The Discovery of Two Lymanα\alpha Emitters Beyond Redshift 6 in the Subaru Deep Field

We have performed a deep optical imaging survey using a narrowband filter ($NB921$) centered at $\lambda =$ 9196 \AA ~ together with $i^\prime$ and $z^\prime$ broadband filters covering an 814 arcmin$^2$ area of the Subaru Deep Field. We obtained a sample of 73 strong $NB921$-excess objects based on the following two color criteria; $z^\prime - NB921 > 1$ and $i^\prime - z^\prime > 1.3$. We then obtained optical spectroscopy of nine objects in our $NB921$-excess sample, and identified at least two Ly$\alpha$ emitters at$z=6.541 \pm 0.002$ and $z=6.578 \pm 0.002$, each of which shows the characteristic sharp cutoff together with the continuum depression at wavelengths shortward of the line peak. The latter object is more distant than HCM-6A at $z=6.56$ and thus this is the most distant known object found so far. These new data allow us to estimate the first meaningful lower limit of the star formation rate density beyond redshift 6; $\rho_{\rm SFR} \sim 5.2 \times 10^{-4} M_\odot$ yr$^{-1}$ Mpc$^{-3}$. Since it is expected that the actual density is higher by a factor of several than this value, our new observation reveals that a moderately high level of star formation activity already occurred at $z \sim$ 6.6.Comment: 13 pages, 3 figures. PASJ (Letters), 55, vol.2, in pres

A new mid-infrared map of the BN/KL region using the Keck telescope

We present a new mid-infrared (12.5micron) map of the BN/KL high-mass star-forming complex in Orion using the LWS instrument at Keck I. Despite poor weather we achieved nearly diffraction-limited images (FWHM = 0.38'') over a roughly 25'' X 25'' region centered on IRc2 down to a flux limit of ~250 mJy. Many of the known infrared (IR) sources in the region break up into smaller sub-components. We have also detected 6 new mid-IR sources. Nearly all of the sources are resolved in our mosaic. The near-IR source ''n'' is slightly elongated in the mid-IR along a NW--SE axis and perfectly bisects the double-peaked radio source ''L''. Source n has been identified as a candidate for powering the large IR luminosity of the BN/KL region (L = 10^5 L_sun). We postulate that the 12 micron emission arises in a circumstellar disk surrounding source n. The morphology of the mid-IR emission and the Orion ''hot core'' (as seen in NH_3 emission), along with the location of water and OH masers, is very suggestive of a bipolar cavity centered on source n and aligned with the rotation axis of the hypothetical circumstellar disk. IRc2, once thought to be the dominant energy source for the BN/KL region, clearly breaks into 4 sub-sources in our mosaic, as seen previously at 3.8 -- 5.0 micron. The anti-correlation of mid-IR emission and NH_3 emission from the nearby hot core indicates that the IRc2 sources are roughly coincident (or behind) the dense hot core. The nature of IRc2 is not clear: neither self-luminous sources (embedded protostars) nor external heating by source I can be definitively ruled out. We also report the discovery of a new arc-like feature SW of the BN object, and some curious morphology surrounding near-IR source ''t".Comment: To appear in The Astronomical Journal, July 2004 (16 pages, 7 figures

Discovery of a candidate protoplanetary disk around the embedded source IRc9 in Orion

We report the detection of spatially-extended mid-infrared emission around the luminous embedded star IRc9 in OMC-1, as seen in 8.8, 11.7, and 18.3 micron images obtained with T-ReCS on Gemini South. The extended emission is asymmetric, and the morphology is reminiscent of warm dust disks around other young stars. The putative disk has a radius of roughly 1.5 arcsec (700 AU), and a likely dust mass of almost 10 Earth masses. The infrared spectral energy distribution of IRc9 indicates a total luminosity of about 100 Lsun, implying that it shall become an early A-type star when it reaches the main sequence. Thus, the candidate disk around IRc9 may be a young analog of the planetary debris disks around Vega-like stars and the disks of Herbig Ae stars, and may provide a laboratory in which to study the earliest phases of planet formation. A disk around IRc9 may also add weight to the hypothesis that an enhanced T Tauri-like wind from this star has influenced the molecular outflow from the OMC-1 core.Comment: 7 pages, 2 figs, Accepted by ApJ Letter

Discovery of Interstellar Propylene (CH_2CHCH_3): Missing Links in Interstellar Gas-Phase Chemistry

We report the discovery of propylene (also called propene, CH_2CHCH_3) with the IRAM 30-m radio telescope toward the dark cloud TMC-1. Propylene is the most saturated hydrocarbon ever detected in space through radio astronomical techniques. In spite of its weak dipole moment, 6 doublets (A and E species) plus another line from the A species have been observed with main beam temperatures above 20 mK. The derived total column density of propylene is 4 10^13 cm^-2, which corresponds to an abundance relative to H_2 of 4 10^-9, i.e., comparable to that of other well known and abundant hydrocarbons in this cloud, such as c-C_3H_2. Although this isomer of C_3H_6 could play an important role in interstellar chemistry, it has been ignored by previous chemical models of dark clouds as there seems to be no obvious formation pathway in gas phase. The discovery of this species in a dark cloud indicates that a thorough analysis of the completeness of gas phase chemistry has to be done.Comment: 13 pages, 2 figures, accepted for publication in ApJ

Spectroscopy of i-Dropout Galaxies with an NB921-Band Depression in the Subaru Deep Field

We report new spectroscopy of two star-forming galaxies with strong Ly_alpha emission at z=6.03 and z=6.04 in the Subaru Deep Field. These two objects are originally selected as i'-dropouts (i'-z' > 1.5) showing an interesting photometric property, the ``NB921 depression''. The NB921-band (centered at 9196A) magnitude is significantly depressed with respect to the z'-band magnitude. The optical spectra of these two objects exhibit asymmetric emission-lines at lambda_obs ~ 8540A and ~ 8560A, suggesting that these objects are Ly_alpha emitters at z~6. The rest-frame equivalent widths of the Ly_alpha emission of the two objects are 94A and 236A; the latter one is the Ly_alpha emitter with the largest Ly_alpha equivalent width at z > 6 ever spectroscopically confirmed. The spectroscopically measured Ly_alpha fluxes of these two objects are consistent with the interpretation that the NB921 depression is caused by the contribution of the strong Ly_alpha emission to the z'-band flux. Most of the NB921-depressed i'-dropout objects are thought to be strong Ly_alpha emitters at 6.0 < z < 6.5; Galactic L and T dwarfs and NB921-dropout galaxies at z > 6.6 do not dominate the NB921-depressed i'-dropout sample. Thus the NB921-depression method is very useful for finding high-z Ly_alpha emitters with a large Ly_alpha equivalent width over a large redshift range, 6.0 < z < 6.5. Although the broadband-selected sample at z ~ 3 contains only a small fraction of objects with a Ly_alpha equivalent width larger than 100A, the i'-dropout sample of the Subaru Deep Field contains a much larger fraction of such strong Ly_alpha emitters. This may imply a strong evolution of the Ly_alpha equivalent width from z > 6 to z ~ 3.Comment: 21 pages, 6 figures, to appear in The Astrophysical Journa

A Potential Galaxy Threshing System in the Cosmos Field

We report on the discovery of a new potential galaxy threshing system in the COSMOS 2 square degree field using the prime-focus camera, Suprime-Cam, on the 8.2 m Subaru Telescope. This system consists of a giant elliptical galaxy with $M_V \approx -21.6$ and a tidally disrupted satellite galaxy with $M_V \approx -17.7$ at a photometric redshift of $z \approx 0.08$. This redshift is consistent with the spectroscopic redshift of 0.079 for the giant elliptical galaxy obtained from the Sloan Digital Sky Survey (SDSS) archive. The luminosity masses of the two galaxies are $3.7 \times 10^{12} \cal{M}_{\odot}$ and $3.1 \times 10^{9} \cal{M}_{\odot}$, respectively. The distance between the two galaxies is greater than 100 kpc. The two tidal tails emanating from the satellite galaxy extend over 150 kpc. This system would be the second well-defined galaxy threshing system found so far.Comment: 17 pages, 7 figures, accepted for the COSMOS special issue of ApJ

Monitoring the Large Proper Motions of Radio Sources in the Orion BN/KL Region

We present absolute astrometry of four radio sources in the Becklin-Neugebauer/Kleinman-Low (BN/KL) region, derived from archival data (taken in 1991, 1995, and 2000) as well as from new observations (taken in 2006). All data consist of 3.6 cm continuum emission and were taken with the Very Large Array in its highest angular resolution A configuration. We confirm the large proper motions of the BN object, the radio source I (GMR I) and the radio counterpart of the infrared source n (Orion-n), with values from 15 to 26 km/s. The three sources are receding from a point between them from where they seem to have been ejected about 500 years ago, probably via the disintegration of a multiple stellar system. We present simulations of very compact stellar groups that provide a plausible dynamical scenario for the observations. The radio source Orion-n appeared as a double in the first three epochs, but as single in 2006. We discuss this morphological change. The fourth source in the region, GMR D, shows no statistically significant proper motions. We also present new, accurate relative astrometry between BN and radio source I that restrict possible dynamical scenarios for the region. During the 2006 observations, the radio source GMR A, located about 1' to the NW of the BN/KL region, exhibited an increase in its flux density of a factor of ~3.5 over a timescale of one hour. This rapid variability at cm wavelengths is similar to that previously found during a flare at millimeter wavelengths that took place in 2003.Comment: Accepted for publication in Ap

Large Scale Flows from Orion-South

Multiple optical outflows are known to exist in the vicinity of the active star formation region called Orion-South (Orion-S). We have mapped the velocity of low ionization features in the brightest part of the Orion Nebula, including Orion-S, and imaged the entire nebula with the Hubble Space Telescope. These new data, combined with recent high resolution radio maps of outflows from the Orion-S region, allow us to trace the origin of the optical outflows. It is confirmed that HH 625 arises from the blueshifted lobe of the CO outflow from 136-359 in Orion-S while it is likely that HH 507 arises from the blueshifted lobe of the SiO outflow from the nearby source 135-356. It is likely that redshifted lobes are deflected within the photon dominated region behind the optical nebula. This leads to a possible identification of a new large shock to the southwest from Orion-S as being driven by the redshifted CO outflow arising from 137-408. The distant object HH 400 is seen to have two even further components and these all are probably linked to either HH 203, HH 204, or HH 528. Distant shocks on the west side of the nebula may be related to HH 269. The sources of multiple bright blueshifted Herbig-Haro objects (HH 202, HH 203, HH 204, HH 269, HH 528) remain unidentified, in spite of earlier claimed identifications. Some of this lack of identification may arise from the fact that deflection in radial velocity can also produce a change in direction in the plane of the sky. The best way to resolve this open question is through improved tangential velocities of low ionization features arising where the outflows first break out into the ionized nebula.Comment: Astronomical Journal, in press. Some figures are shown at reduced resolution. A full-resolution version is available at http://ifront.org/wiki/Orion_South_Outflows_Pape

The Subaru COSMOS 20: Subaru Optical Imaging of the HST COSMOS Field with 20 Filters

We present both the observations and the data reduction procedures of the Subaru COSMOS 20 project that is an optical imaging survey of the HST COSMOS field, carried out by using Suprime-Cam on the Subaru Telescope with the following 20 optical filters: 6 broad-band (B, g', V, r', i', and z'), 2 narrow-band (NB711 and NB816), and 12 intermediate-band filters (IA427, IA464, IA484, IA505, IA527, IA574, IA624, IA679, IA709, IA738, IA767, and IA827). A part of this project is described in Taniguchi et al. (2007) and Capak et al. (2007) for the six broad-band and one narrow-band (NB816) filter data. In this paper, we present details of the observations and data reduction for remaining 13 filters (the 12 IA filters and NB711). In particular, we describe the accuracy of both photometry and astrometry in all the filter bands. We also present optical properties of the Suprime-Cam IA filter system in Appendix.Comment: 15 pages, 8 figures, 7 tables; accepted for publication in PASJ on October 2, 201