206 research outputs found
Time-series spectroscopy of the rapidly oscillating Ap star HR 3831
We present time-series spectroscopy of the rapidly oscillating Ap star HR
3831. This star has a dominant pulsation period of 11.7 minutes and a rotation
period of 2.85 days. We have analysed 1400 intermediate-resolution spectra of
the wavelength region 6100--7100 AA obtained over one week, using techniques
similar to those we applied to another roAp star, Alpha Cir.
We confirm that the H-alpha velocity amplitude of HR 3831 is modulated with
rotation phase. Such a modulation was predicted by the oblique pulsator model,
and rules out the spotted pulsator model. However, further analysis of H-alpha
and other lines reveal rotational modulations that cannot easily be explained
using the oblique pulsator model. In particular, the phase of the pulsation as
measured by the width of the H-alpha line varies with height in the line.
The variation of the H-alpha bisector shows a very similar pattern to that
observed in Alpha Cir, which we have previously attributed to a radial node in
the stellar atmosphere. However, the striking similarities between the two
stars despite the much shorter period of Alpha Cir (6.8 min) argues against
this interpretation unless the structure of the atmosphere is somewhat
different between the two stars. Alternatively, the bisector variation is a
signature of the degree l of the mode and not the overtone value n.
High-resolution studies of the metal lines in roAp stars are needed to
understand fully the form of the pulsation in the atmosphere.Comment: 13 pages, 20 figures, accepted by MNRA
Monster Redshift Surveys through Dispersive Slitless Imaging: The Baryon Oscillation Probe
Wide-field imaging from space should not forget the dispersive dimension. We
consider the capability of space-based imaging with a slitless grism: because
of the low near-infrared background in space and the high sky-density of high
redshift emission line galaxies this makes for a very powerful redshift machine
with no moving parts. A small 1m space telescope with a 0.5 degree field of
view could measure redshifts for 10^7 galaxies at 0.5<z<2 per year, this is a
MIDEX class concept which we have dubbed `The Baryon Oscillation Probe' as the
primary science case would be constraining dark energy evolution via
measurement of the baryonic oscillations in the galaxy power spectrum. These
ideas are generalizable to other missions such as SNAP and DESTINY.Comment: Proceedings of the LBNL conference on WideField Imaging from Space. 8
pages, 3 figure
Environment from cross-correlations: connecting hot gas and the quenching of galaxies
The observable properties of galaxies depend on both internal processes and
the external environment. In terms of the environmental role, we still do not
have a clear picture of the processes driving the transformation of galaxies.
The use of proxies for environment (e.g., host halo mass, distance to the N^th
nearest neighbour, etc.), as opposed to the real physical conditions (e.g., hot
gas density) may bear some responsibility for this. Here we propose a new
method that directly links galaxies to their local environments, by using
spatial cross-correlations of galaxy catalogues with maps from large-scale
structure surveys (e.g., thermal Sunyaev-Zel'dovich [tSZ] effect, diffuse X-ray
emission, weak lensing of galaxies or the CMB). We focus here on the quenching
of galaxies and its link to local hot gas properties. Maps of galaxy
overdensity and quenched fraction excess are constructed from volume-limited
SDSS catalogs, which are cross-correlated with tSZ effect and X-ray maps from
Planck and ROSAT, respectively. Strong signals out to Mpc scales are detected
for most cross-correlations and are compared to predictions from the EAGLE and
BAHAMAS cosmological hydrodynamical simulations. The simulations successfully
reproduce many, but not all, of the observed power spectra, with an indication
that environmental quenching may be too efficient in the simulations. We
demonstrate that the cross-correlations are sensitive to both the internal
(e.g., AGN and stellar feedback) and external processes (e.g., ram pressure
stripping, harassment, strangulation, etc.) responsible for quenching. The
methods outlined in this paper can be adapted to other observables and, with
upcoming surveys, will provide a stringent test of physical models for
environmental transformation.Comment: 23 pages, 11 figures, MNRAS, in pres
Dependence of Star Formation Activity On Stellar Mass and Environment From the Redshift One LDSS-3 Emission Line Survey (ROLES)
Using the sample from the \it Redshift One LDSS3 Emission line Survey \rm
(ROLES), we probe the dependence of star formation rate (SFR) and specific star
formation rate (sSFR) as a function of stellar mass and environment as
defined by local galaxy density, in the CDFS field. Our spectroscopic sample
consists of 312 galaxies with , corresponding to stellar mass
\log(M_*/M_{\sun})>8.5, and with [OII] derived star-formation rates
SFR>0.3M_{\sun}/yr, at . The results have been
compared directly with the Sloan Digital Sky Survey Stripe 82 sample at
. For star-forming galaxies, we confirm that there is
little correlation between SFR and density at . However, for the
lowest mass galaxies in our sample, those with
\log(M_*/M_{\sun})<10, we find that both the median SFR and specific SFR {\it
increase} significantly with increasing local density. The "downsizing" trend
for low mass galaxies to be quenched progressively later in time appears to be
more pronounced in moderately overdense environments. Overall we find that the
evolution of star-formation in galaxies is most strongly driven by their
stellar mass, with local galaxy density playing a role that becomes
increasingly important for lower mass galaxies.Comment: MNRAS accepte
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