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We investigate the (large-scale) bar fraction in a mass-complete sample of M > 1010.5 M disc galaxies at 0.2 < z < 0.6 in the Cosmological Evolution Survey (COSMOS) field. The fraction of barred discs strongly depends on mass, disc morphology and specific star formation rate (SSFR). At intermediate stellar mass (1010.5 < M < 1011 M) the bar fraction in early-type discs is much higher, at all redshifts, by a factor of 2, than that in late-type discs. This trend is reversed at higher stellar mass (M > 1011 M), where the fraction of bars in early-type discs becomes significantly lower, at all redshifts, than that in late-type discs. The bar fractions for galaxies with low and high SSFRs closely follow those of the morphologically selected early- and late-type populations, respectively. This indicates a close correspondence between morphology and SSFR in disc galaxies at these earlier epochs. Interestingly, the total bar fraction in 1010.5 < M < 1011 M discs is built up by a factor of 2 over the redshift interval explored, while for M > 1011 M discs it remains roughly constant. This indicates that, already by z 0.6, spectral and morphological transformations in the most massive disc galaxies have largely converged to the familiar Hubble sequence that we observe in the local Universe, while for intermediate-mass discs this convergence is ongoing until at least z 0.2. Moreover, these results highlight the importance of employing mass-limited samples for quantifying the evolution of barred galaxies. Finally, the evolution of the barred galaxy populations investigated does not depend on the large-scale environmental density (at least, on the scales which can be probed with the available photometric redshifts)., Monthly Notices of the Royal Astronomical Society, 409 (1), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

We investigate the properties of dark matter halos that contain "main-sequence" star-forming galaxies at 1.439.57 M⦿ and SFR~15 M⦿ yr-1, for which the Hα emission line is detected. We find that these galaxies live in halos of Mh=5×1012 M⦿ on average, which will likely become present-day halos equivalent to the typical mass scale of galaxy groups. We then constrain the stellar-to-halo mass ratio at Mh12 M⦿, finding a systematically lower mass ratio than those measured at higher masses.

In this paper, we present the measurements of the [N II] 205 μm line for a flux-limited sample of 122 (ultra-)luminous infrared galaxies [(U)LIRGs] and 20 additional normal galaxies, obtained with the Herschel Space Observatory (Herschel). We explore the far-infrared (FIR) color dependence of the [N II] 205 μm (L_([N II]205μm)) to the total infrared (L_(IR)) luminosity ratio, and find that L_([N II]205μm)/L_(IR) only depends modestly on the 70–160 μm flux density ratio (f_(70)/f_(160)) when f_(70)/f_(160) ≾ 0.6, whereas such dependence becomes much steeper for f_(70/f_(160) > 0.6. We also investigate the relation between L_([N II]205μm) and star formation rate (SFR), and show that L_([N II]205μm) has a nearly linear correlation with SFR, albeit the intercept of such a relation varies somewhat with f_(60)/f_(100), consistent with our previous conclusion that [N II] 205 μm emission can serve as an SFR indicator with an accuracy of ~0.4 dex, or ~0.2 dex if f_(60)/f_(100) is known independently. Furthermore, together with the Infrared Space Observatory measurements of [N II], we use a total of ~200 galaxies to derive the local [N II] 205 μm luminosity function (LF) by tying it to the known IR LF with a bivariate method. As a practical application, we also compute the local SFR volume density (ṗ_(SFR)) using the newly derived SFR calibrator and LF. The resulting log ṗ_(SFR) = -1.96 ± 0.11 M_☉ yr^(−1) Mpc^(−3) agrees well with previous studies. Finally, we determine the electron densities (n_e) of the ionized medium for a subsample of 12 (U)LIRGs with both [N II] 205 μm and [N II] 122 μm data, and find that n_e is in the range of ~1–100 cm^(−3), with a median value of 22 cm^(−3).

著者人数: 19名, Accepted: 2011-02-08, 資料番号: SA1002748000

International audience; We report a discovery of six massive galaxies with both extremely large Ly alpha equivalent widths (EWs) and evolved stellar populations at z similar to 3. These MAssive Extremely STrong Ly alpha emitting Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Ly alpha emitters (LAEs) with 12 optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the spectral energy distribution fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame EWs of EW0 (Ly alpha) similar to 100-300 angstrom, (2) M-star similar to 10(10.5) -10(11.1) M-circle dot, and (3) relatively low specific star formation rates of SFR/M-star similar to 0.03-1 Gyr(-1). Three of the six MAESTLOs have extended Ly alpha emission with a radius of several kiloparsecs, although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for active galactic nuclei, the observed extended Ly alpha emission is likely to be caused by a star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star formation history.

We study the properties of dark matter halos that contain star-forming galaxies at 1.43 ≤ z ≤ 1.74, using the FMOS-COSMOS survey. The sample consists of 516 objects with a detection of the Hα emission line, which represent the star forming population at this epoch, having a stellar mass range of 10^9.57 ≤ M */M ⊙ lesssim 10^11.4 and a star-formation rate range of 15 lesssim SFR/(M ⊙ yr^−1) lesssim ^600. We measure the projected two-point correlation function while carefully taking into account observational biases, and find a significant clustering amplitude at scales of 0.04–10 h ^−1 cMpc, with a correlation length r0 =5.26-0.62^+0.75h^-1cMpc and a bias b =2.44-0.32^+0.38. We interpret our clustering measurement using a halo occupation distribution model. The sample galaxies appear to reside in halos with mass Mh=4.71-1.62^+1.19×10^12h^-1,M⊙ on average, which will likely become present-day halos of mass M h (z = 0) ~ 2 × 10^13 h ^−1 M ⊙, equivalent to the typical halo mass scale of galaxy groups. We then confirm the decline of the stellar-to-halo mass ratio at M h < 10^12 M ⊙, finding M */M h ≈ 5 × 10^−3 at M h = 7. 5 × 10^11 M ⊙, which is lower by a factor of 2–4 than those measured at higher masses (M h ~ 10^12–13 M ⊙). Finally, we use our results to illustrate the future capabilities of Subaru's Prime-Focus Spectrograph, a next-generation instrument that will provide strong constraints on the galaxy-formation scenario by obtaining precise measurements of galaxy clustering at z>1.

By cross-correlating AKARI all sky survey in 6 infrared (IR) bands (9, 18, 65, 90, 140, and 160μm) with the SDSS galaxies, we identified 2357 infrared galaxies with a spectroscopic redshift. This is not just one of the largest samples of local IR galaxies, but AKARI provides crucial FIR bands in accurately measuring galaxy SED across the peak of the dust emission at > 100μm. By fitting modern IR SED models to the AKARI photometry, we measured the total infrared luminosity (LIR) of individual galaxies. \ud Using this LIR, we constructed the luminosity functions of infrared galaxies at a median redshift of z=0.031. The LF agrees well with that at z=0.0082 (the RBGS), showing smooth and continuous evolution toward higher redshift LFs measured in the AKARI NEP deep field. By integrating the IR LF weighted by LIR, we measured the local cosmic IR luminosity density of IR= (3.8+5.8−1.2) × 108 L⊙Mpc−3.\ud \ud We separate galaxies into AGN (active galactic nuclei), star-forming, and composite by using the [NII]/Hα vs [OIII]/Hβ line ratios. The fraction of AGN shows a continuous increase with increasing LIR from 25% to 90% at 9< log LIR Hα and L[OIII] show good correlations with LIR for SFG (star-forming galaxies) and AGN, respectively. The self-absorption corrected Hα/Hβ ratio shows a weak increase with LIR with a substantial scatter. When we separate IR LFs into contributions from AGN and star-forming galaxies (SFG), the AGN contribution becomes dominant at LIR > 1011L⊙, coinciding the break of the both SFG and AGN IR LFs. At LIR ≤ 1011L⊙, SFG dominates IR LFs. Only 1.1±0.1% of Ω IR is produced by LIRG (LIR > 1011L⊙), and only 0.03±0.01% is by ULIRG (LIR > 1012L⊙) in the local Universe. Compared with high redshift results from the AKARI NEP deep survey, we observed a strong evolution of ΩSFGIR α(1+z)4.1±0.4 and ΩAGNIR α(1+z)4.1±0.5. Our results show all of our measured quantities (IR LFs, L∗, ΩAGNIR, ΩSFGIR) show smooth and steady increase from lower redshift (the RBGS) to higher redshift (the AKARI NEP deep survey).

By cross-correlating the AKARI all-sky survey in six infrared (IR) bands (9, 18, 65, 90, 140 and 160 μm) with the Sloan Digital Sky Survey (SDSS) galaxies, we identified 2357 IR galaxies with a spectroscopic redshift. This is not just one of the largest samples of local IR galaxies, but AKARI provides crucial far-IR (FIR) bands for accurately measuring the galaxy spectral energy distribution (SED) across the peak of the dust emission at > 100 μ m. By fitting modern IR SED models to the AKARI photometry, we measured the total infrared luminosity (L_(IR)) of individual galaxies. Using this L_(IR), we constructed the luminosity functions (LF) of IR galaxies at a median redshift of z= 0.031. The LF agrees well with that at z= 0.0082 (the Revised Bright Galaxy Sample), showing smooth and continuous evolution towards higher redshift LFs measured in the AKARI North Ecliptic Pole (NEP) deep field. By integrating the IR LF weighted by L_(IR), we measured the local cosmic IR luminosity density of Ω_(IR_= (3.8^(+5.8)_(−1.2)) × 10^8 L_⊙ Mpc^(−3). We separate galaxies into active galactic nuclei (AGN), star-forming galaxies (SFG) and composite by using the [N ii]/Hα versus [O iii]/Hβ line ratios. The fraction of AGN shows a continuous increase with increasing L_(IR) from 25 to 90 per cent at 9 < log L_(IR) < 12.5. The SFR_(Hα) and L_([OΙΙΙ]) show good correlations with L_(IR) for SFG and AGN, respectively. The self-absorption-corrected Hα/Hβ ratio shows a weak increase with LIR with a substantial scatter. When we separate IR LFs into contributions from AGN and SFG, the AGN contribution becomes dominant at L_(IR) > 10^(11) L_⊙, coinciding with the break of both the SFG and AGN IR LFs. At L_(IR)≤ 10^(11) L_⊙, SFG dominates IR LFs. Only 1.1 ± 0.1 per cent of Ω_(IR) is produced by luminous infrared galaxies (L_(IR) > 10^(11) L_⊙), and only 0.03 ± 0.01 per cent by ultraluminous infrared galaxies (L_(IR) > 10^(12) L_⊙) in the local Universe. Compared with high-redshift results from the AKARI NEP deep survey, we observed a strong evolution of Ω^(SFG)IR^∝ (1 +z)^(4.1±0.4) and Ω^(AGN)IR^∝ (1+z)^(4.1±0.5). Our results show that all of our measured quantities (IR LFs, L^*, Ω^(AGN)IR, Ω^(SFG)IR) show smooth and steady increase from lower redshift (the Revised Bright Galaxy Sample) to higher redshift (the AKARI NEP deep survey).

We discuss the nature of faint 6.7um galaxies detected with the mid-infrared camera ISOCAM on board the Infrared Space Observatory (ISO). The 23 hour integration on the Hawaii Deep Field SSA13 has provided a sample of 65 sources down to 6uJy at 6.7um. For 57 sources, optical or near-infrared counterparts were found with a statistical method. All four Chandra sources, three SCUBA sources, and one VLA/FIRST source in this field were detected at 6.7um with high significance. Using their optical to mid-infrared colors, we divided the 6.7um sample into three categories: low redshift galaxies with past histories of rapid star formation, high redshift ancestors of these, and other star forming galaxies. Rapidly star forming systems at high redshifts dominate the faintest end. Spectroscopically calibrated photometric redshifts were derived from fits to a limited set of template SEDs. They show a high redshift tail in their distribution with faint (1. The 6.7um galaxies tend to have brighter K magnitudes and redder I-K colors than the blue dwarf population at intermediate redshifts. Stellar masses of the 6.7um galaxies were estimated from their rest-frame near-infrared luminosities. Massive galaxies (M_star~10e11M_sun) were found in the redshift range of z=0.2-3. Epoch dependent stellar mass functions indicate a decline of massive galaxies' comoving space densities with redshift. Even with such a decrease, the contributions of the 6.7um galaxies to the stellar mass density in the universe are found to be comparable to those expected from UV bright galaxies detected in deep optical surveys., 31 pages, 15 figures, AJ (accepted), a version with color figures at http://www.ioa.s.u-tokyo.ac.jp/~ysato/pub/3/p3c-ysato.ps.gz