J/MNRAS/435/623 Multiwavelength measurement of galaxy structure (Vika, 2013)
MegaMorph - multiwavelength measurement of galaxy structure.
Sersic profile fits to galaxies near and far.
Vika M., Bamford S.P., Haussler B., Rojas A.L., Borch A., Nichol R.C.
<Mon. Not. R. Astron. Soc., 435, 623-649 (2013)>
=2013MNRAS.435..623V 2013MNRAS.435..623V
ADC_Keywords: Galaxies, photometry ; Morphology
Keywords: methods: data analysis - techniques: image processing -
galaxies: fundamental parameters - galaxies: photometry -
galaxies: structure
Abstract:
We demonstrate a new multiwavelength technique for two-dimensional
parametric modelling of galaxy surface-brightness profiles, which we
have incorporated into the widely used software GALFIT. Our new
method, named GALFITM, extends GALFIT3's current single-band fitting
process by simultaneously using multiple images of the same galaxy to
constrain a wavelength-dependent model. Each standard profile
parameter may vary as a function of wavelength, with a user-definable
degree of smoothness, from constant to fully free. The performance of
GALFITM is evaluated by fitting elliptical Sersic profiles to ugriz
imaging data for 4026 galaxies, comprising the original Sloan Digital
Sky Survey (SDSS) imaging for 163 low-redshift (v≲7000km/s) galaxies
and 3863 artificially redshifted (0.01≲z≲0.25) images of the same
galaxies. Comparing results from single-band and multiband techniques,
we show that GALFITM significantly improves the extraction of
information, particularly from bands with low signal-to-noise ratio
(e.g. u and z SDSS bands) when combined with higher signal-to-noise
images. We also study systematic trends in the recovered parameters,
particularly Sersic index, that appear when one performs measurements
of the same galaxies at successively higher redshifts. We argue that
it is vital that studies investigating the evolution of galaxy
structure are careful to avoid or correct for these biases. The
resulting multiband photometric structural parameters for our sample
of 163 galaxies are provided. We demonstrate the importance of
considering multiband measurements by showing that the Sersic indices
of spiral galaxies increase to redder wavelengths, as expected for
composite bulge-disc systems. Finally, for the ellipticals in our
sample, which should be well represented by single-Sersic models, we
compare our measured parameters to those from previous studies.
Description:
Our primary aim in this paper is to evaluate the benefits of modelling
galaxy structure by simultaneously fitting imaging data at a variety
of wavelengths. For this purpose, we select galaxies that have
parametric surface-brightness profile measurements by previous studies
(using single-band data), and which are located within the footprint
of the SDSS (Abazajian et al. 2009ApJS..182..543A 2009ApJS..182..543A, SDSS DR7). We
compile a sample of 168 galaxies with images in u, g, r, i, z
passbands, which have profile fits presented in one of the following
papers: Pohlen & Trujillo (2006A&A...454..759P 2006A&A...454..759P), Moellenhoff
(2004A&A...415...63M 2004A&A...415...63M, Cat. J/A+A/415/63), Moriondo, Giovanardi & Hunt
(1998A&AS..130...81M 1998A&AS..130...81M) and Caon, Capaccioli & D'Onofrio
(1993MNRAS.265.1013C 1993MNRAS.265.1013C).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 114 163 *Galaxy sample and the fit results as derived
from the multiband fitting
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Note on table1.dat: See Section 3 for more details.
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Galaxy name
11- 23 A13 --- HType Hubble type from NED
25- 29 F5.2 mag umag Apparent u magnitude (error ±0.13)
31- 35 F5.2 mag gmag Apparent g magnitude (error ±0.09)
37- 41 F5.2 mag rmag Apparent r magnitude (error ±0.1)
43- 47 F5.2 mag imag Apparent i magnitude (error ±0.11)
49- 53 F5.2 mag zmag Apparent z magnitude (error ±0.12)
55- 60 F6.2 arcsec re(u) Effective radius in u band (error ±12%)
62- 67 F6.2 arcsec re(g) Effective radius in g band (error ±11%)
69- 74 F6.2 arcsec re(r) Effective radius in r band (error ±12%)
76- 81 F6.2 arcsec re(i) Effective radius in i band (error ±14%)
83- 88 F6.2 arcsec re(z) Effective radius in z band (error ±15%)
90- 94 F5.2 --- n(u) Sersic index for u band (error ±10%)
96- 99 F4.2 --- n(g) Sersic index for g band (error ±11%)
101-104 F4.2 --- n(r) Sersic index for r band (error ±14%)
106-109 F4.2 --- n(i) Sersic index for i band (error ±15%)
111-114 F4.2 --- n(z) Sersic index for z band (error ±17%)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 17-Sep-2014