ALMACAL II: Extreme Star Formation Rate Densities in Dusty Starbursts Revealed by ALMA 20 mas Resolution Imaging

Journal Article · Fri Mar 10 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA5DA4· OSTI ID:22869209

Oteo, I.; Ivison, R. J. ^[1]; Zwaan, M. A.; Biggs, A. D. ^[2]

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1. Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
2. European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)

We present ultrahigh spatial resolution (∼20 mas or 150 pc) ALMA observations of the dust continuum at 920 μm and 1.2 mm in two submillimeter sources at z = 3.442, ALMACAL–1 (A–1: S{sub 870μm}=6.5±0.2 mJy) and ALMACAL–2 (A–2: S{sub 870μm}=4.4±0.2 mJy). About half of the star formation in each of these sources is dominated by a single compact clump (FWHM size of ∼350 pc). In A–1, two additional fainter clumps are found. The star formation rate (SFR) surface densities of all these clumps are extremely high, Σ{sub SFR}∼1200 to ∼3000 M{sub ⊙} yr{sup −1} kpc{sup −2}, the highest rates found in high-redshift galaxies. Given their geometry and identical redshifts, there is a possibility that A–1 and A–2 are the lensed images of a single background source that are gravitationally amplified by the blazar host. If this were the case, the effective radius of the dusty galaxy in the source plane would be R{sub eff}∼40 pc and the demagnified SFR surface density would be Σ{sub SFR} ∼ 10,000 M{sub ⊙} yr{sup −1} kpc{sup −2}, comparable with the eastern nucleus of Arp 220. Although we cannot rule out an AGN contribution, our results suggest that a significant percentage of the enormous far-IR luminosity in some dusty starbursts is extremely compact. The high Σ{sub SFR} in these sources could only be measured thanks to the ultrahigh-resolution ALMA observations used in this work, demonstrating that long-baseline observations are essential to study and interpret the properties of dusty starbursts in the early Universe.

• OSTI ID: 22869209
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 837; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
COSMIC DUST
DENSITY
GALAXIES
GRAVITATIONAL LENSES
INFRARED RADIATION
LUMINOSITY
MOLECULES
RED SHIFT
SPATIAL RESOLUTION
STARS
SURFACES
UNIVERSE