J/ApJS/247/7 Narrowband Ca photometry for dwarf spheroidal galaxies (Han+, 2020)
Narrowband Ca photometry for dwarf spheroidal galaxies.
I. Chemostructural study on Draco, Sextans, and Canes Venatici I.
Han S.-I., Kim H.-S., Yoon S.-J., Lee Y.-W., Arimoto N., Okamoto S.,
Ree C.H.
<Astrophys. J. Suppl. Ser., 247, 7 (2020)>
=2020ApJS..247....7H 2020ApJS..247....7H
ADC_Keywords: Galaxies, photometry; Optical
Keywords: Local Group ; Dwarf spheroidal galaxies ; Galaxy stellar content ;
Galaxy structure ; Stellar abundances
Abstract:
A few dozen dwarf satellite galaxies of the Milky Way have been
discovered, which are often viewed as the remaining building blocks of
our Galaxy. The follow-up spectroscopy showed that dwarf galaxies have
a sizeable spread in their metallicities. Several scenarios were
suggested to explain the metallicity spread, which can be tested by
the structural patterns of stellar subpopulations with distinct
metallicities. However, such chemical plus structural examination,
which we refer to as "chemostructural study", is hindered by the lack
of stars with spectroscopic metallicity. Here we propose the Ca-by
photometry as an alternative way to secure metallicities for a 2-3
orders of magnitude larger stellar sample than the spectroscopic
sample and thus enable us to perform a chemostructural study on dwarf
galaxies. In particular, we use the hk index [=(Ca-b)-(b-y)], whose
validity as a photometric metallicity indicator (and crass
insensitivity to age) for red-giant-branch stars was upheld via
Galactic globular clusters, and observe three dwarf spheroidal
galaxies-Draco, Sextans, and Canes Venatici I (CVnI)-with
Subaru/Suprime-Cam. We find that in all the galaxies the metal-rich
stellar populations are more centrally concentrated than the
metal-poor counterparts, suggesting that the central regions of the
galaxies underwent extended star formation. Such a negative radial
metallicity gradient for Sextans and CVnI opposes the traditional
spectroscopic results. We also find that their metallicity
distribution functions (MDFs) can be characterized by a unimodal,
skewed Gaussian shape with a metal-rich peak and a metal-poor tail.
Description:
We have performed photometric observations with the Suprime-Cam on the
Subaru telescope using the Ca, b, and y filters during the three
observing runs from 2012 December to 2015 April for three dwarf
galaxies, Draco, Sextans, and CVnI. The Suprime-Cam provides a 34'x27'
field of view with a pixel scale of 0.2".
Objects:
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RA (ICRS) DE Designation(s)
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17 20 19.65 +57 55 10.7 Draco = NAME Dra dSph
13 28 08.10 +33 33 36.4 CVnI = NAME CVn I dSph
10 13 02.90 -01 36 53.0 Sextans = NAME Sex dSph
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 73 139435 Photometric measurements for the point sources
in Draco
table3.dat 73 69962 Photometric measurements for the point sources
in Sextans
table4.dat 73 47265 Photometric measurements for the point sources
in Canes Venatici I (CVnI)
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See also:
I/284 : The USNO-B1.0 Catalog (Monet+ 2003)
J/PASP/107/32 : uvby-hk photometry in M22 (Anthony-Twarog+ 1995)
J/AJ/116/1922 : CaII H and K filter photometry III. (Anthony-Twarog+, 1998)
J/AJ/119/1824 : Caby photometry of Ω Centauri (Rey+, 2000)
J/AJ/125/1383 : Stromgren photometry of NGC 6253 (Anthony-Twarog+, 2003)
J/AJ/127/1000 : Stromgren & Ca photom. of NGC 3680 (Anthony-Twarog+, 2004)
J/A+A/459/423 : VI and [Fe/H] of Fornax dSph RGB stars (Battaglia+, 2006)
J/A+A/454/333 : Computed Hbeta indices from ATLAS9 model (Castelli+, 2006)
J/AJ/131/895 : Stars in the Carina dwarf spheroidal galaxy (Koch+, 2006)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/MNRAS/411/1013 : CaII triplet in Sextans dSph galaxy (Battaglia+, 2011)
J/AJ/142/127 : NGC 5822 UBVI and uvbyCaHβ photometry (Carraro+, 2011)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/778/L13 : Subaru new Ca filter transmission function (Lee+, 2013)
J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)
J/ApJS/216/19 : Spectroscopic HK' index for 3 globular clusters (Lim+, 2015)
J/MNRAS/456/3757 : Open-cluster density profiles (Seleznev, 2016)
Byte-by-byte Description of file: table[234].dat
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Bytes Format Units Label Explanations
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1- 10 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
12- 20 F9.6 deg DEdeg Declination in decimal degrees (J2000)
22- 27 F6.3 mag Ca [14.1/28.1] The Subaru/Sprime-Cam Ca narrow
filter magnitude (1)
29- 33 F5.3 mag e_Ca [0.001/1.6] Uncertainty in Ca
35- 40 F6.3 mag b [12.5/27.7] The Subaru/Sprime-Cam b narrow
filter magnitude (1)
42- 46 F5.3 mag e_b [0.001/1.6] Uncertainty in b
48- 53 F6.3 mag y [12.3/27.4] The Subaru/Sprime-Cam y narrow
filter magnitude (1)
55- 59 F5.3 mag e_y [0.001/1.7] Uncertainty in y
61- 66 F6.3 --- CHI [0.2/23.2] DAOPHOT CHI parameter
68- 73 F6.3 --- SHARP [-5.51/11.2] DAOPHOT SHARP parameter
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Note (1): The instrumental Ca, b, and y magnitudes were converted to the
standard system using the Milky Way globular clusters M5 and M15
because the standard stars are too bright for the Suprime-Cam. These
GCs were observed with the du Pont 2.5m telescope using the same new
Ca-by filter set and transformed to the standard Ca-by photometric
system. See section 2 for further explanations.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-Apr-2020