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The influence of diffuse scattered light
摘要： All telescopes and instruments are to some degree affected by scattered light. It is possible to estimate the amount of such scattered light, and even correct for it, with a radially extended point spread function (PSF). The outer parts of the PSF have only rarely been determined, since they are faint and therefore difficult to measure. A mostly complete overview of existing properties and measurements of radially extended PSFs is presented, to both show their similarities and to indicate how bright extended objects can be used to measure the faintest regions. The importance of the far wings of the PSF and their possible temporal variations are demonstrated in three edge-on galaxy models. The same study is applied to the first edge-on galaxy where earlier observations reveal a halo, NGC 5907. All PSFs were collected in two diagrams, after they were offset or normalized, when that was possible. Surface-brightness structures of edge-on galaxies were modelled and analysed to study scattered-light haloes that result when there is an exponential disc. The models were convolved with both a lower-limit PSF and a more average PSF. The PSF of the observed data could be used in the case of NGC 5907. The comparison of the PSFs demonstrates a lower-limit r?2 power-law decline at larger radii. The analysis of the galaxy models shows that the outer parts of the PSF also are important to correctly model and analyse observations and, in particular, fainter regions. The reassessed analysis of the earlier measurements of NGC 5907 reveals an explanation for the faint halo in scattered light, within the quoted level of accuracy.
关键词： telescopes,galaxies: individual: NGC 5907,methods: observational,galaxies: halos,methods: data analysis,galaxies: structure
更新于2025-09-23 15:22:29
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The optical morphologies of galaxies in the IllustrisTNG simulation: a comparison to Pan-STARRS observations
摘要： We have generated synthetic images of ～27 000 galaxies from the IllustrisTNG and the original Illustris hydrodynamic cosmological simulations, designed to match Pan-STARRS observations of log10(M?/M(cid:4)) ≈ 9.8–11.3 galaxies at z ≈ 0.05. Most of our synthetic images were created with the SKIRT radiative transfer code, including the effects of dust attenuation and scattering, and performing the radiative transfer directly on the Voronoi mesh used by the simulations themselves. We have analysed both our synthetic and real Pan-STARRS images with the newly developed statmorph code, which calculates non-parametric morphological diagnostics – including the Gini–M20 and concentration–asymmetry–smoothness statistics – and performs 2D S′ersic ?ts. Overall, we ?nd that the optical morphologies of IllustrisTNG galaxies are in good agreement with observations, and represent a substantial improvement compared to the original Illustris simulation. In particular, the locus of the Gini–M20 diagram is consistent with that inferred from observations, while the median trends with stellar mass of all the morphological, size and shape parameters considered in this work lie within the ～1σ scatter of the observational trends. However, the IllustrisTNG model has some dif?culty with more stringent tests, such as producing a strong morphology–colour relation. This results in a somewhat higher fraction of red discs and blue spheroids compared to observations. Similarly, the morphology–size relation is problematic: while observations show that discs tend to be larger than spheroids at a ?xed stellar mass, such a trend is not present in IllustrisTNG.
关键词： galaxies: statistics,galaxies: formation,galaxies: structure,methods: numerical,techniques: image processing
更新于2025-09-23 15:22:29
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KMTNet Nearby Galaxy Survey. I. Optimal Strategy for Low Surface Brightness Imaging with KMTNet
摘要： In hierarchical galaxy formation models, galaxies evolve through mergers and accretions. Tidally disrupted debris from these processes can remain as diffuse, faint structures, which can provide useful insight into the assembly history of galaxies. To investigate the properties of the faint structures in outskirts of nearby galaxies, we conduct deep and wide-field imaging survey with Korea Microlensing Telescope Network (KMTNet). We present our observing strategy and optimal data reduction process to recover the faint extended features in the imaging data of NGC 1291 taken with KMTNet. Through the dark sky flat-fielding and optimal sky subtraction, we can effectively remove inhomogeneous patterns. In the combined images, the peak-to-peak global sky gradients were reduced to less than ～0.5% and ～0.3% of the original B- and R-band sky levels, respectively. However, we find local spatial fluctuations in the background sky that can affect the precise measurement of the sky value. Consequently, we can reach the surface brightness of mB,1σ～29.5 and mR,1σ～28.5 mag arcsec?2 in azimuthally averaged one-dimensional surface brightness profiles, which is mainly limited by the uncertainty in the sky determination. These results suggest that the deep imaging data produced by KMTNet are suitable to study the faint features of nearby galaxies such as outer disks and dwarf companions, but unideal (not impossible) to detect stellar halos. The one-dimensional profile revealed that NGC 1291 appeared to have a Type I disk out to R ～30 kpc with no obvious color gradient, and excess light due to a stellar halo was undetected.
关键词： galaxies: structure,galaxies: individual (NGC 1291),galaxies: stellar content,techniques: image processing
更新于2025-09-23 15:21:21
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Tidal Features at 0.05 < <i>z</i> < 0.45 in the Hyper Suprime-Cam Subaru Strategic Program: Properties and Formation Channels
摘要： We present 1201 galaxies at 0.05 < z < 0.45 that host tidal features in the first ～200 deg2 of imaging from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We select these galaxies from a sample of 21,208 galaxies with spectroscopic redshifts drawn from the Sloan Digital Sky Survey (SDSS) spectroscopic campaigns. Of these galaxies, we identify 214 shell systems and 987 stream systems. For 575 of these systems, we are additionally able to measure the (g?i) colors of the tidal features. We find evidence for star formation in a subset of the streams, with the exception of streams around massive ellipticals, and find that stream host galaxies span the full range of stellar masses in our sample. Galaxies that host shells are predominantly red and massive: we find that observable shells form more frequently around ellipticals than around disk galaxies of the same stellar mass. Although the majority of the shells in our sample are consistent with being formed by minor mergers, 15% ± 4.4% of shell host galaxies have (g?i) colors as red as their host galaxy, consistent with being formed by major mergers. These “red shell” galaxies are preferentially aligned with the major axis of the host galaxy, as previously predicted from simulations. We suggest that although the bulk of the observable shell population originates from fairly minor mergers, which preferentially form shells that are not aligned with the major axis of the galaxy, major mergers produce a significant number of observable shells.
关键词： techniques: image processing,galaxies: interactions,catalogs,galaxies: structure,galaxies: statistics
更新于2025-09-23 15:21:01
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Massive and dusty Hα emitters in protocluster revealed by ALMA and JVLA
摘要： We investigate the physical properties of Hα emitters (HAEs) associated to the protocluster 4C23.56 at z ～ 2.5 using continuum observations at submm (270 GHz) and radio (3 GHz) frequencies with Atacama Large Mm/submm Array (ALMA) and K. Jansky Very Large Array (JVLA). For more details see Lee et al. (in prep).
关键词： radio continuum: galaxies,galaxies: high-redshift,galaxies: structure,submillimeter,galaxies: evolution
更新于2025-09-23 15:19:57
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Photometric scaling relations of anti-truncated stellar discs in S0-Scd galaxies
摘要： Context. It has been recently found that the characteristic photometric parameters of anti-truncated discs in S0 galaxies follow tight scaling relations. Aims. We investigate whether similar scaling relations are satisfied by galaxies of other morphological types. Methods. We have analysed the trends in several photometric planes relating the characteristic surface brightness and scalelengths of the breaks and the inner and outer discs of local anti-truncated S0–Scd galaxies, using published data and fits performed to the surface brightness profiles of two samples of Type-III galaxies in the R and Spitzer 3.6 μm bands. We have performed linear fits to the correlations followed by different galaxy types in each plane, as well as several statistical tests to determine their significance. Results. We have found that 1) the anti-truncated discs of all galaxy types from Sa to Scd obey tight scaling relations both in R and 3.6 μm, as observed in S0s; 2) the majority of these correlations are significant accounting for the numbers of the available data samples; 3) the trends are clearly linear when the characteristic scalelengths are plotted on a logarithmic scale; and 4) the correlations relating the characteristic surface brightnesses of the inner and outer discs and the breaks with the various characteristic scalelengths significantly improve when the scalelengths are normalized to the optical radius of the galaxy. The observational uncertainties prevent us from discerning robustly whether the trends differ between the different types and bands, but we do not find statistical evidence of significant differences between the distributions of S0s and spirals or of barred and unbarred galaxies. These results suggest that the scaling relations of Type-III discs are independent of the morphological type and the presence (or absence) of bars within the observational uncertainties of the available datasets. However, larger and deeper samples are required to confirm this. Conclusions. The tight structural coupling implied by these scaling relations imposes strong constraints on the mechanisms proposed to explain the formation of anti-truncated stellar discs in the galaxies across the whole Hubble sequence.
关键词： galaxies: fundamental parameters,galaxies: spiral,galaxies: photometry,galaxies: structure,galaxies: evolution,galaxies: elliptical and lenticular, cD
更新于2025-09-19 17:15:36
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Resolving on 100?pc scales the UV-continuum in Lyman-α emitters between redshift 2 and 3 with gravitational lensing
摘要： We present a study of 17 LAEs at redshift 2 < z < 3 gravitationally lensed by massive early-type galaxies (ETGs) at a mean redshift of approximately 0.5. Using a fully Bayesian grid-based technique, we model the gravitational lens mass distributions with elliptical power-law profiles and reconstruct the ultraviolet (UV)-continuum surface-brightness distributions of the background sources using pixellated source models. We find that the deflectors are close to, but not consistent with isothermal models in almost all cases, at the 2σ level. We take advantage of the lensing magnification (typically μ (cid:2) 20) to characterize the physical and morphological properties of these LAE galaxies. From reconstructing the ultraviolet continuum emission, we find that the star formation rates range from 0.3 to 8.5 M(cid:3) yr?1 and that the galaxies are typically composed of several compact and diffuse components, separated by 0.4–4 kpc. Moreover, they have peak star formation rate intensities that range from 2.1 to 54.1 M(cid:3) yr?1 kpc?2. These galaxies tend to be extended with major axis ranging from 0.2 to 1.8 kpc (median 561 pc), and with a median ellipticity of 0.49. This morphology is consistent with disc-like structures of star formation for more than half of the sample. However, for at least two sources, we also find off-axis components that may be associated with mergers. Resolved kinematical information will be needed to confirm the disc-like nature and possible merger scenario for the LAEs in the sample.
关键词： galaxies: structure
更新于2025-09-10 09:29:36