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Register a new userA large, deep 3 deg$^2$ survey of H$alpha$, [OIII], and [OII] emitters from LAGER: constraining luminosity functions
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Ali Ahmad Khostovan
Publication date
2020
fields
Physics
and research's language is
English
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We present our measurements of the H$alpha$, [OIII], and [OII] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 $z = 0.47$ H$alpha$-, 3933 $z = 0.93$ [OIII]-, and 5367 $z = 1.59$ [OII]-selected emission line galaxies in a single 3 deg$^2$ CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5$sigma$ depths of $8.2times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ and comoving volumes of $(1-7)times10^{5}$ Mpc$^3$ making our survey one of the deepest narrowband surveys. We measure the observed luminosity functions and find best-fits of $phi^star = 10^{-3.16pm0.09}$ Mpc$^{-3}$ and $L^star = 10^{41.72pm0.09}$ erg s$^{-1}$ for H$alpha$, $phi^star = 10^{-2.16^{+0.10}_{-0.12}}$ Mpc$^{-3}$ and $L^star = 10^{41.38^{+0.07}_{-0.06}}$ erg s$^{-1}$ for [OIII], and $phi^star = 10^{-1.97^{+0.07}_{-0.07}}$ Mpc$^{-3}$ and $L^star = 10^{41.66pm0.03}$ erg s$^{-1}$ for [OII], with $alpha$ fixed to $-1.75$, $-1.6$, and $-1.3$, respectively. An excess of bright $> 10^{42}$ erg s$^{-1}$ [OIII] emitters is observed and may be due to AGN contamination. Dust corrections are applied assuming $A_{rm{H}alpha} = 1$ mag. We also design our own empirical rest-frame $g - r$ calibration using SDSS DR12 data, test it against our $z = 0.47$ H$alpha$ emitters with $z$COSMOS $1$D spectra, and calibrate it for $(g - r)$ between $-0.8$ and $1.3$ mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as $log_{10}rho_{rm{SFR}}/(rm{M}_odot rm{yr}^{-1} rm{Mpc}^{-3}) = -1.63pm0.04$, $-1.07pm0.06$, and $-0.90pm0.10$ for H$alpha$, [OIII], and [OII], respectively. We find our [OIII] and [OII] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multi-wavelength SFRDs, while the H$alpha$ sample traces $sim 70$ percent of the total $z = 0.47$ SFRD.
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We present results from the largest contiguous narrow-band survey in the near-infrared. We have used WIRCam/CFHT and the lowOH2 filter (1.187$pm$0.005 $mu$m) to survey ~10 deg$^2$ of contiguous extragalactic sky in the SA22 field. A total of ~6000 candidate emission-line galaxies are found. We use deep ugrizJK data to obtain robust photometric redshifts. We combine our data with the High-redshift Emission Line Survey (HiZELS), explore spectroscopic surveys (VVDS, VIPERS) and obtain our own spectroscopic follow-up with KMOS, FMOS and MOSFIRE to derive large samples of high-redshift emission-line selected galaxies: 3471 H$alpha$ emitters at z=0.8, 1343 [OIII]+H$beta$ emitters at z=1.4 and 572 [OII] emitters at z=2.2. We probe co-moving volumes of >10$^6$ Mpc$^3$ and find significant over-densities, including an 8.5$sigma$ (spectroscopically confirmed) over-density of H$alpha$ emitters at z=0.81. We derive H$alpha$, [OIII]+H$beta$ and [OII] luminosity functions at z=0.8,1.4,2.2, respectively, and present implications for future surveys such as Euclid. Our uniquely large volumes/areas allow us to sub-divide the samples in thousands of randomised combinations of areas and provide a robust empirical measurement of sample/cosmic variance. We show that surveys for star-forming/emission-line galaxies at a depth similar to ours can only overcome cosmic-variance (errors <10%) if they are based on volumes >5x10$^{5}$ Mpc$^{3}$; errors on $L^*$ and $phi^*$ due to sample (cosmic) variance on surveys probing ~10$^4$ Mpc$^{3}$ and ~10$^5$ Mpc$^{3}$ are typically very high: ~300% and ~40-60%, respectively.
We investigate the evolution of the H$beta$+[OIII] and [OII] luminosity functions from $z sim 0.8$ to $sim5$ in four redshift slices per emission line using data from the High-{it z} Emission Line Survey (HiZELS). This is the first time that the H$beta$+[OIII] and [OII] luminosity functions have been studied at these redshifts in a self-consistent analysis. This is also the largest sample of [OII] and H$beta$+[OIII] emitters (3475 and 3298 emitters, respectively) in this redshift range, with large co-moving volumes $sim 1 times 10^6$ Mpc$^{-3}$ in two independent volumes (COSMOS and UDS), greatly reducing the effects of cosmic variance. The emitters were selected by a combination of photometric redshift and color-color selections, as well as spectroscopic follow-up, including recent spectroscopic observations using DEIMOS and MOSFIRE on the Keck Telescopes and FMOS on Subaru. We find a strong increase in $L_star$ and a decrease in $phi_star$ for both H$beta$+[OIII] and [OII] emitters. We derive the [OII] star-formation history of the Universe since $zsim5$ and find that the cosmic SFRD rises from $z sim 5$ to $sim 3$ and then drops towards $z sim 0$. We also find that our star-formation history is able to reproduce the evolution of the stellar mass density up to $zsim 5$ based only on a single tracer of star-formation. When comparing the H$beta$+[OIII] SFRDs to the [OII] and H$alpha$ SFRD measurements in the literature, we find that there is a remarkable agreement, suggesting that the H$beta$+[OIII] sample is dominated by star-forming galaxies at high-$z$ rather than AGNs.
We investigate the clustering properties of $sim 7000$ H$beta$+[OIII] and [OII] narrowband-selected emitters at $z sim 0.8 - 4.7$ from the High-$z$ Emission Line Survey. We find clustering lengths, $r_0$, of $1.5 - 4.0h^{-1}$ Mpc and minimum dark matter halo masses of $10^{10.7 - 12.1}rm{M}_odot$ for our $z = 0.8 - 3.2$ H$beta$+[OIII] emitters and $r_0 sim 2.0 - 8.3h^{-1}$ Mpc and halo masses of $10^{11.5 - 12.6}rm{M}_odot$ for our $z = 1.5 - 4.7$ [OII] emitters. We find $r_0$ to strongly increase both with increasing line luminosity and redshift. By taking into account the evolution of the characteristic line luminosity, $L^star(z)$, and using our model predictions of halo mass given $r_0$, we find a strong, redshift-independent increasing trend between $L/L^star(z)$ and minimum halo mass. The faintest H$beta$+[OIII] emitters are found to reside in $10^{9.5}rm{M}_odot$ halos and the brightest emitters in $10^{13.0}rm{M}_odot$ halos. For [OII] emitters, the faintest emitters are found in $10^{10.5} rm{M}_odot$ halos and the brightest emitters in $10^{12.6}rm{M}_odot$ halos. A redshift-independent stellar mass dependency is also observed where the halo mass increases from $10^{11}rm{M}_odot$ to $10^{12.5} rm{M}_odot$ for stellar masses of $10^{8.5}rm{M}_odot$ to $10^{11.5}rm{M}_odot$, respectively. We investigate the interdependencies of these trends by repeating our analysis in a $L_textrm{line} - rm{M}_textrm{star}$ grid space for our most populated samples (H$beta$+[OIII] $z = 0.84$ and [OII] $z = 1.47$) and find that the line luminosity dependency is stronger than the stellar mass dependency on halo mass. For $L > L^star$ emitters at all epochs, we find a relatively flat trend with halo masses of $10^{12.5 - 13}rm{M}_odot$ which may be due to quenching mechanisms in massive halos which is consistent with a transitional halo mass predicted by models.
We present a spectroscopic survey of Ly$alpha$ emitters (LAEs) at $zapprox3.1$ in the Subaru MM-Newton Deep Survey Field. This field has deep imaging data in a series of broad and narrow bands, including two adjacent narrow bands NB497 and NB503 that have allowed us to efficiently select LAE candidates at $zapprox3.1$. Using spectroscopic observations on MMT Hectospec and Magellan M2FS, we obtained a sample of 166 LAEs at $zapprox3.1$ over an effective area of $sim$1.2 deg$^2$, including 16 previously known LAEs. This is so far the largest (spectroscopically confirmed) sample of LAEs at this redshift. We make use of the secure redshifts and multi-band data to measure spectral properties such as Ly$alpha$ luminosity and rest-frame UV slope. We derive a robust Ly$alpha$ luminosity function (LF) that spans a luminosity range from $sim10^{42.0}$ to $>10^{43.5}$ erg s$^{-1}$. Significant overdense and underdense regions are detected in our sample, but the area coverage is wide enough to largely suppress the effect from such cosmic variance. Our Ly$alpha$ LF is generally consistent with those from previous studies at $z sim 3.1$. At the brightest end of the LF, there is a tentative detection of a density excess that is not well described by the Schechter function. The comparison with the LFs at other redshifts suggests that the Ly$alpha$ LF does not show significant evolution at $2<z<5$. Finally, we build the composite spectra of the LAEs and detect the NVI and CIV doublet emission lines at significance of $sim 4 sigma$, suggesting very hard radiation fields in (some of) these LAEs.
We measure the evolution of the rest-frame UV luminosity function (LF) and the stellar mass function (SMF) of Lyman-alpha (Lya) emitters (LAEs) from z~2 to z~6 by exploring ~4000 LAEs from the SC4K sample. We find a correlation between Lya luminosity (LLya) and rest-frame UV (M_UV), with best-fit M_UV=-1.6+-0.2 log10(LLya/erg/s)+47+-12 and a shallower relation between LLya and stellar mass (Mstar), with best-fit log10( Mstar/Msun)=0.9+-0.1 log10(LLya/erg/s)-28+-4.0. An increasing LLya cut predominantly lowers the number density of faint M_UV and low Mstar LAEs. We estimate a proxy for the full UV LFs and SMFs of LAEs with simple assumptions of the faint end slope. For the UV LF, we find a brightening of the characteristic UV luminosity (M_UV*) with increasing redshift and a decrease of the characteristic number density (Phi*). For the SMF, we measure a characteristic stellar mass (Mstar*/Msun) increase with increasing redshift, and a Phi* decline. However, if we apply a uniform luminosity cut of log10 (LLya/erg/s) >= 43.0, we find much milder to no evolution in the UV and SMF of LAEs. The UV luminosity density (rho_UV) of the full sample of LAEs shows moderate evolution and the stellar mass density (rho_M) decreases, with both being always lower than the total rho_UV and rho_M of more typical galaxies but slowly approaching them with increasing redshift. Overall, our results indicate that both rho_UV and rho_M of LAEs slowly approach the measurements of continuum-selected galaxies at z>6, which suggests a key role of LAEs in the epoch of reionisation.
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