| 1. |
- Gouliermis, Dimitrios A., et al.
(författare)
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Hierarchical star formation across the ring galaxy NGC 6503
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 452:4, s. 3508-3528
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep Hubble Space Telescope photometry obtained with the Legacy ExtraGalactic UV Survey. We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95 per cent being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviours, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of similar to 1.7 for length-scales between similar to 20 pc and 2.5 kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances between 1 and 2.5 kpc. About 60 per cent of the young stars belong to the detected stellar structures, while the remaining stars are distributed among the complexes, still inside the ring of the galaxy. The analysis of the time-dependent clustering of young populations shows a significant change from a more clustered to a more distributed behaviour in a time-scale of similar to 60 Myr. The observed hierarchy in stellar clustering is consistent with star formation being regulated by turbulence across the ring. The rotational velocity difference between the edges of the ring suggests shear as the driving mechanism for this process. Our findings reveal the interesting case of an inner ring forming stars in a hierarchical fashion.
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| 2. |
- Jin, Shoko, et al.
(författare)
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The wide-field, multiplexed, spectroscopic facility WEAVE : Survey design, overview, and simulated implementation
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 530:3, s. 2688-2730
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Tidskriftsartikel (refereegranskat)abstract
- WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, saw first light in late 2022. WEAVE comprises a new 2-deg field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366-959nm at R similar to 5000, or two shorter ranges at . After summarizing the design and implementation of WEAVE and its data systems, we present the organization, science drivers, and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for similar to 3 million stars and detailed abundances for similar to 1.5 million brighter field and open-cluster stars; (ii) survey similar to 0.4 million Galactic-plane OBA stars, young stellar objects, and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey similar to 400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionized gas in z < 0.5 cluster galaxies; (vi) survey stellar populations and kinematics in field galaxies at 0.3 less than or similar to z less than or similar to 0.7; (vii) study the cosmic evolution of accretion and star formation using >1 million spectra of LOFAR-selected radio sources; and (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.
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| 3. |
- Royer, Pierre, et al.
(författare)
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Classification of Wolf-Rayet stars in NGC 595 in M 33 through high-spatial resolution observations
- 2003
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Ingår i: A Massive Star Odyssey: From Main Sequence to Supernova (Proceedings of IAU Symposium ; 212). - 1583811338 ; 212, s. 572-572
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Konferensbidrag (refereegranskat)abstract
- NGC 595 is, after NGC 604, the second most luminous HII region in theMilky Ways neighbouring spiral galaxy M 33. Its Wolf-Rayet starcontent has mainly been unveiled by two different channels. On the onehand, the stellar population of NGC 595 has been resolved and its WRstars identified through on-line/off-line HeIIlambda4686 observationsrealised with the HST. Nevertheless, due to the limited number offilters used, this did not give any information on the WR spectralsubtypes. On the other hand, spectroscopic observations of NGC 595,realised at optical and ultraviolet wavelengths, have enabled thedetermination of some spectral subtypes, but this time, the lack ofangular resolution did not allow to resolve the whole population.Thanks to our photometric technique, based on five dedicated narrow-bandfilters, we present here a determination of the spectral subtypes of NGC595 WR stars which for the first time combines high-angular resolutionand high-spectroscopic discrimination capabilities.
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| 4. |
- Wofford, Aida, et al.
(författare)
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Candidate LBV stars in galaxy NGC 7793 found via HST photometry plus MUSE spectroscopy
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 493:2, s. 2410-2428
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Tidskriftsartikel (refereegranskat)abstract
- Only about 19 Galactic and 25 extragalactic bonafide luminous blue variables (LBVs) are known to date. This incomplete census prevents our understanding of this crucial phase of massive star evolution which leads to the formation of heavy binary black holes via the classical channel. With large samples of LBVs one could better determine the duration and maximum stellar luminosity which characterize this phase. We search for candidate LBVs (cLBVs) in a new galaxy, NGC 7793. For this purpose, we combine high spatial resolution images from two Hubble Space Telescope (HST) programs with optical spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE). By combining PSF-fitting photometry measured on F547M, F657N, and F814W images, with restrictions on point-like appearance (at HST resolution) and Ha luminosity, we find 100 potential cLBVs, 36 of which fall in the MUSE fields. Five of the latter 36 sources are promising cLBVs which have M-V <= -7 and a combination of: H alpha with a P-Cygni profile; no [O I]lambda 6300 emission; weak or no [O III]lambda 5007 emission; large [N II]/H alpha relative to HII regions; and [S II]lambda 6716/[S II]lambda 6731 similar to 1. It is not clear if these five cLBVs are isolated from O-type stars, which would favour the binary formation scenario of LBVs. Our study, which approximately covers one fourth of the optical disc of NGC 7793, demonstrates how by combining the above HST surveys with multi-object spectroscopy from 8-m class telescopes, one can efficiently find large samples of cLBVs in nearby galaxies.
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