Search for: All records

Abstract For submillimeter spectroscopy with ground-based single-dish telescopes, removing the noise contribution from the Earth’s atmosphere and the instrument is essential. For this purpose, here we propose a new method based on a data-scientific approach. The key technique is statistical matrix decomposition that automatically separates the signals of astronomical emission lines from the drift noise components in the fast-sampled (1–10 Hz) time-series spectra obtained by a position-switching (PSW) observation. Because the proposed method does not apply subtraction between two sets of noisy data (i.e., on-source and off-source spectra), it improves the observation sensitivity by a factor of $\sqrt{2}$. It also reduces artificial signals such as baseline ripples on a spectrum, which may also help to improve the effective sensitivity. We demonstrate this improvement by using the spectroscopic data of emission lines toward a high-redshift galaxy observed with a 2 mm receiver on the 50 m Large Millimeter Telescope. Since the proposed method is carried out offline and no additional measurements are required, it offers an instant improvement on the spectra reduced so far with the conventional method. It also enables efficient deep spectroscopy driven by the future 50 m class large submillimeter single-dish telescopes, where fast PSW observations by mechanical antenna or mirror drive are difficult to achieve. 

Abstract We report the detection of an ionized gas outflow from an X-ray active galactic nucleus hosted in a massive quiescent galaxy in a protocluster at z = 3.09 (J221737.29+001823.4). It is a type-2 QSO with broad ( W 80 > 1000 km s −1 ) and strong ( log ( L [ OIII ] /erg s −1 ) ≈ 43.4) [O iii ] λ λ 4959,5007 emission lines detected by slit spectroscopy in three-position angles using Multi-Object Infra-Red Camera and Spectrograph (MOIRCS) on the Subaru telescope and the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) on the Keck-I telescope. In the all slit directions, [O iii ] emission is extended to ∼15 physical kpc and indicates a powerful outflow spreading over the host galaxy. The inferred ionized gas mass outflow rate is 22 ± 3 M ⊙ yr −1 . Although it is a radio source, according to the line diagnostics using H β , [O ii ], and [O iii ], photoionization by the central QSO is likely the dominant ionization mechanism rather than shocks caused by radio jets. On the other hand, the spectral energy distribution of the host galaxy is well characterized as a quiescent galaxy that has shut down star formation several hundred Myr ago. Our results suggest a scenario that QSOs are powered after the shutdown of the star formation and help complete the quenching of massive quiescent galaxies at high redshift. 

Abstract We present emission maps ( $1.\prime 5\times 1.\prime 5$scale, corresponding to 0.18 pc) of the DCN (J= 2 − 1) and DCO⁺(J= 2 − 1) lines in the 2 mm band toward the Orion KL region obtained with the 2 mm receiver system named B4R installed on the Large Millimeter Telescope. The DCN emission shows a peak at the Orion KL hot core position, whereas no DCO⁺emission has been detected there. The DCO⁺emission shows enhancement at the west side of the hot core, which is well shielded from the UV radiation from OB massive stars in the Trapezium cluster. We have derived the abundance ratio of DCN/DCO⁺at three representative positions where both species have been detected. The gas components withV_LSR≈ 7.5–8.7 km s⁻¹are associated with low abundance ratios of ∼4–6, whereas much higher abundance ratios (∼22–30) are derived for the gas components withV_LSR≈ 9.2–11.6 km s⁻¹. We have compared the observed abundance ratio to our chemical models and found that the observed differences in the DCN/DCO⁺abundance ratios are explained by different densities. 

Abstract We report a massive quiescent galaxy at z spec = 3.0922 − 0.004 + 0.008 spectroscopically confirmed at a protocluster in the SSA22 field by detecting the Balmer and Ca ii absorption features with the multi-object spectrometer for infrared exploration on the Keck I telescope. This is the most distant quiescent galaxy confirmed in a protocluster to date. We fit the optical to mid-infrared photometry and spectrum simultaneously with spectral energy distribution (SED) models of parametric and nonparametric star formation histories (SFHs). Both models fit the observed SED well and confirm that this object is a massive quiescent galaxy with a stellar mass of log ( M ⋆ / M ⊙ ) = 11.26 − 0.04 + 0.03 and 11.54 − 0.00 + 0.03 , and a star formation rate of SFR/ M ⊙ yr −1 < 0.3 and = 0.01 − 0.01 + 0.03 for parametric and nonparametric models, respectively. The SFH from the former modeling is described as an instantaneous starburst whereas that of the latter modeling is longer-lived, but both models agree with a sudden quenching of the star formation at ∼0.6 Gyr ago. This massive quiescent galaxy is confirmed in an extremely dense group of galaxies predicted as a progenitor of a brightest cluster galaxy formed via multiple mergers in cosmological numerical simulations. We discover three new plausible [O iii ] λ 5007 emitters at 3.0791 ≤ z spec ≤ 3.0833 serendipitously detected around the target. Two of them just between the target and its nearest massive galaxy are possible evidence of their interactions. They suggest the future great size and stellar mass evolution of this massive quiescent galaxy via mergers.