We have performed an unbiased dense core survey toward the Orion A Giant Molecular Cloud in the C^18^O (J=1-0) emission line taken with the Nobeyama Radio Observatory (NRO) 45 m telescope. The effective angular resolution of the map is 26", which corresponds to ~0.05pc at a distance of 414pc. By using the Herschel-Planck H_2_ column density map, we calculate the C^18^O fractional abundance and find that it is roughly constant over the column density range of <~5x10^22^cm^-3^, although a trend of C^18^O depletion is determined toward higher column density. Therefore, C^18^O intensity can follow the cloud structure reasonably well. The mean C^18^O abundance in Orion A is estimated to be 5.7x10^-7^, which is about three times larger than the fiducial value. We identified 746 C^18^O cores with astrodendro and classified 709 cores as starless cores. We compute the core masses by decomposing the Herschel-Planck dust column density using the relative proportions of the C^18^O integrated intensities of line-of-sight components. Applying this procedure, we attempt to remove the contribution of the background emission, i.e., the ambient gas outside the cores. Then, we derived mass function for starless cores and found that it resembles the stellar initial mass function (IMF). The CMF for starless cores, dN/dM, is fitted with a power-law relation of M^{alpha}^ with a power index of {alpha}=-2.25+/-0.16 at the high-mass slope (>~0.44M_{sun}_). We also found that the ratio of each core mass to the total mass integrated along the line of sight is significantly large. Therefore, in the previous studies, the core masses derived from the dust image are likely to be overestimated by at least a factor of a few. Accordingly, such previous studies may underestimate the star formation efficiency of individual cores.
We present the results of C^18^O(J=1-0) mapping observations of a 20'x18' area in the Lynds 1204 molecular cloud associated with the Sharpless 2-140 (S140) HII region. The C^18^O cube ({alpha}-{delta}-{nu}_LSR_) data show that there are three clumps of sizes ~1pc in the region. Two of these have peculiar redshifted velocity components at their edges, which can be interpreted as the results of the interaction between the cloud and the Cepheus Bubble. From the C^18^O cube data, clumpfind identified 123 C^18^O cores, which have mean radius, velocity width in FWHM, and LTE mass of 0.36+/-0.07pc, 0.37+/-0.09km/s, and 41+/-29M_{sun}_, respectively. Considering the uncertainty in the C^18^O abundance, all the cores in S140 are most likely to be gravitationally bound. We derived a C^18^O core mass function (CMF), which shows a power-law-like behavior above a turnover at 30M_{sun}_.
Young stars form in molecular cores, which are dense condensations within molecular clouds. We have searched for molecular cores traced by ^13^CO J=1-->0 emission in the Taurus molecular cloud and studied their properties. Our data set has a spatial dynamic range (the ratio of linear map size to the pixel size) of about 1000 and spectrally resolved velocity information, which together allow a systematic examination of the distribution and dynamic state of ^13^CO cores in a large contiguous region. We use empirical fit to the CO and CO_2_ ice to correct for depletion of gas-phase CO. The ^13^CO core mass function (^13^CO CMF) can be fitted better with a log-normal function than with a power-law function. We also extract cores and calculate the ^13^CO CMF based on the integrated intensity of ^13^CO and the CMF from Two Micron All Sky Survey. We demonstrate that core blending exists, i.e., combined structures that are incoherent in velocity but continuous in column density. The core velocity dispersion (CVD), which is the variance of the core velocity difference {delta}v, exhibits a power-law behavior as a function of the apparent separation L: CVD(km/s){prop.to}L(pc)^0.7^. This is similar to Larson's law for the velocity dispersion of the gas. The peak velocities of ^13^CO cores do not deviate from the centroid velocities of the ambient ^12^CO gas by more than half of the line width. The low velocity dispersion among cores, the close similarity between CVD and Larson's law, and the small separation between core centroid velocities and the ambient gas all suggest that molecular cores condense out of the diffuse gas without additional energy from star formation or significant impact from converging flows.
Minor mergers play a crucial role in galaxy evolution. UGC 10214 (the Tadpole galaxy) is a prime example of this process in which a dwarf galaxy has interacted with a large spiral galaxy ~250 Myr ago and produced a perturbed disc and a giant tidal tail. We used a multi-wavelength dataset that partly consists of new observations (H{alpha}, HI, and CO) and partly of archival data to study the present and past star formation rate (SFR) and its relation to the gas and stellar mass at a spatial resolution down to 4 kpc. UGC 10214 is a high-mass (stellar mass M_*_=1.28x10^11^ M_{sun}_) galaxy with a low gas fraction (M_gas_/M_*_=0.24), a high molecular gas fraction (M_H2_/M_HI_=0.4), and a modest SFR (2-5 M_{sun}_/yr). The global SFR compared to its stellar mass places UGC 10214 on the galaxy main sequence (MS). The comparison of the molecular gas mass and current SFR gives a molecular gas depletion time of about ~2 Gyr (based on H{alpha}), comparable to those of normal spiral galaxies. Both from a comparison of the H{alpha} emission, tracing the current SFR, and far-ultraviolet (FUV) emission, tracing the recent SFR during the past tens of Myr, and also from spectral energy distribution fitting with CIGALE, we find that the SFR has increased by a factor of about 2-3 during the recent past. This increase is particularly noticeable in the centre of the galaxy where a pronounced peak of the H{alpha} emission is visible. A pixel-to-pixel comparison of the SFR, molecular gas mass, and stellar mass shows that the central region has had a depressed FUV-traced SFR compared to the molecular gas and the stellar mass, whereas the H{alpha}-traced SFR shows a normal level. The atomic and molecular gas distribution is asymmetric, but the position-velocity diagram along the major axis shows a pattern of regular rotation. We conclude that the minor merger has most likely caused variations in the SFR in the past that resulted in a moderate increase of the SFR, but it has not perturbed the gas significantly so that the molecular depletion time remains normal.
The Lupus star-forming complex includes some of the closest low-mass star-forming regions, and together they house objects that span evolutionary stages from pre-stellar to pre-MS. By studying 7 objects in the Lupus clouds from prestellar to protostellar stages, we aim to test if a coherence exists between commonly used evolutionary tracers. We present ALMA observations of the 1.3mm continuum and molecular line emission that probe the dense gas and dust of cores (continuum, C^18^O, N_2_D^+^) and their associated molecular outflows (^12^CO). Our selection of sources in a common environment, with identical observing strategy, allows for a consistent comparison across different evolutionary stages. We complement our study with continuum and line emission from the ALMA archive in different bands. The quality of the ALMA molecular data allows us to reveal the nature of the molecular outflows in the sample by studying their morphology and kinematics, through interferometric mosaics covering their full extent. The interferometric images in IRAS 15398-3359 appear to show that it drives a precessing episodic jet-driven outflow with at least 4 ejections separated by periods of time between 50 and 80 years, while data in IRAS 16059-3857 show similarities with a wide-angle wind model also showing signs of being episodic. The outflow of J160115-41523 could be better explain with the wide-angle wind model as well, but new observations are needed to further explore its nature. We find that the most common evolutionary tracers in the literature are useful for broad evolutionary classifications, but are not consistent with each other to provide enough granularity to disentangle different evolutionary stage of sources that belong to the same Class (0, I, II, or III). The evolutionary classification revealed by our analysis coincides with those determined by previous studies for all our sources except J160115-41523. Outflow properties used as protostellar age tracers, such as mass, momentum, energy and opening angle, may suer from differences in the nature of each outflow, and therefore detailed observations are needed to refine evolutionary classifications. We found both AzTEC-lup1-2 and AzTEC-lup3-5 to be in the pre-stellar stage, with the possibility that the latter is a more evolved source. IRAS 15398-3359, IRAS 16059-3857 and J160115-41523, which have clearly detected outflows, are Class 0 sources, although we are not able to determine which is younger and which is older. Finally Sz 102 and Merin 28 are the most evolved sources in our sample and show signs of having associated flows, not as well traced by CO as for the younger sources.
New-generation spectroscopic surveys of the Milky Way plane have been revealing the structure of the interstellar medium, allowing the simultaneous study of dense structures from single star-forming objects or systems to entire spiral arms. The good sensitivity of the new surveys and the development of dedicated algorithms now enable building extensive catalogues of molecular clouds and deriving good estimates of their physical properties. This allows studying the behaviour of these properties across the Galaxy. We present the catalogue of molecular clouds extracted from the ^13^CO (1-0) data cubes of the Forgotten Quadrant Survey, which mapped the Galactic plane in the range 220{deg}<l<240{deg}, and -2.5{deg}<b<0{deg} in ^12^CO (1-0) and ^13^CO (1-0). We compared the properties of the clouds of our catalogue with those of other catalogues. The catalogue contains 87 molecular clouds for which the main physical parameters such as area, mass, distance, velocity dispersion, and virial parameter were derived. These structures are overall less extended and less massive than the molecular clouds identified in the ^12^CO (1-0) data-set because they trace the brightest and densest part of the ^12^CO (1-0) clouds. Conversely, the distribution of aspect ratio, equivalent spherical radius, velocity dispersion, and virial parameter in the two catalogues are similar. The mean value of the mass surface density of molecular clouds is 87+/-55M_{sun}_/pc^2^ and is almost constant across the galactocentric radius, indicating that this parameter, which is a proxy of star formation, is mostly affected by local conditions. In data of the Forgotten Quadrant Survey, we find a good agreement between the total mass and velocity dispersion of the clouds derived from ^12^CO (1-0) and ^13^CO (1-0). This is likely because in the surveyed portion of the Galactic plane, the H_2_ column density is not particularly high, leading to a CO emission with a not very high optical depth. This mitigates the effects of the different line opacities between the two tracers on the derived physical parameters. This is a common feature in the outer Galaxy, but our result cannot be readily generalised to the entire Milky Way because regions with higher particle density could show a different behaviour.
Large area catalogs of galaxy clusters constructed from ROSAT All Sky Survey provide the base for our knowledge on the population of clusters thanks to the long-term multiwavelength efforts to follow-up observations of these clusters.. Advent of large area photometric surveys superseding in depth previous all-sky data allows us to revisit the construction of X-ray cluster catalogs, extending the study to lower cluster masses and to higher redshifts and to provide the modelling of the selection function. We perform a wavelet detection of X-ray sources and make extensive simulations of the detection of clusters in the RASS data. We assign an optical richness to each of the 24,788 detected X-ray sources in the 10,382 square degrees of SDSS BOSS area, using redMaPPer version 5.2 run on Sloan Digital Sky Survey photometry. We name this survey COnstrain Dark Energy with X-ray (CODEX) clusters. We show that there is no obvious separation of sources on galaxy clusters and AGN, based on distribution of systems on their richness. This is a combination of increasing number of galaxy groups and their selection as identification of an X-ray sources either by chance or due to groups hosting an AGN. To clean the sample, we use a cut on the optical richness at the level corresponding to the 10% completeness of the survey and include it into the modelling of cluster selection function. We present the X-ray catalog extending to a redshift of 0.6. CODEX is the first large area X-ray selected catalog of Northern clusters reaching the fluxes of 10^-13^ergs/s/cm^2^. We provide the modelling of the sample selection and discuss the redshift evolution of the high end of the X-ray luminosity function (XLF). Our results on z<0.3 XLF are in agreement with previous studies, while we provide new constraints on the 0.3<z<0.6 XLF. We find a lack of strong redshift evolution of the XLF, provide exact modeling of the effect of low number statistics and AGN contamination and present the resulting constraints on the flat {LAMBDA}CDM.
The first results from a survey of circumstellar CO(1-0) emission are presented. The sources were selected from the IRAS point source catalog according to the IRAS color criteria described in van der Veen and Habing (1988A&A...194..125V). The sources have good quality fluxes at 12, 25, and 60 microns, flux densities larger than 20Jy at 25{mu}m, and are situated more than 5{deg} away from the Galactic plane. The survey is undertaken to study the relationship between mass loss rates, dust properties, and the evolution along the AGB. The sample consists of 787 sources and contains both oxygen and carbon-rich stars, including Mira variables, OH/IR objects, protoplanetary nebulae, planetary nebulae, and 60-micron excess sources. So far, 519 objects, situated on both the northern and the southern sky, have been observed; 163 sources were found to have circumstellar CO emission, and in 58 of these CO emission has not previously been detected.
Using the 22-m 'Mopra' antenna (near Coonabarabran, NSW) of the Australia Telescope National Facility (ATNF), we have observed emission from the 115-GHz J=1-0 transition of CO towards the centre of each of the 1101 clouds listed in the Hartley et al. Catalogue of Southern Dark Clouds (SDC, Cat. <VII/191>). The velocity range covered was -96 to +70km/s, with a velocity resolution of 0.120km/s. CO was detected at 1049 of the positions, with 367 spectra showing emission at more than one radial velocity. Here we present the most comprehensive general survey of the SDC catalogue, with the intensity, velocity and half-width of the CO detection and a code describing the profile shape. The presence of blue- or red-shifted wings in many observations can provide a starting point in searches for star-forming regions.
The results of a CO line survey in central cluster galaxies with cooling flows are presented. Cold molecular gas is detected with the IRAM 30m telescope, through CO(1-0) and CO(2-1) emission lines in 6-10 among 32 galaxies. The corresponding gas masses are between 3x10^8^ and 4x10^10^M_{sun}. These results are in agreement with recent CO detections by Edge (2001MNRAS.328..762E). A strong correlation between the CO emission and the H{alpha} luminosity is also confirmed. Cold gas exists in the center of cooling flow clusters and these detections may be interpreted as evidence of the long searched for very cold residual of the hot cooling gas.
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