Interferometric Observations of High-Mass Star-Forming Clumps with Unusual N2H+/HCO+ Line Ratios

Abstract

The Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey has detected high-mass star-forming clumps with anomalous N${}_2$H${}^{+}$/HCO${}^{+}$(1-0) integrated intensity ratios that are either unusually high ("N${}_2$H${}^{+}$ rich") or unusually low ("N${}_2$H${}^{+}$ poor"). With 3 mm observations from the Australia Telescope Compact Array (ATCA), we imaged two N${}_2$H${}^{+}$ rich clumps, G333.234-00.061 and G345.144-00.216, and two N${}_2$H${}^{+}$ poor clumps, G351.409+00.567 and G353.229+00.672. In these clumps, the N${}_2$H${}^{+}$ rich anomalies arise from extreme self-absorption of the HCO${}^{+}$ line. G333.234-00.061 contains two of the most massive protostellar cores known with diameters of less than 0.1 pc, separated by a projected distance of only 0.12 pc. Unexpectedly, the higher mass core appears to be at an earlier evolutionary stage than the lower mass core, which may suggest that two different epochs of high-mass star formation can occur in close proximity. Through careful analysis of the ATCA observations and MALT90 clumps (including the G333, NGC 6334, and NGC 6357 star formation regions), we find that N${}_2$H${}^{+}$ poor anomalies arise at clump-scales and are caused by lower relative abundances of N${}_2$H${}^{+}$ due to the distinct chemistry of H II regions or photodissociation regions.

arXiv comment18 pages, 18 figures, accepted to ApJ

References in corpus (28)

• GLIMPSE: I. A SIRTF Legacy Project to Map the Inner Galaxy
• Toward Understanding Massive Star Formation
• Clouds, filaments and protostars: the Herschel Hi-GAL Milky Way
• ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns
• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• Global collapse of molecular clouds as a formation mechanism for the most massive stars
• A Class I and Class II Methanol Maser Survey of Extended Green Objects (EGOs) from the GLIMPSE Survey
• Chemistry in Infrared Dark Cloud Clumps: a Molecular Line Survey at 3 mm
• Methanol masers : Reliable tracers of the early stages of high-mass star formation
• MALT90: The Millimetre Astronomy Legacy Team 90 GHz Survey
• The Electron Temperature Gradient in the Galactic Disk
• The Millimeter Astronomy Legacy Team 90 GHz (MALT90) Pilot Survey
• A high-sensitivity 6.7 GHz methanol maser survey toward H2O sources
• Southern class I methanol masers at 36 and 44 GHz
• Class I methanol masers in the outflow of IRAS 16547-4247
• Chemical Evolution in High-Mass Star-Forming Regions: Results from the MALT90 Survey
• Distinct Chemical Regions in the "Prestellar" Infrared Dark Cloud (IRDC) G028.23-00.19
• The Excitation of N${}_2$H${}^{+}$ in Interstellar Molecular Clouds. I - Models
• The Relationship between Class I and Class II Methanol Masers
• Deep Very Large Array Radio Continuum Surveys of GLIMPSE Extended Green Objects (EGOs)
• Characterization of the MALT90 Survey and the Mopra Telescope at 90 GHz
• N2H+ depletion in the massive protostellar cluster AFGL 5142
• A search for 22-GHz water masers within the giant molecular cloud associated with RCW106
• Detection of Class I Methanol (CH3OH) Maser Candidates in Supernova Remnants
• The Protocluster G18.67+0.03: A Test Case for Class I Methanol Masers as Evolutionary Indicators for Massive Star Formation
• Millimeter and submillimeter high angular resolution interferometric observations: dust in the heart of IRAS 18162-2048
• A search for 95 GHz class I methanol masers in molecular outflows
• Submillimeter Array and Very Large Array Observations in the Hypercompact HII region G35.58-0.03

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• The ALMA Survey of 70 $\mu$m dark High-mass clumps in Early Stages (ASHES). I. Pilot Survey: Clump Fragmentation
• Far-Infrared Dust Temperatures and Column Densities of the MALT90 Molecular Clump Sample
• Dense core properties in the Infrared Dark cloud G14.225-0.506 revealed by ALMA
• The ALMA Survey of 70 $\mu \mathrm{m}$ Dark High-mass Clumps in Early Stages (ASHES). II: Molecular Outflows in the Extreme Early Stages of Protocluster Formation
• Linking Dense Gas from the Milky Way to External Galaxies
• Digging into the Interior of Hot Cores with ALMA (DIHCA). I. Dissecting the High-mass Star-Forming Core G335.579-0.292 MM1
• ATLASGAL --- Molecular fingerprints of a sample of massive star forming clumps
• Digging into the Interior of Hot Cores with ALMA (DIHCA). II. Exploring the Inner Binary (Multiple) System Embedded in G335 MM1 ALMA1
• Outflows, envelopes, and disks as evolutionary indicators in Lupus YSOs
• Salt-bearing disk candidates around high-mass young stellar objects
• The onset of energetic particle irradiation in Class 0 protostars
• The structure and early evolution of massive star forming regions - Substructure in the infrared dark cloud SDC13
• Dense Molecular Clumps with Large Blue Asymmetries: Evidence for Collapse