Double-Barred Galaxies: I. A Catalog of Barred Galaxies with Stellar Secondary Bars and Inner Disks

TL;DR

This paper presents a comprehensive catalog of 67 barred galaxies with inner stellar structures, including double bars and inner disks, providing measurements and classifications to aid understanding of galaxy morphology.

Contribution

It introduces a detailed catalog of double-barred and inner-disk galaxies with homogenized measurements, clarifies classifications, and discusses potential misidentifications in galaxy structures.

Findings

50 galaxies are confirmed double-barred systems.

Inner disks are statistically distinct from inner bars.

Misclassification often occurs due to nuclear rings and spirals.

Abstract

I present a catalog of 67 barred galaxies which contain distinct, elliptical stellar structures inside their bars. Fifty of these are double-barred galaxies: a small-scale, "inner" or "secondary" bar is embedded within a large-scale, "outer" or "primary" bar. I provide homogenized measurements of the sizes, ellipticities, and orientations of both inner and outer bars, along with with global parameters for the galaxies. The other 17 are classified as "inner-disk" galaxies, where a large-scale bar harbors an inner elliptical structure which is aligned with the galaxy's outer disk. Four of the double-barred galaxies also possess inner disks, located in between the inner and outer bars. While the inner-disk classification is ad-hoc -- and undoubtedly includes some inner bars with chance alignments (five such probable cases are identified) -- there is good evidence that inner disks form a statistically distinct population, and that at least some are indeed disks rather than bars. In addition, I list 36 galaxies which may be double-barred, but for which current observations are ambiguous or incomplete, and another 23 galaxies which have been previously suggested as potentially being double-barred, but which are probably *not*. False double-bar identifications are usually due to features such as nuclear rings and spirals being misclassified as bars; I provide some illustrated examples of how this can happen.