The MOSDEF Survey: The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2

Mojegan Azadi; Alison Coil; James Aird; Irene Shivaei; Naveen Reddy; Alice Shapley; Mariska Kriek; William R. Freeman; Gene C.K. Leung; Bahram Mobasher; Sedona H. Price; Ryan L. Sanders; Brian Siana; Tom Zick

doi:10.3847/1538-4357/aad3c8

The MOSDEF Survey: The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2

Mojegan Azadi, Alison Coil, James Aird, Irene Shivaei, Naveen Reddy, Alice Shapley, Mariska Kriek, William R. Freeman, Gene C.K. Leung, Bahram Mobasher, Sedona H. Price, Ryan L. Sanders, Brian Siana, Tom Zick

Physics And Astronomy

Research output: Contribution to journal › Article › peer-review

20 Scopus citations

Abstract

We present an analysis using the MOSFIRE Deep Evolution Field (MOSDEF) survey on the nature of "MIR-excess" galaxies, which have star formation rates (SFRs) inferred from mid-infrared (MIR) data that are substantially elevated relative to those estimated from dust-corrected UV data. We use a sample of ∼200 galaxies and active galactic nuclei (AGNs) at 1.40 < z < 2.61 with 24 μm detections (rest-frame 8 μm) from MIPS/Spitzer. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity (L_1R) and to correct the UV light for dust attenuation. We find that extrapolations of the SFR from the observed 24 μm flux, using luminosity-dependent templates based on local galaxies, substantially overestimate in z ∼ 2 galaxies. By including Herschel observations and using a stellar-mass-dependent, luminosity-independent L_1R, we obtain more reliable estimates of the SFR and a lower fraction of MIR-excess galaxies. Once stellar-mass selection biases are taken into account, we identify ∼24% of our galaxies as MIR excess. However, is not elevated in MIR-excess galaxies compared to MIR-normal galaxies, indicating that the intrinsic fraction of MIR excess may be lower. Using X-ray-, IR-, and optically selected AGNs in MOSDEF, we do not find a higher prevalence for AGNs in MIR-excess galaxies relative to MIR-normal galaxies. A stacking analysis of X-ray-undetected galaxies does not reveal a harder spectrum in MIR-excess galaxies relative to MIR-normal galaxies. Our analysis indicates that AGN activity does not contribute substantially to the MIR excess and instead implies that it is likely due to the enhanced polycyclic aromatic hydrocarbon emission.

Original language	English
Article number	63
Journal	Astrophysical Journal
Volume	866
Issue number	1
DOIs	https://doi.org/10.3847/1538-4357/aad3c8
State	Published - Oct 10 2018

Bibliographical note

Funding Information:
We thank the MOSFIRE instrument team for building this powerful instrument. Funding for the MOSDEF survey is provided by NSF AAG grants AST-1312780, 1312547, 1312764, and 1313171 and grant AR-13907 from the Space Telescope Science Institute. We acknowledge Mark Dickinson and Hanae Inami for providing part of the IR data used in this work. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.

Keywords

galaxies: active
galaxies: high-redshift
galaxies: nuclei
galaxies: star formation
infrared: galaxies
ultraviolet: galaxies

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

Access to Document

10.3847/1538-4357/aad3c8

Cite this

Azadi, M., Coil, A., Aird, J., Shivaei, I., Reddy, N., Shapley, A., Kriek, M., Freeman, W. R., Leung, G. C. K., Mobasher, B., Price, S. H., Sanders, R. L., Siana, B., & Zick, T. (2018). The MOSDEF Survey: The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2. Astrophysical Journal, 866(1), Article 63. https://doi.org/10.3847/1538-4357/aad3c8

@article{51be84a23d354e45949e0061cf48f844,

title = "The MOSDEF Survey: The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2",

abstract = "We present an analysis using the MOSFIRE Deep Evolution Field (MOSDEF) survey on the nature of {"}MIR-excess{"} galaxies, which have star formation rates (SFRs) inferred from mid-infrared (MIR) data that are substantially elevated relative to those estimated from dust-corrected UV data. We use a sample of ∼200 galaxies and active galactic nuclei (AGNs) at 1.40 < z < 2.61 with 24 μm detections (rest-frame 8 μm) from MIPS/Spitzer. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity (L1R) and to correct the UV light for dust attenuation. We find that extrapolations of the SFR from the observed 24 μm flux, using luminosity-dependent templates based on local galaxies, substantially overestimate in z ∼ 2 galaxies. By including Herschel observations and using a stellar-mass-dependent, luminosity-independent L1R, we obtain more reliable estimates of the SFR and a lower fraction of MIR-excess galaxies. Once stellar-mass selection biases are taken into account, we identify ∼24% of our galaxies as MIR excess. However, is not elevated in MIR-excess galaxies compared to MIR-normal galaxies, indicating that the intrinsic fraction of MIR excess may be lower. Using X-ray-, IR-, and optically selected AGNs in MOSDEF, we do not find a higher prevalence for AGNs in MIR-excess galaxies relative to MIR-normal galaxies. A stacking analysis of X-ray-undetected galaxies does not reveal a harder spectrum in MIR-excess galaxies relative to MIR-normal galaxies. Our analysis indicates that AGN activity does not contribute substantially to the MIR excess and instead implies that it is likely due to the enhanced polycyclic aromatic hydrocarbon emission.",

keywords = "galaxies: active, galaxies: high-redshift, galaxies: nuclei, galaxies: star formation, infrared: galaxies, ultraviolet: galaxies",

author = "Mojegan Azadi and Alison Coil and James Aird and Irene Shivaei and Naveen Reddy and Alice Shapley and Mariska Kriek and Freeman, {William R.} and Leung, {Gene C.K.} and Bahram Mobasher and Price, {Sedona H.} and Sanders, {Ryan L.} and Brian Siana and Tom Zick",

note = "Funding Information: We thank the MOSFIRE instrument team for building this powerful instrument. Funding for the MOSDEF survey is provided by NSF AAG grants AST-1312780, 1312547, 1312764, and 1313171 and grant AR-13907 from the Space Telescope Science Institute. We acknowledge Mark Dickinson and Hanae Inami for providing part of the IR data used in this work. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Publisher Copyright: {\textcopyright} 2018. The American Astronomical Society. All rights reserved.",

year = "2018",

month = oct,

day = "10",

doi = "10.3847/1538-4357/aad3c8",

language = "English",

volume = "866",

number = "1",

}

Azadi, M, Coil, A, Aird, J, Shivaei, I, Reddy, N, Shapley, A, Kriek, M, Freeman, WR, Leung, GCK, Mobasher, B, Price, SH, Sanders, RL, Siana, B & Zick, T 2018, 'The MOSDEF Survey: The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2', Astrophysical Journal, vol. 866, no. 1, 63. https://doi.org/10.3847/1538-4357/aad3c8

TY - JOUR

T1 - The MOSDEF Survey

T2 - The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2

AU - Azadi, Mojegan

AU - Coil, Alison

AU - Aird, James

AU - Shivaei, Irene

AU - Reddy, Naveen

AU - Shapley, Alice

AU - Kriek, Mariska

AU - Freeman, William R.

AU - Leung, Gene C.K.

AU - Mobasher, Bahram

AU - Price, Sedona H.

AU - Sanders, Ryan L.

AU - Siana, Brian

AU - Zick, Tom

N1 - Funding Information: We thank the MOSFIRE instrument team for building this powerful instrument. Funding for the MOSDEF survey is provided by NSF AAG grants AST-1312780, 1312547, 1312764, and 1313171 and grant AR-13907 from the Space Telescope Science Institute. We acknowledge Mark Dickinson and Hanae Inami for providing part of the IR data used in this work. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Publisher Copyright: © 2018. The American Astronomical Society. All rights reserved.

PY - 2018/10/10

Y1 - 2018/10/10

N2 - We present an analysis using the MOSFIRE Deep Evolution Field (MOSDEF) survey on the nature of "MIR-excess" galaxies, which have star formation rates (SFRs) inferred from mid-infrared (MIR) data that are substantially elevated relative to those estimated from dust-corrected UV data. We use a sample of ∼200 galaxies and active galactic nuclei (AGNs) at 1.40 < z < 2.61 with 24 μm detections (rest-frame 8 μm) from MIPS/Spitzer. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity (L1R) and to correct the UV light for dust attenuation. We find that extrapolations of the SFR from the observed 24 μm flux, using luminosity-dependent templates based on local galaxies, substantially overestimate in z ∼ 2 galaxies. By including Herschel observations and using a stellar-mass-dependent, luminosity-independent L1R, we obtain more reliable estimates of the SFR and a lower fraction of MIR-excess galaxies. Once stellar-mass selection biases are taken into account, we identify ∼24% of our galaxies as MIR excess. However, is not elevated in MIR-excess galaxies compared to MIR-normal galaxies, indicating that the intrinsic fraction of MIR excess may be lower. Using X-ray-, IR-, and optically selected AGNs in MOSDEF, we do not find a higher prevalence for AGNs in MIR-excess galaxies relative to MIR-normal galaxies. A stacking analysis of X-ray-undetected galaxies does not reveal a harder spectrum in MIR-excess galaxies relative to MIR-normal galaxies. Our analysis indicates that AGN activity does not contribute substantially to the MIR excess and instead implies that it is likely due to the enhanced polycyclic aromatic hydrocarbon emission.

AB - We present an analysis using the MOSFIRE Deep Evolution Field (MOSDEF) survey on the nature of "MIR-excess" galaxies, which have star formation rates (SFRs) inferred from mid-infrared (MIR) data that are substantially elevated relative to those estimated from dust-corrected UV data. We use a sample of ∼200 galaxies and active galactic nuclei (AGNs) at 1.40 < z < 2.61 with 24 μm detections (rest-frame 8 μm) from MIPS/Spitzer. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity (L1R) and to correct the UV light for dust attenuation. We find that extrapolations of the SFR from the observed 24 μm flux, using luminosity-dependent templates based on local galaxies, substantially overestimate in z ∼ 2 galaxies. By including Herschel observations and using a stellar-mass-dependent, luminosity-independent L1R, we obtain more reliable estimates of the SFR and a lower fraction of MIR-excess galaxies. Once stellar-mass selection biases are taken into account, we identify ∼24% of our galaxies as MIR excess. However, is not elevated in MIR-excess galaxies compared to MIR-normal galaxies, indicating that the intrinsic fraction of MIR excess may be lower. Using X-ray-, IR-, and optically selected AGNs in MOSDEF, we do not find a higher prevalence for AGNs in MIR-excess galaxies relative to MIR-normal galaxies. A stacking analysis of X-ray-undetected galaxies does not reveal a harder spectrum in MIR-excess galaxies relative to MIR-normal galaxies. Our analysis indicates that AGN activity does not contribute substantially to the MIR excess and instead implies that it is likely due to the enhanced polycyclic aromatic hydrocarbon emission.

KW - galaxies: active

KW - galaxies: high-redshift

KW - galaxies: nuclei

KW - galaxies: star formation

KW - infrared: galaxies

KW - ultraviolet: galaxies

UR - http://www.scopus.com/inward/record.url?scp=85055274992&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85055274992&partnerID=8YFLogxK

U2 - 10.3847/1538-4357/aad3c8

DO - 10.3847/1538-4357/aad3c8

M3 - Article

AN - SCOPUS:85055274992

SN - 0004-637X

VL - 866

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

M1 - 63

ER -

The MOSDEF Survey: The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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