9 research outputs found
The Fate of the Interstellar Medium in Early-type Galaxies. II. Observational Evidence for Morphological Quenching
The mechanism by which galaxies stop forming stars and get rid of their
interstellar medium (ISM) remains elusive. Here, we study a sample of more than
two thousand elliptical galaxies in which dust emission has been detected. This
is the largest sample of such galaxies ever analysed. We infer the timescale
for removal of dust in these galaxies and investigate its dependency on
physical and environmental properties. We obtain a dust removal timescale in
elliptical galaxies of = 2.26 0.18 Gyr, corresponding to a
half-life time of 1.57 0.12 Gyr. This timescale does not depend on
environment, stellar mass or redshift. We observe a departure of dusty
elliptical galaxies from the star formation rate vs. dust mass relation. This
is caused by the star-formation rates declining faster than the dust masses and
indicates that there exists an internal mechanism, which affects star
formation, but leaves the ISM intact. Morphological quenching together with
ionisation or outflows caused by older stellar populations (supernova type Ia
or planetary nebulae) are consistent with these observations.Comment: 10 pages, 3 figures, 2 tables, accepted for publication in Ap
Distinct Modulation of Spontaneous and GABA-Evoked Gating by Flurazepam Shapes Cross-Talk Between Agonist-Free and Liganded GABAA Receptor Activity
GABAA receptors (GABAARs) play a crucial inhibitory role in the CNS. Benzodiazepines (BDZs) are positive modulators of specific subtypes of GABAARs, but the underlying mechanism remains obscure. Early studies demonstrated the major impact of BDZs on binding and more recent investigations indicated gating, but it is unclear which transitions are affected. Moreover, the upregulation of GABAAR spontaneous activity by BDZs indicates their impact on receptor gating but the underlying mechanisms remain unknown. Herein, we investigated the effect of a BDZ (flurazepam) on the spontaneous and GABA-induced activity for wild-type (WT, α1β2γ2) and mutated (at the orthosteric binding site α1F64) GABAARs. Surprisingly, in spite of the localization at the binding site, these mutations increased the spontaneous activity. Flurazepam (FLU) upregulated this activity for mutants and WT receptors to a similar extent by affecting opening/closing transitions. Spontaneous activity affected GABA-evoked currents and is manifested as an overshoot after agonist removal that depended on the modulation by BDZs. We explain the mechanism of this phenomenon as a cross-desensitization of ligand-activated and spontaneously active receptors. Moreover, due to spontaneous activity, FLU-pretreatment and co-application (agonist + FLU) protocols yielded distinct results. We provide also the first evidence that GABAAR may enter the desensitized state in the absence of GABA in a FLU-dependent manner. Based on our data and model simulations, we propose that FLU affects agonist-induced gating by modifying primarily preactivation and desensitization. We conclude that the mechanisms of modulation of spontaneous and ligand-activated GABAAR activity concerns gating but distinct transitions are affected in spontaneous and agonist-evoked activity
A dusty, normal galaxy in the epoch of reionization
Candidates for the modest galaxies that formed most of the stars in the early
universe, at redshifts , have been found in large numbers with extremely
deep restframe-UV imaging. But it has proved difficult for existing
spectrographs to characterise them in the UV. The detailed properties of these
galaxies could be measured from dust and cool gas emission at far-infrared
wavelengths if the galaxies have become sufficiently enriched in dust and
metals. So far, however, the most distant UV-selected galaxy detected in dust
emission is only at , and recent results have cast doubt on whether
dust and molecules can be found in typical galaxies at this early epoch. Here
we report thermal dust emission from an archetypal early universe star-forming
galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and
determine its redshift to be from a spectroscopic detection of
the Ly{\alpha} break. A1689-zD1 is representative of the star-forming
population during reionisation, with a total star-formation rate of about
12M yr. The galaxy is highly evolved: it has a large stellar
mass, and is heavily enriched in dust, with a dust-to-gas ratio close to that
of the Milky Way. Dusty, evolved galaxies are thus present among the fainter
star-forming population at , in spite of the very short time since they
first appeared.Comment: Nature in press. 14 pages, 10 figures, including methods sectio