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SDSS J122958.84+000138.0: A compact, optically red galaxy
摘要： We report a new compact galaxy, SDSS J122958.84+000138.0 (SDSS J1229+0001), which has unique morphological and stellar population properties that are rare in observations of the nearby Universe. SDSS J1229+0001 has an r-band absolute magnitude (Mr) and half-light radius (Rh) of ?17.75 mag and 520 pc, respectively. Located in a fairly low-density environment, morphologically it is akin to a typical early-type galaxy as it has a smooth appearance and red colour. However, interestingly, it possesses centrally concentrated star-forming activity with a significant amount of dust. We present an analysis of its structural and stellar population properties using archival images and VLT/FORS2 spectroscopy. An analysis of the UKIDSS H-band image shows that the observed light distribution is better fitted with a two-component Sérsic function with inner and outer component effective radii of 190 and 330 pc, respectively. The overall half-light radius measured in the H band is much smaller compared to optical, i.e. 290 pc. We prepared a spectral energy distribution from optical to far-infrared and interpret it to derive the star-formation rate, dust mass and stellar mass. We find that SDSS J1229+0001 has dust mass Mdust = 5.1 × 10^5 M☉ with a dust-to-stellar mass ratio log(Mdust/M?) = ?3.5. While the observed stellar population properties are – to some extent – like those of a typical S0 galaxy, a unified view from stellar population and structural properties may suggest that SDSS J1229+0001 is a smoking gun example of a compact early-type galaxy in formation.
关键词： galaxies: formation,galaxies: star formation,galaxies: elliptical and lenticular, cD,galaxies: individual: SDSS J122958.84+000138.0,galaxies: evolution,galaxies: dwarf
更新于2025-09-23 15:22:29
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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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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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THE BOSS EMISSION-LINE LENS SURVEY. IV. SMOOTH LENS MODELS FOR THE BELLS GALLERY SAMPLE
摘要： We present Hubble Space Telescope F606W-band imaging observations of 21 galaxy-Lyα emitter lens candidates in the Baryon Oscillation Spectroscopic Survey Emission-Line Lens Survey (BELLS) for the GALaxy-Lyα EmitteR sYstems (BELLS GALLERY) survey. Seventeen systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately 0.55, while the lensed sources are Lyα emitters (LAEs) at redshifts from two to three. Although most of the lens systems are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field, a thorough exploration of dark substructures in the lens galaxies is required. The Einstein radii of the BELLS GALLERY lenses are, on average, 60% larger than those of the BELLS lenses because of the much higher source redshifts. This will allow for a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average ～13× lensing magnification, the LAEs are frequently resolved into individual star-forming knots with a wide range of properties. They have characteristic sizes from less than 100 pc to several kiloparsecs, rest-frame far-UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.
关键词： galaxies: elliptical and lenticular, cD,gravitational lensing: strong,dark matter,techniques: image processing
更新于2025-09-04 15:30:14