skip to main content

Title: Forecasts for broad-band intensity mapping of the ultraviolet-optical background with CASTOR and SPHEREx

Broad-band tomography statistically extracts the redshift distribution of frequency dependent emission from the cross-correlation of intensity maps with a reference catalog of galaxy tracers. We make forecasts for the performance of future all-sky UV experiments doing broad-band tomography. We consider the Cosmological Advanced Survey Telescope for Optical-UV Research (castor) and the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx). The dominant uncertainty is from variability in the photometric zero-point, which scales with limiting magnitude and mirror size. With this scaling and assuming a galaxy number density characteristic of future spectroscopic data sets, we find that castor measures the UV background SED 2–10 times better than existing data. The applicable redshift range will expand from the current z < 1 to z ≈ 0–3 with castor and z = 5–9 with SPHEREx. We show that castor can provide competitive constraints on the EBL monopole to those available from galaxy number counts and direct measurement techniques. At high redshift especially, these results will help understand galaxy formation and reionization. Our modelling code and chains are publicly available.

; ;
Award ID(s):
Publication Date:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Page Range or eLocation-ID:
p. 5158-5170
Oxford University Press
Sponsoring Org:
National Science Foundation
More Like this

    Recent work has shown that UV-luminous reionization-era galaxies often exhibit strong Lyman-alpha emission despite being situated at redshifts where the IGM is thought to be substantially neutral. It has been argued that this enhanced Ly α transmission reflects the presence of massive galaxies in overdense regions which power large ionized bubbles. An alternative explanation is that massive galaxies shift more of their Ly α profile to large velocities (relative to the systemic redshift) where the IGM damping wing absorption is reduced. Such a mass-dependent trend is seen at lower redshifts, but whether one exists at z ∼ 7 remains unclear owing to the small number of existing systemic redshift measurements in the reionization era. This is now changing with the emergence of [C ii]-based redshifts from ALMA. Here, we report MMT/Binospec Ly α spectroscopy of eight UV-bright (MUV ∼ −22) galaxies at z ≃ 7 selected from the ALMA REBELS survey. We detect Ly α in four of eight galaxies and use the [C ii] systemic redshifts to investigate the Ly α velocity profiles. The Ly α lines are significantly redshifted from systemic (average velocity offset = 223 km s–1) and broad (FWHM ≈ 300–650 km s−1), with two sources showing emission extending to ≈750 km s−1. We find that the broadest Ly α profiles aremore »associated with the largest [C ii] line widths, suggesting a potential link between the Ly α FWHM and the dynamical mass. Since Ly α photons at high velocities transmit efficiently through the z = 7 IGM, our data suggest that velocity profiles play a significant role in boosting the Ly α visibility of the most UV-luminous reionization-era galaxies.

    « less

    The measurement of the expansion history of the Universe from the redshift unknown gravitational wave (GW) sources (dark GW sources) detectable from the network of LIGO-Virgo-KAGRA (LVK) detectors depends on the synergy with the galaxy surveys having accurate redshift measurements over a broad redshift range, large sky coverage, and detectability of fainter galaxies.In this work, we explore the possible synergy of the LVK with the spectroscopic galaxy surveys, such as DESI and SPHEREx, to measure the cosmological parameters which are related to the cosmic expansion history and the GW bias parameters. We show that by using the 3D spatial cross-correlation between the dark GW sources and the spectroscopic galaxy samples, we can measure the value of Hubble constant with about $2{{\ \rm per\ cent}}$ and $1.5{{\ \rm per\ cent}}$ precision from LVK+DESI and LVK+SPHEREx, respectively within the 5 yr of observation time with $50{{\ \rm per\ cent}}$ duty-cycle. Similarly, the dark energy equation of state can be measured with about $10{{\ \rm per\ cent}}$ and $8{{\ \rm per\ cent}}$ precision from LVK+DESI and LVK+SPHEREx, respectively. We find that due to the large sky coverage of SPHEREx than DESI, performance in constraining the cosmological parameters is better from the former thanmore »the latter. By combining Euclid along with DESI and SPHEREx, a marginal gain in the measurability of the cosmological parameters is possible from the sources at high redshift (z ≥ 0.9).

    « less

    We present band 6 ALMA observations of a heavily obscured radio-loud (L1.4 GHz = 1025.4 W Hz−1) active galactic nucleus (AGN) candidate at zphot = 6.83 ± 0.06 found in the 1.5 deg2 COSMOS field. The ALMA data reveal detections of exceptionally strong [C ii]158 $\mu$m (z[C ii] = 6.8532) and underlying dust continuum emission from this object (COS-87259), where the [C ii] line luminosity, line width, and 158 $\mu$m continuum luminosity are comparable to those seen from z ∼ 7 sub-mm galaxies and quasar hosts. The 158 $\mu$m continuum detection suggests a total infrared luminosity of $9\times 10^{12}\, \mathrm{ L}_\odot$ with corresponding very large obscured star formation rate (1300 M⊙ yr−1) and dust mass ($2\times 10^9\, \mathrm{ M}_\odot$). The strong break seen between the VIRCam and IRAC photometry perhaps suggests that COS-87259 is an extremely massive reionization-era galaxy with $M_\ast \approx 1.7\times 10^{11}\, \mathrm{ M}_\odot$. Moreover, the MIPS, PACS, and SPIRE detections imply that this object harbours an AGN that is heavily obscured ($\tau _{_{\mathrm{9.7\,\mu m}}}=2.3$) with a bolometric luminosity of approximately $5\times 10^{13}\, \mathrm{ L}_\odot$. Such a very high AGN luminosity suggests that this object is powered by an ≈1.6 × 10$^9\, \mathrm{ M}_\odot$ black hole if accreting near the Eddington limit, and is effectively a highly obscured version of an extremely ultravioletmore »(UV)-luminous (M1450 ≈ −27.3) z ∼ 7 quasar. Notably, these z ∼ 7 quasars are an exceedingly rare population (∼0.001 deg−2), while COS-87259 was identified over a relatively small field. Future very wide area surveys with e.g. Roman and Euclid have the potential to identify many more extremely red yet UV-bright z ≳ 7 objects similar to COS-87259, providing richer insight into the occurrence of intense obscured star formation and supermassive black hole growth among this population.

    « less

    The connection between the escape fraction of ionizing radiation (fesc) and the properties of galaxies, such as stellar mass ($\rm M_{\rm *}$), age, star-formation rate (SFR), and dust content, are key inputs for reionization models, but many of these relationships remain untested at high redshift. We present an analysis of a sample of 96 $z$ ∼ 3 galaxies from the Keck Lyman Continuum Spectroscopic Survey (KLCS). These galaxies have both sensitive Keck/LRIS spectroscopic measurements of the Lyman continuum (LyC) region, and multiband photometry that places constraints on stellar population parameters. We construct composite spectra from subsamples binned as a function of galaxy property and quantify the ionizing-photon escape for each composite. We find a significant anti-correlation between fesc and $\rm M_{\rm *}$, consistent with predictions from cosmological zoom-in simulations. We also find significant anti-correlation between fesc and E(B−V), encoding the underlying physics of LyC escape in our sample. We also find no significant correlation between fesc and either stellar age or specific SFR (= SFR/$\rm M_{\rm *}$), challenging interpretations that synchronize recent star formation and favorable conditions for ionizing escape. The galaxy properties now shown to correlate with fesc in the KLCS are Lyα equivalent width, UV Luminosity, $\rm M_{\rmmore »*}$, SFR, and E(B−V), but not age or sSFR. This comprehensive analysis of galaxy properties and LyC escape at high redshift will be used to guide future models and observations of the reionization epoch.

    « less

    We report the identification of radio (0.144–3 GHz) and mid-, far-infrared, and sub-mm (24–850μm) emission at the position of one of 41 UV-bright ($\mathrm{M_{\mathrm{UV}}}^{ }\lesssim -21.25$) z ≃ 6.6–6.9 Lyman-break galaxy candidates in the 1.5 deg2 COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor >3) between two narrow/intermediate bands at 9450 and 9700 Å and is undetected in all nine bands blueward of 9600 Å, as expected from a Lyman alpha break at z ≃ 6.8. The full multiwavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M* = 1010.8 M⊙) and extremely red (rest-UV slope β = −0.59) z ≃ 6.8 galaxy with hyperluminous infrared emission (LIR = 1013.6 L⊙) powered by both an intense burst of highly obscured star formation (SFR ≈ 1800 M⊙ yr−1) and an obscured ($\tau _{_{\mathrm{9.7\mu m}}} = 7.7\pm 2.5$) radio-loud (L1.4 GHz ≈ 1025.4 W Hz−1) active galactic nucleus (AGN). The radio emission is compact (1.04 ± 0.12 arcsec) and exhibits an ultra-steep spectrum between 1.32 and 3 GHz ($\alpha =-1.57^{+0.22}_{-0.21}$) that flattens at lower frequencies ($\alpha = -0.86^{+0.22}_{-0.16}$ between 0.144 and 1.32 GHz), consistent with known z > 4 radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11×) galaxymore »overdensity, as common for systems hosting radio-loud AGN. While we find that low-redshift solutions to the optical + near-infrared data are not preferred, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 beyond any doubt. If confirmed to lie at z ≃ 6.8, the properties of COS-87259 would be consistent with a picture wherein AGN and highly obscured star formation activity are fairly common among very massive (M* > 1010 M⊙) reionization-era galaxies.

    « less