Early Science with the Large Millimeter Telescope: Dust constraints in a
  z~9.6 galaxy
  Recent observations with the GISMO (Goddard-IRAM Superconducting 2 Millimeter
Observer) 2 mm camera revealed a detection 8 arcsec away from the lensed galaxy
MACS1149-JD1 at z=9.6. Within the 17.5 arcsec FWHM GISMO beam, this detection
is consistent with the position of the high-redshift galaxy and therefore, if
confirmed, this object could be claimed to be the youngest galaxy producing
significant quantities of dust. We present higher resolution (8.5 arcsec)
observations of this system taken with the AzTEC 1.1 mm camera mounted on the
Large Millimeter Telescope Alfonso Serrano. Dust continuum emission at the
position of MACS1149-JD1 is not detected with an r.m.s. of 0.17 mJy/beam.
However, we find a detection ~ 11 arcsec away from MACS1149-JD1, still within
the GISMO beam which is consistent with an association to the GISMO source.
Combining the AzTEC and GISMO photometry, together with Herschel ancillary
data, we derive a z_phot= 0.7-1.6 for the dusty galaxy. We conclude therefore
that the GISMO and AzTEC detections are not associated with MACS1149-JD1. From
the non-detection of MACS1149-JD1 we derive the following (3 \sigma) upper
limits corrected for gravitational lensing magnification and for cosmic
microwave background effects: dust mass < 1.6 x 10^7 M_sun, IR luminosity < 8 x
10^10 L_sun, star formation rate < 14 M_sun/yr, and UV attenuation < 2.7 mag.
These limits are comparable to those derived for other high-redshift galaxies
from deep Atacama Large Millimeter/submillimeter Array (ALMA) observations.
