The MOSDEF Survey: The Prevalence and Properties of Galaxy-wide AGN-driven Outflows at z ~ 2

Using observations from the first 2 yr of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we study 13 active galactic nucleus (AGN) driven outflows detected from a sample of 67 X-ray, IR, and/or optically selected AGNs at z ~ 2. The AGNs have bolometric luminosities of ~ 10^44 - 10^46 erg s^-1 , including both quasars and moderate-luminosity AGNs. We detect blueshifted, ionized gas outflows in the Hβ, [O III], Hα, and/or [N II] emission lines of 19% of the AGNs, while only 1.8% of the MOSDEF galaxies have similarly detected outflows. The outflow velocities span ∼300 to 1000 km s^−1. Eight of the 13 outflows are spatially extended on similar scales to the host galaxies, with spatial extents of 2.5–11.0 kpc. Outflows are detected uniformly across the star-forming main sequence, showing little trend with the host galaxy star formation rate. Line ratio diagnostics indicate that the outflowing gas is photoionized by the AGNs. We do not find evidence for positive AGN feedback, in either our small MOSDEF sample or a much larger Sloan Digital Sky Survey sample, using the BPT diagram. Given that a galaxy with an AGN is 10 times more likely to have a detected outflow, the outflowing gas is photoionized by the AGNs, and estimates of the mass and energy outflow rates indicate that stellar feedback is insufficient to drive at least some of these outflows; they are very likely to be AGN driven. The outflows have mass-loading factors of the order of unity, suggesting that they help regulate star formation in their host galaxies, though they may be insufficient to fully quench it

THE MOSDEF SURVEY: The Nature of Mid-Infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ~ 2

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 ∼200 galaxies and AGN at 1.40 < z < 2.61 with 24 µm detections (rest-frame 8µm) from MIPS/Spitzer. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity (LIR) 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 LIR in z ∼ 2 galaxies. By including Herschel observations and using a stellar mass-dependent, luminosity-independent LIR , 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, SFRHα 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 MIRexcess 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

The MOSDEF Survey: First Measurement of Nebular Oxygen Abundance at z > 4

We present the first spectroscopic measurement of multiple rest-frame optical emission lines at z > 4. During the MOSFIRE Deep Evolution Field survey, we observed the galaxy GOODSN-17940 with the Keck I/MOSFIRE spectrograph. The K-band spectrum of GOODSN-17940 includes significant detections of the [O II]λλ3726,3729, [Ne III]λ3869, and Hγ emission lines and a tentative detection of Hδ, indicating zspec = 4.4121. GOODSN-17940 is an actively star-forming z > 4 galaxy based on its K-band spectrum and broadband spectral energy distribution. A significant excess relative to the surrounding continuum is present in the Spitzer/IRAC channel 1 photometry of GOODSN-17940, due primarily to strong Hα emission with a rest-frame equivalent width of EW(Hα) = 1200 Å. Based on the assumption of 0.5 Ze models and the Calzetti attenuation curve, GOODSN-17940 is characterized by M* = 5.0 ^ +4.3, -0.2 x 10^9 M⊙ The Balmer decrement inferred from Hα/Hγ is used to dust correct the Hα emission, yielding SFR (Hα) = 320 ^ +190, -140 M⊙ yr^-1.These M* and star formation rate (SFR) values place GOODSN-17940 an order of magnitude in SFR above the z ∼ 4 star-forming “main sequence.” Finally, we use the observed ratio of [Ne III]/[O II] to estimate the nebular oxygen abundance in GOODSN-17940, finding O/H ∼ 0.2 (O/H)e. Combining our new [Ne III]/[O II] measurement with those from stacked spectra at z ∼ 0, 2, and 3, we show that GOODSN-17940 represents an extension to z > 4 of the evolution toward higher [Ne III]/[O II] (i.e., lower O/H) at fixed stellar mass. It will be possible to perform the measurements presented here out to z ∼ 10 using the James Webb Space Telescop