- ID:
- ivo://CDS.VizieR/J/A+A/589/A139
- Title:
- Stellar populations of NGC 3311
- Short Name:
- J/A+A/589/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The history of the mass assembly of brightest cluster galaxies may be studied by mapping the stellar populations at large radial distances from the galaxy centre, where the dynamical times are long and preserve the chemodynamical signatures of the accretion events. To provide extended and robust measurements of the stellar population parameters in NGC 3311, the cD galaxy at the centre of the Hydra I cluster, and out to three effective radius. We wish to characterise the processes that drove the build up of the stellar light at all these radii. We obtained the spectra from several regions in NGC 3311 covering an area of ~3arcmin^2^ in the wavelength range 4800<lambda({AA})<5800, using the FORS2 spectrograph at the Very Large Telescope in the MXU mode. We measured the equivalent width of seven absorption-features defined in the Lick/IDS system, which were modelled by single stellar populations, to provide luminosity-weighted ages, metallicities, and alpha element abundances. The trends in the Lick indices and the distribution of the stellar population parameters indicate that the stars of NGC3311 may be divided in two radial regimes, one within and the another beyond one effective radius, R_e_=8.4kpc, similar to the distinction between the inner galaxy and the external halo derived from the NGC3311 velocity dispersion profile. The inner galaxy (R<R_e_) is old (age ~14Gyr), has negative metallicity gradients and positive alpha element gradients. The external halo is also very old, but has a negative age gradient. The metal and element abundances of the external halo both have a large scatter, indicating that stars from a variety of satellites with different masses have been accreted. The region in the extended halo associated with the off-centred envelope at 0<P.A.({deg})<90 (Arnaboldi et al., 2012A&A...545A..37A) has higher metallicity with respect to the symmetric external halo. The different stellar populations in the inner galaxy and extended halo reflect the dominance of in situ stars in the former and the accreted origin for the large majority of the stars in the latter. The low value of the velocity dispersion in the inner galaxy indicates that its stars are bound to the galaxy's gravitational potential, and the abundances and gradients suggest that the inner galaxy is formed in an outside-in scenario of merging gas-rich lumps, reminiscent of the first phase of galaxy formation. The external halo has a higher velocity dispersion, it is dynamically hotter than the galaxy and its stars are gravitationally driven by the cluster's gravitational potential. The stars in the external halo were removed from their parent galaxies, either disks with truncated star formation, or the outer regions of early-type galaxies. Late mass accretion at large radii is now coming from the tidal stripping of stars from dwarfs and S0 galaxies. These results provide supporting evidence for the recent theoretical models of formation of massive ellipticals as a two-phase process.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/631/A156
- Title:
- Stellar populations of quiescent galaxies
- Short Name:
- J/A+A/631/A156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aim is to determine the distribution of stellar population parameters (extinction, age, metallicity, and star formation rates) of quiescent galaxies within the rest-frame stellar mass-colour diagrams and UVJ colour-colour diagrams corrected for extinction up to z~1. These novel diagrams reduce the contamination in samples of quiescent galaxies owing to dust-reddened galaxies, and they provide useful constraints on stellar population parameters only using rest-frame colours and stellar mass. We set constraints on the stellar population parameters of quiescent galaxies combining the ALHAMBRA multi-filter photo-spectra with our fitting code for spectral energy distribution, MUlti-Filter FITting (MUFFIT), making use of composite stellar population models based on two independent sets of simple stellar population (SSP) models. The extinction obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from the sample of red UVJ galaxies. The distributions of stellar population parameters across these rest-frame diagrams are revealed after the dust correction and are fitted by LOESS, a bi-dimensional and locally weighted regression method, to reduce uncertainty effects. Quiescent galaxy samples defined via classical UVJ diagrams are typically contaminated by a 20% fraction of DSF galaxies. A significant part of the galaxies in the green valley are actually obscured star-forming galaxies (30-65%). Consequently, the transition of galaxies from the blue cloud to the red sequence, and hence the related mechanisms for quenching, seems to be much more efficient and faster than previously reported. The rest-frame stellar mass-colour and UVJ colour-colour diagrams are useful for constraining the age, metallicity, extinction, and star formation rate of quiescent galaxies by only their redshift, rest-frame colours, and/or stellar mass. Dust correction plays an important role in understanding how quiescent galaxies are distributed in these diagrams and is key to performing a pure selection of quiescent galaxies via intrinsic colours.
- ID:
- ivo://CDS.VizieR/J/MNRAS/412/423
- Title:
- Stellar population trends in S0 galaxies
- Short Name:
- J/MNRAS/412/423
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar population age and metallicity trends for a sample of 59 S0 galaxies based on optical Sloan Digital Sky Survey (SDSS) and near-infrared (NIR) J and H photometry. When combined with optical g and r passband imaging data from the SDSS archive and stellar population models, we obtain radial age and metallicity trends out to at least five effective radii for most of the galaxies in our sample. The sample covers a range in stellar mass and light concentration.
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/114
- Title:
- Stellar properties of Kron 3 stars
- Short Name:
- J/MNRAS/476/114
- Date:
- 02 Nov 2021 11:26:14
- Publisher:
- CDS
- Description:
- We present the results of a spectroscopic study of the intermediate age (~=6.5Gyr) massive cluster Kron 3 in the Small Magellanic Cloud. We measure CN and CH band strengths (at ~=3839 and 4300{AA}, respectively) using VLT FORS2 spectra of 16 cluster members and find a sub-population of five stars enriched in nitrogen. We conclude that this is evidence for multiple populations in Kron 3, the fourth intermediate age cluster, after Lindsay 1, NGC 416 and NGC 339 (ages 6-8Gyr), to display this phenomenon originally thought to be a unique characteristic of old globular clusters. At ~=6.5Gyr this is one of the youngest clusters with multiple populations, indicating that the mechanism responsible for their onset must operate until a redshift of at least 0.75, much later than the peak of globular cluster formation at redshift ~3.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A180
- Title:
- Stellar properties of M dwarfs
- Short Name:
- J/A+A/620/A180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Being the most numerous and oldest stars in the galaxy, M dwarfs are objects of great interest for exoplanet searches. The presence of molecules in their atmosphere complicates our understanding of their atmospheric properties. But great advances have recently been made in the modeling of M dwarfs due to the revision of solar abundances. We aim to determine stellar parameters of M dwarfs using high resolution spectra (R~90000) simultaneously in the visible and the near-infrared. The high resolution spectra and broad wavelength coverage provide an unique opportunity to understand the onset of dust and cloud formation at cool temperatures. Furthermore, this study will help in understanding the physical processes which occur in a cool atmospheres, particularly, the redistribution of energy from the optical to the near-infrared. The stellar parameters of M dwarfs in our sample have been determined by comparing the high resolution spectra both in the optical and in the near-infrared simultaneously observed by CARMENES with the synthetic spectra obtained from the BT-Settl model atmosphere. The detailed spectral synthesis of these observed spectra both in the optical and in the near-infrared helps to understand the missing continuum opacity. For the first time, we derive fundamental stellar parameters of M dwarfs using the high resolution optical and near-infrared spectra simultaneously. We determine Teff, logg and [M/H] for 292 M dwarfs of spectral type M0 to M9, where the formation of dust and clouds are important. The derived Teff for the sample ranges from 2300 to 4000K, values of log g ranges from 4.5<=logg<=5.5 and the resulting metallicity ranges from -0.5<=[M/H]<=+0.5. We have also explored the possible differences in Teff, logg and [M/H] by comparing them with other studies of the same sample of M dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/648/591
- Title:
- Stellar rotation in young clusters. II.
- Short Name:
- J/ApJ/648/591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the effective temperatures and gravities of 461 OB stars in 19 young clusters by fitting the H{gamma} profile in their spectra. We use synthetic model profiles for rotating stars to develop a method to estimate the polar gravity for these stars, which we argue is a useful indicator of their evolutionary status. We combine these results with projected rotational velocity measurements obtained in a previous paper on these same open clusters.
- ID:
- ivo://CDS.VizieR/J/MNRAS/390/1437
- Title:
- Stellar streams in Andromeda (M31)
- Short Name:
- J/MNRAS/390/1437
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic analysis of five stellar streams ("A", "B", "Cr", "Cp" and "D") as well as the extended star cluster, EC4, which lies within Stream "C", all discovered in the halo of M31 from our Canada-France-Hawaii Telescope/MegaCam survey. These spectroscopic results were initially serendipitous, making use of our existing observations from the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, and thereby emphasizing the ubiquity of tidal streams that account for ~70 per cent of the M31 halo stars in the targeted fields. Subsequent spectroscopy was then procured in Stream "C" and Stream "D" to trace the velocity gradient along the streams. Nine metal-rich ([Fe/H]~-0.7) stars at v_hel_=-349.5km/s, {sigma}_v,corr_~5.1+/-2.5km/s are proposed as a serendipitous detection of Stream "Cr", with follow-up kinematic identification at a further point along the stream. Seven metal-poor ([Fe/H]~-1.3) stars confined to a narrow, 15km/s velocity bin centred at v_hel_=-285.6, {sigma}_v,corr_=4.3^+1.7^_-1.4_km/s represent a kinematic detection of Stream "Cp", again with follow-up kinematic identification further along the stream. For the cluster EC4, candidate member stars with average [Fe/H]~-1.4, are found at v_hel_=-282 suggesting it could be related to Stream "Cp". No similarly obvious cold kinematic candidate is found for Stream "D", although candidates are proposed in both of two spectroscopic pointings along the stream (both at ~-400km/s). Spectroscopy near the edge of Stream "B" suggests a likely kinematic detection at v_hel_~-330, {sigma}_v,corr_~6.9km/s, while a candidate kinematic detection of Stream "A" is found (plausibly associated to M33 rather than M31) with v_hel_~-170, {sigma}_v,corr_=12.5km/s. The low dispersion of the streams in kinematics, physical thickness and metallicity makes it hard to reconcile with a scenario whereby these stream structures as an ensemble are related to the giant southern stream. We conclude that the M31 stellar halo is largely made up of multiple kinematically cold streams.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/3693
- Title:
- Stellar yields and the initial mass function
- Short Name:
- J/MNRAS/451/3693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a set of 144 Galactic chemical evolution models applied to a Milky Way analogue, computed using four sets of low+intermediate star nucleosynthetic yields, six massive star yield compilations, and six functional forms for the initial mass function. A comparison is made between a grid of multiphase chemical evolution models computed with these yield combinations and empirical data drawn from the Milky Way's disc, including the solar neighbourhood. By means of a {chi}^2^ methodology, applied to the results of these multiphase models, the best combination of stellar yields and initial mass function capable of reproducing these observations is identified.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/111
- Title:
- Stellar yields of rotating first stars. II.
- Short Name:
- J/ApJ/857/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent theory predicts that first stars are born with a massive initial mass of >~100M_{sun}_. Pair-instability supernova (PISN) is a common fate for such massive stars. Our final goal is to prove the existence of PISNe and thus the high-mass nature of the initial mass function in the early universe by conducting abundance profiling, in which properties of a hypothetical first star is constrained by metal-poor star abundances. In order to determine reliable and useful abundances, we investigate the PISN nucleosynthesis taking both rotating and nonrotating progenitors for the first time. We show that the initial and CO core mass ranges for PISNe depend on the envelope structures: nonmagnetic rotating models developing inflated envelopes have a lower shifted CO mass range of ~70-125_M{sun}_, while nonrotating and magnetic rotating models with deflated envelopes have a range of ~80-135_M{sun}_. However, we find no significant difference in explosive yields from rotating and nonrotating progenitors, except for large nitrogen production in nonmagnetic rotating models. Furthermore, we conduct the first systematic comparison between theoretical yields and a large sample of metal-poor star abundances. We find that the predicted low [Na/Mg]~-1.5 and high [Ca/Mg]~0.5-1.3 abundance ratios are the most important to discriminate PISN signatures from normal metal-poor star abundances, and confirm that no currently observed metal-poor star matches with the PISN abundance. An extensive discussion on the nondetection is presented.
- ID:
- ivo://CDS.VizieR/J/AJ/120/1808
- Title:
- Stroemgren photometry in LMC disk
- Short Name:
- J/AJ/120/1808
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report new metallicity determinations for 39 red giants in a 220 arcmin2^2^ region, 1.8{deg} southwest of the bar of the Large Magellanic Cloud. These abundance measurements are based on spectroscopy of the Ca II infrared triplet.