Are we seeing accretion flows in a 250 kpc Ly<i>α</i> halo at <i>z = 3</i>?

Vernet, J.; Lehnert, M. D.; Breuck, C. De; Villar-Martín, M.; Wylezalek, Dominika; Falkendal, Theresa; Drouart, Guillaume; Kolwa, Sthabile; Humphrey, A.; Venemans, Bram; Boulanger, F.

doi:10.1051/0004-6361/201730865

Cited by 32 publications

(26 citation statements)

References 34 publications

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“…Their emission can be powered by the UV radiation from the galaxy but also through the localized dissipation of turbulent energy and through losses of their gravitational potential energy as they fall into the halo. This may have already been observed in Lyα (e.g., Cantalupo et al 2014; MUSE on the ESO/VLT within the context of our scenario (see Borisova et al 2016;Fumagalli et al 2016;Vernet et al 2017).…”

Section: Nature Of Flows Into Galaxies: Observational Testssupporting

confidence: 72%

Are cosmological gas accretion streams multiphase and turbulent?

Cornuault¹,

Lehnert²,

Boulanger³

et al. 2018

A&A

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Simulations of cosmological filamentary accretion reveal flows ("streams") of warm gas, T∼10 4 K, which are efficient in bringing gas into galaxies. We present a phenomenological scenario where gas in such flows -if it is shocked as it enters the halo as we assume -become biphasic and, as a result, turbulent. We consider a collimated stream of warm gas that flows into a halo from an over dense filament of the cosmic web. The post-shock streaming gas expands because it has a higher pressure than the ambient halo gas, and fragments as it cools. The fragmented stream forms a two phase medium: a warm cloudy phase embedded in hot post-shock gas. We argue that the hot phase sustains the accretion shock. During fragmentation, a fraction of the initial kinetic energy of the infalling gas is converted into turbulence among and within the warm clouds. The thermodynamic evolution of the post-shock gas is largely determined by the relative timescales of several processes. These competing timescales characterize the cooling, the expansion of the post-shock gas, the amount of turbulence in the clouds, and the dynamical time of the halo. We expect the gas to become multiphase when the gas cooling and dynamical times are of the same order-of-magnitude. In this framework, we show that this occurs in the important mass range of M halo ∼10 11 to 10 13 M , where the bulk of stars have formed in galaxies. Due to expansion and turbulence, gas accreting along cosmic web filaments may eventually loose coherence and mix with the ambient halo gas. Through both the phase separation and "disruption" of the stream, the accretion efficiency onto a galaxy in a halo dynamical time is lowered. De-collimating flows make the direct interaction between galaxy feedback and accretion streams more likely, thereby further reducing the overall accretion efficiency. As we discuss, moderating the gas accretion efficiency through these mechanisms may help to alleviate a number of significant challenges in theoretical galaxy formation.

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Section: Nature Of Flows Into Galaxies: Observational Testssupporting

confidence: 72%

Are cosmological gas accretion streams multiphase and turbulent?

Cornuault¹,

Lehnert²,

Boulanger³

et al. 2018

A&A

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“…Although there is evidence for filamentary gas accretion into MRC 0943-242, the filamentary material appears to be dusty and metal-enriched (Gullberg et al 2016) and thus is likely to have been stripped from companion galaxies, rather than being low metallicity gas from the cosmic web. In fact, there appears to be no convincing evidence for smooth accretion of pristine gas in MRC 0943-242, although we cannot rule out the presence of faint, filamentary accretion structures of the kind detected near the z = 3.1 radio galaxy MRC 0316-257 (Vernet et al 2017).…”

Section: On the Evolutionary Status Of Mrc 0943-242mentioning

confidence: 64%

The MUSE 3D view of feedback in a high-metallicity radio galaxy at z = 2.9

Silva

Humphrey

Lagos

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present a detailed study of the kinematic, chemical and excitation properties of the giant Lyα emitting nebula and the giant H i absorber associated with the z = 2.92 radio galaxy MRC 0943-242, using spectroscopic observations from VLT/MUSE, VLT/X-SHOOTER and other instruments. Together, these data provide a wide range of restframe wavelength (765Å -6378Å at z = 2.92) and 2D spatial information. We find clear evidence for jet gas interactions affecting the kinematic properties of the nebula, with evidence for both outflows and inflows being induced by radio-mode feedback. We suggest that the regions of relatively lower ionization level, spatially correlated with the radio hotspots, may be due to localised compression of photoionized gas by the expanding radio source, thereby lowering the ionization parameter, or due to a contribution from shock-heating. We find that photoionization of super-solar metallicity gas (Z/Z = 2.1) by an AGN-like continuum (α=-1.0) at a moderate ionization parameter (U = 0.018) gives the best overall fit to the complete X-SHOOTER emission line spectrum. We identify a strong degeneracy between column density and Doppler parameter such that it is possible to obtain a reasonable fit to the H i absorption feature across the range log N(H i/cm −2 ) = 15.20 and 19.63, with the two best-fitting occurring near the extreme ends of this range. The extended H i absorber is blueshifted relative to the emission line gas, but shows a systematic decrease in blueshift towards larger radii, consistent with a large scale expanding shell.

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“…It seems particularly plausible that the large-scale gas halos of high redshift quasars such as these would have low gas metallicity, since the central galaxy is expected to be fed by cold streams of pristine or very low metallicity gas from the cosmic web (e.g. Goerdt et al 2015;Vernet et al 2017). However, observations of the halos of high-z quasars appear to show such halos are already polluted with metals (e.g., Humphrey et al 2013;Prochaska et al 2013).…”

Section: On the Extreme Lyα/heii Ratios Around Z >3 Quasarsmentioning

confidence: 99%

Photoionization models for extreme Lyα λ1216 and Hell λ1640 line ratios in quasar halos, and PopIII vs. AGN diagnostics

Humphrey

Villar-Martı́n

Binette

et al. 2018

A&A

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Aims. We explore potential mechanisms to produce extremely high Lyα/HeII flux ratios, or to enhance the observed number of Lyα photons per incident ionizing photon, in extended AGN-photoionized nebulae at high-redshift. Methods. We compute models to simulate, in the low density regime, photoionization of interstellar gas by the radiation field of a luminous AGN. We explore the impact of ionization parameter, gas metallicity, ionizing spectrum, electron energy distribution, and cloud viewing angle on the relative fluxes of Lyα, HeII and other lines, and on the observed number of Lyα photons per incident ionizing photon. We compare our model results with recent observations of quasar Lyα halos at z∼3.5. Results. Low ionization parameter, a relatively soft or filtered ionizing spectrum, low gas metallicity, κ-distributed electron energies, or reflection of Lyα photons by neutral hydrogen can all result in significantly enhanced Lyα relative to other lines (≥ 10 %), with log Lyα/HeII reaching values of up to 4.6. In the cases of low gas metallicity, reflection by HI, or a hard or filtered ionizing spectrum, the observed number of Lyα photons per incident ionizing photon is itself significantly enhanced above the nominal Case B value of 0.66 due to collisional excitation, reaching values as high as 5.3 in an 'extreme case' model which combines several of these effects. We find that at low gas metallicity (e.g. Z/Z ⊙ =0.1) the production of Lyα photons is predominantly via collisional excitation rather than by recombination. In addition, we find that the collisional excitation of Lyα becomes much more efficient if the ionizing continuum spectrum has been pre-filtered through an optically thin screen of gas closer to the AGN (e.g., by a wide-angle, feedbackdriven outflow.) We also show that the Lyα and HeII emission line ratios of the z∼3.5 quasars studied by Borisova et al. (2016) are consistent with AGN-photoionization of gas with moderate to low metallicity and/or low ionization parameter, without requiring exotic ionization/excitation mechanisms such as strong line-transfer effects. In addition, we present a set of UV-optical diagnostic diagrams to distinguish between photoionization by Pop III stars and photoionization by an AGN.

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Are we seeing accretion flows in a 250 kpc Lyα halo at z = 3?

Cited by 32 publications

References 34 publications

Are cosmological gas accretion streams multiphase and turbulent?

Are cosmological gas accretion streams multiphase and turbulent?

The MUSE 3D view of feedback in a high-metallicity radio galaxy at z = 2.9

Photoionization models for extreme Lyα λ1216 and Hell λ1640 line ratios in quasar halos, and PopIII vs. AGN diagnostics

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