Kinematics and Stellar Populations in Isolated Lenticular Galaxies

Abstract

By combining new long-slit spectral data obtained with the Southern African Large Telescope for nine galaxies with our previously published observations for 12 additional galaxies, we study the stellar and gaseous kinematics as well as radially resolved stellar population properties and ionized-gas metallicity and excitation for a sample of isolated lenticular galaxies. We have found that there is no particular time frame of formation for the isolated lenticular galaxies: the mean stellar ages of the bulges and disks are distributed between 1 and 13 > Gyr, and the bulge and the disk in every galaxy formed synchronously demonstrate similar stellar ages and magnesium-to-iron ratios. Extended ionized-gas disks are found in the majority of the isolated lenticular galaxies, in 72% ±11%. Half of all extended gaseous disks demonstrate a visible counterrotation with respect to their stellar counterparts. We argue that just such a fraction of projected counterrotation is expected if all of the gas in isolated lenticular galaxies is accreted from outside, under the assumption of isotropically distributed external sources. The very narrow range of the gas oxygen abundances we found for the outer ionized-gas disks excited by young stars, [O/H] from 0.0 to +0.2 dex, gives evidence for satellite merging as the most probable source of this accretion. Last, we formulate a hypothesis that the morphological type of a field disk galaxy is completely determined by the outer cold-gas accretion regime.

Integral-field kinematics and stellar populations of early-type galaxies out to three half-light radii

“…Such arguments could also hold for some co-rotating ionised gas structures, since an accreted gas disk should ultimately align with its host galaxy's stars in half of all cases (e.g. Katkov et al 2015); the time-scales of such alignments (or anti-alignments) will vary from object to object, but could potentially be several Gyr in the case of extended accretion (van de Voort et al 2015).…”

Implications for the Origin of Early-type Dwarf Galaxies: A Detailed Look at the Isolated Rotating Early-type Dwarf Galaxy LEDA 2108986 (CG 611), Ramifications for the Fundamental Plane’s Kinematic Scaling, and the Spin–Ellipticity Diagram

“…Far from being unusual, the majority of isolated lenticular galaxies contain ionized gas disks, and half of those disks rotate in the opposite sense to the stellar disk (Katkov et al 2014(Katkov et al , 2015. As Katkov et al (2015) remark, this is expected if all of the gas is acquired by accretion of gas-rich satellites, or perhaps filaments of cold gas.…”

Magnetic fields in ring galaxies

“…The large proportion of observed gas counter-rotation with respect to the stellar components, especially among the S0s in rarified environments, strongly supports an origin through accretion (Katkov et al 2015). Some examples of the outer star forming rings in visually unbarred galaxies are shown in Fig.…”

“…1, has a counter-rotating ring. IC 5285, UGC 5936, and UGC 9980 do not demonstrate observable radial gas velocities, thus ruling out a collisional origin for their rings (Ilyina & Sil'chenko 2011;Ilyina et al 2014;Katkov et al 2015).…”

“…Based on the results of Ilyina & Sil'chenko (2011), Ilyina et al (2014 and Katkov et al (2015) we select a small sample with the properties mentioned above and present it in Fig. 1.…”