Measuring the Heating and Cooling of the Interstellar Medium at High Redshift: PAH and [C II] Observations of the Same Star-forming Galaxies at z ∼ 2
Abstract
Star formation depends critically on cooling mechanisms in the interstellar medium (ISM); however, thermal properties of gas in galaxies at the peak epoch of star formation (z ~ 2) remain poorly understood. A limiting factor in understanding the multiphase ISM is the lack of multiple tracers detected in the same galaxies, such as Polycyclic Aromatic Hydrocarbon (PAH) emission, a tracer of a critical photoelectric heating mechanism in interstellar gas, and [C ii] 158 μm fine-structure emission, a principal coolant. We present ALMA Band 9 observations targeting [C ii] in six z ~ 2 star-forming galaxies with strong Spitzer IRS detections of PAH emission. All six galaxies are detected in dust continuum and marginally resolved. We compare the properties of PAH and [C ii] emission, and constrain their relationship as a function of total infrared luminosity (L_(IR)) and IR surface density. [C ii] emission is detected in one galaxy at high signal-to-noise (34σ), and we place a secure upper limit on a second source. The rest of our sample are not detected in [C ii] likely due to redshift uncertainties and narrow ALMA bandpass windows. Our results are consistent with the deficit in [C ii]/L_(IR) and PAH/L_(IR) observed in the literature. However, the ratio of [C ii] to PAH emission at z ~ 2 is possibly much lower than what is observed in nearby dusty star-forming galaxies. This could be the result of enhanced cooling via [O i] at high-z, hotter gas and dust temperatures, and/or a reduction in the photoelectric efficiency, in which the coupling between interstellar radiation and gas heating is diminished.
Additional Information
© 2020. The American Astronomical Society. Received 2019 November 26; revised 2020 February 12; accepted 2020 February 17; published 2020 April 3. We are very grateful to the referee for the detailed comments and suggestions that significantly improved this work. J.M. and A.P. acknowledge D. Brisbin and C. Ferkinhoff for assistance in interpreting ZEUS [C ii] results. J.M. acknowledges I. Yoon, J. Braatz, and J. Thorley for their insights into ALMA data reduction. We thank J. D. Smith for his helpful discussion. T.D-S. acknowledges support from the CASSACA and CONICYT fund CAS-CONICYT Call 2018. Support for this work was provided by the NSF through award SOSPA5-008 from the NRAO and through the Massachusetts Space Grant Consortium (MASGS). 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#2017.1.01347.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.Attached Files
Published - McKinney_2020_ApJ_892_119.pdf
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Additional details
- Eprint ID
- 102327
- Resolver ID
- CaltechAUTHORS:20200403-115232187
- CAS South America Center for Astronomy
- Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)
- SOSPA5-008
- National Radio Astronomy Observatory
- Massachusetts Space Grant Consortium
- NSF
- Created
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2020-04-03Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)