J/A+A/574/A4 Radio image of Luminous Infrared Galaxies (Vardoulaki+, 2015)
Radio continuum properties of luminous infrared galaxies.
Identifying the presence of an AGN in the radio.
Vardoulaki E., Charmandaris V., Murphy E.J., Diaz-Santos T., Armus L.,
Evans A., Mazzarella J.M., Privon G.C., Stierwalt S., Barcos-Munoz L.
<Astron. Astrophys. 574, A4 (2015)>
=2015A&A...574A...4V 2015A&A...574A...4V
ADC_Keywords: Galaxies, IR ; Galaxies, radio ; Radio continuum
Keywords: galaxies: active - galaxies: starburst - galaxies: nuclei -
radio continuum: galaxies - infrared: galaxies
Abstract:
Luminous Infrared Galaxies (LIRGs) are systems enshrouded in dust,
which absorbs most of their optical/UV emission and radiates it again
in the mid- and far-infrared. Radio observations are largely
unaffected by dust obscuration, enabling us to study the central
regions of LIRGs in an unbiased manner.
The main goal of this project is to examine how the radio properties
of local LIRGs relate to their infrared spectral characteristics. Here
we present an analysis of the radio continuum properties of a subset
of the Great Observatories All-sky LIRG Survey (GOALS), which consists
of 202 nearby systems (z<0.088). Our radio sample consists of 35
systems, containing 46 individual galaxies, that were observed at both
1.49 and 8.44GHz with the VLA with a resolution of about 1-arcsec
(FWHM). The aim of the project is to use the radio imagery to probe
the central kpc of these LIRGs in search of Active Galactic Nuclei
(AGN).
We used the archival data at 1.49 and 8.44GHz to create
radio-spectral-index maps using the standard relation between flux
density Sν and frequency ν, Sν~ν-α, where α
is the radio spectral index. By studying the spatial variations in
α, we classified the objects as radio-AGN, radio-SB, and AGN/SB
(a mixture). We identified the presence of an active nucleus using the
radio morphology, deviations from the radio/infrared correlation, and
spatially resolved spectral index maps, and then correlated this to
the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII] line ratios and
equivalent width of the 6.2um PAH feature) and optical (BPT diagram)
AGN diagnostics.
We find that 21 out of the 46 objects in our sample (∼45%) are
radio-AGN, 9 out of the 46 (∼20%) are classified as starbursts (SB)
based on the radio analysis, and 16 (∼35%) are AGN/SB. After comparing
to other AGN diagnostics we find 3 objects out of the 46 (∼7%) that
are identified as AGN based on the radio analysis, but are not
classified as such based on the mid-infrared and optical AGN
diagnostics presented in this study.
Description:
VLA images at 1.49GHz (name_A2000.fits) and at 8.44GHz
(name_X2000.fits). All images are in J2000 coordinates. Some maps
contain both interacting galaxies of the system, while others are
separated and marked accordingly.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 200 46 Radio and Infrared data for the 35 LIRG systems
of our sample
images/* . 72 Individual FITS images
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/46] Sequential number used in Fig.5 of paper
4- 24 A21 --- Name Name of the galaxy. Systems are marked with
the relative position to each other
(e.g. N, S, E, W)
26- 27 I2 h RAh Right ascension (J2000) (1)
29- 30 I2 min RAm Right ascension (J2000) (1)
32- 35 F4.1 s RAs Right ascension (J2000) (1)
37 A1 --- DE- Declination sign (J2000) (1)
38- 39 I2 deg DEd Declination (J2000) (1)
41- 42 I2 arcmin DEm Declination (J2000) (1)
44- 45 I2 arcsec DEs Declination (J2000) (1)
47- 52 F6.2 mJy S1.49 [4/304] Integrated flux density at 1.49GHz (2)
54- 57 F4.2 mJy e_S1.49 [0.04/1.9] rms uncertainty on S1.49GHz
59- 65 F7.3 mJy S8.44 [0.5/267] Integrated flux density at 8.44GHz (2)
67- 71 F5.3 mJy e_S8.44 [0.002/0.5] rms uncertainty on S8.44GHz
73- 78 F6.3 --- alpha [-0.06/2.6] Radio spectral index α
calculated between 1.49 and 8.44GHz
(Sν∝ν-α)
80- 84 F5.3 --- e_alpha rms uncertainty on alpha
86- 90 F5.2 [W/Hz] logL1.4 Radio luminosity at 1.49GHz (3)
92- 97 F6.3 [Lsun] logLIR ?=- Total infrared luminosity calculated from
14 to 1000m (see Diaz-Santos et al.,
2010ApJ...723..993D 2010ApJ...723..993D, Cat. J/ApJ/723/993)
99-102 F4.2 --- qIR [2.2/3.5]?=- qIR parameter (4)
104-110 F7.3 --- IR8 [4.9/103]?=- Ratio of total IR luminosity to the
luminosity at 8um (see Elbaz et al.,
2011A&A...533A.119E 2011A&A...533A.119E, Cat. J/A+A/533/A119)
111 A1 --- n_IR8 [t] t for total measurement for the system (5)
113-116 A4 --- St1.49 Radio structure at 1.49GHz (6)
118-121 A4 --- St8.44 Radio structure at 8.44GHz (6)
123-146 A24 --- OName Alternative name
148-173 A26 --- VLA1.49 Name of file with 512x512 VLA image at 1.49GHz
(scale=0.4arcsec/pix), in subdirectory images
175-200 A26 --- VLA8.44 Name of file with 128x128 VLA image at 8.44GHz
(scale= 0.05arcsec/pix), in subdirectory images
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Note (1): at the radio position with maximum flux density at 1.49GHz.
Note (2): integrated flux density at 1.49 and 8.44GHz, of the galaxy where flux
above 3σ is being considered in the calculation.
Note (3): Radio luminosity at 1.49GHz calculated using the standard relation
between flux and luminosity; the values of luminosity distance are taken
from Diaz-Santos et al. (2010ApJ...723..993D 2010ApJ...723..993D, Cat. J/ApJ/723/993).
Note (4): The parameter qIR is a measure of the star-formation-rate of a galaxy.
qIR = log10[(FIR(8-1000um)/3.75*1012W/m2)/(S1.4GHz/W/m2/Hz)],
where FIR(8-1000um) s the total flux in the infrared band, from 8 to 1000um
in W/m2 and S1.4GHz is the flux density at 1.4GHz in W/m2/Hz.
(Helou et al., 1985ApJ...298L...7H 1985ApJ...298L...7H).
Note (5): The base-10 logarithm of the total infrared luminosity of
IRAS F14348-1447 is 12.390. Here we give the fractional contribution of the
two components to the total infrared luminosity. The fractional contribution
was calculated by doing photometry on the 8 and 24um maps of the object.
Similarly for IRASF12112+0305 log10(LIR)=12.363 and for
IRAS F17132+5313 log10(LIR)=11.961.
Note (6): Radio structure codes as follows:
COM = compact
EXT = extended
CMX = complex
DB = double
DBDB = double double
DF = diffuse
? = indication of uncertainty in the classification
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Acknowledgements:
Jim Condon, jcondon(at)nrao.edu
(End) Patricia Vannier [CDS] 01-Sep-2014