443 research outputs found
The early data release of the Dark Energy Spectroscopic Instrument
Funding: This material is based upon work supported by the U.S. Department of Energy (DOE), Office of Science, Office of High-Energy Physics, under contract No. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract. Additional support for DESI was provided by the U.S. National Science Foundation (NSF), Division of Astronomical Sciences under contract No. AST0950945 to the NSFʼs National Optical-Infrared Astronomy Research Laboratory; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico (CONACYT); the Ministry of Science and Innovation of Spain (MICINN), and by the DESI Member Institutions: https://www.desi.lbl.gov/collaborating-institutions.The Dark Energy Spectroscopic Instrument (DESI) completed its 5 month Survey Validation in 2021 May. Spectra of stellar and extragalactic targets from Survey Validation constitute the first major data sample from the DESI survey. This paper describes the public release of those spectra, the catalogs of derived properties, and the intermediate data products. In total, the public release includes good-quality spectral information from 466,447 objects targeted as part of the Milky Way Survey, 428,758 as part of the Bright Galaxy Survey, 227,318 as part of the Luminous Red Galaxy sample, 437,664 as part of the Emission Line Galaxy sample, and 76,079 as part of the Quasar sample. In addition, the release includes spectral information from 137,148 objects that expand the scope beyond the primary samples as part of a series of secondary programs. Here, we describe the spectral data, data quality, data products, Large-Scale Structure science catalogs, access to the data, and references that provide relevant background to using these spectra.Peer reviewe
Submanifolds with constant Moebius curvature and flat normal bundle
We classify isometric immersions , and , with constant Moebius curvature and flat normal bundle.Comment: 28 page
On the Moebius deformable hypersurfaces
In the article [\emph{Deformations of hypersurfaces preserving the M\"obius
metric and a reduction theorem}, Adv. Math. 256 (2014), 156--205], Li, Ma and
Wang investigated the interesting class of Moebius deformable hypersurfaces,
that is, the umbilic-free Euclidean hypersurfaces that admit non-trivial deformations preserving the Moebius
metric. The classification of Moebius deformable hypersurfaces of dimension
stated in the aforementioned article, however, misses a large class
of examples. In this article we complete that classification for .Comment: 24 pages - final version - to appear in Rev. Mat. Iberoamerican
Applying unsupervised learning to resolve evolutionary histories and explore the galaxy-halo connection in IllustrisTNG
We examine the effectiveness of identifying distinct evolutionary histories in IllustrisTNG-100 galaxies using unsupervised machine learning with Gaussian Mixture Models. We focus on how clustering compressed metallicity histories and star formation histories produces subpopulations of galaxies with distinct evolutionary properties (for both halo mass assembly and merger histories). By contrast, clustering with photometric colours fail to resolve such histories. We identify several populations of interest that reflect a variety of evolutionary scenarios supported by the literature. Notably, we identify a population of galaxies inhabiting the upper-red sequence, M* > 1010M⊙ that has a significantly higher ex-situ merger mass fraction present at fixed masses, and a star formation history that has yet to fully quench, in contrast to an overlapping, satellite-dominated population along the red sequence, which is distinctly quiescent. Extending the clustering to study four clusters instead of three further divides quiescent galaxies, while star forming ones are mostly contained in a single cluster, demonstrating a variety of supported pathways to quenching. In addition to these populations, we identify a handful of populations from our other clusters that are readily applicable to observational surveys, including a population related to post starburst (PSB) galaxies, allowing for possible extensions of this work in an observational context, and to corroborate results within the IllustrisTNG ecosystem.PostprintPeer reviewe
Galaxy formation in the Planck cosmology - II. Star-formation histories and post-processing magnitude reconstruction
We adapt the L-Galaxies semi-analytic model to follow the star-formation
histories (SFH) of galaxies -- by which we mean a record of the formation time
and metallicities of the stars that are present in each galaxy at a given time.
We use these to construct stellar spectra in post-processing, which offers
large efficiency savings and allows user-defined spectral bands and dust models
to be applied to data stored in the Millennium data repository.
We contrast model SFHs from the Millennium Simulation with observed ones from
the VESPA algorithm as applied to the SDSS-7 catalogue. The overall agreement
is good, with both simulated and SDSS galaxies showing a steeper SFH with
increased stellar mass. The SFHs of blue and red galaxies, however, show poor
agreement between data and simulations, which may indicate that the termination
of star formation is too abrupt in the models.
The mean star-formation rate (SFR) of model galaxies is well-defined and is
accurately modelled by a double power law at all redshifts: SFR proportional to
, where Gyr, is the age of the
stars and is the loopback time to the onset of galaxy formation; above a
redshift of unity, this is well approximated by a gamma function: SFR
proportional to , where Gyr. Individual
galaxies, however, show a wide dispersion about this mean. When split by mass,
the SFR peaks earlier for high-mass galaxies than for lower-mass ones, and we
interpret this downsizing as a mass-dependence in the evolution of the quenched
fraction: the SFHs of star-forming galaxies show only a weak mass dependence.Comment: Accepted version of the paper, to appear in MNRAS. Compared to the
original version, contains more detail on the post-processing of magnitudes,
including a table of rms magnitude errors. SFHs available on Millennium
database http://gavo.mpa-garching.mpg.de/MyMillennium
The Stripe 82 Massive Galaxy Project II: Stellar Mass Completeness of Spectroscopic Galaxy Samples from the Baryon Oscillation Spectroscopic Survey
The Baryon Oscillation Spectroscopic Survey (BOSS) has collected spectra for
over one million galaxies at over a volume of 15.3 Gpc (9,376
deg) -- providing us an opportunity to study the most massive galaxy
populations with vanishing sample variance. However, BOSS samples are selected
via complex color cuts that are optimized for cosmology studies, not galaxy
science. In this paper, we supplement BOSS samples with photometric redshifts
from the Stripe 82 Massive Galaxy Catalog and measure the total galaxy stellar
mass function (SMF) at and . With the total SMF in hand,
we characterize the stellar mass completeness of BOSS samples. The
high-redshift CMASS ("constant mass") sample is significantly impacted by mass
incompleteness and is 80% complete at only in
the narrow redshift range . The low redshift LOWZ sample is 80%
complete at for . To construct
mass complete samples at lower masses, spectroscopic samples need to be
significantly supplemented by photometric redshifts. This work will enable
future studies to better utilize the BOSS samples for galaxy-formation science.Comment: 18 pages, 17 figures, 5 table
MOONS : the new Multi-Object Spectrograph for the VLT
MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual roboticp ositioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64–1.8 μm wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue.Publisher PD
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: mock galaxy catalogues for the low-redshift sample
We present one thousand mock galaxy catalogues for the analysis of the Low
Redshift Sample (LOWZ, effective redshift z ~ 10.32) of the Baryon Oscillation
Spectroscopic Survey Data Releases 10 and 11. These mocks have been created
following the PTHalos method of Manera13 et al. (2013) revised to include new
developments. The main improvement is the introduction of a redshift dependence
in the Halo Occupation Distribution in order to account for the change of the
galaxy number density with redshift. These mock catalogues are used in the
analyses of the LOWZ galaxy clustering by the BOSS collaboration.Comment: 10 pages, 8 figure
Testing homogeneity with the fossil record of galaxies
The standard Friedmann model of cosmology is based on the Copernican
Principle, i.e. the assumption of a homogeneous background on which structure
forms via perturbations. Homogeneity underpins both general relativistic and
modified gravity models and is central to the way in which we interpret
observations of the CMB and the galaxy distribution. It is therefore important
to probe homogeneity via observations. We describe a test based on the fossil
record of distant galaxies: if we can reconstruct key intrinsic properties of
galaxies as functions of proper time along their worldlines, we can compare
such properties at the same proper time for our galaxy and others. We achieve
this by computing the lookback time using radial Baryon Acoustic Oscillations,
and the time along galaxy world line using stellar physics, allowing us to
probe homogeneity, in principle anywhere inside the past light cone. Agreement
in the results would be an important consistency test -- although it would not
in itself prove homogeneity. Any significant deviation in the results however
would signal a breakdown of homogeneity.Comment: Accepted for publication in JCAP. Matches published version. Minor
changes: ref. added and longer discussion on performing the test
observationally. Results unchange
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