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1.
We present the results of 12CO(1-0) and 12CO(2-1) observations on UGC 1347 obtained with BIMA and the IRAM 30 m telescope. UGC 1347 is a member of the Abell 262 cluster. In Abell 262, a nearby spiral rich cluster, the signs of galaxy interaction and therefore the mechanisms which play an important role in galaxy evolution within clusters can be studied with high spatial resolution. Aside from its bright central region, UGC 1347 features a second prominent source at the southern tip of the bar, which has been identified as region with recent enhanced star formation. The CO observations prove the existence of reservoirs of cold molecular gas at the positions of both bright regions.  相似文献   

2.
利用高空间分辨率的12CO(1-0)、13CO(1-0)、12CO(3-2)、12CO(6-5)、HCN(3-2)、\lk HCN(4-3)、 HCO+(3-2)和HCO+(4-3)分子谱线的ALMA (Atacama Large Millimeter/ submillimeter Array)归档数据, 来研究近邻亮红外星系NGC 1614的分子气体性质, 尤其是致密分子气体的性质. 在高分辨率分子气体谱线的积分强度图中, 在星系中心区域($<$ 1kpc)可以看到环状结构, 分子气体主要分布于星系中心区域, 核区分子气体含量较少. 12CO(1-0)显示出向南部、 北部以及东南部的延展结构, 高阶的CO ($J \ge$ 3, J为转振能级量子数)分子谱线和致密分子HCN、HCO+谱线显示, 较致密的分子气体主要集中于星系中心区域. HCN(4-3)/12CO(1-0)和HCN+(4-3)/12CO(1-0)积分强度比值图显示, 致密分子气体主要集中于中心区域的环状结构上. HCN/HCO+强度比值的分布变化表明星暴环的不同区域可能具有不同的激发条件. HCN/HCO+(4-3)强度比值分布在环的东、西部(sim0.44 pm 0.04)高于环的南、北部(sim0.35 pm 0.03). HCN/HCO+(3-2)强度比值较高的区域(sim0.38 pm 0.04)分布在HCN(3-2)峰值位置, 而环的西北、东南部强度比值相对较低(sim0.3 pm 0.03). 对于中心不同区域 HCN/HCO+比值变化的原因进行了讨论.  相似文献   

3.
The molecular gas mass in nearby galaxies is generally estimated using 12CO(1-0) line intensities and assuming the X conversion factor between I(CO) and N(H2) measured in the solar neighborhood. It is however known that this X conversion factor is not universal since it changes with metallicity, cosmic ray density and UV radiation field. Far-IR data in the spectral range 100-1000 μm can be used to estimate the molecular gas content of late-type galaxies in an independent way of CO line measurements once a metallicity-dependent dust to gas ratio is assumed, allowing a direct estimate of X. This exercise is presented here for a large sample of galaxies with available multifrequency data. X spans from ∼ 1020 mol cm-2 (K km s-1)-1 in giant spirals to ∼ 1021 mol cm-2 (K km s-1)-1 in dwarf irregulars. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

4.
Preliminary results are presented of fitting the spectral energy distribution and newly obtained12CO and13CO J =1-0, 2-1 and 3-2 line profiles of CW Leo. This is done with a model which includes a self-consistent calculation of the gas temperature.  相似文献   

5.
With the 13.7 m millimeter wave telescope of Purple Mountain Observatory at Qinghai Station, the simultaneous mapping observations at the 12CO(J=1-0), 13CO(J=1-0) and C18O(J=1-0) lines were performed towards the 24 Galactic high-mass star-forming cores, which are associated with water masers and have available Spitzer's infrared data. The average mapping range was 8′ × 8′. The C18O line emission was detected in all the cores, in which 11 cores were observed to the half maximum of their C18O integrated intensities and the rather extended (5′ − 8′) C18O maps were obtained, while the others were failed to make such a large scale mapping because of the low SNR or the intrinsically extended morphology of the cores. On the 11 completely mapped dense cores, we analyzed their characteristics and made the statistics and comparisons on the integrated intensity ratios between 12CO and 13CO (R12/13), 13CO and C18O(R13/18), as well as 12CO and C18O(R12/18). We concluded that as a tracer of dense gas, C18O is absolutely optically thin and can be used to detect the detailed structures of the cores, and that in general the 3 ratios increase gradually from the core center to the periphery. We found that the integrated intensity ratio R12/13 ranges from 2 to 6; R13/18 fluctuates between 4 and 20, but in central regions it is concentrated in the range 6–12 with a small fluctuation; and R12/18 occupies a wider range 13–90, but it is concentrated between 13 and 50 in the denser regions of the cores.  相似文献   

6.
Bars probably have a great importance in galactic evolution. The barred potential is able to concentrate large quantities of interstellar gas in the vicinity of the nucleus, feeding any nuclear activity, be it central starbursts or black hole accretion discs. The IRAM millimeter interferometer and 30 m telescope have allowed a precise analysis of the molecular gas in the bar and the nucleus of a typical barred spiral galaxy, NGC 1530. In this galaxy, I have detected CO(1→0) along two lanes that trace shocks in the molecular gas. In these lanes, the gas moves toward the centre of the galaxy, with typical in fall velocities of 100 km s-1. I have shown in these shocks an anticorrelation between shear in the gas and star formation efficiency by comparing Hα and CO maps. I have also studied the centre of this galaxy at higher resolution in12CO(1→0), 12CO(2→1),13CO(1→0) and HCN(1→0). In the central region, the gas distribution is a ring or an unresolved spiral, surrounded by two curved arcs. The nuclear ring contains large amounts of dense gas traced by HCN and 13CO, and shows intense star formation, as indicated by the non-thermal centimetre continuum. The arcs, in contrast, are poor in dense gas and form few stars. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

7.
The molecular phase of the ISM constitutes the main source of fuel for the activity in starburst and AGNs. The physical conditions and chemical constitution of the molecular gas will change with, and respond to, the evolution of the activity. This paper includes a short discussion of the 12CO/13CO 1–0 line intensity ratio as a diagnostic tool of the molecular gas properties of luminous galaxies – paired with examples of high-resolution studies of how the line ratio varies within galaxies. A possible connection between the OH megamasers and galaxies with unusually high 12CO/13CO 1–0 line intensity ratios are also briefly discussed.The relative intensities of the dense gas tracers HNC, HCN, HCO+ and CN are a result of both chemistry and starburst evolution. The discussion on the interpretation of HNC 1–0 emission includes the importance of ion-neutral chemistry in a luminous starburst region. Finally, simple cartoon ISM models and how they can be applied to LIRGs and ULIRGs, are presented.  相似文献   

8.
We have made spectral line analysis of CO and its isotopic lines from dark cloud Lynds 183 (L183). Our dataset incorporates 12CO(1-0), 13CO(1-0) and 13CO(2-1) lines using NRAO-12 m and 12CO(3-2), 13CO(3-2) lines using CSO-10 m telescopes, respectively. Observations suggest steep north-south (direction with respect to the offset position (0, 0)) temperature gradient in the cloud. These are likely to be caused by non-uniform, Inter Stellar Radiation Field (ISRF) illumination due to the shadow of nearby L134 cloud complex. As the emission of radiation depends on local properties like density and kinetic temperature, the present study attempts to deduce the irradiation contrast (and the resulting temperature difference) using 1D Monte Carlo radiative transfer code RATRAN. The model results accord with the observed data and shows a temperature difference of ∼7 K mainly within the cloud envelope. This results in a non-uniform intensity distribution of both CO and its species.  相似文献   

9.
Using HST and ground-based optical and NIR imaging data, we investigate whether the blue compact dwarf (BCD) galaxy I Zw 18 possesses an extended low-surface brightness (LSB) old stellar population underlying its star-forming (SF) regions. We show that the exponential intensity decrease observed in the filamentary LSB envelope of the BCD out to 18″ (1.3 kpc at the adopted distance of 15 Mpc) is not due to an evolved stellar disc, but rather due to extended ionized gas emission. Broad-band images reveal, after subtraction of nebular line emission, a compact stellar LSB component extending slightly beyond the SF regions. This stellar host, being blue over a radius range of 5 exponential scale lengths and showing little colour contrast to the SF component, differs strikingly from the red LSB host of standard BCDs. This fact, in connection with the blue colours of component I Zw 18 C (see discussion in Papaderos et al. 2002), suggests that most of the stellar mass in I Zw 18 has formed within the last 0.5 Gyr. Furthermore, we show that the exponential intensity fall-off in the filamentary ionized envelope of I Zw 18 is not particular to this system but a common property of the ionized halo of many SF dwarf galaxies on galactocentric distances of several kpc. In the absence of an appreciable underlying stellar background, extended ionized gas emission dominates in the periphery of I Zw 18, superficially resembling an exponential stellar disc on optical surface brightness profiles. The case of I Zw 18 suggests caution in the search of more distant young galaxy candidates. Intense SF activity in the early phase of dwarf galaxy formation may result in an extended ionized gas halo which can be mistaken for an evolved stellar disc by studying only its exponential surface brightness profile. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

10.
The early-stage structure and evolution of a supernova remnant (SNR) depends largely on its ambient interstellar medium, so the interstellar medium becomes the valid probe for investigating the evolution of SNRs. We have observed the 12CO (J = 1 − 0) line emission around the remnant of SN 1572 with the 13.7m millimeter-wave telescope at the Qinghai Station of PMO, in order to investigate the distribution of the CO molecular gas around SN 1572 and provide some observational basis for studying the relationship of SN 1572 with its ambient molecular gas and the evolution of this SNR. The observed result indicates that the molecular gas in the velocity range of VLSR = −69∼ −58 km/s is associated with SN 1572, and this velocity component comes from a large-scale molecular cloud. The molecular gas is distributed along the periphery of the radio shell, continually but not uniformly, and forms a semi-closed molecular shell around the SNR. The enhanced emission exists in its whole eastern half, especially the CO emission is strongest on the northeastern edge. At the emission peak position, the spectral line exhibits a broadened velocity feature (>5 km/s). Combining with available observations in the optical, infrared, X-ray and other wavebands, it is demonstrated that the fast shock wave and ejecta are expanding into the molecular gas on the northeastern edge, and interacting with the dense gas. This interaction will have an important influence on the future evolution of SN 1572.  相似文献   

11.
High-resolution CO maps are an essential tool to search for observational evidence of AGN fueling in galaxy nuclei. While their capabilities will be surpassed by ALMA, current mm-interferometers can already provide relevant information on scales which are critical for the process of angular momentum transfer in fueling the AGN. In this context we present the latest results issued from the NUclei of GAlaxies (NUGA) project, a high-resolution (0.5′′–1′′) CO survey of low luminosity AGNs conducted with the IRAM Plateau de Bure interferometer (PdBI). The use of more specific molecular tracers of dense gas can probe the feedback influence of activity on the chemistry and energy balance in the interstellar medium of nearby galaxies, a prerequisite to understanding how feedback operate at higher redshift galaxies. We discuss the results obtained in an ongoing study devoted to probe the feedback of activity from nearby Seyferts to high-redshift QSO.  相似文献   

12.
利用ALMA干涉阵望远镜(Atacama Large Millimeter/submillimeter Array)的高分辨(～0.2′′–0.7′′)的多谱线数据,包括CO (1-0)、CO (2-1)、CO (3-2)、HCN (1-0)、HCO+(1-0)、 HCN (3-2)、 HCO+(3-2)、HCN (4-3)和HCO+(4-3),并结合连续谱数据对近邻星系NGC 1068核区的物理性质进行了研究.速度积分强度图显示核周盘(CircumNuclear Disk, CND)呈现不对称的环状结构,尺度～300 pc.各分子谱线均显示, CND上的东发射结(E-knot)比西发射结(W-knot)有着更强的发射,且E-knot处表现出的分子气体的速度比W-knot更高.致密分子气体含量占比(用HCN或HCO+不同转动跃迁线与CO (1-0)的积分强度比值表示),以及致密分子气体比值(HCN/HCO+)均在CND的东部表现出更高的值,意味着CND东部和西部有着不同的物理环境或化学组成. CO ...  相似文献   

13.
We present high resolution millimeter, near-infrared, and optical data on the Wolf-Rayet nucleus of the Liner NGC 6764. The millimeter12CO(1-0) maps were obtained using the Nobeyama Millimeter Interferometer. Near-infrared images in the K-band continuum and the 2.12µm H2, 2.06µm He I, 2.17µm Br, and 1.64µm [Fe II] lines were taken with the MPE imaging spectrometer FAST at the William Herschel Telescope on La Palma, Spain. The optical data were obtained at the 3.5m telescope on Calar Alto, Spain. The measurements indicate a strong concentration of molecular gas and a massive starburst at the nucleus of NGC 6764. The interferometric position velocity map of the nucleus shows the presence of distinct molecular cloud complexes with an apparently asymmetric velocity field shifted towards the blue with respect to the systemic velocity of 2420 km s–1. The distribution of the 2.12µm H2 line flux exhibits extensions approximately perpendicular to the bar which are in agreement with structural features in VLA radio maps and IRAM 30m maps of the12CO(2–1) line emission. This may represent evidence for combination of a nuclear outflow and a central oval distortion of gas predicted by gas dynamical calculations as a response to a bar like potential. A detailed investigation of the Wolf-Rayet-feature at 466 nm indicates that it is spatially extended on a scale of a few arcseconds.  相似文献   

14.
This paper discusses results of multi-wavelength studies of low-mass galaxies with outflows. As a case study the extreme low-metallicity dwarf galaxy I Zw 18 is presented. The results from HST imaging, long-slit echelle spectroscopy and X-ray imaging are discussed in the context of chemical enrichment of dwarf galaxies. If outflows work primarily as a temporary repository of metals and not as a loss of metals into the intergalactic medium, we show that galactic winds can explain the relatively low N/O scatter seen in nearby low-metallicity dwarf galaxies as well as the apparent increase of N/O scatter observed in damped Lyα systems with metallicities near that of I Zw 18and below. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
BIMA SONG is a systematic imaging study of the 3 mm CO J = 1 → 0molecular emission within the centres and discs of 44 nearby spiral galaxies on size scales of a few hundred parsecs (6-9"). The overall goal of the survey is to study the role of molecular gas in the evolution of spiral galaxies. To this end, BIMA SONG addresses 1) the distribution and physical conditions of the molecular gas in galactic discs and its relation to star formation, 2) the effects of a stellar bar on the kinematics of molecular gas, including the possible inflow of gas along a bar, and 3) the distribution and role of molecular gas in the central few hundred parsecs of active and quiescent galaxies. The source list includes all (except M33and M31) 44 galaxies of Hubble types Sa–Sd, with declinations δ >−20°, visual magnitudes B < 11.0, velocities v hel <2000 km s-1, and inclinations i < 70°. Beyond the specific scientific questions we will address, this survey will provide a unique database for astronomers who study galaxies at all wavelengths. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
We present a multitransition study in the 13CO(1-0), 12CO(2-1), 12CO(3-2) and 12CO(4-3) lines of a parsec scale elongated structure connected to a low-mass dense core. Densities larger than n H 2 = 104 cm?3 are inferred in the central regions of this structure, supporting the proposition that it is a genuine filament denser than its environment. The sharp observed drop of the 12CO and 13CO emissions requires a power law density fall-off steeper than r ?1 although a single density law cannot reproduce the spatial shift of 0.1 pc between the 13CO and 12CO drops. Our results support the previous proposition that this elongated structure is a filament threaded by helical magnetic fields, channeling the gas inflow onto the dense core.  相似文献   

17.
We present new radio observations of molecular lines in the region of high mass star formation, namely G122.0-7.1. A large-scale map of the emission observed in the 12CO (J = 1−0) and 13CO (J = 1−0) lines covers the area of 15′ × 9′, revealing two dense regions. The molecular bipolar outflows have been resolved in ASO1 region. It is associated with the known candidate YSO nearby IRAS 0042 + 5530. Also, a new dense region has been discovered in the North-Western part of the G122.0-7.1 at a distance of 5′ from IRAS 0042 + 5530. Its position is close to the peak of 4850 MHz emission. The text was submitted by the authors in English.  相似文献   

18.
We present new observations of the molecular gas distribution in the merging system Arp 299. The first observation set was obtained with the Canada–France–Hawaii Telescope near-IR camera Redeye and the second set comes from the IRAM Plateau de Bure interferometer (combined with short spacings observed at the IRAM 30 m Telescope). In the near IR, H2 ν=1→0 S(1) and Brγ line maps are globally identical: there is bright emission not only at the two galaxy nuclei but also in numerous extranuclear star forming regions. Moreover, there is weaker emission localized in filaments between and around the two nuclei. These filaments correspond to a dust lane observed in optical images from HST. 12CO(1→0), 13CO(1→0) and HCN(1→0) maps are also presented. The structure of the12CO(1→0) map is very close to the NIR observations: the same bright galaxy nuclei and star-forming regions, the same filaments, but half of the total flux is found in weak extended emission. Strong HCN emission is observed in the nucleus A indicating the presence of a large amount of dense gas. Nucleus B1 is weak in 12CO(1→0) emission while nucleus A and star-forming regions C-C′ show more normal 13CO/12CO ratios. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0) and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these molecular lines are free from dust extinction.  相似文献   

20.
We have imaged several known molecular (CO) outflows in H2 v=1-0 S(1) and wide-band K in order to identify the molecular shocks associated with the acceleration of ambient gas by outflows from young stars. We detected H2 line emission in all the flows we observed: L 1157, VLA 1623, NGC 6334I, NGC 2264G, L 1641N and Haro 4-255. A comparison of the H2 data with CO outflow maps strongly suggests that prompt entrainment near the head of a collimated jet probably is the dominant mechanism for producing the CO outflows in these sources.  相似文献   

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