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Daniel J. Farrow

Publications and source records attributed to Daniel J. Farrow.

At least 37 records · Page 2Linked to original sources

The Stellar Mass - Black Hole Mass Relation at $z\sim2$ Down to $\mathcal{M}_\mathrm{BH}\sim10^7 M_\odot$ Determined by HETDEX

We investigate the stellar mass - black hole mass ($\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$) relation with type 1 AGN down to $\mathcal{M}_\mathrm{BH}=10^7 M_\odot$, corresponding to a $\simeq -21$ absolute magnitude in rest-frame ultraviolet (UV), at $z = 2-2.5$. Exploiting the deep and large-area spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), we identify 66 type 1 AGN with $\mathcal{M}_\mathrm{BH}$ ranging from $10^7$ to $10^{10} M_\odot$ that are measured with single-epoch virial method using C{\sc iv} emission lines detected in the HETDEX spectra. $\mathcal{M}_*$ of the host galaxies are estimated from optical to near-infrared photometric data taken with Spitzer, WISE, and ground-based 4-8m class telescopes by CIGALE SED fitting. We further assess the validity of SED fitting in two cases by host-nuclear decomposition performed through surface brightness profile fitting on spatially-resolved host galaxies with JWST/NIRCam CEERS data. We obtain the $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation covering the unexplored low-mass ranges of $\mathcal{M}_\mathrm{BH}~\sim~10^7-10^8~M_\odot$, and conduct forward modelling to fully account for the selection biases and observational uncertainties. The intrinsic $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation at $z\sim 2$ has a moderate positive offset of $0.52\pm0.14$~dex from the local relation, suggestive of more efficient black hole growth at higher redshift even in the low-mass regime of $\mathcal{M}_\mathrm{BH}~\sim~10^7-10^8~M_\odot$. Our $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation is inconsistent with the $\mathcal{M}_\mathrm{BH}$ suppression at the low-$\mathcal{M}_*$ regime predicted by recent hydrodynamic simulations at a $98\%$ confidence level, suggesting that feedback in the low-mass systems may be weaker than those produced in hydrodynamic simulations.

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HETDEX Public Source Catalog 1: 220K Sources Including Over 50K Lyman Alpha Emitters from an Untargeted Wide-area Spectroscopic Survey

We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88<z<3.52 by using the spatial distribution of more than a million Ly-alpha-emitting galaxies over a total target area of 540 deg^2. The catalog comes from contiguous fiber spectra coverage of 25 deg^2 of sky from January 2017 through June 2020, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Lyα-emitting galaxy (LAE) identifications and 123,891 OII-emitting galaxies at z<0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift (z<0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, OII and Ly-alpha line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within deltaz < 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE sample has an r-band continuum counterpart down to a limiting magnitude of r~26.2 mag (AB) indicating that an LAE search of similar sensitivity with photometric pre-selection would miss nearly half of the HETDEX LAE catalog sample. Data access and details about the catalog can be found online at http://hetdex.org/.

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The HETDEX Survey: Emission Line Exploration and Source Classification

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the Universe at $z \sim 2.4$ to 1% precision for both $H(z)$ and $D_A(z)$. HETDEX is in the process of mapping in excess of one million Lyman Alpha emitting (LAE) galaxies and a similar number of lower-z galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Ly$α$ emission from the lower-$z$ interloping galaxies, primarily [OII], with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Angstrom rest-frame equivalent width cut commonly used to distinguish LAEs from lower-$z$ [OII] emitting galaxies. Despite a spectral resolving power, R $\sim800$, that cannot resolve the [OII] doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Ly$α$ by [OII] of 1.2% and a Ly$α$ recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements.

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The Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) III. A red quasar with extremely high equivalent widths showing powerful outflows

We report an Active Galactic Nucleus (AGN) with extremely high equivalent width (EW), EW(LyA+NV,rest)>921 AA in the rest-frame, at z~2.24 in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) as a representative case of the high EW AGN population. The continuum level is a non-detection in the HETDEX spectrum, thus the measured EW is a lower limit. The source is detected with significant emission lines (>7sigma) at LyA+NV, CIV, and moderate emission line (~4sigma) at HeII within the wavelength coverage of HETDEX (3500 AA - 5500 AA). The r-band magnitude is 24.57 from the Hyper Suprime-Cam-HETDEX joint survey with a detection limit of r=25.12 at 5sigma. The LyA emission line spans a clearly resolved region of ~10 arcsec (85 kpc) in diameter. The LyA line profile is strongly double peaked. The spectral decomposed blue gas and red gas Ly$α$ emission are separated by ~1.2 arcsec (10.1 kpc) with a line-of-sight velocity offset of ~1100 km/s. This source is probably an obscured AGN with powerful winds.

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The Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) II. Luminosity Function

We present the LyA emission line luminosity function (LF) of the Active Galactic Nuclei (AGN) in the first release of the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) AGN catalog (Liu et al. 2022, Paper I). The AGN are selected either by emission-line pairs characteristic of AGN or by single broad emission line, free of any photometric pre-selections (magnitude/color/morphology). The sample consists of 2,346 AGN spanning 1.88 5σ$ confidence at r~26 in the deepest $r$-band images we have searched. The LyA line luminosity ranges from ~10^42.3 to ~10^45.9 erg s^-1. Our LyA LF shows a turnover luminosity with opposite slopes on the bright end and the faint end: The space density is highest at L_LyA^*=10^43.4 erg s^-1. We explore the evolution of the AGN LF over a broader redshift range (0.8<z<3); constructing the rest-frame ultraviolet (UV) LF with the 1450 AA monochromatic luminosity of the power-law component of the continuum ($\rm M_{1450}$) from M_1450~-18 to ~-27.5. We divide the sample into three redshift bins (z~1.5, 2.1, and 2.6). In all three redshift bins, our UV LFs indicate that the space density of AGN is highest at the turnover luminosity M_1450^* with opposite slopes on the bright end and the faint end. The M_1450 LFs in the three redshift bins can be well-fit with a luminosity-evolution-density-evolution (LEDE) model: the turnover luminosity (M_1450^*) increases and the turnover density (Phi^*) decreases with increasing redshift.

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Lyα Halos around [O III]-Selected Galaxies in HETDEX

We present extended Lyman-α (Lyα) emission out to 800 kpc of 1034 [O III]-selected galaxies at redshifts 1.9 40 kpc from the galaxy centers. The surface brightness in the inner parts (r<10 kpc) around the [O III]-selected galaxies, however, is ten times fainter than that of the LAEs. Our results are consistent with the notion that photons dominating the outer regions of the Lyα halos are not produced in the central galaxies but originate outside of them.

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The Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) I. Sample selection

We present the first Active Galactic Nuclei (AGN) catalog in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) observed between January 2017 and June 2020. HETDEX is an ongoing spectroscopic survey with no pre-selection based on magnitudes, colors or morphologies, enabling us to select AGN based on their spectral features. Both luminous quasars and low-luminosity Seyferts are found in our catalog. AGN candidates are selected with at least two significant AGN emission lines, such as the LyA and CIV line pair, or with single broad emission lines (FWHM > 1000 km/s). Each source is further confirmed by visual inspections. This catalog contains 5,322 AGN, covering an effective sky coverage of 30.61 deg^2. A total of 3,733 of these AGN have secure redshifts, and we provide redshift estimates for the remaining 1,589 single broad-line AGN with no cross matched spectral redshifts from SDSS DR14Q. The redshift range of the AGN catalog is 0.25 < z < 4.32, with a median of z = 2.1. The bolometric luminosity range is 10^9-10^14 Lsun with a median of 10^12 Lsun. The median r-band magnitude of the AGN is 21.6 mag, with 34% of the AGN have r > 22.5, and 2.6% reaching the detection limit at r ~ 26 mag of the deepest imaging surveys we searched. We also provide a composite spectrum of the AGN sample covering 700 AA - 4400 AA.

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KiDS+VIKING+GAMA: Halo occupation distributions and correlations of satellite numbers with a new halo model of the galaxy-matter bispectrum for galaxy-galaxy-galaxy lensing

Halo models and halo occupation distributions (HODs) are important tools to model the galaxy and matter distribution. We present and assess a new method for constraining the parameters of HODs using the gravitational lensing shear around galaxy pairs, galaxy-galaxy-galaxy-lensing (G3L). In contrast to galaxy-galaxy-lensing, G3L is sensitive to correlations between the per-halo numbers of galaxies from different populations. We use G3L to probe these correlations and test the default hypothesis that they are negligible. We derive a halo model for G3L and validate it with realistic mock data from the Millennium Simulation and a semi-analytic galaxy model. Then, we analyse public data from the Kilo-Degree Survey (KiDS), the VISTA Infrared Kilo-Degree Galaxy Survey (VIKING) and data from the Galaxy And Mass Assembly Survey (GAMA) to infer the HODs of galaxies at $z<0.5$ in five different stellar mass bins between $10^{8.5}h^{-2} M_\odot$ and $10^{11.5}h^{-2} M_\odot$ and two colours (red and blue), as well as correlations between satellite numbers. The analysis recovers the true HODs in the simulated data within the $68\%$ credibility range. The inferred HODs vary significantly with colour and stellar mass. There is also strong evidence ($>3σ$) for correlations, increasing with halo mass, between the numbers of red and blue satellites and galaxies with stellar masses below $10^{10} \Msun. Possible causes of these correlations are the selection of similar galaxies in different samples, the survey flux limit, or physical mechanisms like a fixed ratio between the satellite numbers of distinct populations. The decorrelation for halos with smaller masses is probably an effect of shot noise by low-occupancy halos. The inferred HODs can be used to complement galaxy-galaxy-lensing or galaxy clustering HOD studies or as input to cosmological analyses and improved mock galaxy catalogues.

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Galaxy And Mass Assembly (GAMA): Data Release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

In Galaxy And Mass Assembly Data Release 4 (GAMA DR4), we make available our full spectroscopic redshift sample. This includes 248682 galaxy spectra, and, in combination with earlier surveys, results in 330542 redshifts across five sky regions covering ~250deg^2. The redshift density, is the highest available over such a sustained area, has exceptionally high completeness (95 per cent to r_KIDS=19.65mag), and is well suited for the study of galaxy mergers, galaxy groups, and the low redshift (z<0.25) galaxy population. DR4 includes 32 value-added tables or Data Management Units (DMUs) that provide a number of measured and derived data products including GALEX, ESO KiDS, ESO VIKING, WISE and Herschel Space Observatory imaging. Within this release, we provide visual morphologies for 15330 galaxies to z<0.08, photometric redshift estimates for all 18million objects to r_KIDS~25mag, and stellar velocity dispersions for 111830 galaxies. We conclude by deriving the total galaxy stellar mass function (GSMF) and its sub-division by morphological class (elliptical, compact-bulge and disc, diffuse-bulge and disc, and disc only). This extends our previous measurement of the total GSMF down to 10^6.75 M_sol h^-2_70 and we find a total stellar mass density of rho_*=(2.97+/-0.04)x10^8 M_sol h_70 Mpc^-3 or Omega_*=(2.17+/-0.03)x10^-3 h^-1_70. We conclude that at z<0.1, the Universe has converted 4.9+/-0.1 per cent of the baryonic mass implied by Big Bang Nucleosynthesis into stars that are gravitationally bound within the galaxy population.

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Surface Brightness Profile of Lyman-$α$ Halos out to 320 kpc in HETDEX

We present the median-stacked Lyman-$α$ surface brightness profile of 968 spectroscopically selected Lyman-$α$ emitting galaxies (LAEs) at redshifts $1.9 80\,\mathrm{kpc}$, our profile is flatter than the MUSE model. The measured profile agrees at most radii with that of galaxies in the Byrohl et al. (2021) cosmological radiative transfer simulation at $z=3$. This suggests that the surface brightness of a Lyman-$α$ halo at $r\lesssim 100$ kpc is dominated by resonant scattering of Lyman-$α$ photons from star-forming regions in the central galaxy, whereas at $r > 100$ kpc it is dominated by photons from galaxies in surrounding dark matter halos.

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The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections

We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Ly$α$ emitting galaxies between 1.88<z<3.52, in a 540 deg^2 area encompassing a co-moving volume of 10.9 Gpc^3. No pre-selection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project's observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the COSMOS, Extended Groth Strip, and GOODS-N fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.

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Using GAMA to probe the impact of small-scale galaxy physics on nonlinear redshift-space distortions

We present improved modelling of the redshift-space distortions of galaxy clustering that arise from peculiar velocities. We create mock galaxy catalogues in the framework of the halo model, using data from the Bolshoi project. These mock galaxy populations are inserted into the haloes with additional degrees of freedom that govern spatial and kinematical biases of the galaxy populations relative to the dark matter. We explore this generalised halo model with an MCMC algorithm, comparing the predictions to data from the Galaxy And Mass Assembly (GAMA) survey, and thus derive one of the first constraints on the detailed kinematic degrees of freedom for satellite galaxies within haloes. With this approach, the distortions of the redshift-space galaxy autocorrelations can be accounted for down to spatial separations close to 10 kpc, opening the prospect of improved RSD measurements of the perturbation growth rate by the inclusion of data from nonlinear scales.

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First HETDEX Spectroscopic Determinations of Ly$α$ and UV Luminosity Functions at $z=2-3$: Bridging a Gap Between Faint AGN and Bright Galaxies

We present Ly$α$ and ultraviolet-continuum (UV) luminosity functions (LFs) of galaxies and active galactic nuclei (AGN) at $z=2.0-3.5$ determined by the un-targetted optical spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in $11.4$ deg$^2$ of fiber-spectra sky coverage, obtaining $18320$ galaxies spectroscopically identified with Ly$α$ emission, $2126$ of which host type 1 AGN showing broad (FWHM$~>1000$ km s$^{-1}$) Ly$α$ emission lines. We derive the Ly$α$ (UV) LF over 2 orders of magnitude covering bright galaxies and AGN in $\log L_\mathrm{Lyα}/\mathrm{[erg~s^{-1}]}=43.3-45.5$ ($-27 -21$) type 1 AGN increases from $z\sim2$ to $z\sim0$ as opposed to the evolution of bright ($M_\mathrm{UV}<-21$) type 1 AGN, suggesting the AGN downsizing in the rest-frame UV luminosity.

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Correcting correlation functions for redshift-dependent interloper contamination

The construction of catalogues of a particular type of galaxy can be complicated by interlopers contaminating the sample. In spectroscopic galaxy surveys this can be due to the misclassification of an emission line; for example in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) low redshift [OII] emitters may make up a few percent of the observed Ly$α$ emitter (LAE) sample. The presence of contaminants affects the measured correlation functions and power spectra. Previous attempts to deal with this using the cross-correlation function have assumed sources at a fixed redshift, or not modelled evolution within the adopted redshift bins. However, in spectroscopic surveys like HETDEX, where the contamination fraction is likely to be redshift dependent, the observed clustering of misclassified sources will appear to evolve strongly due to projection effects, even if their true clustering does not. We present a practical method for accounting for the presence of contaminants with redshift-dependent contamination fractions and projected clustering. We show using mock catalogues that our method, unlike existing approaches, yields unbiased clustering measurements from the upcoming HETDEX survey in scenarios with redshift-dependent contamination fractions within the redshift bins used. We show our method returns auto-correlation functions with systematic biases much smaller than the statistical noise for samples with at least as high as 7 per cent contamination. We also present and test a method for fitting for the redshift-dependent interloper fraction using the LAE-[OII] galaxy cross-correlation function, which gives less biased results than assuming a single interloper fraction for the whole sample.

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Detection of Lyman Continuum from 3.0 < z < 3.5 Galaxies in the HETDEX Survey

Questions as to what drove the bulk reionization of the Universe, how that reionization proceeded, and how the hard ionizing radiation reached the intergalactic medium remain open and debated. Observations probing that epoch are severely hampered by the increasing amounts of neutral gas with increasing redshift, so a small, but growing number of experiments are targeting star forming galaxies ($z\sim3$) as proxies. However, these studies, while providing fantastic detail, are time intensive, contain relatively few targets, and can suffer from selection biases. As a complementary alternative, we investigate whether stacking the already vast (and growing) numbers of low-resolution ($Δλ/ λ= 800$) Lyman-$α$ Emitting (LAE) galaxy spectra from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) can be used to measure ionizing photons (restframe 880-910Å) escaping their galaxy hosts. As a blind survey, HETDEX avoids the biases from continuum selected galaxies and its planned 540 square degree coverage promotes the statistical power of large numbers. In this paper, we confirm the feasibility of Lyman continuum detection by carefully selecting a sample of \lyccount\ high redshift ($z\sim$3) LAEs from a subset of HETDEX observations, stacking their spectra and measuring a $\gtrsim$3$σ$ detection of $0.10 μ$Jy restframe Lyman continuum emission, uncorrected for attenuation in the intergalactic medium, over the full sample stack ($3.0 < z < 3.5$ and $-22.0 \lesssim M_{\text{UV}} \lesssim -19.0$).

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The HETDEX Survey: The Ly$α$ Escape Fraction from 3D-HST Emission Line Galaxies at $z \sim 2$

We measure the Ly$α$ escape fraction of 935 [OIII]-emitting galaxies between $1.9 < z < 2.35$ by comparing stacked spectra from the Hubble Space Telescope/WFC3's near-IR grism to corresponding stacks from the Hobby Eberly Telescope Dark Energy Experiment's Internal Data Release 2. By measuring the stacks' H$β$ to Ly$α$ ratios, we determine the Ly$α$ escape fraction as a function of stellar mass, star formation rate, internal reddening, size, and [OIII]/H$β$ ratio. We show that the escape fraction of Ly$α$ correlates with a number of parameters, such as galaxy size, star formation rate, and nebular excitation. However, we also demonstrate that most of these relations are indirect, and the primary variables that control the escape of Ly$α$ are likely stellar mass and internal extinction. Overall, the escape of Ly$α$ declines from $\gtrsim 18\%$ in galaxies with $\log M/M_{\odot} \lesssim 9$ to $\lesssim 1\%$ for systems with $\log M/M_{\odot} \gtrsim 10$, with the sample's mean escape fraction being $6.0^{+0.6\%}_{-0.5\%}$.

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The Stars of the HETDEX Survey. I. Radial Velocities and Metal-Poor Stars from Low-Resolution Stellar Spectra

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution ($R\sim750$) spectra of Lyman-Alpha Emitters. In its search for these galaxies, HETDEX will also observe a few 10$^{5}$ stars. In this paper, we present the first stellar value-added catalog within the internal second data release of the HETDEX Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for 98,736 unique stars between $10 < G < 22$ spread across the HETDEX footprint at relatively high ($b\sim60^\circ$) Galactic latitudes. With these spectra, we measure radial velocities (RVs) for $\sim$42,000 unique FGK-type stars in the catalog and show that the HETDEX spectra are sufficient to constrain these RVs with a 1$σ$ precision of 28.0 km/s and bias of 3.5 km/s with respect to the LAMOST surveys and 1$σ$ precision of 27.5 km/s and bias of 14.0 km/s compared to the SEGUE survey. Since these RVs are for faint ($G\geq16$) stars, they will be complementary to Gaia. Using t-Distributed Stochastic Neighbor Embedding (t-SNE), we also demonstrate that the HETDEX spectra can be used to determine a star's T${\rm{eff}}$, and log g and its [Fe/H]. With the t-SNE projection of the FGK-type stars with HETDEX spectra we also identify 416 new candidate metal-poor ([Fe/H] $< -1$~dex) stars for future study. These encouraging results illustrate the utility of future low-resolution stellar spectroscopic surveys.

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KiDS+VIKING+GAMA: Testing semi-analytic models of galaxy evolution with galaxy-galaxy-galaxy lensing

Several semi-analytic models (SAMs) try to explain how galaxies form, evolve and interact inside the dark matter large-scale structure. These SAMs can be tested by comparing their predictions for galaxy-galaxy-galaxy-lensing (G3L), which is weak gravitational lensing around galaxy pairs, with observations. We evaluate the SAMs by Henriques et al. (2015; H15) and by Lagos et al. (2012; L12), implemented in the Millennium Run, by comparing their predictions for G3L to observations at smaller scales than previous studies and also for pairs of lens galaxies from different populations. We compare the G3L signal predicted by the SAMs to measurements in the overlap of the Galaxy And Mass Assembly survey (GAMA), the Kilo-Degree Survey (KiDS), and the VISTA Kilo-degree Infrared Galaxy survey (VIKING), splitting lens galaxies into two colour and five stellar-mass samples. Using an improved G3L estimator, we measure the three-point correlation of the matter distribution for mixed lens pairs with galaxies from different samples, and unmixed lens pairs with galaxies from the same sample. Predictions by the H15 SAM agree with the observations for all colour-selected and all but one stellar-mass-selected sample with 95% confidence. Deviations occur for lenses with stellar masses below $9.5h^{-2}\mathrm{M}_\odot$ at scales below $0.2h^{-1}\mathrm{Mpc}$. Predictions by the L12 SAM for stellar-mass selected samples and red galaxies are significantly higher than observed, while the predicted signal for blue galaxy pairs is too low. The L12 SAM predicts more pairs of small stellar-mass and red galaxies than the H15 SAM and the observations, as well as fewer pairs of blue galaxies. Likely explanations are different treatments of environmental effects by the SAMs and different models of the initial mass function. We conclude that G3L provides a stringent test for models of galaxy formation and evolution.

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