J/AJ/149/32 Integrated radio continuum spectra of galaxies (Marvil+, 2015)
Integrated radio continuum spectra of galaxies.
Marvil J., Owen F., Eilek J.
<Astron. J., 149, 32 (2015)>
=2015AJ....149...32M 2015AJ....149...32M
ADC_Keywords: Galaxies, radio ; Galaxy catalogs ; Radio continuum
Keywords: galaxies: statistics - radio continuum: galaxies
Abstract:
We investigate the spectral shape of the total continuum radiation,
between 74MHz and 5GHz (400-6cm in wavelength), for a large sample of
bright galaxies. We take advantage of the overlapping survey coverage
of the VLA Low-Frequency Sky Survey, the Westerbork Northern Sky
Survey, the NRAO VLA Sky Survey, and the Green Bank 6cm Survey to
achieve significantly better resolution, sensitivity, and sample size
compared to prior efforts of this nature. For our sample of 250 bright
galaxies we measure a mean spectral index, α, of -0.69 between
1.4 and 4.85GHz, -0.55 between 325MHz and 1.4GHz, and -0.45 between 74
and 325MHz, which amounts to a detection of curvature in the mean
spectrum. The magnitude of this curvature is approximately
Δα=-0.2 per logarithmic frequency decade when fit with a
generalized function having constant curvature. No trend in
low-frequency spectral flattening versus galaxy inclination is evident
in our data, suggesting that free-free absorption is not a satisfying
explanation for the observed curvature. The ratio of thermal to
non-thermal emission is estimated through two independent methods:
(1) using the IRAS far-IR fluxes and (2) with the value of the total
spectral index. Method (1) results in a distribution of 1.4GHz thermal
fractions of 9%±3%, which is consistent with previous studies, while
method (2) produces a mean 1.4GHz thermal fraction of 51% with
dispersion 26%. The highly implausible values produced by method
(2) indicate that the sum of typical power-law thermal and non-thermal
components is not a viable model for the total spectral index between
325 and 1.4GHz. An investigation into relationships between spectral
index, infrared-derived quantities, and additional source properties
reveals that galaxies with high radio luminosity in our sample are
found to have, on average, a flatter radio spectral index, and early
types tend to have excess radio emission when compared to the
radio-infrared ratio of later types. Early types also have radio
emission that is more compact than later type galaxies, as compared to
the optical size of the galaxy. Despite these differences, no relation
between spectral index and galaxy type is detected.
Description:
We selected four Northern Hemisphere large-area radio surveys as the
basis for the spectral data: the VLA Low-Frequency Sky Survey Redux
(VLSSr, Lane et al. 2012, 2012RaSc...47.0K04L; a re-reduction of the
original VLSS survey data, Cohen et al. 2007, cat. VIII/79), the
Westerbork Northern Sky Survey (WENSS; Rengelink et al. 1997, cat.
J/A+AS/124/259; superseded by Leiden et al. 1998, cat. VIII/62), the
National Radio Astronomy Observatory (NRAO) VLA Sky Survey (NVSS;
Condon et al. 1998, cat. VIII/65), and the Green Bank 6cm Survey (GB6;
Gregory et al. 1996, cat. VIII/40).
We record NVSS fluxes for 250 sources, WENSS fluxes for 233 sources,
VLSSr fluxes (greater than 3σ) for 89 sources, and GB6 fluxes
(greater than 5σ) for 85 sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 83 250 Survey measurements
table3.dat 57 250 Far-infrared data and derived quantities
table4.dat 64 250 Additional source properties
table5.dat 83 250 Spectral properties
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See also:
VIII/79 : The VLA Low-frequency Sky Survey at 74MHz (Cohen+ 2007)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/62 : The Westerbork Northern Sky Survey (Leiden, 1998)
VIII/40 : GB6 catalog of radio sources (Gregory+ 1996)
VII/155 : Third Reference Cat. of Bright Galaxies (RC3) (de Vaucouleurs+ 1991)
J/ApJ/554/803 : New VLA Sky Survey (NVSS) Cat of IRAS 2 Jy Galaxies (Yun+ 2001)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- UGC [444/12883] UGC galaxy number (1)
7- 14 F8.1 mJy NVSS [7/3686] NVSS (1.4GHz) flux (2)
16- 23 F8.1 mJy e_NVSS [0.5/111] The 1σ error in NVSS (2)
25 A1 --- l_MAxis [<] Upper limit flag on MAxis
27- 30 I4 arcsec MAxis NVSS fitted (deconvolved) major axis (FWHM) of
radio source (3)
32 A1 --- l_mAxis [<] Upper limit flag on mAxis
34- 37 I4 arcsec mAxis NVSS fitted (deconvolved) minor axis (FWHM) of
radio source (3)
39- 42 I4 deg PA [0/180] Position angle of the major axis (3)
44 A1 --- l_WENSS [<] Upper limit flag on WENSS
46- 51 I6 mJy WENSS WENSS flux (330MHz) (4)
53- 56 I4 mJy e_WENSS ? The 1σ error in WENSS (4)
58 A1 --- l_VLSSr [<] Upper limit flag on VLSSr
60- 65 I6 mJy VLSSr VLSSr flux (74MHz) (5)
67- 70 I4 mJy e_VLSSr ? The 1σ error in VLSSr (5)
72 A1 --- l_GB6 [<] Upper limit flag on FGB6
74- 78 I5 mJy GB6 Green Bank 6cm (5GHz) Survey flux (6)
80- 83 I4 mJy e_GB6 ? The 1σ error in FGB6 (6)
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Note (1): Uppsala General Catalogue of Galaxies (UGC, Nilson 1973, cat. VII/26).
Note (2): Measured from the NVSS survey (National Radio Astronomy Observatory
VLA Sky Survey; Condon et al. 1998, cat. VIII/65) cutout images using the
AIPS task JMFIT, selected from multiple resolutions.
Note (3): From JMFIT.
Note (4): Measured from the WENSS survey (Westerbork Northern Sky Survey;
Rengelink et al. 1997, cat. J/A+AS/124/259; superseded by Leiden et al.
1998, cat. VIII/62) cutout images using the AIPS task JMFIT, selected from
multiple resolutions.
Note (5): Measured from the VLSSr survey (the VLA Low-Frequency Sky Survey
Redux, Lane et al. 2012, 2012RaSc...47.0K04L; a re-reduction of the
original VLSS survey data, Cohen et al. 2007, cat. VIII/79) cutout images.
Flux values are determined by taking the image value at the location of the
optical source center and correcting for the ratio of peak to integrated
flux based on the measured NVSS size. Flux uncertainties are the
source-free rms of the cutout image multiplied by the same size correction
factor that was used for the flux.
Note (6): Green Bank 6cm Survey (Gregory et al. 1996, cat. VIII/40).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- UGC [444/12883] UGC galaxy number
7- 14 F8.1 Jy F60 ? IRAS 60µm flux S60µm
16- 23 F8.1 Jy F100 ? IRAS 100µm flux S100µm
25- 32 F8.1 10-14W/m2 FIR ? Total far-infrared flux (7)
34- 41 F8.1 mJy F1.4 ? Free-free thermal radio flux at 1.4GHz
IRSth,1.4 (8)
43 A1 --- l_f1.4 [<]? Upper limit flag on f1.4
45- 48 I4 % f1.4 ? Thermal fraction at 1.4GHz IRfth,1.4 (9)
50- 57 F8.2 0.01[-] q ? Log of the FIR/radio flux-ratio parameter (10)
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Note (7): The total far-infrared emission between 42.5 and 122.5µm
(Helou et al., 1985ApJ...298L...7H 1985ApJ...298L...7H), calculated with Equation (1):
FIR=1.26*10-14(2.58*F60+F100)W/m2.
Note (8): As estimated from the FIR flux (Marvil et al. 2013, in preparation),
calculated with Equation (4) (see the article).
Note (9): The ratio of the free-free thermal radio flux to the total radio flux
at 1.4GHz (Marvil et al. 2013, in preparation), calculated with
Equation (6):
f1.4=F1.4/FNVSS, where FNVSS is our measurement of the NVSS flux
(tabulated as the total radio flux at 1.4GHz).
Note (10): The log of the ratio of infrared to radio flux, q (Helou et al.,
1985ApJ...298L...7H 1985ApJ...298L...7H), calculated with Equation (7) (see the article).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- UGC [444/12883] UGC galaxy number
7- 16 A10 --- OName Other source name
18- 19 I2 h RAh Hour of Right Ascension (J2000) (11)
21- 22 I2 min RAm Minute of Right Ascension (J2000) (11)
24- 27 F4.1 s RAs Second of Right Ascension (J2000) (11)
29- 30 I2 deg DEd Degree of Declination (J2000) (11)
32- 33 I2 arcmin DEm Arcminute of Declination (J2000) (11)
35- 36 I2 arcsec DEs Arcsecond of Declination (J2000) (11)
38- 41 F4.2 --- b/a [0/1] Optical axial ratio (minor to
major) (12)
45- 46 I2 --- T [-5/99]? Numerical Hubble type (13)
48 A1 --- l_logSigma [>] Lower limit flag on logSigma
50- 53 F4.1 [mJy/arcmin2] logSigma Log of radio surface brightness
at 1.4GHz (logΣ) (14)
55 A1 --- l_comp [<] Upper limit flag on comp
57- 60 F4.2 --- comp Radio compactness parameter (15)
62- 64 I3 Mpc Dist [20/162]? Hubble flow distance (16)
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Note (11): Optical position from the 3rd Catalog of Bright Galaxies
(de Vaucouleurs et al. 1991, cat. VII/155).
Note (12): Derived from the 3rd Catalog of Bright Galaxies (de Vaucouleurs et
al. 1991, cat. VII/155).
Note (13): As listed as T (Hubble stage) in the 3rd Catalog of Bright Galaxies
(de Vaucouleurs et al. 1991, cat. VII/155). The ranges are defined from
early to late morphologies:
-6 to -4 = Ellipticals;
-3 to -1 = Lenticulars;
0 to 8 = Spirals (from Sa to Sd);
9 = Magellanic spiral;
10 = Irregular;
11 = Compact irregular;
90 = Non-Magellanic irregular;
99 = Peculiar.
Note (14): Calculated as the NVSS flux divided by the NVSS solid angle defined
by the fitted source size (major axis diameter by minor axis diameter).
Note (15): The ratio of the fitted NVSS major axis (Gaussian Full-Width at Half
Maximum) to RC3 (3rd Catalog of Bright Galaxies; de Vaucouleurs et al.
1991, cat. VII/155) optical major axis (D25).
Note (16): Calculated from the 3rd Catalog of Bright Galaxies
(de Vaucouleurs et al. 1991, cat. VII/155) velocity (galactic standard of
rest) by adopting a value of Ho=70km/s/Mpc.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- UGC [444/12883] UGC galaxy number
7 A1 --- l_a0 [>] Lower limit flag on a0
9- 16 F8.2 --- a0 [-2.14/0.44]? Spectral index αlow
between 74 and 325MHz (17)
18- 25 F8.2 --- e_a0 ? The 1σ uncertainty on a0 (17)
27 A1 --- l_a1 [>] Lower limit flag on a1
29- 36 F8.2 --- a1 [-1.37/0.55] Spectral index αmid
between 325 and 1400MHz (18)
38- 45 F8.2 --- e_a1 ? The 1σ uncertainty on a1 (18)
47 A1 --- l_a2 [<] Upper limit flag on a2
49- 56 F8.2 --- a2 [-1.67/0.79] Spectral index αhigh
between 1400 and 4850MHz (19)
58- 65 F8.2 --- e_a2 ? The 1σ uncertainty on a2 (19)
67- 74 F8.1 --- R [-7.2/23.7]? Ratio Rlow of 74 to 325MHz flux (20)
76- 83 F8.1 --- e_R ? The 1σ uncertainty on RLow (20)
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Note (17): Measured between the data from the VLA Low-Frequency Sky Survey Redux
(VLSSr; Lane et al. 2012, 2012RaSc...47.0K04L; a re-reduction of the
original VLSS survey data, Cohen et al. 2007, cat. VIII/79), and the
Westerbork Northern Sky Survey (WENSS; Rengelink et al. 1997,
cat. J/A+AS/124/259; superseded by Leiden et al. 1998, cat. VIII/62). Limits
are given when only one flux is detected, calculated as the slope between
the detection and the flux upper limit. No value is given when there are
non-detections at both bands.
Note (18): Measured between the data from the Westerbork Northern Sky Survey
(WENSS; Rengelink et al. 1997, cat. J/A+AS/124/259; superseded by Leiden
et al. 1998, cat. VIII/62), and the National Radio Astronomy Observatory
(NRAO) VLA Sky Survey (NVSS; Condon et al. 1998, cat. VIII/65). No value
is given when there are non-detections at both bands.
Note (19): Measured between the data from the National Radio Astronomy
Observatory (NRAO) VLA Sky Survey (NVSS; Condon et al. 1998, cat. VIII/65),
and the Green Bank 6cm Survey (GB6; Gregory et al. 1996, cat. VIII/40). No
value is given when there are non-detections at both bands.
Note (20): Between the flux measurements from the VLA Low-Frequency Sky Survey
Redux (VLSSr; Lane et al. 2012, 2012RaSc...47.0K04L; a re-reduction of the
original VLSS survey data, Cohen et al. 2007, cat. VIII/79), and the
Westerbork Northern Sky Survey (WENSS; Rengelink et al. 1997,
cat. J/A+AS/124/259; superseded by Leiden et al. 1998, cat. VIII/62).
Negative values are due to the VLSSr flux measurement technique. No value
is given when the WENSS flux is not detected.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 04-Feb-2015