Confirmation of a Kinematic Diagnostic for Face-On B/P Bulges

TL;DR

This study confirms that face-on box/peanut-shaped bulges can be identified by specific minima in the h_4 profile of the LOSVD, validated through high-resolution spectroscopy of three galaxies.

Contribution

First observational confirmation that h_4 minima reliably indicate face-on B/P bulges in barred galaxies.

Findings

NGC 98 shows a clear double minimum in h_4 consistent with B/P bulge presence.

NGC 600 and NGC 1703 do not show h_4 signatures of B/P bulges.

LOSVD broadening at h_4 minima supports the diagnostic's validity.

Abstract

We present the results of high resolution absorption-line spectroscopy of 3 face-on galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for box/peanut (B/P)-shaped bulges. These observations test and confirm, for the first, time the prediction that face-on B/P-shaped bulges can be recognized by two minima in the profile along the bar's major axis of the fourth Gauss-Hermite moment h_4 of the line-of-sight velocity distribution (LOSVD). In NGC 98, a clear double minimum in h_4 is present along the major axis of the bar and before the end of the bar, as predicted. In contrast, in NGC 600, which is also a barred galaxy but lacks a substantial bulge, we do not find any significant kinematic signature for a B/P-shaped bulge. In NGC 1703, which is an unbarred control galaxy, we found no evidence of a B/P bulge. We also show directly that the LOSVD is broader at the location of the h_4 minimum in NGC 98 than elsewhere. This more direct method avoids possible artifacts associated with the degeneracy between the measurement of line-of-sight velocity dispersion and h_4.