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 (SFR) inferred from mid-infrared (MIR) data that is substantially elevated relative to that estimated from dust-corrected UV data. We use a sample of $\sim$200 galaxies and AGN at $1.40<z<2.61$ with 24 $\mu$m detections (rest-frame 8$\mu$m) from MIPS/\textit{Spitzer}. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity (${\mathrm{L}}_{\mathrm{IR}}$) and to correct the UV light for dust attenuation. We find that extrapolations of the SFR from the observed 24 $\mu$m flux, using luminosity-dependent templates based on local galaxies, substantially overestimate ${\mathrm{L}}_{\mathrm{IR}}$ in $z\sim 2$ galaxies. By including \textit{Herschel} observations and using a stellar mass-dependent, luminosity-independent ${\mathrm{L}}_{\mathrm{IR}}$, 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 $\sim 24\%$ of our galaxies as MIR-excess. However, $\mathrm{SF}{\mathrm{R}}_{\mathrm{H}\alpha }$ 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 AGN in MOSDEF, we do not find a higher prevalence for AGN 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 PAH emission.

References in corpus (27)

• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• An ultra-deep near-infrared spectrum of a compact quiescent galaxy at z=2.2
• 3D-HST WFC3-selected Photometric Catalogs in the Five CANDELS/3D-HST Fields: Photometry, Photometric Redshifts and Stellar Masses
• The 3D-HST Survey: Hubble Space Telescope WFC3/G141 grism spectra, redshifts, and emission line measurements for $\sim 100,000$ galaxies
• The MOSFIRE Deep Evolution Field (MOSDEF) Survey: Rest-Frame Optical Spectroscopy for ~1500 H-Selected Galaxies at 1.37 < z < 3.8
• Non-linear Least Squares Fitting in IDL with MPFIT
• Multiwavelength study of massive galaxies at z~2. II. Widespread Compton thick AGN and the concurrent growth of black holes and bulges
• ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Infrared Excess of UV-selected z=2-10 galaxies as a function of UV-continuum Slope and Stellar Mass
• Unveiling obscured accretion in the Chandra Deep Field South
• The Evolution of Normal Galaxy X-ray Emission Through Cosmic History: Constraints from the 6 Ms Chandra Deep Field-South
• Dust temperature and mid-to-total infrared color distributions for star-forming galaxies at 0<z<4
• The XMM-Newton wide-field survey in the COSMOS field: III. optical identification and multiwavelength properties of a large sample of X-ray selected sources
• Spitzer Mid-to-Far-Infrared Flux Densities of Distant Galaxies
• The MOSDEF Survey: Optical AGN Diagnostics at z~2.3
• AEGIS-X: Deep Chandra imaging of the Central Groth Strip
• Extended Mid-Infrared Aromatic Feature Emission in M 82
• The MOSDEF Survey: Dissecting the star-formation rate vs. stellar mass relation using H$\alpha$ and H$\beta$ emission lines at z ~ 2
• Mid-IR Luminosities and UV/Optical Star Formation Rates at z<1.4
• A New Star-Formation Rate Calibration from Polycyclic Aromatic Hydrocarbon Emission Features and Application to High Redshift Galaxies
• Spatially-resolved dust maps from Balmer decrements in galaxies at z~1.4
• X-rays across the galaxy population I: tracing the main sequence of star formation
• The MOSDEF survey: AGN multi-wavelength identification, selection biases and host galaxy properties
• Compton Thick AGN in the XMM-COSMOS survey
• Investigating H$\alpha$, UV, and IR star-formation rate diagnostics for a large sample of z ~ 2 galaxies
• Mid infrared properties of distant infrared luminous galaxies
• The MOSDEF Survey: Metallicity Dependence of the PAH Emission at High Redshift and Implications for 24 micron-inferred IR Luminosities and Star Formation Rates at z~2
• Theoretical Modeling of Emission-Line galaxies: New Classification Parameters for Mid-Infrared and Optical Spectroscopy

Cited by in corpus (21)

• The MOSDEF Survey: The Evolution of the Mass-Metallicity Relation from $z=0$ to $z\sim 3.3$
• On the dust temperatures of high redshift galaxies
• The MOSDEF Survey: the Variation of the Dust Attenuation Curve with Metallicity
• The MOSDEF Survey: The First Direct Measurements of the Nebular Dust Attenuation Curve at High Redshift
• The MOSDEF survey: a census of AGN-driven ionized outflows at $z=1.4-3.8$
• The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyman Alpha Emission of High-Redshift Galaxies
• The Impact of Star-Formation-Rate Surface Density on the Electron Density and Ionization Parameter of High-Redshift Galaxies
• The MOSDEF Survey: The Mass-Metallicity relationship and the existence of the FMR at z~1.5
• The MOSDEF Survey: Environmental dependence of the gas-phase metallicity of galaxies at $1.4\le z\le 2.6$
• CO Emission, Molecular Gas, and Metallicity in Main-Sequence Star-Forming Galaxies at $z\sim 2.3$
• JWST/MIRI Simulated Imaging: Insights into Obscured Star-Formation and AGN for Distant Galaxies in Deep Surveys
• IR SED and Dust Masses of Sub-solar Metallicity Galaxies at z~2.3
• The MOSDEF-LRIS Survey: Connection between Galactic-scale Outflows and the Properties of $z$~2 star-forming Galaxies
• The MOSDEF-LRIS Survey: Probing ISM/CGM Structure of Star-Forming Galaxies at z~2 Using Rest-UV Spectroscopy
• The MOSDEF Survey: An Improved Voronoi Binning Technique on Spatially Resolved Stellar Populations at z~2
• The MOSDEF Survey: Calibrating the relationship between H$\alpha$ star-formation rate and radio continuum luminosity at $1.4<z<2.6$
• The MOSDEF-LRIS Survey: Detection of Inflowing Gas Towards Three Star-forming Galaxies at z ~ 2
• Exploring the Correlation between $\mathrm{H}\alpha$-to-UV Ratio and Burstiness for Typical Star-forming Galaxies at $z\sim 2$
• The MOSDEF Survey: The Dependence of H$\alpha$-to-UV SFR Ratios on SFR and Size at $z\sim 2$
• Improved Measurements of Galaxy Star Formation Stochasticity from the Intrinsic Scatter of Burst Indicators
• The MOSDEF Survey: Probing Resolved Stellar Populations at $z\sim 2$ Using a New Bayesian-defined Morphology Metric Called Patchiness