1,867 research outputs found
Data Deluge in Astrophysics: Photometric Redshifts as a Template Use Case
Astronomy has entered the big data era and Machine Learning based methods
have found widespread use in a large variety of astronomical applications. This
is demonstrated by the recent huge increase in the number of publications
making use of this new approach. The usage of machine learning methods, however
is still far from trivial and many problems still need to be solved. Using the
evaluation of photometric redshifts as a case study, we outline the main
problems and some ongoing efforts to solve them.Comment: 13 pages, 3 figures, Springer's Communications in Computer and
Information Science (CCIS), Vol. 82
Towards More Precise Photometric Redshifts: Calibration Via CCD Photometry
We present the initial results from a deep, multi-band photometric survey of
selected high Galactic latitude redshift fields. Previous work using the
photographic data of Koo and Kron demonstrated that the distribution of
galaxies in the multi-dimensional flux space U B R I is nearly planar. The
position of a galaxy within this plane is determined by its redshift,
luminosity and spectral type. Using recently acquired deep CCD photometry in
existing, published redshift fields, we have redetermined the distribution of
galaxies in this four-dimensional magnitude space. Furthermore, from our CCD
photometry and the published redshifts, we have quantified the
photometric-redshift relation within the standard AB magnitude system. This
empirical relation has a measured dispersion of approximately 0.02 for z < 0.4.
With this work we are reaching the asymptotic intrinsic dispersions that were
predicted from simulated distributions of galaxy colors.Comment: submitted to the Astrophysical Journal Letter
Searching High Redshift Large-Scale Structures: Photometry of Four Fields Around Quasar Pairs at z~1
We have studied the photometric properties of four fields around the
high-redshift quasar pairs QP1310+0007, QP1355-0032, QP0110-0219, and
QP0114-3140 at z ~ 1 with the aim of identifying large-scale structures- galaxy
clusters or groups- around them. This sample was observed with GMOS in Gemini
North and South telescopes in the g', r', i', and z' bands, and our photometry
is complete to a limiting magnitude of i' ~ 24 mag (corresponding to ~ M*_i' +
2 at the redshift of the pairs). Our analysis reveals that QP0110-0219 shows
very strong and QP1310+0007 and QP1355-0032 show some evidence for the presence
of rich galaxy clusters in direct vicinity of the pairs. On the other hand,
QP0114-3140 could be an isolated pair in a poor environment. This work suggest
that z ~ 1 quasar pairs are excellent tracers of high density environments and
this same technique may be useful to find clusters at higher redshifts.Comment: 29 pages, 7 figures, ApJ accepted. Added one figure and 3 references.
Some paragraphs was rewritten in sections 1, 3, 5, and 6, as suggested by
refere
The Evolution of the Global Star Formation History as Measured from the Hubble Deep Field
The Hubble Deep Field (HDF) is the deepest set of multicolor optical
photometric observations ever undertaken, and offers a valuable data set with
which to study galaxy evolution. Combining the optical WFPC2 data with
ground-based near-infrared photometry, we derive photometrically estimated
redshifts for HDF galaxies with J<23.5. We demonstrate that incorporating the
near-infrared data reduces the uncertainty in the estimated redshifts by
approximately 40% and is required to remove systematic uncertainties within the
redshift range 1<z<2. Utilizing these photometric redshifts, we determine the
evolution of the comoving ultraviolet (2800 A) luminosity density (presumed to
be proportional to the global star formation rate) from a redshift of z=0.5 to
z=2. We find that the global star formation rate increases rapidly with
redshift, rising by a factor of 12 from a redshift of zero to a peak at z~1.5.
For redshifts beyond 1.5, it decreases monotonically. Our measures of the star
formation rate are consistent with those found by Lilly et al. (1996) from the
CFRS at z 2, and
bridge the redshift gap between those two samples. The overall star formation
or metal enrichment rate history is consistent with the predictions of Pei and
Fall (1995) based on the evolving HI content of Lyman-alpha QSO absorption line
systems.Comment: Latex format, 10 pages, 3 postscript figures. Accepted for
publication in Ap J Letter
Identifications of FIRST radio sources in the NOAO Deep-Wide Field Survey
In this paper we present the results of an optical and near infrared
identification of 514 radio sources from the FIRST survey (Faint Images of the
Radio Sky Survey at Twenty centimeters) with a flux-density limit of 1 mJy in
the NOAO Deep-Wide Field Survey (NDWFS) Bootes field. Using optical (Bw, R, I)
and K band data with approximate limits of Bw ~ 25.5mag, R ~ 25.8 mag, I ~25.5
mag and K~19.4 mag, optical counterparts have been identified for 378 of 514
FIRST radio sources. This corresponds to an identification rate of 34% in four
bands (BwRIK), 60% in optical bands (BwRI) and 74% in I band. Photometric
redshifts for these sources have been computed using the hyperz code. The
inclusion of quasar template spectra in hyperz is investigated. We note that
the photometric data are, in many cases, best matched to templates with very
short star-formation timescales and the inferred ages of identified galaxies
depend strongly on the assumptions about the star-formation timescale. The
redshifts obtained are fairly consistent with those expected from the K-z
relation for brighter radio sources but there is more scatter in the K-z
diagram at z<1.Comment: 9 pages, 7 figures. Accepted for publication in Astronomische
Nachrichten; will appear in the issue 5/32
Lyman Break Galaxies at z~5: Rest-Frame UV Spectra. III
We present results of optical spectroscopic observations of candidates of
Lyman Break Galaxies (LBGs) at in the region including the GOODS-N
and the J0053+1234 region by using GMOS-N and GMOS-S, respectively. Among 25
candidates, five objects are identified to be at (two of them were
already identified by an earlier study) and one object very close to the
color-selection window turned out to be a foreground galaxy. With this
spectroscopically identified sample and those from previous studies, we derived
the lower limits on the number density of bright ( mag) LBGs at
. These lower limits are comparable to or slightly smaller than the
number densities of UV luminosity functions (UVLFs) that show the smaller
number density among UVLFs in literature. However, by considering
that there remain many LBG candidates without spectroscopic observations, the
number density of bright LBGs is expected to increase by a factor of two or
more. The evidence for the deficiency of UV luminous LBGs with large Ly
equivalent widths was reinforced. We discuss possible causes for the deficiency
and prefer the interpretation of dust absorption.Comment: 28 pages, 5 figures, accepted for publication in Ap
Low X-ray Luminosity Galaxy Clusters. III: Weak Lensing Mass Determination at 0.18 z 0.70
This is the third of a series of papers of low X-ray luminosity galaxy
clusters. In this work we present the weak lensing analysis of eight clusters,
based on observations obtained with the Gemini Multi-Object Spectrograph in the
, and passbands. For this purpose, we have developed a pipeline
for the lensing analysis of ground-based images and we have performed tests
applied to simulated data. We have determined the masses of seven galaxy
clusters, six of them measured for the first time. For the four clusters with
availably spectroscopic data, we find a general agreement between the velocity
dispersions obtained via weak lensing assuming a Singular Isothermal Sphere
profile, and those obtained from the redshift distribution of member galaxies.
The correlation between our weak lensing mass determinations and the X-ray
luminosities are suitably fitted by other observations of the
relation and models
The Statistical Approach to Quantifying Galaxy Evolution
Studies of the distribution and evolution of galaxies are of fundamental
importance to modern cosmology; these studies, however, are hampered by the
complexity of the competing effects of spectral and density evolution.
Constructing a spectroscopic sample that is able to unambiguously disentangle
these processes is currently excessively prohibitive due to the observational
requirements. This paper extends and applies an alternative approach that
relies on statistical estimates for both distance (z) and spectral type to a
deep multi-band dataset that was obtained for this exact purpose.
These statistical estimates are extracted directly from the photometric data
by capitalizing on the inherent relationships between flux, redshift, and
spectral type. These relationships are encapsulated in the empirical
photometric redshift relation which we extend to z ~ 1.2, with an intrinsic
dispersion of dz = 0.06. We also develop realistic estimates for the
photometric redshift error for individual objects, and introduce the
utilization of the galaxy ensemble as a tool for quantifying both a
cosmological parameter and its measured error. We present deep, multi-band,
optical number counts as a demonstration of the integrity of our sample. Using
the photometric redshift and the corresponding redshift error, we can divide
our data into different redshift intervals and spectral types. As an example
application, we present the number redshift distribution as a function of
spectral type.Comment: 40 pages (LaTex), 21 Figures, requires aasms4.sty; Accepted by the
Astrophysical Journa
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