Spectral lines of ammonia, NH3, are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant to freezing onto grain surfaces, which should make it a superior tool for studying the interior parts of cold, dense cores. Here we present high-resolution NH3 observations with the Very Large Array and Green Bank Telescope toward a prestellar core. These observations show an outer region with a fractional NH3 abundance of X(NH3) = (1.975 +/- 0.005) x 10(-8) (+/- 10% systematic), but it also reveals that, after all, the X(NH3) starts to decrease above a H-2 column density of approximate to 2.6 x 10(22) cm(-2). We derive a density model for the core and find that the break point in the fractional abundance occurs at the density n(H-2) similar to 2 x 10(5) cm(-3), and beyond this point the fractional abundance decreases with increasing density, following the power law n (-1.1). This power-law behavior is well reproduced by chemical models where adsorption onto grains dominates the removal of ammonia and related species from the gas at high densities. We suggest that the break-point density changes from core to core depending on the temperature and the grain properties, but that the depletion power law is anyway likely to be close to n (-1) owing to the dominance of accretion in the central parts of starless cores.

An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion / Jaime E. Pineda; Jorma Harju; Paola Caselli; Olli Sipilä; Mika Juvela; Charlotte Vastel; Erik Rosolowsky; Andreas Burkert; Rachel K. Friesen; Yancy Shirley; María José Maureira; Spandan Choudhury; Dominique M. Segura-Cox; Rolf Güsten; Anna Punanova; Luca Bizzocchi; Alyssa A. Goodman. - In: THE ASTRONOMICAL JOURNAL. - ISSN 0004-6256. - ELETTRONICO. - 163:6(2022), pp. 294.1-294.13. [10.3847/1538-3881/ac6be7]

An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion

Luca Bizzocchi;
2022

Abstract

Spectral lines of ammonia, NH3, are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant to freezing onto grain surfaces, which should make it a superior tool for studying the interior parts of cold, dense cores. Here we present high-resolution NH3 observations with the Very Large Array and Green Bank Telescope toward a prestellar core. These observations show an outer region with a fractional NH3 abundance of X(NH3) = (1.975 +/- 0.005) x 10(-8) (+/- 10% systematic), but it also reveals that, after all, the X(NH3) starts to decrease above a H-2 column density of approximate to 2.6 x 10(22) cm(-2). We derive a density model for the core and find that the break point in the fractional abundance occurs at the density n(H-2) similar to 2 x 10(5) cm(-3), and beyond this point the fractional abundance decreases with increasing density, following the power law n (-1.1). This power-law behavior is well reproduced by chemical models where adsorption onto grains dominates the removal of ammonia and related species from the gas at high densities. We suggest that the break-point density changes from core to core depending on the temperature and the grain properties, but that the depletion power law is anyway likely to be close to n (-1) owing to the dominance of accretion in the central parts of starless cores.
2022
An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion / Jaime E. Pineda; Jorma Harju; Paola Caselli; Olli Sipilä; Mika Juvela; Charlotte Vastel; Erik Rosolowsky; Andreas Burkert; Rachel K. Friesen; Yancy Shirley; María José Maureira; Spandan Choudhury; Dominique M. Segura-Cox; Rolf Güsten; Anna Punanova; Luca Bizzocchi; Alyssa A. Goodman. - In: THE ASTRONOMICAL JOURNAL. - ISSN 0004-6256. - ELETTRONICO. - 163:6(2022), pp. 294.1-294.13. [10.3847/1538-3881/ac6be7]
Jaime E. Pineda; Jorma Harju; Paola Caselli; Olli Sipilä; Mika Juvela; Charlotte Vastel; Erik Rosolowsky; Andreas Burkert; Rachel K. Friesen; Yancy Shirley; María José Maureira; Spandan Choudhury; Dominique M. Segura-Cox; Rolf Güsten; Anna Punanova; Luca Bizzocchi; Alyssa A. Goodman
File in questo prodotto:
File Dimensione Formato  
HMM1_ALMA-view__Harju+2022_aj-163:294.pdf

accesso aperto

Tipo: Versione (PDF) editoriale
Licenza: Licenza per Accesso Aperto. Creative Commons Attribuzione (CCBY)
Dimensione 3.1 MB
Formato Adobe PDF
3.1 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/901239
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 14
  • ???jsp.display-item.citation.isi??? 15
social impact