ALBERT

Description: Using star-forming galaxies sample in the nearby Universe (0.02 〈  z  〈 0.10) selected from the Sloan Digital Sky Survey (DR7) and Galaxy Evolution Explorer all-sky survey (GR5), we present a new empirical calibration for predicting dust extinction of galaxies from the Hα-to-FUV flux ratio. We find that the Hα dust extinction ( A Hα ) derived with Hα/Hβ ratio (Balmer decrement) increases with increasing Hα/UV ratio as expected, but there remains a considerable scatter around the relation, which is largely dependent on stellar mass and/or Hα equivalent width (EW Hα ). At fixed Hα/UV ratio, galaxies with higher stellar mass (or galaxies with lower EW Hα ) tend to be more highly obscured by dust. We quantify this trend and establish an empirical calibration for predicting A Hα with a combination of Hα/UV ratio, stellar mass, and EW Hα , with which we can successfully reduce the systematic uncertainties accompanying the simple Hα/UV approach by ~15–30 per cent. The new recipes proposed in this study will provide a convenient tool for predicting dust extinction level of galaxies particularly when Balmer decrement is not available. By comparing A Hα (derived with Balmer decrement) and A UV (derived with IR/UV luminosity ratio) for a subsample of galaxies for which AKARI far-infrared photometry is available, we demonstrate that more massive galaxies tend to have higher extra extinction towards the nebular regions compared to the stellar continuum light. Considering recent studies reporting smaller extra extinction towards nebular regions for high-redshift galaxies, we argue that the dust geometry within high-redshift galaxies resembles low-mass galaxies in the nearby Universe.

Description: We investigate the properties of z  = 2.23 Hα and [O iii ] 5007 emitters using the narrow-band-selected samples obtained from the High- z Emission Line Survey. We construct two samples of the Hα and [O iii ] emitters and compare their integrated physical properties. We find that the distribution of stellar masses, dust extinction, star formation rates (SFRs), and specific SFRs (sSFRs) is not statistically different between the two samples. When we separate the full galaxy sample into three subsamples according to the detections of the Hα and/or [O iii ] emission lines, most of the sources detected with both Hα and [O iii ] show log(sSFR UV ) –9.5. The comparison of the three subsamples suggests that sources with strong [O iii ] line emission tend to have the highest star-forming activity out all galaxies that we study. We argue that the [O iii ] emission line can be used as a tracer of star-forming galaxies at high redshift, and that it is especially useful to investigate star-forming galaxies at z  〉 3, for which Hα emission is no longer observable from the ground.

Description: In animal ribosomes, two stalk proteins P1 and P2 form a heterodimer, and the two dimers, with the anchor protein P0, constitute a pentameric complex crucial for recruitment of translational GTPase factors to the ribosome. To investigate the functional contribution of each copy of the stalk proteins, we constructed P0 mutants, in which one of the two C-terminal helices, namely helix I (N-terminal side) or helix II (C-terminal side) were unable to bind the P1–P2 dimer. We also constructed ‘one-C-terminal domain (CTD) stalk dimers’, P1–P2 C and P1 C –P2, composed of intact P1/P2 monomer and a CTD-truncated partner. Through combinations of P0 and P1–P2 variants, various complexes were reconstituted and their function tested in eEF-2-dependent GTPase and eEF-1α/eEF-2-dependent polyphenylalanine synthesis assays in vitro . Double/single-CTD dimers bound to helix I showed higher activity than that bound to helix II. Despite low polypeptide synthetic activity by a single one-CTD dimer, its binding to both helices considerably increased activity, suggesting that two stalk dimers cooperate, particularly in polypeptide synthesis. This promotion of activity by two stalk dimers was lost upon mutation of the conserved YPT sequence connecting the two helices of P0, suggesting a role for this sequence in cooperativity of two stalk dimers.

Description: We present a Herschel /Spectral and Photometric Imaging Receiver (SPIRE) survey of three protoclusters at z = 2–3 (2QZCluster, HS1700, SSA22). Based on the SPIRE colours ( S 350 / S 250 and S 500 / S 350 ) of 250 μm sources, we selected high-redshift dusty star-forming galaxies potentially associated with the protoclusters. In the 2QZCluster field, we found a 4 overdensity of six SPIRE sources around 4.5 arcmin (~2.2 Mpc) from a density peak of H α emitters at z = 2.2. In the HS1700 field, we found a 5 overdensity of eight SPIRE sources around 2.1 arcmin (~1.0 Mpc) from a density peak of Lyman-break galaxies at z = 2.3. We did not find any significant overdensities in SSA22 field, but we found three 500 μm sources are concentrated 3 arcmin (~1.4 Mpc) east to the Ly α emitters overdensity. If all the SPIRE sources in these three overdensities are associated with protoclusters, the inferred star formation rate densities are 10 3 –10 4 times higher than the average value at the same redshifts. This suggests that dusty star formation activity could be very strongly enhanced in z ~ 2–3 protoclusters. Further observations are needed to confirm the redshifts of the SPIRE sources and to investigate what processes enhance the dusty star formation activity in z ~ 2–3 protoclusters.

Description: Proteins Rpf2 and Rrs1 are required for 60S ribosomal subunit maturation. These proteins are necessary for the recruitment of three ribosomal components (5S ribosomal RNA [rRNA], RpL5 and RpL11) to the 90S ribosome precursor and subsequent 27SB pre-rRNA processing. Here we present the crystal structure of the Aspergillus nidulans ( An ) Rpf2-Rrs1 core complex. The core complex contains the tightly interlocked N-terminal domains of Rpf2 and Rrs1. The Rpf2 N-terminal domain includes a Brix domain characterized by similar N- and C-terminal architecture. The long α-helix of Rrs1 joins the C-terminal half of the Brix domain as if it were part of a single molecule. The conserved proline-rich linker connecting the N- and C-terminal domains of Rrs1 wrap around the side of Rpf2 and anchor the C-terminal domain of Rrs1 to a specific site on Rpf2. In addition, gel shift analysis revealed that the Rpf2-Rrs1 complex binds directly to 5S rRNA. Further analysis of Rpf2-Rrs1 mutants demonstrated that Saccharomyces cerevisiae Rpf2 R236 (corresponds to R238 of An Rpf2) plays a significant role in this binding. Based on these studies and previous reports, we have proposed a model for ribosomal component recruitment to the 90S ribosome precursor.

Description: In the redshift interval of 2 〈 z 〈 3, the physical conditions of the interstellar medium (ISM) in star-forming galaxies are likely to be different from those in the local Universe because of lower gaseous metallicities, higher gas fractions, and higher star formation activities. In fact, observations suggest that higher electron densities, higher ionization parameters, and harder UV radiation fields are common. In this paper, based on the spectra of H α-selected star-forming galaxies at z = 2.5 taken with Multi-Object Spectrometer for InfraRed Exploration on Keck-1 telescope, we measure electron densities ( n e ) using the oxygen line ratio ([O ii ] 3726,3729), and investigate the relationships between the electron density of ionized gas and other physical properties. As a result, we find that the specific star formation rate (sSFR) and the surface density of SFR ( SFR ) are correlated with the electron density at z = 2.5 for the first time. The SFR – n e relation is likely to be linked to the star formation law in H ii regions (where star formation activity is regulated by interstellar pressure). Moreover, we discuss the mode of star formation in those galaxies. The correlation between sSFR and SFR suggests that highly star-forming galaxies (with high sSFR) tend to be characterized by higher surface densities of star formation ( SFR ) and thus higher n e values as well.

Description: This work presents the results from our near-infrared spectroscopy of narrow-band-selected Hα emitters (HAEs) in two rich overdensities (PKS 1138–262 at z  = 2.2 and USS 1558–003 at z  = 2.5) with the Multi-Object Infrared Camera and Spectrograph on the Subaru telescope. These protoclusters are promising candidates for the most massive class of galaxy clusters seen today (Paper I). The confirmed HAEs in the protoclusters at z  〉 2 show high excitation levels as characterized by much higher [O iii ]/Hβ or [O iii ]/Hα line ratios than those of general galaxies at low- z . Such a high excitation level may not only be driven by high specific star formation rates and lower gaseous metallicities, but also be contributed by some other effects. We investigate the environmental dependence of gaseous metallicities by comparing the HAEs in the protoclustrers with those in the general field at similar redshifts. We find that the gaseous metallicities of protocluster galaxies are more chemically enriched than those of field galaxies at a given stellar mass in the range of M *   10 11 M . This can be attributed to many processes, such as intrinsic (or nature) effects, external (or nurture) effects, and/or some systematic sampling effects. The intrinsic (nature) effect leads to the advanced stage of ‘downsizing’ galaxy evolution in protoclusters. On the other hand, the external (nurture) effects include the recycling of chemically enriched gas due to the higher pressure of intergalactic medium and/or stripping of outer gas in the reservoir in protoclusters. We also find that the offset of the mass–metallicity relation in dense environment becomes larger at higher redshifts. This can be naturally understood by the fact that the inflow/outflow rates in star-forming galaxies are much higher at higher redshifts. Therefore, the environmental dependence of such ‘feeding’ and ‘feedback’ mechanisms in galaxy formation is probably playing major roles in producing the offset of the mass–metallicity relation for the protocluster galaxies at z  〉 2.

Description: We exploit wide-field Ly α imaging with Subaru to probe the environment around TN J1338–1942, a powerful radio galaxy with a 〉 100 kpc Ly α halo at z  = 4.11. We used a sample of Ly α emitters (LAEs) down to log ( L Lyα [ erg s –1 ]) ~ 42.8 to measure the galaxy density around TN J1338–1942, compared to a control sample from a blank field taken with the same instrument. We found that TN J1338–1942 resides in a region with a peak overdensity of LAE  = 2.8 ± 0.5 on scales of 8 h – 1 Mpc (on the sky) and 112 h – 1 Mpc (line of sight) in comoving coordinates. Adjacent to this overdensity, we found a strong underdensity where virtually no LAEs are detected. We used a semi-analytical model of LAEs derived from the Millennium Simulation to compare our results with theoretical predictions. While the theoretical density distribution is consistent with the blank field, overdense regions such as that around TN J1338–1942 are very rare, with a number density of 6.4 x 10 – 8 Mpc – 3 (comoving), corresponding to the densest 〈0.4 percentile at z ~= 4.1. We also found that the Ly α luminosity function in the TN J1338–1942 field differs from that in the blank field: the number of bright LAEs (log ( L Lyα [ erg s – 1 ]) 43.3) is enhanced, while the number of fainter LAEs is relatively suppressed. These results suggest that some powerful radio galaxies associated with Ly α nebulae reside in extreme overdensities on ~3–6 Mpc scales, where star formation and AGN activity may be enhanced via frequent galaxy mergers or high rates of gas accretion from the surroundings.

Description: In the redshift interval of 2 〈 z 〈 3, the physical conditions of the interstellar medium (ISM) in star-forming galaxies are likely to be different from those in the local Universe because of lower gaseous metallicities, higher gas fractions, and higher star formation activities. In fact, observations suggest that higher electron densities, higher ionization parameters, and harder UV radiation fields are common. In this paper, based on the spectra of H α-selected star-forming galaxies at z = 2.5 taken with Multi-Object Spectrometer for InfraRed Exploration on Keck-1 telescope, we measure electron densities ( n e ) using the oxygen line ratio ([O ii ] 3726,3729), and investigate the relationships between the electron density of ionized gas and other physical properties. As a result, we find that the specific star formation rate (sSFR) and the surface density of SFR ( SFR ) are correlated with the electron density at z = 2.5 for the first time. The SFR – n e relation is likely to be linked to the star formation law in H ii regions (where star formation activity is regulated by interstellar pressure). Moreover, we discuss the mode of star formation in those galaxies. The correlation between sSFR and SFR suggests that highly star-forming galaxies (with high sSFR) tend to be characterized by higher surface densities of star formation ( SFR ) and thus higher n e values as well.

Description: We report the discovery of an extremely dense group of massive galaxies at the centre of the protocluster at z  = 3.09 in the SSA22 field from near-infrared spectroscopy conducted with the multi-object infrared camera and spectrograph (MOIRCS) on the Subaru Telecope. The newly discovered group comprises seven galaxies confirmed at z spec 3.09 within 180 kpc, including five massive objects with the stellar masses larger than 10 10.5 M and is associated with a bright submillimetre source SSA22-AzTEC14. The dynamical mass of the group estimated from the line-of-sight velocity dispersion of the members is M dyn  ~ 1.6 ± 0.3  x  10 13 M . Such a dense group is expected to be very rare at high redshift, as we have found only a few comparable systems in large-volume cosmological simulations. Such rare groups in simulations are hosted in collapsed haloes with M vir  = 10 13.4 –10 14.0 M and evolve into the brightest cluster galaxies (BCGs) of the most massive clusters at present. The observed AzTEC14 group at z  = 3.09 is therefore very likely to be a proto-BCG in the multiple merger phase. The observed total stellar mass of the group is $5.8^{+5.1}_{-2.0}\times 10^{11} \,\mathrm{M}_{{{\odot }}}$ , which suggests that over half the stellar mass of its descendant had been formed by z  = 3. Moreover, we have identified over two members for each of the four Lyα blobs (LABs) using our new spectroscopic data. This verifies our previous argument that many of the LABs in the SSA22 protocluster associated with multiple developed stellar components.