Dynamical signature of a stellar bulge in a quasar-host galaxy at <i>z</i>  ≃  6

Tripodi, R.; Lelli, Federico; Feruglio, C.; Fiore, F.; Fontanot, Fabio; Bischetti, M.; Maiolino, R.

doi:10.1051/0004-6361/202245202

A&A

2023

DOI: 10.1051/0004-6361/202245202

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Dynamical signature of a stellar bulge in a quasar-host galaxy at z ≃ 6

R. Tripodi

Federico Lelli

C. Feruglio

et al.

Abstract: We present a dynamical analysis of a quasar-host galaxy at z 6 (SDSS J2310+1855) using a high-resolution ALMA observation of the [CII] emission line. The observed rotation curve was fitted with mass models that considered the gravitational contribution of a thick gas disc, a thick star-forming stellar disc, and a central mass concentration, which is likely due to a combination of a spheroidal component (i.e. a stellar bulge) and a supermassive black hole (SMBH). The SMBH mass of 5 × 10 9 M , previously measure… Show more

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2024

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Cited by 5 publications

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Hyperion

Tripodi,

Scholtz,

Maiolino

et al. 2024

A&A

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We present ALMA deep observations of the CII 158 mu m emission line and the continuum at 253 GHz and 99 GHz towards SDSS J0100+2802 at $z 6.3$, the most luminous quasi-stellar object (QSO) at z$>$6. J0100+2802 belongs to the HYPERION sample of luminous QSOs at $z 6-7.5$. The observations have a 2.2 arcsec resolution in band 3 and a 0.9 arcsec resolution in band 6, and are optimized to detect extended emission around the QSO. We detect an interacting, tidally disrupted companion both in CII peaking at $z 6.332$, and in continuum, stretching on scales up to 20 kpc from the quasar, with a knotty morphology. The higher velocity dispersion in the direction of the companion emission and the complex morphology of the tidally stretched galaxy suggest a possible ongoing or future merger. For the newly detected companion, we derive the range of the dust mass dust M_ and of the star formation rate M_ obtained from the modelling of its cold dust spectral energy distribution. This shows that both the QSO and its companion are gas-rich and that a major merger may be at the origin of the boosted star formation. This close interacting companion is undetected by deep JWST imaging observations, showing the effectiveness of ALMA in detecting dust-obscured sources, especially in the vicinity of optically bright quasars. We also detect a broad blueshifted component in the CII spectrum, which we interpret as a gaseous outflow for which we estimate a mass outflow rate in the range $ M out M_ $. J0100+2802 was recently found to reside in a strong overdensity, however this close companion remained undetected by both previous higher resolution ALMA observations and by JWST-NIRCAM imaging. Our results highlight the importance of deep medium-resolution ALMA observations for the study of QSOs and their environment in the Epoch of Reionisation.

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Hyperion

Tripodi,

Scholtz,

Maiolino

et al. 2024

A&A

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Dynamical modelling and the origin of gas turbulence in z ∼ 4.5 galaxies

Roman-Oliveira,

Rizzo,

Fraternali

2024

A&A

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In recent years, a growing number of regularly rotating galaxy discs have been found at z geq 4. Such systems provide us with the unique opportunity to study the properties of dark matter (DM) halos at these early epochs, the turbulence within the interstellar medium and the evolution of scaling relations. Here, we investigate the dynamics of four gas discs in galaxies at z sim 4.5 observed with ALMA in the CII 158 mu m fine-structure line. We aim to derive the structural properties of the gas, stars and DM halos of the galaxies and to study the mechanisms driving the turbulence in high- z discs. We decomposed the rotation curves into baryonic and DM components within the extent of the CII discs, that is, 3 to 5 kpc. Furthermore, we used the gas velocity dispersion profiles as a diagnostic tool in investigating the mechanisms driving the turbulence in the discs. We obtain total stellar, gas and DM masses in the ranges of $ (M/M_ odot = 10.3 - 11.0$, $9.8 - 11.3$, and $11.2 - 13.3$, respectively. We find dynamical evidence in all four galaxies for the presence of compact stellar components conceivably, stellar bulges. The turbulence present in the galaxies appears to be primarily driven by stellar feedback, negating the necessity for large-scale gravitational instabilities. Finally, we investigate the position of our galaxies in the context of local scaling relations, in particular the stellar-to-halo mass and Tully-Fisher analogue relations.

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Hyperion

Tripodi,

Feruglio,

Fiore

et al. 2024

A&A

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We used low- to high-frequency ALMA observations to investigate the cold gas and dust in ten quasistellar objects (QSOs) at $z 6$. Our analysis of the CO(6-5) and CO(7-6) emission lines in the selected QSOs provided insights into their molecular gas masses, which average around M_ This is consistent with typical values for high-redshift QSOs. Proprietary and archival ALMA observations in bands 8 and 9 enabled precise constraints on the dust properties and star formation rate (SFR) of four QSOs in our sample for the first time. The examination of the redshift distribution of dust temperatures revealed a general trend of increasing dust $ with redshift, which agrees with theoretical expectations. In contrast, our investigation of the dust emissivity index indicated a generally constant value with redshift, suggesting shared dust properties among sources. We computed a mean cold dust spectral energy distribution considering all ten QSOs that offers a comprehensive view of the dust properties of high-$z$ QSOs. The QSOs marked by a more intense growth of the supermassive black hole (HYPERION QSOs) showed lower dust masses and higher gas-to-dust ratios on average, but their $ H_2$ gas reservoirs are consistent with those of other QSOs at the same redshift. The observed high SFR in our sample yields high star formation efficiencies and thus very short gas depletion timescales ($ dep $ Gyr). Beyond supporting the paradigm that high-$z$ QSOs reside in highly star-forming galaxies, our findings portrayed an interesting evolutionary path at $z>6$. Our study suggests that QSOs at $z 6$ are undergoing rapid galaxy growth that might be regulated by strong outflows. In the BH -M_ dyn $ plane, our high-$z$ QSOs lie above the relation measured locally. Their inferred evolutionary path shows a convergence toward the massive end of the local relation, which supports the idea that they are candidate progenitors of local massive galaxies. The observed pathway involves intense black hole growth followed by substantial galaxy growth, in contrast with a symbiotic growth scenario. The evidence of a stellar bulge in one of the QSOs of the sample is further aligned with that typical of local massive galaxies.

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Dynamical signature of a stellar bulge in a quasar-host galaxy at z ≃ 6

Cited by 5 publications

References 43 publications

Hyperion

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Dynamical modelling and the origin of gas turbulence in z ∼ 4.5 galaxies

Hyperion

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