J/AJ/152/208 Ages and metallicities for M31 star clusters (Fan+, 2016)
Lick indices and spectral energy distribution analysis based on an M31 star
cluster sample: comparisons of methods and models.
Fan Z., de Grijs R., Chen B., Jiang L., Bian F., Li Z.
<Astron. J., 152, 208-208 (2016)>
=2016AJ....152..208F 2016AJ....152..208F (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Radial velocities ;
Abundances, [Fe/H]
Keywords: galaxies: individual: M31 - galaxies: star clusters: general -
globular clusters: general
Abstract:
Application of fitting techniques to obtain physical parameters-such
as ages, metallicities, and α-element to iron ratios-of stellar
populations is an important approach to understanding the nature of
both galaxies and globular clusters (GCs). In fact, fitting methods
based on different underlying models may yield different results and
with varying precision. In this paper, we have selected 22 confirmed
M31 GCs for which we do not have access to previously known
spectroscopic metallicities. Most are located at approximately one
degree (in projection) from the galactic center. We performed
spectroscopic observations with the 6.5m MMT telescope, equipped with
its Red Channel Spectrograph. Lick/IDS absorption-line indices, radial
velocities, ages, and metallicities were derived based on the EZ_Ages
stellar population parameter calculator. We also applied full spectral
fitting with the ULySS code to constrain the parameters of our sample
star clusters. In addition, we performed χmin2 fitting of the
clusters' Lick/IDS indices with different models, including the
Bruzual & Charlot models (adopting Chabrier or Salpeter stellar
initial mass functions and 1994 or 2000 Padova stellar evolutionary
tracks), the galev, and the Thomas et al. models. For comparison, we
collected their UVBRIJK photometry from the Revised Bologna Catalogue
(v.5) to obtain and fit the GCs' spectral energy distributions (SEDs).
Finally, we performed fits using a combination of Lick/IDS indices and
SEDs. The latter results are more reliable and the associated error
bars become significantly smaller than those resulting from either our
Lick/IDS indices-only or our SED-only fits.
Description:
We have selected 22 confirmed M31 globular clusters from Peacock et
al. 2010 (Cat. J/MNRAS/402/803).
Spectroscopic observations were carried out with the 6.5m MMT/Red
Channel Spectrograph from 2010 October 31 to 2010 November 2 and on
2011 November 4. The telescope is located on Mt. Hopkins in Arizona
(USA) at an altitude of 2581m. The exposure times used ranged from
480-1800s, depending on the cluster brightness. The median seeing was
∼0.98'' and we adopted a slit aperture of 0.75''*180''. The CCD's size
is 450*1032 pixels2. It is characterized by a gain of 1.3e-
ADU-1, with a readout noise of 3.5e-. A grating with 600l/mm with
a blaze 1st/4800 was used. The spectral resolution was R=960 for a
slit of 1'' and a central wavelength of 4701Å; the dispersion was
1.63Å/pixel.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 66 22 Observations of our sample globular clusters
table2.dat 39 22 Radial velocities, Vr, of our sample globular
clusters as well as previously published
measurements
table3.dat 62 22 Ages and metallicities derived from the Lick
absorption-line indices fitted with ULySS
table4.dat 34 22 Ages and metallicities derived from the Lick
absorption-line indices fitted with EZ_Ages
table5.dat 75 22 Ages and metallicities derived from the Lick
absorption-line indices fitted with the
Thomas et al. 2011MNRAS.412.2183T 2011MNRAS.412.2183T models
table6.dat 52 22 Ages and metallicities derived from the Lick
absorption-line indices fitted with the GALEV
models
table7.dat 142 88 Lick/IDS index χmin2 fit results using
Bruzual & Charlot 2003MNRAS.344.1000B 2003MNRAS.344.1000B models
--------------------------------------------------------------------------------
See also:
V/143 : Revised Bologna Catalog of M31 clusters, V.5 (Galleti+ 2012)
J/AJ/152/45 : LAMOST survey of star clusters in M31. II. (Chen+, 2016)
J/AJ/141/61 : Star clusters in M31. II. (Caldwell+, 2011)
J/MNRAS/404/1639 : MILES base models & new line index system (Vazdekis+, 2010)
J/MNRAS/402/803 : M31 globular cluster system (Peacock+, 2010)
J/ApJ/725/200 : Updated catalog of M31 globular-like clusters (Fan+, 2010)
J/AJ/139/1438 : SED and age estimates of M31 globular clusters (Wang+, 2010)
J/A+A/508/1285 : Metallicity estimates of M31 GCs (Galleti+, 2009)
J/A+A/456/985 : Radial velocities of M31 candidate clusters (Galleti+, 2006)
J/MNRAS/372/1259 : Abundances of extragalactic GCs (Sharina+, 2006)
J/AJ/123/2490 : RV and [Fe/H] of M31 GC system (Perrett+, 2002)
J/AJ/122/2458 : M31 globular clusters from HST (Barmby+, 2001)
J/AJ/119/727 : M31 globular clusters photometry (Barmby+, 2000)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Globular cluster identification
12- 13 I2 h RAh Hour of Right Ascension (J2000) (1)
15- 16 I2 min RAm Minute of Right Ascension (J2000) (1)
18- 23 F6.3 s RAs Second of Right Ascension (J2000) (1)
25 A1 --- DE- Sign of the Declination (1)
26- 27 I2 deg DEd Degree of Declination (J2000) (1)
29- 30 I2 arcmin DEm Arcminute of Declination (J2000) (1)
32- 36 F5.2 arcsec DEs Arcsecond of Declination (J2000) (1)
38- 42 F5.2 kpc Rp Projected radius from the galaxy center
(rp) (1)
44- 48 F5.2 mag Vmag V-band magnitude (1)
50- 52 I3 s Exp Exposure time of individual observation
54 I1 --- Nexp ? Number of exposures
56- 66 A11 "Y:M:D" Date Date of observation
--------------------------------------------------------------------------------
Note (1): The coordinates, rp and V-band magnitudes were taken from the
Revised Bologna Catalog (RBC) v.5. (Galleti et al. 2012, Cat. V/143).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Globular cluster identification
12 A1 --- f_Name [1a] Flag on Name (2)
14- 17 I4 km/s RV1 [-673/45] Radial velocity fitted with ULySS
based on the model of Vazdekis et al. 2010
(Cat. J/MNRAS/404/1639) (3)
19- 21 I3 km/s e_RV1 [1/120] Uncertainty in RV1 (3)
23- 26 I4 km/s RV2 [-681/54] Radial velocity fitted with ULySS
based on the PEGASE-HR model (3)
28- 29 I2 km/s e_RV2 [1/60] Uncertainty in RV2 (3)
31- 34 I4 km/s RV3 [-561/33]? Radial velocity from the Revised
Bologna Catalog (RBC) v.5. (Galleti et al.
2012, Cat. V/143)
36- 37 I2 km/s e_RV3 [1/47]? Uncertainty in RV3
39 A1 --- f_RV3 [a] Flag 'a' on RV3 indicates that the RBC
radial velocity was modified in -188±26km/s
at CDS (4)
--------------------------------------------------------------------------------
Note (2): Flag defined as follows:
1 = This flag was not explained in the text;
a = In Table2, the repeated object G339-BA30 (in the paper) was modified in
B339-G077 at CDS.
Note (3): Fitted with Universite de Lyon Spectroscopic analysis Software (ULySS;
http://ulyss.univ-lyon1.fr/; see Koleva et al. 2009A&A...501.1269K 2009A&A...501.1269K,
Chen et al. 2016, Cat. J/AJ/152/45).
Note (4): In Table2 of the paper, the RBC radial velocity of G339-BA30 was
33±30km/s. As we modified G339-BA30 in B339-G077 at CDS, we changed the
RBC radial velocity in -188±26km/s (from the Revised Bologna Catalog v.5.
of Galleti et al. 2012, Cat. V/143).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Globular cluster identification
12- 17 F6.3 yr logAge1 [9.3/10.25] Log of age for the Vazdekis et
al. 2010 (Cat. J/MNRAS/404/1639) SSP
model (5)
19- 23 F5.3 yr e_logAge1 [0/0.07] Error in logAge1 (5)
25- 30 F6.3 yr logAge2 [9.4/10.4] Log of age for the PEGASE-HR SSP
model (6)
32- 36 F5.3 yr e_logAge2 [0/0.042] Error in logAge2 (6)
38- 43 F6.3 [Sun] [Fe/H]1 [-2.32/-0.35] Metallicity for the Vazdekis et
al. 2010 (Cat. J/MNRAS/404/1639) SSP
model (5)
45- 49 F5.3 [Sun] e_[Fe/H]1 [0.01/0.04] Error in [Fe/H]1 (5)
51- 56 F6.3 [Sun] [Fe/H]2 [-2.3/-0.4] Metallicity for the PEGASE-HR SSP
model (6)
58- 62 F5.3 [Sun] e_[Fe/H]2 [0.01/0.03] Error in [Fe/H]2 (6)
--------------------------------------------------------------------------------
Note (5): Logarithmic age and metallicity derived based on the Lick
absorption-line index and fitted with Universite de Lyon Spectroscopic
analysis Software (ULySS; http://ulyss.univ-lyon1.fr/; see Koleva et al.
2009A&A...501.1269K 2009A&A...501.1269K, Chen et al. 2016, Cat. J/AJ/152/45), for the Vazdekis
et al. 2010 (Cat. J/MNRAS/404/1639) Simple Stellar Population (SSP) model.
Note (6): Logarithmic age and metallicity derived based on the Lick
absorption-line index and fitted with ULySS, for PEGASE-HR Simple Stellar
Population (SSP) model (provided by Le Borgne et al. 2004A&A...425..881L 2004A&A...425..881L).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Globular cluster identification
12- 16 F5.2 Gyr logAge3 [2/12.21]?=99.99 Age derived with EZ_Ages (7)
18- 22 F5.2 [Sun] [Fe/H]3 [-1.12/-0.18]?=99.99 Metallicity derived with
EZ_Ages (7)
24- 28 F5.2 [Sun] [Fe/H]4 [-2.25/-0.35] Metallicity derived from [MgFe] (8)
30- 34 F5.2 [Sun] [Fe/H]5 [-2.95/-0.39] Metallicity derived from <Fe> (9)
--------------------------------------------------------------------------------
Note (7): Ages and metallicities derived from the Lick absorption-line indices
fitted with EZ_Ages.
Note (8):
[MgFe]=(Mgb*<Fe>)1/2, where <Fe> =(Fe5270+Fe5335)/2.
Thus, the metallicity can be calculated following Galleti et al. 2009
(Cat. J/A+A/508/1285), using
[Fe/H][MgFe]=-2.563+1.119[MgFe]-0.106[MgFe]2±0.15dex(rms) Eq. (1).
Note (9): Derived from <Fe> =(Fe5270+Fe5335)/2 following Caldwell et al. 2011
(Cat. J/AJ/141/61).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Globular cluster identification
14- 19 F6.3 yr logAge4 [8/10.2] Log of age derived from the Lick
absorption-line index fitted with the Thomas
et al. 2011MNRAS.412.2183T 2011MNRAS.412.2183T models (10)
21 A1 --- --- [-]
22- 26 F5.3 yr e_logAge4 [0/0.22] Negative error in logAge4
28 A1 --- --- [+]
29- 33 F5.3 yr E_logAge4 [0/0.19] Positive error in logAge4
35- 40 F6.3 [Sun] [Z/H] [-2.2/-0.29] Metallicity derived from the Lick
absorption-line index fitted with the Thomas
et al. 2011MNRAS.412.2183T 2011MNRAS.412.2183T models (10)
42 A1 --- --- [-]
43- 47 F5.3 [Sun] e_[Z/H] [0.09/0.47] Negative error in [Z/H]
49 A1 --- --- [+]
50- 54 F5.3 [Sun] E_[Z/H] [0.1/0.75] Positive error in [Z/H]
56- 61 F6.3 [Sun] [a/Fe] [-0.3/0.5] [α/Fe] ratio derived from the
Lick absorption-line index fitted with the
Thomas et al. 2011MNRAS.412.2183T 2011MNRAS.412.2183T models (10)
63 A1 --- --- [-]
64- 68 F5.3 [Sun] e_[a/Fe] [0/0.8] Negative error in [a/Fe]
70 A1 --- --- [+]
71- 75 F5.3 [Sun] E_[a/Fe] [0/0.8] Positive error in [a/Fe]
--------------------------------------------------------------------------------
Note (10): For the evolutionary tracks of Cassisi et al. 1997A&A...317..108C 1997A&A...317..108C and
the Padova models of Thomas et al. 2011MNRAS.412.2183T 2011MNRAS.412.2183T.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Globular cluster identification
12- 17 F6.3 yr logAge5 [6.6/10.2] Log of age derived from the Lick
absorption-line index fitted with the GALEV
models (11)
19 A1 --- --- [-]
20- 24 F5.3 yr e_logAge5 [0/0.315] Negative error in logAge5
26 A1 --- --- [+]
27- 31 F5.3 yr E_logAge5 [0/0.85] Positive error in logAge5
33- 38 F6.3 [Sun] [Fe/H]6 [-2.2/0.24] Metallicity derived from the Lick
absorption-line index fitted with the GALEV
models (11)
40 A1 --- --- [-]
41- 45 F5.3 [Sun] e_[Fe/H]6 [0.075/0.76] Negative error in [Fe/H]
47 A1 --- --- [+]
48- 52 F5.3 [Sun] E_[Fe/H]6 [0.001/1.5] Positive error in [Fe/H]
--------------------------------------------------------------------------------
Note (11): Fitted with the Galaxy Evolutionary Synthesis Models (GALEV; Lilly &
Fritze-v. Alvensleben 2006A&A...457..467L 2006A&A...457..467L; Kotulla et al.
2009MNRAS.396..462K 2009MNRAS.396..462K; see also Section 4.3 for additional details about the
GALEV models).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- IMF Initial Mass Function (C=Chabrier, or
S=Salpeter) (1)
3- 5 A3 --- SET Stellar Evolutionary Tracks (P00 or P94) (2)
7- 16 A10 --- Name Globular cluster identification
18- 23 F6.3 yr logAge6 [6.4/10.1] Lick/IDS log of age (3)
25 A1 --- --- [-]
26- 30 F5.3 yr e_logAge6 [0.02/0.45] Negative error in logAge6
32 A1 --- --- [+]
33- 37 F5.3 yr E_logAge6 [0.024/0.44] Positive error in logAge6
39- 44 F6.3 [Sun] [Fe/H]7 [-2.25/0.28] Lick/IDS metallicity (3)
46 A1 --- --- [-]
47- 51 F5.3 [Sun] e_[Fe/H]7 [0/0.5] Negative error in [Fe/H]7
53 A1 --- --- [+]
54- 58 F5.3 [Sun] E_[Fe/H]7 [0.048/0.55] Positive error in [Fe/H]7
60- 65 F6.3 yr logAge7 [8.9/10.2] SED log of age (4)
67 A1 --- --- [-]
68- 72 F5.3 yr e_logAge7 [0.004/0.62] Negative error in logAge7
74 A1 --- --- [+]
75- 79 F5.3 yr E_logAge7 [0/0.63] Positive error in logAge7
81- 86 F6.3 [Sun] [Fe/H]8 [-2.25/0.56] SED metallicity (4)
88 A1 --- --- [-]
89- 93 F5.3 [Sun] e_[Fe/H]8 [0/0.74] Negative error in [Fe/H]8
95 A1 --- --- [+]
96-100 F5.3 [Sun] E_[Fe/H]8 [0/0.86] Positive error in [Fe/H]8
102-107 F6.3 yr logAge8 [6.6/10.14] Log of age from both fits (5)
109 A1 --- --- [-]
110-114 F5.3 yr e_logAge8 [0.01/0.7] Negative error in logAge8
116 A1 --- --- [+]
117-121 F5.3 yr E_logAge8 [0/3.5] Positive error in logAge8
123-128 F6.3 [Sun] [Fe/H]9 [-2.25/-0.17] Metallicity from both fits (5)
130 A1 --- --- [-]
131-135 F5.3 [Sun] e_[Fe/H]9 [0/0.57] Negative error in [Fe/H]9
137 A1 --- --- [+]
138-142 F5.3 [Sun] E_[Fe/H]9 [0.06/0.73] Positive error in [Fe/H]9
--------------------------------------------------------------------------------
Note (1): Source of the stellar initial mass function:
S = Stellar initial mass function (IMF) of Salpeter 1955ApJ...121..161S 1955ApJ...121..161S;
C = Stellar initial mass function (IMF) of Chabrier 2003PASP..115..763C 2003PASP..115..763C.
Note (2): Source of stellar evolutionary tracks:
P00 = 2000 Padova stellar evolutionary tracks;
P94 = 1994 Padova stellar evolutionary tracks.
Note (3): Derived only from Lick/IDS absorption-line index fits.
Note (4): Derived, only based on Spectral Energy Distribution (SED) fitting.
Note (5): Derived from both the Lick/IDS absorption indices and the SED fits.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Sylvain Guehenneux [CDS] 31-May-2017