Inclination dependence of Lyman-<i>α</i>properties in a turbulent disk galaxy

Behrens, Christoph; Braun, H.

doi:10.1051/0004-6361/201424755

Cited by 49 publications

(63 citation statements)

References 33 publications

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“…Its Lyα photometric properties characterize Mrk 1486 as one of the highest Lyα luminosites (L Lyα = 1.11 × 10 42 erg s −1 ), Lyα equivalent widths (EW(Lyα) = 45 Å), and Lyα escape fractions of the LARS sample (fesc(Lyα) = 0.174; Hayes et al 2014). While these properties indicate a very easy escape of Lyα photons from the galaxy, this result clearly contradicts recent numerical simulations that suggest the formation of either a very attenuated Lyα emission line or a pronounced Lyα absorption feature in the spectra of highly inclined low-mass disk galaxies (Laursen & Sommer-Larsen 2007;Laursen et al 2009;Verhamme et al 2012;Behrens & Braun 2014). Based on the calculation of Lyα and UV continuum radiative transfer inside the ISM of high-resolution, dusty, isolated disk simulations, all numerical works have clearly highlighted a strong inclination effect on the Lyα properties of disk galaxies.…”

Section: Introductionmentioning

confidence: 70%

“…Without calling into question the accuracy of the work of Verhamme et al (2012) and Behrens & Braun (2014), the discrepancy observed between the Lyα properties of Mrk 1486 and the simulated galaxies seems to originate in a small difference in the galactic wind properties of these objects. Although the simulated galaxies of Verhamme et al (2012) and Behrens & Braun (2014) exhibit very extended tenuous and ionized outflowing materials from the disk, the galactic winds of Mrk 1486 differ from the simulated ones in that they entrain a higher mass of neutral gas (HI) at large distances from the galaxy disk.…”

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 86%

“…Although the simulated galaxies of Verhamme et al (2012) and Behrens & Braun (2014) exhibit very extended tenuous and ionized outflowing materials from the disk, the galactic winds of Mrk 1486 differ from the simulated ones in that they entrain a higher mass of neutral gas (HI) at large distances from the galaxy disk. These very extended HI outflowing materials from the core of Mrk 1486 may explain why the scattering of Lyα photons toward the observer is more efficient than in the simulated galaxies.…”

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 88%

“…As mentioned above, recent numerical simulations have highlighted the strong dependence of the Lyα properties of disk galaxies on the inclination at which they are observed (Verhamme et al 2012;Behrens & Braun 2014). These results are based on radiative transfer calculations of Lyα and UV continuum photons through high-resolution hydrodynamical simulations of isolated low-mass disk galaxies showing similar physical properties as Mrk 1486 (very inclined disk-like galaxies, same sources of Lyα photons, presence of large-scale galactic winds in the minor axis of the elongated galaxy, a stellar mass M * for the simulated galaxies that is similar or twice as low as the one of Mrk 1486).…”

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 91%

“…In particular, this may explain the origin of very bright Lyα emission lines observed from elongated disk objects at high redshift (Shibuya et al 2014). In conclusion, this mechanism may challenge the strong observational biases in surveys of Lyα-emitting galaxies (as edge-on disk galaxies might also be detected as LAEs) and the robustness of the viewing angle effect on the Lyα properties of disk galaxies (Laursen & Sommer-Larsen 2007;Verhamme et al 2012;Behrens & Braun 2014).…”

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 99%

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The Lyman alpha reference sample

Duval

Östlin

Hayes

et al. 2016

A&A

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Context. Recent numerical simulations suggest that the strength of the Lyman alpha (Lyα) line of star-forming disk galaxies strongly depends on the inclination at which they are observed: from edge-on to face-on, we expect to see a change from a strongly attenuated Lyα line to a strong Lyα emission line. Aims. We aim to understand how a strong Lyα emission line is able to escape from the low-redshift highly inclined (edge-on) disk galaxy Mrk 1486 (z ∼ 0.0338). To our knowledge, this work is the first observational study of Lyα transport inside an edge-on disk galaxy. Methods. Using a large set of HST imaging and spectroscopic data, we investigated the interstellar medium (ISM) structure and the dominant source of Lyα radiation inside Mrk 1486. Moreover, using a 3D Monte Carlo Lyα radiation transfer code, we studied the radiative transfer of Lyα and UV continuum photons inside a 3D geometry of neutral hydrogen (HI) and dust that models the ISM structure at the galaxy center. Our numerical simulations predicted the Lyα line profile that we then compared to the one observed in the HST/COS spectrum of Mrk 1486. Results. While a pronounced Lyα absorption line emerges from the disk of Mrk 1486, very extended Lyα structures are observed at large radii from the galaxy center: a large Lyα-halo and two very bright Lyα regions located slightly above and below the disk plane. The analysis of IFU Hα spectroscopic data of Mrk 1486 indicates the presence of two bipolar outflowing halos of HI gas at the same location as these two bright Lyα regions. Comparing different diagnostic diagrams (such as [OIII] 5007 /Hβ versus [OI] 6300 /Hα) to photo-and shock-ionization models, we find that the Lyα production of Mrk 1486 is dominated by photoionization inside the galaxy disk. From this perspective, our numerical simulations succeed in reproducing the strength and shape of the observed Lyα emission line of Mrk 1486 by assuming a scenario in which the Lyα photons are produced inside the galaxy disk, travel along the outflowing halos, and scatter on cool HI materials toward the observer. Conclusions. Extended bipolar galactic winds are frequently observed from star-forming disk galaxies. Given the advantage Lyα photons take of such outflowing HI materials to easily escape from Mrk 1486, this mechanism may explain the origin of strong Lyα emission lines frequently observed from highly inclined galaxies at high-redshift. This therefore challenges the robustness of the expected viewing-angle effect on the Lyα properties of star-forming disk galaxies.

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Section: Introductionmentioning

confidence: 70%

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 86%

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 88%

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 91%

Section: Hi and Dust Clumpiness Inside The Disk And The Outflowing Halosmentioning

confidence: 99%

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The Lyman alpha reference sample

Duval

Östlin

Hayes

et al. 2016

A&A

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The Lyman alpha reference sample

Herenz

Gruyters

Orlitová

et al. 2016

A&A

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We present integral field spectroscopic observations with the Potsdam Multi-Aperture Spectrophotometer of all 14 galaxies in the z ∼ 0.1 Lyman Alpha Reference Sample (LARS). We produce 2D line-of-sight velocity maps and velocity dispersion maps from the Balmer α (Hα) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Lyα radiation field. We show our kinematic maps that are spatially registered onto the Hubble Space Telescope Hα and Lyman α (Lyα) images. We can conjecture a causal connection between spatially resolved Hα kinematics and Lyα photometry for individual galaxies, however, no general trend can be established for the whole sample. Furthermore, we compute the intrinsic velocity dispersion σ 0 , the shearing velocity v shear , and the v shear /σ 0 ratio from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54 km s −1 median) and low shearing velocities (65 km s −1 median). The v shear /σ 0 values range from 0.5 to 3.2 with an average of 1.5. It is noteworthy that five galaxies of the sample are dispersion-dominated systems with v shear /σ 0 < 1, and are thus kinematically similar to turbulent star-forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Lyα properties, we find that dispersion-dominated systems show higher Lyα equivalent widths and higher Lyα escape fractions than systems with v shear /σ 0 > 1. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Lyα radiation.

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Resonant line transfer in a fog: using Lyman-alpha to probe tiny structures in atomic gas

Grönke

Dijkstra

McCourt

et al. 2017

A&A

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Motivated by observational and theoretical work which both suggest very small scale ( 1 pc) structure in the circumgalactic medium of galaxies and in other environments, we study Lyman-α (Lyα) radiative transfer in an extremely clumpy medium with many "clouds" of neutral gas along the line of sight. While previous studies have typically considered radiative transfer through sightlines intercepting 10 clumps, we explore the limit of a very large number of clumps per sightline (up to fc ∼ 1000). Our main finding is that, for covering factors greater than some critical threshold, a multiphase medium behaves similar to a homogeneous medium in terms of the emergent Lyα spectrum. The value of this threshold depends on both the clump column density and on the movement of the clumps. We estimate this threshold analytically and compare our findings to radiative transfer simulations with a range of covering factors, clump column densities, radii, and motions. Our results suggest that (i) the success in fitting observed Lyα spectra using homogeneous "shell models" (and the corresponding failure of multiphase models) hints towards the presence of very small-scale structure in neutral gas, in agreement within a number of other observations; and (ii) the recurrent problems of reproducing realistic line profiles from hydrodynamical simulations may be due to their inability to resolve small-scale structure, which causes simulations to underestimate the effective covering factor of neutral gas clouds.

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Inclination dependence of Lyman-αproperties in a turbulent disk galaxy

Cited by 49 publications

References 33 publications

The Lyman alpha reference sample

The Lyman alpha reference sample

The Lyman alpha reference sample

Resonant line transfer in a fog: using Lyman-alpha to probe tiny structures in atomic gas

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