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  • 1
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    Predicting dust extinction properties of star-forming galaxies from H{alpha}/UV ratio (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-24
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    [O III] emission line as a tracer of star-forming galaxies at high redshifts: comparison between H{alpha} and [O III] emitters at z=2.23 in HiZELS (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-31
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Magnetic soliton confinement and discretization effects arising from macroscopic coherence in a chiral spin soliton lattice (2015)
    American Physical Society (APS)
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    Publication Date: 2015-12-18
    Description: Author(s): Y. Togawa, T. Koyama, Y. Nishimori, Y. Matsumoto, S. McVitie, D. McGrouther, R. L. Stamps, Y. Kousaka, J. Akimitsu, S. Nishihara, K. Inoue, I. G. Bostrem, Vl. E. Sinitsyn, A. S. Ovchinnikov, and J. Kishine Understanding the conditions determining the appearance of stable chiral spin topological excitations is a central problem in condensed matter physics and related fields. This work provides the first unambiguous demonstration of discretization due to the macroscopic phase coherence and metastability for chiral topological excitations, and evidence of the mechanisms underlying its appearance. This was achieved through the use of an advanced Lorentz electron microscope with the highest possible resolution imaging of spin textures. The results provide new insights into dynamics in the phase transition of the chiral system, and will raise new questions concerning the mechanisms governing loss of chiral ordering. [Phys. Rev. B 92, 220412(R)] Published Thu Dec 17, 2015
    Keywords: Magnetism
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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  • 4
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    The spatially resolved dynamics of dusty starburst galaxies in a z ~ 0.4 cluster: beginning the transition from spirals to S0s (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-02
    Description: To investigate what drives the reversal of the morphology–density relation at intermediate/high redshift, we present a multiwavelength analysis of 27 dusty starburst galaxies in the massive cluster Cl 0024+17 at z  = 0.4. We combine Hα dynamical maps from the VLT/FLAMES multi-IFU system with far-infrared imaging using Herschel /SPIRE and millimetre spectroscopy from IRAM/NOEMA, in order to measure the dynamics, star formation rates and gas masses of this sample. Most galaxies appear to be rotationally supported, with a median ratio of rotational-support to line-of-sight velocity dispersion v / ~ 5 ± 2, and specific angular momentum R  = 0.83 ± 0.06 – comparable to field spirals of a similar mass at this redshift. The star formation rates of 3–26 M  yr –1 and average 12 CO-derived gas mass of ~ 1  x  10 10  M suggest gas depletion time-scales of ~1 Gyr (~0.25 of the cluster crossing time). We derive characteristic dust temperatures (mean T d  = 26 ± 1 K) consistent with local galaxies of similar far-infrared luminosity, suggesting that the low-density gas is yet to be stripped. Taken together, these results suggest that these starbursts have only recently accreted from the field, with star formation rates likely enhanced due to the effects of ram pressure. In order to make the transition to cluster S0s these galaxies must lose ~40 per cent of their specific angular momentum. We suggest this must occur ≥1 Gyr later, after the molecular gas has been depleted and/or stripped, via multiple tidal interactions with other cluster members.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Mutation analysis and molecular modeling for the investigation of ligand-binding modes of GPR84 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-29
    Description: GPR84 is a G protein-coupled receptor for medium-chain fatty acids. Capric acid and 3,3'-diindolylmethane are specific agonists for GPR84. We built a homology model of a GPR84-capric acid complex to investigate the ligand-binding mode using the crystal structure of human active-state β2-adrenergic receptor. We performed site-directed mutagenesis to subject ligand-binding sites to our model using GPR84-Giα fusion proteins and a [ 35 S]GTPS-binding assay. We compared the activity of the wild type and mutated forms of GPR84 by [ 35 S]GTPS binding to capric acid and diindolylmethane. The mutations L100D `Ballesteros–Weinstein numbering: 3.32), F101Y (3.33) and N104Q (3.36) in the transmembrane helix III and N357D (7.39) in the transmembrane helix VII resulted in reduced capric acid activity but maintained the diindolylmethane responses. Y186F (5.46) and Y186H (5.46) mutations had no characteristic effect on capric acid but with diindolylmethane they significantly affected the G protein activation efficiency. The L100D (3.32) mutant responded to decylamine, a fatty amine, instead of a natural agonist, the fatty acid capric acid, suggesting that we have identified a mutated G protein-coupled receptor-artificial ligand pairing. Our molecular model provides an explanation for these results and interactions between GPR84 and capric acid. Further, from the results of a double stimulation assay, we concluded that diindolylmethane was a positive allosteric modulator for GPR84.
    Print ISSN: 0021-924X
    Electronic ISSN: 1756-2651
    Topics: Biology , Chemistry and Pharmacology
    Published by Oxford University Press on behalf of The Japanese Biochemical Society (JBS).
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  • 6
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    Correlation between star formation activity and electron density of ionized gas at z = 2.5 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-07
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    An early phase of environmental effects on galaxy properties unveiled by near-infrared spectroscopy of protocluster galaxies at z 〉 2 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-02-08
    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.
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    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Long-term trends in nitrogen and phosphorus concentrations in the Hii River as influenced by atmospheric deposition from East Asia (2015)
    Wiley
    Details
    Publication Date: 2015-02-01
    Description: Deposition of atmospheric nutrients is known to alter oligotrophic ecosystems such as the open ocean, but the role of such nutrients in the further deterioration of eutrophic aquatic ecosystems is largely unknown. The Hii River watershed in Japan encompasses lagoons that have been eutrophic since 1980s. This study examined the atmospheric deposition of nitrogen and phosphorus in the Hii River watershed and the nitrogen and phosphorus concentrations in the Hii River over an 11-yr period. Total nitrogen (TN) concentrations of both precipitation and river water were significantly higher in cold months (November–March) than in warm months (April–October). Most of the TN was nitrate, which suggests that the TN source was atmospheric nitrogen from East Asia transported by seasonal winds. In contrast, total phosphorus (TP) concentrations of both precipitation and river water were significantly higher in warm months. Over time, the TN concentration in the river water showed a decreasing trend although the trend was not significant, while the TP concentration increased significantly. This was attributed to an increase in the atmospheric deposition of TP originating from East Asia since 2000. The increase in the deposition of atmospheric phosphorus might also have increased phosphorus leakage from the soils. In this work, the TN : TP ratios for both atmospheric deposition and river water indicate that changes in atmospheric nutrient deposition affect loading rates and N : P ratios. These changes, especially the latter, could have significant ecological effects in eutrophic systems by lowering the N : P ratios, which could induce cyanobacteria blooms.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
    Published by Wiley on behalf of The Association for the Sciences of Limnology and Oceanography (ASLO).
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  • 9
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    Large-scale environment of z ~ 5.7 C IV absorption systems -II. Spectroscopy of Lyman {alpha} emitters (2015)
    Oxford University Press
    Details
    Publication Date: 2015-02-14
    Description: The flow of baryons to and from a galaxy, which is fundamental for galaxy formation and evolution, can be studied with galaxy-metal absorption system pairs. Our search for galaxies around C iv absorption systems at z  ~ 5.7 showed an excess of photometric Lyman α emitter (LAE) candidates in the fields J1030+0524 and J1137+3549. Here, we present spectroscopic follow-up of 33 LAEs in both fields. In the first field, three out of the five LAEs within 10 h –1 projected comoving Mpc from the C iv system are within ±500 km s –1 from the absorption at $z_{{\rm C\,{\small iv}}}=5.7242\pm 0.0001$ . The closest candidate (LAE 103027+052419) is robustly confirmed at $212.8^{+14}_{-0.4}\;h^{-1}$ physical kpc from the C iv system. In the second field, the LAE sample is selected at a lower redshift ( z  ~ 0.04) than the C iv absorption system as a result of the filter transmission and, thus, do not trace its environment. The observed properties of LAE 103027+052419 indicate that it is near the high-mass end of the LAE distribution, probably having a large H i column density and large-scale outflows. Therefore, our results suggest that the C iv system is likely produced by a star-forming galaxy which has been injecting metals into the intergalactic medium since z  〉 6. Thus, the C iv system is either produced by LAE 103027+052419, implying that outflows can enrich larger volumes at z  〉 6 than at z  ~ 3.5, or an undetected dwarf galaxy. In either case, C iv systems like this one trace the ionized intergalactic medium at the end of cosmic hydrogen reionization and may trace the sources of the ionizing flux density.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Correlation between star formation activity and electron density of ionized gas at z = 2.5 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-12
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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