Molecular gas content of shell galaxies

Mancillas, B.; Combes, F.; Duc, Pierre–Alain

doi:10.1051/0004-6361/201935968

Cited by 12 publications

(13 citation statements)

References 54 publications

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“…The stellar population properties of the stars in the outer shell region therefore suggest an ex-situ origin and an evolutionary path different from the galaxy centre. This also agrees with the conclusions from cosmological simulations (Pop et al 2018;Mancillas et al 2019a;Karademir et al 2019). However, this does not completely resolve the issue of the origin of the shells -are the shells made from stellar materials accreted from the nearby NGC 470 or are they relics of a disrupted satellite galaxy?…”

Section: Discussionsupporting

confidence: 91%

“…It has a projected spatial separation of 5.4 (∼47 kpc) from its nearest neighbour (the spiral galaxy NGC 470), with both galaxies having identical systemic velocities. While it is clear that the gas-poor NGC 474 is interacting with its gas-rich neighbour (Schiminovich et al 1997;Cullen et al 2006;Rampazzo et al 2006;Mancillas et al 2019a), the debate about the origin of the observed shell system and its evolutionary link with the ongoing interaction is still open (Schombert & Wallin 1987;Forbes 1999).…”

Section: Introductionmentioning

confidence: 99%

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NGC 474 as viewed with KCWI: diagnosing a shell galaxy

Alabi

Ferré-Mateu

Forbes

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Abstract We present new spectra obtained using Keck/KCWI and perform kinematics and stellar population analyses of the shell galaxy NGC 474, from both the galaxy centre and a region from the outer shell. We show that both regions have similarly extended star formation histories although with different stellar population properties. The central region of NGC 474 is dominated by intermediate-aged stars (8.3 ± 0.3 Gyr) with subsolar metallicity ([Z/H]=−0.24 ± 0.07 dex) while the observed shell region, which hosts a substantial population of younger stars, has a mean luminosity-weighted age of 4.0 ± 0.5 Gyr with solar metallicities ([Z/H]=−0.03 ± 0.09 dex). Our results are consistent with a scenario in which NGC 474 experienced a major to intermediate merger with a log$(M_*/\rm M_\odot )\mathord {\sim }10$ mass satellite galaxy at least $\mathord {\sim }2$ Gyr ago which produced its shell system. This work shows that the direct spectroscopic study of low-surface brightness stellar features, such as shells, is now feasible and opens up a new window to understanding galaxy formation and evolution.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

NGC 474 as viewed with KCWI: diagnosing a shell galaxy

Alabi

Ferré-Mateu

Forbes

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…One may thus wonder what the origin of the gas that fueled this starburst and the formation of the GCs is. Indeed, the nucleus of NGC 474 does not host any detectable H 2 , and we note that no HI has been detected at the vicinity of the shell (Schiminovich et al 1997;Rampazzo et al 2006;Mancillas et al 2019b). This suggests that these episodes of star formation were very efficient at consuming or ejecting the gas and calls for a dedicated numerical study of star cluster formation in shell-forming galaxy interactions.…”

Section: Constraintmentioning

confidence: 75%

“…Moreover, Sikkema et al (2007) noticed pronounced dust lanes (estimated mass of ∼10 4 M ) in the central 15 of NGC 474, which align with the location of ionized gas. No molecular gas was found in the central region of NGC 474 (upper limit: M(H 2 ) < 10 7.7 M , see Combes et al 2007;Mancillas et al 2019b). Schiminovich et al (1997) and Rampazzo et al (2006) found a HI tail due to the interaction with NGC 470 (the spiral galaxy westward of NGC 474 in Fig.…”

Section: Constraintmentioning

confidence: 93%

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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“…In Dupraz & Combes (1986), the simulation of a merger of an elliptical primary with a spiral secondary produced a very similar morphology of tidal structures as seen in NGC 474, that is shells, whose surface brightness varies in azimuth, combined with a long radial stream. Moreover, NGC 474 contains HI gas (Schiminovich et al 1997;Mancillas et al 2019) and unrelaxed dust patches in the center (Sikkema et al 2007), which suggest an accretion of a gas-rich spiral. Even more evidence has been provided by the recent spectroscopic studies.…”

Section: Observational Characteristics Of Ngc 474mentioning

confidence: 99%

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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Molecular gas content of shell galaxies

Cited by 12 publications

References 54 publications

NGC 474 as viewed with KCWI: diagnosing a shell galaxy

NGC 474 as viewed with KCWI: diagnosing a shell galaxy

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

Origin of the spectacular tidal shells of galaxy NGC474

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