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Are High-redshift Galaxies Hot? Temperature of z > 5 Galaxies and Implications for Their Dust Properties

Faisst, Andreas L. and Capak, Peter L. and Yan, Lin and Pavesi, Riccardo and Riechers, Dominik A. and Barišić, Ivana and Cooke, Kevin C. and Kartaltepe, Jeyhan S. and Masters, Daniel C. (2017) Are High-redshift Galaxies Hot? Temperature of z > 5 Galaxies and Implications for Their Dust Properties. Astrophysical Journal, 847 (1). Art. No. 21. ISSN 1538-4357.

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Recent studies have found a significant evolution and scatter in the relationship between the UV spectral slope (β_(UV)) and the infrared excess (IRX; L_(IR)/L_(UV)) at z > 4, suggesting different dust properties of these galaxies. The total far-infrared (FIR) luminosity is key for this analysis, but it is poorly constrained in normal (main-sequence) star-forming z > 5 galaxies, where often only one single FIR point is available. To better inform estimates of the FIR luminosity, we construct a sample of local galaxies and three low-redshift analogues of z > 5 systems. The trends in this sample suggest that normal high-redshift galaxies have a warmer infrared (IR) spectral energy distribution (SED) compared to average z < 4 galaxies that are used as priors in these studies. The blueshifted peak and mid-IR excess emission could be explained by a combination of a larger fraction of metal-poor interstellar medium being optically thin to ultraviolet (UV) light and a stronger UV radiation field due to high star formation densities. Assuming a maximally warm IR SED suggests a 0.6 dex increase in total FIR luminosities, which removes some tension between the dust attenuation models and observations of the IRX−β relation at z > 5. Despite this, some galaxies still fall below the minimum IRX−β relation derived with standard dust cloud models. We propose that radiation pressure in these highly star-forming galaxies causes a spatial offset between dust clouds and young star-forming regions within the lifetime of O/B stars. These offsets change the radiation balance and create viewing-angle effects that can change UV colors at fixed IRX. We provide a modified model that can explain the location of these galaxies on the IRX−β diagram.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Faisst, Andreas L.0000-0002-9382-9832
Capak, Peter L.0000-0003-3578-6843
Yan, Lin0000-0003-1710-9339
Pavesi, Riccardo0000-0002-2263-646X
Riechers, Dominik A.0000-0001-9585-1462
Barišić, Ivana0000-0001-6371-6274
Cooke, Kevin C.0000-0002-2200-9845
Kartaltepe, Jeyhan S.0000-0001-9187-3605
Masters, Daniel C.0000-0001-5382-6138
Additional Information:© 2017 American Astronomical Society. Received 2017 June 1. Accepted 2017 August 22. Published 2017 September 15. The authors would like to thank Nick Scoville, Caitlin Casey, Ranga-Ram Chary, Rychard Bouwens, Kirsten Larson, Shoubaneh Hemmati, and Lee Armus for valuable discussions which improved this manuscript. Furthermore, the authors thank the anonymous referee for the valuable feedback. D.R. and R.P. acknowledge support from the National Science Foundation under grant number AST-1614213 to Cornell University. R.P. acknowledges support through award SOSPA3-008 from the NRAO. We thank the ALMA staff for facilitating the observations and aiding in the calibration and reduction process. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00064.S, ADS/JAO.ALMA#2012.1.00523.S, ADS/JAO.ALMA#2012.1.00919.S, and ADS/JAO.ALMA#2015.1.00928.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC 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. This work is based in part on observations made with the Spitzer Space Telescope and the W.M. Keck Observatory, along with archival data from the NASA/ESA Hubble Space Telescope, the Subaru Telescope, the Canada–France–Hawaii Telescope, and the ESO Vista telescope obtained from the NASA/IPAC Infrared Science Archive. This research made use of the NASA/IPAC Extragalactic Database (NED), which is 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
National Radio Astronomy ObservatorySOSPA3-008
Subject Keywords:dust, extinction; galaxies: formation; galaxies: ISM
Issue or Number:1
Record Number:CaltechAUTHORS:20170921-133839132
Persistent URL:
Official Citation:Andreas L. Faisst et al 2017 ApJ 847 21
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81692
Deposited By: Ruth Sustaita
Deposited On:21 Sep 2017 21:41
Last Modified:03 Oct 2019 18:45

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