5 research outputs found
To See or Not to See a Galaxy? That is the Question
``When did the first galaxies form?'' is still one of the greatest unanswered
questions in astronomy. Theory and current stellar population models imply that
the first galaxies formed at least at z=14-15. Yet, the highest redshift galaxy
to have been securely confirmed remains GN-z11, at z11. The galaxy
``HD1'' was recently proposed to be a z=13.27 galaxy based on its potential
Lyman break and tentative [O III] 88 {\mu}m detection with ALMA. We hereby aim
to test this scenario with new ALMA Band 4, DDT observations of what would be
the [C II] 158 {\mu}m emission, if HD1 is at z13.27. We carefully analyse
the new ALMA Band 4 observations as well as re-analysing the existing ALMA Band
6 data on the source to determine the proposed redshift. We find a tentative
feature in the Band 4 data that is spatially offset by 1.7" and
spectrally offset by 190 km s-1 from the previously-reported ``[O
III] 88 {\mu}m'' feature. Through various statistical tests, we demonstrate
that these tentative features are fully consistent with being random noise
features. The chances of finding a noise peak of the same significance as the
tentative [C II] and [O III] features are 50\% and 100\%, respectively. Given
the noise properties of the ALMA data, we recover at least a 50\% chance of
finding two, matched noise peaks that are spatially and
spectrally offset by 10 kpc and 1000 km s-1. We conclude that we are more
likely to be recovering noise features than both [O III] and [C II] emission
from a source at . Although we find no evidence of a
galaxy, we cannot entirely rule out this scenario. Non-detections are also
possible for a source with a low interstellar gas-phase metallicity
and density. Determining where and exactly what type of galaxy HD1 is, will now
likely require JWST/NIRSpec spectroscopy.Comment: Submitted to A&A, 9 pages, 6 figures
A solar metallicity galaxy at 7? Detection of the [N II] 122 m and [O III] 52 m lines
We present the first detection of the [N II] 122 m and [O III] 52 m
lines for a reionisation-epoch galaxy. Based on these lines and previous [C II]
158 m and [O III] 88 m measurements, we estimate an electron density
of 500 cm and a gas-phase metallicity for A1689-zD1, a gravitationally-lensed, dusty galaxy at = 7.133.
Other measurements or indicators of metallicity so far in galaxy ISMs at 6 are typically an order of magnitude lower than this. The unusually
high metallicity makes A1689-zD1 inconsistent with the fundamental metallicity
relation, although there is likely significant dust obscuration of the stellar
mass, which may partly resolve the inconsistency. Given a solar metallicity,
the dust-to-metals ratio is a factor of several lower than expected, hinting
that galaxies beyond 7 may have lower dust formation efficiency.
Finally, the inferred nitrogen enrichment compared to oxygen, on which the
metallicity measurement depends, indicates that star-formation in the system is
older than about 250 Myr, pushing the beginnings of this galaxy to 10.Comment: 10 pages, 7 figures; submitted to MNRA
Extreme damped Lyman- absorption in young star-forming galaxies at
The onset of galaxy formation is thought to be initiated by the infall of
neutral, pristine gas onto the first protogalactic halos. However, direct
constraints on the abundance of neutral atomic hydrogen (HI) in galaxies have
been difficult to obtain at early cosmic times. Here we present spectroscopic
observations with JWST of three galaxies at redshifts , about
Myr after the Big Bang, that show strong damped Lyman-
absorption ( cm) from HI in their local
surroundings, an order of magnitude in excess of the Lyman- absorption
caused by the neutral intergalactic medium at these redshifts. Consequently,
these early galaxies cannot be contributing significantly to reionization, at
least at their current evolutionary stages. Simulations of galaxy formation
show that such massive gas reservoirs surrounding young galaxies so early in
the history of the universe is a signature of galaxy formation in progress.Comment: Submitte
Strong damped Lyman-α absorption in young star-forming galaxies at redshifts 9 to 11
Primordial neutral atomic gas, mostly composed of hydrogen, is the raw material for star formation in galaxies. However, there are few direct constraints on the amount of neutral atomic hydrogen (HÂ
i
) in galaxies at early cosmic times. We analyzed James Webb Space Telescope (JWST) near-infrared spectroscopy of distant galaxies, at redshifts ≳8. From a sample of 12 galaxies, we identified three that show strong damped Lyman-α absorption due to HÂ
i
in their local surroundings. The galaxies are located at spectroscopic redshifts of 8.8, 10.2, and 11.4, corresponding to 400 to 600 million years after the Big Bang. They have HÂ
i
column densities ≳10
22
cm
−2
, which is an order of magnitude higher than expected for a fully neutral intergalactic medium, and constitute a gas-rich population of young star-forming galaxies.</p