Comparing Observed Stellar Kinematics and Surface Densities in a Low-latitude Bulge Field to Galactic Population Synthesis Models

Terry, Sean K.; Barry, Richard; Bennett, D. P.; Bhattacharya, Aparna; Anderson, Jay; Penny, Matthew T.

doi:10.3847/1538-4357/ab629b

Cited by 6 publications

(11 citation statements)

References 84 publications

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“…As already discussed in e.g. Kuijken & Rich (2002); Clarkson et al (2008); Calamida et al (2014); Bernard et al (2018); Terry et al (2020), µ * can be used to distinguish efficiently between foreground stars and bulge stars, even if there is a clear overlap between the distribu-tions, at µ * ∼ −5 mas/yr. A bump in the red distribution is also evident at µ * ∼ −2 mas/yr, due to the contamination by foreground objects.…”

Section: Astrometric Cleaning Proceduresmentioning

confidence: 93%

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Blanco DECam Bulge Survey (BDBS)

Marchetti

Johnson

Joyce

et al. 2022

A&A

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Aims. The Blanco DECam Bulge Survey (BDBS) has imaged more than 200 square degrees of the southern Galactic bulge, providing photometry in the ugrizy filters for ∼ 250 million unique stars. The presence of a strong foreground disk population, along with complex reddening and extreme image crowding, has made it difficult to constrain the presence of young and intermediate age stars in the bulge population. Methods. We employed an accurate cross-match of BDBS with the latest data release (EDR3) from the Gaia mission, matching more than 140 million sources with BDBS photometry and Gaia EDR3 photometry and astrometry. We relied on Gaia EDR3 astrometry, without any photometric selection, to produce clean BDBS bulge colour-magnitude diagrams (CMDs). Gaia parallaxes were used to filter out bright foreground sources, and a Gaussian mixture model fit to Galactic proper motions could identify stars kinematically consistent with bulge membership. We applied this method to 127 different bulge fields of 1 deg 2 each, with | | ≤ 9.5 • and −9.5 • ≤ b ≤ −2.5 • . Results. The astrometric cleaning procedure removes the majority of blue stars in each field, especially near the Galactic plane, where the ratio of blue to red stars is 10%, increasing to values ∼ 20% at higher Galactic latitudes. We rule out the presence of a widespread population of stars younger than 2 Gyr. The vast majority of blue stars brighter than the turnoff belong to the foreground population, according to their measured astrometry. We introduce the distance between the observed red giant branch bump and the red clump as a simple age proxy for the dominant population in the field, and we confirm the picture of a predominantly old bulge. Further work is needed to apply the method to estimate ages to fields at higher latitudes, and to model the complex morphology of the Galactic bulge. We also produce transverse kinematic maps, recovering expected patterns related to the presence of the bar and of the X-shaped nature of the bulge.

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Section: Astrometric Cleaning Proceduresmentioning

confidence: 93%

“…In this appendix we further clean the bulge CMDs shown in Fig. 11, reducing the completeness of the fields, but increasing their purity (see also Bernard et al 2018;Terry et al 2020). In 11 is likely to be a residual foreground contaminant to the bulge CMDs.…”

Section: Appendix A: Choosing the Number Of Components For The Gaussi...mentioning

confidence: 99%

Blanco DECam Bulge Survey (BDBS)

Marchetti

Johnson

Joyce

et al. 2022

A&A

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“…If there are no systematic errors, the mean value of σ µ i ,VVV − σ µ i ,HST should be consistent with 0. However, we found the mean and standard deviation values of σ µ l ,VVV − σ µ l ,HST = 0.124 ± 0.135 mas/yr and σ µ b ,VVV − σ µ b ,HST = 0.153 ± 0.144 mas/yr when we used the 39 fields without the outlier indicated in the figure that is specified by Terry et al (2020). This implies the existence of systematic offset between the VVV and HST measurements.…”

Section: Virac Red Giants' Proper Motionsmentioning

confidence: 83%

“…3 shows the comparison as a function of extinction A I . We used 35 fields observed by Koz lowski et al (2006) and 4 fields summarized in Table 2 of Terry et al (2020) for the comparison, and the HST values are taken from the two papers. If there are no systematic errors, the mean value of σ µ i ,VVV − σ µ i ,HST should be consistent with 0.…”

Section: Virac Red Giants' Proper Motionsmentioning

confidence: 99%

A Parametric Galactic Model toward the Galactic Bulge Based on Gaia and Microlensing Data

Koshimoto,

Baba,

Bennett

2021

Preprint

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We developed a parametric Galactic model toward the Galactic bulge by fitting to spatial distributions of the Gaia DR2 disk velocity, VVV proper motion, BRAVA radial velocity, OGLE-III red clump star count, and OGLE-IV star count and microlens rate, optimized for use in microlensing studies. We include the asymmetric drift of Galactic disk stars and the dependence of velocity dispersion on Galactic location in kinematic model, which has been ignored in most previous models used for microlensing studies. We show that our model predicts a microlensing parameter distribution that is significantly different from the one with a typically used model in the previous studies. Through our modeling, we estimate various fundamental model parameters for our Galaxy, including the initial mass function (IMF) in the inner Galaxy. Combined constraints from star counts and the microlensing event timescale distribution from the OGLE-IV survey, in addition to a prior on the bulge stellar mass, enable us to successfully measure IMF slopes using a broken power law form over a broad mass range, α bd = 0.22 +0.20 −0.55 for M < 0.08 M , α ms = 1.16 +0.08 −0.15 for 0.08 M ≤ M < M br , and α hm = 2.32 +0.14 −0.10 for M ≥ M br , as well as a break mass at M br = 0.90 +0.05 −0.14 M . This is significantly different from the Kroupa IMF for local stars, but similar to the Zoccali IMF measured from a bulge luminosity function. We also estimate the dark matter mass fraction in the bulge region of 28 ± 7% which could be larger than a previous estimate. Because our model is purely parametric, it can be universally applied using the parameters provided in this paper.

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“…Specifically, the Besançon (Robin et al 2003) and GalMod (Pasetto et al 2018) models have been used in many different studies, to explore the structure, kinematics, and formation history of the Milky Way (Czekaj et al 2014;Robin et al 2017). In addition, they have also been used to simulate astronomical sky surveys (Penny et al 2013(Penny et al , 2019Rauer et al 2014;Kauffmann et al 2020), and their predictions have been tested against real observations (Schultheis et al 2006;Bochanski et al 2007;Pietrukowicz et al 2012;Schmidt et al 2020;Terry et al 2020).…”

Section: Introductionmentioning

confidence: 99%

MOA-2019-BLG-008Lb: A New Microlensing Detection of an Object at the Planet/Brown Dwarf Boundary

Bachelet

Tsapras

Gould

et al. 2022

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We report on the observations, analysis and interpretation of the microlensing event MOA-2019-BLG-008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finite-source effects were observed. Therefore, the angular Einstein ring radius θ E cannot be measured from the light curve alone. However, the large event duration, t E ∼ 80 days, allows a precise measurement of the microlensing parallax π E. In addition to the constraints on the angular radius θ * and the apparent brightness I s of the source, we employ the Besançon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two galactic models: the companion is likely a resident of the brown dwarf desert with a mass M p ∼ 30 M Jup, and the host is a main-sequence dwarf star. The lens lies along the line of sight to the Galactic bulge, at a distance of ≤4 kpc. We estimate that in about 10 yr the lens and source will be separated by ∼55 mas, and it will be possible to confirm the exact nature of the lensing system by using high-resolution imaging from ground- or space-based observatories.

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Comparing Observed Stellar Kinematics and Surface Densities in a Low-latitude Bulge Field to Galactic Population Synthesis Models

Cited by 6 publications

References 84 publications

Blanco DECam Bulge Survey (BDBS)

Blanco DECam Bulge Survey (BDBS)

A Parametric Galactic Model toward the Galactic Bulge Based on Gaia and Microlensing Data

MOA-2019-BLG-008Lb: A New Microlensing Detection of an Object at the Planet/Brown Dwarf Boundary

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