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Register a new userSuperBoRG: Exploration of point sources at $zsim8$ in HST parallel fields
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To extend the search for quasars in the epoch of reionization beyond the tip of the luminosity function, we explore point source candidates at redshift $zsim8$ in SuperBoRG, a compilation of $sim$0.4deg$^2$ archival medium-deep ($m_{rm F160W}sim 26.5$ABmag, 5$sigma$) parallel IR images taken with the Hubble Space Telescope (HST). Initial candidates are selected by using the Lyman-break technique. We then carefully analyze source morphology, and robustly identify 3 point sources at $zsim8$. Photometric redshift analysis reveals that they are preferentially fit by extra-galactic templates, and we conclude that they are unlikely to be low-$z$ interlopers, including brown dwarfs. A clear IRAC ch2 flux excess is seen in one of the point sources, which is expected if the source has strong H$beta$+[O III] emission with rest-frame equivalent width of $sim3000$AA. Deep spectroscopic data taken with Keck/MOSFIRE, however, do not reveal Ly$alpha$ emission from the object. In combination with the estimated H$beta$+[O III] equivalent width, we place an upper limit on its Ly$alpha$ escape fraction $f_{rm esc, Lyalpha}< 2 %$. We estimate the number density of these point sources $sim1times10^{-6}$Mpc$^{-3}$mag$^{-1}$ at $M_{rm UV}sim-23$mag. The final interpretation of our results remains inconclusive: extrapolation from low-$z$ studies of $faint$ quasars suggests that $>100times$ survey volume may be required to find one of this luminosity. The James Webb Space Telescope will be able to conclusively determine the nature of our luminous point source candidates, while the Roman Space Telescope will probe $sim 200$ times the area of the sky with the same observing time considered in this HST study.
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The Hubble Space Telescope (HST) has been providing tremendous survey efficiency via its pure-parallel mode, by observing another field in parallel with the primary instrument in operation for the primary observation. In this study, we present a new archival project, SuperBoRG, which aims at compiling data taken in extragalactic parallel programs of HST with WFC3 in the past decade; including pure-parallel (BoRG, HIPPIES, and COS-GTO) and coordinated-parallel (CLASH and RELICS) programs. The total effective area reaches $sim0.41$deg$^2$ from 4.1Msec, or 47days, of observing time, which is the largest collection of optical-NIR imaging data of HST for extragalactic science. We reduce all data in a consistent manner with an updated version of our data reduction pipeline. When available, infrared imaging data from the Spitzer Space Telescope are included in photometric analyses. The dataset consists of 316 independent sightlines and is highly effective for identification of high-$z$ luminous sources ($M_mathrm{UV}<-21$mag) at $zsim7$ to $12$, helping to minimize the effects of cosmic variance. As a demonstration, we present three new $z>7$ source candidates, including one luminous galaxy candidate at $z_mathrm{phot}sim10.4$ with $M_mathrm{UV}sim-21.9$ mag; for this object the best-fit spectral energy distribution implies a large amount of stellar mass ($log M_*/M_odot sim 10$) and moderate dust attenuation ($A_V sim 1.4$mag), though the possibility of it being a low-$z$ interloper cannot completely be rejected ($sim23%$) with the current dataset. The dataset presented in this study is also suited for intermediate and low-$z$ science cases.
We present a complete census of all Herschel-detected sources within the six massive lensing clusters of the HST Frontier Fields (HFF). We provide a robust legacy catalogue of 263 sources with Herschel fluxes, primarily based on imaging from the Herschel Lensing Survey (HLS) and PEP/HerMES Key Programmes. We optimally combine Herschel, Spitzer and WISE infrared (IR) photometry with data from HST, VLA and ground-based observatories, identifying counterparts to gain source redshifts. For each Herschel-detected source we also present magnification factor (mu), intrinsic IR luminosity and characteristic dust temperature, providing a comprehensive view of dust-obscured star formation within the HFF. We demonstrate the utility of our catalogues through an exploratory overview of the magnified population, including more than 20 background sub-LIRGs unreachable by Herschel without the assistance gravitational lensing.
We present a full data analysis of the pure-parallel Hubble Space Telescope (HST) imaging observations in the Brightest of Reionizing Galaxies Survey (BoRG[z9]) in Cycle 22. The medium-deep exposures with five HST/WFC3IR+UVIS filter bands from 79 independent sightlines (~370 arcmin^2) provide the least biased determination of number density for z>9 bright galaxies against cosmic variance. After a strict two-step selection for candidate galaxies, including dropout color and photometric redshift analyses, and revision of previous BoRG candidates, we identify one source at z~10 and two sources at z~9. The z~10 candidate shows evidence of line-of-sight lens magnification (mu~1.5), yet it appears surprisingly luminous (MUV ~ -22.6pm0.3 mag), making it one of the brightest candidates at z > 8 known (~ 0.3 mag brighter than the z = 8.68 galaxy EGSY8p7, spectroscopically confirmed by Zitrin and collaborators). For z ~ 9 candidates, we include previous data points at fainter magnitudes and find that the data are well fitted by a Schechter luminosity function with alpha ~ -2.1, MUV ~ -21.5 mag, and log phi ~ -4.5 Mpc^-3mag^-1, for the first time without fixing any parameters. The inferred cosmic star formation rate density is consistent with unaccelerated evolution from lower redshift.
We make publicly available a catalog of calibrated environmental measures for galaxies in the five 3D-HST/CANDELS deep fields. Leveraging the spectroscopic and grism redshifts from the 3D-HST survey, multi wavelength photometry from CANDELS, and wider field public data for edge corrections, we derive densities in fixed apertures to characterize the environment of galaxies brighter than $JH_{140} < 24$ mag in the redshift range $0.5<z<3.0$. By linking observed galaxies to a mock sample, selected to reproduce the 3D-HST sample selection and redshift accuracy, each 3D-HST galaxy is assigned a probability density function of the host halo mass, and a probability that is a central or a satellite galaxy. The same procedure is applied to a $z=0$ sample selected from SDSS. We compute the fraction of passive central and satellite galaxies as a function of stellar and halo mass, and redshift, and then derive the fraction of galaxies that were quenched by environment specific processes. Using the mock sample, we estimate that the timescale for satellite quenching is $t_{rm quench} sim 2-5$ Gyr; longer at lower stellar mass or lower redshift, but remarkably independent of halo mass. This indicates that, in the range of environments commonly found within the 3D-HST sample, satellites are quenched by exhaustion of their gas reservoir in absence of cosmological accretion. We find that the quenching times can be separated into a delay phase during which satellite galaxies behave similarly to centrals at fixed stellar mass, and a phase where the star formation rate drops rapidly ($sim 0.4-0.6$ Gyr), as shown previously at $z=0$. We conclude that this scenario requires satellite galaxies to retain a large reservoir of multi-phase gas upon accretion, even at high redshift, and that this gas sustains star formation for the long quenching times observed.
The James Webb Space Telescope will allow to spectroscopically study an unprecedented number of galaxies deep into the reionization era, notably by detecting [OIII] and H$beta$ nebular emission lines. To efficiently prepare such observations, we photometrically select a large sample of galaxies at $zsim8$ and study their rest-frame optical emission lines. Combining data from the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) survey and from HST, we perform spectral energy distribution (SED) fitting, using synthetic SEDs from a large grid of photoionization models. The deep Spitzer/IRAC data combined with our models exploring a large parameter space enables to constrain the [OIII]+H$beta$ fluxes and equivalent widths for our sample, as well as the average physical properties of $zsim8$ galaxies, such as the ionizing photon production efficiency with $log(xi_mathrm{ion}/mathrm{erg}^{-1}hspace{1mm}mathrm{Hz})geq25.77$. We find a relatively tight correlation between the [OIII]+H$beta$ and UV luminosity, which we use to derive for the first time the [OIII]+H$beta$ luminosity function (LF) at $zsim8$. The $zsim8$ [OIII]+H$beta$ LF is higher at all luminosities compared to lower redshift, as opposed to the UV LF, due to an increase of the [OIII]+H$beta$ luminosity at a given UV luminosity from $zsim3$ to $zsim8$. Finally, using the [OIII]+H$beta$ LF, we make predictions for JWST/NIRSpec number counts of $zsim8$ galaxies. We find that the current wide-area extragalactic legacy fields are too shallow to use JWST at maximal efficiency for $zsim8$ spectroscopy even at 1hr depth and JWST pre-imaging to $gtrsim30$ mag will be required.
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