Probing spectral line gradients beyond one effective radius in NGC 3610

The outer region [(0.75-1.25)r e in the B band] of the merger remnant elliptical galaxy NGC 3610 is studied using extremely high signal-to-noise ratio Keck spectra, with a supplementary spectrum of the galaxy center. Stellar population parameters - age, [Z/H], and [α/Fe] - are measured in several apertures along the slit. Using the multi-index simultaneous fitting method of R. Proctor and coauthors, no significant stellar population gradients are detected in the outer parts of the galaxy. The overall gradients relative to the galaxy center are consistent with those found in many other early-type galaxies, although the metallicity gradient is much steeper than would be expected if NGC 3610 formed in a major merger event. Standard analysis methods that use the Hβ index are found to produce spurious radially variable gradients.