The Volumetric Star Formation Law in the Almost Edge-on Galaxy NGC 4302 Revealed by ALMA

Abstract

We observe the almost edge-on (i $\sim$ 90 degrees) galaxy NGC 4302 using ALMA (CO) and VLA (H I) to measure the gas disk thickness for investigating the volumetric star formation law (SFL). The recent star formation rate (SFR) is estimated based on a linear combination of IR 24 micron and H$\alpha$ emissions. The measured scale heights of CO and H I increase significantly with radius. Using the scale heights along with the vertically integrated surface densities, we derive the mid-plane volume densities of the gas (${\rho }_{\mathrm{HI}}$, ${\rho }_{{\mathrm{H}}_2}$, and ${\rho }_{\mathrm{gas}}$ = ${\rho }_{\mathrm{HI}}$+${\rho }_{{\mathrm{H}}_2}$) and the SFR (${\rho }_{\mathrm{SFR}}$) and compare the volumetric SFL (${\rho }_{\mathrm{SFR}}\propto {\rho }_{\mathrm{gas}}^n$) with the vertically integrated SFL (${\Sigma }_{\mathrm{SFR}}\propto {\Sigma }_{\mathrm{gas}}^N$). We find tight power-law correlations between the SFR and the gas (H I, H${}_2$, and the total gas) in both volume and surface densities. The power-law indices of the total gas and H I for the volumetric SFL are noticeably smaller than the indices for the vertically integrated SFL while the H${}_2$ indices for both cases are similar to each other. In terms of the star formation efficiency (SFE), we find that the molecular and total gas SFEs are roughly constant, while the atomic SFE is clearly decreasing with radius in both cases.

9 pages, 5 figures, Accepted for publication in ApJ

References in corpus (10)

• HyperLEDA. III. The catalogue of extragalactic distances
• The Role of Pressure in GMC Formation II: The H_2 - Pressure Relation
• The Arecibo Legacy Fast ALFA Survey: III. HI Source Catalog of the Northern Virgo Cluster Region
• The Interstellar Medium and Star Formation in Edge-On Galaxies. II. NGC 4157, 4565, and 5907
• Distribution and kinematics of atomic and molecular gas inside the Solar circle
• The volumetric star formation law for nearby galaxies -- Extension to dwarf galaxies and low-density regions
• Investigating Disk-Halo Flows and Accretion: A Kinematic and Morphological Analysis of Extraplanar HI in NGC 3044 and NGC 4302
• Star Formation and Gas Accretion in Nearby Galaxies
• Molecular Gas Distribution in Barred and Non-Barred Galaxies along the Hubble Sequence
• Volumetric Star Formation Prescriptions in Vertically Resolved Edge-on Galaxies

Cited by in corpus (1)

• On volume density and star formation in nearby molecular clouds