%0 Generic %1 oteo2016almacal %A Oteo, I. %A Zwaan, M. A. %A Ivison, R. J. %A Smail, I. %A Biggs, A. D. %D 2016 %K alma compact forming galaxies high resolution star %T ALMACAL II: Extreme star-formation-rate densities in a pair of dusty starbursts at $z = 3.442$ revealed by ALMA 20-milliarcsec resolution imaging %U http://arxiv.org/abs/1607.06464 %X We present ALMA ultra-high-spatial resolution ($20 \, mas$) observations of dust continuum at $920 \, m$ and $1.2 \, mm$ in a pair of submm galaxies (SMGs) at $z = 3.442$, ALMACAL-1 (A-1: $S_870 \mu m = 6.5 0.2 \, mJy$) and ALMACAL-2 (A-2: $S_870 m = 4.4 0.2 \, mJy$). The spectroscopic redshifts of A-1 and A-2 have been confirmed via serendipitous detection of up to nine emission lines. Our ultra-high-spatial resolution data reveal that about half of the star formation in each of these starbursts is dominated by a single compact clump (FWHM size of $350 \, pc$). This structure is confirmed by independent datasets at $920 \, m$ and $1.2 \, mm$. The star-formation rate (SFR) surface densities of all these clumps are extremely high, $\Sigma_SFR 1200$ to $3000 \, M_\, yr^-1 \, kpc^-2$, the highest found in high-redshift galaxies. There is a small probability that A-1 and A-2 are the lensed components of a background source gravitationally amplified by the blazar host. If this was the case, the effective radius of the source would be $R_eff 40 \, pc$, and the de-magnified SFR surface density would be $\Sigma_SFR 10000 \, M_\, \rm yr^-1 \, kpc^-2$, comparable with the eastern nucleus of Arp 220. Despite being unable to rule out an AGN contribution, our results suggest that a significant percentage of the enormous far-IR luminosity in some dusty starbursts is concentrated in very small star-forming regions. The high $\Sigma_SFR$ in our pair of SMGs could only be measured thanks to the ultra-high-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.

@misc{oteo2016almacal, abstract = {We present ALMA ultra-high-spatial resolution ($\sim 20 \, {\rm mas}$) observations of dust continuum at $920 \, {\rm \mu m}$ and $1.2 \, {\rm mm}$ in a pair of submm galaxies (SMGs) at $z = 3.442$, ALMACAL-1 (A-1: $S_{\rm 870 \mu m} = 6.5 \pm 0.2 \, {\rm mJy}$) and ALMACAL-2 (A-2: $S_{\rm 870 \mu m} = 4.4 \pm 0.2 \, {\rm mJy}$). The spectroscopic redshifts of A-1 and A-2 have been confirmed via serendipitous detection of up to nine emission lines. Our ultra-high-spatial resolution data reveal that about half of the star formation in each of these starbursts is dominated by a single compact clump (FWHM size of $\sim 350 \, {\rm pc}$). This structure is confirmed by independent datasets at $920 \, {\rm \mu m}$ and $1.2 \, {\rm mm}$. The star-formation rate (SFR) surface densities of all these clumps are extremely high, $\Sigma_{\rm SFR} \sim 1200$ to $\sim 3000 \, {M_\odot \, {\rm yr}^{-1} \, {\rm kpc}^{-2}}$, the highest found in high-redshift galaxies. There is a small probability that A-1 and A-2 are the lensed components of a background source gravitationally amplified by the blazar host. If this was the case, the effective radius of the source would be $R_{\rm eff} \sim 40 \, {\rm pc}$, and the de-magnified SFR surface density would be $\Sigma_{\rm SFR} \sim 10000 \, {M_\odot \, {\rm yr}^{-1} \, {\rm kpc}^{-2}}$, comparable with the eastern nucleus of Arp 220. Despite being unable to rule out an AGN contribution, our results suggest that a significant percentage of the enormous far-IR luminosity in some dusty starbursts is concentrated in very small star-forming regions. The high $\Sigma_{\rm SFR}$ in our pair of SMGs could only be measured thanks to the ultra-high-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.}, added-at = {2016-07-25T10:18:16.000+0200}, author = {Oteo, I. and Zwaan, M. A. and Ivison, R. J. and Smail, I. and Biggs, A. D.}, biburl = {https://www.bibsonomy.org/bibtex/2ff3c4f8f2ccf22f882c642a9414c87f4/miki}, description = {[1607.06464] ALMACAL II: Extreme star-formation-rate densities in a pair of dusty starbursts at $z = 3.442$ revealed by ALMA 20-milliarcsec resolution imaging}, interhash = {900d7b4bee67a05fc2a0519551f011b3}, intrahash = {ff3c4f8f2ccf22f882c642a9414c87f4}, keywords = {alma compact forming galaxies high resolution star}, note = {cite arxiv:1607.06464Comment: Submitted to ApJ. Comments are welcome}, timestamp = {2016-07-25T10:18:16.000+0200}, title = {ALMACAL II: Extreme star-formation-rate densities in a pair of dusty starbursts at $z = 3.442$ revealed by ALMA 20-milliarcsec resolution imaging}, url = {http://arxiv.org/abs/1607.06464}, year = 2016 }