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Register a new userThe clustering of H$beta$+[OIII] and [OII] emitters since $z sim 5$: dependencies with line luminosity and stellar mass
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Ali Ahmad Khostovan
Publication date
2017
fields
Physics
and research's language is
English
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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.
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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 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.
We investigate the dependence of galaxy clustering at $z sim 4 - 7$ on UV-luminosity and stellar mass. Our sample consists of $sim$ 10,000 Lyman-break galaxies (LBGs) in the XDF and CANDELS fields. As part of our analysis, the $M_star - M_{rm UV}$ relation is estimated for the sample, which is found to have a nearly linear slope of $dlog_{10} M_star / d M_{rm UV} sim 0.44$. We subsequently measure the angular correlation function and bias in different stellar mass and luminosity bins. We focus on comparing the clustering dependence on these two properties. While UV-luminosity is only related to recent starbursts of a galaxy, stellar mass reflects the integrated build-up of the whole star formation history, which should make it more tightly correlated with halo mass. Hence, the clustering segregation with stellar mass is expected to be larger than with luminosity. However, our measurements suggest that the segregation with luminosity is larger with $simeq 90%$ confidence (neglecting contributions from systematic errors). We compare this unexpected result with predictions from the textsc{Meraxes} semi-analytic galaxy formation model. Interestingly, the model reproduces the observed angular correlation functions, and also suggests stronger clustering segregation with luminosity. The comparison between our observations and the model provides evidence of multiple halo occupation in the small scale clustering.
Recent surveys have identified a seemingly ubiquitous population of galaxies with elevated [OIII]/H$beta$ emission line ratios at $z > 1$, though the nature of this phenomenon continues to be debated. The [OIII]/H$beta$ line ratio is of interest because it is a main component of the standard diagnostic tools used to differentiate between active galactic nuclei (AGN) and star-forming galaxies, as well as the gas-phase metallicity indicators $O_{23}$ and $R_{23}$. Here, we investigate the primary driver of increased [OIII]/H$beta$ ratios by median-stacking rest-frame optical spectra for a sample of star-forming galaxies in the 3D-HST survey in the redshift range $zsim1.4-2.2$. Using $N = 4220$ star-forming galaxies, we stack the data in bins of mass and specific star formation rates (sSFR) respectively. After accounting for stellar Balmer absorption, we measure [OIII]$lambda5007$AA/H$beta$ down to $mathrm{M} sim 10^{9.2} mathrm{M_odot}$ and sSFR $sim 10^{-9.6} mathrm{yr}^{-1}$, more than an order of magnitude lower than previous work at similar redshifts. We find an offset of $0.59pm0.05$ dex between the median ratios at $zsim2$ and $zsim0$ at fixed stellar mass, in agreement with existing studies. However, with respect to sSFR, the $z sim 2$ stacks all lie within 1$sigma$ of the median SDSS ratios, with an average offset of only $-0.06pm 0.05$. We find that the excitation properties of galaxies are tightly correlated with their sSFR at both $zsim2$ and $zsim0$, with a relation that appears to be roughly constant over the last 10 Gyr of cosmic time.
We study the angular correlation function of star-forming galaxies and properties of their host dark matter halos at z>1 using the Hyper-Suprime Cam (HSC) SSP survey. We use [OII] emitters identified using two narrow-band (NB) filters, NB816 and NB921, in the Deep/UltraDeep layers, which respectively cover large angular areas of 16.3 deg^2 and 16.9 deg^2. Our sample contains 8302 and 9578 [OII] emitters at z=1.19 (NB816) and z=1.47 (NB921), respectively. We detect a strong clustering signal over a wide angular range, 0.001 < theta < 1 [deg], with the bias $b=1.61^{+0.13}_{-0.11}$ (z=1.19) and $b=2.09^{+0.17}_{-0.15}$ (z=1.47). We also find a clear deviation of the correlation from a simple power-law form. To interpret the measured clustering signal, we adopt a halo occupation distribution (HOD) model that is constructed to explain the spatial distribution of galaxies selected by a star formation rate. The observed correlation function and number density are simultaneously explained by the best-fitting HOD model. From the constrained HOD model, the average mass of halos hosting the [OII] emitters is derived to be $log{M_{eff}/(h^{-1}M_odot)}=12.70^{+0.09}_{-0.07}$ and $12.61^{+0.09}_{-0.05}$ at z=1.19 and 1.47, respectively, which will become halos with the present-day mass, $Msim 1.5 times 10^{13}h^{-1}M_odot$. The satellite fraction of the [OII] emitter sample is found to be $f_{sat}sim 0.15$. All these values are consistent with the previous studies of similar samples, but we obtain tighter constraints even in a larger parameter space due to the larger sample size from the HSC. The results obtained for host halos of [OII] emitters in this paper enable the construction of mock galaxy catalogs and the systematic forecast study of cosmological constraints from upcoming emission line galaxy surveys such as the Subaru PFS survey.
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