110 research outputs found
The Mean Ultraviolet Spectrum of a Representative Sample of Faint z~3 Lyman Alpha Emitters
We discuss the rest-frame ultraviolet emission line spectra of a large (~100)
sample of low luminosity redshift z~3.1 Lyman alpha emitters (LAEs) drawn from
a Subaru imaging survey in the SSA22 survey field. Our earlier work based on
smaller samples indicated that such sources have high [OIII]/[OII] line ratios
possibly arising from a hard ionising spectrum that may be typical of similar
sources in the reionisation era. With optical spectra secured from VLT/VIMOS,
we re-examine the nature of the ionising radiation in a larger sample using the
strength of the high ionisation diagnostic emission lines of CIII]1909,
CIV1549, HeII1640, and OIII]1661,1666 in various stacked subsets. Our analysis
confirms earlier suggestions of a correlation between the strength of Ly-alpha
and CIII] emission and we find similar trends with broad band UV luminosity and
rest-frame UV colour. Using various diagnostic line ratios and our stellar
photoionisation models, we determine both the gas phase metallicity and
hardness of the ionisation spectrum characterised by xi_ion - the number of
Lyman continuum photons per UV luminosity. We confirm our earlier suggestion
that xi_ion is significantly larger for LAEs than for continuum-selected Lyman
break galaxies, particularly for those LAEs with the faintest UV luminosities.
We briefly discuss the implications for cosmic reionisation if the metal-poor
intensely star-forming systems studied here are representative examples of
those at much higher redshift.Comment: 15 pages, 9 figures. Accepted for publication in MNRA
The ab initio model potential method with the spin-free relativistic scheme by eliminating small components Hamiltonian
A spectroscopic search for AGN activity in the reionization era
The ubiquity of Lyman alpha (Ly) emission in a sample of four bright
[O III]-strong star-forming galaxies with redshifts above 7 has led to the
suggestion that such luminous sources represent a distinct population compared
to their fainter, more numerous, counterparts. The presence of Ly
emission within the reionization era could indicate that these sources created
early ionized bubbles due to their unusually strong radiation, possibly due to
the presence of active galactic nuclei. To test this hypothesis we have secured
long integration spectra with XSHOOTER on the VLT for three 7 sources
selected to have similar luminosities and prominent excess fluxes in the IRAC
3.6 or 4.5m band, usually attributed to strong [O III] emission. We
secured additional spectroscopy for one of these galaxies at =7.15 using
MOSFIRE at the Keck telescope. For this, the most well-studied source in our
sample with the strongest IRAC excess, we detect prominent nebular emission
from He II and NV indicative of a non-thermal source. For the other two sources
at =6.81 and =6.85, for which no previous optical/near infrared
spectroscopy was initially available, Ly is seen in one and CIII]
emission in the other. Although a modest sample, our results further support
the hypothesis that the phenomenon of intense [O III] emission is associated
preferentially with sources lying in early ionized bubbles. However, even
though one of our sources at =7.15 clearly indicates the presence of
non-thermal radiation, such ionized bubbles may not uniquely arise in this
manner. We discuss the unique advantages of extending such challenging
diagnostic studies with JWST.Comment: 11 pages, 7 figures, submitted to Ap
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