Wide-field Near-infrared Survey Research Articles

Finding Lensed Direct-collapse Black Holes and Supermassive Primordial Stars

Direct-collapse black holes (DCBHs) may be the seeds of the first quasars, over 200 of which have now been detected at z > 6. The James Webb Space Telescope (JWST) could detect DCBHs in the near-infrared (NIR) at z ≲ 20 and probe the evolution of primordial quasars at their earliest stages, but only in narrow fields that may not capture many of them. Wide-field NIR surveys by Euclid and the Nancy Grace Roman Space Telescope (RST) would enclose far greater numbers of DCBHs but only directly detect them at z ≲ 6–8 because of their lower sensitivities. However, their large survey areas will cover thousands of galaxy clusters and massive galaxies that could gravitationally lens flux from DCBHs, boosting them above current Euclid and RST detection limits and revealing more of them than could otherwise be detected. Here, we estimate the minimum number density of strongly lensed DCBHs and supermassive primordial stars required for detection in surveys by Euclid, RST, and JWST at z ≲ 20. We find that for reasonable estimates of host halo numbers RST, Euclid, and JWST could potentially find hundreds of strongly lensed DCBHs at z = 7–20. RST would detect the most objects at z ≲ 10 and JWST would find the most at higher redshifts. Lensed supermassive primordial stars could potentially also be found, but in fewer numbers because of their short lifetimes.

Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey – IV. Upper Sco★

We present the results of a proper motion wide-field near-infrared survey of the entire Upper Sco (USco) association (∼160 square degrees) released as part of the United Kingdom Infrared Telescope Infrared Deep Sky (UKIDSS) Galactic Clusters Survey (GCS) Data Release 10 (DR10). We have identified a sample of ∼400 astrometric and photometric member candidates combining proper motions and photometry in five near-infrared passbands and another 286 with HK photometry and 2MASS/GCS proper motions. We also provide revised membership for all previously published USco low-mass stars and substellar members based on our selection and identify new candidates, including in regions affected by extinction. We find negligible variability between the two K-band epochs, below the 0.06 mag rms level. We estimate an upper limit of 2.2 per cent for wide common proper motions with projected physical separations less than ∼15 000 au. We derive a disc frequency for USco low-mass stars and brown dwarfs between 26 and 37 per cent, in agreement with estimates in IC 348 and σ Ori. We derive the mass function of the association and find it consistent with the (system) mass function of the solar neighbourhood and other clusters surveyed by the GCS in the 0.2–0.03 M⊙ mass range. We confirm the possible excess of brown dwarfs in USco.

Detectability of high-redshift superluminous supernovae with upcoming optical and near-infrared surveys

Observations of high-redshift supernovae (SNe) open a novel opportunity to study the massive star population in the early Universe. We study the detectability of superluminous SNe with upcoming optical and near-infrared (NIR) surveys. Our calculations are based on the cosmic star formation history, the SN occurence rate, the characteristic colour and the light curve of the SNe that are all calibrated by available observations. We show that 15-150 SNe up to z ~ 4 will be discovered by the proposed Subaru/Hyper Suprime-Cam deep survey: 30 deg^2 survey with 24.5 AB mag depth in z-band for 3 months. With its ultra-deep layer (3.5 deg^2 with 25.6 AB mag depth in z-band for 4 months), the highest redshift can be extended to z ~ 5. We further explore the detectability by upcoming NIR survey utilizing future satellites such as Euclid, WFIRST, and WISH. The wide-field NIR surveys are very efficient to detect high-redshift SNe. With a hypothetical deep NIR survey for 100 deg^2 with 26 AB mag depth at 1-4 um, at least ~ 50 SNe will be discovered at z>3 in half a year. The number of the detected SNe can place a strong constraint on the stellar initial mass function or its slope especially at the high-mass end. Superluminous SNe at high redshifts can be distinguished from other types of SNe by the long time-scale of their light curves in the observer's frame, the optical colours redder than other core-collapse SNe and the NIR colours redder than any other types of SNe.

Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey - I. The Pleiades★

We present the results of a deep wide-field near-infrared survey of the entire Pleiades cluster recently released as part of the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 9 (DR9). We have identified a sample of ∼1000 Pleiades cluster member candidates combining photometry in five near-infrared passbands and proper motions derived from the multiple epochs provided by the UKIDSS GCS DR9. We also provide revised membership for all previously published Pleiades low-mass stars and brown dwarfs in the past decade recovered in the UKIDSS GCS DR9 Pleiades survey based on the new photometry and astrometry provided by the GCS. We find no evidence of K-band variability in the Pleiades members larger than ∼0.08 mag. In addition, we infer a substellar binary frequency of 22–31 per cent in the 0.075–0.03 M⊙ range for separations less than ∼100 au. We employed two independent but complementary methods to derive the cluster luminosity and mass functions: a probabilistic analysis and a more standard approach consisting of stricter astrometric and photometric cuts. We found that the resulting luminosity and mass functions obtained from both methods are very similar. We derive the Pleiades mass function in the 0.6–0.03 M⊙ range and found that it is best reproduced by a lognormal representation with a mean characteristic mass of 0.20 ± 0.05 M⊙, in agreement with earlier studies and the extrapolation of the field mass function.

Deep wide-field near-infrared survey of the Carina Nebula

(abbreviated) We used HAWK-I at the ESO VLT to produce a near-infrared survey of the Carina Nebula that is deep enough to detect the full low-mass stellar population. The results of a recent deep X-ray survey are used to distinguish between young stars in Carina and background contaminants. We find that the ages of the low-mass stars (derived from color-magnitude diagrams of the invidual cluster in the Carina Nebula) agree with previous age estimates for the massive stars. About 3200 of the X-ray selected stars have masses >= 1 Msun; this number is in good agreement with extrapolations of the field IMF based on the number of high-mass stars and shows that there is no deficit of low-mass stars. The near-infrared excess fractions for the stellar populations in Carina are lower than typical for other, less massive clusters of similar age, suggesting a faster timescale of circumstellar disk dispersal than in the more quiescent regions, most likely due to the very high level of massive star feedback. Narrow-band images reveal six molecular hydrogen jets. However, none of the optical HH objects shows molecular hydrogen emission, suggesting that the jet-driving protostars are located very close to the edges of the globules in which they are embedded. This adds strong support to the scenario that their formation was triggered by the advancing ionization fronts.

DENIS J081730.0–615520: AN OVERLOOKED MID-T DWARF IN THE SOLAR NEIGHBORHOOD

Recent wide-field near-infrared surveys have uncovered a large number of cool brown dwarfs (BDs), extending the temperature sequence down to less than 500 K and constraining the faint end of the luminosity function (LF). One interesting implication of the derived LF is that the BD census in the immediate (<10 pc) solar neighborhood is still largely incomplete, and some bright (J < 16) BDs remain to be identified in existing surveys. These objects are especially interesting as they are the ones that can be studied in most detail, especially with techniques that require large fluxes (e.g., time-variability, polarimetry, and high-resolution spectroscopy) that cannot realistically be applied to objects uncovered by deep surveys. By cross-matching the DEep Near-Infrared Survey of the Southern sky (DENIS) and the Two Micron All Sky Survey point-source catalogs, we have identified an overlooked BD—DENIS J081730.0−615520—that is the brightest field mid-T dwarf in the sky (J = 13.6). We present astrometry and spectroscopy follow-up observations of this BD. Our data indicate a spectral type T6 and a distance—from parallax measurement—of 4.9 ± 0.3 pc, placing this mid-T dwarf among the three closest isolated BDs to the Sun.

A wide deep infrared look at the Pleiades with UKIDSS: new constraints on the substellar binary fraction and the low-mass initial mass function

Abstract We present the results of a deep wide-field near-infrared survey of 12 deg2 of the Pleiades conducted as part of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey (GCS). We have extracted over 340 high-probability proper motion (PM) members down to 0.03 M⊙ using a combination of UKIDSS photometry and PM measurements obtained by cross-correlating the GCS with data from the Two Micron All Sky Survey, the Isaac Newton Telescope and the Canada–France–Hawaii Telescope. Additionally, we have unearthed 73 new candidate brown dwarf (BD) members on the basis of five-band UKIDSS photometry alone. We have identified 23 substellar multiple system candidates out of 63 candidate BDs from the (Y−K, Y) and (J−K, J) colour–magnitude diagrams, yielding a binary frequency of 28–44 per cent in the 0.075−0.030 M⊙ mass range. Our estimate is three times larger than the binary fractions reported from high-resolution imaging surveys of field ultracool dwarfs and Pleiades BDs. However, it is marginally consistent with our earlier ‘peculiar’ photometric binary fraction of 50 ± 10 per cent presented by Pinfield et al., in good agreement with the 32–45 per cent binary fraction derived from the recent Monte Carlo simulations of Maxted &amp; Jeffries and compatible with the 26 ± 10 per cent frequency recently estimated by Basri &amp; Reiners. A tentative estimate of the mass ratios from photometry alone seems to support the hypothesis that binary BDs tend to reside in near equal-mass ratio systems. In addition, the recovery of four Pleiades members targeted by high-resolution imaging surveys for multiplicity studies suggests that half of the binary candidates may have separations below the resolution limit of the Hubble Space Telescope or current adaptive optics facilities at the distance of the Pleiades (a ∼7 au). Finally, we have derived luminosity and mass functions from the sample of photometric candidates with membership probabilities. The mass function is well modelled by a lognormal peaking at 0.24 M⊙ and is in agreement with previous studies in the Pleiades.

Stellar Populations at Higher Redshifts

We will review some recent advances in understanding the evolution of stellar populations in galaxies at relatively higher redshifts (z ≳ 0.5). We will focus on “mass assembly”, “down-sizing” and “high-z zoo” which have been among the most major topics and have seen great observational achievements in the past few years. In particular, wide-field near-infrared surveys, large spectroscopic surveys, and the Spitzer observations at infrared wavelengths, have unveiled underlying stellar masses and dusty star formation in high-z galaxies, which have been crucial in making such recent progresses.