2018A&A...616A..60O


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.10CEST02:34:56

2018A&A...616A..60O - Astronomy and Astrophysics, volume 616A, 60-60 (2018/8-1)

Puzzling Lyman-alpha line profiles in green pea galaxies.

ORLITOVA I., VERHAMME A., HENRY A., SCARLATA C., JASKOT A., OEY M.S. and SCHAERER D.

Abstract (from CDS):


Context. The Lyman-alpha (Lyα) line of hydrogen is of prime importance for detecting galaxies at high redshift. For a correct data interpretation, numerical radiative transfer models are necessary due to Lyα resonant scattering off neutral hydrogen atoms.
Aims. Recent observations have discovered an escape of ionizing Lyman-continuum radiation from a population of compact, actively star-forming galaxies at redshift z∼0.2-0.3, also known as "green peas". For the potential similarities with high-redshift galaxies and impact on the reionization of the universe, we study the green pea Lyα spectra, which are mostly double-peaked, unlike in any other galaxy sample. If the double peaks are a result of radiative transfer, they can be a useful source of information on the green pea interstellar medium and ionizing radiation escape.
Methods. We select a sample of twelve archival green peas and we apply numerical radiative transfer models to reproduce the observed Lyα spectral profiles, using the geometry of expanding, homogeneous spherical shells. We use ancillary optical and ultraviolet data to constrain the model parameters, and we evaluate the match between the models and the observed Lyα spectra. As a second step, we allow all the fitting parameters to be free, and examine the agreement between the interstellar medium parameters derived from the models and those from ancillary data.
Results. The peculiar green pea double-peaked Lyα line profiles are not correctly reproduced by the constrained shell models. Conversely, unconstrained models fit the spectra, but parameters derived from the best-fitting models are not in agreement with the ancillary data. In particular: 1) the best-fit systemic redshifts are larger by 10-250km/s than those derived from optical emission lines; 2) the double-peaked Lyα profiles are best reproduced with low-velocity (≤150km/s) outflows that contradict the observed ultraviolet absorption lines of low-ionization-state elements with characteristic velocities as large as 300km/s; and 3) the models need to consider intrinsic Lyα profiles that are on average three times broader than the observed Balmer lines.
Conclusions. Differences between the modelled and observed velocities are larger for targets with prominent Lyα blue peaks. The blue peak position and flux appear to be connected to low column densities of neutral hydrogen, leading to Lyα and Lyman-continuum escape. This is at odds with the kinematic origin of the blue peak in the homogeneous shell models. Additional modelling is needed to explore alternative geometries such as clumpy media and non-recombination Lyα sources to further constrain the role and significance of the Lyα double peaks.

Abstract Copyright: © ESO 2018

Journal keyword(s): radiative transfer - line: profiles - ultraviolet: galaxies - galaxies: ISM - galaxies: starburst

Simbad objects: 12

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Number of rows : 12

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 SHOC 148 Sy1 03 03 21.4140573561 -07 59 23.198200042     19.61     ~ 24 0
2 SDSS J081552.00+215623.6 EmG 08 15 51.9998642751 +21 56 23.654686991           ~ 15 0
3 SDSS J091113.34+183108.1 Q? 09 11 13.3463735767 +18 31 08.195621007           ~ 16 0
4 LARS 14 EmG 09 26 00.4041863336 +44 27 36.112149583           ~ 54 0
5 SDSS J105330.82+523752.8 Q? 10 53 30.8078248454 +52 37 52.791228755           ~ 17 0
6 SHOC 333 Q? 11 33 03.7903352741 +65 13 41.383553219           ~ 22 0
7 SDSS J113722.14+352426.6 EmG 11 37 22.1365215852 +35 24 26.609901733           ~ 15 0
8 SDSS J121903.98+152608.5 EmG 12 19 03.9837736479 +15 26 08.534277420           ~ 21 0
9 SDSS J124423.37+021540.4 EmG 12 44 23.376 +02 15 40.46           ~ 19 0
10 SDSS J124834.63+123402.9 Q? 12 48 34.6371259178 +12 34 02.983896253           ~ 15 0
11 SDSS J142405.72+421646.3 EmG 14 24 05.7326459184 +42 16 46.261788537           ~ 14 0
12 LIRAS J145735.11+223202.4 AGN 14 57 35.1471572321 +22 32 01.902381520           ~ 20 0

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2020.07.10-02:34:56

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