LBT observations of compact star-forming galaxies with extremely high
OIII/OII flux ratios: HeI emission-line ratios as diagnostics of Lyman
continuum leakage
Y. Izotov, T. Thuan, and N. Guseva. (2017)cite arxiv:1706.08769Comment: 16 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stx1629
Abstract
We present Large Binocular Telescope spectrophotometric observations of five
low-redshift (z<0.070) compact star-forming galaxies (CSFGs) with extremely
high emission-line ratios O32 = OIII5007/OII3727, ranging from 23 to 43.
Galaxies with such high O32 are thought to be promising candidates for leaking
large amounts of Lyman continuum (LyC) radiation and, at high redshifts, for
contributing to the reionization of the Universe. The equivalent widths
EW(Hbeta) of the Hbeta emission line in the studied galaxies are very high,
~350-520A, indicating very young ages for the star formation bursts, <3 Myr.
All galaxies are characterized by low oxygen abundances 12+logO/H = 7.46 - 7.79
and low masses Mstar~10^6-10^7 Msun, much lower than the Mstar for known
low-redshift LyC leaking galaxies, but probably more typical of the
hypothetical population of low-luminosity dwarf LyC leakers at high redshifts.
A broad Halpha emission line is detected in the spectra of all CSFGs, possibly
related to expansion motions of supernova remnants. Such rapid ionized gas
motions would facilitate the escape of the resonant Ly$\alpha$ emission from
the galaxy. We show that high O32 may not be a sufficient condition for LyC
leakage and propose new diagnostics based on the HeI 3889/6678 and 7065/6678
emission-line flux ratios. Using these diagnostics we find that three CSFGs in
our sample are likely to have density-bounded HII regions and are thus leaking
large amounts of LyC radiation. The amount of leaking LyC radiation is probably
much lower in the other two CSFGs.
Description
[1706.08769] LBT observations of compact star-forming galaxies with extremely high [OIII]/[OII] flux ratios: HeI emission-line ratios as diagnostics of Lyman continuum leakage
%0 Generic
%1 izotov2017observations
%A Izotov, Y. I.
%A Thuan, T. X.
%A Guseva, N. G.
%D 2017
%K Lyc emission escape fraction lines
%R 10.1093/mnras/stx1629
%T LBT observations of compact star-forming galaxies with extremely high
OIII/OII flux ratios: HeI emission-line ratios as diagnostics of Lyman
continuum leakage
%U http://arxiv.org/abs/1706.08769
%X We present Large Binocular Telescope spectrophotometric observations of five
low-redshift (z<0.070) compact star-forming galaxies (CSFGs) with extremely
high emission-line ratios O32 = OIII5007/OII3727, ranging from 23 to 43.
Galaxies with such high O32 are thought to be promising candidates for leaking
large amounts of Lyman continuum (LyC) radiation and, at high redshifts, for
contributing to the reionization of the Universe. The equivalent widths
EW(Hbeta) of the Hbeta emission line in the studied galaxies are very high,
~350-520A, indicating very young ages for the star formation bursts, <3 Myr.
All galaxies are characterized by low oxygen abundances 12+logO/H = 7.46 - 7.79
and low masses Mstar~10^6-10^7 Msun, much lower than the Mstar for known
low-redshift LyC leaking galaxies, but probably more typical of the
hypothetical population of low-luminosity dwarf LyC leakers at high redshifts.
A broad Halpha emission line is detected in the spectra of all CSFGs, possibly
related to expansion motions of supernova remnants. Such rapid ionized gas
motions would facilitate the escape of the resonant Ly$\alpha$ emission from
the galaxy. We show that high O32 may not be a sufficient condition for LyC
leakage and propose new diagnostics based on the HeI 3889/6678 and 7065/6678
emission-line flux ratios. Using these diagnostics we find that three CSFGs in
our sample are likely to have density-bounded HII regions and are thus leaking
large amounts of LyC radiation. The amount of leaking LyC radiation is probably
much lower in the other two CSFGs.
@misc{izotov2017observations,
abstract = {We present Large Binocular Telescope spectrophotometric observations of five
low-redshift (z<0.070) compact star-forming galaxies (CSFGs) with extremely
high emission-line ratios O32 = [OIII]5007/[OII]3727, ranging from 23 to 43.
Galaxies with such high O32 are thought to be promising candidates for leaking
large amounts of Lyman continuum (LyC) radiation and, at high redshifts, for
contributing to the reionization of the Universe. The equivalent widths
EW(Hbeta) of the Hbeta emission line in the studied galaxies are very high,
~350-520A, indicating very young ages for the star formation bursts, <3 Myr.
All galaxies are characterized by low oxygen abundances 12+logO/H = 7.46 - 7.79
and low masses Mstar~10^6-10^7 Msun, much lower than the Mstar for known
low-redshift LyC leaking galaxies, but probably more typical of the
hypothetical population of low-luminosity dwarf LyC leakers at high redshifts.
A broad Halpha emission line is detected in the spectra of all CSFGs, possibly
related to expansion motions of supernova remnants. Such rapid ionized gas
motions would facilitate the escape of the resonant Ly$\alpha$ emission from
the galaxy. We show that high O32 may not be a sufficient condition for LyC
leakage and propose new diagnostics based on the HeI 3889/6678 and 7065/6678
emission-line flux ratios. Using these diagnostics we find that three CSFGs in
our sample are likely to have density-bounded HII regions and are thus leaking
large amounts of LyC radiation. The amount of leaking LyC radiation is probably
much lower in the other two CSFGs.},
added-at = {2017-06-28T07:01:09.000+0200},
author = {Izotov, Y. I. and Thuan, T. X. and Guseva, N. G.},
biburl = {https://www.bibsonomy.org/bibtex/2389f6ec1ee839b8dd3c13886163676fa/miki},
description = {[1706.08769] LBT observations of compact star-forming galaxies with extremely high [OIII]/[OII] flux ratios: HeI emission-line ratios as diagnostics of Lyman continuum leakage},
doi = {10.1093/mnras/stx1629},
interhash = {7a69aaebd49925774bf5b55498f40fcf},
intrahash = {389f6ec1ee839b8dd3c13886163676fa},
keywords = {Lyc emission escape fraction lines},
note = {cite arxiv:1706.08769Comment: 16 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society},
timestamp = {2017-06-28T07:01:09.000+0200},
title = {LBT observations of compact star-forming galaxies with extremely high
[OIII]/[OII] flux ratios: HeI emission-line ratios as diagnostics of Lyman
continuum leakage},
url = {http://arxiv.org/abs/1706.08769},
year = 2017
}