5,849 research outputs found
Retired galaxies: not to be forgotten in the quest of the star formation -- AGN connection
We propose a fresh look at the Main Galaxy Sample of the Sloan Digital Sky
Survey by packing the galaxies in stellar mass and redshift bins. We show how
important it is to consider the emission-line equivalent widths, in addition to
the commonly used emission-line ratios, to properly identify retired galaxies
(i.e. galaxies that have stopped forming stars and are ionized by their old
stellar populations) and not mistake them for galaxies with low-level nuclear
activity. We find that the proportion of star-forming galaxies decreases with
decreasing redshift in each mass bin, while that of retired galaxies increases.
Galaxies with have formed all their stars at
redshift larger than 0.4. The population of AGN hosts is never dominant for
galaxy masses larger than . We warn about the effects of
stacking galaxy spectra to discuss galaxy properties. We estimate the lifetimes
of active galactic nuclei (AGN) relying entirely on demographic arguments ---
i.e. without any assumption on the AGN radiative properties. We find
upper-limit lifetimes of about 1--5 Gyr for detectable AGN in galaxies with
masses between --. The lifetimes of the AGN-dominated
phases are a few yr. Finally, we compare the star-formation histories of
star-forming, AGN and retired galaxies as obtained by the spectral synthesis
code STARLIGHT. Once the AGN is turned on it inhibits star formation for the
next 0.1 Gyr in galaxies with masses around , 1
Gyr in galaxies with masses around .Comment: accepted for MNRAS figure resolution has been degraded with respect
to what will be published in MNRA
Strongly quadrature-dependent noise in superconducting micro-resonators measured at the vacuum-noise limit
We measure frequency- and dissipation-quadrature noise in superconducting
lithographed microwave resonators with sensitivity near the vacuum noise level
using a Josephson parametric amplifier. At an excitation power of 100~nW, these
resonators show significant frequency noise caused by two-level systems. No
excess dissipation-quadrature noise (above the vacuum noise) is observed to our
measurement sensitivity. These measurements demonstrate that the excess
dissipation-quadrature noise is negligible compared to vacuum fluctuations, at
typical readout powers used in micro-resonator applications. Our results have
important implications for resonant readout of various devices such as
detectors, qubits and nano-mechanical oscillators.Comment: 13 pages, 4 figure
Intrinsic surface depression of the order parameter under mixed (s+id)-wave pair symmetry and its effect on the critical current of high-Tc SIS Josephson junctions
An intrinsic gap depression at the Superconductor-Insulator interface due to
the very short value of the coherence length in High-Tc Superconductors [HTSs]
is considered, in the framework of a mixed (s+id)-wave pair symmetry for the
order parameter ranging from pure s to pure d-wave. This gap depression acts as
the main physical agent causing the relevant reduction of IcRn(T) values with
respect to BCS expectations in HTS SIS Josephson junctions. Good agreement with
various experimental data is obtained with both pure s-wave and pure d-wave
symmetries of the order parameter, but with amounts of gap depression depending
on the pair symmetry adopted. Regardless of the pair symmetry considered, these
results prove the importance of the surface order-parameter depression in the
correct interpretation of the Ic(T)Rn(T) data in HTS SIS junctions. In a case
of planar YBCO-based junction the use of the de Gennes condition allowed us to
tentatively obtain an upper limit for the amount of d-wave present in the order
parameter of YBCO.Comment: 11 pages REVTeX file, 6 PostScript figures, to be published in J.
Superconductivit
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