J/ApJ/947/31 Calibrating X-ray binary LFs via opt. data. II. M81 (Hunt+, 2023)
Calibrating X-ray binary luminosity functions via optical reconnaissance.
II. The high-mass XLF and globular cluster population of X-ray binaries in the
low star-forming spiral M81.
Hunt Q., Gallo E., Chandar R., Mok A., Prestwich A.
<Astrophys. J., 947, 31 (2023)>
=2023ApJ...947...31H 2023ApJ...947...31H
ADC_Keywords: Binaries, X-ray; Photometry, HST; Optical; Colors
Keywords: X-ray binary stars ; Globular star clusters
Abstract:
We characterize the optical counterparts to the compact X-ray source
population within the nearby spiral galaxy M81 using multiband Hubble
Space Telescope (HST) imaging data. By comparing the optical
luminosities and colors measured for candidate donor stars and host
clusters to stellar and cluster evolutionary models, respectively, we
estimate the likely masses and upper age limits of the field and
cluster X-ray binaries. We identify 15 low-mass X-ray binaries (i.e.,
donor star mass ≲3M☉) within ancient globular clusters, as well
as 42 candidate high-mass X-ray binaries (i.e., donor star mass
≳8M☉). To estimate the likelihood of misclassifications, we
inject 4000 artificial sources into the HST mosaic image and conclude
that our classifications of globular clusters and high-mass X-ray
binaries are reliable at the >90% level. We find that globular
clusters that host X-ray binaries are on average more massive and more
compact than globular clusters that do not. However, there is no
apparent correlation between the X-ray brightness of the clusters and
their masses or densities, nor are X-ray binary hosts more X-ray
luminous than the general field population of low-mass X-ray binaries.
This work represents one of the first in-depth analyses of the
population of X-ray binaries within globular clusters in a spiral
galaxy.
Description:
Following Hunt+ 2021, J/ApJ/912/31, we make use of the X-ray
point-source catalog constructed by L19 (Lehmer+ 2019, J/ApJS/243/3),
in which deep Chandra imaging data are examined for 38 nearby
galaxies. Within M81, L19 identify 252 compact X-ray sources.
By comparison, the HST footprint shown in Figure 1 includes 240 of the
252 compact X-ray sources from L19. Archival HST imaging downloaded
from the Hubble Legacy Archive (HLA) was used for the identification
and classification of optical counterparts to the X-ray sources.
For M81, a total of roughly 35 hours worth of ACS/WFC observations
spanning 33 fields in three bands --F814W (I band), F606W (V band),
and F435W for (B band)-- were obtained between 2004 September and
2006 March by J. Huchra (Prop. ID 10250) and A. Zezas (Prop. ID 10584).
Of these, 27 fields have sufficient observations for this work.
Each field spans 3.4'x3.4', yielding roughly 674000arcsec2 of
coverage over the entire galaxy.
See Section 2.
Objects:
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RA (ICRS) DE Designation(s)
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09 55 33.17 +69 03 55.0 M81 = NGC 3031
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 86 240 Properties and classifications of M81 X-ray sources
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
IX/57 : The Chandra Source Catalog (CSC), Release 2.0 (Evans+, 2019)
J/ApJ/595/685 : HST imaging in Chandra Deep Field-South (Grogin+, 2003)
J/ApJ/613/279 : ACS Virgo Cluster Survey. III. M87 (Jordan+, 2004)
J/ApJS/150/19 : ChaMP. I. First X-ray source catalog (Kim+, 2004)
J/ApJS/169/401 : ChaMP X-ray point source catalog (Kim+, 2007)
J/ApJ/662/525 : LMXBs in globular clusters of 5 galaxies (Kundu+, 2007)
J/ApJ/689/983 : LMXBs in early-type galaxies. I. Chandra (Humphrey+, 2008)
J/ApJ/714/25 : AMUSE-Virgo survey. II. (Gallo+, 2010)
J/AJ/139/2620 : Spectroscopy of M81 globular clusters (Nantais+, 2010)
J/AJ/139/1413 : M81 star cluster candidates (Nantais+, 2010)
J/MNRAS/405/1293 : Compact star clusters in M81 (Santiago-Cortes+, 2010)
J/AJ/142/183 : HST photometry of globulars in M81 (NGC 3031) (Nantais+, 2011)
J/ApJ/754/67 : Longslit spectroscopy of local bulges (Fabricius+, 2012)
J/MNRAS/419/2095 : HMXBs in nearby galaxies (Mineo+, 2012)
J/ApJS/212/21 : A deep Chandra ACIS survey of M83 (Long+, 2014)
J/ApJ/862/73 : Deep Chandra obs. of X-ray point sources in M87 (Luan+, 2018)
J/ApJS/243/3 : Chandra observations of SINGS galaxies (Lehmer+, 2019)
J/ApJ/890/150 : X-ray binaries in M101 with HST optical data (Chandar+, 2020)
J/ApJS/248/31 : HST & Chandra obs. of elliptical galaxies (Lehmer+, 2020)
J/ApJ/912/31 : M83 X-ray binary classifications from HST (Hunt+, 2021)
J/MNRAS/509/180 : GC in 5 nearby spiral galaxies (Lomeli-Nunez+, 2022)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- ID Lehmer+ 2019, J/ApJS/243/3 identifier
(<[LET2019] NGC 3031 NNN> in Simbad)
10- 13 A4 --- --- [2CXO]
15- 30 A16 --- 2CXO CSC identifier (JHHMMSS.s+DDMMSS)
32- 38 F7.3 deg RAdeg [148.5/149.3]? Right Ascension (J2000)
40- 45 F6.3 deg DEdeg [68.9/69.2]? Declination (J2000)
47- 50 F4.1 [10-7W] logLx [35.6/39.4] log X-ray luminosity; erg/s
52- 58 F7.3 mag VMag [-10.62/-0.55]? Absolute V band magnitude
estimated at a distance of 3.63Mpc
60- 65 F6.3 mag B-V [-2.2/3.6]? The (B-V) color
67- 72 F6.3 mag V-I [-0.5/2.6]? The (V-I) color
74- 80 A7 --- Class Classification (1)
82 A1 --- f_Class [i] i = an XRB associated with a cluster
84- 86 F3.1 --- CF [1/3] Confidence flag (1=most certain
classifications) (2)
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Note (1): Classification as follows:
SNR = Supernova remnant (6 occurrences)
(SNR) = a SNR identified using our HR-LX criterion (19 occurrences)
Gal = Galaxy (10 occurrences)
HM = High mass X-ray binary (42 occurrences)
IM = Intermediate mass X-ray binary (35 occurrences)
LM = Low mass X-ray binary (122 occurrences)
Nucleus = nucleus (1 occurrence)
Star = star (5 occurrences)
Note (2): A confidence flag is assigned to each source based on the "strength"
of the identification of the X-ray emitter: a CF of 1 represents
the most certain classifications (i.e. those determined in other
studies, or XRBs with a clear donor, with multiple candidates of
similar mass, or a clear absence of a donor); CF ratings of 2 or 3
may indicate that a source is in a dust-obscured region, such as
near the nucleus or along a dust lane, since the presence of
heavy dust could potentially mask high-mass stars, background
galaxies, and clusters, leading to possible misidentifications.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 14-Apr-2025