scholarly journals A method to estimate stellar ages from kinematical data

2018 ◽  
Vol 476 (1) ◽  
pp. 184-197 ◽  
Author(s):  
F Almeida-Fernandes ◽  
H J Rocha-Pinto
Keyword(s):  
Stellar Ages ◽  
Kinematical Data

scholarly journals Realistic mock observations of the sizes and stellar mass surface densities of massive galaxies in FIRE-2 zoom-in simulations

2020 ◽  
Vol 501 (2) ◽  
pp. 1591-1602
Author(s):  
T Parsotan ◽  
R K Cochrane ◽  
C C Hayward ◽  
D Anglés-Alcázar ◽  
R Feldmann ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Surface Density ◽  
Stellar Mass ◽  
Massive Galaxies ◽  
Star Forming ◽  
Stellar Feedback ◽  
Central Surface ◽  
Stellar Ages ◽  
The Galaxy ◽  
Zoom In

ABSTRACT The galaxy size–stellar mass and central surface density–stellar mass relationships are fundamental observational constraints on galaxy formation models. However, inferring the physical size of a galaxy from observed stellar emission is non-trivial due to various observational effects, such as the mass-to-light ratio variations that can be caused by non-uniform stellar ages, metallicities, and dust attenuation. Consequently, forward-modelling light-based sizes from simulations is desirable. In this work, we use the skirt  dust radiative transfer code to generate synthetic observations of massive galaxies ($M_{*}\sim 10^{11}\, \rm {M_{\odot }}$ at z = 2, hosted by haloes of mass $M_{\rm {halo}}\sim 10^{12.5}\, \rm {M_{\odot }}$) from high-resolution cosmological zoom-in simulations that form part of the Feedback In Realistic Environments project. The simulations used in this paper include explicit stellar feedback but no active galactic nucleus (AGN) feedback. From each mock observation, we infer the effective radius (Re), as well as the stellar mass surface density within this radius and within $1\, \rm {kpc}$ (Σe and Σ1, respectively). We first investigate how well the intrinsic half-mass radius and stellar mass surface density can be inferred from observables. The majority of predicted sizes and surface densities are within a factor of 2 of the intrinsic values. We then compare our predictions to the observed size–mass relationship and the Σ1−M⋆ and Σe−M⋆ relationships. At z ≳ 2, the simulated massive galaxies are in general agreement with observational scaling relations. At z ≲ 2, they evolve to become too compact but still star forming, in the stellar mass and redshift regime where many of them should be quenched. Our results suggest that some additional source of feedback, such as AGN-driven outflows, is necessary in order to decrease the central densities of the simulated massive galaxies to bring them into agreement with observations at z ≲ 2.

scholarly journals The stellar mass assembly of low-redshift, massive, central galaxies in SDSS and the TNG300 simulation

2020 ◽  
Vol 497 (4) ◽  
pp. 4262-4275
Author(s):  
Thomas M Jackson ◽  
A Pasquali ◽  
C Pacifici ◽  
C Engler ◽  
A Pillepich ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Stellar Mass ◽  
Spectral Energy ◽  
Distribution Fitting ◽  
Stellar Ages ◽  
Mass Assembly ◽  
Galaxy Assembly ◽  
The Times ◽  
Stellar Masses ◽  
Kinetic Mode

ABSTRACT The stellar mass assembly of galaxies can be affected by both secular and environmental processes. In this study, for the first time, we investigate the stellar mass assembly of $\sim 90\, 000$ low-redshift, central galaxies selected from SDSS group catalogues ($M_{\rm Stellar}\gtrsim 10^{9.5}\, \mathrm{M}_{\odot }$, $M_{\rm Halo}\gtrsim 10^{12}\, \mathrm{M}_{\odot }$) as a function of both stellar mass and halo mass. We use estimates of the times at which 10, 50, and 90 per cent of the stellar mass were assembled from photometric spectral energy distribution fitting, allowing a more complete investigation than single stellar ages alone. We consider trends in both stellar mass and halo mass simultaneously, finding dependences of all assembly times on both. We find that galaxies with higher stellar masses (at constant halo mass) have on average older lookback times, similar to previous studies of galaxy assembly. We also find that galaxies at higher halo mass (at constant stellar mass) have younger lookback times, possibly due to a larger reservoir of gas for star formation. An exception to this is a subsample with high stellar-to-halo mass ratios, which are likely massive, field spirals. We compare these observed trends to those predicted by the TNG300 simulation, finding good agreement overall as a function of either stellar mass or halo mass. However, some differences in the assembly times (of up to ∼3 Gyr) appear when considering both stellar mass and halo mass simultaneously, noticeably at intermediate stellar masses (MStellar ∼ 1011 M⊙). These discrepancies are possibly linked to the quenched fraction of galaxies and the kinetic mode active galactic nucleus feedback implemented in TNG300.

scholarly journals A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey

2018 ◽  
Vol 615 ◽  
pp. L5 ◽  
Author(s):  
A. Irrgang ◽  
S. Kreuzer ◽  
U. Heber ◽  
W. Brown
Keyword(s):  
Main Sequence ◽  
Galactic Center ◽  
Radial Velocities ◽  
Stellar Ages ◽  
The Galaxy ◽  
Quantitative Spectral Analysis ◽  
Kinematic Studies ◽  
Ejection Mechanism ◽  
Photometric Measurements ◽  
Stellar Masses

Context. Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. Aims. To test the hypothesis of an origin in the Galactic center using kinematic investigations, the current space velocities of the HVSs need to be determined. With the advent of Gaia’s second data release, accurate radial velocities from spectroscopy are complemented by proper motion measurements of unprecedented quality. Based on a new spectroscopic analysis method, we provide revised distances and stellar ages, both of which are crucial to unravel the nature of the HVSs. Methods. We reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey using a new grid of synthetic spectra, which account for deviations from local thermodynamic equilibrium, to derive effective temperatures, surface gravities, radial velocities, and projected rotational velocities. Stellar masses, radii, and ages were then determined by comparison with stellar evolutionary models that account for rotation. Finally, these results were combined with photometric measurements to obtain spectroscopic distances. Results. The resulting atmospheric parameters are consistent with those of main sequence stars with masses in the range 2.5–5.0 M⊙. The majority of the stars rotate at fast speeds, providing further evidence for their main sequence nature. Stellar ages range from 90 to 400 Myr and distances (with typical 1σ-uncertainties of about 10–15%) from 30 to 100 kpc. Except for one object (B 711), which we reclassify as A-type star, all stars are of spectral type B. Conclusions. The spectroscopic distances and stellar ages derived here are key ingredients for upcoming kinematic studies of HVSs based on Gaia proper motions.

scholarly journals Masses and ages for metal-poor stars

2019 ◽  
Vol 627 ◽  
pp. A173 ◽  
Author(s):  
M. Valentini ◽  
C. Chiappini ◽  
D. Bossini ◽  
A. Miglio ◽  
G. R. Davies ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Age Determination ◽  
High Resolution Spectroscopy ◽  
Chemical Abundances ◽  
Abundance Pattern ◽  
Halo Stars ◽  
Stellar Ages ◽  
First Results ◽  
Detailed Chemical

Context. Very metal-poor halo stars are the best candidates for being among the oldest objects in our Galaxy. Samples of halo stars with age determination and detailed chemical composition measurements provide key information for constraining the nature of the first stellar generations and the nucleosynthesis in the metal-poor regime. Aims. Age estimates are very uncertain and are available for only a small number of metal-poor stars. We present the first results of a pilot programme aimed at deriving precise masses, ages, and chemical abundances for metal-poor halo giants using asteroseismology and high-resolution spectroscopy. Methods. We obtained high-resolution UVES spectra for four metal-poor RAVE stars observed by the K2 satellite. Seismic data obtained from K2 light curves helped improve spectroscopic temperatures, metallicities, and individual chemical abundances. Mass and ages were derived using the code PARAM, investigating the effects of different assumptions (e.g. mass loss and [α/Fe]-enhancement). Orbits were computed using Gaia DR2 data. Results. The stars are found to be normal metal-poor halo stars (i.e. non C-enhanced), and an abundance pattern typical of old stars (i.e. α and Eu-enhanced), and have masses in the 0.80−1.0 M⊙ range. The inferred model-dependent stellar ages are found to range from 7.4 Gyr to 13.0 Gyr with uncertainties of ∼30%−35%. We also provide revised masses and ages for metal-poor stars with Kepler seismic data from the APOGEE survey and a set of M4 stars. Conclusions. The present work shows that the combination of asteroseismology and high-resolution spectroscopy provides precise ages in the metal-poor regime. Most of the stars analysed in the present work (covering the metallicity range of [Fe/H] ∼ −0.8 to −2 dex) are very old >9 Gyr (14 out of 19 stars), and all of the stars are older than >5 Gyr (within the 68 percentile confidence level).

scholarly journals The Luminosity Determination

1995 ◽  
Vol 10 ◽  
pp. 399-402
Author(s):  
A.E. Gómez ◽  
C. Turon
Keyword(s):  
Main Sequence ◽  
Small Volume ◽  
Absolute Magnitude ◽  
Fitting Procedure ◽  
Trigonometric Parallaxes ◽  
The Mean ◽  
The Absolute ◽  
Absolute Magnitudes ◽  
Kinematical Data ◽  
Magnitude Determination

The Hertzprung-Russel (HR) diagram luminosity calibration relies basically on three kinds of data: trigonometric parallaxes, kinematical data (proper motions and radial velocities) and cluster distances obtained by the zero-age main sequence fitting procedure. The most fundamental method to calculate the absolute magnitude is the use of trigonometric parallaxes, but up to now, accurate data only exist for stars contained in a small volume around the sun. Individual absolute magnitudes are obtained using trigonometric parallaxes or photometric and spectroscopic calibrations. In these calibrations the accuracy on the absolute magnitude determination ranges from ±0.m2 in the main sequence to ±0m5 in the giant branch. On the other hand, trigonometric parallaxes, kinematical data or cluster distances have been used to make statistical calibrations of the absolute magnitude. The standard error on the mean absolute magnitude calibrations ranges from ±0m3 to ±0m6 on the mean sequence, from ±0m5 to ±0m7 on thegiant branch and is of about 1mfor supergiants.Future improvements in the absolute magnitude determination will depend on the improvement of the basic data from the ground and space. A brief overview of the new available data is presented. In particular, the analysis of the first 30 months data of the Hipparcos mission (H30) (from the 37 months data of the whole mission) allows to perform a statistical evaluation of the improvements expected in the luminosity determination.

scholarly journals An investigation of chromospheric activity spanning the Vaughan-Preston gap: impact on stellar ages

2009 ◽  
Vol 499 (1) ◽  
pp. L9-L12 ◽  
Author(s):  
G. Pace ◽  
J. Melendez ◽  
L. Pasquini ◽  
G. Carraro ◽  
J. Danziger ◽  
...  
Keyword(s):  
Chromospheric Activity ◽  
Stellar Ages

scholarly journals Kinematical data on early-type galaxies. I.

1997 ◽  
Vol 122 (3) ◽  
pp. 521-528 ◽  
Author(s):  
F. Simien ◽  
Ph. Prugniel
Keyword(s):  
Early Type ◽  
Kinematical Data

scholarly journals Uncertainties in asteroseismic grid-based estimates of stellar ages

2015 ◽  
Vol 575 ◽  
pp. A12 ◽  
Author(s):  
G. Valle ◽  
M. Dell’Omodarme ◽  
P. G. Prada Moroni ◽  
S. Degl’Innocenti
Keyword(s):  
Stellar Ages ◽  
Grid Based

Stellar Ages and Metallicities along the Bars of Barred Spirals

2001 ◽  
pp. 335-335
Author(s):  
S. Lourenso ◽  
J. E. Beckman ◽  
A. Vazdekis ◽  
R. F. Peletier
Keyword(s):  
Stellar Ages

Accurate Parallaxes and Stellar Ages Determinations

1995 ◽  
pp. 135-142 ◽  
Author(s):  
Y. Lebreton ◽  
E. Michel ◽  
M. J. Goupil ◽  
A. Baglin ◽  
J. Fernandes
Keyword(s):  
Stellar Ages
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