Multicolor surface photometry of 17 ellipticals

Abstract

view Abstract Citations (248) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multicolor Surface Photometry of 17 Ellipticals Franx, Marijn ; Illingworth, Garth ; Heckman, Timothy Abstract Multicolor two-dimensional surface photometry of 17 elliptical galaxies is presented. Radial profiles have been derived for surface brightness, color, ellipticity, position angle, and the residuals from the fitted ellipses described by cos(nφ) and sin(nφ) terms, where n=3 and 4. The effects of seeing with noncircular PSFs on the observed brightness profiles and on the ellipticities and position angles have been investigated analytically. At radii as large as 5 times the seeing FWHM, seeing can affect the ellipticity at the 10% level and introduce uncertainty in the position angles of several degrees, particularly for very round ellipticals. The profiles are compared with data from other authors, and the uncertainties estimated. The agreement is encouraging. The rms mean differences are only 0.02 in ellipticity and 2^deg^ in position angle. Even for the roundest galaxies (ɛ~0.03), the mean ellipticities and position angles can be determined to such accuracy. Larger differences remain for the surface-brightness profiles. Systematic gradients of +/- 0.1 mag per decade in radius still occur between the surface-brightness profiles from different authors. The main problem in deriving accurate colors is the uncertainty in establishing the background level on the small-format CCD detectors currently used. The average color gradients in U - R and B - R are -0.23 and -0.07 mag per decade in radius. The formal errors in the color gradients are comparable to the gradients for many galaxies, especially for B - R. The color gradients of all galaxies are equal to the mean within the errors. The color gradients are consistent with being due to gradients in metallicity. The observed color gradients would result from a decrease in the metallicity by a factor of ~2 per decade in radius. The profiles of ellipticity, position angle, and the residuals to the ellipse fitting generally show considerable structure. Deviations from ellipses at the level of 0.5% are common. The detection of a faint, inclined disklike distortion at a radius of 70" (~30 kpc for H_0_ = 50 km s^-1^ Mpc^-1^) in NGC 1700 exemplifies the usefulness of the high-order terms for detecting low-surface-brightness structures. A phase-amplitude representation of the 3φ and 4φ terms has also been found to be useful for identifying faint structures. Several cases have been found of structures with constant position angle (phase) in galaxies whose major-axis position angle varies dramatically. Publication: The Astronomical Journal Pub Date: August 1989 DOI: 10.1086/115157 Bibcode: 1989AJ.....98..538F Keywords: Astronomical Photometry; Elliptical Galaxies; Brightness; Ellipticity; Position; Seeing (Astronomy); Tables (Data); Astrophysics; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (17) NED (17)