35,310 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 SAMI Galaxy Survey: Unveiling the nature of kinematically offset active galactic nuclei
We have observed two kinematically offset active galactic nuclei (AGN), whose
ionised gas is at a different line-of-sight velocity to their host galaxies,
with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas
kinematics very different to the stellar kinematics, indicating a recent merger
or accretion event. We demonstrate that the star formation associated with this
event was triggered within the last 100 Myr. The other galaxy shows simple disc
rotation in both gas and stellar kinematics, aligned with each other, but in
the central region has signatures of an outflow driven by the AGN. Other than
the outflow, neither galaxy shows any discontinuity in the ionised gas
kinematics at the galaxy's centre. We conclude that in these two cases there is
no direct evidence of the AGN being in a supermassive black hole binary system.
Our study demonstrates that selecting kinematically offset AGN from
single-fibre spectroscopy provides, by definition, samples of kinematically
peculiar objects, but IFS or other data are required to determine their true
nature.Comment: MNRAS accepted. 14 pages, 11 figure
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