Tien-Hao Hsieh (ASIAA), Nadia Murillo (RIKEN), Arnaud Belloche (MPIfR), Naomi Hirano (ASIAA), Catherine Walsh (University of Leeds), Ewine F. van Dishoeck (Leiden), Jes K. Jørgensen (Niels Bohr Institute), Shih-Ping Lai (NTHU)
We present our ALMA survey in N2H+ and HCO+ toward 39 Class 0 and Class I sources in the Perseus molecular cloud. The unbiased survey with the large sample is used to reveal the evolution of episodic accretion from the Class 0 to Class I stage in a statistical way. N2H+ and HCO+ are destroyed via gas-phase reactions with CO and H2O, respectively, and are thus used to trace the CO and H2O snowline locations. If the snowline location is at a much larger radius than that expected from the current luminosity, then a past accretion burst has likely occurred that has shifted the snowline outward. Since H2O and CO have different freeze-out times, i.e. 1,000 yr for H2O and 10,000 yr for CO, this difference allows us to estimate the time from the previous burst. We identify 8, 16, and 1 sources have experienced an accretion burst in the past <1000 yr, 1000−10,000 yr, and >10,000 yr, respectively. Statistically, we estimate the interval of ∼2400 yr in Class 0 sources and ∼8,000 yr in Class I sources. This result suggests that at an earlier evolutionary stage, either disk fragmentation occurs more frequently or the fragments tend to fall more often onto the central source, triggering accretion bursts more frequently. The mass accretion rate during the burst estimated from the accretion luminosity is ∼ (1.8−4.2)×10^5 Msun/yr, which shows no obvious variation from Class 0 to Class I.