Galaxy evolution in the VIMOS public extragalactic redshift survey (VIPERS)

In this work I present the first measurements of the galaxy stellar mass function (GSMF) from the first public release of the VIPERS catalogue, containing ∼55,000 objects. First, I present the survey design, its scientific goal, the redshift measurements and validation. Then, I provide details about the estimate of galaxy stellar masses, star formation rates, and other physical quantities. I derive the GSMF of different galaxy types (e.g. active and passive galaxies) and as a function of the environment (defined through the local galaxy density contrast). These estimates represent new observational evidence useful to characterise the mechanism of galaxy evolution

An alternate approach to measure specific star formation rates at 2<z<7

We trace the specific star formation rate (sSFR) of massive star-forming galaxies ($\gtrsim\!10^{10}\,\mathcal{M}_\odot$) from $z\sim2$ to 7. Our method is substantially different from previous analyses, as it does not rely on direct estimates of star formation rate, but on the differential evolution of the galaxy stellar mass function (SMF). We show the reliability of this approach by means of semi-analytical and hydrodynamical cosmological simulations. We then apply it to real data, using the SMFs derived in the COSMOS and CANDELS fields. We find that the sSFR is proportional to $(1+z)^{1.1\pm0.2}$ at $z>2$, in agreement with other observations but in tension with the steeper evolution predicted by simulations from $z\sim4$ to 2. We investigate the impact of several sources of observational bias, which however cannot account for this discrepancy. Although the SMF of high-redshift galaxies is still affected by significant errors, we show that future large-area surveys will substantially reduce them, making our method an effective tool to probe the massive end of the main sequence of star-forming galaxies.Comment: ApJ accepte

SILVERRUSH. V. Census of Lyα, [O III] λ5007, Hα, and [C II] 158 μm Line Emission with ~1000 LAEs at z = 4.9–7.0 Revealed with Subaru/HSC

We investigate Lyα, [O III] λ5007, Hα, and [C II] 158 μm emission from 1124 galaxies at z = 4.9–7.0. Our sample is composed of 1092 Lyα emitters (LAEs) at z = 4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper-Suprime-Cam (HSC) narrowband surveys covered by Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) and 34 galaxies at z = 5.148–7.508 with deep ALMA [C II] 158 μm data in the literature. Fluxes of strong rest-frame optical lines of [O III] and Hα (Hβ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 μm photometry. At z = 4.9, we find that the rest-frame Hα equivalent width and the Lyα escape fraction f_(Lyα) positively correlate with the rest-frame Lyα equivalent width EW^0_( Lyα). The f_(Lyα)-EW^0_( Lyα) correlation is similarly found at z ~ 0–2, suggesting no evolution of the correlation over z ≃ 0–5. The typical ionizing photon production efficiency of LAEs is log(ξ_(ion)/[Hz erg^(−1)]) ≃ 25.5, significantly (60%–100%) higher than those of LBGs at a given UV magnitude. At z = 5.7–7.0, there exists an interesting turnover trend that the [O III]/Hα flux ratio increases in EW^0_( Lyα) ≃ 0-30 Å and then decreases out to EW^0_( Lyα) ≃ 130 Å. We also identify an anticorrelation between a ratio of [C II] luminosity to star formation rate (L [C II]/SFR) and EW^0_( Lyα) at the >99% confidence level.. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models and find that a simple anticorrelation between EW^0_( Lyα) and metallicity explains self-consistently all of the correlations of Lyα, Hα, [O III]/Hα, and [C II] identified in our study, indicating detections of metal-poor (~0.03 Z⊙) galaxies with EW^0_( Lyα) ≃ 200 Å

A Method to Distinguish Quiescent and Dusty Star-forming Galaxies with Machine Learning

Large photometric surveys provide a rich source of observations of quiescent galaxies, including a surprisingly large population at z > 1. However, identifying large, but clean, samples of quiescent galaxies has proven difficult because of their near-degeneracy with interlopers such as dusty, star-forming galaxies. We describe a new technique for selecting quiescent galaxies based upon t-distributed stochastic neighbor embedding (t-SNE), an unsupervised machine-learning algorithm for dimensionality reduction. This t-SNE selection provides an improvement both over UVJ, removing interlopers that otherwise would pass color selection, and over photometric template fitting, more strongly toward high redshift. Due to the similarity between the colors of high- and low-redshift quiescent galaxies, under our assumptions, t-SNE outperforms template fitting in 63% of trials at redshifts where a large training sample already exists. It also may be able to select quiescent galaxies more efficiently at higher redshifts than the training sample

SILVERRUSH. V. Census of Lyα, [O III] λ5007, Hα, and [C II] 158 μm Line Emission with ~1000 LAEs at z = 4.9–7.0 Revealed with Subaru/HSC

We investigate Lyα, [O III] λ5007, Hα, and [C II] 158 μm emission from 1124 galaxies at z = 4.9–7.0. Our sample is composed of 1092 Lyα emitters (LAEs) at z = 4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper-Suprime-Cam (HSC) narrowband surveys covered by Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) and 34 galaxies at z = 5.148–7.508 with deep ALMA [C II] 158 μm data in the literature. Fluxes of strong rest-frame optical lines of [O III] and Hα (Hβ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 μm photometry. At z = 4.9, we find that the rest-frame Hα equivalent width and the Lyα escape fraction f_(Lyα) positively correlate with the rest-frame Lyα equivalent width EW^0_( Lyα). The f_(Lyα)-EW^0_( Lyα) correlation is similarly found at z ~ 0–2, suggesting no evolution of the correlation over z ≃ 0–5. The typical ionizing photon production efficiency of LAEs is log(ξ_(ion)/[Hz erg^(−1)]) ≃ 25.5, significantly (60%–100%) higher than those of LBGs at a given UV magnitude. At z = 5.7–7.0, there exists an interesting turnover trend that the [O III]/Hα flux ratio increases in EW^0_( Lyα) ≃ 0-30 Å and then decreases out to EW^0_( Lyα) ≃ 130 Å. We also identify an anticorrelation between a ratio of [C II] luminosity to star formation rate (L [C II]/SFR) and EW^0_( Lyα) at the >99% confidence level.. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models and find that a simple anticorrelation between EW^0_( Lyα) and metallicity explains self-consistently all of the correlations of Lyα, Hα, [O III]/Hα, and [C II] identified in our study, indicating detections of metal-poor (~0.03 Z⊙) galaxies with EW^0_( Lyα) ≃ 200 Å

A Method to Distinguish Quiescent and Dusty Star-forming Galaxies with Machine Learning

Large photometric surveys provide a rich source of observations of quiescent galaxies, including a surprisingly large population at z > 1. However, identifying large, but clean, samples of quiescent galaxies has proven difficult because of their near-degeneracy with interlopers such as dusty, star-forming galaxies. We describe a new technique for selecting quiescent galaxies based upon t-distributed stochastic neighbor embedding (t-SNE), an unsupervised machine-learning algorithm for dimensionality reduction. This t-SNE selection provides an improvement both over UVJ, removing interlopers that otherwise would pass color selection, and over photometric template fitting, more strongly toward high redshift. Due to the similarity between the colors of high- and low-redshift quiescent galaxies, under our assumptions, t-SNE outperforms template fitting in 63% of trials at redshifts where a large training sample already exists. It also may be able to select quiescent galaxies more efficiently at higher redshifts than the training sample

Photometric Redshift Calibration Requirements for WFIRST Weak Lensing Cosmology: Predictions from CANDELS

In order for Wide-Field Infrared Survey Telescope (WFIRST) and other Stage IV dark energy experiments (e.g., Large Synoptic Survey Telescope; LSST, and Euclid) to infer cosmological parameters not limited by systematic errors, accurate redshift measurements are needed. This accuracy can be met by using spectroscopic subsamples to calibrate the photometric redshifts for the full sample. In this work we employ the Self Organizing Map (SOM) spectroscopic sampling technique, to find the minimal number of spectra required for the WFIRST weak lensing calibration. We use galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) to build the LSST+WFIRST lensing analog sample of ~36 k objects and train the LSST+WFIRST SOM. We find that 26% of the WFIRST lensing sample consists of sources fainter than the Euclid depth in the optical, 91% of which live in color cells already occupied by brighter galaxies. We demonstrate the similarity between faint and bright galaxies as well as the feasibility of redshift measurements at different brightness levels. Our results suggest that the spectroscopic sample acquired for calibration to the Euclid depth is sufficient for calibrating the majority of the WFIRST color-space. For the spectroscopic sample to fully represent the synthetic color-space of WFIRST, we recommend obtaining additional spectroscopy of ~0.2-1.2 k new sources in cells occupied by mostly faint galaxies. We argue that either the small area of the CANDELS fields and the small overall sample size or the large photometric errors might be the reason for no/less bright galaxies mapped to these cells. Acquiring the spectra of these sources will confirm the above findings and will enable the comprehensive calibration of the WFIRST color-redshift relation.Comment: 13 pages, 15 figures, accepted for publication in Ap

Photometric Redshift Calibration Requirements for WFIRST Weak-lensing Cosmology: Predictions from CANDELS

In order for the Wide-Field Infrared Survey Telescope (WFIRST) and other stage IV dark energy experiments (e.g., Large Synoptic Survey Telescope, LSST; and Euclid) to infer cosmological parameters not limited by systematic errors, accurate redshift measurements are needed. This accuracy can be met by using spectroscopic subsamples to calibrate the photometric redshifts for the full sample. In this work, we find the minimal number of spectra required for the WFIRST weak-lensing redshift calibration by employing the Self-Organizing Map (SOM) spectroscopic sampling technique. We use galaxies from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) to build the LSST+WFIRST lensing analog sample of ~36,000 objects and to train the LSST+WFIRST SOM. We find that 26% of the WFIRST lensing sample consists of sources fainter than the Euclid depth in the optical, 91% of which live in color cells already occupied by brighter galaxies. We demonstrate the similarity between faint and bright galaxies as well as the feasibility of redshift measurements at different brightness levels. Our results suggest that the spectroscopic sample acquired for calibration to the Euclid depth is sufficient for calibrating the majority of the WFIRST color space. For the spectroscopic sample to fully represent the synthetic color space of WFIRST, we recommend obtaining additional spectroscopy of ~0.2–1.2k new sources in cells occupied by mostly faint galaxies. We argue that either the small area of the CANDELS fields and the small overall sample size or the large photometric errors might be the reason for no/fewer bright galaxies mapped to these cells. Acquiring the spectra of these sources will confirm the above findings and will enable the comprehensive calibration of the WFIRST color–redshift relation

Balmer Break Galaxy Candidates at z ∼ 6: A Potential View on the Star Formation Activity at z ≳ 14

We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z ~ 6 over a 0.41 deg² effective area in the COSMOS field. Based on rich imaging data, including data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K–[3.6] colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z ~ 6, although contamination from active galactic nuclei at z ~ 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z ~ 6 have stellar masses of ≈5 × 10¹⁰ M_⊙ dominated by old stellar populations with ages of ≳ 700 Myr. Assuming that all three candidates are real BBGs at z ~ 6, we estimate the stellar mass density to be 2.4_(-1.3)^(+2.3) x {10⁴ M_⊙ Mpc⁻³. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z ~ 6. We estimate the star formation rate density (SFRD) contributed by progenitors of the BBGs to be 2.4–12 × 10⁻⁵ M_⊙ yr⁻¹ Mpc⁻³ at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8