817 research outputs found
Isolating quantum coherence with pathway-selective coherent multi-dimensional spectroscopy
Coherent coupling between spatially separated systems has long been explored
as a necessary requirement for quantum information and cryptography. Recent
discoveries suggest such phenomena appear in a much wider range of processes,
including light-harvesting in photosynthesis. These discoveries have been
facilitated by developments in coherent multi-dimensional spectroscopy (CMDS)
that allow interactions between different electronic states to be identified in
crowded spectra. For complex systems, however, spectral broadening and multiple
overlapping peaks limit the ability to separate, identify and properly analyse
all contributions. Here we demonstrate how pathway-selective CMDS can overcome
these limitations to reveal, isolate and allow detailed analysis of weak
coherent coupling between spatially separated excitons localised to different
semiconductor quantum wells. Selective excitation of the coherence pathways, by
spectrally shaping the laser pulses, provides access to previously hidden
details and enables quantitative analysis that can facilitate precise and
detailed understanding of interactions in this and other complex systems
Rapid Environmental Quenching of Satellite Dwarf Galaxies in the Local Group
In the Local Group, nearly all of the dwarf galaxies (M_star < 10^9 M_sun)
that are satellites within 300 kpc (the virial radius) of the Milky Way (MW)
and Andromeda (M31) have quiescent star formation and little-to-no cold gas.
This contrasts strongly with comparatively isolated dwarf galaxies, which are
almost all actively star-forming and gas-rich. This near dichotomy implies a
rapid transformation of satellite dwarf galaxies after falling into the halos
of the MW or M31. We combine the observed quiescent fractions for satellites of
the MW and M31 with the infall times of satellites from the Exploring the Local
Volume in Simulations (ELVIS) suite of cosmological zoom-in simulations to
determine the typical timescales over which environmental processes within the
MW/M31 halos remove gas and quench star formation in low-mass satellite
galaxies. The quenching timescales for satellites with M_star < 10^8 M_sun are
short, < 2 Gyr, and quenching is more rapid at lower M_star. These satellite
quenching timescales can be 1 - 2 Gyr longer if one includes the time that
satellites were environmentally preprocessed by low-mass groups prior to MW/M31
infall. We compare with quenching timescales for more massive satellites from
previous works to synthesize the nature of satellite galaxy quenching across
the observable range of M_star = 10^{3-11} M_sun. The satellite quenching
timescale increases rapidly with satellite M_star, peaking at ~9.5 Gyr for
M_star ~ 10^9 M_sun, and the timescale rapidly decreases at higher M_star to <
5 Gyr at M_star > 5 x 10^9 M_sun. Overall, galaxies with M_star ~ 10^9 M_sun,
similar to the Magellanic Clouds, exhibit the longest quenching timescales,
regardless of environmental or internal mechanisms.Comment: 6 pages, 3 figures. Accepted in ApJ Letters. Matches published
versio
The WHIQII Survey: Metallicities and Spectroscopic Properties of Luminous Compact Blue Galaxies
As part of the WIYN High Image Quality Indiana Irvine (WHIQII) survey, we
present 123 spectra of emission-line galaxies, selected on intermediate
redshift (.4<z<.8) galaxies with blue colors that appear physically compact.
The sample includes 15 true Luminous Compact Blue Galaxies (LCBGs) and an
additional 27 slightly less extreme emission-line systems. These galaxies
represent a highly evolving class that may play an important role in the
decline of star formation since z~1, but their exact nature and evolutionary
pathways remain a mystery. Here, we use emission lines to determine
metallicities and ionization parameters, constraining their intrinsic
properties and state of star formation. Some LCBG metallicities are consistent
with a "bursting dwarf" scenario, while a substantial fraction of others are
not, further confirming that LCBGs are a highly heterogeneous population but
are broadly consistent with the intermediate redshift field. In agreement with
previous studies, we observe overall evolution in the luminosity-metallicity
relation at intermediate redshift. Our sample, and particularly the LCBGs,
occupy a region in the empirical R23-O32 plane that differs from luminous local
galaxies and is more consistent with dwarf Irregulars at the present epoch,
suggesting that cosmic "downsizing" is observable in even the most fundamental
parameters that describe star formation. These properties for our sample are
also generally consistent with lying between local galaxies and those at high
redshift, as expected by this scenario. Surprisingly, our sample exhibits no
detectable correlation between compactness and metallicity, strongly suggesting
that at these epochs of rapid star formation, the morphology of compact
star-forming galaxies is largely transient.Comment: ApJ accepted, 17 pages, 20 figures, 2 tables (complete tables in
published version
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