NGC 474 as viewed with KCWI: diagnosing a shell galaxy

Alabi, Adebusola B.; Ferré-Mateu, Anna; Forbes, Duncan A.; Romanowsky, Aaron J.; Brodie, Jean P.

doi:10.1093/mnras/staa1992

Cited by 10 publications

(34 citation statements)

References 62 publications

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“…These two scenarios might be further explored using spectroscopic data of the other shells and a chemo-dynamical numerical model of the collision. We further note that Alabi et al (2020) 3 suggested a more massive progenitor, namely 10 10 M , based on a higher metallicity measurement. One would thus need observations revealing the kinematics and the stellar populations -age and metallicity -within the other shells, for instance using integral field spectroscopy.…”

Section: What Is the Progenitor Of The Shell?mentioning

confidence: 70%

Shedding light on the formation mechanism of shell galaxy NGC 474 with MUSE

Fensch

Duc

Lim

et al. 2020

A&A

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Stellar shells around galaxies could provide precious insights into their assembly history. However, their formation mechanism remains poorly empirically constrained, regarding in particular the type of galaxy collisions at their origin. We present MUSE at VLT data of the most prominent outer shell of NGC 474, to constrain its formation history. The stellar shell spectrum is clearly detected, with a signal-to-noise ratio of ∼65 pix −1. We used a full spectral fitting method to determine the line-of-sight velocity and the age and metallicity of the shell and associated point-like sources within the MUSE field of view. We detect six globular cluster (GC) candidates and eight planetary nebula (PN) candidates that are all kinematically associated with the stellar shell. We show that the shell has an intermediate metallicity, [M/H] = −0.83 +0.12 −0.12 , and a possible α-enrichment, [α/Fe] ∼ 0.3. Assuming the material of the shell comes from a lower mass companion, and that the latter had no initial metallicity gradient, such a stellar metallicity would constrain the mass of the progenitor at around 7.4 × 10 8 M , implying a merger mass ratio of about 1:100. However, our census of PNe and earlier photometry of the shell would suggest a much higher ratio, around 1:20. Given the uncertainties, this difference is only significant at the 1σ level. We discuss the characteristics of the progenitor, and in particular whether the progenitor could also be composed of stars from the low-metallicity outskirts of a more massive galaxy. Ultimately, the presented data do not allow us to put a firm constraint on the progenitor mass. We show that at least two GC candidates possibly associated with the shell are quite young, with ages below 1.5 Gyr. We also note the presence of a young (∼1 Gyr) stellar population in the center of NGC 474. The two may have resulted from the same event.

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Section: What Is the Progenitor Of The Shell?mentioning

confidence: 70%

Shedding light on the formation mechanism of shell galaxy NGC 474 with MUSE

Fensch

Duc

Lim

et al. 2020

A&A

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“…The stream appears to be a continuation of a linear structure stretching from the irregular shell A to the galaxy center from the south. The shell B is the one studied spectrocopically in Alabi et al (2020) and Fensch et al (2020). The galaxy NGC 474 has very bright shells up to the galactocentric distance of about 30 kpc.…”

Section: Observational Characteristics Of Ngc 474mentioning

confidence: 99%

“…The galaxy NGC 474, studied in this paper, contains some of the brightest known shells that have around 25 mag arcsec −2 in the R-band (Turnbull et al 1999). The relative faintness of shells made their spectroscopic observations in integrated starlight impossible until recently (Alabi et al 2020;Fensch et al 2020). There are however several measurements of shell kinematics using individual kinematic tracers: red-giant-branch stars of the so-called Western Shelf in M31 Andromeda galaxy (Fardal et al 2012); globular clusters (Romanowsky et al 2012) and planetary nebulae (Longobardi et al 2015) in giant elliptical galaxy M87; a combination of globular clusters, planetary nebulae, and H II regions in the Umbrella Galaxy NGC 4651 (Foster et al 2014); and RR Lyrae and blue-horizontal-branch stars in the Milky Way (Donlon et al 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Two teams independently published IFU spectra of one of the shells of the galaxy NGC 474. Alabi et al (2020) used KCWI@Keck and Fensch et al (2020) used MUSE@VLT. The galaxy hosts many shells and streams, some of which are exceptionally bright.…”

Section: Introductionmentioning

confidence: 99%

“…They made NGC 474 to appear in the first atlas of peculiar galaxies (Arp 1966). The works by Alabi et al (2020) and Fensch et al (2020) studied the star formation histories and chemical properties of the shell, of the associated globular clusters, and of the center of the galaxy. Fensch et al (2020) studied also the kinematics of the shell and of the associated globular clusters and planetary nebulae.…”

Section: Introductionmentioning

confidence: 99%

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Origin of the spectacular tidal shells of galaxy NGC474

Bílek,

Fensch,

Ebrová

et al. 2021

Preprint

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Context. The lenticular galaxy NGC 474 hosts a rich system of tidal shells and streams, some of which are exceptionally bright. Two teams recently presented spectroscopic observations of the brightest shells. These were the first shell spectra ever observed in integrated starlight. The authors studied the stellar populations of the shell, of the center of the galaxy and of its globular clusters. The precise formation scenario for the tidal features of this prominent galaxy however still remained unclear.Aims. Here, we add further clues on their formation from the radii of the shells, and we present a scenario for the formation of the tidal features that seems to be unique and explaining all available data. Methods. Shell radii are analyzed with the shell identification method, and we run self-consistent simulations of the formation of the tidal features. We consider Newtonian as well as MOND gravity. Results. Observations suggest that the tidal features originate from the accretion of a spiral galaxy. The shell identification method yields that the merging galaxies collided first 1.3 Gyr ago and then again 0.9 Gyr ago, thereby forming the shells in two generations. This would also explain the young ages of stellar populations in the center of the galaxy and the young age of the globular clusters. The analytic models of shell propagation, that underlie the shell identification method, are verified by a simulation. The simulations reproduce well the observed morphology of the tidal features. The accreted spiral likely reached NGC 474 nearly radially, in the plane of the sky, from the south, its rotation axis pointing toward us. It should have had a stellar mass of around 1/6 of NGC 474, i.e. 10 9.8 M . It seems that all tidal features in the galaxy originate from one merger.

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Origin of the spectacular tidal shells of galaxy NGC 474

Bílek

Fensch

Ebrová

et al. 2022

A&A

View full text Add to dashboard Cite

Context. The lenticular galaxy NGC 474 hosts a rich system of tidal shells and streams, some of which are exceptionally bright. Two teams recently presented spectroscopic observations of the brightest shells. These were the first shell spectra ever observed in integrated starlight. The authors studied the stellar populations of the shell, of the center of the galaxy, and of its globular clusters. The precise formation scenario for the tidal features of this prominent galaxy still remained unclear, however. Aims. Here, we add further clues on their formation from the radii of the shells, and we present a scenario for the formation of the tidal features that seems to be unique and can explain all available data. Methods. Shell radii were analyzed with the shell identification method, and we ran self-consistent simulations of the formation of the tidal features. We considered Newtonian as well as MOND gravity. Results. Observations suggest that the tidal features originate from the accretion of a spiral galaxy. According to the shell identification method, the merging galaxies first collided 1.3 Gyr ago and then again 0.9 Gyr ago, thereby forming the shells in two generations. This would also explain the young ages of stellar populations in the center of the galaxy and the young age of the globular clusters. The analytic models of shell propagation that underlie the shell identification method are verified by a simulation. The simulations reproduce the observed morphology of the tidal features well. The accreted spiral likely reached NGC 474 on the plane of the sky nearly radially from the south, its rotation axis pointing toward us. It probably had a stellar mass of about one-sixth of NGC 474, that is, 109.8 M⊙. Apparently, all tidal features in the galaxy originate from one merger.

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NGC 474 as viewed with KCWI: diagnosing a shell galaxy

Cited by 10 publications

References 62 publications

Shedding light on the formation mechanism of shell galaxy NGC 474 with MUSE

Shedding light on the formation mechanism of shell galaxy NGC 474 with MUSE

Origin of the spectacular tidal shells of galaxy NGC474

Origin of the spectacular tidal shells of galaxy NGC 474

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