1,023 research outputs found
Searching for galaxy clusters in the Kilo-Degree Survey
In this paper, we present the tools used to search for galaxy clusters in the
Kilo Degree Survey (KiDS), and our first results. The cluster detection is
based on an implementation of the optimal filtering technique that enables us
to identify clusters as over-densities in the distribution of galaxies using
their positions on the sky, magnitudes, and photometric redshifts. The
contamination and completeness of the cluster catalog are derived using mock
catalogs based on the data themselves. The optimal signal to noise threshold
for the cluster detection is obtained by randomizing the galaxy positions and
selecting the value that produces a contamination of less than 20%. Starting
from a subset of clusters detected with high significance at low redshifts, we
shift them to higher redshifts to estimate the completeness as a function of
redshift: the average completeness is ~ 85%. An estimate of the mass of the
clusters is derived using the richness as a proxy. We obtained 1858 candidate
clusters with redshift 0 < z_c < 0.7 and mass 13.5 < log(M500/Msun) < 15 in an
area of 114 sq. degrees (KiDS ESO-DR2). A comparison with publicly available
Sloan Digital Sky Survey (SDSS)-based cluster catalogs shows that we match more
than 50% of the clusters (77% in the case of the redMaPPer catalog). We also
cross-matched our cluster catalog with the Abell clusters, and clusters found
by XMM and in the Planck-SZ survey; however, only a small number of them lie
inside the KiDS area currently available.Comment: 13 pages, 15 figures. Accepted for publication on Astronomy &
Astrophysic
ISO-SWS spectroscopy of NGC 1068
We present ISO-SWS spectroscopy of NGC 1068 for the wavelength range 2.4 to
45um, detecting a total of 36 emission lines. Most of the observed transitions
are fine structure and recombination lines originating in the narrow line
region. We compare the line profiles of optical lines and reddening-insensitive
infrared lines to constrain the dynamical structure and extinction properties
of the NLR. The considerable differences found are most likely explained by two
effects. (1) The spatial structure of the NLR is a combination of a highly
ionized outflow cone and lower excitation extended emission. (2) Parts of the
NLR, mainly in the receding part at velocities above systemic, are subject to
extinction that is significantly suppressing optical emission. Line asymmetries
and net blueshifts remain, however, even for infrared fine structure lines
suffering very little obscuration. This may be either due to an intrinsic
asymmetry of the NLR, or due to a very high column density obscuring component
which is hiding part of the NLR even from infrared view. Mid-infrared emission
of molecular hydrogen in NGC 1068 arises in a dense molecular medium at
temperatures of a few hundred Kelvin that is most likely closely related to the
warm and dense components seen in the near-infrared H2 transitions, and in
millimeter wave tracers of molecular gas. Any emission of the putative pc-scale
molecular torus is likely overwhelmed by this larger scale emission.Comment: aastex (V4), 9 eps figures. Accepted by Ap
Euclid preparation: XXI. Intermediate-redshift contaminants in the search for z>6 galaxies within the Euclid Deep Survey
The author list was incorrect in the published version. The name of the collaboration has been added here
Mid-J CO Emission From NGC 891: Microturbulent Molecular Shocks in Normal Star Forming Galaxies
We have detected the CO(6-5), CO(7-6), and [CI] 370 micron lines from the
nuclear region of NGC 891 with our submillimeter grating spectrometer ZEUS on
the CSO. These lines provide constraints on photodissociation region (PDR) and
shock models that have been invoked to explain the H_2 S(0), S(1), and S(2)
lines observed with Spitzer. We analyze our data together with the H_2 lines,
CO(3-2), and IR continuum from the literature using a combined PDR/shock model.
We find that the mid-J CO originates almost entirely from shock-excited warm
molecular gas; contributions from PDRs are negligible. Also, almost all the H_2
S(2) and half of the S(1) line is predicted to emerge from shocks. Shocks with
a pre-shock density of 2x10^4 cm^-3 and velocities of 10 km/s and 20 km/s for
C-shocks and J-shocks, respectively, provide the best fit. In contrast, the
[CI] line emission arises exclusively from the PDR component, which is best
parameterized by a density of 3.2x10^3 cm^-3 and a FUV field of G_o = 100 for
both PDR/shock-type combinations. Our mid-J CO observations show that
turbulence is a very important heating source in molecular clouds, even in
normal quiescent galaxies. The most likely energy sources for the shocks are
supernovae or outflows from YSOs. The energetics of these shock sources favor
C-shock excitation of the lines.Comment: 18 pages, 2 figures, 6 tables, accepted by Ap
The Energetics of Molecular Gas in NGC 891 from H2 and FIR Spectroscopy
We have studied the molecular hydrogen energetics of the edge-on spiral
galaxy NGC\,891, using a 34-position map in the lowest three pure rotational
H lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1),
and S(2) lines are bright with an extinction corrected total luminosity of
L, or 0.09\% of the total-infrared luminosity
of NGC\,891. The H line ratios are nearly constant along the plane of the
galaxy -- we do not observe the previously reported strong drop-off in the
S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so we find
no evidence for the very massive cold CO-free molecular clouds invoked to
explain the past observations. The H level excitation temperatures increase
monotonically indicating more than one component to the emitting gas. More than
99\% of the mass is in the lowest excitation (T 125 K) ``warm''
component. In the inner galaxy, the warm H emitting gas is 15\% of
the CO(1-0)-traced cool molecular gas, while in the outer regions the fraction
is twice as high. This large mass of warm gas is heated by a combination of the
far-UV photons from stars in photo-dissociation regions (PDRs) and the
dissipation of turbulent kinetic energy. Including the observed far-infrared
[OI] and [CII] fine-structure line emission and far-infrared continuum emission
in a self-consistent manner to constrain the PDR models, we find essentially
all of the S(0) and most (70\%) of the S(1) line arises from low excitation
PDRs, while most (80\%) of the S(2) and the remainder of the S(1) line emission
arises from low velocity microturbulent dissipation.Comment: Accepted for publication in The Astrophysical Journal. Figure 10
available at http://www.physics.uoc.gr/~vassilis/papers/ngc891.pd
Euclid preparation:XXVI. the Euclid Morphology Challenge: Towards structural parameters for billions of galaxies
The various Euclid imaging surveys will become a reference for studies of galaxy morphology by delivering imaging over an unprecedented area of 15 000 square degrees with high spatial resolution. In order to understand the capabilities of measuring morphologies from Euclid-detected galaxies and to help implement measurements in the pipeline of the Organisational Unit MER of the Euclid Science Ground Segment, we have conducted the Euclid Morphology Challenge, which we present in two papers. While the companion paper focusses on the analysis of photometry, this paper assesses the accuracy of the parametric galaxy morphology measurements in imaging predicted from within the Euclid Wide Survey. We evaluate the performance of five state-of-the-art surface-brightness-fitting codes, DeepLeGATo, Galapagos-2, Morfometryka, ProFit and SourceXtractor++, on a sample of about 1.5 million simulated galaxies (350 000 above 5s) resembling reduced observations with the Euclid VIS and NIR instruments. The simulations include analytic Sérsic profiles with one and two components, as well as more realistic galaxies generated with neural networks. We find that, despite some code-specific differences, all methods tend to achieve reliable structural measurements (< 10% scatter on ideal Sérsic simulations) down to an apparent magnitude of about IE = 23 in one component and IE = 21 in two components, which correspond to a signal-to-noise ratio of approximately 1 and 5, respectively. We also show that when tested on non-analytic profiles, the results are typically degraded by a factor of 3, driven by systematics. We conclude that the official Euclid Data Releases will deliver robust structural parameters for at least 400 million galaxies in the Euclid Wide Survey by the end of the mission. We find that a key factor for explaining the different behaviour of the codes at the faint end is the set of adopted priors for the various structural parameters.</p
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