J/ApJ/834/9 Spectroscopy obs. of LeoA, Aqr & Sgr dwarf gal. (Kirby+, 2017)
Chemistry and kinematics of the late-forming dwarf irregular galaxies
Leo A, Aquarius, and Sagittarius DIG.
Kirby E.N., Rizzi L., Held E.V., Cohen J.G., Cole A.A., Manning E.M.,
Skillman E.D., Weisz D.R.
<Astrophys. J., 834, 9-9 (2017)>
=2017ApJ...834....9K 2017ApJ...834....9K (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Radial velocities ; Galaxies, nearby ; Spectroscopy ;
Photometry, VRI
Keywords: galaxies: abundances; galaxies: dwarf; Local Group; stars: abundances;
galaxies: individual: (Leo A, DDO 210, Sgr dIG)
Abstract:
We present Keck/DEIMOS spectroscopy of individual stars in the
relatively isolated Local Group dwarf galaxies Leo A, Aquarius, and
the Sagittarius dwarf irregular galaxy. The three galaxies-but
especially Leo A and Aquarius-share in common delayed star formation
histories (SFHs) relative to many other isolated dwarf galaxies. The
stars in all three galaxies are supported by dispersion. We found no
evidence of stellar velocity structure, even for Aquarius, which has
rotating HI gas. The velocity dispersions indicate that all three
galaxies are dark-matter-dominated, with dark-to-baryonic mass ratios
ranging from 4.4-0.8+1.0 (SagDIG) to 9.6-1.8+2.5 (Aquarius).
Leo A and SagDIG have lower stellar metallicities than Aquarius, and
they also have higher gas fractions, both of which would be expected
if Aquarius were further along in its chemical evolution. The
metallicity distribution of Leo A is inconsistent with a closed or
leaky box model of chemical evolution, suggesting that the galaxy was
pre-enriched or acquired external gas during star formation. The
metallicities of stars increased steadily for all three galaxies, but
possibly at different rates. The [α/Fe] ratios at a given [Fe/H]
are lower than that of the Sculptor dwarf spheroidal galaxy, which
indicates more extended SFHs than Sculptor, consistent with
photometrically derived SFHs. Overall, the bulk kinematic and chemical
properties for the late-forming dwarf galaxies do not diverge
significantly from those of less delayed dwarf galaxies, including
dwarf spheroidal galaxies.
Description:
Kirby+ (2014, J/MNRAS/439/1015) already published some Keck/DEIMOS
spectroscopy of stars in Leo A and Aquarius. We obtained additional
DEIMOS spectra of individual stars in those galaxies, as well as
Sagittarius dwarf irregular galaxy (SagDIG).
We observed the three galaxies with DEIMOS over several nights in 2013
and 2014. We set the central wavelength to 7800Å with a resolving
power of R∼7000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 94 320 Radial velocities and membership
table3.dat 101 179 Chemical abundances
table4.dat 265 3 Galaxy properties
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See also:
J/MNRAS/455/2163 : BI LCs of DDO210 pulsating variables (Ordonez+, 2016)
J/ApJS/216/10 : DUSTiNGS. I. The Good Source Catalog (Boyer+, 2015)
J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
J/ApJ/798/77 : Metallicity of RGB stars in 6 M31 dwarf galaxies (Ho+, 2015)
J/A+A/572/A42 : SagDIG carbon and oxygen stars (Momany+, 2014)
J/ApJS/214/19 : Suprime-Cam wide-field photometry of Leo A (Stonkute+, 2014)
J/A+A/570/A78 : Deep VI photometry of Sgr dIrr (Beccari+, 2014)
J/ApJ/790/73 : RGB iron & alpha abundances in M31 satellites (Vargas+, 2014)
J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)
J/MNRAS/444/1812 : M54 and Sgr dSph red giants abundances (Mucciarelli+, 2014)
J/MNRAS/439/1015 : Velocities of red giants in 7 LG dwarf gal. (Kirby+, 2014)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/AJ/146/46 : Star Formation Rate in nearby galaxies (Karachentsev+, 2013)
J/ApJ/778/149 : Abundances for 3 stars in Sgr dSph (McWilliam+, 2013)
J/ApJ/768/172 : Kinematic analysis of red giant in M31 dSphs (Collins+, 2013)
J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)
J/ApJ/756/74 : 2MASS view of Sgr dSph. VII. Kinematics (Frinchaboy+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/752/45 : SPLASH: Stellar spectrosc. of M31 satellites (Tollerud+, 2012)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/ApJ/711/361 : Local Group dE galaxies. II. (Geha+, 2010)
J/ApJ/708/1290 : A 2MASS view of the Sgr dSph. VI. (Chou+, 2010)
J/ApJ/706/599 : Hα and UV SFR in the local volume (Lee+, 2009)
J/AJ/137/3100 : Radial velocities of 4 dSph galaxies (Walker+, 2009)
J/A+A/465/815 : Abundances of Sgr dSph stars (Sbordone+, 2007)
J/AJ/128/2170 : Hα imaging of irregular galaxies (Hunter+, 2004)
J/AJ/123/3154 : RV light curves of variable stars in Leo A (Dolphin+, 2002)
J/AJ/119/777 : BVRI photometry of Sagittarius DIG (Lee+, 2000)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Gal Dwarf galaxy abbreviation (1)
10- 25 A16 --- Name Object name (G1)
27- 28 I2 h RAh Hour of Right Ascension (J2000)
30- 31 I2 min RAm Minute of Right Ascension (J2000)
33- 37 F5.2 s RAs Second of Right Ascension (J2000)
39 A1 --- DE- Sign of the Declination (J2000)
40- 41 I2 deg DEd Degree of Declination (J2000)
43- 44 I2 arcmin DEm Arcminute of Declination (J2000)
46- 49 F4.1 arcsec DEs Arcsecond of Declination (J2000)
51- 55 F5.2 mag Imag0 [17.5/23.8] Extinction-corrected I band
Vega magnitude (2)
57- 61 F5.2 mag (V-I)0 [-0.6/3.6] Reddening-corrected (V-I) Vega
color index (2)
63 I1 --- N [1/3] Number of masks for this target
65- 67 I3 0.1nm-1 S/N [1/109] Signal-to-noise ratio (3)
69- 74 F6.1 km/s HRV [-291/211]? Heliocentric radial velocity
76- 79 F4.1 km/s e_HRV [1/35]? Error on HRV
81 A1 --- Mm [NY] Membership in dwarf galaxy
83- 94 A12 --- f_Mm ? Reason(s) for non-membership (4)
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Note (1): Galaxy abbreviation as follows:
LeoA = Leo A; 168 sources
Aquarius = Aquarius Dwarf Galaxy; 58 sources
SagDIG = Sagittarius dIG ; 94 sources
Note (2): For Leo A, we used the V and I Subaru/Suprime-Cam catalog of Stonkute+
(2014, J/ApJS/214/19). For Aquarius, we used the catalog of
McConnachie+ (2006MNRAS.373..715M 2006MNRAS.373..715M), who observed the galaxy with
Suprime-Cam in the V and I filters. For SagDIG, we used two different
photometry catalogs. We combined Momany+ (2002A&A...384..393M 2002A&A...384..393M)
photometry from the ESO Multimode Instrument at the ESO New Technology
Telescope (NTT) with Momany+ (2014, J/A+A/572/A42) photometry from
the HST/Advanced Camera for Surveys (ACS). The NTT photometry was
obtained in V and I filters, and we converted the ACS F475W, F606W,
and F814W magnitudes into V and I with the transformation equations of
Saha+ (2011PASP..123..481S 2011PASP..123..481S). All magnitudes were corrected for
extinction with the Schlegel+ (1998ApJ...500..525S 1998ApJ...500..525S) dust maps.
Note (3): To convert to S/N per pixel, multiply by 0.57.
Note (4): Reason for non-membership flag as follows:
galaxy = Spectrum indicates that the object is a galaxy (25 sources),
not an individual star.
TiO = TiO bands present in spectrum (not necessarily an
indicator of membership).
CN = Spectrum shows strong CN features (not an indicator of membership).
v = Non-member by radial velocity.
CMD = Non-member by location in CMD.
Na = Non-member by presence of strong NaI 8190 doublet.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Gal Dwarf galaxy abbreviation
10- 23 A14 --- Name Object name (G1)
27- 30 I4 K Teff [3984/4987] Effective temperature
32- 35 F4.2 [cm/s2] log(g) [0.4/1.7] Surface gravity
37- 41 F5.2 [Sun] [Fe/H] [-2.7/-0.5] Iron abundance relative to Sun
43- 46 F4.2 [Sun] e_[Fe/H] [0.1/0.5] Uncertainty in [Fe/H]
48- 52 F5.2 [Sun] [Mg/Fe] [-0/1.2]? Magnesium-to-iron ratio
relative to Sun
54- 57 F4.2 [Sun] e_[Mg/Fe] [0.2/0.5]? Uncertainty in [Mg/Fe]
59- 63 F5.2 [Sun] [Si/Fe] [-0.7/1.2]? Silicon-to-iron ratio
relative to Sun
65- 68 F4.2 [Sun] e_[Si/Fe] [0.2/0.5]? Uncertainty in [Si/Fe]
70- 74 F5.2 [Sun] [Ca/Fe] [-0.8/1.1]? Calcium-to-iron ratio
relative to Sun
76- 79 F4.2 [Sun] e_[Ca/Fe] [0.1/0.5]? Uncertainty in [Ca/Fe]
81- 85 F5.2 [Sun] [Ti/Fe] [-0.8/1.1]? Titanium-to-iron ratio
relative to Sun
87- 90 F4.2 [Sun] e_[Ti/Fe] [0.1/0.5]? Uncertainty in [Ti/Fe]
92- 96 F5.2 [Sun] [a/Fe] [-0.8/1.2]? Alpha-to-iron ratio
relative to Sun
98-101 F4.2 [Sun] e_[a/Fe] [0.1/0.5]? Uncertainty in [a/Fe]
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Gal Galaxy name
10- 13 I4 kpc Dist [827/1047] Distance
15- 16 I2 kpc e_Dist [11/53] Dist uncertainty
18 I1 --- r_Dist [1/3] Distance reference (1)
20- 22 F3.1 10+6Lsun LV [1.7/6.6] Luminosity
24- 26 F3.1 10+6Lsun e_LV [0.2/1.4] LV uncertainty
28 I1 --- r_LV [4/6] LV reference (1)
30- 33 F4.2 arcmin rh [0.9/2.2] Half-light radius in arcmin
35- 38 F4.2 arcmin e_rh [0.03/0.2] rh uncertainty
40 I1 --- r_rh [4/6] rh reference (1)
42- 44 I3 pc rhpc [277/517] Half-light radius in parsec
46- 47 I2 pc e_rhpc [16/29] rhpc uncertainty
49 I1 --- r_rhpc [4/6] rhpc reference (1)
51- 53 F3.1 10+6Msun M* [1.5/3.3] Stellar mass
55- 57 F3.1 10+6Msun e_M* [0.2/0.7] M* uncertainty
59 I1 --- r_M* [7] Stellar mass reference (1)
61- 63 F3.1 10-5Msun/yr SFRHa [0/9.3] Hα star formation rate
65- 68 A4 --- r_SFRHa SFRHa reference(s) (1)
70- 72 F3.1 10-4Msun/yr SFRUV [0/7.2] UV star formation rate
74- 75 I2 --- r_SFRUV [8/11] SFRUV reference (1)
77- 79 F3.1 10+6Msun M(HI) [2.2/8.3] HI gas mass
81- 83 F3.1 10+6Msun e_M(HI) [0.3/1.2] M(HI) uncertainty
85- 86 I2 --- r_M(HI) [12] M(HI) reference (1)
88- 93 F6.1 km/s V(HI) [-140.3/23.7] HI velocity
95- 96 I2 --- r_V(HI) [12] V(HI) reference (1)
98-100 F3.1 km/s sigHI [6.2/8.2] HI velocity dispersion
102-103 I2 --- r_sigHI [12] sigHI reference (1)
105-107 I3 --- Nm [25/127] Number of members
109-114 F6.1 km/s HRV [-142/27] Heliocentric velocity
116-118 F3.1 km/s e_HRV [0.9/2] Negative uncertainty on HRV
120-122 F3.1 km/s E_HRV [1/2] Positive uncertainty on HRV
124-128 F5.1 km/s Vgsr [-30.7/6.2] GSR velocity
130-132 F3.1 km/s sigma [7.8/9.4] Velocity dispersion
134-136 F3.1 km/s e_sigma [0.6/1.1] Negative uncertainty on sigma
138-140 F3.1 km/s E_sigma [0.8/1.8] Positive uncertainty on sigma
142-144 F3.1 10+7Msun M1/2 [1.8/4] Mass within the half-light
radius (2)
146-148 F3.1 10+7Msun e_M1/2 [0.3/0.4] Negative uncertainty on M1/2
150-152 F3.1 10+7Msun E_M1/2 [0.4/0.4] Positive uncertainty on M1/2
154-155 I2 Msun/Lsun M/L [10/21] Mass-to-light ratio within
the half-light radius
157 I1 Msun/Lsun e_M/L [3/4] Negative uncertainty on M/L
159 I1 Msun/Lsun E_M/L [3/6] Positive uncertainty on M/L
161-163 F3.1 --- Mt/Mb [4.4/9.6] Total (dynamical) mass divided
by baryonic mass (3)
165-167 F3.1 --- e_Mt/Mb [0.8/1.8] Negative uncertainty on Mt/Mb
169-171 F3.1 --- E_Mt/Mb [1/2.5] Positive uncertainty on Mt/Mb
173-177 F5.2 [-] [Fe/H] [-1.9/-1.5] Average [Fe/H]
179-182 F4.2 [-] e_[Fe/H] [0.06/0.09] Positive uncertainty on [Fe/H]
184-187 F4.2 [-] E_[Fe/H] [0.06/0.2] Negative uncertainty on [Fe/H]
189-191 F3.1 10-2 peffL [2.4/5.5] Effective yield (leaky box);
in 10-2Z☉, see equation 3
193-195 F3.1 10-2 e_peffL [0.4/1.1] Negative uncertainty on peffL
197-199 F3.1 10-2 E_peffL [0.4/1.2] Positive uncertainty on peffL
201-203 F3.1 10-2 peffP [2.4/5.3] Effective yield (pre-enriched);
in 10-2Z☉, see equation 4
205-207 F3.1 10-2 e_peffP [0.3/1.2] Negative uncertainty on peffP
209-211 F3.1 10-2 E_peffP [0.4/1.4] Positive uncertainty on peffP
213 A1 --- l_[Fe/H]0 Upper limit flag on [Fe/H]0
214-218 F5.2 [-] [Fe/H]0 Initial metallicity of the gas for
the pre-enriched model
220-223 F4.2 [-] e_[Fe/H]0 [0.12]? [Fe/H]0 negative uncertainty
225-228 F4.2 [-] E_[Fe/H]0 [0.1]? [Fe/H]0 positive uncertainty
229 A1 --- f_[Fe/H]0 [d] d: Upper limit with 95% confidence
231-235 F5.2 --- dlnPP [-1.8/12.2] ΔlnP value
for the pre-enriched model (4)
237-239 F3.1 10-2 peffA [2.1/4.4] Effective yield (accretion);
in 10-2Z☉, see equations 5 & 6
241-243 F3.1 10-2 e_peffA [0.3/0.7] Negative uncertainty on peffA
245-247 F3.1 10-2 E_peffA [0.3/0.8] Positive uncertainty on peffA
249-251 F3.1 --- M [2.3/7.1] Accretion parameter M (5)
253-255 F3.1 --- e_M [0.9/3.8] Negative uncertainty on M
257-259 F3.1 --- E_M [1.9/6.2] Positive uncertainty on M
261-265 F5.2 --- dlnPA [-1.2/11.1] ΔlnP value
for the accretion model (4)
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Note (1): Reference as follows:
1 = Tammann et al. (2011A&A...531A.134T 2011A&A...531A.134T).
2 = Cole et al. (2014ApJ...795...54C 2014ApJ...795...54C).
3 = Momany et al. (2005A&A...439..111M 2005A&A...439..111M).
LV and rh based on surface brightness profiles from:
4 = de Vaucouleurs et al. (1991, VII/155),
5 = McConnachie et al. (2006MNRAS.373..715M 2006MNRAS.373..715M), and
6 = Lee & Kim (2000, J/AJ/119/777).
Both values are updated for the distances adopted here. LV is corrected
for extinction based on Schlafly & Finkbeiner (2011ApJ...737..103S 2011ApJ...737..103S).
7 = Based on stellar mass-to-light ratios from Woo+ (2008MNRAS.390.1453W 2008MNRAS.390.1453W).
8 = Karachentsev & Kaisina (2013, J/AJ/146/46).
9 = van Zee (2000AJ....119.2757V 2000AJ....119.2757V).
10 = Hunter & Elmegreen (2004, J/AJ/128/2170).
11 = Hunter et al. (2010AJ....139..447H 2010AJ....139..447H).
12 = Measured from the HI maps of Hunter et al. (2012, J/AJ/144/134).
HI masses updated for the distances adopted here. The uncertainty in
M(HI) incorporates error on the 21cm flux--assumed to be 11%--and
uncertainty in distance.
Note (2): Mass within the half-light radius, calculated as
M1/2=4G-1σv2rh (Wolf+ 2010MNRAS.406.1220W 2010MNRAS.406.1220W).
Note (3): Total (dynamical) mass divided by baryonic mass (Mb=M*+M(HI))
within the half-light radius. The calculation assumes that half of the
stellar mass and half of the gas mass is located within the
half-light radius.
Note (4): Logarithm of the strength with which the pre-enriched or accretion
model is favored over the leaky box model.
Negative values of ΔlnP indicate that the model is disfavored.
Note (5): In the accretion model (Lenden-Bell, 1975VA.....19..299L 1975VA.....19..299L; see also
Kirby+, 2011ApJ...727...78K 2011ApJ...727...78K), M is the ratio of the final mass to the
initial gas mass. See equations 5 and 6.
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Global notes:
Note (G1): Sources in LeoA are from Stonkute+, 2014, J/ApJS/214/19;
Sources in Aquarius come from Kirby+, 2013, J/ApJ/779/102;
<[KCG2013] Aqr NNNN> in Simbad and
Sources in SagDIG come from Momany+, 2014, J/A+A/572/A42.
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-May-2017