Euclid preparation Bretonnière, H.; Kuchner, U.; Merlin, E. ...
Astronomy and astrophysics (Berlin),
03/2023, Letnik:
671
Journal Article
Recenzirano
Odprti dostop
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 5
σ
) 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
I
E
= 23 in one component and
I
E
= 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.
Point‐Source Extraction with MOPEX Makovoz, David; Marleau, Francine R.
Publications of the Astronomical Society of the Pacific,
10/2005, Letnik:
117, Številka:
836
Journal Article
Recenzirano
Odprti dostop
MOPEX (Mosaicking and Point‐source Extraction) is a package developed at theSpitzerScience Center for astronomical image processing. We report on the point‐source extraction capabilities of MOPEX. ...Point‐source extraction is implemented as a two‐step process: point‐source detection and profile fitting. Nonlinear matched filtering of input images can be performed optionally to increase the signal‐to‐noise ratio and improve detection of faint point sources. Point response function (PRF) fitting of point sources produces the final point‐source list, which includes the fluxes and improved positions of the point sources, along with other parameters characterizing the fit. Passive and active deblending allows for successful fitting of confused point sources. Aperture photometry can also be computed for every extracted point source for an unlimited number of aperture sizes. The PRF is estimated directly from the input images. The implementation of efficient methods of background and noise estimation and a modified simplex algorithm contribute to the computational efficiency of MOPEX. The package is implemented as a loosely connected set of Perl scripts, each script running a number of modules written in C/C++. Input parameter setting is done through name lists, ASCII configuration files. We present applications of point‐source extraction to the mosaic images taken at 24 and 70 μm with the Multiband Imaging Photometer (MIPS) as part of theSpitzerextragalactic First Look Survey, and to a Digital Sky Survey image. Completeness and reliability of point‐source extraction is computed using simulated data.
It was first observed in the 1970s that the dwarf galaxies surrounding our Milky Way, so-called satellites, appear to be arranged in a thin, vast plane. Similar discoveries have been made around ...additional galaxies in the local Universe such as Andromeda, Centaurus A, and potentially M83. In the specific cases with available kinematic data, the dwarf satellites also appear to preferentially co-orbit their massive host galaxy. Planes of satellites are rare in the lambda cold dark matter (\(\Lambda\)CDM) paradigm, although they may be a natural consequence of projection effects. Such a phase-space correlation, however, remains difficult to explain. In this work we analyzed the 2D spatial distribution of 2210 dwarf galaxies around early-type galaxies (ETGs) in the low-to-medium density fields of the "Mass Assembly of early-Type GaLAxies with their fine Structures" (MATLAS) survey. Under the assumption that the dwarfs are satellite members of the central massive ETG, we identified flattened structures using both a variation in the Hough transform and total least square (TLS) fitting. In 119 satellite systems, we find 31 statistically significant flattened dwarf structures using a combination of both methods with subsequent Monte Carlo (MC) simulations with random data. The vast majority of these dwarf structures lie within the estimated virial radii of the massive host. The major axes of these systems are aligned better than 30{\deg} with the estimated orientation of the large-scale structure in nine (50%) cases. Additional distance measurements and future kinematic studies will be required to confirm the planar nature of these structures and to determine if they are corotating systems.
Supermassive black holes underwent periods of exponential growth during which we see them as quasars in the distant Universe. The summed emission from these quasars generates the cosmic X-ray ...background, the spectrum of which has been used to argue that most black-hole growth is obscured. There are clear examples of obscured black-hole growth in the form of 'type-2' quasars, but their numbers are fewer than expected from modelling of the X-ray background. Here we report the direct detection of a population of distant type-2 quasars, which is at least comparable in size to the well-known unobscured type-1 population. We selected objects that have mid-infrared and radio emissions characteristic of quasars, but which are faint at near-infrared and optical wavelengths. We conclude that this population is responsible for most of the black-hole growth in the young Universe and that, throughout cosmic history, black-hole growth occurs in the dusty, gas-rich centres of active galaxies.
Spitzer observations of Abell 1763 Biviano, A.; Fadda, D.; Durret, F. ...
Astronomy and astrophysics (Berlin),
08/2011, Letnik:
532
Journal Article
Recenzirano
Context. The study of galaxy luminosity functions (LFs) in different environments provides powerful constraints on the physics of galaxy evolution. The infrared (IR) LF is a particularly useful tool ...since it is directly related to the distribution of galaxy star-formation rates (SFRs). Aims. We aim to determine the galaxy IR LF as a function of the environment in a supercluster at redshift 0.23 to shed light on the processes driving galaxy evolution in and around clusters. Methods. We base our analysis on multi-wavelength data, which include optical, near-IR, and mid- to far-IR photometry, as well as redshifts from optical spectroscopy. We identify 467 supercluster members in a sample of 24-μm-selected galaxies, on the basis of their spectroscopic (153) and photometric (314) redshifts. IR luminosities and stellar masses are determined for supercluster members via spectral energy distribution fitting. Galaxies with active galactic nuclei are identified by a variety of methods and excluded from the sample. SFRs are obtained for the 432 remaining galaxies from their IR luminosities via the Kennicutt relation. Results. We determine the IR LF of the whole supercluster as well as the IR LFs of three different regions in the supercluster: the cluster core, a large-scale filament, and the cluster outskirts (excluding the filament). A comparison of the IR LFs of the three regions, normalized by the average number densities of r-band selected normal galaxies, shows that the filament (respectively, the core) contains the highest (respectively, the lowest) fraction of IR-emitting galaxies at all levels of IR luminosities, and the highest (respectively, the lowest) total SFR normalized by optical galaxy richness. Luminous IR galaxies (LIRGs) are almost absent in the core region. The relation between galaxy specific SFRs and stellar masses does not depend on the environment, and it indicates that most supercluster LIRGs are rather massive galaxies with relatively low specific SFRs. A comparison with previous IR LF determinations from the literature confirms that the mass-normalized total SFR in clusters increases with redshift, but more rapidly than previously suggested for redshifts ≲ 0.4. Conclusions. The IR LF shows an environmental dependence that is not simply related to the local galaxy density. The filament, an intermediate-density region in the A1763 supercluster, contains the highest fraction of IR-emitting galaxies. We interpret our findings within a possible scenario for the evolution of galaxies in and around clusters.
PDF
