 --- r_Date4.9 [1/15]? Reference for Date4.9 (1) 40- 50 A11 "date" Date8.5 Date of observation at 8.5 GHz 52- 53 I2 --- r_Date8.5 [1/17]? Reference for Date8.5 (1) 55- 65 A11 "date" DateVLBI Date of VLBI observation 67- 68 I2 --- r_DateVLBI [1/19]? Reference for DateVLBI (1) 70- 75 A6 --- Note Note(s) (2)
Note (1): Reference as follows: 1 = This work (VLA project AY0052 and VLBA project BY 0020); 2 = VLA project AA052; 3 = VLA project AA073; 4 = VLA project AB375; 5 = VLA project AB568; 6 = VLA project AB611; 7 = VLA project AB922; 8 = VLA project AH167; 9 = VLA project AS704; 10 = Cai et al. (2002A&A...381..401C); 11 = Chambers et al. (1996ApJS..106..247C); 12 = Dallacasa et al. (2002A&A...389..126D); 13 = Fanti et al. (2001, J/A+A/369/380); 14 = Helmboldt et al. (2007, J/ApJ/658/203); 15 = Lehar et al. (1997AJ....114...48L); 16 = Myers et al. (2003, Cat. VIII/72); 17 = Patnaik et al. (1992, Cat. VIII/60); 18 = Peck & Taylor (2000ApJ...534...90P); 19 = Perlman et al. (2002AJ....124.2401P). Note (2): Note as follows: N1 = No flux calibration on the VLA-A 4.9 GHz image; N2 = No flux calibration on the VLA-A 8.5 GHz image; N3 = Not detected on the VLA-A 4.9 GHz image; N4 = Not detected on the VLBA 1.4 GHz image; N5 = All data are flagged on the VLA-A 4.9 GHz image.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 10 A10 --- Name Object name (JHHMM+DDMM) 12- 16 F5.3 --- z [0.122/3.200]? Redshift 17 A1 --- n_z [*abc] Note on z (1) 18 A1 --- u_z [:] Uncertainty flag on z 20- 24 A5 --- SEDType Optical+NIR SED type from Yan et al. (2012AJ....144..124Y) (2) 26- 27 A2 --- GType Hubble type for pure "G"-type objects in column "SEDType" (3) 29- 32 F4.2 Jy S365MHz [0.25/8.31] Flux density at 365 MHz 34- 37 F4.2 Jy S1.4GHz [0.32/4.86] Flux density at 1.4 GHz 39- 42 F4.2 Jy S4.9CHz [0.07/3.09] Flux density at 4.9 GHz 44- 47 F4.2 --- alphal [0.02/1.28] Low-frequency spectral index, αl, between 365 MHz and 1.4 GHz 49- 53 F5.2 --- alphah [-1.41/0.37] High-frequency spectral index, αh, between 1.4 and 4.9 GHz 55- 57 A3 --- Class Radio spectral classification (4) 58 A1 --- n_Class [a] Note on Class (5) 59 A1 --- u_Class [:] Uncertainty flag on Class 61- 65 F5.3 arcsec LAS [0.002/6.6] Largest angular size between major components 66 A1 --- u_LAS [:] Uncertainty flag on LAS 68- 73 F6.3 kpc LLS [0.014/45.7] Largest linear size 74 A1 --- n_LLS [≲] Note on LLS (6) 76- 79 F4.2 GHz Freq [1.4/8.5] Frequency with which the LAS and LLS are measured 81- 85 A5 --- Tel Telescope with which the LAS and LLS are measured 87- 92 A6 --- Morph Radio source morphological classification (7) 94 A1 --- Eval1 [YN] Whether the object remains a good candidate for an absorption-line search at radio frequencies (Y=Yes, N=No) 96- 97 A2 --- Eval2 Whether the object is an intervening system (I) or candidate (I:)
Note (1): Note as follows: * = Photometric redshift fit by its optical+NIR SED in Yan et al. (2012AJ....144..124Y); a = The redshift listed is for a background radio source that has an SDSS detected Galaxy in the foreground; b = The redshift listed is for a background radio source that is gravitationally lensed by a foreground Galaxy at z=0.349; c = This is an intervening system with a foreground Galaxy at z=0.206. The radio source redshift is unknown. Note (2): The optical+NIR SEDs were divided into four classes in Yan et al. (2012AJ....144..124Y): G = Pure galaxy; G+Q = Galaxy with a quasar signature in the bluer bands; Q = Quasar; Q+abs = Quasar with extinction signatures in the bluer bands. Note (3): We fit the G-type objects with template spectra of five Hubble types (E, S0, Sa, Sb, and Sc), and give the best-fit Hubble types. Note (4): Classification as follows: SS = Steep Spectrum; FS = Flat Spectrum; USS = Ultra-Steep Spectrum; GPS = Giga-Hertz Peak Spectrum. Note (5): Note as follows: a = The classification has been modified using additional information to the spectral indices in columns "alphal" and "alphah". Note (6): Note as follows: ∼ = A photometric redshift is used; < = z=1.6 is used to obtain the largest size possible. Note (7): Morphological classification as follows: CPLX = Complex; CJ = Core-jet; GA = Gravitational arc; PS = Point source; SL = Single lobe; CSO = Compact symmetric object; CSO: = CSO candidate; LSO = Large symmetric object; MSO = Medium-size symmetric object.
Byte-by-byte Description of file: table10.dat
Bytes Format Units Label Explanations
1- 10 A10 --- Name Object name (JHHMM+DDMM) 12- 15 F4.2 arcsec MajAxis4.9 [0.42/0.97]? Major axis size at 4.9 GHz 17- 20 F4.2 arcsec MinAxis4.9 [0.40/0.49]? Minor axis size at 4.9 GHz 22- 26 F5.1 deg PA4.9 [-89.4/87.8]? Position angle of the restored beam at 4.9 GHz 28- 31 F4.2 mJy/beam rms4.9 [0.12/0.77]? Map rms (σ) in the vicinity of the source at 4.9 GHz 32 A1 --- n_rms4.9 [*] Note on rms4.9 (G1) 34- 38 F5.1 mJy/beam Smax4.9 [21.6/578.7]? Maximum flux density in the map at 4.9 GHz 39 A1 --- n_Smax4.9 [*] Note on Smax4.9 (G1) 41- 44 F4.2 arcsec MajAxis8.5 [0.24/0.74]? Major axis size at 8.5 GHz 46- 49 F4.2 arcsec MinAxis8.5 [0.23/0.42]? Minor axis size at 8.5 GHz 51- 56 F6.1 deg PA8.5 [-175.8/174.3]? Position angle of the restored beam at 8.5 GHz 58- 61 F4.2 mJy/beam rms8.5 [0.06/0.71]? Map rms (σ) in the vicinity of the source at 8.5 GHz 62 A1 --- n_rms8.5 [*] Note on rms8.5 (G1) 64- 68 F5.1 mJy/beam Smax8.5 [10.0/605.1]? Maximum flux density in the map at 8.5 GHz 69 A1 --- n_Smax8.5 [*] Note on Smax8.5 (G1) 71- 75 F5.2 arcsec MajAxis1.4 [8.12/61.82]? Major axis size at 1.4 GHz 77- 81 F5.2 arcsec MinAxis1.4 [4.86/55.91]? Minor axis size at 1.4 GHz 83- 87 F5.1 deg PA1.4 [-33.9/78.2]? Position angle of the restored beam at 1.4 GHz 89- 92 F4.2 mJy/beam rms1.4 [0.11/3.50]? Map rms (σ) in the vicinity of the source at 1.4 GHz 94- 98 F5.1 mJy/beam Smax1.4 [7.5/401.1]? Maximum flux density in the map at 1.4 GHz
Byte-by-byte Description of file: table11.dat table12.dat table13.dat
Bytes Format Units Label Explanations
1- 10 A10 --- Name Object name (JHHMM+DDMM) 12- 13 A2 --- m_Name Multiplicity index on Name 15- 16 I2 h RAh ? Hour of Right Ascension (J2000) (1) 18- 19 I2 min RAm ? Minute of Right Ascension (J2000) 21- 27 F7.4 s RAs ? Second of Right Ascension (J2000) 29 A1 --- DE- ? Sign of the Declination (J2000) 30- 31 I2 deg DEd ? Degree of Declination (J2000) 33- 34 I2 arcmin DEm ? Arcminute of Declination (J2000) 36- 41 F6.3 arcsec DEs ? Arcsecond of Declination (J2000) 43- 47 F5.1 mJy/beam Speak [0.4/650.6] Peak flux density 48 A1 --- n_Speak [*] Note on Speak (not in table 13) (G1) 50- 54 F5.1 mJy Sint [1.8/929.4] Integrated flux density 55 A1 --- n_Sint [*] Note on Sint (not in table 13) (G1) 57- 62 F6.2 arcsec MajAxis [0.03/109] Deconvolved major axis 64- 68 F5.2 arcsec MinAxis [0.00/63] Deconvolved minor axis 70- 74 F5.1 deg PA [0.1/179.2] Position angle of the Gaussian component 76- 79 F4.1 --- alpha [-3.6/3.1]? Spectral index (α) calculated between 4.9 and 8.5 GHz (only in table 12)
Note (1): No position in Table 12.
Global notes: Note (G1): Note as follows: * = Flux densities lack accurate flux calibrations. See Table 1 for details.
History: From electronic version of the journal References: Yan et al. Paper I. 2012AJ....144..124Y
(End) Tiphaine Pouvreau [CDS] 16-Mar-2018
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