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Mergers, active galactic nuclei and ‘normal’ galaxies: contributions to the distribution of star formation rates and infrared luminosity functions

Hopkins, Philip F. and Younger, Joshua D. and Hayward, Christopher C. and Narayanan, Desika and Hernquist, Lars (2010) Mergers, active galactic nuclei and ‘normal’ galaxies: contributions to the distribution of star formation rates and infrared luminosity functions. Monthly Notices of the Royal Astronomical Society, 402 (3). pp. 1693-1713. ISSN 0035-8711.

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We use a novel method to predict the contribution of normal star-forming galaxies, merger-induced bursts and obscured active galactic nuclei (AGN), to infrared luminosity functions (LFs) and global star formation rate (SFR) densities. We use empirical halo occupation constraints to populate haloes with galaxies and determine the distribution of normal and merging galaxies. Each system can then be associated with high-resolution hydrodynamic simulations. We predict the distribution of observed luminosities and SFRs, from different galaxy classes, as a function of redshift from z= 0 to 6. We provide fitting functions for the predicted LFs, quantify the uncertainties, and compare with observations. At all redshifts, ‘normal’ galaxies dominate the LF at moderate luminosities ∼L_* (the ‘knee’). Merger-induced bursts increasingly dominate at L ≫ L_*; at the most extreme luminosities, AGN are important. However, all populations increase in luminosity at higher redshifts, owing to increasing gas fractions. Thus, the ‘transition luminosity’ between normal and merger-dominated sources increases from the luminous infrared galaxy (LIRG)–ultraluminous infrared galaxy threshold at z∼ 0 to bright Hyper-LIRG thresholds at z∼ 2. The transition to dominance by obscured AGN evolves similarly, at factor of several higher L_(IR). At all redshifts, non-merging systems dominate the total luminosity/SFR density, with merger-induced bursts constituting ∼5–10 per cent and AGN ∼1–5 per cent. Bursts contribute little to scatter in the SFR–stellar mass relation. In fact, many systems identified as ‘ongoing’ mergers will be forming stars in their ‘normal’ (non-burst) mode. Counting this as ‘merger-induced’ star formation leads to a stronger apparent redshift evolution in the contribution of mergers to the SFR density. We quantify how the evolution in LFs depends on evolution in galaxy gas fractions, merger rates, and possible evolution in the Schmidt–Kennicutt relation. We discuss areas where more detailed study, with full radiative transfer treatment of complex three-dimensional clumpy geometries in mixed AGN–star-forming systems, is necessary.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Hayward, Christopher C.0000-0003-4073-3236
Narayanan, Desika0000-0002-7064-4309
Hernquist, Lars0000-0001-6950-1629
Alternate Title:Mergers, AGN, and 'Normal' Galaxies: Contributions to the Distribution of Star Formation Rates and Infrared Luminosity Functions
Additional Information:© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2009 November 4. Received 2009 October 23; in original form 2009 September 17. We thank Eliot Quataert, Lin Yan, Dave Sanders, Nick Scoville and Kevin Bundy for helpful discussions throughout the development of this manuscript. Support for PFH was provided by the Miller Institute for Basic Research in Science, University of California Berkeley. JDY acknowledges support from NASA through Hubble Fellowship grant HF-51266.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Many of the computations in this paper were run on the Odyssey cluster supported by the FAS Research Computing Group at Harvard University.
Funding AgencyGrant Number
Miller Institute for Basic Research in ScienceUNSPECIFIED
NASA Hubble FellowshipHF-51266.01
NASANAS 5-26555
Harvard UniversityUNSPECIFIED
Subject Keywords:galaxies: active, galaxies: evolution, galaxies: formation, cosmology: theory
Issue or Number:3
Record Number:CaltechAUTHORS:20200521-163330430
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Official Citation:Philip F. Hopkins, Joshua D. Younger, Christopher C. Hayward, Desika Narayanan, Lars Hernquist, Mergers, active galactic nuclei and ‘normal’ galaxies: contributions to the distribution of star formation rates and infrared luminosity functions, Monthly Notices of the Royal Astronomical Society, Volume 402, Issue 3, March 2010, Pages 1693–1713,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103397
Deposited By: George Porter
Deposited On:22 May 2020 18:24
Last Modified:22 May 2020 18:24

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