J/ApJ/939/38 Faint stars in a faint galaxy. II. Bootes I dsph (Filion+, 2022)
Faint stars in a faint galaxy.
II. The low-mass stellar initial mass function of the Bootes I ultrafaint
dwarf spheroidal galaxy.
Filion C., Platais I., Wyse R.F.G., Kozhurina-Platais V.
<Astrophys. J., 939, 38 (2022)>
=2022ApJ...939...38F 2022ApJ...939...38F
ADC_Keywords: Galaxies, dwarf; Photometry, HST; Optical; Proper motions
Keywords: Initial mass function ; Space astrometry ; Low mass stars ;
Proper motions ; Dwarf spheroidal galaxies
Abstract:
This paper presents improved constraints on the low-mass stellar
initial mass function (IMF) of the Bootes I (Boo I) ultrafaint dwarf
galaxy, based on our analysis of recent deep imaging from the Hubble
Space Telescope. The identification of candidate stellar members of
Boo I in the photometric catalog produced from these data was achieved
using a Bayesian approach, informed by complementary archival imaging
data for the Hubble Ultra Deep Field. Additionally, the existence of
earlier-epoch data for the fields in Boo I allowed us to derive proper
motions for a subset of the sources and thus identify and remove
likely Milky Way stars. We were also able to determine the absolute
proper motion of Boo I, and our result is in agreement with, but
completely independent of, the measurement(s) by Gaia. The
best-fitting parameter values of three different forms of the low-mass
IMF were then obtained through forward modeling of the color-magnitude
data for likely Boo I member stars within an approximate Bayesian
computation Markov Chain Monte Carlo algorithm. The best-fitting
single power-law IMF slope is α=-1.95-0.28+0.32, while the
best-fitting broken power-law slopes are α1=-1.67-0.57+0.48
and α2=-2.57-1.04+0.93. The best-fitting lognormal
characteristic mass and width parameters are
Mc=0.17-0.11+0.05M☉ and σ=0.49-0.20+0.13. These
broken power-law and lognormal IMF parameters for Boo I are consistent
with published results for the stars within the Milky Way, and thus it
is plausible that Bootes I and the Milky Way are populated by the same
stellar IMF.
Description:
In this analysis we used the catalog of DAOPHOT point-spread function
(PSF) photometry (Stetson 1987PASP...99..191S 1987PASP...99..191S) obtained in Paper I
(Filion+ 2020ApJ...901...82F 2020ApJ...901...82F). These data were produced from imaging
taken under our HST GO program 15317 (PI I. Platais), and the
observing strategy, data reduction, and photometric analysis of these
data are detailed in Paper I. This photometric catalog was produced
from HST ACS/WFC imaging of three slightly overlapping fields (or
pointings) centered on Boo I, taken using the F606W and F814W filters.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
14 00 00.00 +14 30 00.0 Boo I = NAME Bootes I
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
photo.dat 88 7911 Catalog containing HST photometry in the
Vega magnitude system
astro.dat 96 3634 Catalog containing relative proper motions
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Description of file:
hlspboocatshstacs-wfcbooif606w-f814wv1_photometric-catalog.csv and
hlspboocatshstacs-wfcbooif606w-f814wv1_astrometric-catalog.csv are
the original files in CSV format as downloaded at:
http://archive.stsci.edu/hlsp/boocats (DOI: 10.17909/g37r-1r51)
See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
J/AJ/136/2321 : Washington photometry of Bootes I stars (Hughes+, 2008)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011)
J/MNRAS/439/788 : Stromgren and Washington photometry in Boo I (Hughes+, 2014)
J/ApJ/797/115 : HSTPROMO I. Observations and NGC7078 results (Bellini+, 2014)
J/ApJ/826/110 : Boo-127 and Boo-980 high-resolution spectra (Frebel+, 2016)
J/MNRAS/461/3702 : gi photometry of Bootes I (Roderick+, 2016)
J/ApJ/852/49 : Properties of metal-poor stars in APOGEE DR13 (Hayes+, 2018)
J/AJ/159/272 : Orion Nebula Cluster PMs with HST (Platais+, 2020)
J/ApJS/251/2 : CDWFS: Chandra survey in Bootes. I. (Masini+, 2020)
J/ApJ/920/92 : VLT Spectroscopy of Ultra-faint Dwarf Gal. (Jenkins+, 2021)
Byte-by-byte Description of file: photo.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- ID [1/30451] Photometric catalog identifier
7- 13 F7.4 mag F606W [19.7/30.1] DAOPHOT PSF photometric Vega
magnitude in the HST ACS/WFC F606W filter
15- 21 F7.4 mag F814W [18.48/29.1] DAOPHOT PSF photometric Vega
magnitude in the HST ACS/WFC F814W filter
23- 28 F6.4 mag e_F606W [0.01/0.6] F606W uncertainty
30- 35 F6.4 mag e_F814W [0.007/0.6] F814W uncertainty
37- 43 F7.4 --- shF606W [-4.7/1.9] DAOPHOT sharp statistic in the
F606W filter
45- 51 F7.4 --- shF814W [-3.3/1.6] DAOPHOT sharp statistic in the
F814W filter
53- 63 F11.7 deg RAdeg [209.93/210.11] Right ascension (J2000)
65- 74 F10.7 deg DEdeg [14.44/14.6] Declination (J2000)
76- 80 F5.3 --- PMm [0/1] Bayesian probability of membership from
photometry
82- 86 F5.3 --- PNMm [0.001/1] Bayesian probability of
non-membership from photometry
88 I1 --- Mm [0/1] Flag indicating if source meets all
criteria for membership (1=yes, 0=no)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: astro.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 I7 --- ID [1017/2757029] Astrometric catalog ID
9- 14 F6.2 mas/yr pmRA [-17/14.5] Weighted proper motion in X (pmx)
16- 21 F6.2 mas/yr pmDE [-16.2/15.5] Weighted proper motion in Y (pmy)
23- 26 F4.2 mas/yr e_pmRA [0.02/2.5] pmRA uncertainty
28- 31 F4.2 mas/yr e_pmDE [0.02/2.5] pmDE uncertainty
33- 38 F6.3 mag mag [11.7/27.3] Proxy stellar magnitude (mastrom)
40 I1 --- N1 [2/8] Number of first-epoch datapoints
42- 43 I2 --- N2 [1/16] Number of second-epoch datapoints
45 I1 --- Ndel [0/4] Number of deleted datapoints
47- 51 F5.3 pix Resmax [0.015/1.1] Largest residual in either
proper-motion fit
53- 59 F7.2 pix Xpos [43/4113] X-coordinate in ACS/WFC pixels
aligned with RA
61- 67 F7.2 pix Ypos [-119/4211] Y-coordinate in ACS/WFC pixels
aligned with DEC
69- 81 F13.9 deg RAdeg [209.93/210.11] Right ascension (J2000)
83- 94 F12.9 deg DEdeg [14.44/14.6] Declination (J2000)
96 I1 --- Point [1/5] Pointing/field center to which source
belongs (1, 3 or 5)
--------------------------------------------------------------------------------
History:
Downloaded at: http://archive.stsci.edu/hlsp/boocats
(MAST doi:10.17909/g37r-1r51)
References:
Filion et al. Paper I. 2020ApJ...901...82F 2020ApJ...901...82F
(End) Emmanuelle Perret [CDS] 05-Sep-2024