ALMA [NII] 205 micron Imaging Spectroscopy of the Interacting Galaxy System BRI 1202-0725 at Redshift 4.7

Abstract

We present the results from Atacama Large Millimeter/submillimeter Array (ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII]) and the underlying continuum of BRI 1202-0725, an interacting galaxy system at $z=$ 4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two Lyman-$\alpha$ emitters (LAEs), all within $\sim$25 kpc of the QSO. We detect the QSO and SMG in both [NII] and continuum. At the $\sim$$1"$ (or 6.6 kpc) resolution, both QSO and SMG are resolved in [NII], with the de-convolved major axes of $\sim$9 and $\sim$14 kpc, respectively. In contrast, their continuum emissions are much more compact and unresolved even at an enhanced resolution of $\sim$$0.7"$. The ratio of the [NII] flux to the existing CO (7$-$6) flux is used to constrain the dust temperature ($T_{\mathrm{dust}}$) for a more accurate determination of the FIR luminosity $L_{\mathrm{FIR}}$. Our best estimated $T_{\mathrm{dust}}$ equals $43(\pm 2)$ K for both galaxies (assuming an emissivity index $\beta =1.8$). The resulting $L_{\mathrm{CO}(7-6)}/L_{\mathrm{FIR}}$ ratios are statistically consistent with that of local luminous infrared galaxies, confirming that $L_{\mathrm{CO}(7-6)}$ traces the star formation (SF) rate (SFR) in these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of 5.1 $(6.9)\times 10^3{M}_{\odot }$ yr${}^{-1}$ ($\pm$ 30%) assuming Chabrier initial mass function, takes place within a diameter (at half maximum) of 1.3 (1.5) kpc, and shall consume the existing 5 $(5)\times 10^{11}{M}_{\odot }$ of molecular gas in 10 $(7)\times 10^7$ years.

4 pages, 1 table, 4 figures; accepted for publication in the ApJ Letters

References in corpus (7)

• A Detection of [CII] line emission in the z=4.7 QSO BR1202-0725
• ALMA Reveals Weak [NII] Emission in "Typical" Galaxies and Intense Starbursts at z=5-6
• The Global Star Formation Laws of Galaxies from a Radio Continuum Perspective
• Warm Molecular Gas in Luminous Infrared Galaxies
• BR1202-0725: An Extreme Multiple Merger at z = 4.7
• ALMA Observations of Warm Molecular Gas and Cold Dust in NGC 34
• Measuring Star-formation Rate and Far-Infrared Color in High-redshift Galaxies Using the CO (7-6) and [NII] 205 micron Lines

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• Dense and warm neutral gas in BR1202-0725 at z = 4.7 as traced by the [O I] 145 um line
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• Etching glass in the early Universe: Luminous HF and water emission in a QSO-SMG pair at z=4.7
• The [NII] 205 $\mu$m line emission from high-z SMGs and QSOs