J/MNRAS/436/413 VISTA ZJKs photometry of Sgr dSph (McDonald+, 2013)
VISTA's view of the Sagittarius dwarf spheroidal galaxy and southern
Galactic bulge.
McDonald I., Zijlstra A.A., Sloan G.C., Kerins E.J., Lagadec E.,
Minniti D., Santucho M.V., Gurovich S., Dominguez Romero M.J.L.
<Mon. Not. R. Astron. Soc., 436, 413-429 (2013)>
=2013MNRAS.436..413M 2013MNRAS.436..413M
ADC_Keywords: Galaxies, nearby ; Milky Way ; Photometry, infrared
Keywords: stars: AGB and post-AGB - stars: evolution -
stars: fundamental parameters - stars: late type - Galaxy: bulge -
galaxies: individual: Sgr dSph
Abstract:
We present the deepest near-infrared (ZJKs) photometry yet
obtained of the Sagittarius dwarf spheroidal (Sgr dSph), using Visible
and Infrared Survey Telescope for Astronomy (VISTA) to survey 11
square degrees centred on its core. We list locations and ZJKs-band
magnitudes for over 2.9 million sources in the field. We discuss the
isolation of the Sgr dSph from the foreground and Galactic Bulge
populations, identify the Sgr dSph's horizontal branch in the
near-infrared for the first time and map the density of the galaxy's
stars. We present isochrones for the Sgr dSph and Bulge populations.
These are consistent with the previously reported properties of the
Sgr dSph core: namely that it is dominated by a population between
[Fe/H]~-1dex and solar, with a significant [α/Fe] versus [Fe/H]
gradient. While strong contamination from the Galactic Bulge prevents
accurate measurement of the (Galactic) north side of the Sgr dSph, the
dwarf galaxy can be well approximated by a roughly ovaloid projection
of characteristic size 4°x2°, beyond which the projected
stellar density is less than half that of the region surrounding the
core. The galaxy's major axis is perpendicular to the Galactic Plane,
as in previous studies. We find slight evidence to confirm a
metallicity gradient in the Sgr dSph and use isochrones to fit a
distance of 24.3±2.3kpc. We were unable to fully constrain the
metallicity distribution of the Sgr dSph due to the Bulge
contamination and strong correlation of [α/Fe] with metallicity;
however, we find that metal-poor stars ([Fe/H]≲-1) make up ≲29% of
the Sgr dSph's upper red giant branch population. The Bulge population
is best fitted by a younger population with [Fe/H] ~ 0 and
[α/Fe] ~ 0 or slightly higher. We find no evidence for a
split, peanut- or X-shaped Bulge population in this line of sight
(l=5.6±∼1°, b=-14.1±∼3°).
Description:
The VISTA Infrared Camera (VIRCAM) surveyed the core of the Sgr dSph
over 16 nights between 2012 April 06 and 2012 June 07. VIRCAM consists
of 16 imaging chips which create a pawprint that must be moved around
the sky to create a contiguous imaging tile of around 1.5 square
degrees.
The simultaneous ZJKs-band images allowed for a relatively simple
merging procedure. Objects identified in different filters were simply
grouped by finding the nearest J- and Ks-band neighbour to each Z-band
detection.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 154 2921918 Details of the identified sources
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See also:
I/322 : UCAC4 Catalogue (Zacharias+, 2012)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
J/MNRAS/439/2618 : VISTA variables in Sagittarius dSph (McDonald+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [VSgr]
5- 20 A16 --- VSgr Source Name (HHMMSSss+DDMMSSs)
22- 30 F9.5 deg RAdeg Right ascension (J2000)
32- 40 F9.5 deg DEdeg Declination (J2000)
42- 47 F6.3 mag Zmag [9.4/23.6]?=0 VISTA Z magnitude
49- 53 F5.3 mag e_Zmag ?=0 rms uncertainty on Zmag
55- 60 F6.3 mag Jmag [9.2/23.1]?=0 VISTA J magnitude
62- 66 F5.3 mag e_Jmag ?=0 rms uncertainty on Jmag
68- 73 F6.3 mag Ksmag [8.4/19.9]?=0 VISTA Ks magnitude
75- 79 F5.3 mag e_Ksmag ?=0 rms uncertainty on Ksmag
81- 90 A10 --- UCAC4 ?=- UCAC4 cross-identification (I/322)
93- 99 F7.3 arcsec dist1 Distance between source and closest UCAC4 (1)
101-117 A17 --- 2MASS ?=- 2MASS cross-identification (II/246)
(HHMMSSss+DDMMSSA) (1)
120-126 F7.3 arcsec dist2 Distance between source and closest 2MASS (1)
128-147 A20 --- WISE ?=- WISE cross-identification (II/311)
(JHHMMSS.ss+DDMMSS.s) (1)
148-154 F7.3 arcsec dist3 Distance between source and closest WISE (1)
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Note (1): Where there is no close match, the distance to the nearest match is
given, but the match is not named to avoid improper cross-identification.
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Acknowledgements:
Iain Mcdonald, Iain.Mcdonald-2(at)manchester.ac.uk
References:
McDonald et al., Paper I 2012MNRAS.427.2647M 2012MNRAS.427.2647M, Cat. J/MNRAS/427/2647
McDonald et al., Paper III 2014MNRAS.439.2618M 2014MNRAS.439.2618M, Cat. J/MNRAS/439/2618
(End) Patricia Vannier [CDS] 19-Oct-2014