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Microwave Continuum Emission and Dense Gas Tracers in NGC 3627: Combining Jansky VLA and ALMA Observations

Murphy, Eric J. and Dong, Dillon and Leroy, Adam K. and Momjian, Emmanuel and Condon, James J. and Helou, George and Meier, David S. and Ott, Jürgen and Schinnerer, Eva and Turner, Jean L. (2015) Microwave Continuum Emission and Dense Gas Tracers in NGC 3627: Combining Jansky VLA and ALMA Observations. Astrophysical Journal, 813 (2). Art. No. 118. ISSN 0004-637X.

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We present Karl G. Jansky Very Large Array Ka band (33 GHz) and Atacama Large Millimeter Array (ALMA) Band 3 (94.5 GHz) continuum images covering the nucleus and two extranuclear star-forming regions within the nearby galaxy NGC 3627 (M 66), observed as part of the Star Formation in Radio Survey. Both images achieve an angular resolution of ≾2", allowing us to map radio spectral indices and estimate thermal radio fractions at a linear resolution of ≾90 pc. The thermal fraction at 33 GHz reaches unity at and around the peaks of each H ii region; the spectral index between 33 and 94.5 GHz additionally becomes both increasingly negative and positive away from the H ii region peaks, indicating an increase of non-thermal emission from diffusing cosmic-ray electrons and the possible presence of cold dust, respectively. While the ALMA observations were optimized for collecting continuum data, they also detected line emission from the J = 1 → 0 transitions of HCN and HCO^+. The peaks of dense molecular gas traced by these two spectral lines are spatially offset from the peaks of the continuum emission for both extranuclear star-forming regions, indicating that our data reach an angular resolution at which one can spatially distinguish sites of recent star formation from the sites of future star formation. Finally, we find trends of decreasing dense gas fraction and velocity dispersion with increasing star formation efficiency among the regions observed, indicating that the dynamical state of the dense gas, rather than its abundance, plays a more significant role in the star formation process.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Murphy, Eric J.0000-0001-7089-7325
Dong, Dillon0000-0001-9584-2531
Leroy, Adam K.0000-0002-2545-1700
Momjian, Emmanuel0000-0003-3168-5922
Condon, James J.0000-0003-4724-1939
Helou, George0000-0003-3367-3415
Meier, David S.0000-0001-9436-9471
Ott, Jürgen0000-0001-8224-1956
Schinnerer, Eva0000-0002-3933-7677
Turner, Jean L.0000-0003-4625-2951
Additional Information:© 2015 American Astronomical Society. Received 2015 May 24; accepted 2015 August 21; published 2015 November 5. We would like to thank the anonymous referee for useful comments that helped to improve the content and presentation of this paper. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2012.1.00456.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This research has made use of the NASA/IPAC Extragalactic Database (NED), as well as the NASA/IPAC Infrared Science Archive, both of which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies: individual (NGC 3627) ; galaxies: star formation; H ii regions; ISM: molecules; radio continuum: general
Issue or Number:2
Record Number:CaltechAUTHORS:20151222-105559496
Persistent URL:
Official Citation:Eric J. Murphy et al 2015 ApJ 813 118
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63138
Deposited By: Ruth Sustaita
Deposited On:22 Dec 2015 19:11
Last Modified:09 Mar 2020 13:19

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