Variability of the NGC 1333 IRAS 4A Outflow: Molecular Hydrogen and Silicon Monoxide Images

The NGC 1333 region was observed in the H2 1-0 S(1) line. The H2 images cover a 5' x 7' region around IRAS 4. Numerous H2 emission features were detected. The northeast-southwest bipolar outflow driven by IRAS 4A was studied by combining the H2 images with SiO maps published previously. The SiO-H2 outflows are continuous on the southwestern side but show a gap on the northeastern side. The southwestern outflow lobe curves smoothly, and the position angle increases with the distance from the driving source. The base and the outer tip of the northeastern outflow lobe are located at positions opposite to the corresponding parts of the southwestern lobe. This point-symmetry suggests that the outflow axis may be drifting or precessing clockwise in the plane of the sky and that the cause of the axis drift may be intrinsic to the outflow engine. The axis drift model is supported by the asymmetric lateral intensity profile of the SiO outflow. The axis drift rate is about 0.011 deg yr-1. The middle part of the northeastern outflow does not exactly follow the point symmetry because of the superposition of two different kinds of directional variability: the axis drift of the driving source and the deflection by a dense core. The axis drift model provides a good explanation for the large deflection angle of the northeastern outflow. Other H2 emission features around the IRAS 4 region are discussed briefly. Some of them are newly found outflows, and some are associated with outflows already known before

Spectral Classification and Effective Temperatures of L and T Dwarfs Based of Near-Infrared Spectra

We have obtained near-infrared spectra of L dwarfs, L/T transition objects and T dwarfs using Subaru. Resulting spectra are examined in detail to see their dependence on the spectral types. We have obtained bolometric luminosities of the objects with known parallaxes in our sample, first by integrating the spectra and second by K band bolometric correction. We derive the relation between effective temperature and spectral type.Comment: To appear in May 20, 2004 issue of ApJ There is a companion paper by Tsuji, Nakajima and Yanagisaw

An Observational Pursuit for Population III Stars in a Ly_alpha Emitter at z=6.33 through HeII Emission

We present a very deep near-infrared spectroscopic observation of a strong Ly_alpha emitter at z=6.33, SDF J132440.6+273607, which we used to search for HeII 1640. This emission line is expected if the target hosts a significant number of population III stars. Even after 42 ksec of integration with the Subaru/OHS spectrograph, no emission-line features are detected in the JH band, which confirms that SDF J132440.6+273607 is neither an active galactic nucleus nor a low-$z$ emission-line object. We obtained a 2sigma upper-limit of 9.06e-18 ergs/s/cm^2 on the HeII 1640 emission line flux, which corresponds to a luminosity of 4.11e42 ergs/s. This upper-limit on the HeII 1640 luminosity implies that the upper limit on population III star-formation rate is in the range 4.9--41.2 M_sun/yr if population III stars suffer no mass loss, and in the range 1.8--13.2 M_sun/yr if strong mass loss is present. The non-detection of HeII in SDF J132440.6+273607 at z=6.33 may thus disfavor weak feedback models for population III stars.Comment: 13 pages, 3 figures, to appear in The Astrophysical Journal Letter

Physical conditions of the interstellar medium in star-forming galaxies at z~1.5

We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at $z\sim1.5$ in the Subaru Deep Field. These galaxies are selected as [OII]$\lambda$3727 emitters at $z\approx$ 1.47 and 1.62 from narrow-band imaging. We detect H$\alpha$ emission line in 115 galaxies, [OIII]$\lambda$5007 emission line in 45 galaxies, and H$\beta$, [NII]$\lambda$6584, and [SII]$\lambda\lambda$6716,6731 in 13, 16, and 6 galaxies, respectively. Including the [OII] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate physical conditions of the interstellar medium in star-forming galaxies at $z\sim$1.5. We find a tight correlation between H$\alpha$ and [OII], which suggests that [OII] can be a good star formation rate (SFR) indicator for galaxies at $z\sim1.5$. The line ratios of H$\alpha$/[OII] are consistent with those of local galaxies. We also find that [OII] emitters have strong [OIII] emission lines. The [OIII]/[OII] ratios are larger than normal star-forming galaxies in the local Universe, suggesting a higher ionization parameter. Less massive galaxies have larger [OIII]/[OII] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.Comment: Fixed a minor issue with LaTeX table numberin

A Search for Molecular Gas toward a BzK-selected Star-forming Galaxy at z = 2.044

We present a search for CO(3-2) emission in SDF-26821, a BzK-selected star-forming galaxy (sBzK) at z = 2.044, using the 45-m telescope of the Nobeyama Radio Observatory and the Nobeyama Millimeter Array. We do not detect significant emission and derive 2 \sigma limits: the CO luminosity of L'CO < 3.1 x 10^10 K km s^{-1} pc^{-2}, the ratio of far-infrared luminosity to CO luminosity of L_FIR/L'CO > 57 Lsun (K km s^{-1} pc^{-2})^{-1}, and the molecular gas mass of M_H2 < 2.5 x 10^10 Msun, assuming a velocity width of 200 km s^{-1} and a CO-to-H2 conversion factor of alpha_CO=0.8 Msun (K km s^{-1} pc^{-2})^{-1}. The ratio of L_FIR/L'CO, a measure of star formation efficiency (SFE), is comparable to or higher than the two z ~ 1.5 sBzKs detected in CO(2-1) previously, suggesting that sBzKs can have a wide range of SFEs. Comparisons of far-infrared luminosity, gas mass, and stellar mass among the sBzKs suggest that SDF-26821 is at an earlier stage of forming stars with a similar SFE and/or more efficiently forming stars than the two z ~ 1.5 sBzKs. The higher SFEs and specific star formation rates of the sBzKs compared to local spirals are indicative of the difference in star formation modes between these systems, suggesting that sBzKs are not just scaled-up versions of local spirals.Comment: 4 pages, 4 figures, Accepted for publication in PAS

Signature of Electron Capture in Iron-Rich Ejecta of SN 2003du

Late-time near-infrared and optical spectra are presented for the normal-bright SN2003du. At about 300 days after the explosion, the emission profiles of well isolated [FeII] lines (in particular that of the strong 1.644mu feature) trace out the global kinematic distribution of radioactive material in the expanding. In SN2003du, the 1.644 mu [FeII] line shows a flat-topped, profile, indicative of a thick but hollow-centered expanding shell, rather than a strongly-peaked profile that would be expected from a ``center-filled'' distribution.Based on detailed models for exploding Chandrasekhar mass white dwarfs, we show that the feature is consistent with spherical explosion models.Our model predicts central region of non-radioactive electron-capture elements up to 2500--3000km/s as a consequence of burning under high density, and an extended region of 56Ni up to 9,000--10,000km/s. Furthermore our analysis indicates that the 1.644mu [FeII] profile is not consistent with strong mixing between the regions of electron- capture isotopes and the 56Ni layers as is predicted by detailed 3D models for nuclear deflagration fronts. We discuss the possibility that the flat-topped profile could be produced as a result of an infrared catastrophe and conclude that such an explanation is unlikely. We put our results in context to other SNeIa and briefly discuss the implications of our result for the use of SNe Ia as cosmological standard candles.Comment: 12 pages + 8 figures, ApJ (in press, Dec. 20, 2004) For high resolution figures send E-mail to [email protected]

Near-Infrared Observations of Powerful High-Redshift Radio Galaxies: 4C 40.36 and 4C 39.37

We present near-infrared imaging and spectroscopic observations of two FR II high-redshift radio galaxies (HzRGs), 4C 40.36 (z=2.3) and 4C 39.37 (z=3.2), obtained with the Hubble, Keck, and Hale Telescopes. High resolution images were taken with filters both in and out of strong emission lines, and together with the spectroscopic data, the properties of the line and continuum emissions were carefully analyzed. Our analysis of 4C 40.36 and 4C 39.37 shows that strong emission lines (e.g., [O III] 5007 A and H alpha+[N II]) contribute to the broad-band fluxes much more significantly than previously estimated (80% vs. 20-40%), and that when the continuum sources are imaged through line-free filters, they show an extremely compact morphology with a high surface brightness. If we use the R^1/4-law parametrization, their effective radii (r(e)) are only 2-3 kpc while their restframe B-band surface brightnesses at r(e) are I(B) ~ 18 mag/arcsec^2. Compared with z ~ 1 3CR radio galaxies, the former is x3-5 smaller, while the latter is 1-1.5 mag brighter than what is predicted from the I(B)-r(e) correlation. Although exponential profiles produce equally good fits for 4C 40.36 and 4C 39.37, this clearly indicates that with respect to the z~1 3CR radio galaxies, the light distribution of these two HzRGs is much more centrally concentrated. Spectroscopically, 4C 40.36 shows a flat (fnu=const) continuum while 4C 39.37 shows a spectrum as red as that of a local giant elliptical galaxy. Although this difference may be explained in terms of a varying degree of star formation, the similarities of their surface brightness profiles and the submillimeter detection of 4C 39.37 might suggest that the intrinsic spectra is equally blue (young stars or an AGN), and that the difference is the amount of reddening.Comment: 30 pages, 6 tables, 10 figures; Accepted for publication in Astronomical Journa

Signature of Electron Capture in Iron‐rich Ejecta of SN 2003du

Late-time near-infrared and optical spectra of the normal-bright Type Ia supernova 2003du about 300 days after the explosion are presented. At this late epoch, the emission profiles of well-isolated [Fe II] lines (in particular that of the strong 1.644 μm feature) trace out the global kinematic distribution of radioactive material in the expanding supernova ejecta. In SN 2003du, the 1.644 μm [Fe II] line seems to show a flat-topped profile, indicative of a thick but hollow-centered expanding shell, rather than a strongly peaked profile that would be expected from a center-filled distribution. Based on detailed models for exploding Chandrasekhar-mass white dwarfs, we show that the feature is consistent with spherical explosion models. Our model predicts a central region of nonradioactive electron capture elements up to 2500-3000 km s-1 as a consequence of burning under high density and an extended region of radioactive 56Ni up to 9000-10,000 km s-1. Furthermore, our analysis indicates that the 1.644 μm [Fe II] line profile is not consistent with strong mixing between the regions of electron-capture isotopes and the 56Ni layers, as is predicted by detailed three-dimensional models for nuclear deflagration fronts. We discuss the possibility that the flat-topped profile could be produced as a result of an infrared catastrophe and conclude that such an explanation is unlikely. We discuss the limitations of our analysis and place our results into context by comparison with constraints on the distribution of radioactive 56Ni in other SNe Ia and briefly discuss the potential implications of our result for the use of SNe Ia as cosmological standard candles

High-redshift Ly alpha emitters with a large equivalent width: Properties of i-dropout galaxies with an NB921-band depression in the Subaru Deep Field

We report new follow-up spectroscopy of i-dropout galaxies with an NB921-band depression found in the Subaru Deep Field. The NB921-depressed i-dropout selection method is expected to select galaxies with large equivalent width Ly alpha emission over a wide redshift range, 6.0<z<6.5. Two of four observed targets show a strong emission line with a clear asymmetric profile, identified as Ly alpha emitters at z=6.11 and 6.00. Their rest-frame equivalent widths are 153A and 114A, which are lower limits on the intrinsic equivalent widths. Through our spectroscopic observations (including previous ones) of NB921-depressed i-dropout galaxies, we identified 5 galaxies in total with a rest-frame equivalent width larger than 100A at 6.0<z<6.5 out of 8 photometric candidates, which suggests that the NB921-depressed i-dropout selection method is possibly an efficient way to search for Ly alpha emitters with a large Ly alpha equivalent width, in a wider redshift range than usual narrow-band excess techniques. By combining these findings with our previous observational results, we infer that the fraction of broad-band selected galaxies having a rest-frame equivalent width larger than 100A is significantly higher at z~6 (the cosmic age of ~1 Gyr) than that at z~3 (~2 Gyr), being consistent with the idea that the typical stellar population of galaxies is significantly younger at z~6 than that at z~3. The NB921-depressed i-dropout galaxies may be interesting candidates for hosts of massive, zero-metallicity Population III stars.Comment: 9 pages, 5 figures, accepted for publication in A&