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We have analyzed multi-passband photometric observations, obtained with the {\it Hubble Space Telescope}, of the massive ($1.8 \times 10^5 M_\odot$), intermediate-age (1.8 Gyr-old) Large Magellanic Cloud star cluster NGC 1783. The morphology of the cluster's red giant branch does not exhibit a clear broadening beyond its intrinsic width; the observed width is consistent with that owing to photometric uncertainties alone and independent of our photometric selection boundaries applied to obtain our sample of red-giant stars. The color dispersion of the cluster's red-giant stars around the best-fitting ridgeline is $0.062 \pm 0.009$ mag, which is equivalent to the width of $0.080 \pm 0.001$ mag derived from artificial simple stellar population tests, that is, tests based on single-age, single-metallicity stellar populations. NGC 1783 is comparably massive as other star clusters that show clear evidence of multiple stellar populations. After incorporating mass-loss recipes from its current age of 1.8 Gyr to an age of 6 Gyr, NGC 1783 is expected to remain as massive as some other clusters that host clear multiple populations at these intermediate ages. If we were to assume that mass is an important driver of multiple population formation, then NGC 1783 should have exhibited clear evidence of chemical abundance variations. However, our results support the absence of any chemical abundance variations in NGC 1783.
Using an unconventional single line diagnostic that unambiguously identifies AGNs in composite galaxies we report statistical differences in the properties (stellar age, [OII] luminosity, colour) between active and inactive galaxies at 0.62<z<1.2 extracted from the VIMOS Public Extragalactic Redshift Survey (VIPERS). The nuclear activity is probed by the high-ionization [NeV] emission line and along with their parent samples, the galaxies are properly selected according to their stellar mass, redshift, and colour distributions. We report younger underlying stellar ages and higher [OII] luminosities of active galaxies in the green valley and in the blue cloud compared to control samples. We observe higher fractions of green galaxies hosting AGN activity at progressively bluer (r-K) colours. Depending on the location of the host galaxy in the NUVrK colour diagram we find higher AGN fractions in massive blue galaxies and in the least massive red galaxies, in agreement with the picture that black holes vary their properties when hosted in either star-forming or passive galaxies. Exactly where the fast quenching processes are expected to play a role, we identify a novel class of active galaxies in the blue cloud with signatures typical for a suddenly suppression of their star formation activity after a burst happening in the recent past. Their optical spectra resemble those of post-starburst galaxies, that would never be identified in a spectroscopic search using classical selection techniques. Broadly, these active galaxies selected on the [NeV] line are not commonly represented in shallow X-ray, mid-IR, or classical line diagnostics. If we consider that our results are limited by the shallow observational limits and rapid AGN variability, the impact of AGN feedback on galaxy formation and evolution may represent an important channel of fast-transiting galaxies moving to the red sequence.
We study the origin of the non-thermal profiles observed in filamentary structures in galactic molecular clouds by means of numerical dynamical simulations. We find that such profiles are intrinsic features of the end products of dissipationless collapse in cylindrical symmetry. Moreover, for sufficiently cold initial conditions, we obtain end states characterized by markedly anticorrelated radial density and temperature profiles. Gravitational, dissipationless dynamics alone is thus sufficient to reproduce, at least qualitatively, many of the properties of the observed non-thermal structures.
The currents carried by the jets of active galactic nuclei (AGNs) can be probed using maps of the Faraday rotation measure (RM), since a jet current will be accompanied by a toroidal magnetic (B) field, which will give rise to a systematic change in the RM across the jet. The aim of this study is to identify new AGNs displaying statistically significant transverse RM gradients across their parsec-scale jets, and to look for overall patterns in the implied directions for the toroidal B-field components and jet currents. We have carried out new analyses of Faraday RM maps derived from previously published 8.1, 8.4, 12.1 and 15.3 GHz data obtained in 2006 on the NRAO VLBA. In a number of important ways, our procedures were identical to those of the original authors, but several other key aspects of the new imaging and analysis differ from the original methods. Our new analysis has substantially increased the number of AGNs known to display transverse RM gradients. The collected data on parsec and kiloparsec scales indicate that the current typically flows inward along the jet axis and outward in a more extended region surrounding the jet, typical to the current structure of a coaxial cable, accompanied by a self-consistent system of nested helical B fields, whose toroidal components give rise to the observed transverse RM gradients. These new results make it possible for the first time to conclusively demonstrate the existence of a preferred direction for the toroidal B-field components - and therefore of the currents - of AGN jets. Discerning the origin of this current-field system is of cardinal importance for understanding the physical mechanisms leading to the formation of the intrinsic jet B field, which likely plays an important role in the propagation and collimation of the jets; one possibility is the action of a "cosmic battery".
We present a new catalogue of cool supergiants in a section of the Perseus arm, most of which had not been previously identified. To generate it, we have used a set of well-defined photometric criteria to select a large number of candidates (637) that were later observed at intermediate resolution in the the Infrared Calcium Triplet spectral range, using a long-slit spectrograph. To separate red supergiants from luminous red giants, we used a statistical method, developed in previous works and improved in the present paper. We present a method to assign probabilities of being a red supergiant to a given spectrum and use the properties of a population to generate clean samples, without contamination from lower-luminosity stars. We compare our identification with a classification done using classical criteria and discuss their respective efficiencies and contaminations as identification methods. We confirm that our method is as efficient at finding supergiants as the best classical methods, but with a far lower contamination by red giants than any other method. The result is a catalogue with 197 cool supergiants, 191 of which did not appear in previous lists of red supergiants. This is the largest coherent catalogue of cool supergiants in the Galaxy.
We explore scenarios for the dynamical ejection of stars BN and x from source I in the Kleinmann-Low nebula of the Orion Nebula Cluster (ONC), which is important for being the closest region of massive star formation. This ejection would cause source I to become a close binary or a merger product of two stars. We thus consider binary-binary encounters as the mechanism to produce this event. By running a large suite of $N$-body simulations, we find that it is nearly impossible to match the observations when using the commonly adopted masses for the participants, especially a source I mass of $7\:{\rm{M}}_\odot$. The only way to recreate the event is if source I is more massive, i.e., $\sim20\:{\rm{M}}_\odot$. However, even in this case, the likelihood of reproducing the observed system is low. We discuss the implications of these results for understanding this important star-forming region.
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We have analyzed multi-passband photometric observations, obtained with the {\it Hubble Space Telescope}, of the massive ($1.8 \times 10^5 M_\odot$), intermediate-age (1.8 Gyr-old) Large Magellanic Cloud star cluster NGC 1783. The morphology of the cluster's red giant branch does not exhibit a clear broadening beyond its intrinsic width; the observed width is consistent with that owing to photometric uncertainties alone and independent of our photometric selection boundaries applied to obtain our sample of red-giant stars. The color dispersion of the cluster's red-giant stars around the best-fitting ridgeline is $0.062 \pm 0.009$ mag, which is equivalent to the width of $0.080 \pm 0.001$ mag derived from artificial simple stellar population tests, that is, tests based on single-age, single-metallicity stellar populations. NGC 1783 is comparably massive as other star clusters that show clear evidence of multiple stellar populations. After incorporating mass-loss recipes from its current age of 1.8 Gyr to an age of 6 Gyr, NGC 1783 is expected to remain as massive as some other clusters that host clear multiple populations at these intermediate ages. If we were to assume that mass is an important driver of multiple population formation, then NGC 1783 should have exhibited clear evidence of chemical abundance variations. However, our results support the absence of any chemical abundance variations in NGC 1783.
Using an unconventional single line diagnostic that unambiguously identifies AGNs in composite galaxies we report statistical differences in the properties (stellar age, [OII] luminosity, colour) between active and inactive galaxies at 0.62<z<1.2 extracted from the VIMOS Public Extragalactic Redshift Survey (VIPERS). The nuclear activity is probed by the high-ionization [NeV] emission line and along with their parent samples, the galaxies are properly selected according to their stellar mass, redshift, and colour distributions. We report younger underlying stellar ages and higher [OII] luminosities of active galaxies in the green valley and in the blue cloud compared to control samples. We observe higher fractions of green galaxies hosting AGN activity at progressively bluer (r-K) colours. Depending on the location of the host galaxy in the NUVrK colour diagram we find higher AGN fractions in massive blue galaxies and in the least massive red galaxies, in agreement with the picture that black holes vary their properties when hosted in either star-forming or passive galaxies. Exactly where the fast quenching processes are expected to play a role, we identify a novel class of active galaxies in the blue cloud with signatures typical for a suddenly suppression of their star formation activity after a burst happening in the recent past. Their optical spectra resemble those of post-starburst galaxies, that would never be identified in a spectroscopic search using classical selection techniques. Broadly, these active galaxies selected on the [NeV] line are not commonly represented in shallow X-ray, mid-IR, or classical line diagnostics. If we consider that our results are limited by the shallow observational limits and rapid AGN variability, the impact of AGN feedback on galaxy formation and evolution may represent an important channel of fast-transiting galaxies moving to the red sequence.
We study the origin of the non-thermal profiles observed in filamentary structures in galactic molecular clouds by means of numerical dynamical simulations. We find that such profiles are intrinsic features of the end products of dissipationless collapse in cylindrical symmetry. Moreover, for sufficiently cold initial conditions, we obtain end states characterized by markedly anticorrelated radial density and temperature profiles. Gravitational, dissipationless dynamics alone is thus sufficient to reproduce, at least qualitatively, many of the properties of the observed non-thermal structures.
The currents carried by the jets of active galactic nuclei (AGNs) can be probed using maps of the Faraday rotation measure (RM), since a jet current will be accompanied by a toroidal magnetic (B) field, which will give rise to a systematic change in the RM across the jet. The aim of this study is to identify new AGNs displaying statistically significant transverse RM gradients across their parsec-scale jets, and to look for overall patterns in the implied directions for the toroidal B-field components and jet currents. We have carried out new analyses of Faraday RM maps derived from previously published 8.1, 8.4, 12.1 and 15.3 GHz data obtained in 2006 on the NRAO VLBA. In a number of important ways, our procedures were identical to those of the original authors, but several other key aspects of the new imaging and analysis differ from the original methods. Our new analysis has substantially increased the number of AGNs known to display transverse RM gradients. The collected data on parsec and kiloparsec scales indicate that the current typically flows inward along the jet axis and outward in a more extended region surrounding the jet, typical to the current structure of a coaxial cable, accompanied by a self-consistent system of nested helical B fields, whose toroidal components give rise to the observed transverse RM gradients. These new results make it possible for the first time to conclusively demonstrate the existence of a preferred direction for the toroidal B-field components - and therefore of the currents - of AGN jets. Discerning the origin of this current-field system is of cardinal importance for understanding the physical mechanisms leading to the formation of the intrinsic jet B field, which likely plays an important role in the propagation and collimation of the jets; one possibility is the action of a "cosmic battery".
We present a new catalogue of cool supergiants in a section of the Perseus arm, most of which had not been previously identified. To generate it, we have used a set of well-defined photometric criteria to select a large number of candidates (637) that were later observed at intermediate resolution in the the Infrared Calcium Triplet spectral range, using a long-slit spectrograph. To separate red supergiants from luminous red giants, we used a statistical method, developed in previous works and improved in the present paper. We present a method to assign probabilities of being a red supergiant to a given spectrum and use the properties of a population to generate clean samples, without contamination from lower-luminosity stars. We compare our identification with a classification done using classical criteria and discuss their respective efficiencies and contaminations as identification methods. We confirm that our method is as efficient at finding supergiants as the best classical methods, but with a far lower contamination by red giants than any other method. The result is a catalogue with 197 cool supergiants, 191 of which did not appear in previous lists of red supergiants. This is the largest coherent catalogue of cool supergiants in the Galaxy.
We explore scenarios for the dynamical ejection of stars BN and x from source I in the Kleinmann-Low nebula of the Orion Nebula Cluster (ONC), which is important for being the closest region of massive star formation. This ejection would cause source I to become a close binary or a merger product of two stars. We thus consider binary-binary encounters as the mechanism to produce this event. By running a large suite of $N$-body simulations, we find that it is nearly impossible to match the observations when using the commonly adopted masses for the participants, especially a source I mass of $7\:{\rm{M}}_\odot$. The only way to recreate the event is if source I is more massive, i.e., $\sim20\:{\rm{M}}_\odot$. However, even in this case, the likelihood of reproducing the observed system is low. We discuss the implications of these results for understanding this important star-forming region.
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One unsettled problem in cosmology is that the baryon fractions identified as stars and cold gas in halos of galaxies and galaxy groups are lower than the universal fraction. The detection of the missing baryon component and the study of its properties are crucial for understanding how physical processes produce the galaxy population we observe. Numerical simulations show that part of the missing baryons are in a warm-hot circum-galactic medium (CGM). Such a gas component, predominantly ionized, can be investigated via its thermal and kinetic Sunyaev-Zel'dovich effects (tSZE and kSZE), the distortions of the Cosmic Microwave Background (CMB) spectrum by free electrons in thermal and bulk motions, respectively. Detection of kSZE has been reported recently at $2-4\sigma$ level based on the collective signals associated with large-scale structure traced by galaxies. However, it is difficult to explain the results in terms of baryons associated with galaxy systems of different masses, and so their implication for the missing baryon problem in halos is uncertain. Here we present the first measurement of kSZE as a function of mass of galaxy groups down to $\sim10^{12.3}{\rm M_\odot}$, from about 40,000 galaxy groups with known masses and peculiar velocities, using the Planck CMB maps. The gas fractions in galaxy groups are inferred to be comparable to the cosmic fraction, indicating that the missing baryons are found. Combined with tSZE measurements, our results imply that the CGM is warm-hot, with effective temperatures about $10^5$ - $10^6{\rm K}$.
One of the fundamental tasks of dynamical astronomy is to infer the distribution of mass in a stellar system from a snapshot of the positions and velocities of its stars. The usual approach to this task (e.g., Schwarzschild's method) involves fitting parametrized forms of the gravitational potential and the phase-space distribution to the data. We review the practical and conceptual difficulties with this approach and describe a novel statistical method for determining the mass distribution that does not require determining the phase-space distribution of the stars. We show that this new estimator out-performs other distribution-free estimators for the harmonic and Kepler potentials.
The abundances derived from planetary nebula emission show the presence of a metallicity gradient within the disk of the Milky Way up to Galactocentric distances of ~10 kpc, which are consistent with findings from studies of different types of sources, including H II regions and young B-type stars. The radial dependence of these abundances further from the Galactic centre is in dispute. We aim to derive the abundances of neon, sulphur and argon from a sample of planetary nebulae towards the Galactic anti-centre, which represent the abundances of the clouds from which they were formed, as they remain unchanged throughout the course of stellar evolution. We then aim to compare these values with similarly analysed data from elsewhere in the Milky Way in order to observe whether the abundance gradient continues in the outskirts of our Galaxy. We have observed 23 planetary nebulae at Galactocentric distances of 8-21 kpc with Spitzer IRS. The abundances were calculated from infrared emission lines, for which we observed the main ionisation states of neon, sulphur, and argon, which are little affected by extinction and uncertainties in temperature measurements or fluctuations within the planetary nebula. We have complemented these observations with others from optical studies in the literature, in order to reduce or avoid the need for ionisation correction factors in abundance calculations. The overall abundances of our sample of planetary nebulae in the Galactic anti-centre are lower than those in the solar neighbourhood. The abundances of neon, sulphur, and argon from these stars are consistent with a metallicity gradient from the solar neighbourhood up to Galactocentric distances of ~20 kpc, albeit with varying degrees of dispersion within the data.
The local Seyfert 2 galaxy NGC5135, thanks to its almost face-on appearance, a bulge overdensity of stars, the presence of a large-scale bar, an AGN and a Supernova Remnant, is an excellent target to investigate the dynamics of inflows, outflows, star formation and AGN feedback. Here we present a reconstruction of the gas morphology and kinematics in the inner regions of this galaxy, based on the analysis of Atacama Large Millimeter Array (ALMA) archival data. To our purpose, we combine the available $\sim$100 pc resolution ALMA 1.3 and 0.45 mm observations of dust continuum emission, the spectroscopic maps of two transitions of the CO molecule (tracer of molecular mass in star forming and nuclear regions), and of the CS molecule (tracer of the dense star forming regions) with the outcome of the SED decomposition. By applying the $^{\rm 3D}$BAROLO software (3D-Based Analysis of Rotating Object via Line Observations), we have been able to fit the galaxy rotation curves reconstructing a 3D tilted-ring model of the disk. Most of the observed emitting features are described by our kinematic model. We also attempt an interpretation for the emission in few regions that the axisymmetric model fails to reproduce. The most relevant of these is a region at the northern edge of the inner bar, where multiple velocity components overlap, as a possible consequence of the expansion of a super-bubble.
Using a large sample of emission line galaxies selected from the Sloan Digital Sky Survey, we investigate the kinematics of the neutral gas in the interstellar medium (ISM) based on the Na I$\lambda\lambda$5890,5896 (Na D) doublet absorption line. By removing the Na D contribution from stellar atmospheres, we isolate the line profile of the Na D excess, which represents the neutral gas in the ISM. The kinematics traced by the Na D excess show high velocity and velocity dispersion for a fraction of galaxies, indicating the presence of neutral gas outflows. We find that the kinematics measured from the Na D excess are similar between AGNs and star-forming galaxies. Moreover, by comparing the kinematics traced by the Na D excess and those by the [O III]$\lambda$5007 line taken from Woo et al. (2017), which traces ionized outflows driven by AGNs, we find no correlation between them. These results demonstrate that the neutral gas in the ISM traced by the Na D excess and the ionized gas traced by [O III] are kinematically independent, and AGN has no impact on the neutral gas outflows. In contrast to [O III], we find that the measured line-of-sight velocity shift and velocity dispersion of the Na D excess increase for more face-on galaxies due to the projection effect, supporting that Na D outflows are radially driven (i.e., perpendicular to the major axis of galaxies), presumably due to star formation.
A galaxy morphological type is correlated with the color indices, luminosity, de Vaucouleurs radius, inverse concentration index etc. To study these relations we have to operate with big samples of galaxies, so the visual morphological inspection is not always possible. We evaluated a new approach. Namely, we applied the "color--concentration index" diagram and machine learning methods for the morphological classification of galaxies from the SDSS at z<0.1. With this aim, we visually identified morphological T-types of about 1500 galaxies, which formed our training samples. Method 1. We plotted the diagrams of color indices g-i and one of such parameters as the inverse concentration index, absolute magnitude, de Vaucouleurs radius. We discovered that these parameters may be used for galaxy classification into three classes: E -- elliptical and lenticular, S -- types Sa-Scd, and L -- types Sd-Sdm and irregular s. The accuracy is 98% for E, 88% for S, and 57% for L types. The combinations of "color indices g-i and inverse concentration index R50/R90' and "color indices g-i and absolute magnitude M_r" give the best result. We applied this method to classify 317018 galaxies from SDSS DR5 (143263 E, 112 578 S, 61177 L types). Method 2. We used a training sample classified visually into two classes: early E (E, S0, S0a) and late L (Sa to Irr) types. We checked Naive Bayes, Random Forest, and Support Vector Classifier. We used absolute magnitudes, all the color indices and inverse concentration indexes as the attributes of galaxy. To define an accuracy of classifiers we applied the 5-folds validation and found that Random Forest provides the highest accuracy (91% of galaxies were correctly classified (96% for E and 80% for L types)). We tested it to classify 60561 galaxies from SDSS DR9 with a good accuracy onto two classes (47% E and 53% L types of galaxies).
Recently Hure et al. (2011) used a position-dynamical mass diagram to re-analyze position-velocity data from H2O maser disks associated with active galactic nuclei and claim that a maser disk with nearly perfect Keplerian rotation could have disk mass comparable to the black hole mass. This would imply that ignoring the effects of disk self-gravity can lead to large systematic errors in the measurement of black hole mass. We examine their methods and find that their large estimated disk masses are likely the result of bias in their data collection process and their use of projected instead of 3-dimensional position and velocity information. To place better constraints on the disk masses of Keplerian maser systems, we incorporate disk self-gravity into a 3-dimensional Bayesian modelling program for maser disks and also evaluate constraints based on the physical conditions for disks which support water maser emission. We find that there is little evidence that disk masses are dynamically important at the ~<1% level compared to the black holes.
[ABRIDGED] Context. O stars are excellent tracers of the intervening ISM because of their high luminosity, blue intrinsic SED, and relatively featureless spectra. We are currently conducting GOSSS, which is generating a large sample of O stars with accurate spectral types within several kpc of the Sun. Aims. To obtain a global picture of the properties of dust extinction in the solar neighborhood based on optical-NIR photometry of O stars with accurate spectral types. Methods. We have processed a photometric set with the CHORIZOS code to measure the amount and type of extinction towards 562 O-type stellar systems. We have tested three different families of extinction laws and analyzed our results with the help of additional archival data. Results. The Ma\'iz Apell\'aniz et al. (2014) family of extinction laws provides a better description of Galactic dust that either the Cardelli et al. (1989) or Fitzpatrick (1999) families, so it should be preferentially used. In many cases O stars and late-type stars experience similar amounts of extinction at similar distances but some O stars are located close to the molecular clouds left over from their births and have larger extinctions than the average for nearby late-type populations. In qualitative terms, O stars experience a more diverse extinction than late-type stars, as some are affected by the small-grain-size, low-R_5495 effect of molecular clouds and others by the large-grain-size, high-R_5495 effect of H II regions. Late-type stars experience a narrower range of grain sizes or R_5495, as their extinction is predominantly caused by the average, diffuse ISM. We propose that the reason for the existence of large-grain-size, high-R_5495 regions in the ISM in the form of H II regions and hot-gas bubbles is the selective destruction of small dust grains by EUV photons and possibly by thermal sputtering by atoms or ions.
We present a study of the relative orientation between the plane-of-the-sky magnetic field and the filamentary structures hosting the Planck Galactic Cold Clumps. In our analysis, the magnetic field angles are obtained from the sub-millimeter linear polarization measurements by the Planck satellite. We use an improved version of the Rolling Hough Transform method to detect the filamentary structures in the Planck data. We separate the polarization angles in the filaments and their background using the assumption of a linear contribution of both components to the observed Stokes Q and U parameters in optically thin media. After geometrically separating the clump and filament contributions to the signal, we observe a tendency for perpendicular alignment of the matter with the magnetic field in the clumps located in high-density environments. The filaments without the clump contribution exhibit mostly parallel alignment with the filament magnetic field orientation. We find that the filamentary structures embedded in dense environments do not show any particular preferential alignment whereas those embedded in low-density environments are mostly aligned with the background magnetic field orientation. However, the filamentary structures that are sufficiently denser than their surrounding exhibit a tendency to be perpendicular to the background magnetic field. We also find that in dense environments the magnetic fields in the background and in the filamentary structures are less likely to be aligned with each other.
We report serendipitous optical imaging of CVSO30c, an exoplanet candidate associated with the pre-main sequence T Tauri star CVSO30 resides in the 25 Ori stellar cluster. We perform PSF modeling on our seeing limited optical image to remove the lights from the host star (CVSO30), allowing us to extract photometry of CVSO30c to be g = 23.2+/-0.2 (statistic)+/-0.1 (systematic) and r = 21.5+/-0.1 (statistic)+/-0.1 (systematic) magnitudes, respectively. This is 170 and 80 times too bright in the g and r-band, respectively, if CVSO30c were an L0 substellar object as suggested by previous studies. The optical/infrared colors of CVSO 30c are indicative of a stellar, not substellar object, while the object's color-magnitude diagram position is strikingly inconsistent with expected values for a low mass member of 25 Ori. Broad-band photometry for CVSO30c is instead better fit by contaminants such as a background K3 giant or M subdwarf. Our study demonstrates that optical seeing limited data can help clarify the nature of candidate wide separation planet-mass companions in young star-forming regions.
Providing initial conditions is an essential procedure for numerical simulations of galaxies. The initial conditions for idealised individual galaxies in $N$-body simulations should resemble observed galaxies and be dynamically stable for time scales much longer than their characteristic dynamical times. However, generating a galaxy model ab initio as a system in dynamical equilibrium is a difficult task, since a galaxy contains several components, including a bulge, disc, and halo. Moreover, it is desirable that the initial-condition generator be fast and easy to use. We have now developed an initial-condition generator for galactic $N$-body simulations that satisfies these requirements. The developed generator adopts a distribution-function-based method, and it supports various kinds of density models, including custom-tabulated inputs and the presence of more than one disc. We tested the dynamical stability of systems generated by our code, representing early- and late-type galaxies, with $N=$~2,097,152 and 8,388,608 particles, respectively, and we found that the model galaxies maintain their initial distributions for at least 1~Gyr. The execution times required to generate the two models were $8.5$ and $221.7$ seconds, respectively, which is negligible compared to typical execution times for $N$-body simulations. The code is provided as open-source software and is publicly and freely available at \url{https://bitbucket.org/ymiki/magi}.
Glycolaldehyde (HOCH$_2$CHO) and ethylene glycol ((CH$_2$OH)$_2$) are two complex organic molecules detected in the hot cores and hot corinos of several star-forming regions. The ethylene glycol/glycolaldehyde abundance ratio seems to show an increase with the source luminosity. In the literature, several surface-chemistry formation mechanisms have been proposed for these two species. With the UCLCHEM chemical code, we explored the different scenarios and compared the predictions for a range of sources of different luminosities with the observations. None of the scenarios reproduce perfectly the trend. A better agreement is, however, found for a formation through recombination of two HCO radicals followed by successive hydrogenations. The reaction between HCO and CH$_2$OH could also contribute to the formation of glycolaldehyde in addition to the hydrogenation pathway. The predictions are improved when a trend of decreasing H$_2$ density within the core region with T $\geq$ 100 K as a function of luminosity, is included in the model. Destruction reactions of complex organic molecules in the gas phase would also need to be investigated, since they can affect the abundance ratios once the species have desorbed in the warm inner regions of the star-forming regions.
Eclipsing binaries are instrumental to our understanding of fundamental stellar parameters. With the arrival of ultra-wide cameras and large area photometric monitoring programs, numerous eclipsing binaries systems have been reported photometrically. However, due to the expensive efforts to follow up them spectroscopically, most of their basic properties remain unexplored. In this paper we exploited the eclipsing binary light curves delivered by the all-sky Catalina sky surveys, in tandem with the single shot spectroscopic survey from SDSS, and identify a double-lined M-dwarf eclipsing binary SDSSJ1156-0207. Because this system is very faint (V=15.89 mag), we obtained follow-up radial velocity measurements using Gemini Multi-Object Spectrograph onboard Gemini north telescope. This provides us a spectral resolution R~4000, enabling us to determine the mass and radius of each stellar components when jointly fitted with light curve. Our best-fit results indicate that both components are of M dwarf, with the primary component to be 0.54+/-0.20 M_sun and 0.46+/-0.08 R_sun, while the secondary component to be 0.19+/-0.08 M_sun and 0.30+/-0.08 R_sun. High resolution spectroscopic observations in the future will help pin down the stellar parameters, providing insights to the stellar models at low mass regimes, as well as shedding lights on the internal structure of close-in low mass objects and their inflation mechanism.
Independent tests aiming to constrain the value of the cosmological constant $\Lambda$ are usually difficult because of its extreme smallness $\left(\Lambda \simeq 1\times 10^{-52}~\textrm{m}^{-2}\right)$. Bounds on it from Solar System orbital motions determined with spacecraft tracking are currently at the $\simeq 10^{-43}-10^{-44}~\textrm{m}^{-2}$ level, but they may turn out to be somewhat optimistic since $\Lambda$ has not yet been explicitly modeled in the planetary data reductions. Accurate $\left(\sigma_{\tau_\textrm{p}}\simeq 1-10~\mu\textrm{s}\right)$ timing of expected pulsars orbiting the Black Hole at the Galactic Center, preferably along highly eccentric and wide orbits, might, at least in principle, improve the planetary constraints by several orders of magnitude. By assuming for such a hypothetical pulsar the orbit of, say, the very far star S85, characterized by an eccentricity as large as $e = 0.78$ and an orbital period as long as $P_\textrm{b}=3580\pm 2550~\textrm{yr}$, the cosmological constant would induce an instantaneous timing orbital shift $\Delta\delta\tau^\Lambda_\textrm{p}\left(E\right)$ as large as just $\simeq 1-10~\mu\textrm{s}$ for some given values of its eccentric anomaly $E$ at different epochs. By looking at the average time shift per orbit $\overline{\Delta\delta\tau}^\Lambda_\textrm{p}$ of closer pulsars, a S2-like orbital configuration with $e=0.8839,~P_\textrm{b}=16~\textrm{yr}$ would allow to obtain an upper bound as little as $\left|\Lambda\right|\lesssim 9\times 10^{-47}~\textrm{m}^{-2}$. Our results can be easily extended to modified models of gravity using $\Lambda-$type parameters.
This paper describes the second data release (DR2) of the Beijing-Arizona Sky Survey (BASS). DR2 includes the observations as of July 2017 taken by both BASS and Mayall $z$-band Legacy Survey (MzLS). BASS and MzLS respectively completed about 72% and 76% of their observations. Both surveys will be served for spectroscopic targeting of the upcoming Dark Energy Spectroscopic Instrument. This is our first time to include the MzLS data. Both BASS and MzLS data are reduced by the same pipeline. We have updated the basic data reduction and photometric methods in DR2. Especially source detections are performed on stacked images and photometric measurements are co-added from single-epoch images based on these sources. The 5$\sigma$ depths with complete three exposures and corrections of the Galactic extinction are 23.9, 23.6, and 23.2 mag for $g$, $r$, and $z$ bands, respectively. The BASS website (this http URL) provides links to data download and detailed information.
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One unsettled problem in cosmology is that the baryon fractions identified as stars and cold gas in halos of galaxies and galaxy groups are lower than the universal fraction. The detection of the missing baryon component and the study of its properties are crucial for understanding how physical processes produce the galaxy population we observe. Numerical simulations show that part of the missing baryons are in a warm-hot circum-galactic medium (CGM). Such a gas component, predominantly ionized, can be investigated via its thermal and kinetic Sunyaev-Zel'dovich effects (tSZE and kSZE), the distortions of the Cosmic Microwave Background (CMB) spectrum by free electrons in thermal and bulk motions, respectively. Detection of kSZE has been reported recently at $2-4\sigma$ level based on the collective signals associated with large-scale structure traced by galaxies. However, it is difficult to explain the results in terms of baryons associated with galaxy systems of different masses, and so their implication for the missing baryon problem in halos is uncertain. Here we present the first measurement of kSZE as a function of mass of galaxy groups down to $\sim10^{12.3}{\rm M_\odot}$, from about 40,000 galaxy groups with known masses and peculiar velocities, using the Planck CMB maps. The gas fractions in galaxy groups are inferred to be comparable to the cosmic fraction, indicating that the missing baryons are found. Combined with tSZE measurements, our results imply that the CGM is warm-hot, with effective temperatures about $10^5$ - $10^6{\rm K}$.
One of the fundamental tasks of dynamical astronomy is to infer the distribution of mass in a stellar system from a snapshot of the positions and velocities of its stars. The usual approach to this task (e.g., Schwarzschild's method) involves fitting parametrized forms of the gravitational potential and the phase-space distribution to the data. We review the practical and conceptual difficulties with this approach and describe a novel statistical method for determining the mass distribution that does not require determining the phase-space distribution of the stars. We show that this new estimator out-performs other distribution-free estimators for the harmonic and Kepler potentials.
The abundances derived from planetary nebula emission show the presence of a metallicity gradient within the disk of the Milky Way up to Galactocentric distances of ~10 kpc, which are consistent with findings from studies of different types of sources, including H II regions and young B-type stars. The radial dependence of these abundances further from the Galactic centre is in dispute. We aim to derive the abundances of neon, sulphur and argon from a sample of planetary nebulae towards the Galactic anti-centre, which represent the abundances of the clouds from which they were formed, as they remain unchanged throughout the course of stellar evolution. We then aim to compare these values with similarly analysed data from elsewhere in the Milky Way in order to observe whether the abundance gradient continues in the outskirts of our Galaxy. We have observed 23 planetary nebulae at Galactocentric distances of 8-21 kpc with Spitzer IRS. The abundances were calculated from infrared emission lines, for which we observed the main ionisation states of neon, sulphur, and argon, which are little affected by extinction and uncertainties in temperature measurements or fluctuations within the planetary nebula. We have complemented these observations with others from optical studies in the literature, in order to reduce or avoid the need for ionisation correction factors in abundance calculations. The overall abundances of our sample of planetary nebulae in the Galactic anti-centre are lower than those in the solar neighbourhood. The abundances of neon, sulphur, and argon from these stars are consistent with a metallicity gradient from the solar neighbourhood up to Galactocentric distances of ~20 kpc, albeit with varying degrees of dispersion within the data.
The local Seyfert 2 galaxy NGC5135, thanks to its almost face-on appearance, a bulge overdensity of stars, the presence of a large-scale bar, an AGN and a Supernova Remnant, is an excellent target to investigate the dynamics of inflows, outflows, star formation and AGN feedback. Here we present a reconstruction of the gas morphology and kinematics in the inner regions of this galaxy, based on the analysis of Atacama Large Millimeter Array (ALMA) archival data. To our purpose, we combine the available $\sim$100 pc resolution ALMA 1.3 and 0.45 mm observations of dust continuum emission, the spectroscopic maps of two transitions of the CO molecule (tracer of molecular mass in star forming and nuclear regions), and of the CS molecule (tracer of the dense star forming regions) with the outcome of the SED decomposition. By applying the $^{\rm 3D}$BAROLO software (3D-Based Analysis of Rotating Object via Line Observations), we have been able to fit the galaxy rotation curves reconstructing a 3D tilted-ring model of the disk. Most of the observed emitting features are described by our kinematic model. We also attempt an interpretation for the emission in few regions that the axisymmetric model fails to reproduce. The most relevant of these is a region at the northern edge of the inner bar, where multiple velocity components overlap, as a possible consequence of the expansion of a super-bubble.
Using a large sample of emission line galaxies selected from the Sloan Digital Sky Survey, we investigate the kinematics of the neutral gas in the interstellar medium (ISM) based on the Na I$\lambda\lambda$5890,5896 (Na D) doublet absorption line. By removing the Na D contribution from stellar atmospheres, we isolate the line profile of the Na D excess, which represents the neutral gas in the ISM. The kinematics traced by the Na D excess show high velocity and velocity dispersion for a fraction of galaxies, indicating the presence of neutral gas outflows. We find that the kinematics measured from the Na D excess are similar between AGNs and star-forming galaxies. Moreover, by comparing the kinematics traced by the Na D excess and those by the [O III]$\lambda$5007 line taken from Woo et al. (2017), which traces ionized outflows driven by AGNs, we find no correlation between them. These results demonstrate that the neutral gas in the ISM traced by the Na D excess and the ionized gas traced by [O III] are kinematically independent, and AGN has no impact on the neutral gas outflows. In contrast to [O III], we find that the measured line-of-sight velocity shift and velocity dispersion of the Na D excess increase for more face-on galaxies due to the projection effect, supporting that Na D outflows are radially driven (i.e., perpendicular to the major axis of galaxies), presumably due to star formation.
A galaxy morphological type is correlated with the color indices, luminosity, de Vaucouleurs radius, inverse concentration index etc. To study these relations we have to operate with big samples of galaxies, so the visual morphological inspection is not always possible. We evaluated a new approach. Namely, we applied the "color--concentration index" diagram and machine learning methods for the morphological classification of galaxies from the SDSS at z<0.1. With this aim, we visually identified morphological T-types of about 1500 galaxies, which formed our training samples. Method 1. We plotted the diagrams of color indices g-i and one of such parameters as the inverse concentration index, absolute magnitude, de Vaucouleurs radius. We discovered that these parameters may be used for galaxy classification into three classes: E -- elliptical and lenticular, S -- types Sa-Scd, and L -- types Sd-Sdm and irregular s. The accuracy is 98% for E, 88% for S, and 57% for L types. The combinations of "color indices g-i and inverse concentration index R50/R90' and "color indices g-i and absolute magnitude M_r" give the best result. We applied this method to classify 317018 galaxies from SDSS DR5 (143263 E, 112 578 S, 61177 L types). Method 2. We used a training sample classified visually into two classes: early E (E, S0, S0a) and late L (Sa to Irr) types. We checked Naive Bayes, Random Forest, and Support Vector Classifier. We used absolute magnitudes, all the color indices and inverse concentration indexes as the attributes of galaxy. To define an accuracy of classifiers we applied the 5-folds validation and found that Random Forest provides the highest accuracy (91% of galaxies were correctly classified (96% for E and 80% for L types)). We tested it to classify 60561 galaxies from SDSS DR9 with a good accuracy onto two classes (47% E and 53% L types of galaxies).
Recently Hure et al. (2011) used a position-dynamical mass diagram to re-analyze position-velocity data from H2O maser disks associated with active galactic nuclei and claim that a maser disk with nearly perfect Keplerian rotation could have disk mass comparable to the black hole mass. This would imply that ignoring the effects of disk self-gravity can lead to large systematic errors in the measurement of black hole mass. We examine their methods and find that their large estimated disk masses are likely the result of bias in their data collection process and their use of projected instead of 3-dimensional position and velocity information. To place better constraints on the disk masses of Keplerian maser systems, we incorporate disk self-gravity into a 3-dimensional Bayesian modelling program for maser disks and also evaluate constraints based on the physical conditions for disks which support water maser emission. We find that there is little evidence that disk masses are dynamically important at the ~<1% level compared to the black holes.
[ABRIDGED] Context. O stars are excellent tracers of the intervening ISM because of their high luminosity, blue intrinsic SED, and relatively featureless spectra. We are currently conducting GOSSS, which is generating a large sample of O stars with accurate spectral types within several kpc of the Sun. Aims. To obtain a global picture of the properties of dust extinction in the solar neighborhood based on optical-NIR photometry of O stars with accurate spectral types. Methods. We have processed a photometric set with the CHORIZOS code to measure the amount and type of extinction towards 562 O-type stellar systems. We have tested three different families of extinction laws and analyzed our results with the help of additional archival data. Results. The Ma\'iz Apell\'aniz et al. (2014) family of extinction laws provides a better description of Galactic dust that either the Cardelli et al. (1989) or Fitzpatrick (1999) families, so it should be preferentially used. In many cases O stars and late-type stars experience similar amounts of extinction at similar distances but some O stars are located close to the molecular clouds left over from their births and have larger extinctions than the average for nearby late-type populations. In qualitative terms, O stars experience a more diverse extinction than late-type stars, as some are affected by the small-grain-size, low-R_5495 effect of molecular clouds and others by the large-grain-size, high-R_5495 effect of H II regions. Late-type stars experience a narrower range of grain sizes or R_5495, as their extinction is predominantly caused by the average, diffuse ISM. We propose that the reason for the existence of large-grain-size, high-R_5495 regions in the ISM in the form of H II regions and hot-gas bubbles is the selective destruction of small dust grains by EUV photons and possibly by thermal sputtering by atoms or ions.
We present a study of the relative orientation between the plane-of-the-sky magnetic field and the filamentary structures hosting the Planck Galactic Cold Clumps. In our analysis, the magnetic field angles are obtained from the sub-millimeter linear polarization measurements by the Planck satellite. We use an improved version of the Rolling Hough Transform method to detect the filamentary structures in the Planck data. We separate the polarization angles in the filaments and their background using the assumption of a linear contribution of both components to the observed Stokes Q and U parameters in optically thin media. After geometrically separating the clump and filament contributions to the signal, we observe a tendency for perpendicular alignment of the matter with the magnetic field in the clumps located in high-density environments. The filaments without the clump contribution exhibit mostly parallel alignment with the filament magnetic field orientation. We find that the filamentary structures embedded in dense environments do not show any particular preferential alignment whereas those embedded in low-density environments are mostly aligned with the background magnetic field orientation. However, the filamentary structures that are sufficiently denser than their surrounding exhibit a tendency to be perpendicular to the background magnetic field. We also find that in dense environments the magnetic fields in the background and in the filamentary structures are less likely to be aligned with each other.
We report serendipitous optical imaging of CVSO30c, an exoplanet candidate associated with the pre-main sequence T Tauri star CVSO30 resides in the 25 Ori stellar cluster. We perform PSF modeling on our seeing limited optical image to remove the lights from the host star (CVSO30), allowing us to extract photometry of CVSO30c to be g = 23.2+/-0.2 (statistic)+/-0.1 (systematic) and r = 21.5+/-0.1 (statistic)+/-0.1 (systematic) magnitudes, respectively. This is 170 and 80 times too bright in the g and r-band, respectively, if CVSO30c were an L0 substellar object as suggested by previous studies. The optical/infrared colors of CVSO 30c are indicative of a stellar, not substellar object, while the object's color-magnitude diagram position is strikingly inconsistent with expected values for a low mass member of 25 Ori. Broad-band photometry for CVSO30c is instead better fit by contaminants such as a background K3 giant or M subdwarf. Our study demonstrates that optical seeing limited data can help clarify the nature of candidate wide separation planet-mass companions in young star-forming regions.
Providing initial conditions is an essential procedure for numerical simulations of galaxies. The initial conditions for idealised individual galaxies in $N$-body simulations should resemble observed galaxies and be dynamically stable for time scales much longer than their characteristic dynamical times. However, generating a galaxy model ab initio as a system in dynamical equilibrium is a difficult task, since a galaxy contains several components, including a bulge, disc, and halo. Moreover, it is desirable that the initial-condition generator be fast and easy to use. We have now developed an initial-condition generator for galactic $N$-body simulations that satisfies these requirements. The developed generator adopts a distribution-function-based method, and it supports various kinds of density models, including custom-tabulated inputs and the presence of more than one disc. We tested the dynamical stability of systems generated by our code, representing early- and late-type galaxies, with $N=$~2,097,152 and 8,388,608 particles, respectively, and we found that the model galaxies maintain their initial distributions for at least 1~Gyr. The execution times required to generate the two models were $8.5$ and $221.7$ seconds, respectively, which is negligible compared to typical execution times for $N$-body simulations. The code is provided as open-source software and is publicly and freely available at \url{https://bitbucket.org/ymiki/magi}.
Glycolaldehyde (HOCH$_2$CHO) and ethylene glycol ((CH$_2$OH)$_2$) are two complex organic molecules detected in the hot cores and hot corinos of several star-forming regions. The ethylene glycol/glycolaldehyde abundance ratio seems to show an increase with the source luminosity. In the literature, several surface-chemistry formation mechanisms have been proposed for these two species. With the UCLCHEM chemical code, we explored the different scenarios and compared the predictions for a range of sources of different luminosities with the observations. None of the scenarios reproduce perfectly the trend. A better agreement is, however, found for a formation through recombination of two HCO radicals followed by successive hydrogenations. The reaction between HCO and CH$_2$OH could also contribute to the formation of glycolaldehyde in addition to the hydrogenation pathway. The predictions are improved when a trend of decreasing H$_2$ density within the core region with T $\geq$ 100 K as a function of luminosity, is included in the model. Destruction reactions of complex organic molecules in the gas phase would also need to be investigated, since they can affect the abundance ratios once the species have desorbed in the warm inner regions of the star-forming regions.
Eclipsing binaries are instrumental to our understanding of fundamental stellar parameters. With the arrival of ultra-wide cameras and large area photometric monitoring programs, numerous eclipsing binaries systems have been reported photometrically. However, due to the expensive efforts to follow up them spectroscopically, most of their basic properties remain unexplored. In this paper we exploited the eclipsing binary light curves delivered by the all-sky Catalina sky surveys, in tandem with the single shot spectroscopic survey from SDSS, and identify a double-lined M-dwarf eclipsing binary SDSSJ1156-0207. Because this system is very faint (V=15.89 mag), we obtained follow-up radial velocity measurements using Gemini Multi-Object Spectrograph onboard Gemini north telescope. This provides us a spectral resolution R~4000, enabling us to determine the mass and radius of each stellar components when jointly fitted with light curve. Our best-fit results indicate that both components are of M dwarf, with the primary component to be 0.54+/-0.20 M_sun and 0.46+/-0.08 R_sun, while the secondary component to be 0.19+/-0.08 M_sun and 0.30+/-0.08 R_sun. High resolution spectroscopic observations in the future will help pin down the stellar parameters, providing insights to the stellar models at low mass regimes, as well as shedding lights on the internal structure of close-in low mass objects and their inflation mechanism.
Independent tests aiming to constrain the value of the cosmological constant $\Lambda$ are usually difficult because of its extreme smallness $\left(\Lambda \simeq 1\times 10^{-52}~\textrm{m}^{-2}\right)$. Bounds on it from Solar System orbital motions determined with spacecraft tracking are currently at the $\simeq 10^{-43}-10^{-44}~\textrm{m}^{-2}$ level, but they may turn out to be somewhat optimistic since $\Lambda$ has not yet been explicitly modeled in the planetary data reductions. Accurate $\left(\sigma_{\tau_\textrm{p}}\simeq 1-10~\mu\textrm{s}\right)$ timing of expected pulsars orbiting the Black Hole at the Galactic Center, preferably along highly eccentric and wide orbits, might, at least in principle, improve the planetary constraints by several orders of magnitude. By assuming for such a hypothetical pulsar the orbit of, say, the very far star S85, characterized by an eccentricity as large as $e = 0.78$ and an orbital period as long as $P_\textrm{b}=3580\pm 2550~\textrm{yr}$, the cosmological constant would induce an instantaneous timing orbital shift $\Delta\delta\tau^\Lambda_\textrm{p}\left(E\right)$ as large as just $\simeq 1-10~\mu\textrm{s}$ for some given values of its eccentric anomaly $E$ at different epochs. By looking at the average time shift per orbit $\overline{\Delta\delta\tau}^\Lambda_\textrm{p}$ of closer pulsars, a S2-like orbital configuration with $e=0.8839,~P_\textrm{b}=16~\textrm{yr}$ would allow to obtain an upper bound as little as $\left|\Lambda\right|\lesssim 9\times 10^{-47}~\textrm{m}^{-2}$. Our results can be easily extended to modified models of gravity using $\Lambda-$type parameters.
This paper describes the second data release (DR2) of the Beijing-Arizona Sky Survey (BASS). DR2 includes the observations as of July 2017 taken by both BASS and Mayall $z$-band Legacy Survey (MzLS). BASS and MzLS respectively completed about 72% and 76% of their observations. Both surveys will be served for spectroscopic targeting of the upcoming Dark Energy Spectroscopic Instrument. This is our first time to include the MzLS data. Both BASS and MzLS data are reduced by the same pipeline. We have updated the basic data reduction and photometric methods in DR2. Especially source detections are performed on stacked images and photometric measurements are co-added from single-epoch images based on these sources. The 5$\sigma$ depths with complete three exposures and corrections of the Galactic extinction are 23.9, 23.6, and 23.2 mag for $g$, $r$, and $z$ bands, respectively. The BASS website (this http URL) provides links to data download and detailed information.
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We present a multi-wavelength analysis of a $\sim$30$' \times$30$'$ area around the Sh 2-53 region (hereafter S53 complex), which is associated with at least three H II regions, two mid-infrared bubbles (N21 and N22), and infrared dark clouds. The $^{13}$CO line data trace the molecular content of the S53 complex in a velocity range of 36--60 km s$^{-1}$, and show the presence of at least three molecular components within the selected area along this direction. Using the observed radio continuum flux of the H II regions, the derived spectral types of the ionizing sources agree well with the previously reported results. The S53 complex harbors clusters of young stellar objects (YSOs) that are identified using the photometric 2--24 $\mu$m magnitudes. It also hosts several massive condensations (3000-30000 $M_\odot$) which are traced in the {\em Herschel} column density map. The complex is found at the junction of at least five molecular filaments, and the flow of gas toward the junction is evident in the velocity space of the $^{13}$CO data. Together, the S53 complex is embedded in a very similar "hub-filament" system to those reported in Myers, and the active star formation is evident towards the central "hub" inferred by the presence of the clustering of YSOs.
Multi-color photometry is presented for a sample of 60 dwarf ellipticals (dE) selected by morphology. The sample uses data from GALEX, SDSS and WISE to investigate the colors in filters NUV, ugri and W1 (3.4mum). We confirm the blueward shift in the color-magnitude relation for dwarf ellipticals, compared to CMR for bright ellipticals, as seen in previous studies. However, we find the deviation in color across the UV to near-IR for dE's is a strong signal of a younger age for dwarf ellipticals, one that indicates decreasing mean age with lower stellar mass. Lower mass dE's are found to have mean ages of 4 Gyrs and mean [Fe/H] values of -1.2. Age and metallicity increase to the most massive dE's with mean ages similar to normal ellipticals (12 Gyrs) and their lowest metallicities ([Fe/H] = -0.3). Deduced initial star formation rates for dE's, combined with their current metallicities and central stellar densities, suggests a connection between field LSB dwarfs and cluster dE's, where the cluster environment halts star formation for dE's triggering a separate evolutionary path.
Obtaining large samples of galaxy clusters is important for cosmology, since cluster counts as a function of redshift and mass can constrain the parameters of our Universe. They are also useful to understand the formation and evolution of clusters. We develop an improved version of the AMACFI cluster finder (now AMASCFI) and apply it to the 154 deg2 of the Canada France Hawaii Telescope Legacy Survey (CFHTLS) to obtain a catalogue of 1371 cluster candidates with mass M200 > 10^14 Msun and redshift z < 0.7. We derive the selection function of AMASCFI from the Millennium simulation, and cluster masses from a richness-mass scaling relation built from matching our candidates with X-ray detections. We study the evolution of these clusters with mass and redshift by computing the i'-band galaxy luminosity functions (GLFs) for the early- (ETGs) and late-type galaxies (LTGs). This sample is 90% pure and 70% complete, therefore our results are representative the cluster population in these redshift and mass ranges. We find an increase of both the ETG and LTG faint populations with decreasing redshift (with Schechter slopes alpha_ETG = -0.65 +/- 0.03 at z=0.6 and alpha_ETG = -0.79 +\- 0.02 at z=0.2) and also a decrease of the LTG bright end, but not of the ETG's. Our large sample allows us to break the degeneracy between mass and redshift, finding that the redshift evolution is more pronounced in high-mass clusters, but that there is no significant dependence of the faint end on mass for a given redshift. These results show that the cluster red sequence is mainly formed at redshift z > 0.7, and that faint ETGs continue to enrich the red sequence through quenching of brighter LTGs at z < 0.7. The efficiency of this quenching is higher in large-mass clusters while the accretion rate of faint LTGs is lower as the more massive clusters have already emptied most of their environment at higher redshifts.
The number of star clusters that populate the Large Magellanic Cloud (LMC) at deprojected distances < 4 deg has been recently found to be nearly double the known size of the system. Because of the unprecedented consequences of this outcome in our knowledge of the LMC cluster formation and dissolution histories, we closely revisited such a compilation of objects and found that only ~ 35 per cent of the previously known catalogued clusters has been included. The remaining entries are likely related to stellar overdensities of the LMC composite star field, because there is a remarkable enhancement of objects with assigned ages older than log(t yr-1) ~ 9.4, which contrasts with the existence of the LMC cluster age gap; the assumption of a cluster formation rate similar to that of the LMC star field does not help to conciliate so large amount of clusters either; and nearly 50 per cent of them come from cluster search procedures known to produce more than 90 per cent of false detections. The lack of further analyses to confirm the physical reality as genuine star clusters of the identified overdensities also glooms those results. We support that the actual size of the LMC main body cluster population is close to that previously known.
Determining molecular abundance ratios is important not only for the study of the Galactic chemistry but also because they are useful to estimate physical parameters in a large variety of interstellar medium environments. The CO is one of the most important molecules to trace the molecular gas in the interstellar medium, and the 13CO/C18O abundance ratio is usually used to estimate molecular masses and densities of regions with moderate to high densities. Nowadays this kind of isotopes ratios are in general indirectly derived from elemental abundances ratios. We present the first 13CO/C18O abundance ratio study performed from CO isotopes observations towards a large sample of Galactic sources of different nature at different locations. To study the 13CO/C18O abundance ratio it was used 12CO J=3-2 data obtained form the CO High-Resolution Survey, 13CO and C18O J=3-2 data from the 13CO/C18O (J=3-2) Heterodyne Inner Milky Way Plane Survey, and some complementary data extracted from the James Clerk Maxwell Telescope database. It was analyzed a sample of 198 sources composed by young stellar objects (YSOs), HII and diffuse HII regions as catalogued in the Red MSX Source Survey in 27.5 < l < 46.5 and |b| < 0.5. Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5 kpc. We found that YSOs have, in average, smaller 13CO/C18O abundance ratios than HII and diffuse HII regions. Taking into account that the gas associated with YSOs should be less affected by the radiation than in the case of the others sources, selective far-UV photodissociation of C18O is confirmed. The 13CO/C18O abundance ratios obtained in this work are systematically lower than the predicted from the known elemental abundance relations. These results would be useful in future studies of molecular gas related to YSOs and HII regions based on the observation of these isotopes.
The characterization of our Galaxy's longest filamentary gas features has been the subject of several studies in recent years, producing not only a sizeable sample of large-scale filaments, but also confusion as to whether all these features (e.g. "Bones", "Giant Molecular Filaments") are essentially the same. They are not. We undertake the first standardized analysis of the physical properties (densities, temperatures, morphologies, radial profiles) and kinematics of large-scale filaments in the literature. We expand and improve upon prior analyses by using the same data sets, techniques, and spiral arm models to disentangle the filaments' inherent properties from selection criteria and methodology. Our results suggest that the myriad filament finding techniques are uncovering different physical structures, with length (11-269 pc), width (1-40 pc), mass ($\rm 3\times10^3 \; M_\odot - 1.1 \times10^{6} \; M_\odot$), aspect ratio (3:1 - 117:1), and dense gas fraction (0.2-100%) varying by at least an order of magnitude across the sample of 45 filaments. As part of this analysis, we develop a radial profile fitting code, $RadFil$, which is publicly available. We also perform a $position-position-velocity$ $(p-p-v)$ analysis on a subset of the filaments and find that while 60%-70% lie in the plane of the Galaxy, only 30-45% also exhibit kinematic proximity to purported spiral arms. In a parameter space defined by aspect ratio, temperature, and density, we broadly distinguish three filament categories, which could be indicative of different formation mechanisms or histories. Highly elongated "Bone-like" filaments show the most potential for tracing gross spiral structure (e.g. arms), while other categories could simply be large concentrations of molecular gas (GMCs, core complexes).
We propose a modified version of the observed non-linear relation between the X-ray (2 keV) and the ultraviolet (2500 \AA) emission in quasars (i.e. $L_{\rm X}\propto L_{\rm UV}^{\gamma}$) which involves the full width at half-maximum, FWHM, of the broad emission line, i.e. $L_{\rm X}\propto L_{\rm UV}^{\hat\gamma}~FWHM^{\hat\beta}$. By analysing a sample of 550 optically selected non-jetted quasars in the redshift range of 0.36-2.23 from the Sloan Digital Sky Survey cross matched with the XMM-Newton catalogue 3XMM-DR6, we found that the additional dependence of the observed $L_{\rm X}-L_{\rm UV}$ correlation on the FWHM of the MgII broad emission line is statistically significant. Our statistical analysis leads to a much tighter relation with respect to the one neglecting FWHM, and it does not evolve with redshift. We interpret this new relation within an accretion disc corona scenario where reconnection and magnetic loops above the accretion disc can account for the production of the primary X-ray radiation. For a broad line region size depending on the disc luminosity as $R_{\rm blr}\propto L_{\rm disc}^{0.5}$, we find that $L_{\rm X}\propto L_{\rm UV}^{4/7} ~FWHM^{4/7}$, which is in very good agreement with the observed correlation.
The most common observed feature of the X-ray outflows in active galactic nuclei (AGN) is their broad ionization distribution spanning up to $\sim$ 5 orders of magnitude in ionization levels. This feature is quantified in terms of absorption measure distribution (AMD), defined as the distribution of column density with the ionization parameter. Recently, the photoionization models with constant pressure assumption are shown to well reproduce the observed shape of AMD. However, there exist inconsistencies in the normalization and the position of discontinuities presented in the AMD shape between the observation and model. In this work, we show that AMD normalization differs by one order of magnitude depending on the shape of ionizing spectral energy distribution (SED).
We study the moderate-to-high radiative luminosity active galactic nuclei (HLAGN) within the VLA-COSMOS 3 GHz Large Project. The survey covers 2.6 square degrees centered on the COSMOS field with a 1$\sigma$ sensitivity of 2.3 $\mathrm{\mu Jy}$/beam across the field. This provides the simultaneously largest and deepest radio continuum survey available to date with exquisite multi-wavelength coverage. The survey yields 10,830 radio sources with signal-to-noise ratios $\geq$5. A subsample of 1,604 HLAGN is analyzed here. These were selected via a combination of X-ray luminosity and mid-infrared colors. We derive luminosity functions for these AGN and constrain their cosmic evolution out to a redshift of $z\sim6$, for the first time decomposing the star formation and AGN contributions to the radio continuum emission in the AGN. We study the evolution of number density and luminosity density finding a peak at $z\sim1.5$ followed by a decrease out to a redshift $z\sim6$.
We present the first results of a new spectroscopic survey of the cluster Abell 85 targeting 1466 candidate cluster members within the central $\sim$1 deg$^2$ of the cluster and having magnitudes $m_r < 20.5$ using VIMOS/VLT and HYDRA/WIYN. A total of 520 galaxies are confirmed as either relaxed cluster members or part of an infalling population. A significant fraction are low mass; the median stellar mass of the sample is $10^{9.6} M_{\odot} $, and 25% have stellar masses below $10^9 M_{\odot}$ (i.e. 133 dwarf galaxies). We also identify seven active galactic nuclei (AGN), four of which reside in dwarf host galaxies. We probe the evolution of star formation rates, based on H$\alpha$ emission and continuum modeling, as a function of both mass and environment. We find that more star forming galaxies are observed at larger clustercentric distances, while infalling galaxies show evidence for recently enhanced star forming activity. Main sequence galaxies, defined by their continuum star formation rates, show different evolutionary behavior based on their mass. At the low mass end, the galaxies have had their star formation recently quenched, while more massive galaxies show no significant change. The timescales probed here favor fast quenching mechanisms, such as ram-pressure stripping. Galaxies within the green valley, defined similarly, do not show evidence of quenching. Instead, the low mass galaxies maintain their levels of star forming activity, while the more massive galaxies have experienced a recent burst.
We make the first data release (DR1) of the ongoing ESO Public Survey SAMPLING (this http URL). DR1 comprises of 124 fields distributed in $70^\circ < l < 216^\circ$, $-35^\circ < b < 25^\circ$. The 12CO and 13CO (2-1) cubes are gridded in $8"$ pixels, with an effective resolution of $36"$. The channel width is 0.33\kms\ and the RMS noise is $T_{\rm mb}<0.2$ K. Once completed, SAMPLING and complementary surveys will initiate the first major step forward to characterize molecular clouds and star formation on truly Galactic scales.
Using the Wald formalism, we investigate the thermodynamics of charged black holes in the Einstein-\ae ther-Maxwell theory, considering both universal and Killing horizons. In particular, by aid of a scaling symmetry of the action, we obtain the Smarr integral formula. Assuming the canonical form, $M = 2TS + Q\Phi$, we find that the entropy in general takes a very complicated form, and is a function of various parameters. Only in very particular cases, it is given by one fourth of the area of the horizon.
Searches for the prebiotically-relevant cyanamide (NH$_2$CN) towards solar-type protostars have not been reported in the literature. We here present the first detection of this species in the warm gas surrounding two solar-type protostars, using data from the Atacama Large Millimeter/Submillimeter Array Protostellar Interferometric Line Survey (PILS) of IRAS 16293-2422 B and observations from the IRAM Plateau de Bure Interferometer of NGC1333 IRAS2A. We furthermore detect the deuterated and $^{13}$C isotopologues of NH$_2$CN towards IRAS 16293-2422 B. This is the first detection of NHDCN in the interstellar medium. Based on a local thermodynamic equilibrium analysis, we find that the deuteration of cyanamide ($\sim$ 1.7%) is similar to that of formamide (NH$_2$CHO), which may suggest that these two molecules share NH$_2$ as a common precursor. The NH$_2$CN/NH$_2$CHO abundance ratio is about 0.2 for IRAS 16293-2422 B and 0.02 for IRAS2A, which is comparable to the range of values found for Sgr B2. We explored the possible formation of NH$_2$CN on grains through the NH$_2$ + CN reaction using the chemical model MAGICKAL. Grain-surface chemistry appears capable of reproducing the gas-phase abundance of NH$_2$CN with the correct choice of physical parameters.
Obtaining accurate and precise masses and ages for large numbers of giant
stars is of great importance for unraveling the assemblage history of the
Galaxy. In this paper, we estimate masses and ages of 6940 red giant branch
(RGB) stars with asteroseismic parameters deduced from \emph{Kepler} photometry
and stellar atmospheric parameters derived from LAMOST spectra. The typical
uncertainties of mass is a few per cent, and that of age is $\sim$\,20 per
cent. The sample stars reveal two separate sequences in the age --
[$\alpha$/Fe] relation -- a high--$\alpha$ sequence with stars older than
$\sim$\,8\,Gyr and a low--$\alpha$ sequence composed of stars with ages ranging
from younger than 1\,Gyr to older than 11\,Gyr. We further investigate the
feasibility of deducing ages and masses directly from LAMOST spectra with a
machine learning method based on kernel based principal component analysis,
taking a sub-sample of these RGB stars as a training data set. We demonstrate
that ages thus derived achieve an accuracy of $\sim$\,24 per cent. We also
explored the feasibility of estimating ages and masses based on the
spectroscopically measured carbon and nitrogen abundances.
The results are quite satisfactory and significantly improved compared to the
previous studies.
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