Star formation in the outskirts of DDO 154: A top-light IMF in a nearly dormant disc

Abstract

We present optical photometry of Hubble Space Telescope (HST) ACS/WFC data of the resolved stellar populations in the outer disc of the dwarf irregular galaxy DDO 154. The photometry reveals that young main sequence stars are almost absent from the outermost HI disc. Instead, most are clustered near the main stellar component of the galaxy. We constrain the stellar initial mass function (IMF) by comparing the luminosity function of the main sequence stars to simulated stellar populations assuming a constant star formation rate over the dynamical timescale. The best-fitting IMF is deficient in high mass stars compared to a canonical Kroupa IMF, with a best-fit slope $\alpha =-2.45$ and upper mass limit $M_U=16M_{\odot }$. This top-light IMF is consistent with predictions of the Integrated Galaxy-wide IMF theory. Combining the HST images with HI data from The HI Nearby Galaxy Survey Treasury (THINGS) we determine the star formation law (SFL) in the outer disc. The fit has a power law exponent $N=2.92\pm 0.22$ and zero point $A=4.47\pm 0.65\times 10^{-7}{M}_{\odot }{\text{yr}}^{-1}{\text{kpc}}^{-2}$. This is depressed compared to the Kennicutt-Schmidt Star Formation Law, but consistent with weak star formation observed in diffuse HI environments. Extrapolating the SFL over the outer disc implies that there could be significant star formation occurring that is not detectable in H$\alpha$. Last, we determine the Toomre stability parameter $Q$ of the outer disc of DDO 154 using the THINGS HI rotation curve and velocity dispersion map. 72% of the HI in our field has $Q\le 4$ and this incorporates 96% of the observed MS stars. Hence 28% of the HI in the field is largely dormant.

arXiv comment14 pages, 15 figures, accepted for publication in MNRAS

References in corpus (128)

• The chemical composition of the Sun
• Galactic Stellar and Substellar Initial Mass Function
• On the variation of the Initial Mass Function
• The Global Schmidt Law in Star Forming Galaxies
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Embedded Clusters in Molecular Clouds
• The Star Formation Efficiency in Nearby Galaxies: Measuring Where Gas Forms Stars Effectively
• The Star Formation Law in Nearby Galaxies on Sub-Kpc Scales
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• THINGS: The HI Nearby Galaxy Survey
• SINGS: The SIRTF Nearby Galaxies Survey
• The Photometric Performance and Calibration of the HST Advanced Camera For Surveys
• WFPC2 Stellar Photometry with HSTphot
• A Universal Stellar Initial Mass Function? A Critical Look at Variations
• Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
• High-Resolution Rotation Curves and Galaxy Mass Models from THINGS
• The Formation of a Star Cluster: Predicting the Properties of Stars and Brown Dwarfs
• Molecular Gas and Star Formation in Nearby Disk Galaxies
• Galaxy And Mass Assembly: Stellar Mass Estimates
• Gas-to-Dust mass ratios in local galaxies over a 2 dex metallicity range
• A systematic variation of the stellar initial mass function in early-type galaxies
• Numerical Methods of Star Formation History Measurement and Applications to Seven Dwarf Spheroidals
• The ACS Nearby Galaxy Survey Treasury
• Comparison of H-alpha and UV Star Formation Rates in the Local Volume: Systematic Discrepancies for Dwarf Galaxies
• Updated Nearby Galaxy Catalog
• Star Formation Thresholds in Galactic Disks
• Starbursts and Star Clusters in the Ultraviolet
• The Stellar Initial Mass Function in Early-Type Galaxies From Absorption Line Spectroscopy. II. Results
• The Star Formation History of the Large Magellanic Cloud
• KINGFISH -- Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel: Survey Description and Image Atlas
• On the formation of massive stars
• On the fraction of star formation occurring in bound stellar clusters
• The Star Formation History of the Small Magellanic Cloud
• Regulation of Star Formation Rates in Multiphase Galactic Disks: a Thermal/Dynamical Equilibrium Model
• Extremely Inefficient Star Formation in the Outer Disks of Nearby Galaxies
• Forged in FIRE: cusps, cores, and baryons in low-mass dwarf galaxies
• A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local Universe
• The Panchromatic Hubble Andromeda Treasury
• The ACS Nearby Galaxy Survey Treasury VIII. The Global Star Formation Histories of 60 Dwarf Galaxies in the Local Volume
• The Type Ia Supernova Rate
• The Spatial Distribution of Star Formation in the Solar Neighbourhood: Do all stars form in clusters?
• The maximum stellar mass, star-cluster formation and composite stellar populations
• Spectral synthesis including massive binaries
• The Big Problems in Star Formation: the Star Formation Rate, Stellar Clustering, and the Initial Mass Function
• Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity
• Recent Star Formation in the Extreme Outer Disk of M83
• Evidence for a Non-Uniform Initial Mass Function in the Local Universe
• An excess of massive stars in the local 30 Doradus starburst
• (Star)bursts of FIRE: observational signatures of bursty star formation in galaxies
• Radial distribution of stars, gas and dust in SINGS galaxies. II. Derived dust properties
• The Extragalactic Distance Database: Color-Magnitude Diagrams
• Galaxy And Mass Assembly (GAMA): The star formation rate dependence of the stellar initial mass function
• A Correlation Between Surface Densities of Young Stellar Objects and Gas in Eight Nearby Molecular Clouds
• The relation between the most-massive star and its parental star cluster mass
• On the galaxy stellar mass function, the mass-metallicity relation, and the implied baryonic mass function
• The stellar mass-halo mass relation of isolated field dwarfs: a critical test of $\Lambda$CDM at the edge of galaxy formation
• The Stellar Initial Mass Function of Ultra-Faint Dwarf Galaxies: Evidence for IMF Variations with Galactic Environment
• The Variation of Integrated Star IMFs among Galaxies
• The Nature of Starbursts: I. The Star Formation Histories of Eighteen Nearby Starburst Dwarf Galaxies
• Radiation-Hydrodynamic Simulations of the Formation of Orion-Like Star Clusters II. The Initial Mass Function from Winds, Turbulence, and Radiation
• Discovery of an extended ultraviolet disk in the nearby galaxy NGC4625
• The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects
• The Star Formation Law in Molecule-Poor Galaxies
• The Nature of Starbursts : II. The Duration of Starbursts in Dwarf Galaxies
• IAC-Star: a Code for Synthetic Color-Magnitude Diagram Computation
• The evolution of CNO isotopes: a new window on cosmic star-formation history and the stellar IMF in the age of ALMA
• Evidence for a non-universal stellar initial mass function from the integrated properties of SDSS galaxies
• The Star Formation Law at Low Surface Density
• Variations in Stellar Clustering with Environment: Dispersed Star Formation and the Origin of Faint Fuzzies
• The Kinematics of the Scorpius-Centaurus OB Association from Gaia DR1
• Converting H$\alpha$ Luminosities into Star Formation Rates
• Color and stellar population gradients in galaxies. Correlation with mass
• The Panchromatic Hubble Andromeda Treasury XI: The Spatially-Resolved Recent Star Formation History of M31
• Star Formation in the Field and Clusters of NGC 5253
• Diverging UV and Halpha fluxes of star forming galaxies predicted by the IGIMF theory
• 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 Histories of Local Group Dwarf Galaxies III. Characterizing Quenching in Low-Mass Galaxies
• Comparing the Ancient Star Formation Histories of the Magellanic Clouds
• The optimally-sampled galaxy-wide stellar initial mass function - Observational tests and the publicly available GalIMF code
• Stellar Populations in Three Outer Fields of the LMC
• The supernova rate in local galaxy clusters
• Galaxy And Mass Assembly (GAMA): the Stellar Mass Budget by Galaxy Type
• Clustered star formation as a natural explanation of the Halpha cutoff in disc galaxies
• On the Origin of Stellar Masses
• Star formation in extremely faint dwarf galaxies
• The ACS Nearby Galaxy Survey Treasury I. The Star Formation History of the M81 Outer Disk
• Gas, Dust, and Young Stars in the Outer Disk of M 31
• Variability in the stellar initial mass function at low and high mass: 3-component IMF models
• The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxies
• The Rate of Type Ia Supernovae at High Redshift
• Ultra-Deep Hubble Space Telescope Imaging of the Small Magellanic Cloud: The Initial Mass Function of Stars with M <~ 1 Msun
• Evidence of a non universal stellar Initial Mass Function. Insights from HST optical imaging of 6 Ultra Faint Dwarf Milky Way Satellites
• The influence of multiple stars on the high-mass stellar initial mass function and age-dating of young massive star clusters
• The Stellar Populations of M33's Outer Regions III: Star Formation History
• The Star Formation History of the very metal poor BCD IZw18 from HST/ACS data
• The Stellar Populations of M33's Outer Regions IV: Inflow History and Chemical Evolution
• Resolved photometry of extragalactic young massive star clusters
• Is the Initial Mass Function of Low Surface Brightness Galaxies Dominated by Low Mass Stars?
• Spatially resolved variations of the IMF mass normalisation in early-type galaxies as probed by molecular gas kinematics
• The Recent Cluster Formation Histories of NGC 5253 and NGC 3077: Environmental Impact on Star Formation
• The Universal Initial Mass Function In The XUV Disk of M83
• The fundamental gas depletion and stellar-mass buildup times of star forming galaxies
• Stellar clusterings around "Isolated" Massive YSOs in the LMC
• Kinematic constraints on the stellar and dark matter content of spiral and S0 galaxies
• The Star Clusters of the Small Magellanic Cloud: Structural Parameters
• Do all stars in the solar neighbourhood form in clusters? A cautionary note on the use of the distribution of surface densities
• The Contributions of Interactive Binary Stars to Double Main Sequence Turn-Offs and Dual Red Clump of Intermediate-Age Star Clusters
• Stellar populations and Star Formation History of the Metal-Poor Dwarf Galaxy DDO 68
• Mass-loss and expansion of ultra compact dwarf galaxies through gas expulsion and stellar evolution for top-heavy stellar initial mass functions
• The Nature of Starbursts: III. The Spatial Distribution of Star Formation
• The Hubble Deep Field and the Disappearing Dwarf Galaxies
• Combined Effects of Binaries and Stellar Rotation on the Color-Magnitude Diagrams of Intermediate-Age Star Clusters
• Gaseous infall triggering starbursts in simulated dwarf galaxies
• Binary populations in Milky Way satellite galaxies: constraints from multi-epoch data in the Carina, Fornax, Sculptor and Sextans dwarf spheroidal galaxies
• Star Formation History in two fields of the Small Magellanic Cloud Bar
• The Local Volume HI Survey: star formation properties
• The Initial Mass Function of Early-type Galaxies: no correlation with [Mg/Fe]
• Towards a unified model of stellar rotation
• The ACS Nearby Galaxy Survey Treasury XI. The Remarkably Undisturbed NGC 2403 Disk
• The IMF as a function of supersonic turbulence
• Star formation in grand-design, spiral galaxies. Young, massive clusters in the near-infrared
• Radial measurements of IMF-sensitive absorption features in two massive ETGs
• The stellar initial mass function at 0.9<z<1.5
• CO map and steep Kennicutt-Schmidt relation in the extended UV disk of M63
• The initial mass function and star formation law in the outer disc of NGC 2915
• Disk Stability and Neutral Hydrogen as a Tracer of Dark Matter
• Formation and evolution of blue compact dwarfs: The origin of their steep rotation curves
• Isolating the young stellar population in the outer disk of NGC 300

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• A new formulation of the external field effect in MOND and numerical simulations of ultra-diffuse dwarf galaxies $-$ application to NGC 1052-DF2 and NGC 1052-DF4
• Chemical evolution of ultra-faint dwarf galaxies in the self-consistently calculated IGIMF theory
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• Was the Milky Way a chain galaxy? Using the IGIMF theory to constrain the thin-disk star formation history and mass
• Constraints on the star formation histories of galaxies in the Local Cosmological Volume
• The effect of the environment-dependent stellar initial mass function on the photometric properties of star-forming galaxies
• The radial distribution of supernovae compared to star formation tracers
• Wolf-Rayet galaxies in SDSS-IV MaNGA. II. Metallicity dependence of the high-mass slope of the stellar initial mass function
• The Impact of Early Massive Galaxy Formation on the Cosmic Microwave Background
• The Initial Mass Function in the Extended Ultraviolet Disk of M83
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• Stellar population synthesis models with a physically varying IMF
• Resolved HI in two ultra-diffuse galaxies from contrasting non-cluster environments
• Near-identical star formation rate densities from H$\alpha$ and FUV at redshift zero
• DIISC-II: Unveiling the Connections between Star Formation and ISM in the Extended Ultraviolet Disk of NGC 3344
• WALLABY Pilot Survey: Hydra Cluster Galaxies UV and HI morphometrics
• IMF-induced intrinsic uncertainties on measuring galaxy distances based on the number of giant stars: the case of the ultra-diffuse galaxy NGC 1052-DF2
• The systematically varying stellar IMF
• Metal-THINGS: gas metallicity gradients in nearby galaxies
• The chemical DNA of the Magellanic Clouds VI. Origin and evolution of neutron-capture elements in the SMC
• Star Formation Beyond the Optical Disk : The Low-Density Outskirts of NGC2090