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We present an imaging molecular line survey in the 3-mm band (85-114 GHz) focused on one of the nearest galaxies with an active galactic nucleus (AGN), NGC 1068, based on observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA). Distributions of 23 molecular transitions are obtained in the central ~3 kpc region, including both the circumnuclear disk (CND) and starburst ring (SBR) with 60 and 350 pc resolution. The column densities and relative abundances of all the detected molecules are estimated under the assumption of local thermodynamic equilibrium in the CND and SBR. Then, we discuss the physical and chemical effects of the AGN on molecular abundance corresponding to the observation scale. We found that H13CN, SiO, HCN, and H13CO+ are abundant in the CND relative to the SBR. In contrast, 13CO is more abundant in the SBR. Based on the calculated column density ratios of N(HCN)/N(HCO+), N(HCN)/N(CN), and other molecular distributions, we conclude that the enhancement of HCN in the CND may be due to high-temperature environments resulting from strong shocks, which are traced by the SiO emission. Moreover, the abundance of CN in the CND is significantly lower than the expected value of the model calculations in the region affected by strong radiation. The expected strong X-ray irradiation from the AGN has a relatively lower impact on the molecular abundance in the CND than mechanical feedback., 33 pages, 20 figures, 4 tables, accepted for publication in ApJ

We report the results of the performance characterization of a prototype wavefront sensor for millimetric adaptive optics (MAO) installed on the Nobeyama 45 m radio telescope. MAO is a key component to realize a future large-aperture submillimeter telescope, such as Large Submillimeter Telescope (LST) or Atacama Large Aperture Submillimeter Telescope (AtLAST). The difficulty of MAO is, however, real-time sensing of wavefront deformation with ~10 um accuracy across the aperture. Our wavefront sensor operating at 20 GHz measures the radio path length between a certain position of the primary mirror surface to the focal point where a 20 GHz coherent receiver is placed. With the 2-element prototype, we sampled two positions on the primary mirror surface (at radii of 5 m and 16 m) at a sampling rate of 10 Hz. Then an excess path length (EPL) between the two positions was obtained by differentiating the two optical paths. A power spectral density of the EPL shows three components: a low-frequency drift (1/f^n), oscillations, and a white noise. A comparison of EPL measurements under a variety of wind conditions suggests that the former two are likely induced by the wind load on the telescope structure. The power of the white noise corresponds to a 1sigma statistical error of 8 um in EPL measurements. The 8 um r.m.s. is significant with respect to the mirror surface accuracy required by the LST and AtLAST (~20-40 um r.m.s.), which demonstrates that our technique is also useful for the future large-aperture submillimeter telescopes., 10 pages, 9 figures. Published in SPIE Proc

The cosmic star formation rate (SFR) density continues to decrease after it peaks at z ~ 2. Previous studies suggested that the environmental quenching of star formation is one of the plausible causes for this decrease. Though several scenarios have been proposed for the environmental quenching process, it is not clear what the dominant mechanism is for individual clusters and galaxies. In order to understand the mechanism of environmental quenching, we used ALMA to investigate the physical properties of 4 member galaxies located at the center (~ 0.2 R_200) of SPT-CL J0615-5746 (SPT0615) at z = 0.972. Since SPT0615 is considered to be filled with high temperature ICM, it is expected that environmental quenching will be observed in the center of the cluster. Four member galaxies are detected in dust continuum, and three of these are also detected in CO(J = 5 – 4) with the significance over 5σ. The inferred SFR and molecular mass are high (SFR ~ 10 – 10^2 M_Sun/yr and M_mol ~ 10^10 M_Sun), implying the existence of active star formation. In addition, a CO(J = 5 – 4) tail feature is detected in one of those galaxies with the significance 5.7σ, which is likely to be molecular gas stripped from this galaxy by interaction with the ICM. In this galaxy, HST rest–frame UV to NIR images show that star formation takes place even in the stripped gas. Here we show, for the first time, gas stripping in a cluster at z ~ 1.

We report the current status of the NASCO (NAnten2 Super CO survey as legacy) project which aims to provide all-sky CO data cube of southern hemisphere using the NANTEN2 4-m submillimeter telescope installed at the Atacama Desert through developing a new multi-beam receiver and a new telescope control system. The receiver consists of 5 beams. The four beams, located at the four corners of a square with the beam separation of 720$''$, are installed with a 100 GHz band SIS receiver having 2-polarization sideband-separation filter. The other beam, located at the optical axis, is installed with a 200 GHz band SIS receiver having 2-polarization sideband-separation filter. The cooled component is modularized for each beam, and cooled mirrors are used. The IF bandwidths are 8 and 4 GHz for 100 and 200 GHz bands, respectively. Using XFFTS spectrometers with a bandwidth of 2 GHz, the lines of $^{12}$CO, $^{13}$CO, and C$^{18}$O of $J$=1$-$0 or $J$=2$-$1 can be observed simultaneously for each beam. The control system is reconstructed on the ROS architecture, which is an open source framework for robot control, to enable a flexible observation mode and to handle a large amount of data. The framework is commonly used and maintained in a robotic field, and thereby reliability, flexibility, expandability, and efficiency in development are improved as compared with the system previously used. The receiver and control system are installed on the NANTEN2 telescope in December 2019, and its commissioning and science verification are on-going. We are planning to start science operation in early 2021., Comment: submitted to SPIE Astronomical Telescopes + Instrumentation (AS20), paper No. 11453-146

We present our ALMA Cycle 4 measurements of the [C II] emission line and the underlying far-infrared (FIR) continuum emission from four optically low-luminosity (M-1450 > -25) quasars at z >= 6 discovered by the Subaru Hyper Suprime Cam (HSC) survey. The [C II] line and FIR continuum luminosities lie in the ranges L-[C II] = (3.8-10.2) x 10(8) L-circle dot and L-FIR = (1.2-2.0) x 10(11) L-circle dot, which are at least one order of magnitude smaller than those of optically-luminous quasars at z >= 6. We estimate the star formation rates (SFRs) of our targets as similar or equal to 23-40 M-circle dot yr(-1). Their line and continuum-emitting regions are marginally resolved, and found to be comparable in size to those of optically-luminous quasars, indicating that their SFR or likely gas mass surface densities (key controlling parameter of mass accretion) are accordingly different. The L-[C II]/L-FIR ratios of the hosts, similar or equal to (2.2-8.7) x 10 (-3), are fully consistent with local star-forming galaxies. Using the [C II] dynamics, we derived their dynamical masses within a radius of 1.5-2.5 kpc as similar or equal to (1.4-8.2) x 10(10)M(circle dot). By interpreting these masses as stellar ones, we suggest that these faint quasar hosts are on or even below the star-forming main sequence at z similar to 6, i.e., they appear to be transforming into quiescent galaxies. This is in contrast to the optically-luminous quasars at those redshifts, which show starburst-like properties. Finally, we find that the ratios of black hole mass to host galaxy dynamical mass of most of the low-luminosity quasars, including the HSC ones, are consistent with the local value. The mass ratios of the HSC quasars can be reproduced by a semi-analytical model that assumes merger-induced black hole host galaxy evolution.

We present the first 100 pc scale view of the dense molecular gas in the central ~ 1.3 kpc region of the type-1 Seyfert NGC 1097 traced by HCN (J=4-3) and HCO+ (J=4-3) lines afforded with ALMA band 7. This galaxy shows significant HCN enhancement with respect to HCO+ and CO in the low-J transitions, which seems to be a common characteristic in AGN environments. Using the ALMA data, we study the characteristics of the dense gas around this AGN and search for the mechanism of HCN enhancement. We find a high HCN (J=4-3) to HCO+ (J=4-3) line ratio in the nucleus. The upper limit of the brightness temperature ratio of HCN (v2=1^{1f}, J=4-3) to HCN (J=4-3) is 0.08, which indicates that IR pumping does not significantly affect the pure rotational population in this nucleus. We also find a higher HCN (J=4-3) to CS (J=7-6) line ratio in NGC 1097 than in starburst galaxies, which is more than 12.7 on the brightness temperature scale. Combined from similar observations from other galaxies, we tentatively suggest that this ratio appears to be higher in AGN-host galaxies than in pure starburst ones similar to the widely used HCN to HCO+ ratio. LTE and non-LTE modeling of the observed HCN and HCO+ lines using J=4-3 and 1-0 data from ALMA, and J=3-2 data from SMA, reveals a high HCN to HCO+ abundance ratio (5 < [HCN]/[HCO+] < 20: non-LTE analysis) in the nucleus, and that the high-J lines (J=4-3 and 3-2) are emitted from dense (10^{4.5} < n_H2 [/cc] < 10^6), hot (70 < Tkin [K] < 550) regions. Finally we propose that the high temperature chemistry is more plausible to explain the observed enhanced HCN emission in NGC 1097 than the pure gas phase PDR/XDR chemistry.

著者人数: 26名, Accepted: 2013-06-01, 資料番号: SA1004664000