Evidence for a Dusty Dark Dwarf Galaxy in the Quadruple Lens MG 0414+0534

Abstract

We report the 4 σ detection of a faint object with a flux of ∼ 0.3 mJy, in the vicinity of the quadruply lensed QSO MG 0414+0534 using the Atacama Large Millimeter/submillimeter array (ALMA) Band 7. The object is most probably a dusty dark dwarf galaxy, which has not been detected in either the optical, near-infrared (NIR) or radio (cm) bands. An anomaly in the flux ratio of the lensed images observed in Band 7 and the mid-infrared (MIR) band and the reddening of the QSO light color can be simultaneously explained if we consider the object as a lensing substructure with an ellipticity ∼ 0.7 at a redshift of 0.5 z 1. Using the best-fit lens models with three lenses, we find that the dark matter plus baryon mass associated with the object is ∼ 10 9 M ⊙ , the dust mass is ∼ 10 7 M ⊙ and the linear size is 5 kpc. Thus our findings suggest that the object is a dusty dark dwarf galaxy. A substantial portion of faint submillimeter galaxies (SMGs) in the universe may be attributed to such dark objects.

A flux-ratio anomaly in the CO spectral line emission from gravitationally lensed quasar MG J0414+0534

“…A possible detection of mm-continuum emission from this optically dark sub-halo (object Y, located 0.6 arcsec East of image A2) was recently reported by Inoue et al (2017) from deep Atacama Large (sub-)Millimetre Array (ALMA) observations. If genuine, this would confirm that the flux-ratio anomaly between the two merging images is due to a single low mass sub-halo, as predicted from cold dark matter models.…”

“…These artefacts, including object Y, do not remain in the data after subsequent steps of self-calibration. The rms noise in our naturally-weighted image, after correcting for the residual antenna-based phase errors is 19 µJy beam −1 , in comparison to the 65 µJy beam −1 from the analysis by Inoue et al (2017). To test that we did not bias the result with our choice of model during self-calibration, we also used an initial model that included object Y (as described in Section 2).…”

Through a lens darkly: magnified views of massive galaxy formation

“…The total ux-density is S 340 GHz = 24.3 ± 1.2 mJy, of which about 50 percent is contained in the compact images. Contrary to the ndings of Inoue et al (2017), we do not detect a source near image A2 (object Y). We do nd a 4σ surface brightness peak at this position in the pipelinereduced data before self-calibration, in addition to a number of higher signi cance artefacts that are caused by residual phase errors; given that the noise is correlated in the sky-plane for interferometric data, the requirements for blind detections in the radio are typically > 6.5σ.…”

“…A possible detection of mm-continuum emission from this optically dark sub-halo (object Y, located 0.6 arcsec East of image A2) was recently reported by Inoue et al (2017) from deep Atacama Large (sub-)Millimetre Array (ALMA) observations. If genuine, this would con rm that the ux ratio anomaly between the two merging images is due to a single low mass sub-halo, as predicted from cold dark matter models.…”

“…These artefacts, including object Y, do not remain in the data after subsequent steps of self-calibration. The rms noise in our naturally-weighted image, after correcting for the residual antenna-based phase errors is 19 µJy beam −1 , in comparison to the 65 µJy beam −1 from the analysis by Inoue et al (2017). To test that we did not bias the result with our choice of model during self-calibration, we also used an initial model that included object Y (as described in Section 5.2).…”