Intermediate-Band Surface Photometry of the Edge-on Galaxy NGC 4565

Abstract

We present a deep, 42.79 hr image of the nearby, edge-on galaxy NGC 4565 in the Beijing-Arizona-Taipei-Connecticut 6660 Å band using the large-format CCD system on the 0.6 m Schmidt telescope at the Xinglong Station of the National Astronomical Observatories of China. Following the procedures previously developed by our team for the analysis of deep images of galaxies, we obtain a final image that is calibrated to an accuracy of 0.02 mag in zero point and for which we can measure galaxy surface brightness to an accuracy of 0.25 mag at a surface brightness of 27.5 mag arcsec-2 at 6660 Å, corresponding to a distance of 22 kpc from the center of the disk. The integrated magnitude of NGC 4565 in our filter is m6660=8.99 (=R magnitude of 9.1) to a surface brightness of 28 mag arcsec-2. We analyze the faint outer parts of this galaxy using a two-dimensional model comprised of three components: an exponential thin disk, an exponential thick disk, and a power-law halo. Combined with a need to provide a cutoff radius for the disk, a total of 12 parameters are included in our model. We determine the best values of our model parameters via 10,000 random initial values, 3700 of which converge to final values. We then plot the χ2 for each converged fit versus parameter value for each of the 12 parameters. The thin-disk and thick-disk parameters that we determine here are consistent with those of previous studies of this galaxy. However, our very deep image permits a better determination of the power-law fit to the halo, constraining this power law to be between r-3.2 and r-4.0, with a best-fit value of r-3.88. We find the axis ratio of the halo to be 0.44 and its core radius to be 14.4 kpc (for an adopted distance of 14.5 Mpc). We also agree with others that the bulge of NGC 4565 is fitted well by an exponential luminosity distribution with a scale height similar to that found for the thin disk.