A CLASSICAL MORPHOLOGICAL ANALYSIS OF GALAXIES IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S ⁴ G)

Abstract

The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is the largest available database of deep, homogeneous middle-infrared (mid-IR) images of galaxies of all types. The survey, which includes 2352 nearby galaxies, reveals galaxy morphology only minimally affected by interstellar extinction. This paper presents an atlas and classifications of S 4 G galaxies in the Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) system. The CVRHS system follows the precepts of classical de Vaucouleurs (1959) morphology, modified to include recognition of other features such as inner, outer, and nuclear lenses, nuclear rings, bars, and disks, spheroidal galaxies, X patterns and box/peanut structures, OLR subclass outer rings and pseudorings, bar ansae and barlenses, parallel sequence late-types, thick disks, and embedded disks in 3D early-type systems. We show that our CVRHS classifications are internally consistent, and that nearly half of the S 4 G sample consists of extreme late-type systems (mostly bulgeless, pure disk galaxies) in the range Scd-Im. The most common family classification for mid-IR types S0/a to Sc is SA while that for types Scd to Sm is SB. The bars in these two type domains are very different in mid-IR structure and morphology. This paper examines the bar, ring, and type classification fractions in the sample, and also includes several montages of images highlighting the various kinds of "stellar structures" seen in mid-IR galaxy morphology.

Boxy/Peanut/X-shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

“…The insert in the upper frame shows the median-stacked surface brightness excess of barlens, X-shaped, and SA galaxies, relative to their exponential outer disk profiles extrapolated to the center. Decomposition parameters for the disks are from Salo et al (2015), and the bar family classification is from Buta et al (2015). In the large frame, the excess brightness of barlens (bl) and X samples is shown relative to SA galaxies.…”

“…Slopes of the inner rotation curves for S 4 G galaxies, calculated from the 3.6 μm images. The red circles indicate galaxies with a barlens identification (Laurikainen et al 2011;Buta et al 2015), whereas green ( <  i 60 ) and blue crosses ( >  i 60 )represent galaxies with an X signature. In the upper frame the inner slope is shown vs. galaxy stellar mass (M * from Munoz-Mateos et al 2015), whereas in the lower frame, the slope is normalized by V h r max and displayed vs. galaxy inclination.…”

“…Normalized dV dr cir indicates scaling of the inner slope with V h r max : the X-shaped galaxies with <  i 60 and normalized > dV dr 8 cir are marked with an asterisk. The barlens classifications are from Buta et al (2015) and Laurikainen et al (2011), and the X classifications are from .…”

MUSE tells the story of NGC 4371: The dawning of secular evolution

“…In this case then, barlenses are just the inner parts of bars that are more extended than the outer parts in the vertical direction, as well as along the bar minor axis in the disc plane. As we see below, our spectroscopic analyses do not reach far enough from the galaxy centre to include the outer lens, the ansae, and the inner ring mentioned by Buta et al (2015). Therefore, these components are not addressed here.…”

“…The calibrated science frames are combined into the final data cube in the second step. This includes the process of flux calibration, sky subtraction adopting a model sky spectrum computed from the sky field, astrometric registration, correction for differential atmospheric refraction, and resampling of the data cube based on the drizzle algorithm (see Weilbacher et al 2012 Gallo et al 2010), and classified as a barred S0 (lenticular) galaxy (Buta et al 2015). Buta et al also mention that NGC 4371 has a nuclear ring, a barlens, an inner ring (i.e.…”