The external origin of the gas in S0 galaxies

Bertola, F.; Buson, L. M.; Zeilinger, W. W.

doi:10.1086/186675

Cited by 142 publications

(150 citation statements)

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“…This is in agreement with photometric and kinematical studies in ETGs showing in many cases gas/star misalignment and gas/star angular momentum decoupling (Bertola et al 1992;van Dokkum & Franx 1995;Caon et al 2000;Sarzi et al 2006). Kinematical and morphological peculiarities are present in 50% of our sample, suggesting that accretion is frequent.…”

Section: Origin Of the Gassupporting

confidence: 91%

“…Narrowband imaging centered around Hα+ [NII]λ6584 shows that the ionized gas has a variety of morphologies, from regular, disklike structures, to filamentary structures (Demoulin-Ulrich et al 1984;Buson et al 1993;Macchetto et al 1996;Zeilinger et al 1996;Martel et al 2004;Sarzi et al 2006). Evidence of the acquisition of external gas comes from kinematical studies showing that the angular momentum of the gas is often decoupled from that of the stars (Bertola et al 1992;van Dokkum & Franx 1995;Caon et al 2000), even if according to Sarzi et al (2006) the angular momenta are inconsistent with a purely external origin for the gas. That the ionized gas emission is always associated with dust (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Nearby early-type galaxies with ionized gas

Annibali

Bressan

Rampazzo

et al. 2010

A&A

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122

162

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Aims. A significant fraction of early-type galaxies (ETGs) exhibit emission lines in their optical spectra. We attempt to identify the producing the emission mechanism and the ionized gas in ETGs, and its connection with the host galaxy evolution. Methods. We analyzed intermediate-resolution optical spectra of 65 ETGs, mostly located in low density environments and exhibiting spectros-copic diagnostic lines of ISM from which we had previously derived stellar population properties. To extract the emission lines from the galaxy spectra, we developed a new fitting procedure that accurately subtracts the underlying stellar continuum, and accounts for the uncertainties caused by the age-metallicity degeneracy. Results. Optical emission lines are detected in 89% of the sample. The incidence and strength of emission correlate with neither the E/S0 classification, nor the fast/slow rotator classification. By means of the classical [OIII]/Hβ versus [NII]/Hα diagnostic diagram, the nuclear galaxy activity is classified such that 72% of the galaxies with emission are LINERs, 9% are Seyferts, 12% are composite/transition objects, and 7% are non-classified. Seyferts have young luminostiy-weighted ages ( 5 Gyr), and appear, on average, significantly younger than LINERs and composites. Excluding the Seyferts from our sample, we find that the spread in the ([OIII], Hα, or [NII]) emission strength increases with the galaxy central velocity dispersion σ c . Furthermore, the [NII]/Hα ratio tends to increase with σ c . The [NII]/Hα ratio decreases with increasing galactocentric distance, indicative of either a decrease in the nebular metallicity, or a progressive "softening" of the ionizing spectrum. The average nebular oxygen abundance is slightly less than solar, and a comparison with the results obtained in Paper III from Lick indices shows that it is ≈0.2 dex lower than that of stars. Conclusions. The nuclear (r < r e /16) emission can be attributed to photoionization by PAGB stars alone only for ≈22% of the LINER/composite sample. On the other hand, we cannot exclude an important role of PAGB star photoionization at larger radii. For the major fraction of the sample, the nuclear emission is consistent with excitation caused by either a low-accretion rate AGN or fast shocks (200-500 km s −1 ) in a relatively gas poor environment (n 100 cm −3 ), or both. The derived [SII]6717/6731 ratios are consistent with the low gas densities required by the shock models. The derived nebular metallicities are indicative of either an external origin of the gas, or an overestimate of the oxygen yields by SN models.

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Section: Origin Of the Gassupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Nearby early-type galaxies with ionized gas

Annibali

Bressan

Rampazzo

et al. 2010

A&A

Self Cite

122

162

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“…They had come to complex conclusions. On one hand, the circumnuclear ionized gas of S0 galaxies is kinematically decoupled from a stellar component in at least 40% of all cases, which implies its external origin (Bertola, Buson, & Zeilinger 1992). On the other hand, the velocity dispersion of the circumnuclear ionized gas matches well the stellar velocity dispersion, sometimes over extended areas, and this fact gives an evidence for an internal gas origin, say, by mass loss from bulge giant stars (Bertola et al 1995).…”

Section: Introductionmentioning

confidence: 87%

Inner Polar Rings in Regular Lenticular Galaxies

Сильченко¹,

Afanasiev²

2004

Astron J

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We have investigated a sample of S0 galaxies, mostly with circumnuclear dust lanes orthogonal to their major axes, chosen from Hubble Space Telescope Wide Field Planetary Camera 2 images. Two-dimensional spectroscopy undertaken with the Multipupil Fiber Spectrograph of the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences has revealed that indeed the ionized gas in the centers of these eight lenticular galaxies rotate in the planes nearly orthogonal to the rotation (and symmetry) planes of their central stellar components. Although almost all the galaxies are located in dense environments, an external origin of this rotation plane tilt is not obvious because all the galaxies but one are known to have extended H i disks, and in two cases where the angular resolution of H i observations allows, we find orthogonality of the external H i and inner ionized gas disks. We discuss a possible relation of the inner gas polar rings to a triaxiality of galactic potential. The stellar populations in the nuclei of all but two galaxies are very old, which excludes recent star formation bursts and proves that the polar orbits of the circumnuclear gas are rather stable. In the nuclei of NGC 2655 and NGC 4111, we have found signatures of star formation bursts some 1.5-2 Gyr ago. This finding can be related to very central gas in NGC 2655, which is coplanar to the circumnuclear stellar disk and to radial gas inflow in NGC 4111; just these gas reservoirs and not the polar rings may be responsible for fueling nuclear star formation.

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“…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).…”

Section: Kinematics Of Hrg 54103mentioning

confidence: 99%

The ring galaxy HRG 54 103: a first study

Faúndez-Abans

Fernandes

Oliveira-Abans

et al. 2009

A&A

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Aims. We report the first study of the peculiar ring galaxy HRG 54103 which was previously classified as a Saturn-like type galaxy. Methods. The study is based on low resolution spectroscopy and photometric observations in the optical band to highlight the characteristics of this almost isolated galaxy. The colour distribution of HRG 54103 was examined through direct CCD BVRI Kron-Cousins system imagery. Color-color diagrams of the bulge and ring are displayed and further compared with the star-forming ring galaxy HRG 2302.Results. The results of image enhancement of the morphological structure of this galaxy are discussed. The nuclear emission-line spectrum resembles that of a Seyfert2/LINER object, with z = 0.022 and heliocentric V = 6483 ± 18 km s −1 , in agreement with the literature. The nuclear, bulge and ring section radial velocities along the ring major axis show a peculiar distribution, which together and the disk-ring asymmetry suggest a possible merger event in the recent past of this object, which could also have caused its formation.

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The external origin of the gas in S0 galaxies

Cited by 142 publications

References 0 publications

Nearby early-type galaxies with ionized gas

Nearby early-type galaxies with ionized gas

Inner Polar Rings in Regular Lenticular Galaxies

The ring galaxy HRG 54 103: a first study

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