ORCID Profile
0000-0003-4945-0056
Current Organisations
UK Astronomy Technology Centre
,
James Cook University
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Publisher: Oxford University Press (OUP)
Date: 12-10-2019
Abstract: We present an extensive study of the Sagittarius II (Sgr II) stellar system using MegaCam g and i photometry, narrow-band, metallicity-sensitive calcium H& K doublet photometry and Keck II/DEIMOS multiobject spectroscopy. We derive and refine the Sgr II structural and stellar properties inferred at the time of its discovery. The colour–magnitude diagram implies Sgr II is old (12.0 ± 0.5 Gyr) and metal poor. The CaHK photometry confirms the metal-poor nature of the satellite ([Fe/H] CaHK = −2.32 ± 0.04 dex) and suggests that Sgr II hosts more than one single stellar population ($\\sigma _\\mathrm{[FeH]}^\\mathrm{CaHK} = 0.11^{+0.05}_{-0.03}$ dex). Using the Ca infrared triplet measured from our highest signal-to-noise spectra, we confirm the metallicity and dispersion inferred from the Pristine photometric metallicities ([Fe/H]spectro = −2.23 ± 0.05 dex, $\\sigma _\\mathrm{[Fe/H]}^\\mathrm{spectro} = 0.10 ^{+0.06}_{-0.04}$ dex). The velocity dispersion of the system is found to be $\\sigma _{v} = 2.7^{+1.3}_{-1.0} {\\rm \\, km \\,\\, s^{-1}}$ after excluding two potential binary stars. Sgr II’s metallicity and absolute magnitude (MV = −5.7 ± 0.1 mag) place the system on the luminosity–metallicity relation of the Milky Way dwarf galaxies despite its small size. The low but resolved metallicity and velocity dispersions paint the picture of a slightly dark-matter-dominated satellite ($M/L = 23.0^{+32.8}_{-23.0}$ M⊙ L$^{-1}_{\\odot }$). Furthermore, using the Gaia Data Release 2, we constrain the orbit of the satellite and find an apocentre of $118.4 ^{+28.4}_{-23.7} {\\rm \\, kpc}$ and a pericentre of $54.8 ^{+3.3}_{-6.1} {\\rm \\, kpc}$. The orbit of Sgr II is consistent with the trailing arm of the Sgr stream and indicates that it is possibly a satellite of the Sgr dSph that was tidally stripped from the dwarf’s influence.
Publisher: American Astronomical Society
Date: 21-09-2012
Publisher: Oxford University Press (OUP)
Date: 08-07-2017
Publisher: Oxford University Press (OUP)
Date: 13-10-2015
Publisher: EDP Sciences
Date: 12-2018
DOI: 10.1051/0004-6361/201833914
Abstract: We observed the late-type peculiar galaxy NGC 4424 during the Virgo Environmental Survey Tracing Galaxy Evolution (VESTIGE), a blind narrow-band H α +[NII] imaging survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii Telescope (CFHT). The presence of a ∼110 kpc (in projected distance) HI tail in the southern direction indicates that this galaxy is undergoing a ram pressure stripping event. The deep narrow-band image revealed a low surface brightness (Σ(H α ) ≃ 4 × 10 −18 erg s −1 cm −2 arcsec −2 ) ionised gas tail ∼10 kpc in length extending from the centre of the galaxy to the north-west, thus in the direction opposite to the HI tail. Chandra and XMM X-rays data do not show a compact source in the nucleus or an extended tail of hot gas, while IFU spectroscopy (MUSE) indicates that the gas is photo-ionised in the inner regions and shock-ionised in the outer parts. Medium-resolution (MUSE) and high-resolution (Fabry-Perot) IFU spectroscopy confirms that the ionised gas is kinematically decoupled from the stellar component and indicates the presence of two kinematically distinct structures in the stellar disc. The analysis of the SED of the galaxy indicates that the activity of star formation was totally quenched in the outer disc ∼250–280 Myr ago, while only reduced by ∼80% in the central regions. All this observational evidence suggests that NGC 4424 is the remnant of an unequal-mass merger that occurred ≲500 Myr ago when the galaxy was already a member of the Virgo cluster, and is now undergoing a ram pressure stripping event that has removed the gas and quenched the activity of star formation in the outer disc. The tail of ionised gas probably results from the outflow produced by a central starburst fed by the collapse of gas induced by the merging episode. This outflow is sufficiently powerful to overcome the ram pressure induced by the intracluster medium on the disc of the galaxy crossing the cluster. This analysis thus suggests that feedback can participate in the quenching process of galaxies in high-density regions.
Publisher: Oxford University Press (OUP)
Date: 10-02-2016
DOI: 10.1093/MNRAS/STW080
Publisher: Zenodo
Date: 2021
Publisher: Oxford University Press (OUP)
Date: 17-07-2020
Abstract: Metal-poor stars are important tools for tracing the early history of the Milky Way, and for learning about the first generations of stars. Simulations suggest that the oldest metal-poor stars are to be found in the inner Galaxy. Typical bulge surveys, however, lack low metallicity ($\\rm {[Fe/H]} \\lt -1.0$) stars because the inner Galaxy is predominantly metal-rich. The aim of the Pristine Inner Galaxy Survey (PIGS) is to study the metal-poor and very metal-poor (VMP, $\\rm {[Fe/H]} \\lt -2.0$) stars in this region. In PIGS, metal-poor targets for spectroscopic follow-up are selected from metallicity-sensitive CaHK photometry from the CFHT. This work presents the ∼250 deg2 photometric survey as well as intermediate-resolution spectroscopic follow-up observations for ∼8000 stars using AAOmega on the AAT. The spectra are analysed using two independent tools: ULySS with an empirical spectral library, and FERRE with a library of synthetic spectra. The comparison between the two methods enables a robust determination of the stellar parameters and their uncertainties. We present a s le of 1300 VMP stars – the largest s le of VMP stars in the inner Galaxy to date. Additionally, our spectroscopic data set includes ∼1700 horizontal branch stars, which are useful metal-poor standard candles. We furthermore show that PIGS photometry selects VMP stars with unprecedented efficiency: 86 per cent/80 per cent (lower/higher extinction) of the best candidates satisfy $\\rm {[Fe/H]} \\lt -2.0$, as do 80 per cent/63 per cent of a larger, less strictly selected s le. We discuss future applications of this unique data set that will further our understanding of the chemical and dynamical evolution of the innermost regions of our Galaxy.
Publisher: EDP Sciences
Date: 06-2018
DOI: 10.1051/0004-6361/201732407
Abstract: The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band (NB) Hα +[NII] imaging survey carried out with MegaCam at the Canada–France–Hawaii Telescope. The survey covers the whole Virgo cluster region from its core to one virial radius (104 deg 2 ). The sensitivity of the survey is of f ( Hα ) ~ 4 × 10 −17 erg s −1 cm −2 (5 σ detection limit) for point sources and Σ( Hα ) ~ 2 × 10 −18 erg s −1 cm −2 arcsec −2 (1 σ detection limit at 3 arcsec resolution) for extended sources, making VESTIGE the deepest and largest blind NB survey of a nearby cluster. This paper presents the survey in all its technical aspects, including the survey design, the observing strategy, the achieved sensitivity in both the NB Hα +[NII] and in the broad-band r filter used for the stellar continuum subtraction, the data reduction, calibration, and products, as well as its status after the first observing semester. We briefly describe the Hα properties of galaxies located in a 4 × 1 deg 2 strip in the core of the cluster north of M87, where several extended tails of ionised gas are detected. This paper also lists the main scientific motivations for VESTIGE, which include the study of the effects of the environment on galaxy evolution, the fate of the stripped gas in cluster objects, the star formation process in nearby galaxies of different type and stellar mass, the determination of the Hα luminosity function and of the Hα scaling relations down to ~10 6 M ⊙ stellar mass objects, and the reconstruction of the dynamical structure of the Virgo cluster. This unique set of data will also be used to study the HII luminosity function in hundreds of galaxies, the diffuse Hα +[NII] emission of the Milky Way at high Galactic latitude, and the properties of emission line galaxies at high redshift.
Publisher: Oxford University Press (OUP)
Date: 26-11-0011
Abstract: Our Galaxy is known to contain a central boxy eanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large s le of metal-poor ($\\rm {[Fe/H]}\\, \\lt -1.0$) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H] , until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for $-3.0 \\lt \\rm {[Fe/H]}\\, \\lt -0.5$, with a gradient of −44 ± 4 km s−1 dex−1. These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping on to the boxy eanut-shaped bulge for former disc stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy.
Publisher: SPIE
Date: 29-08-2022
DOI: 10.1117/12.2629990
Publisher: Oxford University Press (OUP)
Date: 19-02-2014
DOI: 10.1093/MNRAS/STU135
Publisher: Oxford University Press (OUP)
Date: 21-04-2014
DOI: 10.1093/MNRAS/STU496
Publisher: Oxford University Press (OUP)
Date: 04-06-2013
DOI: 10.1093/MNRAS/STT777
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Ruben Sanchez-Janssen.