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Abstract:

We present Lyα and ultraviolet (UV)-continuum luminosity functions (LFs) of galaxies and active galactic nuclei (AGNs) at z = 2.0-3.5 determined by the untargeted optical spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in 11.4 deg2 of fiber spectra sky coverage, obtaining 18,320 galaxies spectroscopically identified with Lyα emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s-1) Lyα emission lines. We derive the Lyα (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in (-27 < MUV < -20) by the 1/Vmax estimator. Our results reveal that the bright-end hump of the Lyα LF is composed of type 1 AGNs. In conjunction with previous spectroscopic results at the faint end, we measure a slope of the best-fit Schechter function to be αSch=-1.70-0.14+0.13, which indicates that αSch steepens from z = 2-3 toward high redshift. Our UV LF agrees well with previous AGN UV LFs and extends to faint-AGN and bright-galaxy regimes. The number fraction of Lyα-emitting objects (XLAE) increases from MUV∗ ∼ -21 to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that XLyα decreases from faint magnitudes to MUV∗, suggesting a valley in the XLyα-magnitude relation at MUV∗. Comparing our UV LF of type 1 AGNs at z = 2-3 with those at z = 0, we find that the number density of faint (MUV > -21) type 1 AGNs increases from z ∼ 2 to 0, as opposed to the evolution of bright (MUV < -21) type 1 AGNs, suggesting AGN downsizing in the rest-frame UV luminosity.

Abstract:

We present the evolution of the star formation dispersion–stellar mass relation (σ_SFR–M_⋆) in the DEVILS D10 region using new measurements derived using the PROSPECT spectral energy distribution fitting code. We find that σ_SFR–M_⋆ shows the characteristic ‘U-shape’ at intermediate stellar masses from 0.1 < z < 0.7 for a number of metrics, including using the deconvolved intrinsic dispersion. A physical interpretation of this relation is the combination of stochastic star formation and stellar feedback causing large scatter at low stellar masses and AGN feedback causing asymmetric scatter at high stellar masses. As such, the shape of this distribution and its evolution encodes detailed information about the astrophysical processes affecting star formation, feedback and the lifecycle of galaxies. We find that the stellar mass that the minimum σ_SFR occurs evolves linearly with redshift, moving to higher stellar masses with increasing lookback time and traces the turnover in the star-forming sequence. This minimum σ_SFR point is also found to occur at a fixed specific star formation rate (sSFR) at all epochs (sSFR ∼ 10^−9.6 Gyr⁻¹). The physical interpretation of this is that there exists a maximum sSFR at which galaxies can internally self-regulate on the tight sequence of star formation. At higher sSFRs, stochastic stellar processes begin to cause galaxies to be pushed both above and below the star-forming sequence leading to increased SFR dispersion. As the Universe evolves, a higher fraction of galaxies will drop below this sSFR threshold, causing the dispersion of the low stellar mass end of the star-forming sequence to decrease with time.

Abstract:

We present the 1.4 GHz radio luminosity functions (RLFs) of galaxies in the Cosmic Evolution Survey (COSMOS) field, measured above and below the 5σ detection threshold, using a Bayesian model-fitting technique. The radio flux densities from Very Large Array (VLA)-COSMOS 3-GHz data are extracted at the position of stellar-mass-selected galaxies. We fit a local RLF model, which is a combination of active galactic nuclei and star-forming galaxies (SFGs), in 10 redshift bins with a pure luminosity evolution model. Our RLF exceeds previous determinations at low radio luminosities at z < 1.6 with the same radio data, due to our ability to directly constrain the knee and faint-end slope of the RLF. Beyond z ∼2, we find that the SFG part of the RLF exhibits a negative evolution (L∗ moves to lower luminosities) due to the decrease in low stellar-mass galaxies in our sample at high redshifts. From the RLF for SFGs, we determine the evolution in the cosmic star formation rate density (SFRD), which we find to be consistent with the established behaviour up to z ∼1 using far-infrared data, but exceeds that from the previous radio-based work for the reasons highlighted above. Beyond z ∼1.5 the cosmic SFRD declines. We note that the relation between radio luminosity and star formation rate is crucial in measuring the cosmic SFRD from radio data at z > 1.5. We investigate the effects of stellar mass on the total RLF by splitting our sample into low (108.5 ≤ M/M ≤ 1010) and high ($Mgt 10^{10}, mathrm{M}_{odot }$) stellar-mass subsets. We find that the SFRD is dominated by sources in the high stellar masses bin, at all redshifts.

Abstract:

MIGHTEE is a galaxy evolution survey using siltaneous radio continuum, spectropolarimetry, and spectral line observations from the South African MeerKAT telescope. When complete, the survey will image 20 deg2 over the COSMOS, E-CDFS, ELAIS-S1, and XMM-Newton Large Scale Structure field (XMM-LSS) extragalactic deep fields with a central frequency of 1284 MHz. These were selected based on the extensive ltiwavelength data sets from numerous existing and forthcoming observational campaigns. Here, we describe and validate the data processing strategy for the total intensity continuum aspect of MIGHTEE, using a single deep pointing in COSMOS (1.6 deg2) and a three-pointing mosaic in XMM-LSS (3.5 deg2). The processing includes the correction of direction-dependent effects, and results in theal noise levels below 2 ${}$Jy beam-1 in both fields, limited in the central regions by classical confusion at 8 arcsec angular resolution, and meeting the survey specifications. We also produce images at 5 arcsec resolution that are 3 times shallower. The resulting image products fo the basis of the Early Science continuum data release for MIGHTEE. From these images we extract catalogues containing 9896 and 20 274 radio components in COSMOS and XMM-LSS, respectively. We also process a close-packed mosaic of 14 additional pointings in COSMOS and use these in conjunction with the Early Science pointing to investigate methods for primary beam correction of broad-band radio images, an analysis that is of relevance to all full-band MeerKAT continuum observations, and wide-field interferometric imaging in general. A public release of the MIGHTEE Early Science continuum data products accompanies this article.

Abstract:

We present a novel 2D flux density model for observed H i emission lines combined with a Bayesian stacking technique to measure the baryonic Tully-Fisher relation below the nominal detection threshold. We simulate a galaxy catalogue, which includes H i lines described with either Gaussian or busy function profiles, and H i data cubes with a range of noise and survey areas similar to the MeerKAT International Giga-Hertz Tiered Extragalactic Exploration (MIGHTEE) survey. With prior knowledge of redshifts, stellar masses, and inclinations of spiral galaxies, we find that our model can reconstruct the input baryonic Tully-Fisher parameters (slope and zero-point) most accurately in a relatively broad redshift range from the local Universe to z = 0.3 for all the considered levels of noise and survey areas and up to z = 0.55 for a nominal noise of 90 μJy/channel over 5 deg2. Our model can also determine the MHI - M∗ relation for spiral galaxies beyond the local Universe and account for the detailed shape of the H I emission line, which is crucial for understanding the dynamics of spiral galaxies. Thus, we have developed a Bayesian stacking technique for measuring the baryonic Tully-Fisher relation for galaxies at low stellar and/or H I masses and/or those at high redshift, where the direct detection of H I requires prohibitive exposure times.