A pilot method to determine the high mass end of the Stellar Initial Mass Function in galaxies using UVIT, H$\alpha$-MUSE observations and applied to NGC628

Abstract

We present a pilot method to estimate the high-mass initial mass function (IMF) across the arm, interarm, and spur regions in galaxies and apply it to NGC 628. We extracted star-forming complexes (SFCs) from H$\alpha$ VLT/MUSE and UVIT (FUV and NUV) observations of NGC 628 and used ALMA observations to define the molecular gas distribution. We find that the extinction-corrected H$\alpha$ and FUV luminosities correlate well. Using the fact that O stars have a shorter lifetime (10${}^7$ yr) compared to B stars (10${}^8$ yr), we estimated the approximate number of O stars from H$\alpha$ emission, and the number of B0 ($M_{\ast }>10M_{\odot }$), and B1 ($10M_{\odot }\ge M_{\ast }\ge 3M_{\odot }$) stars using FUV, NUV observations. We derived the IMF index ($\alpha$) for different regions using O to B0 (${\alpha }_1$) and B0 to B1 (${\alpha }_2$) stellar ratios. Our findings indicate that if we assume H$\alpha$ arises only from O8-type stars, the resulting ${\alpha }_1$ value is consistent with the canonical IMF index. It steepens when we assume O stars with masses up to 100 $M_{\odot }$ with mean ${\alpha }_1=3.16\pm 0.62$. However, the ${\alpha }_2$ does not change for large variations in the O-star population, and the mean $\alpha =2.64\pm 0.14$. When we include only blue SFCs ($FUV-NUV\le 0.3$), mean ${\alpha }_2$ is $2.43\pm 0.06$. The IMF variation for SFCs in arms and spurs is insignificant. We also find that ${\alpha }_2$ correlates with different properties of the SFCs, the most prominent being the extinction-corrected UV color (FUV-NUV).

Accepted in ApJ

References in corpus (20)

• Array Programming with NumPy
• UV Star Formation Rates in the Local Universe
• VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
• A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local Universe
• A z=0 Multi-wavelength Galaxy Synthesis I: A WISE and GALEX Atlas of Local Galaxies
• Legacy ExtraGalactic UV Survey (LEGUS) with The Hubble Space Telescope. I. Survey Description
• Distances to PHANGS Galaxies: New Tip of the Red Giant Branch Measurements and Adopted Distances
• PHANGS CO kinematics: disk orientations and rotation curves at 150 pc resolution
• On The Extended Knotted Disks of Galaxies
• The Stellar Mass Spectrum in Warm and Dusty Gas: Deviations from Salpeter in the Galactic Centre and in Circum-Nuclear Starburst Regions
• Sizes and Shapes of Young Star Cluster Light Profiles in M83
• Hierarchical Star Formation in Nearby LEGUS Galaxies
• Testing the universality of the IMF with Bayesian statistics: young clusters
• Resolving the core of R136 in the optical
• The Initial Mass Function in the Extended Ultraviolet Disk of M83
• Understanding the secular evolution of NGC 628 using UVIT
• A Comparative Study of Star Forming Dwarf Galaxies using the UVIT
• A Comparison of the UV and HI Properties of the Extended UV (XUV) Disk Galaxies NGC 2541, NGC 5832 and ESO406-042
• The recent star formation history of NGC 628 on resolved scales
• Understanding the Stellar Initial Mass Function