6,656 research outputs found
Rediscovery and status of Cylindera (s. str.) lunalonga (Schaupp, 1884) (Coleoptera: Carabidae: Cicindelinae) in the San Joaquin Valley of California with a comparison to a Sierra Nevada population
Surveys for adult Cylindera (s. str.) lunalonga (Schaupp) (Coleoptera: Carabidae: Cicindelinae) were conducted between 2001 and 2011 at over 80 sites throughout the species’ historic range in the San Joaquin Valley and Sierra Nevada Mountains of California. Previously considered extirpated from the Valley, these surveys resulted in finding adults at 18 sites, several with large populations (>50 individuals). As suggested by historic records, our studies confirmed that the Valley populations of Cy. lunalonga occur in what were historically wetland sites, but are now lowland agricultural croplands. Adults were always associated with wet, muddy soil within and along the edges of irrigation ditches. A comparison of morphology, behavior, habitat, and conservation is made with the only known extant Sierra Nevada population
Testing the Modern Merger Hypothesis via the Assembly of Massive Blue Elliptical Galaxies in the Local Universe
The modern merger hypothesis offers a method of forming a new elliptical
galaxy through merging two equal-mass, gas-rich disk galaxies fuelling a
nuclear starburst followed by efficient quenching and dynamical stabilization.
A key prediction of this scenario is a central concentration of young stars
during the brief phase of morphological transformation from highly-disturbed
remnant to new elliptical galaxy. To test this aspect of the merger hypothesis,
we use integral field spectroscopy to track the stellar Balmer absorption and
4000\AA\ break strength indices as a function of galactic radius for 12 massive
(), nearby (),
visually-selected plausible new ellipticals with blue-cloud optical colours and
varying degrees of morphological peculiarities. We find that these index values
and their radial dependence correlate with specific morphological features such
that the most disturbed galaxies have the smallest 4000\AA\ break strengths and
the largest Balmer absorption values. Overall, two-thirds of our sample are
inconsistent with the predictions of the modern merger hypothesis. Of these
eight, half exhibit signatures consistent with recent minor merger
interactions. The other half have star formation histories similar to local,
quiescent early-type galaxies. Of the remaining four galaxies, three have the
strong morphological disturbances and star-forming optical colours consistent
with being remnants of recent, gas-rich major mergers, but exhibit a weak,
central burst consistent with forming of their stars. The final
galaxy possesses spectroscopic signatures of a strong, centrally-concentrated
starburst and quiescent core optical colours indicative of recent quenching
(i.e., a post-starburst signature) as prescribed by the modern merger
hypothesis.Comment: 25 pages, 37 figures, accepted to MNRA
A Herschel Study of 24 micron-Selected AGNs and Their Host Galaxies
We present a sample of 290 24-micron-selected active galactic nuclei (AGNs)
mostly at z ~ 0.3 -- 2.5, within 5.2 square degrees distributed as 25' X 25'
fields around each of 30 galaxy clusters in the Local Cluster Substructure
Survey (LoCuSS). The sample is nearly complete to 1 mJy at 24 microns, and has
a rich multi-wavelength set of ancillary data; 162 are detected by Herschel. We
use spectral templates for AGNs, stellar populations, and infrared emission by
star forming galaxies to decompose the spectral energy distributions (SEDs) of
these AGNs and their host galaxies, and estimate their star formation rates
(SFRs), AGN luminosities, and host galaxy stellar masses. The set of templates
is relatively simple: a standard Type-1 quasar template; another for the
photospheric output of the stellar population; and a far infrared star-forming
template. For the Type-2 AGN SEDs, we substitute templates including internal
obscuration, and some Type-1 objects require a warm component (T > 50 K). The
individually Herschel- detected Type-1 AGNs and a subset of 17 Type-2 ones
typically have luminosities > 10^{45} ergs/s, and supermassive black holes of ~
3 X 10^8 Msun emitting at ~ 10% of the Eddington rate. We find them in about
twice the numbers of AGN identified in SDSS data in the same fields, i.e., they
represent typical high luminosity AGN, not an infrared-selected minority. These
AGNs and their host galaxies are studied further in an accompanying paper
Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal Interactions in the Shapley Supercluster
We present two new examples of galaxies undergoing transformation in the
Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10
Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and
SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in
ugriK bands and in Halpha narrow-band are used to disentangle the effects of
tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies,
SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending
respectively 30kpc and 41kpc in projection from their disks. The galaxies'
gaseous disks are truncated and the kinematics of the stellar and gas
components are decoupled, supporting the RPS scenario. The emission of the
ionized gas extends in the direction of a possible companion for both galaxies
suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by
ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and
starting about 250Myr ago, consistent with the age of the young stellar
populations. A link between the observed gas stripping and the cluster-cluster
interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of
ram pressure acting almost edge-on are able to fully reproduce the gas velocity
field of SOS-90630, but cannot at the same time reproduce the extended tail of
outflowing gas. This suggests that an additional disturbance from a TI is
required. This study adds a piece of evidence that RPS may take place in
different environments with different impacts and witnesses the possible effect
of cluster-cluster merger on RPS.Comment: 27 pages, 28 figures, MNRAS accepte
The Different Environmental Dependencies of Star-formation for Giant and Dwarf Galaxies
We examine the origins of the bimodality observed in the global properties of
galaxies around a stellar mass of 3x10^10 M_sun by comparing the environmental
dependencies of star-formation for the giant and dwarf galaxy populations. The
Sloan Digital Sky Survey DR4 spectroscopic dataset is used to produce a sample
of galaxies in the vicinity of the supercluster centered on the cluster A2199
at z=0.03 that is ~90% complete to a magnitude limit of M*+3.3. From these we
measure global trends with environment for both giant (M_r<-20 mag) and dwarf
(-19<M_r<-17.8 mag) subsamples using the luminosity-weighted mean stellar age
and H_alpha emission as independent measures of star-formation history. The
fraction of giant galaxies classed as old (t>7 Gyr) or passive (EW[H_alpha]<4
A) falls gradually from ~80% in the cluster cores to ~40% in field regions
beyond 3-4 R_virial, as found in previous studies. In contrast, we find that
the dwarf galaxy population shows a sharp transition at ~1 R_virial, from being
predominantly old/passive within the cluster, to outside where virtually all
galaxies are forming stars and old/passive galaxies are only found as
satellites to more massive galaxies. These results imply fundamental
differences in the evolution of giant and dwarf galaxies: whereas the
star-formation histories of giant galaxies are determined primarily by their
merger history, star-formation in dwarf galaxies is much more resilient to the
effects of major mergers. Instead dwarf galaxies become passive only once they
become satellites within a more massive halo, by losing their halo gas
reservoir to the host halo, or through other environment-related processes such
as galaxy harassment and/or ram-pressure stripping.Comment: 4 pages, 4 figures, accepted for publication in ApJ
ACCESS - V. Dissecting ram-pressure stripping through integral-field spectroscopy and multi-band imaging
We study the case of a bright (L>L*) barred spiral galaxy from the rich
cluster A3558 in the Shapley supercluster core (z=0.05) undergoing ram-pressure
stripping. Integral-field spectroscopy, complemented by multi-band imaging,
allows us to reveal the impact of ram pressure on the interstellar medium. We
study in detail the kinematics and the physical conditions of the ionized gas
and the properties of the stellar populations. We observe one-sided extraplanar
ionized gas along the full extent of the galaxy disc. Narrow-band Halpha
imaging resolves this outflow into a complex of knots and filaments. The gas
velocity field is complex with the extraplanar gas showing signature of
rotation. In all parts of the galaxy, we find a significant contribution from
shock excitation, as well as emission powered by star formation. Shock-ionized
gas is associated with the turbulent gas outflow and highly attenuated by dust.
All these findings cover the whole phenomenology of early-stage ram-pressure
stripping. Intense, highly obscured star formation is taking place in the
nucleus, probably related to the bar, and in a region 12 kpc South-West from
the centre. In the SW region we identify a starburst characterized by a 5x
increase in the star-formation rate over the last ~100 Myr, possibly related to
the compression of the interstellar gas by the ram pressure. The scenario
suggested by the observations is supported and refined by ad hoc
N-body/hydrodynamical simulations which identify a rather narrow temporal range
for the onset of ram-pressure stripping around t~60 Myr ago, and an angle
between the galaxy rotation axis and the intra-cluster medium wind of ~45 deg.
Taking into account that the galaxy is found ~1 Mpc from the cluster centre in
a relatively low-density region, this study shows that ram-pressure stripping
still acts efficiently on massive galaxies well outside the cluster cores.Comment: 46 pages, 21 figures, accepted for publication; MNRAS 201
Peculiar Velocities of Nonlinear Structure: Voids in McVittie Spacetime
As a study of peculiar velocities of nonlinear structure, we analyze the
model of a relativistic thin-shell void in the expanding universe. (1) Adopting
McVittie (MV) spacetime as a background universe, we investigate the dynamics
of an uncompensated void with negative MV mass. Although the motion itself is
quite different from that of a compensated void, as shown by Haines & Harris
(1993), the present peculiar velocities are not affected by MV mass. (2) We
discuss how precisely the formula in the linear perturbation theory applies to
nonlinear relativistic voids, using the results in (1) as well as the previous
results for the homogeneous background (Sakai, Maeda, & Sato 1993). (3) We
re-examine the effect of the cosmic microwave background radiation. Contrary to
the results of Pim & Lake (1986, 1988), we find that the effect is negligible.
We show that their results are due to inappropriate initial conditions. Our
results (1)-(3) suggest that the formula in the linear perturbation theory is
approximately valid even for nonlinear voids.Comment: 12 pages, aastex, 4 ps figures separate, Fig.2 added, to appear in
Ap
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