J/AJ/100/1091 UBR photometry of 39 elliptical galaxies (Peletier+ 1990)
CCD Surface Photometry of galaxies with dynamical data. II.
UBR photometry of 39 elliptical galaxies
PELETIER R.F., DAVIES R.L., ILLINGWORTH G.D., DAVIS L.E., CAWSON M.
<Astron. J. 100, 1091 (1990)>
=1990AJ....100.1091P 1990AJ....100.1091P
ADC_Keywords: Galaxies, optical; Photometry, CCD
Abstract:
We have obtained U,B, and R CCD surface photometry for a sample of
39 elliptical galaxies. For each galaxy we have determined the
surface brightness profile, U-R and B-R color profiles, and the
ellipticity and position angle profiles, all as function of major
axis radius, using a two-dimensional ellipse fitting program. In
addition, we have derived the sin and cos(3.theta) and 4.theta
terms that describe the high-order deviations of the B and R
isophotes from ellipses. While it is very common for ellipticals
to display measurable 3.theta and 4.theta terms, the amplitudes of
these terms rarely exceed 0.5%. The isophotes of elliptical
galaxies are very well characterized by ellipses. The surface
brightness and color profiles are given to radii at which the
error in the profile reaches 0.1 mag from the uncertainty in the
brightness of the night sky. We have carried out a series of
simulations of the effects of seeing on luminosity and ellipticity
profiles, to determine the radius beyond which the errors in our
data from seeing are less than 0.05 mag and 0.02 in ellipticity.
Measurable effects of seeing extend to surprisingly large
radii, as much as 5-10 seeing radii, depending upon the
ellipticity of the galaxy and the form of the surface brightness
profile. Ellipticity and position angle profiles are usually the
same in all passbands with no indication that the contours of
constant color are more or less flattened than the isophotes,
i.e., the isochromes and isophotes have the same shapes, but the
insensitivity of the ellipticity to differences between these
properties makes this a weak argument. The high-order terms,
particularly the 3.theta terms, appear to be sensitive diagnostics
for the existence of dust in ellipticals. We find that all the
galaxies in this sample either become bluer in B-R and U-R with
increasing radius or are of constant color. Mean values for the
logarithmic gradients in color are -0.09 mag/arcsec2 per dex in
radius in B-R, and -0.20 mag/arcsec2 per dex in radius in U-R.
These color changes are consistent with a decrease in the [Fe/H]
of approximately 0.20 per decade in radius. Surprisingly, there is
no correlation of color gradient with luminosity. It is striking,
however, that the lowest luminosity galaxies in the sample (i.e.,
those with M(B) > -20) do not show any color gradients. They have
boxy isophotes, and are also rotationally flattened. While these
properties may be related to the fact that they are companions of
larger ellipsoidal systems, it could provide an important clue to
the formation of ellipticals. Low luminosity ellipticals that are
not close companions to giant ellipticals need to be studied.
List of the 39 galaxies observed:
NGC 315 NGC 720 NGC 741
NGC 1052 NGC 1129 NGC 1600
Abell 496 NGC 2300 NGC 2768
NGC 2778 NGC 2832 NGC 3377
NGC 3379 NGC 3605 NGC 3665
NGC 3801 NGC 4261 NGC 4278
NGC 4374 NGC 4387 NGC 4406
NGC 4472 NGC 4478 NGC 4486
NGC 4551 NGC 4636 NGC 4649
NGC 4697 NGC 4874 NGC 4889
NGC 5638 NGC 5813 NGC 5831
NGC 5845 IC 1101 NGC 6051
NGC 6086 NGC 6269 NGC 7626
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table9 114 3698 Galaxy Parameters
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Byte-by-byte Description of file: table9
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Name of the elliptical galaxies
11 A1 --- n_mag [RBU] magnitude band
15- 21 F7.3 arcsec Radius Radius along the major axis
24- 30 F7.3 mag/arcsec2 mag R, B or U magnitude depending on m_mag
34- 39 F6.4 --- Ell [0/1[? Ellipticity = 1-b/a
44- 49 F6.2 deg PosAngl [0/180[? Position Angle from N to E
54- 60 F7.4 mag/arcsec2 Sin3 []? 3θ term in Fourier expansion
of isophote shape
65- 71 F7.4 mag/arcsec2 Cos3 []? 3θ term in Fourier expansion
of isophote shape
76- 82 F7.4 mag/arcsec2 Sin4 []? 4θ term in Fourier expansion
of isophote shape
87- 93 F7.4 mag/arcsec2 Cos4 []? 4θ term in Fourier expansion
of isophote shape
100-104 F5.3 mag/arcsec2 B-R []? B-R color
110-114 F5.3 mag/arcsec2 U-R []? U-R color
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Courtesy: Reynier Peletier
(End) Joseph Florsch [CDS] 06-Apr-1994