Nuclear discs as clocks for the assembly history of early-type galaxies: the case of NGC 4458

Sarzi, Marc; Ledo, H.; Coccato, L.; Corsini, E. M.; Dotti, Massimo; Khochfar, Sadegh; Maraston, Claudia; Morelli, L.; Pizzella, A.

doi:10.1093/mnras/stw099

Cited by 8 publications

(8 citation statements)

References 63 publications

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“…Sarzi et al (2016) find that the age of hot nuclear stellar disc in elliptical galaxy NGC 4458 is at least 6 Gyr old, while Corsini et al (2016) measured the age of the nuclear stellar disc in the SB0 galaxy NGC 1023 is about 2 Gyr. On the other hand, spectral synthesis fits to the detailed XSHOOTER spectra of the LLAMA sample (Burtscher et al in preparation) show that while an old population dominates the optical continuum, a younger component with an age of 0.1-1 Gyr is nearly always present at a level of a few to 20 per cent.…”

Section: Central Velocity Dispersionmentioning

confidence: 97%

“…There is another explanation that most of the stars embedded in nuclear disk have not formed recently, and this stellar component is not dynamically cold anymore. Sarzi et al (2016) find that the age of hot nuclear stellar disk in elliptical galaxy NGC 4458 is at least 6 Gyr old, while Corsini et al (2016) measured the age of the nuclear stellar disk in the SB0 galaxy NGC 1023 is about 2 Gyr. On the other hand, spectral synthesis fits to the detailed XSHOOTER spectra of the LLAMA sample (Burtscher et al in prep.…”

Section: Central Velocity Dispersionmentioning

confidence: 97%

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LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

Davies

Hicks

et al. 2017

Monthly Notices of the Royal Astronomical Society

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In a complete sample of local 14-195 keV selected AGNs and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, 8 AGNs and 5 inactive galaxies. The stellar velocity fields show a disk-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disk structure, and which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.

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Section: Central Velocity Dispersionmentioning

confidence: 97%

Section: Central Velocity Dispersionmentioning

confidence: 97%

LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

Davies

Hicks

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…This way, it is possible i) to establish a direct association between photometric and kinematic components; and ii) to use the photometric information as priors in the spectroscopic decomposition to constrain the flux of the components. The use of photometric priors in the spectroscopic decomposition to improve the accuracy of the kinematics and stellar population measurements has been successfully applied in several cases (e.g., Coccato et al 2014Coccato et al , 2015Sarzi et al 2016;Tabor et al 2017). The photometric decomposition is performed using the twodimensional fitting algorithm galfit (Peng et al 2002).…”

Section: Photometric Decompositionmentioning

confidence: 99%

The properties of the kinematically distinct components in NGC 448 and NGC 4365

Nedelchev

Coccato²,

Corsini

et al. 2019

A&A

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Aims. We study the kinematically distinct components in two early-type galaxies NGC 448 and NGC 4365 aided by integral-field observations with the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope. NGC 448 has previously been shown to host a counter-rotating stellar disk. NGC 4365 harbours a central (apparently) decoupled core that has been suggested to not be physically distinct from the main body and instead stems from the different orbital types in the core and main body due to its triaxial nature. We aim to measure the brightness profiles, kinematics, and stellar population properties of the peculiar kinematic structures in these galaxies and shed light on their true nature and formation mechanism. Methods. We use a kinematic decomposition technique to separate the individual contributions to the spectra of the two distinct kinematic components observed at each spatial position in the field of view. Furthermore, by folding back the outcome of a photometric decomposition we reduce the intrinsic degeneracies in recovering the kinematics and the best-fitting stellar spectral templates. Finally, by extracting the Lick line-strength indices for the individual components and fitting them to single stellar population models we derive their ages, metallicities, and α/Fe overabundances. Results. The two kinematically decoupled stellar components in NGC 448 have similar ages, but different chemical compositions. The distinct kinematic feature in NGC 448 has a nearly exponential surface-brightness light profile, dominates in the innermost ∼ 10 ′′ , is smaller in size, and is very likely an embedded counter-rotating disk as also indicated by its kinematics. It has higher metallicity than the main galaxy stellar body and lower α/Fe overabundance. By contrast, we do not find evidence for true decoupling in the two distinct kinematic components in NGC 4365. This confirms earlier work suggesting that the kinematically distinct core is likely not a separate dynamical structure, but most certainly likely a projection effect stemming from the orbital structure of this galaxy that was previously found to be intrinsically triaxial in shape. Conclusions. Our findings indicate that the kinematically decoupled component in NGC 448 is truly decoupled, has external origin, and was formed through either the acquisition of gas and a subsequent star-formation episode or it formed from the direct accretion of stars from a companion. Conversely, the presence of a kinematically distinct component in NGC 4365 is not associated to a true kinematic decoupling and is instead most likely due to projection effect stemming from the triaxial nature of this galaxy.

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“…More detailed observations of the stellar populations in the KDC would be required to date its formation (e.g. Sarzi et al 2016).…”

Section: Inner Kpc and Decoupled Corementioning

confidence: 99%

The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties

Young

Meier

Bureau

et al. 2021

ApJ

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We present ALMA observations of CO isotopologues and high-density molecular tracers (HCN, HCO+, CN, etc.) in NGC 7465, an unusually gas-rich early-type galaxy that acquired its cold gas recently. In the inner 300 pc, the molecular gas kinematics are misaligned with respect to all other galaxy components; as the gas works its way inward, it is torqued into polar orbits about the stellar kinematically decoupled core (KDC), indicating that the stellar KDC is not related to the current gas accretion event. The galaxy also exhibits unusually high 12CO/13CO line ratios in its nucleus but typical 13CO/C18O ratios. Our calculations show that this result does not necessarily indicate an unusual [12CO/13CO] abundance ratio but rather that 12CO (1–0) is optically thin due to high temperatures and/or large line widths associated with the inner decoupled, misaligned molecular structure. Line ratios of the higher-density tracers suggest that the densest phase of molecular gas in NGC 7465 has a lower density than is typical for nearby galaxies, possibly as a result of the recent gas accretion. All of the observed molecular properties of NGC 7465 are consistent with it having acquired its molecular (and atomic) gas from a spiral galaxy. Further detailed studies of the CO isotopologues in other early-type galaxies would be valuable for investigating the histories of those that may have acquired their gas from dwarfs. Finally, these ALMA data also show an unidentified line source that is probably a background galaxy similar to those found at z = 1–3 in blind CO surveys.

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Nuclear discs as clocks for the assembly history of early-type galaxies: the case of NGC 4458

Cited by 8 publications

References 63 publications

LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

The properties of the kinematically distinct components in NGC 448 and NGC 4365

The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties

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