A deep search for large complex organic species toward IRAS16293-2422 B at 3 mm with ALMA

Complex organic molecules (COMs) have been detected ubiquitously inprotostellar systems. However, at shorter wavelengths (~0.8mm) it is moredifficult to detect larger molecules than at longer wavelengths (~3mm) becauseof the increase of millimeter dust opacity, line confusion, and unfavorablepartition function. We aim to search for large molecules (>8 atoms) in the ALMABand 3 spectrum of IRAS 16293-2422 B. We search for more than 70 molecules andidentify as many lines as possible in the spectrum. The spectral settings wereset to specifically target three-carbon species such as propanol and glycerol.We identify lines of 31 molecules including many oxygen-bearing COMs such asCH3OH and c-C2H4O and a few nitrogen- and sulfur-bearing ones such as HOCH2CNand CH3SH. The largest detected molecules are gGg-(CH2OH)2 and CH3COCH3. We donot detect glycerol or propanol but provide upper limits for them which are inline with previous laboratory and observational studies. The line density inBand 3 is only ~2.5 times lower in frequency space than in Band 7. From thedetected lines in Band 3 at a $\gtrsim 6\sigma$ level, ~25-30% of them couldnot be identified indicating the need for more laboratory data of rotationalspectra. We find similar column densities and column density ratios of COMs(within a factor ~2) between Band 3 and Band 7. The effect of dust opticaldepth for IRAS 16293-2422 B at an off-source location on column densities andcolumn density ratios is minimal. Moreover, for warm protostars, longwavelength spectra are not only crowded, but also take longer integration timesto reach the same sensitivity limit. The 3mm search has not yet resulted indetection of larger and more complex molecules in warm sources. A full deepALMA Band 2-3 (i.e., 3-4 mm) survey is needed to assess whether low frequencydata have the potential to reveal more complex molecules in warm sources.