Narrow-band Observations Research Articles

Alone on a wide wide sea. The origin of SECCO 1, an isolated star-forming gas cloud in the Virgo cluster*†‡

SECCO1 is an extremely dark, low-mass (M_star=10^5 M_sun), star-forming stellar system lying in the Low Velocity Cloud (LVC) substructure of the Virgo cluster of galaxies, and hosting several HII regions. Here we review our knowledge of this remarkable system, and present the results of (a) additional analysis of our panoramic spectroscopic observations with MUSE, (b) the combined analysis of Hubble Space Telescope and MUSE data, and (c) new narrow-band observations obtained with OSIRIS@GTC to search for additional HII regions in the surroundings of the system. We provide new evidence supporting an age as young as 4 Myr for the stars that are currently ionising the gas in SECCO1. We identify only one new promising candidate HII region possibly associated with SECCO1, thus confirming the extreme isolation of the system. We also identify three additional candidate pressure-supported dark clouds in Virgo among the targets of the SECCO survey. Various possible hypotheses for the nature and origin of SECCO1 are considered and discussed, also with the help of dedicated hydrodynamical simulations showing that a hydrogen cloud with the characteristics of SECCO1 can likely survive for >1 Gyr while traveling within the LVC Intra Cluster Medium.

Barest Pixel Composite for Agricultural Areas Using Landsat Time Series

Many soil remote sensing applications rely on narrow-band observations to exploit molecular absorption features. However, broadband sensors are invaluable for soil surveying, agriculture, land management and mineral exploration, amongst others. These sensors provide denser time series compared to high-resolution airborne imaging spectrometers and hold the potential of increasing the observable bare-soil area at the cost of spectral detail. The wealth of data coming along with these applications can be handled using cloud-based processing platforms such as Earth Engine. We present a method for identifying the least-vegetated observation, or so called barest pixel, in a dense time series between January 1985 and March 2017, based on Landsat 5, 7 and 8 observations. We derived a Barest Pixel Composite and Bare Soil Composite for the agricultural area of the Swiss Plateau. We analysed the available data over time and concluded that about five years of Landsat data were needed for a full-coverage composite (90% of the maximum bare soil area). Using the Swiss harmonised soil data, we derived soil properties (sand, silt, clay, and soil organic matter percentages) and discuss the contribution of these soil property maps to existing conventional and digital soil maps. Both products demonstrate the substantial potential of Landsat time series for digital soil mapping, as well as for land management applications and policy making.

Broadband echosounder measurements of the frequency response of fishes and euphausiids in the Gulf of Alaska

Abstract Broadband acoustic scattering techniques are not widely used in fisheries acoustics, but this may change due to the recent commercial availability of a broadband echosounder system operating at frequencies commonly used in fisheries surveys. A four-channel (15–150 kHz) broadband echosounder was used to investigate the potential of broadband methods to improve species discrimination during a walleye pollock (Gadus chalcogrammus) survey in the Gulf of Alaska. Narrowband echosounders combined with mid-water and bottom trawls were used to identify aggregations of interest for broadband measurements. Broadband frequency responses were measured for multiple pelagic and semi-demersal fishes as well as euphausiids. No clear patterns in the broadband frequency responses were identified that would aid in discrimination among the commonly encountered swimbladder-bearing species. The results are consistent with narrowband observations and suggest that both techniques face the same challenges when attempting to discriminate among acoustically similar species as frequency responses overlap within the measured bandwidth. However, examples are presented in which broadband frequency responses provide additional information about near-resonant scatterers. The benefits of broadband operations have not been fully realized and widespread adoption of broadband techniques and improved processing algorithms may yield improved acoustic-based species discrimination for use during fisheries surveys.

Retrieval of Biophysical Crop Variables from Multi-Angular Canopy Spectroscopy

The future German Environmental Mapping and Analysis Program (EnMAP) mission, due to launch in late 2019, will deliver high resolution hyperspectral data from space and will thus contribute to a better monitoring of the dynamic surface of the earth. Exploiting the satellite’s ±30° across-track pointing capabilities will allow for the collection of hyperspectral time-series of homogeneous quality. Various studies have shown the possibility to retrieve geo-biophysical plant variables, like leaf area index (LAI) or leaf chlorophyll content (LCC), from narrowband observations with fixed viewing geometry by inversion of radiative transfer models (RTM). In this study we assess the capability of the well-known PROSPECT 5B + 4SAIL (Scattering by Arbitrarily Inclined Leaves) RTM to estimate these variables from off-nadir observations obtained during a field campaign with respect to EnMAP-like sun–target–sensor-geometries. A novel approach for multiple inquiries of a large look-up-table (LUT) in hierarchical steps is introduced that accounts for the varying instances of all variables of interest. Results show that anisotropic effects are strongest for early growth stages of the winter wheat canopy which influences also the retrieval of the variables. RTM inversions from off-nadir spectra lead to a decreased accuracy for the retrieval of LAI with a relative root mean squared error (rRMSE) of 18% at nadir vs. 25% (backscatter) and 24% (forward scatter) at off-nadir. For LCC estimations, however, off-nadir observations yield improvements, i.e., rRMSE (nadir) = 24% vs. rRMSE (forward scatter) = 20%. It follows that for a variable retrieval through RTM inversion, the final user will benefit from EnMAP time-series for biophysical studies regardless of the acquisition angle and will thus be able to exploit the maximum revisit capability of the mission.

No Ly α emitters detected around a QSO at z = 6.4: Suppressed by the QSO?

Abstract Understanding how quasars’ (QSOs’) ultraviolet (UV) radiation affects galaxy formation is vital to our understanding of the reionization era. Using a custom-made narrow-band filter, NB906, on Subaru/Suprime-Cam, we investigated the number density of Ly α emitters (LAEs) around a QSO at z = 6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field of view of Suprime-Cam, our survey area is ∼5400 cMpc2, much larger than previous studies at z = 5.7 (∼200 cMpc2). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies. Based on this, we expected to detect ∼100 LAEs down to NB906 = 25 ABmag. However, our 6.4 h exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 pMpc across. A simple argument suggests that a strong UV radiation from the QSO can suppress star formation in haloes with Mvir < 1010 M⊙ within a pMpc from the QSO, but the deficit at the edge of the field (5 pMpc) remains to be explained.

Wideband DOA estimation for SOBFN

This study considers the problem of wideband direction of arrival (DOA) estimation for spatial optical beam-forming network (SOBFN). Since its system configuration is different from that of the traditional microwave beam-forming networks, the authors first establish the observation model of SOBFN when multiple broadband signals are received. Two kinds of DOA estimation strategies are proposed for wideband direction finding based on the established signal model. The proposed methods decompose the wideband array output into narrowband outputs in several discrete frequency bins. Then, they take advantages of the spatial sparsity of the discrete narrowband observation models to estimate the spatial power spectrum, either coherently or non-coherently. A coarse DOA estimate is obtained via peak-searching in the reconstructed spectrum. The preliminary result is then refined by a linear interpolation procedure. Profound experiments are carried out to demonstrate and compare the performance of the two strategies. Simulation results show that the proposed approaches can achieve wideband DOA estimation of high precision and super-resolution for SOBFN. Moreover, coherent process is proved to have superior performance than the non-coherent strategy.

A search for Ly α emitters around a concentrated region of strong Ly α absorbers at z = 2.3

Abstract In order to investigate the physical relationship between strong Ly α absorbers ($\log N_{{\rm H}\,{{\small I}}} \ge 20.0\:$cm−2) such as damped Ly α absorption systems (DLAs) and young star-forming galaxies at high redshift, we have conducted narrow-band observations of Ly α emitters (LAEs) in a concentrated region of strong Ly α absorbers at z = 2.3, the J1230+34 field. Using a catalog of Ly α absorbers with $\log N_{\rm H\,{{\small I}}} \ge 20.0\:$cm−2 based on the Baryon Oscillation Spectroscopic Survey, we found six fields where three or more absorbers are concentrated within a (50 Mpc)3 cubic box in the comoving scale. Among them, we focus on the J1230+34 field, where two DLAs and two sub-DLAs are present. Our narrow-band imaging observations with Subaru/Suprime-Cam using a custom-made filter, NB400 (λc = 4003 Å and FWHM = 92 Å) yield a sample of 149 LAEs in this field. In the large scale (∼50 Mpc), we have found no differences between the obtained Ly α luminosity function and those in the blank fields at similar redshifts. We also compare the frequency distribution of the Ly α rest-frame equivalent width ($\mathit {EW}_{0}$) in the target field and other fields including both overdensity region and blank field, but find no differences. On the other hand, in the small scale (∼10 Mpc), we have found a possible overdensity of LAEs around a DLA with the highest ${\rm H}\,{\small I}$ column density ($N_{\rm H\,{{\small I}}} = 21.08\:$cm−2) in the target field while there are no density excesses around the other absorbers with a lower $N_{\rm H\,{{\small I}}}$.

Active Cooling Camera Modification for Improved Astronomy Data Collection

Using Digital Single Lens Reflex (DLSR) cameras modified to be sensitive into the infrared are an inexpensive entry into astrophotography. Such a camera was used for wide-field, narrowband observations of the Cygnus Superbubble in the Observing Nebulosities project (Christopherson and Kaltcheva, 2015). One of the downfalls to using a DLSR for such a study is the inefficiency of collecting data from the buildup of heat in the sensor during data collection and the noise introduced into the images as a result. For this project an active cooling modification was designed and installed on a DSLR camera allowing the camera sensor to be cooled and held at a temperature below ambient conditions to reduce noise in speed up the data collection process.

Similarities and uniqueness of Lyα emitters among star-forming galaxies at z = 2.5

We conducted a deep narrow-band imaging survey with the Subaru Prime Focus Camera on the Subaru Telescope and constructed a sample of Ly$\alpha$ emitters (LAEs) at z=2.53 in the UDS-CANDELS field where a sample of H$\alpha$ emitters (HAEs) at the same redshift is already obtained from our previous narrow-band observation at NIR. The deep narrow-band and multi broadband data allow us to find LAEs of stellar masses and star-formation rates (SFRs) down to $\gtrsim$$10^8$ M$_\odot$ and $\gtrsim$0.2 M$_\odot$/yr, respectively. We show that the LAEs are located along the same mass-SFR sequence traced by normal star-forming galaxies such as HAEs, but towards a significantly lower mass regime. Likewise, LAEs seem to share the same mass--size relation with typical star-forming galaxies, except for the massive LAEs, which tend to show significantly compact sizes. We identify a vigorous mass growth in the central part of LAEs: the stellar mass density in the central region of LAEs increases as their total galaxy mass grows. On the other hand, we see no Ly$\alpha$ line in emission for most of the HAEs. Rather, we find that the Ly$\alpha$ feature is either absent or in absorption (Ly$\alpha$ absorbers; LAAs), and its absorption strength may increase with reddening of the UV continuum slope. We demonstrate that a deep Ly$\alpha$ narrow-band imaging like this study is able to search for not only LAEs but also LAAs in a certain redshift slice. This work suggests that LAEs trace normal star-forming galaxies in the low-mass regime, while they remain as a unique population because the majority of HAEs are not LAEs.

Acoustic observations and characterization of oceanic methane gas bubbles rising from the seabed

Methane, a potent greenhouse gas, can be found escaping the ocean seabed as gas bubbles in a wide range of geographic locations and water depths. As they rise toward the sea surface, methane gas bubbles undergo a complicated evolution. During ascent, methane gas is transferred into aqueous solution and other dissolved gases are transferred into the bubble. The gas transfer rate—a key factor in determining the ultimate fate of the methane—may be inhibited by hydrate formation in deep, cold water, or potentially by surfactants and adsorbed particulates at any depth. The presence of methane gas bubbles from both natural and anthropogenic sources is often identified using acoustic echo sounders. Beyond simple detection, acoustic techniques can be used to characterize methane bubbles in several ways. For example, narrow-band observations of seep target strength can be used with knowledge of bubble size distributions to estimate methane flux. Similar acoustic observations can be coupled with bubble-evolution models to constrain the fate of bubbles as they rise. Broadband techniques offer the potential to directly observe bubble size and rise speed, and consequently depth-dependent gas flux. The application of these and other techniques for detecting and characterizing methane gas-bubble seeps will be discussed.

A deep/wide 1–2 GHz snapshot survey of SDSS Stripe 82 using the Karl G. Jansky Very Large Array in a compact hybrid configuration

We have used the Karl G. Jansky Very Large Array to image ~100 sq. deg. of SDSS Stripe 82 at 1-2 GHz. The survey consists of 1,026 snapshot observations of 2.5 minutes duration, using the hybrid CnB configuration. The survey has good sensitivity to diffuse, low surface brightness structures and extended radio emission, making it highly synergistic with existing 1.4 GHz radio observations of the region. The principal data products are continuum images, with 16 x 10 arcsecond resolution, and a catalogue containing 11,782 point and Gaussian components resulting from fits to the thresholded Stokes-I brightness distribution, forming approximately 8,948 unique radio sources. The typical effective 1{\sigma} noise level is 88 {\mu}Jy / beam. Spectral index estimates are included, as derived from the 1 GHz of instantaneous bandwidth. Astrometric and photometric accuracy are in excellent agreement with existing narrowband observations. A large-scale simulation is used to investigate clean bias, which we extend into the spectral domain. Clean bias remains an issue for snapshot surveys with the VLA, affecting our total intensity measurements at the ~1{\sigma} level. Statistical spectral index measurements are in good agreement with existing measurements derived from matching separate surveys at two frequencies. At flux densities below ~35{\sigma} the median in-band spectral index measurements begin to exhibit a bias towards flatness that is dependent on both flux density and the intrinsic spectral index. In-band spectral curvature measurements are likely to be unreliable for all but the very brightest components. Image products and catalogues are publicly available via an FTP server.

A DEEPER LOOK AT FAINT Hα EMISSION IN NEARBY DWARF GALAXIES

ABSTRACT We present deep Hα imaging of three nearby dwarf galaxies, carefully selected to optimize observations with the Maryland-Magellan Tunable Filter (MMTF) on the Magellan 6.5 m telescope. An effective bandpass of ∼13 Å is used, and the images reach 3σ flux limits of ∼8 × 10−18 erg s−1 cm−2, which is about an order of magnitude lower than standard narrowband observations obtained by the most recent generation of local Hα galaxy surveys. The observations were originally motivated by the finding that the Hα/FUV flux ratio of galaxies systematically declines as global galactic properties such as the star formation rate (SFR) and stellar mass decrease. The three dwarf galaxies selected for study have SFRs that, when calculated from their Hα luminosities using standard conversion recipes, are ∼50% of those based on the FUV. Follow-up studies of many of the potential causes for the trends in the Hα/FUV flux ratio have been performed, but the possibility that previous observations have missed a non-negligible fraction of faint ionized emission in dwarf galaxies has not been investigated. The MMTF observations reveal both diffuse and structured Hα emission (filaments, shells, possible single-star H ii regions) spanning extents up to 2.5 times larger relative to previous observations. However, only up to an additional ∼5% of Hα flux is captured, which does not account for the trends in the Hα/FUV ratio. Beyond investigation of the Hα/FUV ratio, the impact of the newly detected extended flux on our understanding of star formation, the properties of H ii regions, and the propagation of ionizing photons warrant further investigation.

Study of long path VLF signal propagation characteristics as observed from Indian Antarctic station, Maitri

To examine the quality and propagation characteristics of the Very Low Frequency (VLF) radio waves in a very long propagation path, Indian Centre for Space Physics, Kolkata, participated in the 27th Indian scientific expedition to Antarctica during 2007–2008. One Stanford University made AWESOME VLF receiving system was installed at the Indian Antarctic station Maitri and about five weeks of data were recorded successfully from the Indian transmitter VTX and several other transmitting stations worldwide. The quality of the signal from the VTX transmitter was found to be very good, consistent and highly stable in day and night. The signal shows the evidences of the presence of the 24h solar radiation in the Antarctic region during local summer. Here we report the both narrow band and broadband VLF observations from this site. The diurnal variations of VTX signal (18.2kHz) are presented systematically for Antarctica path and also compared the same with the variations for a short propagation path (VTX-Kolkata). We compute the spatial distribution of the VTX signal along the VTX-Antarctica path using the most well-known LWPC model for an all-day and all-night propagation conditions. The calculated signal amplitudes corresponding to those conditions relatively corroborate the observations. We also present the attenuation rate of the dominant waveguide modes corresponding to those propagation conditions where the effects of the Antarctic polar ice on the attenuation of different propagating waveguide modes are visible.

Progenitor constraints on the Type-Ia supernova SN2011fe from pre-explosion Hubble Space Telescope He ii narrow-band observations

Abstract We present Hubble Space Telescope (HST) imaging observations of the site of the Type-Ia supernova SN2011fe in the nearby galaxy M101, obtained about 1 yr prior to the event, in a narrow band centred on the He ii λ4686 Å emission line. In a ‘single-degenerate’ progenitor scenario, the hard photon flux from an accreting white dwarf (WD), burning hydrogen on its surface over ∼1 Myr should, in principle, create a He iii Strömgren sphere or shell surrounding the WD. Depending on the WD luminosity, the interstellar density, and the velocity of an outflow from the WD, the He iii region could appear unresolved, extended, or as a ring, with a range of possible surface brightnesses. We find no trace of He ii λ4686 Å line emission in the HST data. Using simulations, we set 2σ upper limits on the He ii λ4686 Å luminosity of LHeii < 3.4 × 1034 erg s−1 for a point source, corresponding to an emission region of radius r < 1.8 pc. The upper limit for an extended source is LHeii < 1.7 × 1035 erg s−1, corresponding to an extended region with r ∼ 11 pc. The largest detectable shell, given an interstellar-medium density of 1 cm−3, has a radius of ∼6 pc. Our results argue against the presence, within the ∼105 yr prior to the explosion, of a supersoft X-ray source of luminosity Lbol ≳ 3 × 1037 erg s−1, or of a super-Eddington accreting WD that produces an outflowing wind capable of producing cavities with radii of 2–6 pc.

Reconstruction of High Dynamic Range Images: Simulations of LBT Observations of a Stellar Jet, a Pathfinder Study for Future AO-Assisted Giant Telescopes

We present simulated Large Binocular Telescope (LBT) infrared narrow-band observations of a star-jet system, in conjunction with improved and optimized deconvolution and image reconstruction algorithms, considering two cases of interest: single-dish direct imaging with an AO-assisted camera and imaging through a Fizeau interferometer that combines the beams of the two mirrors of LBT. We aim at understanding what accuracy can be obtained with the use of present AO-assisted large telescopes (such as LBT) and what improvements an interferometric instrument (such as LINC-NIRVANA) will be able to provide. The proposed deconvolution method is based on the target decomposition as a sum of a point source (the star) and an extended source (the jet). By assuming Poisson noise we add to the negative logarithm of the likelihood a regularization term enforcing smoothness of the jet component. Finally, we use a Richardson-Lucy-like method for the minimization of this function. This approach is an improvement of a method proposed by Lucy in 1994 for accurate photometric restoration of HST images and called two channel photometric restoration. We denote the new method as the multi-component Richardson-Lucy (MC-RL) method. The analysis of the reconstructed objects shows that the MC-RL method applied to the interferometric observations allows us to evaluate the width and the spatial intensity profile of the jet down to 20 mas with an accuracy better than about 20% in the best case of a central star fainter than 10 mag. These limits allow us to obtain a very good reconstruction of the jet acceleration region very close to the exciting source, which would provide fundamental scientific information on the jet collimation degree and eventually on its launching mechanism. As concerns the proposed MC-RL method, it demonstrates a good performance in the reconstruction of images with a very high dynamic range. It can be improved in several directions, by increasing both its efficiency, thanks to recently proposed acceleration techniques, and its accuracy by means of more sophisticated regularization terms. We are also planning to apply the method to simulated observations of upcoming super giant earth-based telescopes.

CORONAGRAPHIC OBSERVATIONS OF FOMALHAUT AT SOLAR SYSTEM SCALES

We report on a search for low mass companions within 10 AU of the star Fomalhaut, using narrow band observations at 4.05 microns obtained with the Apodizing Phase Plate (APP) coronagraph on the VLT/NaCo. Our observations place a model dependent upper mass limit of 12-20 Jupiter masses from 4 to 10 AU, covering the semi-major axis search space between interferometric imaging measurements and other direct imaging non-detections. These observations rule out models where the large semi-major axis for the putative candidate companion Fomalhaut b is explained by dynamical scattering from a more massive companion in the inner stellar system, where such giant planets are thought to form.

Lyα EMISSION FROM HIGH-REDSHIFT SOURCES IN COSMOS

We investigate spectroscopically measured Ly{\alpha} equivalent widths and escape fractions of 244 sources of which 95 are Lyman Break Galaxies (LBGs) and 106 Lyman Alpha Emitters (LAEs) at z~4.2, z~4.8, and z~5.6 selected from intermediate and narrow band observations. The sources were selected from the Cosmic Evolution Survey (COSMOS), and observed with the DEIMOS spectrograph. We find that the distribution of equivalent widths shows no evolution with redshift for both the LBG selected sources and the intermediate/narrowband LAEs. We also find that the Ly{\alpha} escape fraction of intermediate and narrow band LAEs is on average higher and has a larger variation than the escape fraction of LBG selected sources. The escape fraction does not show a dependence with redshift. Similar to what has been found for LAEs at low redshifts, the sources with the highest extinctions show the lowest escape fractions. The range of escape fractions increases with decreasing extinction. This is evidence that the dust extinction is the most important factor affecting the escape of Ly{\alpha} photons, but at low extinctions other factors such as HI covering fraction and gas kinematics can be just as effective at inhibiting the escape of Ly{\alpha} photons.

Earliest recorded ground-based decameter wavelength observations of Saturn’s lightning during the giant E-storm detected by Cassini spacecraft in early 2006

We report the history of the first recorded ground-based radio detection of Saturn’s lightning using the Ukrainian UTR-2 radiotelescope at frequencies from 20 to 25MHz. The observations were performed between 29 January and 3 February 2006, during which lighting activity (E-storm) on Saturn was detected by the radio experiment onboard Cassini spacecraft. The minimum detectable flux density (1σ-level) at UTR-2 reached 40Jy (1Jy=10-26Wm-2Hz-1) for narrowband observations (Δf=10kHz) and 4Jy for broadband observations (Δf=1MHz), for an effective telescope area of ≈100,000m2 and integration time of 20ms. Selection criteria including comparison of simultaneous ON/OFF-source observations were applied to distinguish detection of lightning-associated radio pulses from interference. This allowed us to identify about 70 events with signal-to-noise ratio more than 5. Measured flux densities (between 50 and 700Jy) and burst durations (between 60 and 220ms) are in good agreement with extrapolation of previous Cassini measurements to a ground-based observer. This first detection demonstrates the possibility of Solar System planetary lightning studies using large, present and future ground-based radio instruments. The developed methods of observations and identification criteria are also implemented on the UTR-2 radio telescope for the investigation of the next Saturn’s storms. Together with recently published UTR-2 measurements of activity measured after the 2006 storm reported here, the results have significant implications for detectable planetary radio emission in our Solar System and beyond.

CANDIDATES OF Hα EMITTING REGIONS IN THE MAGELLANIC STREAM IV CLOUD

From H\alpha narrow band observations, we identified three H\alpha emitting regions in the direction of Magellanic Stream IV (MS IV). They consist of three parallel filaments with 2 arcmin width and 6 -- 30 arcmin length at 12 arcmin intervals. The mean surface brightness of them is $\sim 2 \times 10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Because of their low surface brightness, the regions were not detected in previous H\alpha surveys. In HI map, the position of the filaments overlap MS, suggesting that they are parts of MS, but there also exists a local HI structure. If the filaments associate with MS, the sizes are 30 pc $\times$ 100 -- 500 pc. The filaments lie at the leading edge of a downstream cloud, which supports a shock heating and its propagation (shock cascade) model for the ionizing source. If they are local objects, on the other hand, Fossil Str\"omgren Trails of more than two stars is a possible interpretation, and the sizes would be 0.1 pc $\times$ 0.3 -- 1.5 pc at 180 pc distance. The positional information of the H\alpha filaments presented in this letter enables us future spectroscopic observations to clarify their nature.

Clustering of Lyα emitters around luminous quasars at z= 2-3: an alternative probe of reionization on galaxy formation

Narrow-band observations fail to detect Lyα emission within a volume centred on the z= 2.168 quasar PKS 0424–131. This is in contrast to surveys of Lyα emitters in the field at similar redshifts and flux limits, which indicate that tens of sources should be visible within the same volume. The observed difference indicates that the quasar environment has a significant influence on the observed density of Lyα emitters. To quantify this effect, we have constructed a semi-analytic model to simulate the effect of a luminous quasar on nearby Lyα emitters. We find the null detection around PKS 0424–131 implies that the minimum isothermal temperature of Lyα emitter host haloes is greater than (68 per cent level), corresponding to a virial mass of ∼1.2 × 1012 M⊙. This indicates that the intense ultraviolet emission of the quasar may be suppressing the star formation in nearby galaxies. Our study illustrates that low-redshift quasar environments may serve as a surrogate for studying the radiative suppression of galaxy formation during the epoch of reionization.