Science Goals

Our program addresses several key science questions, which are outlined briefly below.

Dust in "typical" galaxies at z~2

The UV slope can provide an accurate estimate of the dust extinction in the local Universe (Calzetti et al. 2000); however, this extinction correction is uncertain at high redshift where the dust is observed to have different characteristics (e.g. Pope et al. 2008; Casey et al. 2014) and is much more widely distributed across the galaxy (e.g. Ivison et al. 2011). We require direct observations of the dust emission in typical star-forming galaxies at high redshift in order to complete the census of dust-obscured activity in our Universe.

At z < 4, the mm flux is sensitive to the large dust grains that dominate the dust mass and is a proxy for ISM mass (e.g. Eales et al. 2012; Scoville et al. 2014). Using this technique, Scoville et al. (2014) found a rapid increase in the mm-estimated ISM mass with redshift (for a stellar mass-selected sample); this result is in agreement with results from high redshift CO observations and shows how powerful and inexpensive the mm ISM mass technique is. We will use mm detections of the intrinsically low luminosity galaxies in this redshift range to estimate the ISM mass, and when combined with the HST-derived stellar masses and unobscured SFRs, we will provide a complete census of star formation in these galaxies.

Infrared luminosity of the faintest sources detectable with Herschel and LMT surveys down to the confusion limit. LIRG and ULIRG regimes are light and dark shaded regions, respectively. Click on the image to see a full-size version.

Constraints on dust emission at z > 4

At z > 4, the mm regime shifts to the peak of the IR dust distribution providing a good estimate of the total IR luminosity and the dust-obscured SFR. The ultra-faint mm counts at the highest redshifts are essentially unknown and so our observations will provide the first constraints on dust activity in the early Universe. Studies of the highest redshift galaxies detected in the HST Frontier Fields data rely on the UV slope to infer the dust obscuration and calculate the total SFR. The IRX-β relationship (LIR/LUV as a function of UV slope) is commonly used to relate the UV slope to the dust-obscured star formation rate, and deviations from this relationship can be linked to the geometry of dust obscuration.

Recently, Casey et al. (2014) found a deviation from the standard IRX-β relationship for IR-selected galaxies with high IR luminosities – but this has not been tested for the lower luminosity galaxies that dominate the star formation. With this program, we will test this relationship between the UV slope and dust-obscured SFR and put constraints on the nature of dust obscuration in high redshift galaxies.

Activity in intermediate-redshift cluster galaxies

Our millimeter images will also put constraints on the dust-obscured star formation activity in cluster galaxies at intermediate redshifts. More details to come.

Sunyaev-Zel'dovich effect

Our program will be able to detect the increment in the thermal SZ signal at 1.1mm with AzTEC for the FF clusters. More details to come.

Improved angular resolution

In addition to the aforementioned benefits of enhanced infrared luminosity sensitivity, our program provides crucial measurements of ISM mass and dust-obscured star formation activity at a resolution (8 arcsec) similar to MIPS [24]. Therefore, the galaxies we detect can be matched in a very straightforward way to shorter-wavelength catalogues of the Frontier Fields. The figure on the right demonstrates our improvement in angular resolution with AzTEC on the 32-m LMT compared to Herschel as well as AzTEC on the ASTE telescope.

A lensed sub-millimeter galaxy (SMG) in the background of the cluster RXJ1347, imaged in the IR/sub-mm/mm bands from Spitzer, Herschel, and with AzTEC on ASTE (10-m telescope, with beam FWHM of 30 arcsec) and AzTEC on the 32-m LMT (beam FWHM of 8 arcsec). Click on the image to see a full-size version.

References: