TY - JOUR
T1 - Bridging Star-forming Galaxy and AGN Ultraviolet Luminosity Functions at z =4 with the SHELA Wide-field Survey
AU - Stevans, Matthew L.
AU - Finkelstein, Steven L.
AU - Wold, Isak
AU - Kawinwanichakij, Lalitwadee
AU - Papovich, Casey
AU - Sherman, Sydney
AU - Ciardullo, Robin
AU - Florez, Jonathan
AU - Gronwall, Caryl
AU - Jogee, Shardha
AU - Somerville, Rachel S.
AU - Yung, L. Y.Aaron
N1 - Funding Information:
The authors acknowledge Raquel Martinez, Karl Gebhardt, and Eric J. Gawiser for the interesting discussions we had and their suggestions, which improved the quality of this research. We thank Neal J. Evans and William P. Bowman for useful comments on the draft of this paper. M.L.S. and S.L.F. acknowledge support from the University of Texas at Austin, the NASA Astrophysics and Data Analysis Program through grant NNX16AN46G, and the National Science Foundation AAG Award AST-1614798. The work of C.P. and L.K. is supported by the National Science Foundation through grants AST 1413317 and 1614668. The Institute for Gravitation and the Cosmos is supported by the Eberly College of Science and the Office of the Senior Vice President for Research at the Pennsylvania State University. S.J., S.S., and J.F. acknowledge support from the University of Texas at Austin and NSF grants NSF AST-1614798 and NSF AST-1413652. R.S.S. and A.Y. thank the Downsbrough family for their generous support and gratefully acknowledge funding from the Simons Foundation. Facilities: CTIO, SST(IRAC).
Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved..
PY - 2018/8/10
Y1 - 2018/8/10
N2 - We present a joint analysis of the rest-frame ultraviolet (UV) luminosity functions of continuum-selected star-forming galaxies and galaxies dominated by active galactic nuclei (AGNs) at z ∼4. These 3740 z ∼4 galaxies are selected from broadband imaging in nine photometric bands over 18 deg2 in the Spitzer/HETDEX Exploratory Large Area Survey field. The large area and moderate depth of our survey provide a unique view of the intersection between the bright end of the galaxy UV luminosity function (M AB < -22) and the faint end of the AGN UV luminosity function. We do not separate AGN-dominated galaxies from star-formation-dominated galaxies, but rather fit both luminosity functions simultaneously. These functions are best fit with a double power law for both the galaxy and AGN components, where the galaxy bright-end slope has a power-law index of -3.80 ±0.10 and the corresponding AGN faint-end slope is . We cannot rule out a Schechter-like exponential decline for the galaxy UV luminosity function, and in this scenario the AGN luminosity function has a steeper faint-end slope of . Comparison of our galaxy luminosity function results with a representative cosmological model of galaxy formation suggests that the molecular gas depletion time must be shorter, implying that star formation is more efficient in bright galaxies at z =4 than at the present day. If the galaxy luminosity function does indeed have a power-law shape at the bright end, the implied ionizing emissivity from AGNs is not inconsistent with previous observations. However, if the underlying galaxy distribution is Schechter, it implies a significantly higher ionizing emissivity from AGNs at this epoch.
AB - We present a joint analysis of the rest-frame ultraviolet (UV) luminosity functions of continuum-selected star-forming galaxies and galaxies dominated by active galactic nuclei (AGNs) at z ∼4. These 3740 z ∼4 galaxies are selected from broadband imaging in nine photometric bands over 18 deg2 in the Spitzer/HETDEX Exploratory Large Area Survey field. The large area and moderate depth of our survey provide a unique view of the intersection between the bright end of the galaxy UV luminosity function (M AB < -22) and the faint end of the AGN UV luminosity function. We do not separate AGN-dominated galaxies from star-formation-dominated galaxies, but rather fit both luminosity functions simultaneously. These functions are best fit with a double power law for both the galaxy and AGN components, where the galaxy bright-end slope has a power-law index of -3.80 ±0.10 and the corresponding AGN faint-end slope is . We cannot rule out a Schechter-like exponential decline for the galaxy UV luminosity function, and in this scenario the AGN luminosity function has a steeper faint-end slope of . Comparison of our galaxy luminosity function results with a representative cosmological model of galaxy formation suggests that the molecular gas depletion time must be shorter, implying that star formation is more efficient in bright galaxies at z =4 than at the present day. If the galaxy luminosity function does indeed have a power-law shape at the bright end, the implied ionizing emissivity from AGNs is not inconsistent with previous observations. However, if the underlying galaxy distribution is Schechter, it implies a significantly higher ionizing emissivity from AGNs at this epoch.
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U2 - 10.3847/1538-4357/aacbd7
DO - 10.3847/1538-4357/aacbd7
M3 - Article
AN - SCOPUS:85051562686
SN - 0004-637X
VL - 863
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 63
ER -