The Initial Mass Function of the Galactic Bulge Down to ~0.15 Msun

Abstract

We present a luminosity function (LF) for lower main sequence stars in the Galactic bulge near (l,b)=(0,-6) to J=24, corresponding to M_J~9.3. This LF is derived from HST + NICMOS observations with the F110W and F160W filters. The main sequence locus in the infrared shows a strong change in slope at J~20.5 (M_J~5.75) which is well fit by new low mass models that include water and molecular hydrogen opacity. Our derived mass function (which is not corrected for binary companions) is the deepest measured to date in the bulge, and extends to 0.15 $M_{\odot }$ with a power law slope of $\alpha =-1.33\pm 0.07$; a Salpeter mass function would have $\alpha =-2.35$. We also combine our J band LF with previously published data for the evolved stars to produce a bulge LF spanning ~15 magnitudes. We show that this mass function has negligible dependence on the adopted bulge metallicity and distance modulus. Although shallower than the Salpeter slope, the slope of the bulge IMF is steeper than that recently found for the Galactic disk ($\alpha =-0.8$ and $\alpha =-0.54$ from the data of Reid & Gizis, 1997, and Gould et al. 1997, respectively, in the same mass interval), but is virtually identical to the disk IMF derived by Kroupa et al. (1993). The bulge IMF is also quite similar to the mass functions derived for those globular clusters which are believed to have experienced little or no dynamical evolution. Finally, we derive the $M/L_J$ ratio of the bulge to be $\sim 0.9\pm 0.1$ $M_{\odot }/L_{\odot }$, and briefly discuss the implications of this bulge IMF for the interpretation of the microlensing events observed in the direction of the Galactic bulge.

43 pages, 10 figures. Accepted for publication in The Astrophysical Journal

References in corpus (22)

• The Cosmic Baryon Budget
• The NextGen Model Atmosphere grid for $3000\le \Teff \le 10000\K$
• Early Star Formation and the Evolution of the Stellar Initial Mass Function in Galaxies
• On the effects of dynamical evolution on the initial mass function of globular clusters
• Evolutionary synthesis of stellar populations: a modular tool
• The Luminosity Function and Mass Function in the Galactic Bulge
• L Dwarfs and the Substellar Mass Function
• The MACHO Project: 45 Candidate Microlensing Events from the First Year Galactic Bulge Data
• M Dwarfs From Hubble Space Telescope Star Counts III: The Groth Strip
• The Optical Depth to Gravitational Microlensing in the Direction of the Galactic Bulge
• Microlensing by the Galactic Bar
• Statistical Determination of the MACHO Mass Spectrum
• The Luminosity Function of the Globular Cluster NGC 6397 Near the Limit of Hydrogen Burning
• A Comparison of Deep HST Luminosity Functions of Four Globular Clusters
• Implications of New JHK Photometry and a Deep Infrared Luminosity Function for the Galactic Bulge
• Hubble Space Telescope Observations of the Draco Dwarf Spheroidal
• HST Imaging of the Globular Clusters in the Fornax Cluster: Color and Luminosity Distributions
• The Stellar Populations of Pixels and Frames
• Deep H-band Galaxy Counts and Half-light Radii from HST/NICMOS Parallel Observations
• Metal Rich RR Lyrae Variables: I. The Evolutionary Scenario
• HST-NICMOS Color Transformations and Photometric Calibrations
• The Effects of Amplification Bias in Gravitational Microlensing Experiments

Cited by in corpus (127)

• Galactic Stellar and Substellar Initial Mass Function
• On the variation of the Initial Mass Function
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• A Universal Stellar Initial Mass Function? A Critical Look at Variations
• Dynamical evolution of star clusters in tidal fields
• The origin of sdB stars (II)
• Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve
• Unbound or Distant Planetary Mass Population Detected by Gravitational Microlensing
• Age and Metallicity Distribution of the Galactic Bulge from Extensive Optical and Near-IR Stellar Photometry
• The Ultraviolet Spectrum of MS 1512-cB58: An Insight into Lyman Break Galaxies
• Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The initial mass function : from Salpeter 1955 to 2005
• The K20 survey. VI. The Distribution of the Stellar Masses in Galaxies up to z~2
• No large population of unbound or wide-orbit Jupiter-mass planets
• The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Young Clusters
• Predictions of the WFIRST Microlensing Survey I: Bound Planet Detection Rates
• Evidence of Cosmic Evolution of the Stellar Initial Mass Function
• A Long-Wavelength View on Galaxy Evolution from Deep Surveys by the Infrared Space Observatory
• A Cluster of Black Holes at the Galactic Center
• A binary model for the UV-upturn of elliptical galaxies (MNRAS version)
• Chemodynamical history of the Galactic Bulge
• Stellar Contribution to the Galactic Bulge Microlensing Optical Depth
• Simulation of a Space-Based Microlensing Survey for Terrestrial Extra-Solar Planets
• The MACHO project: Microlensing Optical Depth towards the Galactic Bulge from Difference Image Analysis
• MOA-2009-BLG-387Lb: A massive planet orbiting an M dwarf
• Made-to-Measure models of the Galactic Box/Peanut bulge: stellar and total mass in the bulge region
• Masses and Orbital Constraints for the OGLE-2006-BLG-109Lb,c Jupiter/Saturn Analog Planetary System
• On the Mass-to-Light ratio and the Initial Mass Function in disc galaxies
• Measuring the Remnant Mass Function of the Galactic Bulge
• Systematic Analysis of 22 Microlensing Parallax Candidates
• Transiting extrasolar planetary candidates in the Galactic bulge
• Really Cool Stars and the Star Formation History at the Galactic Center
• Microlensing Constraints on the Frequency of Jupiter-Mass Companions: Analysis of Five Years of PLANET Photometry
• The evolution of early-type galaxies at z~1 from the K20 survey
• Stellar density profile and mass of the Milky Way Bulge from VVV data
• Integrated Spectroscopy of Bulge Globular Clusters and Fields. II. Implications for stellar population models and elliptical galaxies
• On the Similarity between Cluster and Galactic Stellar Initial Mass Functions
• Evolving to Type Ia Supernovae with Short Delay Times
• The progenitors of Type Ia supernovae with long delay times
• Formation & evolution of the Galactic bulge: constraints from stellar abundances
• Dense Stellar Populations: Initial Conditions
• POINT-AGAPE Pixel Lensing Survey of M31 : Evidence for a MACHO contribution to Galactic Halos
• On the Constancy of the Characteristic Mass of Young Stars
• On the distance of the globular cluster M4 (NGC 6121) using RR Lyrae stars: I. optical and near-infrared Period-Luminosity and Period-Wesenheit relations
• The Nuclear Cluster of the Milky Way: Total Mass and Luminosity (long version)
• The puzzlingly small CaII triplet absorption in elliptical galaxies
• Producing type Iax supernovae from a specific class of helium-ignited WD explosions?
• The gravitational wave signal from diverse populations of double white dwarf binaries in the Galaxy
• Galactic Globular Clusters as a test for Very Low-Mass stellar models
• The global mass functions of 35 Galactic globular clusters: I. Observational data and correlations with cluster parameters
• On the temporal evolution of the stellar mass function in Galactic clusters
• MOA-II Galactic Microlensing Constraints: The Inner Milky Way has a Low Dark Matter Fraction and a Near Maximal Disk
• Chemical evolution in a model for the joint formation of quasars and spheroids
• On a new Near-Infrared method to estimate the absolute ages of star clusters: NGC3201 as a first test case
• A parametric description of the 3D structure of the Galactic Bar/Bulge using the VVV survey
• Spectroscopic Survey of the Galaxy with Gaia II. The expected science yield from the Radial Velocity Spectrometer
• The infrared eye of the Wide-Field Camera 3 on the Hubble Space Telescope reveals multiple main sequences of very low-mass stars in NGC 2808
• Faint Stars in the Ursa Minor Dwarf Spheroidal Galaxy: Implications for the Low-Mass Stellar Initial Mass Function at High Redshift
• A Short Timescale Candidate Microlensing Event in the POINT-AGAPE Pixel Lensing Survey of M31
• Constraints on Planetary Companions in the Magnification A=256 Microlensing Event: OGLE-2003-BLG-423
• Stellar Ages through the Corners of the Boxy Bulge
• Ultra-Deep Hubble Space Telescope Imaging of the Small Magellanic Cloud: The Initial Mass Function of Stars with M <~ 1 Msun
• Limits on the Abundance of Galactic Planets From Five Years of Planet Observations
• Testing intermediate-age stellar evolution models with VLT photometry of LMC clusters. I. The data
• The WFC3 Galactic Bulge Treasury Program: Relative Ages of Bulge Stars of High and Low Metallicity
• The Wendelstein Calar Alto Pixellensing Project(WeCAPP): First MACHO Candidates
• The Mass and Radius of the Neutron Star in the Bulge Low-Mass X-ray Binary KS 1731-260
• Testing the universal stellar IMF on the metallicity distribution in the bulges of the Milky Way and M31
• The dynamical formation of LMXBs in dense stellar environments: globular clusters and the inner bulge of M31
• The 3D structure of the Galactic bulge
• Microlensing towards the SMC: a new analysis of OGLE and EROS results
• Microlensing constraints on the Galactic Bulge Initial Mass Function
• Gas Giants in Hot Water: Inhibiting Giant Planet Formation and Planet Habitability in Dense Star Clusters Through Cosmic Time
• Observation of Microlensing towards the Galactic Spiral Arms. EROS II 3 year survey
• Optical Depths and Timescale Distributions in Galactic Microlensing
• Search for Low-Mass Exoplanets by Gravitational Microlensing at High Magnification
• New insights on the Galactic Bulge Initial Mass Function
• Microlensing as a probe of the Galactic structure; 20 years of microlensing optical depth studies
• The Origin of the Stellar Mass Distribution and Multiplicity
• The Structure of HE 1104-1805 from Infrared to X-Ray
• Constraining Globular Cluster Age Uncertainties Using the IR Color-Magnitude Diagram
• Mapping the stellar age of the Milky Way bulge with the VVV. I. The method
• A Parametric Galactic Model toward the Galactic Bulge Based on Gaia and Microlensing Data
• Applications of Microlensing to Stellar Astrophysics
• A Comprehensive Bayesian Discrimination of the Simple Stellar Population Model, Star Formation History and Dust Attenuation Law in the Spectral Energy Distribution Modeling of Galaxies
• Probability of Detecting a Planetary Companion during a Microlensing Event
• The Initial Mass Function of the Inner Galaxy Measured From OGLE-III Microlensing Timescales
• The Angstrom Project: a microlensing survey of the structure and composition of the bulge of the Andromeda galaxy
• The M31 microlensing event WeCAPP-GL1/Point-AGAPE-S3: evidence for a MACHO component in the dark halo of M31?
• Lyman Break Galaxies and the Reionization of the Intergalactic Medium
• Microlensing Maps for the Milky Way Galaxy
• Microlensing by Stellar Black Holes Around Sgr A*
• The near-IR Ca II triplet - sigma relation for bulges of spiral galaxies
• A bottom-heavy initial mass function for the likely-accreted blue-halo stars of the Milky Way
• Microlensing Sensitivity to Earth-mass Planets in the Habitable Zone
• A new analysis of the MEGA M31 microlensing events
• Weighing the two stellar components of the Galactic Bulge
• The WFC3 Galactic Bulge Treasury Program: A First Look at Resolved Stellar Population Tools
• Microlensing toward crowded fields: Theory and applications to M31
• The Age of the Old Metal-Poor Globular Cluster NGC6397 Using WFC3/IR Photometry
• The absolute age of the globular cluster M15 using near-infrared adaptive optics images from PISCES/LBT
• The gravitational-wave signal generated by a galactic population of double neutron-star binaries
• HST observations of the metal rich globular clusters NGC6496 and NGC6352
• On the absolute age of the metal-rich globular M71 (NGC 6838): I. optical photometry
• Microlensing by Kuiper, Oort, and Free-Floating Planets
• Bayesian Approach for Determining Microlens System Properties with High-Angular-Resolution Follow-up Imaging
• The Galactic Bulge: A Review
• Bringing closure to microlensing mass measurement
• The Nature of Parallax Microlensing Events Towards the Galactic Bulge
• The Sagittarius dwarf galaxy as a microlensing target
• Photometric Monitoring of Open Clusters I. The Survey
• Impact of distance determinations on Galactic structure. II. Old tracers
• The Reduced Proper Motion selected halo: methods and description of the catalogue
• From Theory to Observations and viceversa: theoretical uncertainties and observational constraints
• The Milky Way rotation curve in Horava - Lifshitz theory
• Comparing Observed Stellar Kinematics and Surface Densities in a Low Latitude Bulge Field to Galactic Population Synthesis Models
• Cosmological History of Stars and Metals
• Stellar collisions in globular clusters: Constraints on the initial mass function of the first generation of stars
• Influence of the Galactic gravitational field on the positional accuracy of extragalactic sources
• Stellar photometry with Multi Conjugate Adaptive Optics
• Microlensing Optical Depth Revisited with Recent Star Counts
• Hot Subdwarfs from the Stable Roche Lobe Overflow Channel
• The Small Magellanic Cloud through the lens of the James Webb Space Telescope : binaries and mass function within the galaxy outskirts
• A deep HST view of the open cluster NGC2158: binaries, mass functions, and M-dwarf discontinuity
• Stellar Evolutionary Models: challenges from observations of stellar systems
• Color-Shift Measurement in Microlensing-Induced Stellar Variation from Future Space-Based Surveys