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14. The HydraI Multi-Color Surface Photometry

On the following pages (pp. -) we show the surface photometry for the 64 galaxies in the HydraI photometric sample (Table , p. ). We plot the surface brightness $\mu$ (in ${^{\rm m} /{\rm arcsec}^{2}}$ ); from top to bottom on the panels the passband is Gunn r (squares), Johnson B (crosses), and Johnson U (triangles). We plot the colors (B-r) (crosses) and (U-r) (triangles). Note that Johnson U photometry is only available for 22 of the 64 galaxies (cf. Table , p. ). We plot the ellipticity, the position angle, and the Fourier coefficients c₃, s₃, c₄, and s₃ for Gunn r only.

All the plots have the same axis intervals. This makes a galaxy-to-galaxy comparison easy. An axis interval for the Fourier coefficients as large as $\pm0.13$ is needed to accommodate the `semi-spiral' galaxy R224 (p. ) and the very disky galaxy R338 (p. ). Other very disky galaxies include R250 (p. ), R266 (p. ), and R295 (p. ). Only the interval for the position angle is shifted in the cases where the position angle profile crosses $0^\circ$ or $180^\circ$ .

The interval on the $\log(r/{\rm arcsec})$ -axis is 0.0-1.9, corresponding to a range in r of 1''-79''. The surface brightnesses $\mu$ are plotted from 1'' to the radius where the uncertainty on $\mu$ exceeds $0.2{^{\rm m} /{\rm arcsec}^{2}}$ . The colors are plotted from 2'' to the radius where the uncertainty on the color exceeds $\sqrt{2} \cdot 0\hbox{$.\!\!^{\rm m}$ }2$ . The other quantities are plotted from 2'' to either the radius where the ellipticity and the position angle are no longer free parameters in the fit (cf. Sect. , p. ), or the maximum radius for the $\mu$ plot, whichever is the smallest.

Given in the title for each plot is the galaxy ID from Richter (1989) (e.g. R269), the common galaxy name if available (e.g. N3311), and the morphological type listed by Richter.

The surface brightnesses and the colors are on the standard photometric system (cf. Sect. , p. ), but no offsets for galactic extinction, k-correction, or cosmological dimming have been applied. This is the standard way of presenting surface photometry. The errorbars for the surface brightnesses and the colors include a conservative estimate of the uncertainty on the background subtraction of 1% for Gunn r and 0.5% for Johnson B and U.

For the galaxies that have been observed more than once the best seeing observation was chosen (cf. Table , p. ). The only exception to this is the Johnson B observation of R166, where an observation with a marginally (0.02'') worse seeing was chosen. By doing so it was achieved that all 64 pairs of Gunn r and Johnson B observations shown here were observed just after each other (within $\sim$ 10 minutes).

The seeing for the shown observations is in the range 0.77''-1.37'' for Gunn r, 0.81''-1.70'' for Johnson B, and 1.01''-1.57'' for Johnson U. The mean values are 0.95'', 1.04'', and 1.20'', respectively. For Gunn r, the seeing range corresponds to a range in $\log(r/'')$ of -0.11 to +0.14.

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Next: About this document ... Up: Properties of E and Previous: 13. The HydraI Galaxy

Properties of E and S0 Galaxies in the Clusters HydraI and Coma
Master's Thesis, University of Copenhagen, July 1997

Bo Milvang-Jensen (milvang@astro.ku.dk)