NRO 45-m Telescope Research Articles

Molecular gas excitation in the circumgalactic medium of MACS1931–26

The evolution of galaxies is largely affected by exchanging material with their close environment, the circumgalactic medium (CGM). In this work, we investigate the CGM and the interstellar medium (ISM) of the bright central galaxy (BCG) of the galaxy cluster, MACS1931−26 at z ∼ 0.35. We detected [CI](2−1), 12CO(1−0), and 12CO(7−6) emission lines with the APEX 12-m and NRO 45-m telescopes. We complemented these single-dish observations with 12CO(1−0), 12CO(3−2), and 12CO(4−3) ALMA interferometric data and inferred the cold molecular hydrogen physical properties. Using a modified large velocity gradient (LVG) model, we modelled the CO and CI emission of the CGM and BCG to extract the gas thermodynamical properties, including the kinetic temperature, the density, and the virialisation factor. Our study shows that the gas in the BCG is highly excited, comparable to the gas in local ultra luminous infrared galaxies (ULIRGs), while the CGM is likely less excited, colder, less dense, and less bound compared to the ISM of the BCG. The molecular hydrogen mass of the whole system derived using [CI](2−1) is larger than the mass derived from 12CO(1−0) in literature, showing that part of the gas in this system is CO-poor. Additional spatially resolved CI observations in both transitions, [CI](1−0) and [CI](2−1), and the completion of the CO SLED with higher CO transitions are crucial to trace the different phases of the gas in such systems and constrain their properties.

THE DEUTERIUM FRACTION IN MASSIVE STARLESS CORES AND DYNAMICAL IMPLICATIONS

ABSTRACT We study deuterium fractionation in two massive starless/early-stage cores, C1-N and C1-S, in Infrared Dark Cloud G028.37+00.07, which was first identified by Tan et al. with ALMA. Line emission from multiple transitions of N2H+ and N2D+ were observed with the ALMA, CARMA, SMA, JCMT, NRO 45 m, and IRAM 30 m telescopes. By simultaneously fitting the spectra, we estimate the excitation conditions and deuterium fraction, D frac N 2 H + ≡ [ N 2 D + ] / [ N 2 H + ] , with values of D frac N 2 H + ≃ 0.2–0.7, several orders of magnitude above the cosmic [D]/[H] ratio. Additional observations of o-H2D+ are also presented that help constrain the ortho-to-para ratio of H2, which is a key quantity affecting the degree of deuteration. We then present chemodynamical modeling of the two cores, especially exploring the implications for the collapse rate relative to free-fall, α ff. In order to reach the high level of observed deuteration of N 2 H + , we find that the most likely evolutionary history of the cores involves collapse at a relatively slow rate, ≲ one-tenth of free-fall.

Z45: A new 45-GHz band dual-polarization HEMT receiver for the NRO 45-m radio telescope

Abstract We developed a dual-linear-polarization HEMT (High Electron Mobility Transistor) amplifier receiver system of the 45-GHz band (hereafter Z45), and installed it in the Nobeyama 45-m radio telescope. The receiver system is designed to conduct polarization observations by taking the cross-correlation of two linearly polarized components, from which we process full Stokes spectroscopy. We aim to measure the magnetic field strength through the Zeeman effect of the emission line of CCS (JN = 43–32) toward pre-protostellar cores. A linear-polarization receiver system has a smaller contribution of instrumental polarization components to the Stokes V spectra than that of the circular polarization system, so that it is easier to obtain the Stokes V spectra. The receiver has an RF frequency of 42–46 GHz and an intermediate frequency (IF) band of 4–8 GHz. The typical noise temperature is about 50 K, and the system noise temperature ranges from 100 to 150 K over the frequency of 42–46 GHz. The receiver system is connected to two spectrometers, SAM45 and PolariS. SAM45 is a highly flexible FX-type digital spectrometer with a finest frequency resolution of 3.81 kHz. PolariS is a newly developed digital spectrometer with a finest frequency resolution of 60 Hz, and which has a capability to process the full-Stokes spectroscopy. The half-power beam width (HPBW) was measured to be 37″ at 43 GHz. The main beam efficiency of the Gaussian main beam was derived to be 0.72 at 43 GHz. The SiO maser observations show that the beam pattern is reasonably round at about 10% of the peak intensity and the side-lobe level was less than 3% of the peak intensity. Finally, we present some examples of astronomical observations using Z45.

Molecular gas and nuclear activity in early-type galaxies: any link with radio loudness?

Aims. We want to study the amount of molecular gas in a sample of nearby early-type galaxies (ETGs) which host low-luminosity Active Galactic Nuclei (AGN). We look for possible differences between the radio-loud (RL) and radio-quiet (RQ) AGN. Methods. We observed the CO(1-0) and CO(2-1) spectral lines with the IRAM 30m and NRO 45m telescopes for eight galaxies. They belong to a large sample of 37 local ETGs which host both RQ and RL AGN. We gather data from the literature for the entire sample. Results. We report the new detection of CO(1-0) emission in four galaxies (UGC0968, UGC5617, UGC6946, and UGC8355) and CO(2-1) emission in two of them (UGC0968 and UGC5617). The CO(2-1)/CO(1-0) ratio in these sources is $\sim0.7\pm0.2$. Considering both the new observations and the literature, the detection rate of CO in our sample is 55 $\pm$ 9%, with no statistically significant difference between the hosts of RL and RQ AGNs. For all the detected galaxies we converted the CO luminosities into the molecular masses, $M_{H_2}$, that range from 10$^{6.5}$ to 10$^{8.5}$ M$_{\odot}$, without any statistically significant differences between RL and RQ galaxies. This suggests that the amount of molecular gas does not likely set the radio-loudness of the AGN. Furthermore, despite the low statistical significance, the presence of a weak trend between the H$_{2}$ mass with various tracers of nuclear activity (mainly [O III] emission line nuclear power) cannot be excluded.

Large-Field CO (J = 1→0) Observations of the Starburst Galaxy M 82

Abstract We present large-field (15.7 $ \times$ 16.9 arcmin$ ^2$ ) CO ($ J$$ =$ 1$ \rightarrow$ 0) observations of the starburst galaxy M 82, at an angular resolution of 22$ ''$ with the NRO 45-m telescope. The CO emission was detected in the galactic disk, outflow (driven by the galactic wind) up to $ \sim$ 2 kpc above the galactic plane in the halo, and in tidal streams. The kinematics of the outflow (including CO line splitting) suggests that it has the shape of a cylinder that is diverging outwards. The mass and kinetic energy of the molecular gas outflow are estimated to be (0.26–1.0) $ \times$ 10$ ^{9}\ M_{\odot}$ and (1–4) $ \times$ 10$ ^{56}$ erg. A clump of CO gas was discovered 3.5 kpc above the galactic plane; it coincides with a dark lane previously found in X-ray observations, and a peak in H I emission. A comparison with H I, hot molecular hydrogen and dust suggests that the molecular gas shows signatures of warm and cool components in the outflow and tidal streams, respectively.

Measurements of an Antenna Surface for a Millimeter-Wave Space Radio Telescope. II. Metal Mesh Surface for Large Deployable Reflector

Abstract Large deployable antennas with a mesh surface woven by fine metal wires are an important technology for communications satellites and space radio telescopes. However, it is difficult to make metal mesh surfaces with sufficient radio-frequency (RF) performance for frequencies higher than millimeter waves. In this paper, we present the RF performance of metal mesh surfaces at 43 GHz. For this purpose, we developed an apparatus to measure the reflection coefficient, transmission coefficient, and radiative coefficient of the mesh surface. The reflection coefficient increases as a function of the metal mesh surface tension, whereas the radiative coefficient decreases. The anisotropic aspects of the reflection coefficient and the radiative coefficient are also clearly seen. They depend on the front and back sides of the metal mesh surface and the rotation angle. The transmission coefficient was measured to be almost constant. The measured radiative coefficients and transmission coefficients would cause significant degradation of the system noise temperature. In addition, we carried out an astronomical observation of a well-known SiO maser source, R Cas, by using a metal mesh mirror on the NRO 45-m radio telescope Coudé system. The metal mesh mirror considerably increases the system noise temperature, and slightly decreases the peak antenna temperature. These results are consistent with laboratory measurements.

NRO legacy project: M 33 all disk survey of Giant Molecular Clouds (GMCs) with NRO-45m and ASTE-10m telescopes

We present the results of the Nobeyama Radio Observatory (NRO) M 33 All Disk (30′ × 30′, or 7.3 kpc × 7.3 kpc) Survey of Giant Molecular Clouds (NRO MAGiC) based on 12 CO(J = 1–0) observations using the NRO 45-m telescope and 12 CO(J = 3–2) observations using the ASTE 10-m telescope. The spatial resolution of the resultant 12 CO(J = 1–0) map is 193, corresponding to 81 pc, which is sufficient to identify each Giant Molecular Cloud (GMC) in the disk. We found clumpy structures with a typical spatial scale of ~100 pc, corresponding to GMCs, and no diffuse, smoothly distributed component of molecular gas at this sensitivity. We obtained a map of the molecular fraction, f mol = ΣH2 /(ΣHi + ΣH2 ), at a 100-pc resolution. This is the first f mol map covering an entire galaxy with a GMC-scale resolution. The correlation between f mol and gas surface density shows two distinct sequences. The presence of two correlation sequences can be explained by differences in metallicity, i.e. , higher (~2-fold) metallicity in the central region (r , increased scale height toward the outer disk.

A Large Expanding Molecular Arc in the Sagittarius B1 Complex

Abstract Results of molecular line observations toward the Sagittarius B1 complex are reported. Maps of the HCN, HCO$^+$ and SiO J$=$ 1–0 emissions were taken with the NRO 45-m telescope. With these data, combined with the ASTE CO J$=$ 3–2 survey data, we have investigated the spatial structure, kinematics and physical conditions of two peculiar molecular features: CO0.55$+$0.07 and SiO0.56$-$0.01. The CO arc, CO0.55$+$0.07, shows clear expanding motion with sizes of 8.5 $\times$ 6.8 pc$^2$ and an expansion velocity of 40 km s$^{-1}$. The SiO shell, SiO0.56$-$0.01, has a size of 3.0 $\times$ 3.4 pc$^2$, and surrounds an X-ray Fe line source, G0.570$-$0.018. The mass and the kinetic energy of CO0.55$+$0.07 are estimated to be 10$^{5.5}{M_\odot}$ and 10$^{51.5}$erg, respectively. The kinetic energy of SiO0.56$-$0.01 is $\sim$10$^{50.4}$erg. An LVG analysis shows that the typical density and kinetic temperature are 10$^{3.8}$cm$^{-3}$ and 28 K, respectively. High-density clumps with a density of 10$^{4.0{-}4.5}$cm$^{-3}$ associated with CO0.55$+$0.07 and SiO0.56$-$0.01 have been found, supporting the idea that they consist of swept-up material. The huge kinetic energy of CO0.55$+$0.07 is considered to be injected by a series of supernova explosions that took place within $\sim$2 $\times$ 10$^{5}$yr, which would suggest that it is a ‘bubble’ created by a massive stellar cluster, whose mass is estimated to be 10$^{3.5{-}4.5}{M_\odot}$. The origin of SiO0.56$-$0.01 is rather unclear, but we suggest that it could be related to the X-ray source G0.570$-$0.018.

Arclike Distribution of High CO ([FORMULA][F]J=3-2[/F][/FORMULA])/CO ([FORMULA][F]J=1-0[/F][/FORMULA]) Ratio Gas Surrounding the Central Star Cluster of the Supergiant H ii Region NGC 604

We report the discovery of a high CO(J=3-2)/CO(J=1-0) ratio gas with an arc-like distribution (``high-ratio gas arc'') surrounding the central star cluster of the supergiant HII region NGC 604 in the nearby spiral galaxy M 33, based on multi-J CO observations of a 5' $\times$ 5' region of NGC 604 conducted using the ASTE 10-m and NRO 45-m telescopes. The discovered ``high-ratio gas arc'' extends to the south-east to north-west direction with a size of $\sim$ 200 pc. The western part of the high-ratio gas arc closely coincides well with the shells of the HII regions traced by H$\alpha$ and radio continuum peaks. The CO(J=3-2)/CO(J=1-0) ratio, R_{3-2/1-0}, ranges between 0.3 and 1.2 in the observed region, and the R_{3-2/1-0} values of the high-ratio gas arc are around or higher than unity, indicating very warm (T_kin > 60 K) and dense (n(H_2) > 10^{3-4} cm^{-3}) conditions of the high-ratio gas arc. We suggest that the dense gas formation and second-generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova of the first-generation stars of NGC 604, i.e., the central star cluster of NGC 604.

Water-Vapor Maser Disk at the Nucleus of the Seyfert 2 Galaxy NGC 3079

Abstract We observed a Seyfert 2/LINER galaxy NGC 3079 using the NRO 45-m telescope from 1992 to 2002, and the Very Long Baseline Array (VLBA) in 2001 December, at 22 GHz. The 45-m telescope detected weak red-shifted and systemic features as well as strong blue-shifted features. High spatial resolution observations with the VLBA indicated that the $\mathrm{H_2O}$ maser spots are distributed along the north-south direction, showing blue-shifted velocities in the north and red-shifted in the south. We propose a nearly edge-on molecular gas disk in the nuclear region of NGC 3079, whose radius varies from 0.4 to 1.2 pc and whose thickness is 0.3 pc. The disk is rotating at $V_\mathrm{rot} = 200 \hbox{--} 100 \,\mathrm{km} \,\mathrm{s}^{-1}$, having a large velocity dispersion of $\Delta V \approx 50 \,\mathrm{km} \,\mathrm{s}^{-1}$. The binding mass within the disk is $\sim 10^6 \,{{{M}_{\odot}}}$. The disk is inclined such that the east side is nearest to us. The large luminosity of the maser emission and exceptionally strong blue-shifted features of NGC 3079 are probably the result of local shocks in the disk. Three continuum components are interpreted as jets emitted from the nucleus. The velocities of the components relative to the dynamical center of the masing disk are $(0.09 \hbox{--} 0.17) \,c, <0.005 \,c$, and $<0.05 \,c$.

Rotating molecular gas associated with a silhouette disk in the center of the radio galaxy 3C 31

We have carried out aperture synthesis CO(J=1-0) observations of the FRI radio galaxy 3C 31 (NGC 383), using the Nobeyama Millimeter Array (NMA) and the RAINBOW interferometer, which achieves a large collecting area by adding the NRO 45m telescope. Our high-resolution (1.9″×1.4″) CO 3D observations reveal a very massive ( $\sim 10^9 M_\odot$ ), circularly-rotating molecular gas ring, which coincides nicely with the silhouette disk seen in the Hubble Space Telescope (HST) optical images. This is the first map depicting the molecular gas distribution and kinematics associated with a silhouette disk in the heart of a radio galaxy. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Variation of Molecular Cloud Properties across the Spiral Arm in M 51

Abstract We present the results of high-resolution ${{13\atop} \mathrm{CO}}$ ($ J = 1 \hbox{--} 0$) mapping observations with the NRO 45m telescope of the area toward the southern bright arm region of M 51, including the galactic center, in order to study the physical conditions of the molecular clouds in the arm and the interarm. The obtained map shows the central depression of the ${{13\atop} \mathrm{CO}}$ ($ J = 1 \hbox{--} 0$) emission, the circumnuclear ring (radius $ \sim$$ {10{}^{\mathrm {\prime \prime }}}$–$ {20{}^{\mathrm {\prime \prime }}}$), and the spiral arm structure. The arm-to-interarm ratio of the ${{13\atop} \mathrm{CO}}$ ($ J = 1 \hbox{--} 0$) integrated intensity is 2–4. We also have found a feature different from that found in the ${{12\atop} \mathrm{CO}}$ results. For example, the ${{13\atop} \mathrm{CO}}$ distribution shows a depression in part of the spiral arm. The $ {{12\atop} \mathrm{CO}}/{{13\atop} \mathrm{CO}}$ ratio spatially varies, and shows high values ($ \sim 20$) for the interarm and the central region, but low values ($ \sim 10$) for the arm. Their values indicate that there is a denser gas in the spiral arm than in the interarm. The distribution of the ${{13\atop} \mathrm{CO}}$ shows a better correspondence with that of the $ \mathrm{H}\alpha$ emission than with the ${{12\atop} \mathrm{CO}}$ in the disk region, except for the central region. We found that the ${{13\atop} \mathrm{CO}}$ emission is located on the downstream side of the ${{12\atop} \mathrm{CO}}$ arm, namely there is an offset between the ${{12\atop} \mathrm{CO}}$ and the ${{13\atop} \mathrm{CO}}$ as well as the $ \mathrm{H}\alpha$ emission. This suggests that there is a time delay between the accumulation of gas caused by the density wave and dense gas formation, accordingly star formation. This time delay is estimated to be $ \sim 10^7 \,\mathrm{yr}$ based on the assumption of galactic rotation derived by the rotation curve and the pattern speed of the M 51 spiral pattern. It is similar to the growth timescale of a gravitational instability in the spiral arm of M 51, suggesting that the gravitational instability plays an important role for dense gas formation.

CO Observations of Luminous IR Galaxies at Intermediate Redshift

Abstract We present new measurements of the 12CO (J = 1-0) emission from 16 luminous infrared galaxies (LIGs) at intermediate redshift (cz ∼ 10000-50000 km s−1). These new data were selected by isolated and normal morphology. Although there already exist measurements of CO emission from LIGs in the literature, they are mostly strongly interacting/merging systems. The new CO data represent an important new addition to the literature in that they both expand the relatively small number of samples of LIGs measured in CO, and they include an interesting subset of LIGs that were selected based on isolated and normal morphology. The CO observations were performed using the NRO 45-m telescope. >From measurements of the CO emission and the IRAS database, we discuss the molecular gas and dust properties of late-type galaxies at intermediate redshift. Comparisons of the CO and dust properties of the new result with those from other CO measurements have revealed the characteristics of this sample: (1) It shows the deepest CO observations of IRAS galaxies at intermediate redshift without any strong interaction features. (2) It has typical properties of normal IRAS galaxies in terms of star-formation efficiency, color-color diagrams and galactic nuclear activity. (3) It has a smaller gas-to-dust ratio than normal IRAS galaxies. This can be explained by a two-component dust model; our sample consists of mostly warm dust.

Millimeter-Wave Continuum Around NGC 7538-IRS1, IRS2, and IRS3

Millimeter-wave continuum sources in NGC 7538 region were observed with the NRO 45-m telescope and Nobeyama Millimeter Array. NRO 45-m telescope observations showed that the compact region which includes IRS1, IRS2, and IRS3 has a strong millimeter-wave intensity excess, cf. figures 1, and 2.

Dynamic Structure of the Horsehead Nebula

We have made a preliminary map of the Horsehead nebula in CO (J=1-0) using the NRO 45-m telescope. The HPBW is 15″, the grid spacing 10″, and the velocity resolution is ∼0.1km/s. Figure 1 shows the integrated intensity with a velocity interval 10-11.5 km/s, which we found represents well the shape of the dark globule of the Horsehead. The coincidence of the CO feature and the dark nebulocity is strikingly well, especially at the sharp edges in the south and in the west (from the neck to the ears). The quality of the data are not satisfactory, though. The typical noise level is 1 K rms in TA, and the accuracies of the pointing and the intensity calibration is rather low due to the bad weather during the observation. Some scanning effects in the intensities can be recognized in Figure 1. One of the reason why the gap obtically seen beneath the jaw is not clear in the CO map may be attributed to the pointing errors.

CS(J = 2-1) Observations of B335

CS(J = 2-1) observations of B335 are carried out using the NRO 45-m telescope with a 16″ beam. We get many self-reversed profiles with good S/N ratio. Assuming that this region consists of a core and a halo, we get the molecular hydrogen density and the CS relative abundance in the halo. The CS wings are located within the cavity of the CO wing (Goldsmith et al. 1984).

CO Observations of High-Velocity Flows in the Core of the NGC 7538 Molecular Cloud

Observation of the high-velocity flows in the core region of the NGC7538 molecular cloud are carried out with CO (J=1-0) molecular line using NRO 45-m radio telescope. The beam size is 14″ and the mapping area covers about 4'x3′. Four high-velocity flows are found in the core region. The high-velocity flows are prominent at and around IRS1, 9, and 11.