J/MNRAS/499/2327 Ages and abundances from spectral fitting (Goncalves+, 2020)
How well can we determine ages and chemical abundances from spectral fitting of
integrated light spectra?
Goncalves G., Coelho P., Schiavon R., Usher C.
<Mon. Not. R. Astron. Soc., 499, 2327-2339 (2020)>
=2020MNRAS.499.2327G 2020MNRAS.499.2327G (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Milky Way ; Magellanic Clouds ;
Galaxies, nearby ; Abundances, [Fe/H] ; Abundances, peculiar ;
Radial velocities ; Spectra, optical
Keywords: techniques: spectroscopic - Galaxy: abundances -
Galaxy: fundamental parameters - Galaxy: globular clusters: general -
galaxies: stellar content
Abstract:
The pixel-to-pixel spectral fitting technique is often used in studies
of stellar populations. It enables the user to infer several
parameters from integrated light spectra such as ages and chemical
abundances. In this paper, we examine the question of how the inferred
parameters change with the choice of wavelength range used. We have
employed two different libraries of integrated light spectra of
globular clusters (GCs) from the literature and fitted them to stellar
population models using the code STARLIGHT. We performed tests using
different regions of the spectra to infer reddening, ages, [Fe/H], and
[α/Fe]. Comparing our results to age values obtained from
isochrone fitting and chemical abundances from high-resolution
spectroscopy, we find that: (1) the inferred parameters change with
the wavelength range used; (2) the method in general retrieves good
reddening estimates, specially when a wider wavelength range is
fitted; (3) the ideal spectral regions for determination of age,
[Fe/H], and [α/Fe] are 4170-5540, 5280-7020, and 4828-5364Å,
respectively; (4) the retrieved age values for old metal-poor objects
can be several Gyr younger than those resulting from isochrone
fitting. We conclude that, depending on the parameter of interest and
the accuracy requirements, fitting the largest possible wavelength
range may not necessarily be the best strategy.
Description:
In this study, we have used data from the WiFes Atlas of Galactic
Globular clusters Spectra (WAGGS) project (Usher et al.
2017MNRAS.468.3828U 2017MNRAS.468.3828U). The WAGGS library contains objects from the
Milky Way, the Magellanic Clouds and the Fornax galaxy, thus covering
a wide range in ages and chemical abundances.
The data were taken with the WiFeS integral field spectrograph (Dopita
et al. 2007Ap&SS.310..255D 2007Ap&SS.310..255D, 2010Ap&SS.327..245D 2010Ap&SS.327..245D) on the Australian
National University 2.3m telescope. The spectra were taken in four
different arms, using different grating set-ups: U7000, covering
3270-4350Å range; B7000, covering 4170-5540Å; R7000 covering
5280-7020Å; and I7000 covering 6800-9050Å. All four gratings
give spectral resolutions of δλ/λ∼6800.
In order to obtain the reference values for ages and chemical
abundances for the globular clusters, we have used table 1 of Usher et
al. (2017MNRAS.468.3828U 2017MNRAS.468.3828U) as a starting point, and performed an
extensive search in literature. Searching object by object, we
gathered information from literature prioritizing works that provide
[α/Fe] (here represented by [Mg/Fe]) as well as [Fe/H] and their
uncertainties. This compilation is shown in Table 1.
We measured the radial velocities of the observations using the task
fxcor in IRAF (http://ast.noao.edu/data/software).
Finally, we have used the software Starlight (Cid Fernandes et al.
2005MNRAS.358..363C 2005MNRAS.358..363C), a full spectral fitting code widely used in
galaxy studies. This spectral fitting allows us to infer
light-weighted and mass-weighted ages and chemical abundances.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 68 86 Globular clusters present in the WAGGS data base
and the reference values for ages and chemical
abundances
rv.dat 48 281 Radial velocities (calculated as described in
Section 3.1) and average signal to noise for
each spectrum of the WAGGS library
fitparam.dat 100 94 Resulting parameters from the fits in RW and
their uncertainties from the perturbed spectra
of the WAGGS library
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Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Globular cluster name
9- 14 A6 --- Galaxy Host galaxy of the globular cluster
16- 22 F7.3 deg RAdeg Right ascension (J2000)
24- 30 F7.3 deg DEdeg Declination (J2000)
32- 37 F6.3 [-] [Fe/H] Fe/H abundance ratio
39- 43 F5.3 [-] e_[Fe/H] ? Error on [Fe/H]
45- 50 F6.3 [-] [Mg/Fe] ? Mg/Fe abundance ratio
52- 56 F5.3 [-] e_[Mg/Fe] ? Error on [Mg/Fe]
58- 62 F5.2 Gyr Age ? Age of the globular cluster
64- 68 F5.3 Gyr e_Age ? Error on Age
--------------------------------------------------------------------------------
Byte-by-byte Description of file: rv.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Globular cluster name
9- 32 A24 --- Spec Name of the spectrum file (G1)
34- 39 F6.1 km/s RV ? Radial velocity
41- 44 F4.1 km/s e_RV ? Error on RV
46- 48 I3 --- SNR Signal to noise ratio
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Byte-by-byte Description of file: fitparam.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Globular cluster name
9- 32 A24 --- Spec Name of the spectrum file (G1)
34- 39 F6.3 [yr] logtlight Logarithm of the fitted light-weighted age
41- 45 F5.3 [yr] e_logtlight Error on logtlight
47- 52 F6.3 [yr] logtmass Logarithm of the fitted mass-weighted age
54- 58 F5.3 [yr] e_logtmass Error on logtmass
60- 64 F5.2 [-] [Fe/H]l Fe/H light-weighted abundance ratio
66- 69 F4.2 [-] e_[Fe/H]l Error on [Fe/H]l
71- 75 F5.2 [-] [Fe/H]m Fe/H mass-weighted abundance ratio
77- 80 F4.2 [-] e_[Fe/H]m Error on [Fe/H]m
82- 85 F4.2 [-] [a/Fe]l α/Fe light-weighted abundance ratio
87- 90 F4.2 [-] e_[a/Fe]l Error on [a/Fe]l
92- 95 F4.2 [-] [a/Fe]m α/Fe mass-weighted abundance ratio
97- 100 F4.2 [-] e_[a/Fe]m Error on [a/Fe]m
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Global Notes:
Note (G1): The name of the spectrum file contains the globular cluster name, the
arm used to obtain the spectrum (U7000, covering 3270-4350Å;
B7000, covering 4170-5540Å; R7000 covering 5280-7020Å; and
I7000 covering 6800-9050Å) and the date of the observation.
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 04-Sep-2023