J/ApJS/244/29 Microlensing events toward the Galactic bulge (Mroz+, 2019)
Microlensing optical depth and event rate toward the Galactic bulge from 8yr of
OGLE-IV observations.
Mroz P., Udalski A., Skowron J., Szymanski M.K., Soszynski I.,
Wyrzykowski L., Pietrukowicz P., Kozlowski S., Poleski R., Ulaczyk K.,
Rybicki K., Iwanek P.
<Astrophys. J. Suppl. Ser., 244, 29 (2019)>
=2019ApJS..244...29M 2019ApJS..244...29M
ADC_Keywords: Gravitational lensing; Milky Way; Photometry, RI
Keywords: Galaxy: bulge ; Galaxy: kinematics and dynamics ; Galaxy: structure ;
gravitational lensing: micro
Abstract:
The number and properties of observed gravitational microlensing
events depend on the distribution and kinematics of stars and other
compact objects along the line of sight. In particular, precise
measurements of the microlensing optical depth and event rate toward
the Galactic bulge enable strict tests of competing models of the
Milky Way. Previous estimates, based on samples of up to a few hundred
events, gave larger values than expected from the Galactic models and
were difficult to reconcile with other constraints on the Galactic
structure. Here we used long-term photometric observations of the
Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE)
to select a homogeneous sample of 8000 gravitational microlensing
events. We created the largest and most accurate microlensing optical
depth and event rate maps of the Galactic bulge. The new maps ease the
tension between the previous measurements and Galactic models. They
are consistent with some earlier calculations based on bright stars
and are systematically ∼30% smaller than the other estimates based on
"all-source" samples of microlensing events. The difference is caused
by the careful estimation of the source star population. The new maps
agree well with predictions based on the Besancon model of the Galaxy.
Apart from testing the Milky Way models, our maps may have numerous
other applications, such as the measurement of the initial mass
function or constraining the dark matter content in the Milky Way
center. The new maps will also inform the planning of future
space-based microlensing experiments by revising the expected number
of events.
Description:
The photometric data analyzed in this paper were collected as part of
the Optical Gravitational Lensing Experiment (OGLE) sky survey. All
analyzed observations were collected during the fourth phase of the
project (OGLE-IV; Udalski+ 2015AcA....65....1U 2015AcA....65....1U) during 2010-2017. The
survey uses the dedicated 1.3m Warsaw Telescope, located at Las
Campanas Observatory, Chile. The OGLE-IV camera covers a field of view
of 1.4deg2 with a pixel scale of 0.26"/pixel.
We searched for microlensing events in 121 fields located toward the
Galactic bulge that have been observed for at least two observing
seasons. These fields cover an area of over 160deg2 and contain over
400 million sources in OGLE databases. Typical exposure times are
100-120s, and the vast majority of observations are taken through the
I-band filter, closely resembling that of a standard Cousins system.
The magnitude range of the survey is 12<I<21, but the limiting
magnitude depends on the crowding of a given field.
Nine fields that are observed with the highest cadence (BLG500,
BLG501, BLG504, BLG505, BLG506, BLG511, BLG512, BLG534, and BLG611)
have already been analyzed by Mroz+ (2017Natur.548..183M 2017Natur.548..183M).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 294 5790 Best-fitting parameters of the analyzed
microlensing events in low-cadence OGLE fields
table5.dat 66 3842 Surface density of stars in OGLE-IV subfields
calculated using image-level simulations
table6.dat 51 121 Basic information about analyzed fields
table7.dat 73 121 Microlensing optical depth and event rates in the
OGLE-IV fields (averaged over sources brighter
than I=21).
phot/* . 5790 Calibrated I-band photometry of individual events,
in ASCII format
eff/* . 121 Event detection efficiencies in individual fields
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See also:
J/AcA/50/1 : OGLE microlensing events in Galactic Bulge (Udalski+, 2000)
J/AcA/50/421 : OGLE-II DIA BUL_SC1 field (Wozniak, 2000)
J/AcA/51/175 : OGLE-II DIA microlensing events (Wozniak+, 2001)
J/AcA/52/217 : OGLE II. VI photometry of Galactic Bulge (Udalski+, 2002)
J/A+A/454/185 : EROS-2 microlensing parameters (Hamadache+, 2006)
J/A+A/466/157 : Bulge Microlensing Events (Soto+, 2007)
J/A+A/453/635 : Modelling the Gal. Interstellar Extinction (Marshall+, 2006)
J/ApJ/636/240 : OGLE II microlensing parameters (Sumi+, 2006)
J/ApJ/711/L48 : 2008 OGLE Bulge microlensing alerts (Cohen+, 2010)
J/A+A/529/A102 : MOA-2007-BLG-387Lb light curve I band (Batista+, 2011)
J/ApJ/778/150 : Microlensing events toward the Bulge from MOA-II (Sumi+, 2013)
J/ApJS/216/12 : OGLE-III Gal. bulge microlensing events (Wyrzykowski+, 2015)
J/ApJ/827/139 : Microlensing optical depths from MOA-II (Sumi+, 2016)
J/MNRAS/458/3012 : OGLE-III Parallax microlensing events (Wyrzykowski+, 2016)
J/AJ/154/210 : 2015 high-cadence Spitzer microlensing events (Zhu+, 2017)
J/A+A/605/A89 : Abundances of microlensed Bulge stars. VI. (Bensby+, 2017)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)
J/AJ/155/186 : The KMTNet/K2-C9 (Kepler) Data Release (Kim+, 2018)
http://ogle.astrouw.edu.pl/cgi-ogle/get_o4_tau.py : Web interface associated
to this paper
http://www.astrouw.edu.pl/ogle/ogle4/microlensing_maps/ : Associated data
to this paper
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Name Star name
18- 23 A6 --- Field OGLE-IV field name
24 A1 --- --- [.]
25- 26 I02 --- sField OGLE-IV subfield name within Field
28- 33 I6 --- Star [50/208567] Star ID in the OGLE-IV database
35- 36 I2 h RAh [17/18] Hour of Right Ascension (J2000)
38- 39 I2 min RAm Minute of Right Ascension (J2000)
41- 45 F5.2 s RAs Second of Right Ascension (J2000)
47- 47 A1 --- DE- [-] Sign of the Declination (J2000)
48- 49 I2 deg DEd [19/38] Degree of Declination (J2000)
51- 52 I2 arcmin DEm Arcminute of Declination (J2000)
54- 57 F4.1 arcsec DEs Arcsecond of Declination (J2000)
59- 67 F9.5 deg RAdeg [258.28/284.31] Right Ascension (J2000)
69- 77 F9.5 deg DEdeg [-38.4/-19.2] Declination (J2000)
79- 86 F8.5 deg GLON [-8.6/9.9] Galactic longitude
88- 96 F9.5 deg GLAT [-14.9/6.3] Galactic latitude
98-108 F11.3 d t0-best Best-fit t0, time of closest approach,
Heliocentric Julian Date
110-116 F7.3 d tE-best [1.58/303] Best-fit tE, Einstein timescale
118-122 F5.3 --- u0-best [0/1] Best-fit u0, projected separation
124-129 F6.3 mag Is-best [13.9/21] Best-fit I-band source magnitude
131-135 F5.3 --- fs-best [0.01/3.8] Best-fit blending parameter (1)
137-147 F11.3 d t0-med Median t0, time of closest approach,
Heliocentric Julian Date
149-155 F7.3 d e_t0-med [-37.2/0] Negative error bar, t0-med
157-162 F6.3 d E_t0-med [0/43] Positive error bar, t0-med
164-171 F8.3 d tE-med [1.7/8812] Median tE, Einstein timescale
173-181 F9.3 d e_tE-med [-4821/-0.04] Negative error bar, tE-med
183-191 F9.3 d E_tE-med [0.06/19953] Positive error bar, tE-med
193-197 F5.3 --- u0-med [0/1.3] Median u0, projected separation
199-204 F6.3 --- e_u0-med [-0.8/0] Negative error bar, u0-med
206-210 F5.3 --- E_u0-med [0/1.5] Positive error bar, u0-med
212-217 F6.3 mag Is-med [13.9/26.5] Median I-band source magnitude
219-224 F6.3 mag e_Is-med [-6.8/-0.005] Negative error bar, Is-med
226-230 F5.3 mag E_Is-med [0.006/5.2] Positive error bar, Is-med
232-236 F5.3 --- fs-med [0/3.5] Median blending parameter (1)
238-243 F6.3 --- e_fs-med [-0.6/0] Negative error bar, fs-med
245-249 F5.3 --- E_fs-med [0/0.9] Positive error bar, fs-med
251-256 F6.2 --- Weight [2/129.2] Inverse of the detection efficiency
258-294 A37 --- EWS OGLE EWS ID(s)
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Note (1): The blending parameter is defined as the ratio between the source
flux and the total flux of the detected object (i.e., the sum of the
fluxes of the source and unrelated blends).
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field OGLE-IV field name
7 A1 --- --- [.]
8- 9 I02 --- sField OGLE-IV subfield name within Field
11- 17 F7.3 deg RAdeg [258.28/286.67] Right ascension (J2000)
19- 25 F7.3 deg DEdeg [-38.4/-19.2] Declination (J2000)
27- 32 F6.3 deg GLON [-8.6/10.6] Galactic longitude
34- 40 F7.3 deg GLAT [-16.5/6.4] Galactic latitude
42- 46 F5.1 arcmin-2 sigma18 [3.7/369.7] Star surface density in
the range 14<I<18
48- 53 F6.1 arcmin-2 sigma21 [42.8/4609.2] Star surface density in
the range 14<I<21
55- 59 I5 --- N18 [603/60940] Number of stars in
the range 14<I<18
61- 66 I6 --- N21 [7183/756286] Number of stars in
the range 14<I<21
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field OGLE-IV field name
8- 15 F8.4 deg RAdeg [259/286] Right ascension (J2000)
17- 24 F8.4 deg DEdeg [-38/-19.7] Declination (J2000)
26- 32 F7.4 deg GLON [-8/10] Galactic longitude
34- 41 F8.4 deg GLAT [-16/6] Galactic latitude
43- 45 F3.1 10+6 Ns [0.5/7.1] Number of monitored stars
47- 51 I5 --- Nep [36/12099] Number of epochs
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field OGLE-IV field name
8- 14 F7.4 deg GLON [-8/10] Galactic longitude
16- 23 F8.4 deg GLAT [-16/6] Galactic latitude
25- 28 F4.2 10-6 tau [0/3.7] Optical depth τ300
30- 33 F4.2 10-6 e_tau [0/1.3] Uncertainty of tau
35- 38 F4.1 10-6/yr Gam [0/26.5] Event rate Γ per star
per 106 year
40- 42 F3.1 10-6/yr e_Gam [0/7.1] Uncertainty of gam
44- 48 F5.1 deg-2/yr Gam.d [0/265.3] Event rate Γdeg2
per unit area (in square degree)
per year
50- 53 F4.1 deg-2/yr e_Gam.d [0/16.3] Uncertainty of gam-deg2
55- 58 F4.1 d tE-mean [0/79.6] Mean Einstein timescale <tE>
60- 63 F4.1 d e_tE-mean [0/79.6] Uncertainty of tE-mean
65- 67 I3 --- Nev [0/441] Number of detected events
69- 73 F5.2 10+6 N21 [0.4/19.1] Number of sources brighter
than I=21
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Byte-by-byte Description of file: phot/*
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Bytes Format Units Label Explanations
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1- 13 F13.5 d HJD Heliocentric Julian Date
15- 20 F6.3 mag Imag [12.2/23.8] I-band magnitude
22- 26 F5.3 mag e_Imag [0.003/4] I-band magnitude uncertainty
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Byte-by-byte Description of file (#): eff/*
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Bytes Format Units Label Explanations
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1- 6 F6.3 [d] logtE-min [-1/2.4] Minimal log(tE)
8- 13 F6.3 [d] logtE-max [-0.9/2.5] Maximal log(tE)
15- 22 F8.6 --- Eff [0.0005/0.41] Detection efficiency
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History:
From electronic version of the journal for the tables.
Individual files and subdirectory phot & eff downloaded from:
http://www.astrouw.edu.pl/ogle/ogle4/microlensing_maps/
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 21-Feb-2020