249 research outputs found
The DEEP2 Galaxy Redshift Survey: Spectral classification of galaxies at z~1
We present a Principal Component Analysis (PCA)-based spectral
classification, eta, for the first 5600 galaxies observed in the DEEP2 Redshift
Survey. This parameter provides a very pronounced separation between absorption
and emission dominated galaxy spectra - corresponding to passively evolving and
actively star-forming galaxies in the survey respectively. In addition it is
shown that despite the high resolution of the observed spectra, this parameter
alone can be used to quite accurately reconstruct any given galaxy spectrum,
suggesting there are not many `degrees of freedom' in the observed spectra of
this galaxy population. It is argued that this form of classification, eta,
will be particularly valuable in making future comparisons between high and
low-redshift galaxy surveys for which very large spectroscopic samples are now
readily available, particularly when used in conjunction with high-resolution
spectral synthesis models which will be made public in the near future. We also
discuss the relative advantages of this approach to distant galaxy
classification compared to other methods such as colors and morphologies.
Finally, we compare the classification derived here with that adopted for the
2dF Galaxy Redshift Survey and in so doing show that the two systems are very
similar. This will be particularly useful in subsequent analyses when making
comparisons between results from each of these surveys to study evolution in
the galaxy populations and large-scale structure.Comment: 10 pages, 9 figures, Accepted for publication in Ap
Optical Spectroscopy of Supernova 1993J During Its First 2500 Days
We present 42 low-resolution spectra of Supernova (SN) 1993J, our complete
collection from the Lick and Keck Observatories, from day 3 after explosion to
day 2454, as well as one Keck high-dispersion spectrum from day 383. SN 1993J
began as an apparent SN II, albeit an unusual one. After a few weeks, a
dramatic transition took place, as prominent helium lines emerged in the
spectrum. SN 1993J had metamorphosed from a SN II to a SN IIb. Nebular spectra
of SN 1993J closely resemble those of SNe Ib and Ic, but with a persistent
H_alpha line. At very late times, the H_alpha emission line dominated the
spectrum, but with an unusual, box-like profile. This is interpreted as an
indication of circumstellar interaction.Comment: 19 pages plus 13 figures, AASTeX V5.0. One external table in AASTeX
V4.0, in landscape format. Accepted for publication in A
GASKAP -- The Galactic ASKAP Survey
A survey of the Milky Way disk and the Magellanic System at the wavelengths
of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule
will be carried out with the Australian Square Kilometre Array Pathfinder
telescope. The survey will study the distribution of HI emission and absorption
with unprecedented angular and velocity resolution, as well as molecular line
thermal emission, absorption, and maser lines. The area to be covered includes
the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg,
spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire
area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The
brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K
at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific
goals, from studies of galaxy evolution to star formation, with particular
contributions to understanding stellar wind kinematics, the thermal phases of
the interstellar medium, the interaction between gas in the disk and halo, and
the dynamical and thermal states of gas at various positions along the
Magellanic Stream.Comment: 45 pages, 8 figures, Pub. Astron. Soc. Australia (in press
The DEEP2 Galaxy Redshift Survey: Clustering of Galaxies in Early Data
We measure the two-point correlation function xi(r) using a sample of 2219
galaxies in an area of 0.32 degrees^2 at z=0.7-1.35 from the first season of
the DEEP2 Galaxy Redshift Survey. We find that xi(r) can be approximated by a
power-law, xi(r)=(r/r_0)^-gamma, on scales 0.1-20 Mpc/h. In a sample with an
effective redshift of z_eff=0.82, for a Lcdm cosmology we find r_0=3.53 +/-0.81
Mpc/h (comoving) and gamma=1.66 +/-0.12, while in a higher-redshift sample with
z_eff=1.14 we find r_0=3.14 +/-0.72 Mpc/h and gamma=1.61 +/-0.11. We find that
red, absorption-dominated, passively-evolving galaxies have a larger clustering
scale length, r_0, and more prominent ``fingers of God'' than blue,
emission-line, actively star-forming galaxies. Intrinsically brighter galaxies
also cluster more strongly than fainter galaxies at z~1, with a significant
luminosity-bias seen for galaxies fainter than M*. Our results are suggestive
of evolution in the galaxy clustering within our survey volume and imply that
the DEEP2 galaxies, with a median brightness one magnitude fainter than M* have
an effective bias b=0.97 +/-0.13 if sigma_{8 DM}=1 today or b=1.20 +/-0.16 if
sigma_{8 DM}=0.8 today. Given the strong luminosity-dependence in the bias that
we measure at z~1, the galaxy bias at M* may be significantly greater. We note
that our star-forming sample at z~1 has very similar selection criteria as the
Lyman-break galaxies at z~3 and that our red, absorption-line sample displays a
clustering strength comparable to the expected clustering of the Lyman-break
galaxy descendants at z~1. Our results demonstrate that the clustering
properties in the galaxy distribution seen in the local Universe were largely
in place by z~1.Comment: 17 pages, 8 figures, Revised version accepted by ApJ, minor changes
to text and figure
The DEEP2 Galaxy Redshift Survey: Design, Observations, Data Reduction, and Redshifts
We describe the design and data sample from the DEEP2 Galaxy Redshift Survey,
the densest and largest precision-redshift survey of galaxies at z ~ 1
completed to date. The survey has conducted a comprehensive census of massive
galaxies, their properties, environments, and large-scale structure down to
absolute magnitude M_B = -20 at z ~ 1 via ~90 nights of observation on the
DEIMOS spectrograph at Keck Observatory. DEEP2 covers an area of 2.8 deg^2
divided into four separate fields, observed to a limiting apparent magnitude of
R_AB=24.1. Objects with z < 0.7 are rejected based on BRI photometry in three
of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5
times more efficiently than in a purely magnitude-limited sample. Approximately
sixty percent of eligible targets are chosen for spectroscopy, yielding nearly
53,000 spectra and more than 38,000 reliable redshift measurements. Most of the
targets which fail to yield secure redshifts are blue objects that lie beyond z
~ 1.45. The DEIMOS 1200-line/mm grating used for the survey delivers high
spectral resolution (R~6000), accurate and secure redshifts, and unique
internal kinematic information. Extensive ancillary data are available in the
DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into
one of the richest multiwavelength regions on the sky. DEEP2 surpasses other
deep precision-redshift surveys at z ~ 1 in terms of galaxy numbers, redshift
accuracy, sample number density, and amount of spectral information. We also
provide an overview of the scientific highlights of the DEEP2 survey thus far.
This paper is intended as a handbook for users of the DEEP2 Data Release 4,
which includes all DEEP2 spectra and redshifts, as well as for the
publicly-available DEEP2 DEIMOS data reduction pipelines. [Abridged]Comment: submitted to ApJS; data products available for download at
http://deep.berkeley.edu/DR4
Human-to-monkey transfer learning identifies the frontal white matter as a key determinant for predicting monkey brain age
The application of artificial intelligence (AI) to summarize a whole-brain magnetic resonance image (MRI) into an effective “brain age” metric can provide a holistic, individualized, and objective view of how the brain interacts with various factors (e.g., genetics and lifestyle) during aging. Brain age predictions using deep learning (DL) have been widely used to quantify the developmental status of human brains, but their wider application to serve biomedical purposes is under criticism for requiring large samples and complicated interpretability. Animal models, i.e., rhesus monkeys, have offered a unique lens to understand the human brain - being a species in which aging patterns are similar, for which environmental and lifestyle factors are more readily controlled. However, applying DL methods in animal models suffers from data insufficiency as the availability of animal brain MRIs is limited compared to many thousands of human MRIs. We showed that transfer learning can mitigate the sample size problem, where transferring the pre-trained AI models from 8,859 human brain MRIs improved monkey brain age estimation accuracy and stability. The highest accuracy and stability occurred when transferring the 3D ResNet [mean absolute error (MAE) = 1.83 years] and the 2D global-local transformer (MAE = 1.92 years) models. Our models identified the frontal white matter as the most important feature for monkey brain age predictions, which is consistent with previous histological findings. This first DL-based, anatomically interpretable, and adaptive brain age estimator could broaden the application of AI techniques to various animal or disease samples and widen opportunities for research in non-human primate brains across the lifespan
The DEEP2 Galaxy Redshift Survey: First results on galaxy groups
We use the first 25% of the DEEP2 Galaxy Redshift Survey spectroscopic data
to identify groups and clusters of galaxies in redshift space. The data set
contains 8370 galaxies with confirmed redshifts in the range 0.7 <= z <= 1.4,
over one square degree on the sky. Groups are identified using an algorithm
(the Voronoi-Delaunay Method) that has been shown to accurately reproduce the
statistics of groups in simulated DEEP2-like samples. We optimize this
algorithm for the DEEP2 survey by applying it to realistic mock galaxy catalogs
and assessing the results using a stringent set of criteria for measuring
group-finding success, which we develop and describe in detail here. We find in
particular that the group-finder can successfully identify ~78% of real groups
and that ~79% of the galaxies that are true members of groups can be identified
as such. Conversely, we estimate that ~55% of the groups we find can be
definitively identified with real groups and that ~46% of the galaxies we place
into groups are interloper field galaxies. Most importantly, we find that it is
possible to measure the distribution of groups in redshift and velocity
dispersion, n(sigma,z), to an accuracy limited by cosmic variance, for
dispersions greater than 350km/s. We anticipate that such measurements will
allow strong constraints to be placed on the equation of state of the dark
energy in the future. Finally, we present the first DEEP2 group catalog, which
assigns 32% of the galaxies to 899 distinct groups with two or more members,
153 of which have velocity dispersions above 350km/s. We provide locations,
redshifts and properties for this high-dispersion subsample. This catalog
represents the largest sample to date of spectroscopically detected groups at
z~1.Comment: 19 pages, 13 figures, 3 tables. v1: Submitted to ApJ v2: Updated with
minor changes to agree with version to appear in Ap
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