Serendipitous ALMA Detection of a Distant CO-emitting X-Ray Bright Galaxy
Abstract
We report the detection of a distant star-forming galaxy, ALMA J010748.3-173028, which is identified by a 13σ emission line at 99.75 GHz (SΔv = 3.1 Jy km s-1), behind the nearby merging galaxies VV114 using the Atacama Large Millimeter/submillimeter Array (ALMA) Band 3. We also find an 880 μm counterpart with ALMA Band 7 (S 880μm = 11.2 mJy). A careful comparison of the intensities of the line and the continuum suggests that the line is a redshifted 12CO transition. A photometric redshift analysis using the infrared to radio data favors a CO redshift of z = 2.467, although z = 3.622 is acceptable. We also find a hard X-ray counterpart, suggesting the presence of a luminous (L X ~ 1044 erg s-1) active galactic nucleus obscured by a large hydrogen column (N H ~ 2 × 1023 cm-2 if z = 2.47). A cosmological simulation shows that the chance detection rate of a CO-emitting galaxy at z > 1 with >=1 Jy km s-1 is ~10-3 per single ALMA field of view and 7.5 GHz bandwidth at 99.75 GHz. This demonstrates that ALMA has sufficient sensitivity to find an emission-line galaxy such as ALMA J010748.3-173028 even by chance, although the likelihood of stumbling across such a source is not high.
- Publication:
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The Astrophysical Journal
- Pub Date:
- February 2014
- DOI:
- 10.1088/2041-8205/781/2/L39
- Bibcode:
- 2014ApJ...781L..39T
- Keywords:
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- galaxies: formation;
- galaxies: starburst;
- quasars: general;
- submillimeter: galaxies;
- X-rays: galaxies