The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698

Abstract

The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner region of the bulge structure is elongated perpendicularly to the major axis of the disk, this is also true for the outer parts of the bulge if a parametric photometric decomposition is adopted. At the same time the stellar component is characterized by an inner velocity gradient and a central zero-velocity plateau along the minor and major axis of the disk respectively. This remarkable geometric and kinematic decoupling suggests that a second event occurred in the formation history of this galaxy.Comment: 12 pages, LaTex, with 4 PostScript figures. Accepted for publication in The Astrophysical Journal Letter

The ring galaxy HRG 54 103: a first study

“…In spite of the low resolution spectroscopy, our results suggest a presence of velocity gradients along the disk major axis for HRG 54103, such as some Sa galaxies (e.g. NGC 4698; NGC 2855; see Bertola et al 1999 andCorsini et al 2002, respectively).…”

“…(1) at the Observatório do Pico dos Dias (OPD) -Laboratório Nacional de Astrofísica, Brazil, on the 1.6-m telescope using the direct CCD camera with BVRI Kron-Cousins filters (Bessel 1990) and a 384 × 578-pixel chip with a scale of 0.284 arcsec pix −1 (0.128 kpc pix −1 and 0.451 kpc arcsec −1 ); three frames in each filter with individual exposure times of 600 s were taken under photometric conditions better than 1. 2 FWHM seeing; the stars used for extinction and calibration are from Landolt (1992); (2) spectroscopic observations performed at CTIO (Cerro Tololo Inter-American Observatory) with the 1.5-m telescope equipped with a Cassegrain spectrograph and Loral 1k # 1 + Arcon 3.9 (1200 × 800 square pixels, pixel size of 15 μm, scale of 1.3 pix −1 ).…”

“…In spite of gravitational perturbations, some stellar and gaseous components with a misaligned or even opposite angular momentum with respect to its core, conserve some dynamical memory of processes which drive galaxy formation and evolution. In normal galaxies, kinematically-decoupled components ranging from the counter-rotating-decoupled disks of ionized gas are observed in a large fraction of S0 galaxies (Bertola et al 1992;Kuijken et al 1996;Plana & Boulesteix 1996), and orthogonally-rotating stellar cores are found in Sa spirals (Bertola et al 1999;Sarzi et al 2000). These characteristics are usually hidden from preliminary morphological inspection and are serendipitously discovered only by detailed kinematics studies (see Bertola & Corsini 1998 as review).…”

The Intrinsic Shape of Galaxy Bulges

“…Méndez-Abreu et al (2010) relaxed this condition and found that only 18% of the observed bulges have a probability > 50% of being elongated along the polar axis with no bulges reaching a probability > 90%. In fact, to date NGC 4698 (Bertola et al, 1999), NGC 4672 (Sarzi et al, 2000), and UGC 10043 (Matthews & de Grijs, 2004) are the only spiral galaxies known to host a prominent bulge sticking out from the plane of the disc.…”

The formation of stellar nuclear discs in bar-induced gas inflows

“…McDermid et al (2006) found NDs and counter-rotating cores in the central kpc of earlytype galaxies and evidence for recent circum-nuclear star formation. The presence of dynamically decoupled features such as a counter-rotating disc in NGC 4458 (Morelli et al 2004, c 0000 RAS 2010) and a disc rotating perpendicular to the main galactic disc (Bertola et al 1999;Pizzella et al 2002;Corsini et al 1999Corsini et al , 2012 can be explained by the capture of external gas. However interactions may not be the main mechanisms driving gas to nuclei in more isolated galaxies, where observations show that there is continuing star formation in some NDs e.g.…”