675 research outputs found
The environmental dependence of the stellar mass-size relation in STAGES galaxies
We present the stellar mass-size relations for elliptical, lenticular, and
spiral galaxies in the field and cluster environments using HST/ACS imaging and
data from the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). We use a
large sample of ~1200 field and cluster galaxies, and a sub-sample of cluster
core galaxies, and quantify the significance of any putative environmental
dependence on the stellar mass-size relation. For elliptical, lenticular, and
high-mass (log M*/M_sun > 10) spiral galaxies we find no evidence to suggest
any such environmental dependence, implying that internal drivers are governing
their size evolution. For intermediate/low-mass spirals (log M*/M_sun < 10) we
find evidence, significant at the 2-sigma level, for a possible environmental
dependence on galaxy sizes: the mean effective radius a_e for lower-mass
spirals is ~15-20 per cent larger in the field than in the cluster. This is due
to a population of low-mass large-a_e field spirals that are largely absent
from the cluster environments. These large-a_e field spirals contain extended
stellar discs not present in their cluster counterparts. This suggests the
fragile extended stellar discs of these spiral galaxies may not survive the
environmental conditions in the cluster. Our results suggest that internal
physical processes are the main drivers governing the size evolution of
galaxies, with the environment possibly playing a role affecting only the discs
of intermediate/low-mass spirals.Comment: 16 pages, 10 figures, accepted to MNRA
Inequivalent contact structures on Boothby-Wang 5-manifolds
We consider contact structures on simply-connected 5-manifolds which arise as
circle bundles over simply-connected symplectic 4-manifolds and show that
invariants from contact homology are related to the divisibility of the
canonical class of the symplectic structure. As an application we find new
examples of inequivalent contact structures in the same equivalence class of
almost contact structures with non-zero first Chern class.Comment: 27 pages; to appear in Math. Zeitschrif
Evolution of optically faint AGN from COMBO-17 and GEMS
We have mapped the AGN luminosity function and its evolution between z=1 and
z=5 down to apparent magnitudes of . Within the GEMS project we have
analysed HST-ACS images of many AGN in the Extended Chandra Deep Field South,
enabling us to assess the evolution of AGN host galaxy properties with cosmic
time.Comment: to appear in proceedings 'Multiwavelength AGN Surveys', Cozumel 200
Stellar science from a blue wavelength range - A possible design for the blue arm of 4MOST
From stellar spectra, a variety of physical properties of stars can be
derived. In particular, the chemical composition of stellar atmospheres can be
inferred from absorption line analyses. These provide key information on large
scales, such as the formation of our Galaxy, down to the small-scale
nucleosynthesis processes that take place in stars and supernovae. By extending
the observed wavelength range toward bluer wavelengths, we optimize such
studies to also include critical absorption lines in metal-poor stars, and
allow for studies of heavy elements (Z>38) whose formation processes remain
poorly constrained. In this context, spectrographs optimized for observing blue
wavelength ranges are essential, since many absorption lines at redder
wavelengths are too weak to be detected in metal-poor stars. This means that
some elements cannot be studied in the visual-redder regions, and important
scientific tracers and science cases are lost. The present era of large public
surveys will target millions of stars. Here we describe the requirements
driving the design of the forthcoming survey instrument 4MOST, a multi-object
spectrograph commissioned for the ESO VISTA 4m-telescope. We focus here on
high-density, wide-area survey of stars and the science that can be achieved
with high-resolution stellar spectroscopy. Scientific and technical
requirements that governed the design are described along with a thorough line
blending analysis. For the high-resolution spectrograph, we find that a
sampling of >2.5 (pixels per resolving element), spectral resolution of 18000
or higher, and a wavelength range covering 393-436 nm, is the most
well-balanced solution for the instrument. A spectrograph with these
characteristics will enable accurate abundance analysis (+/-0.1 dex) in the
blue and allow us to confront the outlined scientific questions. (abridged)Comment: 14 pages, 8 figures, accepted for publication in A
Limiting behaviour of Fréchet means in the space of phylogenetic trees
As demonstrated in our previous work on T4, the space of phylogenetic trees with four leaves, the topological structure of the space plays an important role in the non-classical limiting behaviour of the sample FrĂ©chet means in T4. Nevertheless, the techniques used in that paper cannot be adapted to analyse FrĂ©chet means in the space Tm of phylogenetic trees with m(â©Ÿ5)m(â©Ÿ5) leaves. To investigate the latter, this paper first studies the log map of Tm. Then, in terms of a modified version of this map, we characterise FrĂ©chet means in Tm that lie in top-dimensional or co-dimension one strata. We derive the limiting distributions for the corresponding sample FrĂ©chet means, generalising our previous results. In particular, the results show that, although they are related to the Gaussian distribution, the forms taken by the limiting distributions depend on the co-dimensions of the strata in which the FrĂ©chet means lie
Towards an understanding of the rapid decline of the cosmic star formation rate
We present a first analysis of deep 24 micron observations with the Spitzer
Space Telescope of a sample of nearly 1500 galaxies in a thin redshift slice,
0.65<z<0.75. We combine the infrared data with redshifts, rest-frame
luminosities, and colors from COMBO-17, and with morphologies from Hubble Space
Telescope images collected by the GEMS and GOODS projects. To characterize the
decline in star-formation rate (SFR) since z~0.7, we estimate the total thermal
infrared (IR) luminosities, SFRs, and stellar masses for the galaxies in this
sample. At z~0.7, nearly 40% of intermediate and high-mass galaxies (with
stellar masses >2x10^10 solar masses) are undergoing a period of intense star
formation above their past-averaged SFR. In contrast, less than 1% of
equally-massive galaxies in the local universe have similarly intense star
formation activity. Morphologically-undisturbed galaxies dominate the total
infrared luminosity density and SFR density: at z~0.7, more than half of the
intensely star-forming galaxies have spiral morphologies, whereas less than
\~30% are strongly interacting. Thus, a decline in major-merger rate is not the
underlying cause of the rapid decline in cosmic SFR since z~0.7. Physical
properties that do not strongly affect galaxy morphology - for example, gas
consumption and weak interactions with small satellite galaxies - appear to be
responsible.Comment: To appear in the Astrophysical Journal 1 June 2005. 14 pages with 8
embedded figure
Cosmological weak lensing with the HST GEMS survey
We present our cosmic shear analysis of GEMS, one of the largest wide-field
surveys ever undertaken by the Hubble Space Telescope. Imaged with the Advanced
Camera for Surveys (ACS), GEMS spans 795 square arcmin in the Chandra Deep
Field South. We detect weak lensing by large-scale structure in high resolution
F606W GEMS data from ~60 resolved galaxies per square arcminute. We measure the
two-point shear correlation function, the top-hat shear variance and the shear
power spectrum, performing an E/B mode decomposition for each statistic. We
show that we are not limited by systematic errors and use our results to place
joint constraints on the matter density parameter Omega_m and the amplitude of
the matter power spectrum sigma_8. We find sigma_8(Omega_m/0.3)^{0.65}=0.68 +/-
0.13 where the 1sigma error includes both our uncertainty on the median
redshift of the survey and sampling variance.
Removing image and point spread function (PSF) distortions are crucial to all
weak lensing analyses. We therefore include a thorough discussion on the degree
of ACS PSF distortion and anisotropy which we characterise directly from GEMS
data. Consecutively imaged over 20 days, GEMS data also allows us to
investigate PSF instability over time. We find that, even in the relatively
short GEMS observing period, the ACS PSF ellipticity varies at the level of a
few percent which we account for with a semi-time dependent PSF model. Our
correction for the temporal and spatial variability of the PSF is shown to be
successful through a series of diagnostic tests.Comment: 17 pages, 16 figures. Version accepted by MNRA
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