WHAT IS THE PHYSICAL ORIGIN OF STRONG Lyα EMISSION? I. DEMOGRAPHICS OF Lyα EMITTER STRUCTURES

Shibuya, Tetsuo; Ouchi, Masami; Nakajima, Kengo; Yuma, Suraphong; Hashimoto, T.; Shimasaku, Kazuhiro; Mori, Masao; Umemura, Masayuki

doi:10.1088/0004-637x/785/1/64

Cited by 53 publications

(78 citation statements)

References 84 publications

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“…was about 0.6, suggesting the presence of elongated structures due to merging activity or clumps of star formation. However, Shibuya et al (2014) found that the LAEs in their sample with EW(Lyα) > 100 Å tended to be characterized by a small ellipticity both in the rest-frame UV and optical. This is supported by the theoretical results of Verhamme et al (2012) and Laursen et al (2009), which showed that Lyα photons could more easily escape from face-on disks (ellipticity ∼0), generally characterized by low column density of HI along the line of sight.…”

Section: Ellipticity and Clumpinessmentioning

confidence: 86%

“…Late-stage mergers could instead be characterized by turbulent star-formation episodes and, as a consequence, patchy Lyα emissions, just like the ones observed within one galaxy with numerous star-forming regions. This may indicate that the clumpy Lyα emitting galaxies observed at high redshift (Bond et al 2012;Gronwall et al 2011;Shibuya et al 2014) could also be experiencing early-stage merging events (Cooke et al 2010). Of the twelve LARS galaxies, whose continuum morphologies are consistent with them being merging systems, six are LAEs.…”

Section: Local Universe Larsmentioning

confidence: 97%

“…Of the twelve LARS galaxies, whose continuum morphologies are consistent with them being merging systems, six are LAEs. This does not mean that every observed LAE must necessarily be a merging system (Shibuya et al 2014;Law et al 2012). However, we can not verify the claim by Shibuya et al (2014) that mergers are rare in LAEs with EW(Lyα) > 100 Å, because LARS galaxies all present lower Lyα equivalent widths.…”

Section: Local Universe Larsmentioning

confidence: 99%

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The Lyman alpha reference sample

Guaita

Melinder

Hayes

et al. 2015

A&A

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Context. The transport of Lyα photons in galaxies is a complex process and the conditions under which Lyα photons manage to escape from certain galaxies is still under investigation. The Lyman alpha reference sample (LARS) is a sample of 14 local starforming galaxies, designed to study Lyα in detail and relate it to rest-frame UV and optical emission. Aims. With the aim of identifying rest-frame UV and optical properties, which are typical of Lyα emitters (LAEs, galaxies with EW(Lyα) > 20 Å) at both low and high redshift, we investigated the morphological properties of the LARS galaxies, in particular the ones that exhibit intense Lyα radiation. Methods. We measured sizes and morphological parameters in the continuum, Lyα, and Hα images. We studied morphology by using the Gini coefficient vs. M20 and asymmetry vs. concentration diagrams. We then simulated LARS galaxies at z ∼ 2 and 5.7, performing the same morphological measurements. We also investigated the detectability of LARS galaxies in current deep field observations. The subsample of LAEs within LARS (LARS-LAEs) was stacked to provide a comparison to stacking studies performed at high redshift. Results. LARS galaxies have continuum size, stellar mass, and rest-frame absolute magnitude typical of Lyman break analogues in the local Universe and also similar to 2 < z < 3 star-forming galaxies and massive LAEs. LARS optical morphology is consistent with the one of merging systems, and irregular or starburst galaxies. For the first time we quantify the morphology in Lyα images: even if a variety of intrinsic conditions of the interstellar medium can favour the escape of Lyα photons, LARS-LAEs appear small in the continuum, and their Lyα is compact. LARS galaxies tend to be more extended in Lyα than in the rest-frame UV. It means that Lyα photons escape by forming haloes around HII regions of LARS galaxies. Conclusions. The stack of LARS-LAE Lyα images is peaked in the centre, indicating that the conditions, which make a galaxy an LAE, tend to produce a concentrated surface brightness profile. On the other hand, the stack of all LARS galaxies is shallower and more extended. This can be caused by the variety of dust and HI amount and distribution, which produces a more complex, patchy, and extended profile, like the one observed for Lyman break galaxies that can contribute to the stack. We cannot identify a single morphological property that controls whether a galaxy emits a net positive Lyα flux. However, the LARS-LAEs have continuum properties consistent with merging systems.

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Section: Ellipticity and Clumpinessmentioning

confidence: 86%

Section: Local Universe Larsmentioning

confidence: 97%

Section: Local Universe Larsmentioning

confidence: 99%

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The Lyman alpha reference sample

Guaita

Melinder

Hayes

et al. 2015

A&A

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“…The clear advantage that Lyα photons take of the bipolar outflowing halos of Mrk 1486 to easily escape from this object suggests that the same mechanism may be at work in a large number of highly inclined disk galaxies that are observed at low-z and high-z. This may require a critical review of the strong observational biases in surveys of high-z Lyα-emitting galaxies (as edge-on disk galaxies are also detected as LAEs; Shibuya et al 2014) and the robustness of the viewing angle effect on the Lyα properties of disk galaxies. in the 3D geometry Fig. A.1.…”

Section: Discussionmentioning

confidence: 99%

“…Given the clear advantage Lyα photons take of the outflowing halos of Mrk 1486 to easily escape toward the observer, we may generalize this mechanism to a large number of edge-on disk galaxies. 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: 94%

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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Extended Lymanαhaloes around individual high-redshift galaxies revealed by MUSE

Wisotzki

Bacon

Blaizot

et al. 2016

A&A

306

416

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We report the detection of extended Lyα emission around individual star-forming galaxies at redshifts z = 3−6 in an ultradeep exposure of the Hubble Deep Field South obtained with MUSE on the ESO-VLT. The data reach a limiting surface brightness (1σ) of ∼1 × 10 −19 erg s −1 cm −2 arcsec −2 in azimuthally averaged radial profiles, an order of magnitude improvement over previous narrowband imaging. Our sample consists of 26 spectroscopically confirmed Lyα-emitting, but mostly continuum-faint (m AB > ∼ 27) galaxies. In most objects the Lyα emission is considerably more extended than the UV continuum light. While five of the faintest galaxies in the sample show no significantly detected Lyα haloes, the derived upper limits suggest that this is due to insufficient S/N. Lyα haloes therefore appear to be ubiquitous even for low-mass (∼10 8 −10 9 M ) star-forming galaxies at z > 3. We decompose the Lyα emission of each object into a compact component tracing the UV continuum and an extended halo component, and infer sizes and luminosities of the haloes. The extended Lyα emission approximately follows an exponential surface brightness distribution with a scale length of a few kpc. While these haloes are thus quite modest in terms of their absolute sizes, they are larger by a factor of 5−15 than the corresponding rest-frame UV continuum sources as seen by HST. They are also much more extended, by a factor ∼5, than Lyα haloes around low-redshift star-forming galaxies. Between ∼40% and > ∼ 90% of the observed Lyα flux comes from the extended halo component, with no obvious correlation of this fraction with either the absolute or the relative size of the Lyα halo. Our observations provide direct insights into the spatial distribution of at least partly neutral gas residing in the circumgalactic medium of low to intermediate mass galaxies at z > 3.

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WHAT IS THE PHYSICAL ORIGIN OF STRONG Lyα EMISSION? I. DEMOGRAPHICS OF Lyα EMITTER STRUCTURES

Cited by 53 publications

References 84 publications

The Lyman alpha reference sample

The Lyman alpha reference sample

The Lyman alpha reference sample

Extended Lymanαhaloes around individual high-redshift galaxies revealed by MUSE

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