arXiv subjects

Jae-Woo Kim

Publications and source records attributed to Jae-Woo Kim.

At least 37 records · Page 2Linked to original sources

arXiv2022

Circumnuclear Medium around the Central AGN in a Cool-Core Cluster, Abell 1644-South

We present the circumnuclear multi-phase gas properties of the brightest cluster galaxy (BCG) in the center of Abell 1644-South. A1644-S is the main cluster in a merging system, which is well known for X-ray hot gas sloshing in its core. The sharply peaked X-ray profile of A1644-S implies the presence of a strongly cooling gas core. In this study, we analyze ALMA CO (1-0) data, JVLA HI data, and KaVA 22 GHz data for the central region of A1644-S to probe the potential origin of the cool gas and its role in (re)powering the central active galactic nucleus (AGN). We find CO clumps distributed in an arc shape along the X-ray gas sloshing, which is suggestive of a connection between the cold gas and the hot intracluster medium (ICM). HI and CN are detected in absorption against the AGN continuum emission. The absorption dip is observed at the systemic velocity of the BCG with an extended, redshifted tail. Based on the spatial and spectral configurations of the HI, CN and CO gases, it is inferred that cool gas spirals into the core of the BCG, which is then fed to the central AGN. Indeed, our KaVA observation reveals a parsec-scale bipolar jet, implying that this AGN could have been (re)powered quite recently. Combining this, we suggest that some cold gas in A1644-S could have been formed from the cooling of the ICM, triggering the activity of the central AGN in the early development of a cool-core cluster.

astro-ph.GA↗

arXiv2022

Is Abell 2261 a fossil galaxy cluster in a transitional dynamical state?

Abell 2261 (A2661) is a well-studied fossil cluster, but previous studies give contradictory results on its dynamical states, such as its X-ray central entropy and magnitude gap. To improve our understanding of its dynamical state, we conduct multi-object spectroscopic observations with Hectospec on the MMT, covering an area out to 5 virial radii from the cluster center, and get improved completeness and membership. Using this new data, we calculate multiple dynamical indicators including gaussianity, distance offset, and velocity offset. These indicators suggest that A2261 is moderately relaxed. However, Dressler-Shectman test reveals a group candidate to the south, at a projected distance that is near the virial radius, and that overlaps with an X-ray tail-like feature. One of the galaxies associated with that group would be sufficiently bright to reduce the fossil magnitude gap. This raises the possibility that A2261 could have recently transit in fossil status, if the group had previously crossed the cluster and is only now found outside. In the cluster outskirts, we see an extended feature of galaxies located on the opposite side of the cluster to the group candidate. On even larger scales, we find this feature connects, both on the sky and in velocity space, with a long (~4.4Mpc) filamentary structure in the Sloan Digital Sky Survey data. This could support the idea that a group was fed into the cluster through the filament, temporarily breaking the fossil status, and resulting in a minor merger that weakly disturbed the intracluster medium of the cluster.

astro-ph.GA↗

arXiv2021

The variability of brightest cluster galaxies at high radio frequencies

Variability of a galaxy's core radio source can be a significant consequence of AGN accretion. However, this variability has not been well studied, particularly at high radio frequencies. As such, we report on a campaign monitoring the high radio frequency variability of 20 nearby, cool-core brightest cluster galaxies. From our representative sample, we show that most vary significantly over timescales of approximately one year and longer. Our highest cadence observations are at 15 GHz and are from the Owens Valley Radio Observatory (OVRO). They have a median time interval of 7 days and mostly span between 8 and 13 years. We apply a range of variability detection techniques to the sources' lightcurves to analyse changes on week to decade long timescales. Most notably, at least half of the sources show 20 per cent peak to trough variability on 3 year timescales, while at least a third vary by 60 per cent on 6 year timescales. Significant variability, which is important to studies of the Sunyaev-Zel'dovich Effect in the radio/sub-mm, is therefore a common feature of these sources. We also show how the variability relates to spectral properties at frequencies of up to 353 GHz using data from the Korean VLBI network (KVN), the NIKA2 instrument of the IRAM 30m telescope, and the SCUBA-2 instrument of the James Clerk Maxwell Telescope.

astro-ph.GA↗

arXiv2021

Intracluster Light Properties in a Fossil Cluster at z=0.47

Galaxy clusters contain a diffuse stellar component outside the cluster's galaxies, which is observed as faint intracluster light (ICL). Using Gemini/GMOS-N deep imaging and multi-object spectroscopy of a massive fossil cluster at a redshift of $z=0.47$, RX J105453.3+552102 (J1054), we improve the observational constraints on the formation mechanism of the ICL. We extract the ICL surface brightness and colour profiles out to 155 kpc from the brightest cluster galaxy (BCG) with a detection limit of 28.7 mag/arcsec$^2$ (1$σ$, 4.8" x 4.8"; i-band). The colour of the diffuse light is similar to that of the BCG and central bright galaxies out to $\sim$ 70 kpc, becoming slightly bluer toward the outside. We find that the ICL distribution shows better agreement with the spatial distribution of member galaxies than with the BCG-dominated cluster luminosity distribution. We report the ICL fraction of J1054 as $15.07 \pm 4.57 \%$ in the range of $60 \sim 155$ kpc from the BCG, which appears to be higher than the ICL fraction-redshift trend in previous studies. Our findings suggest that intracluster stars seems not to be explained by one dominant production mechanism. However, a significant fraction of the ICL of J1054 may have been generated from the outskirts of infalling/satellite galaxies more recently rather than by the BCG at the early stage of the cluster.

astro-ph.GA↗

arXiv2020

The SAMI Galaxy Survey: Kinematics of stars and gas in brightest group galaxies; the role of group dynamics

We study the stellar and gas kinematics of the brightest group galaxies (BGGs) in dynamically relaxed and unrelaxed galaxy groups for a sample of 154 galaxies in the SAMI galaxy survey. We characterize the dynamical state of the groups using the luminosity gap between the two most luminous galaxies and the BGG offset from the luminosity centroid of the group. We find that the misalignment between the rotation axis of gas and stellar components is more frequent in the BGGs in unrelaxed groups, although with quite low statistical significance. Meanwhile galaxies whose stellar dynamics would be classified as `regular rotators' based on their kinemetry are more common in relaxed groups. We confirm that this dependency on group dynamical state remains valid at fixed stellar mass and Sersic index. The observed trend could potentially originate from a differing BGG accretion history in virialised and evolving groups. Amongst the halo relaxation probes, the group BGG offset appears to play a stronger role than the luminosity gap on the stellar kinematic differences of the BGGs. However, both the group BGG offset and luminosity gap appear to roughly equally drive the misalignment between the gas and stellar component of the BGGs in one direction. This study offers the first evidence that the dynamical state of galaxy groups may influence the BGG's stellar and gas kinematics and calls for further studies using a larger sample with higher signal-to-noise.

astro-ph.GA↗

arXiv2020

The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at $z \sim 5$ in the ELAIS-N1 Field

The intergalactic medium (IGM) at $z\sim$ 5 to 6 is largely ionized, and yet the main source for the IGM ionization in the early universe is uncertain. Of the possible contributors are faint quasars with $-26 \lesssim M_{\rm 1450} \lesssim -23$, but their number density is poorly constrained at $z\sim5$. In this paper, we present our survey of faint quasars at $z\sim5$ in the European Large-Area {\it ISO} Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg$^2$ and examine if such quasars can be the dominant source of the IGM ionization. We use the deep optical/near-infrared data of the ELAIS-N1 field as well as the additional medium-band observations to find $z \sim 5$ quasars through a two-step approach using the broadband color selection, and SED fitting with the medium-band information included. Adopting Bayesian information criterion, we identify ten promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at $z\sim5$ and supporting the reliability of the quasar selection. Using the promising candidates, we derive the $z\sim5$ quasar luminosity function at $-26 \lesssim M_{\rm 1450} \lesssim -23$. The number density of faint $z\sim5$ quasars in the ELAIS-N1 field is consistent with several previous results that quasars are not the main contributors to the IGM-ionizing photons at $z\sim5$

astro-ph.GA↗

arXiv2019

More connected, more active: galaxy clusters and groups at z~1 and the connection between their quiescent galaxy fractions and large-scale environments

High-redshift galaxy clusters, unlike local counterparts, show diverse star formation activities. However, it is still unclear what keeps some of the high-redshift clusters active in star formation. To address this issue, we performed a multi-object spectroscopic (MOS) observation of 226 high-redshift (0.8 < z < 1.3) galaxies in galaxy cluster candidates and the areas surrounding them. Our spectroscopic observation reveals six to eight clusters/groups at z ~ 0.9 and z ~ 1.3. The redshift measurements demonstrate the reliability of our photometric redshift measurements, which in turn gives credibility for using photometric redshift members for the analysis of large-scale structures (LSSs). Our investigation of the large-scale environment (~10 Mpc) surrounding each galaxy cluster reveals LSSs --- structures up to ~10 Mpc scale --- around many of, but not all, the confirmed overdensities and the cluster candidates. We investigate the correlation between quiescent galaxy fraction of galaxy overdensities and their surrounding LSSs, with a larger sample of ~ 20 overdensities including photometrically selected overdensities at 0.6 < z < 0.9. Interestingly, galaxy overdensities embedded within these extended LSSs show a lower fraction of quiescent galaxies (~ 20 %) than isolated ones at similar redshifts (with a quiescent galaxy fraction of ~ 50 %). Furthermore, we find a possible indication that clusters/groups with a high quiescent galaxy fraction are more centrally concentrated. Based on these results, we suggest that LSSs are the main reservoirs of gas and star-forming galaxies to keep galaxy clusters fresh and extended in size at z ~ 1.

astro-ph.GA↗

arXiv2018

Medium-resolution Optical and Near-Infrared Spectral Atlas of 16 2MASS-selected NIR-red Active Galactic Nuclei at $z \sim 0.3$

We present medium-resolution spectra ($R \sim 2000$--4000) at 0.4--1.0\,$μ$m and 0.7--2.5\,$μ$m of 16 active galactic nuclei (AGNs) selected with red color in the near-infrared (NIR) of $J - K > 2.0$ mag at $z \sim 0.3$. We fit the H$β$, H$α$, P$β$, and P$α$ lines from these spectra to obtain their luminosities and line widths. We derive the $E(B-V)$ color excess values of the NIR-red AGNs using two methods, one based on the line-luminosity ratios and another based on the continuum slopes. The two $E(B-V)$ values agree with each other at rms dispersion $\sim$ 0.249. About half of the NIR-red AGNs have $g'-K < 5$ magnitude, and we find that these NIR red, but blue in optical-NIR AGNs, have $E(B-V) \sim 0$, suggesting that a significant fraction of the NIR color-selected red AGNs are unobscured or only mildly obscured. After correcting for the dust extinction, we estimate the black hole (BH) masses and the bolometric luminosities of the NIR-red AGNs using the Paschen lines to calculate their Eddington ratios ($λ_{\rm Edd}$). The median Eddington ratios of nine NIR-red AGNs ($\log (λ_{\rm Edd}) \simeq -0.654 \pm 0.176$) are only mildly higher than those of unobscured type 1 AGNs ($\log (λ_{\rm Edd}) \simeq -0.961 \pm 0.008$). Moreover, we find that the $M_{\rm BH}$--$σ_{\ast}$ relation for three NIR-red AGNs is consistent with that of unobscured type 1 AGNs at similar redshift. These results suggest that the NIR red color selection alone is not effective at picking up dusty, intermediate-stage AGNs.

astro-ph.GA↗

arXiv2018

The Infrared Medium-deep Survey. VI. Discovery of Faint Quasars at $z\sim5$ with a Medium-band-based Approach

The faint quasars with $M_{1450}>-24$ mag are known to hold the key to the determination of the ultraviolet emissivity for the cosmic re-ionization. But only a few have been identified so far because of the limitations on the survey data. Here, we present the first results of the $z\sim5$ faint quasar survey with the Infrared Medium-deep Survey (IMS), which covers $\sim100$ deg$^{2}$ areas in $J$-band to the depths of $J_{\rm AB}\sim23$ mag. To improve selection methods, the medium-band follow-up imaging has been carried out using the SED camera for QUasars in Early uNiverse (SQUEAN) on the Otto Struve 2.1 m Telescope. The optical spectra of the candidates were obtained with 8-m class telescopes. We newly discovered 10 quasars with $-25<M_{1450}<-23$ at $z\sim5$, among which three have been missed in a previous survey using the same optical data over the same area, implying the necessity for improvements in high redshift faint quasars selection. We derived photometric redshifts from the medium-band data, and find that they have high accuracies of $\langle|Δz|/(1+z)\rangle=0.016$. The medium-band-based approach allows us to rule out many of the interlopers that contaminate $\gtrsim20~\%$ of the broad-band-selected quasar candidates. These results suggest that the medium-band-based approach is a powerful way to identify $z\sim5$ quasars and measure their redshifts at high accuracy (1-2 %). It is also a cost-effective way to understand the contribution of quasars to the cosmic re-ionization history.

astro-ph.GA↗

arXiv2018

The Infrared Medium-deep Survey. IV. Low Eddington Ratio of A Faint Quasar at $z\sim6$: Not Every Supermassive Black Hole is Growing Fast in the Early Universe

To date, most of the luminous quasars known at $z\sim6$ have been found to be in maximal accretion with the Eddington ratios, $λ_{\rm{Edd}}\sim1$, suggesting enhanced nuclear activities in the early universe. However, this may not be the whole picture of supermassive black hole (SMBH) growth since previous studies have not reached on faint quasars that are more likely to harbor SMBHs with low $λ_{\rm{Edd}}$. To gain a better understanding on the accretion activities in quasars in the early universe, we obtained a deep near-infrared (NIR) spectrum of a quasar, IMS J220417.92+011144.8 (hereafter IMS J2204+0112), one of the faintest quasars that have been identified at $z\sim6$. From the redshifted C IV $λ1549$ emission line in the NIR spectrum, we find that IMS J2204+0112 harbors a SMBH with about a billion solar mass and $λ_{\rm{Edd}} \sim 0.1$, but with a large uncertainty in both quantities (0.41 dex). IMS J2204+0112 has one of the lowest Eddington ratios among quasars at $z\sim6$, but a common value among quasars at $z\sim2$. Its low $λ_{\rm{Edd}}$ can be explained with two scenarios; the SMBH growth from a stellar mass black hole through short-duration super-Eddington accretion events or from a massive black hole seed ($\sim10^{5}\,M_{\odot}$) with Eddington-limited accretion. NIR spectra of more faint quasars are needed to better understand the accretion activities of SMBHs at $z \sim 6$.

astro-ph.GA↗

arXiv2017

The Infrared Medium-deep Survey. III. Survey of Luminous Quasars at 4.7 $\leq$ z $\leq$ 5.4

We present our first results of the survey for high redshift quasars at $5 \lesssim {\rm z} \lesssim 5.7$. The search for quasars in this redshift range has been known to be challenging due to limitations of filter sets used in previous studies. We conducted a quasar survey for two specific redshift ranges, 4.60 $\leq$ z $\leq$ 5.40 and 5.50 $\leq$ z $\leq$ 6.05, using multi-wavelength data that include observations using custom-designed filters, $is$ and $iz$. Using these filters and a new selection technique, we were able to reduce the fraction of interlopers. Through optical spectroscopy, we confirmed seven quasars at 4.7 $\leq$ z $\leq$ 5.4 with $-27.4 < M_{1450} < -26.4$ which were discovered independently by another group recently. We estimated black hole masses and Eddington ratios of four of these quasars from optical and near-infrared spectra, and found that these quasars are undergoing nearly Eddington-limited accretion which is consistent with the rapid growth of supermassive black holes in luminous quasars at z $\sim$ 5.

astro-ph.GA↗

arXiv2017

The dependence of cluster galaxy properties on the central entropy of their host cluster

We present a study of the connection between brightest cluster galaxies (BCGs) and their host galaxy clusters. Using galaxy clusters at $0.1<z<0.3$ from the Hectospec Cluster Survey (HeCS) with X-ray information from the Archive of {\it Chandra} Cluster Entropy Profile Tables (ACCEPT), we confirm that BCGs in low central entropy clusters are well aligned with the X-ray center. Additionally, the magnitude difference between BCG and the 2nd brightest one also correlates with the central entropy of the intracluster medium. From the red-sequence (RS) galaxies, we cannot find significant dependence of RS color scatter and stellar population on the central entropy of the intracluster medium of their host cluster. However, BCGs in low entropy clusters are systematically less massive than those in high entropy clusters, although this is dependent on the method used to derive the stellar mass of BCGs. In contrast, the stellar velocity dispersion of BCGs shows no dependence on BCG activity and cluster central entropy. This implies that the potential of the BCG is established earlier and the activity leading to optical emission lines is dictated by the properties of the intracluster medium in the cluster core.

astro-ph.GA↗

arXiv2016

Massive Galaxies are Larger in Dense Environments: Environmental Dependence of Mass-Size Relation of Early-Type Galaxies

Under the $Λ$ cold dark matter ($Λ$CDM) cosmological models, massive galaxies are expected to be larger in denser environments through frequent hierarchical mergers with other galaxies. Yet, observational studies of low-redshift early-type galaxies have shown no such trend, standing as a puzzle to solve during the past decade. We analyzed 73,116 early-type galaxies at $0.1\leq z < 0.15$, adopting a robust nonparametric size measurement technique and extending the analysis to many massive galaxies. We find for the first time that local early-type galaxies heavier than $10^{11.2}M_{\odot}$ show a clear environmental dependence in mass-size relation, in such a way that galaxies are as much as 20-40% larger in densest environments than in underdense environments. Splitting the sample into the brightest cluster galaxies (BCGs) and non-BCGs does not affect the result. This result agrees with the $Λ$CDM cosmological simulations and suggests that mergers played a significant role in the growth of massive galaxies in dense environments as expected in theory.

astro-ph.GA↗

arXiv2015

Discovery of A Faint Quasar at z~6 and Implications for Cosmic Reionization

Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars ($M_{1450}>-24$ mag) at $z \gtrsim6$, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z~6 in a 12.5 deg$^{2}$ region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at $\sim8443~\rmÅ$, with emission lines redshifted to $z=5.944 \pm 0.002$ and rest-frame ultraviolet continuum magnitude $M_{1450}=-23.59\pm0.10$ AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z~6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars . This suggests that the number of $M_{1450}\sim-23$ mag quasars at z~6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.

astro-ph.GA↗

arXiv2015

The Very Early Light Curve of SN 2015F in NGC 2442: A Possible Detection of Shock-Heated Cooling Emission and Constraints on SN Ia Progenitor System

The main progenitor candidate of Type Ia supernovae (SNe Ia) is white dwarfs in binary systems where the companion star is another white dwarf (double degenerate system) or a less evolved non-degenerate star with R* >~ 0.1 Rsun (single degenerate system), but no direct observational evidence exists that tells which progenitor system is more common. Recent studies suggest that the light curve of a supernova shortly after its explosion can be used to set a limit on the progenitor size, R*. Here, we report a high cadence monitoring observation of SN 2015F, a normal SN Ia, in the galaxy NGC 2442 starting about 84 days before the first light time. With our daily cadence data, we catch the emergence of the radioactively powered light curve, but more importantly detect with a > 97.4% confidence a possible dim precursor emission that appears at roughly 1.5 days before the rise of the radioactively powered emission. The signal is consistent with theoretical expectations for a progenitor system involving a companion star with R* = ~0.1 -- 1 Rsun or a prompt explosion of a double degenerate system, but inconsistent with a typically invoked size of white dwarf progenitor of R* ~ 0.01 Rsun. Upper limits on the precursor emission also constrain the progenitor size to be R* < 0.1 Rsun, and a companion star size of R* < ~1.0 Rsun, excluding a very large companion star in the progenitor system. Additionally, we find that the distance to SN 2015F is 23.9 +-0.4 Mpc.

astro-ph.HE↗

arXiv2015

Evolution of Star-formation Properties of High-redshift Cluster Galaxies since $z = 2$

Using a stellar mass limited sample of $\sim 46,600$ galaxies ($M_* > 10^{9.1}\,M_{\odot}$) at $0.5 < z < 2$, we show that the tellar mass, rather than the environment, is the main parameter controlling quenching of star formation in galaxies with $M_* > 10^{10}\,M_{\odot}$ out to $z=2$. On the other hand, the environmental quenching becomes efficient at $z < 1$ regardless of galaxy mass, and it serves as a main star formation quenching mechanism for lower mass galaxies. Our result is based on deep optical and near-infrared imaging data over 2800 arcmin$^2$, enabling us to negate cosmic variance and identify 46 galaxy cluster candidates with $M \sim 10^{14}\,M_{\odot}$. From $M_* \sim 10^{9.5}$ to $10^{10.5}\,M_{\odot}$, the fraction of quiescent galaxies increases by a factor of $\sim 10$ over the entire redshift range, but the difference between cluster and field environment is negligible. Rapid evolution in the quiescent fraction is seen from $z=2$ to $z=1.3$ for massive galaxies suggesting a build-up of massive quiescent galaxies at $z > 1.3$. For galaxies with $M_* < 10^{10}\,M_{\odot}$ at $z < 1.0$, the quiescent fraction is found to be as much as a factor of 2 larger in clusters than in field, showing the importance of environmental quenching in low mass galaxies at low redshift. Most high mass galaxies are already quenched at $z > 1$, therefore environmental quenching does not play a significant role for them, although the environmental quenching efficiency is nearly identical between high and low mass galaxies.

astro-ph.GA↗

arXiv2015

Linking galaxies to dark matter haloes at $z\sim1$ : dependence of galaxy clustering on stellar mass and specific star formation rate

We study the dependence of angular two-point correlation functions on stellar mass ($M_{*}$) and specific star formation rate (sSFR) of $M_{*}>10^{10}M_{\odot}$ galaxies at $z\sim1$. The data from UKIDSS DXS and CFHTLS covering 8.2 deg$^{2}$ sample scales larger than 100 $h^{-1}$Mpc at $z\sim1$, allowing us to investigate the correlation between clustering, $M_{*}$, and star formation through halo modeling. Based on halo occupation distributions (HODs) of $M_{*}$ threshold samples, we derive HODs for $M_{*}$ binned galaxies, and then calculate the $M_{*}/M_{\rm halo}$ ratio. The ratio for central galaxies shows a peak at $M_{\rm halo}\sim10^{12}h^{-1}M_{\odot}$, and satellites predominantly contribute to the total stellar mass in cluster environments with $M_{*}/M_{\rm halo}$ values of 0.01--0.02. Using star-forming galaxies split by sSFR, we find that main sequence galaxies ($\rm log\,sSFR/yr^{-1}\sim-9$) are mainly central galaxies in $\sim10^{12.5} h^{-1}M_{\odot}$ haloes with the lowest clustering amplitude, while lower sSFR galaxies consist of a mixture of both central and satellite galaxies where those with the lowest $M_{*}$ are predominantly satellites influenced by their environment. Considering the lowest $M_{\rm halo}$ samples in each $M_{*}$ bin, massive central galaxies reside in more massive haloes with lower sSFRs than low mass ones, indicating star-forming central galaxies evolve from a low $M_{*}$--high sSFR to a high $M_{*}$--low sSFR regime. We also find that the most rapidly star-forming galaxies ($\rm log\,sSFR/yr^{-1}>-8.5$) are in more massive haloes than main sequence ones, possibly implying galaxy mergers in dense environments are driving the active star formation. These results support the conclusion that the majority of star-forming galaxies follow secular evolution through the sustained but decreasing formation of stars.

astro-ph.GA↗

arXiv2015

CF-HiZELS, a 10 deg$^2$ emission-line survey with spectroscopic follow-up: Hα, [OIII]+Hβ and [OII] luminosity functions at z=0.8, 1.4 and 2.2

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 $μ$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$α$ emitters at z=0.8, 1343 [OIII]+H$β$ 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$σ$ (spectroscopically confirmed) over-density of H$α$ emitters at z=0.81. We derive H$α$, [OIII]+H$β$ 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 $ϕ^*$ 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.

astro-ph.GA↗