We report the rest-frame ultraviolet luminosity function of g-dropout galaxies in 177 protocluster candidates (PC UVLF) at z ∼ 4 selected in the Hyper Suprime-Cam Subaru Strategic Program. Comparing ...it with the UVLF of field galaxies at the same redshift, we find that the PC UVLF shows a significant excess toward the bright end. This excess cannot be explained by the contribution of only active galactic nuclei, and we also find that this excess is more significant in higher density regions. Assuming that all protocluster members are located on the star formation main sequence, the PC UVLF can be converted into a stellar mass function. Consequently, our protocluster members are inferred to have a 2.8 times more massive characteristic stellar mass than that of the field Lyman break galaxies at the same redshift. This study, for the first time, clearly shows that the enhancement in star formation or stellar mass in overdense regions can generally be seen as early as at z ∼ 4. We also estimate the star formation rate density (SFRD) in protocluster regions as 6%-20% of the cosmic SFRD, based on the measured PC UVLF after correction for the selection incompleteness in our protocluster sample. This high value suggests that protoclusters make a nonnegligible contribution to the cosmic SFRD at z ∼ 4, as previously suggested by simulations. Our results suggest that protoclusters are essential components for galaxy evolution at z ∼ 4.
We construct light cones for the semi-analytic galaxy formation simulation of Guo et al. and make mock catalogues for comparison with deep high-redshift surveys. Photometric properties are calculated ...with two different stellar population synthesis codes in order to study sensitivity to this aspect of the modelling. The catalogues are publicly available and include photometry for a large number of observed bands from 4000 Å to 6 μ m, as well as rest-frame photometry and other intrinsic properties of the galaxies (e.g. positions, peculiar velocities, stellar masses, sizes, morphologies, gas fractions, star formation rates, metallicities, halo properties). Guo et al. tuned their model to fit the low-redshift galaxy population but noted that at z≥ 1 it overpredicts the abundance of galaxies below the 'knee' of the stellar mass function. Here we extend the comparison to deep galaxy counts in the B, i, J, K and IRAC 3.6, 4.5 and 5.8 μ m bands, to the redshift distributions of K and 5.8 μ m selected galaxies, the evolution of rest-frame luminosity functions in the B and K bands and the evolution of rest-frame optical versus near-infrared colours. The B, i and J counts are well reproduced, but at longer wavelengths the overabundant high-redshift galaxies produce excess faint counts. At bright magnitudes, counts in the IRAC bands are underpredicted, reflecting overly low stellar metallicities and the neglect of polycyclic aromatic hydrocarbon emission. The predicted redshift distributions for K and 5.8 μ m selected samples highlight the effect of emission from thermally pulsing asymptotic giant branch (AGB) stars. The full treatment of the Maraston model predicts three times as many z∼ 2 galaxies in faint 5.8 μ m selected samples as the model of Bruzual & Charlot, whereas the two models give similar predictions for K-band selected samples. Although luminosity functions are adequately reproduced out to z∼ 3 in rest-frame B, the same is true at rest-frame K only if thermally pulsating AGB emission is included, and then only at high luminosity. Fainter than L
★, the two synthesis models agree but overpredict the number of galaxies, another reflection of the overabundance of ∼1010 M⊙ model galaxies at z≥ 1. The model predicts that red, passive galaxies should already be in place at z= 2 as required by observations.
We have carried out deep and wide field imaging observations with narrow bands, targeting 11 quasar fields to systematically study the possible photoevaporation effect of quasar radiation on ...surrounding low mass galaxies at z ∼ 2-3. We focused on Ly emitters (LAEs) at the same redshifts as quasars that lie within the quasar proximity zones, where the UV radiation from the quasars is higher than the average background at that epoch. We found that LAEs with high rest-frame equivalent width of Ly emission (EW0) of 150 with low stellar mass ( 108 M ) are predominantly scarce in the quasar proximity zones, suggesting that quasar photoevaporation effects may be taking place. The halo mass of LAEs with EW0 > 150 is estimated to be either from spectral energy distribution fitting or the main sequence. Based on a hydrodynamical simulation, the predicted delay in star formation under a local UV background intensity with erg s−1 cm−2 Hz−1 sr−1 for galaxies having less than this halo mass is about >20 Myr, which is longer than the expected age of LAEs with EW0 > 150 . On the other hand, photoevaporation seems to be less effective around very luminous quasars, which is consistent with the idea that these are still in an early stage of activity.
Abstract
We conduct a systematic search for galaxy protoclusters at z ∼ 3.8 based on the latest internal data release (S16A) of the Hyper Suprime-Cam Subaru strategic program (HSC-SSP). In the Wide ...layer of the HSC-SSP, we investigate the large-scale projected sky distribution of g-dropout galaxies over an area of 121 deg2, and identify 216 large-scale overdense regions (>4 σ overdensity significance) that are likely protocluster candidates. Of these, 37 are located within 8΄ (3.4 physical Mpc) of other protocluster candidates of higher overdensity, and are expected to merge into a single massive structure by z = 0. Therefore, we find 179 unique protocluster candidates in our survey. A cosmological simulation that includes projection effects predicts that more than 76% of these candidates will evolve into galaxy clusters with halo masses of at least 1014 M⊙ by z = 0. The unprecedented size of our protocluster candidate catalog allows us to perform, for the first time, an angular clustering analysis of the systematic sample of protocluster candidates. We find a correlation length of 35.0 h−1 Mpc. The relation between correlation length and number density of z ∼ 3.8 protocluster candidates is consistent with the prediction of the ΛCDM model, and the correlation length is similar to that of rich clusters in the local universe. This result suggests that our protocluster candidates are tracing similar spatial structures to those expected from the progenitors of rich clusters, and enhances the confidence that our method for identifying protoclusters at high redshifts is robust. In years to come, our protocluster search will be extended to the entire HSC-SSP Wide sky coverage of ∼ 1400 deg2 to probe cluster formation over a wide redshift range of z ∼ 2–6.
Motivated by recent observational studies of the environment of z∼ 6 QSOs, we have used the Millennium Run (MR) simulations to construct a very large (∼4°× 4°) mock redshift survey of star-forming ...galaxies at z∼ 6. We use this simulated survey to study the relation between density enhancements in the distribution of i775-dropouts and Lyα emitters, and their relation to the most massive haloes and protocluster regions at z∼ 6. Our simulation predicts significant variations in surface density across the sky with some voids and filaments extending over scales of 1°, much larger than probed by current surveys. Approximately one-third of all z∼ 6 haloes hosting i-dropouts brighter than z= 26.5 mag (≈M*UV,z=6) become part of z= 0 galaxy clusters. i-dropouts associated with protocluster regions are found in regions where the surface density is enhanced on scales ranging from a few to several tens of arcminutes on the sky. We analyse two structures of i-dropouts and Lyα emitters observed with the Subaru Telescope and show that these structures must be the seeds of massive clusters in formation. In striking contrast, six z∼ 6 QSO fields observed with Hubble Space Telescope show no significant enhancements in their i775-dropout number counts. With the present data, we cannot rule out the QSOs being hosted by the most massive haloes. However, neither can we confirm this widely used assumption. We conclude by giving detailed recommendations for the interpretation and planning of observations by current and future ground- and space-based instruments that will shed new light on questions related to the large-scale structure at z∼ 6.
We report on the results of Hubble Space Telescope optical and UV imaging, Spitzer mid-IR photometry, and optical spectroscopy of a sample of 30 low-redshift (z ~ 0.1 to 0.3) galaxies chosen from the ...Sloan Digital Sky Survey and Galaxy Evolution Explorer surveys to be accurate local analogs of the high-redshift Lyman break galaxies. The Lyman break analogs (LBAs) are similar in stellar mass, metallicity, dust extinction, star formation rate (SFR), physical size, and gas velocity dispersion, thus enabling a detailed investigation of many processes that are important in star-forming galaxies at high redshift. The main optical emission-line properties of LBAs, including evidence for outflows, are also similar to those typically found at high redshift. This indicates that the conditions in their interstellar medium are comparable. In the UV, LBAs are characterized by complexes of massive clumps of star formation, while in the optical they most often show evidence for (post-)mergers and interactions. In six cases, we find a single extremely massive (up to several X109 M ) compact (radius ~102 pc) dominant central object (DCO). The DCOs are preferentially found in LBAs with the highest mid-IR luminosities (L 24 Delta *mm = 1010.3-1011.2 L ) and correspondingly high SFRs (15-100 M yr-1). We show that the massive star-forming clumps (including the DCOs) have masses much larger than the nuclear super star clusters seen in normal late-type galaxies. However, the DCOs do have masses, sizes, and densities similar to the excess light/central cusps seen in typical elliptical galaxies with masses similar to the LBA galaxies. We suggest that the DCOs form in the present-day examples of the dissipative mergers at high redshift that are believed to have produced the central cusps in local ellipticals (consistent with the disturbed optical morphologies of the LBAs). More generally, the properties of the LBAs are consistent with the idea that instabilities in a gas-rich disk lead to very massive star-forming clumps that eventually coalesce to form a spheroid. Finally, we comment on the apparent lack of energetically significant active galactic nuclei in the DCOs. We speculate that the DCOs are too young at present to grow a supermassive black hole because they are still in a supernova-dominated outflow phase (age less than 50 Myr).
We present the results of a survey of the brightest UV-selected galaxies in protoclusters. These proto-brightest cluster galaxy (proto-BCG) candidates are drawn from 179 overdense regions of ...g-dropout galaxies at z ∼ 4 from the Hyper Suprime-Cam Subaru Strategic Program identified previously as good protocluster candidates. This study is the first to extend the systematic study of the progenitors of BCGs from z ∼ 2 to z ∼ 4. We carefully remove possible contaminants from foreground galaxies and, for each structure, select the brightest galaxy that is at least 1 mag brighter than the fifth-brightest galaxy. We select 63 proto-BCG candidates and compare their properties with those of galaxies in the field and those of other galaxies in overdense structures. The proto-BCG candidates and their surrounding galaxies have different rest-UV color (i − z) distributions to field galaxies and other galaxies in protoclusters that do not host proto-BCGs. In addition, galaxies surrounding proto-BCGs are brighter than those in protoclusters without proto-BCGs. The image stacking analysis reveals that the average effective radius of proto-BCGs is ∼28% larger than that of field galaxies. The i − z color differences suggest that proto-BCGs and their surrounding galaxies are dustier than other galaxies at z ∼ 4. These results suggest that specific environmental effects or assembly biases have already emerged in some protoclusters as early as z ∼ 4, and we suggest that proto-BCGs have different star formation histories than other galaxies in the same epoch.
ABSTRACTMotivated by recent observational studies of the environment of z similar to 6 QSOs, we have used the Millennium Run (MR) simulations to construct a very large ( similar to 4 degree 4 degree ...) mock redshift survey of star-forming galaxies at z similar to 6. We use this simulated survey to study the relation between density enhancements in the distribution of i775-dropouts and Ly alpha emitters, and their relation to the most massive haloes and protocluster regions at z similar to 6. Our simulation predicts significant variations in surface density across the sky with some voids and filaments extending over scales of 1 degree , much larger than probed by current surveys. Approximately one-third of all z similar to 6 haloes hosting i-dropouts brighter than z = 26.5 mag ( approximately M*UV,z=6) become part of z = 0 galaxy clusters. i-dropouts associated with protocluster regions are found in regions where the surface density is enhanced on scales ranging from a few to several tens of arcminutes on the sky. We analyse two structures of i-dropouts and Ly alpha emitters observed with the Subaru Telescope and show that these structures must be the seeds of massive clusters in formation. In striking contrast, six z similar to 6 QSO fields observed with Hubble Space Telescope show no significant enhancements in their i775-dropout number counts. With the present data, we cannot rule out the QSOs being hosted by the most massive haloes. However, neither can we confirm this widely used assumption. We conclude by giving detailed recommendations for the interpretation and planning of observations by current and future ground- and space-based instruments that will shed new light on questions related to the large-scale structure at z similar to 6.
We present a new analysis of the dust obscuration in starburst galaxies at low and high redshifts. This study is motivated by our unique sample of the most extreme UV-selected starburst galaxies in ...the nearby universe (z < 0.3), found to be good analogs of high-redshift Lyman break galaxies (LBGs) in most of their physical properties. We find that the dust properties of the Lyman break analogs (LBAs) are consistent with the relation derived previously by Meurer et al. (M99) that is commonly used to dust-correct star formation rate (SFR) measurements at a very wide range of redshifts. We directly compare our results with high-redshift samples (LBGs, 'BzK,' and submillimeter galaxies at z ~ 2-3) having IR data either from Spitzer or Herschel. The attenuation in typical LBGs at z ~ 2-3 and LBAs is very similar. Because LBAs are much better analogs to LBGs compared to previous local star-forming samples, including M99, the practice of dust-correcting the SFRs of high-redshift galaxies based on the local calibration is now placed on a much more solid ground. We illustrate the importance of this result by showing how the locally calibrated relation between UV measurements and extinction is used to estimate the integrated, dust-corrected SFR density at z 2-6.
Characterizing high-z quasar environments is key to understanding the coevolution of quasars and the surrounding galaxies. To restrict their global picture, we statistically examine the g-dropout ...galaxy overdensity distribution around 570 faint quasar candidates at z ∼ 4, based on the Hyper Suprime-Cam Subaru Strategic Program survey. We compare the overdensity significances of g-dropout galaxies around the quasars with those around g-dropout galaxies, and find no significant difference between their distributions. A total of 4 (22) out of the 570 faint quasars, , are found to be associated with the >4 overdense regions within an angular separation of 1.8 (3.0) arcmin, which is the typical size of protoclusters at this epoch. This is similar to the fraction of g-dropout galaxies associated with the >4 overdense regions. This result is consistent with our previous work in which and of luminous quasars detected in the Sloan Digital Sky Survey exist in the >4 overdense regions within 1 8 and 3 0 separations, respectively. Therefore, we suggest that the galaxy number densities around quasars are independent of their luminosity, and most quasars do not preferentially appear in the richest protocluster regions at z ∼ 4. The lack of an apparent positive correlation between the quasars and the protoclusters implies that (i) the gas-rich major merger rate is relatively low in the protocluster regions, (ii) most high-z quasars may appear through secular processes, or (iii) some dust-obscured quasars exist in the protocluster regions.
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