J/A+A/409/115 VLA imaging of IRAS 1 Jy ULIRG sample (Nagar+, 2003)
The AGN content of ultraluminous IR galaxies:
High resolution VLA imaging of the IRAS 1 Jy ULIRG sample.
Nagar N.M., Wilson A.S., Falcke H., Veilleux S., Maiolino R.
<Astron. Astrophys. 409, 115 (2003)>
=2003A&A...409..115N 2003A&A...409..115N
ADC_Keywords: Surveys ; Galaxies, IR ; Active gal. nuclei ; Radio sources
Keywords: accretion, accretion disks - galaxies: active - galaxies: jets -
radio continuum: galaxies - surveys
Abstract:
This paper presents the results of a high resolution radio imaging
survey of 83 of the 118 ultraluminous infrared galaxies (ULIRGs) in
the IRAS 1Jy ULIRG sample (Kim & Sanders, 1998ApJS..119...41K 1998ApJS..119...41K,
Veilleux et al., 2002, Cat. J/ApJS/143/315). We have observed these
ULIRGs at 15-GHz with the Very Large Array (VLA). We find that ∼75% of
Seyferts (both type 1 and 2) and LINERs have radio nuclei which are
compact at our 150mas resolution. The detection rate of HII nuclei
is significantly lower (32%); the detections among these are
preferentially HII+LINER/Seyfert composite nuclei. Among ULIRGs with
multiple optical or near-IR nuclei our observations detected only one
(or no) nucleus; in these the radio detection is typically towards the
brightest near-IR nucleus. The compactness of the radio sources, the
higher detection rates in AGN-type nuclei than HII nuclei, the
preferential detection of nuclei with unresolved point sources in the
near-IR, the low soft X-ray to nuclear radio luminosity ratio (arguing
against thermal emission powering the radio nuclei), and the lack of
correlation between radio power and Hα luminosity, all support
an origin of the detected radio nuclei in AGN related activity. This
result is especially interesting for LINER ULIRGs for which signatures
of AGNs have often been ambiguous in other wavebands. Such a high
incidence of AGN would provide, for the first time, a large sample in
which to study the interplay between AGN, starbursts, and galaxy
mergers.
Description:
Results of new 15GHz VLA A-array observations (150mas resolution)
of 83 ULIRGs drawn from the IRAS 1Jy ULIRG sample are listed in the
table. These include all (67) of the IRAS 1Jy sample with declination
>0°, plus an additional 16 ULIRGs from the sample with declination
between 0 and -20 degrees. For each target ULIRG, we list the source
name, the activity type and class, the position of the radio source(s)
from our 15GHz observations, the offset between the 15GHz radio
position and that of the near-infrared nucleus (taken from Kim et al.
2002, Cat. J/ApJS/143/277), the peak and total radio flux densities
from a gaussian fit to the nuclear radio source, the redshift, the
(assumed isotropic) monochromatic radio power, and any comments.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 89 84 New 2cm VLA observations of the IRAS 1Jy ULIRG
sample.
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See also:
II/156 : IRAS Faint Source Catalog, |b|>10, Version 2.0 (Moshir+ 1989)
J/ApJS/143/315 : IRAS 1Jy sample of ultraluminous galaxies II. (Veilleux+ 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- FSC IRAS FSC name (FHHMMm+DDMM or ZHHMMm+DDMM)
12- 13 A2 --- n_FSC Multiplicity index on FSC (1)
15- 17 A3 --- AType Nuclear activity type (2)
19- 20 I2 h RAh ? 15GHz radio right ascension (J2000)
22- 23 I2 min RAm ? 15GHz radio right ascension (J2000)
25- 30 F6.3 s RAs ? 15GHz radio right ascension (J2000)
32 A1 --- DE- ? 15GHz radio declination sign (J2000)
33- 34 I2 deg DEd ? 15GHz radio declination (J2000)
36- 37 I2 arcmin DEm ? 15GHz radio declination (J2000)
39- 43 F5.2 arcsec DEs ? 15GHz radio declination (J2000)
45- 48 F4.2 arcsec Delta ? Offset between the 15GHz radio position and
the position of the near-IR nucleus as
listed in KVS (Veilleux et al., 2002,
Cat. J/ApJS/143/315)
50- 56 F7.1 mJy Speak ? Peak flux density at 15GHz (in mJy/beam)
58 A1 --- l_Stot Limit flag on Stot
59- 65 F7.1 mJy Stot Total flux at 15GHz
67- 71 F5.3 --- z Redshift of the ULIRG from Veilleux et al.,
1999, Cat. J/ApJ/522/113
73 A1 --- l_logPcore Limit flag on logPcore
74- 78 F5.2 [W/Hz] logPcore Core radio power at 15GHz
80- 89 A10 --- Com Comments (3)
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Note (1): When the radio source is clearly identifiable with one
subcomponent of a multi-component ULIRG, then the component (following
the naming convention of KVS, J/ApJS/143/315) is also listed.
Note (2): Nuclear activity type:
L: LINER
S: Seyfert
H: HII region type spectrum
2: no broad Hα or broad Paα detected
1: broad Hα or broad Paα are detected (Veilleux et al.,
1999, Cat. J/ApJ/522/113, 1999ApJ...522..139V 1999ApJ...522..139V)
":" represents an uncertain classification.
H II: display spectra which are transitional between H II regions
and Seyferts/LINERs
Note (3): Comments:
1: phase-calibration not used; the radio position listed is taken
from the VLA calibrator database;
2: uncertain detection. Flux measured by summing within an aperture
rather than by a Gaussian fit;
3: known to have a milli-arcsec scale radio core
(Smith et al., 1998ApJ...492..137S 1998ApJ...492..137S, 1998ApJ...493L..17S 1998ApJ...493L..17S);
4: known to have a milli-arcsec scale radio core
(Ulvestad et al., 1999ApJ...517L..81U 1999ApJ...517L..81U);
5: known to have a milli-arcsec scale radio core;
6: broad Pa (but not broad Hα) is detected in this object, so
it is counted as a Seyfert 1 in this paper;
7: the highly accurate radio position (Ma et al., 1998, Cat. I/251)
is offset from both near-IR nuclei, but is closer to the "W" nucleus.
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Acknowledgements: Neil Nagar
(End) Neil Nagar [Kapteyn Institute], Patricia Bauer [CDS] 16-Sep-2003