The low-mass initial mass function of the field population in the Large Magellanic Cloud with Hubble Space Telescope WFPC2 Observations

Abstract

We present V- and I-equivalent HST/WFPC2 stellar photometry of an area in the Large Magellanic Cloud (LMC), located on the western edge of the bar of the galaxy, which accounts for the general background field of its inner disk. The WFPC2 observations reach magnitudes as faint as V=25 mag, and the large sample of more than 80,000 stars allows us to determine in detail the Present-Day Mass Function (PDMF) of the detected main-sequence stars, which is identical to the Initial Mass Function (IMF) for masses M <~ 1 M_solar. The low-mass main-sequence mass function of the LMC field is found not to have a uniform slope throughout the observed mass range, i.e. the slope does not follow a single power law. This slope changes at about 1 M_solar to become more shallow for stars with smaller masses down to the lowest observed mass of ~ 0.7 M_solar, giving clear indications of flattening for even smaller masses. We verified statistically that for stars with M <~ 1 M_solar the IMF has a slope Gamma around -2, with an indicative slope Gamma =~ -1.4 for 0.7 <~ M/M_solar <~ 0.9, while for more massive stars the main-sequence mass function becomes much steeper with Gamma =~ -5. The main-sequence luminosity function (LF) of the observed field is in very good agreement with the Galactic LF as it was previously found. Taking into account several assumptions concerning evolutionary effects, which should have changed through time the stellar content of the observed field, we reconstruct qualitatively its IMF for the whole observed mass range (0.7 <~ M/M_solar <~ 2.3) and we find that the number of observed evolved stars is not large enough to have affected significantly the form of the IMF, which thus is found almost identical to the observed PDMF.

16 pages in ApJ Journal format, 7 figures, Submitted to ApJ. The size of the postscript files of the images has been reduced because of disk space limitations

References in corpus (61)

• Galactic Stellar and Substellar Initial Mass Function
• Evolutionary tracks and isochrones for low- and intermediate-mass stars: from 0.15 to 7 M_sun, and from Z=0.0004 to 0.03
• The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems
• Theoretical isochrones in several photometric systems I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets
• The Stellar IMF from Turbulent Fragmentation
• The Formation of Massive Stars from Turbulent Cores
• WFPC2 Stellar Photometry with HSTphot
• The Formation of a Star Cluster: Predicting the Properties of Stars and Brown Dwarfs
• The formation of massive black holes through collision runaway in dense young star clusters
• A Census of the Young Cluster IC 348
• The Formation of Brown Dwarfs as Ejected Stellar Embryos
• On the Formation of Massive Stars
• Galactic-Field IMFs of Massive Stars
• The Formation of a Bound Star Cluster: From the Orion Nebula Cluster to the Pleiades
• On the formation of massive stars
• The hierarchical formation of a stellar cluster
• Massive star formation: Nurture, not nature
• The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit
• The Formation Mechanism of Brown Dwarfs
• Massive Stars: Their Environment and Formation
• A UBVR CCD Survey of the Magellanic Clouds
• Constraints on the Stellar/Sub-stellar Mass Function in the Inner Orion Nebula Cluster
• The Charge Transfer Efficiency and Calibration of WFPC2
• The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Young Clusters
• The Formation of Stellar Clusters: Mass Spectra from Turbulent Molecular Cloud Fragmentation
• Accretion in stellar clusters and the IMF
• L Dwarfs and the Substellar Mass Function
• Effects of the Equation of State on the Formation of Star Clusters
• The Formation of Stellar Clusters in Turbulent Molecular Clouds: Effects of the Equation of State
• Galaxy number counts - V. Ultra-deep counts: The Herschel and Hubble Deep Fields
• The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Taurus
• Observations and Implications of the Star Formation History of the LMC
• A Study of the Luminosity and Mass Functions of the Young IC 348 Cluster using FLAMINGOS Wide-Field Near-Infrared Images
• Mass segregation in young compact star clusters in the Large Magellanic Cloud: II. Mass Functions
• Statistics of N-Body Simulations. III. Unequal Masses
• Analysis of Clumps in Molecular Cloud Models: Mass Spectrum, Shapes, Alignment and Rotation
• On the origin of brown dwarfs and free-floating planetary mass objects
• The initial stellar mass function from random sampling in hierarchical clouds II: statistical fluctuations and a mass dependence for starbirth positions and times
• The Star Formation History of the Large Magellanic Cloud
• Mass Segregation in Young Magellanic Clouds Star Clusters: Four Clusters observed with HST
• Mass Function of the Arches Cluster from Gemini Adaptive Optics Data
• Stellar Populations in Three Outer Fields of the LMC
• From the Top to the Bottom of the Main Sequence: A Complete Mass Function of the Young Open Cluster M35
• A Comparison of Deep HST Luminosity Functions of Four Globular Clusters
• Variability in the stellar initial mass function at low and high mass: 3-component IMF models
• The dependence of the sub-stellar IMF on the initial conditions for star formation
• The Role of Tidal Interactions in Star Formation
• On the Power-Law Tail in the Mass Function of Protostellar Condensations and Stars
• Mass segregation in rich clusters in the Large Magellanic Cloud - III. Implications for the initial mass function
• Hubble Space Telescope Photometry of Hodge 301: An "Old" Star Cluster in 30 Doradus
• A New Approach to Determine the Initial Mass Function in the Solar Neighborhood
• The Theoretical Mass--Magnitude Relation of Low-Mass Stars and its Metallicity Dependence
• The Effect of Star Formation History on the Inferred Initial Stellar Mass Function
• HST Observations of the Field Star Population in the Large Magellanic Cloud
• Population and dynamical state of the eta Chamaeleontis sparse young open cluster
• Constraints on the star formation history of the Large Magellanic Cloud
• Ultraviolet and Optical Observations of OB Associations and Field Stars in the Southwest Region of the Large Magellanic Cloud
• Variability in the stellar initial mass function at high mass: coalescence models for starburst clusters
• A Comprehensive Look at LH72 in the Context of Supergiant Shell LMC-4
• The Initial Mass Function toward the low-mass end in the Large Magellanic Cloud with HST/WFPC2 Observations
• Discovery of a luminous white dwarf in a young star cluster in the Large Magellanic Cloud

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