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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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ASTROSAT/UVIT Survey of M31, First Results: UV-bright Stars in the Bulge
摘要： A survey of M31 is being carried out with the ASTROSAT Observatory in ultraviolet (UV), soft X-rays, and hard X-rays using the UltraViolet Imaging Telescope (UVIT), soft X-ray telescope, LAXPC, and CZT instruments. Here we analyze UVIT observations of the ?rst ?eld covering the central (7′) part of the bulge of M31. The UV bands observed cover the range 120–280 nm with four ?lters with a spatial resolution of 1″. They are sensitive to the UV emission from hot stars (Teff > 10000 K), so can be used to detect the hottest stars in the bulge of M31. We cross-match the UVIT sources with sources from Panchromatic Hubble Andromeda Treasury to obtain multi-band spectral energy distributions (SEDs) for 26 sources. Fits of the SEDs with stellar models show that these are likely main-sequence stars with masses in the range 5–20 Me. This provides evidence for a low, but signi?cant (～10?5 Me yr?1), rate of star formation in the bulge of M31, which has occurred in the very recent past (～10–100 million years).
关键词： galaxies: individual (M31),galaxies: stellar content,galaxies: bulges
更新于2025-09-23 15:21:21
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The effects of spatial resolution on integral field spectrograph surveys at different redshifts ? The CALIFA perspective
摘要： Context. Over the past decade, 3D optical spectroscopy has become the preferred tool for understanding the properties of galaxies and is now increasingly used to carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass, ATLAS3D, PINGS, and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS, GLACE, and IMAGES have targeted the most luminous galaxies to study mainly their kinematic properties. The on-going CALIFA survey (z ～ 0.02) is the ?rst of a series of upcoming integral ?eld spectroscopy (IFS) surveys with large samples representative of the entire population of galaxies. Others include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at higher redshift. Given the importance of spatial scales in IFS surveys, the study of the e?ects of spatial resolution on the recovered parameters becomes important. Aims. We explore the capability of the CALIFA survey and a hypothetical higher redshift survey to reproduce the properties of a sample of objects observed with better spatial resolution at lower redshift. Methods. Using a sample of PINGS galaxies, we simulated observations at di?erent redshifts. We then studied the behaviour of di?erent parameters as the spatial resolution degrades with increasing redshift. Results. We show that at the CALIFA resolution, we are able to measure and map common observables in a galaxy study: the number and distribution of H ii regions (Hα ?ux structure), the gas metallicity (using the O3N2 method), the gas ionization properties (through the [N ii]/Hα and [O iii]/Hβ line ratios), and the age of the underlying stellar population (using the D4000 index). This supports the aim of the survey to characterise the observable properties of galaxies in the Local Universe. Our analysis of simulated IFS data cubes at higher redshifts highlights the importance of the projected spatial scale per spaxel as the most important ?gure of merit in the design of an integral ?eld survey.
关键词： stars: formation,galaxies: stellar content,galaxies: ISM,galaxies: abundances,techniques: spectroscopic
更新于2025-09-23 15:21:01
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The Stellar Contents of Intermediate-mass Disk Galaxies in the Virgo Cluster. I. GMOS Spectra
摘要： The stellar contents of six intermediate-mass early-type disk galaxies in the Virgo cluster are examined using deep long slit spectra. The isophotal and photometric properties of the galaxies at near- and mid-infrared wavelengths are also examined. Characteristic ages and metallicities are found by making comparisons with the strengths of lines measured from model spectra. The light from the central regions of these galaxies at visible/red wavelengths is not dominated by old populations. Rather, the central regions of four galaxies (NGC 4305, NGC 4306, NGC 4497, and NGC 4620) are dominated by populations with ages ～1.5–3 Gyr. Centrally concentrated line emission is found in two of the galaxies (NGC 4491 and NGC 4584), and the relative strengths of Hα and [S II]6746 are consistent with this emission originating in star-forming regions. The disks of these galaxies are dominated by populations that are at least 1 Gyr older than those near the centers, indicating that the quenching of star formation progressed from large radii inwards, and did not occur over a short timescale. NGC 4497 has the oldest disk, with a luminosity-weighted age of 10 Gyr. The metallicities of the galaxies in this sample are consistent with their integrated brightnesses, suggesting that they have not been subjected to large-scale stellar stripping. [Mg/Fe] is roughly solar, suggesting that these systems retained and enriched gas over timescales of at least 1 Gyr. The progenitors of these galaxies were likely late-type systems that were accreted by Virgo during intermediate or early epochs and have since been depleted of gas and dust.
关键词： galaxies: evolution,galaxies: stellar content
更新于2025-09-23 15:21:01
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Artificial Star Test for Crowded Field CCD Photometry
摘要： A new method of performing an arti?cial star test (AST) for crowded ?eld stellar CCD photometry is proposed. This AST method is superior in the cases when it is necessary to account for varying photometric quality across the study ?eld, arising due to crowding variations. For this purpose, the color-magnitude diagrams (CMDs) of AST stars with statistically reliable error estimates, as well as completeness maps, can be generated at a required spatial resolution.
关键词： techniques: photometric,catalogs,galaxies: stellar content
更新于2025-09-23 15:21:01
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Near-infrared spectroscopic indices for unresolved stellar populations
摘要： Context. A new generation of spectral synthesis models has been developed in recent years, but there is no matching set of template galaxy spectra, in terms of quality and resolution, for testing and refining the new models. Aims. Our main goal is to find and calibrate new near-infrared spectral indices along the Hubble sequence of galaxies which will be used to obtain additional constraints to the population analysis based on medium-resolution integrated spectra of galaxies. Methods. Spectra of previously studied and well-understood galaxies with relatively simple stellar populations (e.g., ellipticals or bulge dominated galaxies) are needed to provide a baseline data set for spectral synthesis models. Results. X-shooter spectra spanning the optical and infrared wavelengths (350–2400 nm) of bright nearby elliptical galaxies with a resolving power of R ～ 4000–5400 were obtained. Heliocentric systemic velocity, velocity dispersion, and Mg, Fe, and Hβ line-strength indices are presented. Conclusions. We present a library of very-high-quality spectra of galaxies covering a large range of age, metallicity, and morphological type. Such a dataset of spectra will be crucial to addressing important questions of the modern investigation concerning galaxy formation and evolution.
关键词： galaxies: formation,galaxies: stellar content,infrared: galaxies,surveys,galaxies: abundances
更新于2025-09-23 15:19:57
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The X-shooter Spectral Library (XSL)
摘要： We present the ?rst release of the X-shooter Spectral Library (XSL). This release contains 237 stars. The spectra in this release span a wavelength range of 3000–10 200 ? and have been observed at a resolving power of R ≡ λ/Δλ ～ 10 000. The spectra were obtained at ESO’s 8-m Very Large Telescope (VLT). The sample contains O–M, long-period variable, C and S stars. The spectra are ?ux-calibrated and telluric-corrected. We describe a new technique for the telluric correction. The wavelength coverage, spectral resolution, and spectral type of this library make it well suited to stellar population synthesis of galaxies and clusters, kinematical investigation of stellar systems, and the study of the physics of cool stars.
关键词： stars: fundamental parameters,galaxies: stellar content,stars: atmospheres,stars: AGB and post-AGB,stars: abundances
更新于2025-09-23 15:19:57
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Erratum: Modelling and interpreting spectral energy distributions of galaxies with beagle
摘要： The paper ‘Modelling and interpreting spectral energy distributions of galaxies with BEAGLE’ was published in MNRAS, 2016, 462 (Chevallard & Charlot 2016). During one of the revisions of the manuscript, the last term of equation (25) was inadvertently removed. The correct form of equation (25) is therefore log US = (cid:2) ?3.638 + 0.055 x + 0.680 x2 ?3.640 for x (cid:2) ?0.04, for x > ?0.04, where x = log(ZISM/Z(cid:2)).
关键词： methods: data analysis,methods: statistical,dust, extinction,galaxies: stellar content,H II regions,galaxies: evolution
更新于2025-09-10 09:29:36
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A deconvolution technique to correct deep images of galaxies from instrumental scattered light
摘要： Deep imaging of the di?use light that is emitted by stellar ?ne structures and outer halos around galaxies is often now used to probe their past mass assembly. Because the extended halos survive longer than the relatively fragile tidal features, they trace more ancient mergers. We use images that reach surface brightness limits as low as 28.5?29 mag arcsec?2 (g-band) to obtain light and color pro?les up to 5–10 e?ective radii of a sample of nearby early-type galaxies. These were acquired with MegaCam as part of the CFHT MATLAS large programme. These pro?les may be compared to those produced using simulations of galaxy formation and evolution, once corrected for instrumental e?ects. Indeed they can be heavily contaminated by the scattered light caused by internal re?ections within the instrument. In particular, the nucleus of galaxies generates arti?cial ?ux in the outer halo, which has to be precisely subtracted. We present a deconvolution technique to remove the arti?cial halos that makes use of very large kernels. The technique, which is based on PyOperators, is more time e?cient than the model-convolution methods that are also used for that purpose. This is especially the case for galaxies with complex structures that are hard to model. Having a good knowledge of the point spread function (PSF), including its outer wings, is critical for the method. A database of MegaCam PSF models corresponding to di?erent seeing conditions and bands was generated directly from the deep images. We show that the di?erence in the PSFs in di?erent bands causes arti?cial changes in the color pro?les, in particular a reddening of the outskirts of galaxies having a bright nucleus. The method is validated with a set of simulated images and applied to three representative test cases: NGC 3599, NGC 3489, and NGC 4274, which exhibits a prominent ghost halo for two of them. This method successfully removes this.
关键词： galaxies: photometry,techniques: photometric,galaxies: elliptical and lenticular, cD,galaxies: evolution,galaxies: stellar content,techniques: image processing
更新于2025-09-04 15:30:14
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<i>Spitzer</i> mid-infrared point sources in the fields of nearby galaxies
摘要： Aims. To complement the study of transient phenomena and to assist subsequent observations in the mid-infrared, we extract point source photometry from archival mosaics of nearby galaxies with high star formation rates within 4 Mpc. Methods. Point spread function photometry was performed on sources detected in both Spitzer IRAC 3.6 μm and 4.5 μm bands at greater than 3σ above background. These data were then supplemented by aperture photometry in the IRAC 5.8 μm and 8.0 μm bands conducted at the positions of the shorter wavelength sources. For sources with no detected object in the longer wavelengths, we estimated magnitude limits based on the local sky background. Results. We present Spitzer IRAC mid-infrared point source catalogs for mosaics covering the ?elds of the nearby ((cid:46)4 Mpc) galaxies NGC 55, NGC 253, NGC 2366, NGC 4214, and NGC 5253. We detect a total of 20159 sources in these ?ve ?elds. The individual galaxy point source breakdown is the following: NGC 55, 8746 sources; NGC 253, 9001 sources; NGC 2366, 505 sources; NGC 4214, 1185 sources; NGC 5253, 722 sources. The completeness limits of the full catalog vary with bandpass and were found to be m3.6 = 18.0, m4.5 = 17.5, m5.8 = 17.0, and m8.0 = 16.5 mag. For all galaxies, this corresponds to detection of point sources brighter than M3.6 = ?10. These catalogs can be used as a reference for stellar population investigations, individual stellar object studies, and in planning future mid-infrared observations with the James Webb Space Telescope.
关键词： catalogs,stars: massive,galaxies: stellar content
更新于2025-09-04 15:30:14