- ID:
- ivo://CDS.VizieR/J/A+A/618/A121
- Title:
- Azimuthal anistropy of stellar galactic disks
- Short Name:
- J/A+A/618/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ellipsoid of stellar random motions is a fundamental ingredient of galaxy dynamics. Yet it has long been difficult to constrain this component in disks others than the Milky Way. This article presents the modeling of the azimuthal-to-radial axis ratio of the velocity ellipsoid of galactic disks from stellar dispersion maps using integral field spectroscopy data of the CALIFA survey. The measured azimuthal anisotropy is shown to be not strongly dependent on the assumed vertical-to-radial dispersion ratio of the ellipsoid. The anisotropy distribution shows a large diversity in the orbital structure of disk galaxies from tangential to radial stellar orbits. Globally, the orbits are isotropic in inner disk regions and become more radial as a function of radius, although this picture tends to depend on galaxy morphology and luminosity. The Milky Way orbital anisotropy profile measured from the Second Gaia Data Release is consistent with those of CALIFA galaxies. A new correlation is evidenced, linking the absolute magnitude or stellar mass of the disks to the azimuthal anisotropy. More luminous disks have more radial orbits and less luminous disks have isotropic and somewhat tangential orbits. This correlation is consistent with the picture in galaxy evolution in which orbits become more radial as the mass grows and is redistributed as a function of time. With the help of circular velocity curves, it is also shown that the epicycle theory fails to reproduce the diversity of the azimuthal anisotropy of stellar random motions, as it predicts only nearly radial orbits in the presence of flat curves. The origin of this conflict is yet to be identified. It also questions the validity of the vertical-to-radial axis ratio of the velocity ellipsoid derived by many studies in the framework of the epicyclic approximation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/131/2035
- Title:
- B and R magnitudes for spiral galaxies
- Short Name:
- J/AJ/131/2035
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is an observational fact that bulges of spiral galaxies contain a high fraction of old and metal-rich stars. Following this observational fact, we have investigated the colors of 21 bulges hosted by a selected sample of high surface brightness spiral galaxies and low surface brightness galaxies observed in the B and R optical bands and the J and Ks near-IR bands.
- ID:
- ivo://CDS.VizieR/J/MNRAS/355/1251
- Title:
- Bar-induced strengths in spiral galaxies
- Short Name:
- J/MNRAS/355/1251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Bar-induced perturbation strengths are calculated for a well-defined magnitude-limited sample of 180 spiral galaxies, based on the Ohio State University Bright Galaxy Survey. We use a gravitational torque method, the ratio of the maximal tangential force to the mean axisymmetric radial force, as a quantitative measure of the bar strength.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A34
- Title:
- Barlenses in the CALIFA survey
- Short Name:
- J/A+A/618/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is theoretically predicted that, at low galaxy inclinations, boxy/peanut bar components have a barlens appearance of a round central component embedded in the narrow bar. We investigate barlenses in the Calar Alto Legacy Integral Field Area (CALIFA) survey galaxies, studying their morphologies, stellar populations, and metallicities. We show that, when present, barlenses account for a significant portion of light of photometric bulges, i.e., the excess light on top of the disks, which highlights the importance of bars in accumulating central galaxy mass concentrations in the cosmic timescale. We made multi-component decompositions for a sample of 46 barlens galaxies drawn from the CALIFA survey, where M_{star}_/M_{sun}_=10^9.7^-10^11.4^ and z=0.005-0.03. Unsharp masks of the Sloan Digital Sky Survey (SDSS) r'-band mosaics were used to identify the boxy/peanut or X-shaped features. Barlenses are identified in the images using our simulation snapshots as an additional guide. Our decompositions with GALFIT include bulges, disks, and bars as well as barlenses as a separate component. For 26 of the decomposed galaxies the CALIFA DR2 V500 grating data cubes were used to explore stellar ages and metallicities at the regions of various structure components. We find that 25+/-2% of the 1064 galaxies in the whole CALIFA sample show either X-shaped or barlens features. In the decomposed galaxies with barlenses, on average 13%+/-2% of the total galaxy light belongs to this component, leaving less than 10% for possible separate bulge components. Most importantly, bars and barlenses are found to have similar cumulative stellar age and metallicity distributions. The metallicities in barlenses are on average near solar, but exhibit a large range. In some of the galaxies barlenses and X-shaped features appear simultaneously, in which case the bar origin of the barlens is unambiguous. This is the first time that a combined morphological and stellar population analysis is used to study barlenses. We show that their stars are accumulated in a prolonged time period concurrently with the evolution of the narrow bar.
- ID:
- ivo://CDS.VizieR/J/MNRAS/473/4731
- Title:
- Barred galaxies structural decomposition
- Short Name:
- J/MNRAS/473/4731
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of two-component (disc+bar) and three-component (disc+bar+bulge) multiwavelength 2D photometric decompositions of barred galaxies in five Sloan Digital Sky Survey (SDSS) bands (ugriz). This sample of ~3500 nearby (z<0.06) galaxies with strong bars selected from the Galaxy Zoo citizen science project is the largest sample of barred galaxies to be studied using photometric decompositions that include a bar component. With detailed structural analysis, we obtain physical quantities such as the bar- and bulge-to-total luminosity ratios, effective radii, Sersic indices and colours of the individual components. We observe a clear difference in the colours of the components, the discs being bluer than the bars and bulges. An overwhelming fraction of bulge components have Sersic indices consistent with being pseudo-bulges. By comparing the barred galaxies with a mass-matched and volume-limited sample of unbarred galaxies, we examine the connection between the presence of a large-scale galactic bar and the properties of discs and bulges. We find that the discs of unbarred galaxies are significantly bluer compared to the discs of barred galaxies, while there is no significant difference in the colours of the bulges. We find possible evidence of secular evolution via bars that leads to the build-up of pseudo-bulges and to the quenching of star formation in the discs. We identify a subsample of unbarred galaxies with an inner lens/oval and find that their properties are similar to barred galaxies, consistent with an evolutionary scenario in which bars dissolve into lenses. This scenario deserves further investigation through both theoretical and observational work.
- ID:
- ivo://CDS.VizieR/J/MNRAS/439/1749
- Title:
- Barred S0 galaxies in the Coma cluster
- Short Name:
- J/MNRAS/439/1749
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study uses r-band images from the Eighth Data Release of the Sloan Digital Sky Survey (SDSS DR8) to study bars in lenticular (S0) galaxies in one of the nearest rich cluster environments, the Coma cluster. We develop techniques for bar detection and assess their success when applied to SDSS image data. To detect and characterize bars, we perform 2D bulge+disc+bar light decompositions of galaxy images with galfit. Using a sample of artificial galaxy images, we determine the faintest magnitude at which bars can be successfully measured at the depth and resolution of SDSS. We perform detailed decompositions of 83 S0 galaxies in Coma, 64 from a central sample, and 19 from a cluster outskirt sample. For the central sample, the S0 bar fraction is 72^+5^_-6_%. This value is significantly higher than that obtained using an ellipse-fitting method for bar detection, 48^+6^_-6_%. At a fixed luminosity, barred S0s are redder in g-r colour than unbarred S0s by 0.02mag. The frequency and strength of bars increase towards fainter luminosities. Neither central metallicity nor stellar age distributions differ significantly between barred and unbarred S0s. There is an increase in the bar fraction towards the cluster core, but this is at a low significance level. Bars have at most a weak correlation with cluster-centric radius.
- ID:
- ivo://CDS.VizieR/J/A+A/430/411
- Title:
- B-band photometry of ellipticals in Virgo
- Short Name:
- J/A+A/430/411
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a complete CCD imaging survey of 226 elliptical galaxies in the North-East quadrant of the Virgo cluster, representative of the properties of giant and dwarf elliptical galaxies in this cluster. We fit their radial light profiles with the Sersic r^1/n^ model of light distribution. We confirm the result of Graham & Guzman (2003AJ....125.2936G) that the apparent dichotomy between E and dE galaxies in the luminosity-<{mu}>_e_ plane no longer appears when other structural parameters are considered and can be entirely attributed to the onset of "core" galaxies at B_T_~-20.5mag. When "core" galaxies are not considered, E and dE form a unique family with n linearly increasing with the luminosity. For 90 galaxies we analyze the B-I color indices, both in the nuclear and in the outer regions. Both indices are bluer toward fainter luminosities. We find also that the outer color gradients do not show any significant correlation with the luminosity. The scatter in all color indicators increases significantly toward lower luminosities, e.g. galaxies fainter than B_T_~-15 have a B-I spread>0.5mag.
- ID:
- ivo://CDS.VizieR/J/AJ/148/75
- Title:
- Bent-tailed radio galaxies Chandra Deep Field South
- Short Name:
- J/AJ/148/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the 1.4GHz Australia Telescope Large Area Survey, supplemented by the 1.4GHz Very Large Array images, we undertook a search for bent-tailed (BT) radio galaxies in the Chandra Deep Field South. Here we present a catalog of 56 detections, which include 45 BT sources, 4 diffuse low-surface-brightness objects (1 relic, 2 halos, and 1 unclassified object), and a further 7 complex, multi-component sources. We report BT sources with rest-frame powers in the range 10^22^<=P_1.4 GHz_<=10^26^W/Hz, with redshifts up to 2 and linear extents from tens of kiloparsecs up to about 1Mpc. This is the first systematic study of such sources down to such low powers and high redshifts and demonstrates the complementary nature of searches in deep, limited area surveys as compared to shallower, large surveys. Of the sources presented here, one is the most distant BT source yet detected at a redshift of 2.1688. Two of the sources are found to be associated with known clusters: a wide-angle tail source in A3141 and a putative radio relic which appears at the infall region between the galaxy group MZ 00108 and the galaxy cluster AMPCC 40. Further observations are required to confirm the relic detection, which, if successful, would demonstrate this to be the least powerful relic yet seen with P_1.4GHz_=9x10^22^W/Hz. Using these data, we predict future 1.4GHz all-sky surveys with a resolution of ~10 arcsec and a sensitivity of 10{mu}Jy will detect of the order of 560,000 extended low-surface-brightness radio sources of which 440,000 will have a BT morphology.
- ID:
- ivo://CDS.VizieR/J/MNRAS/457/4160
- Title:
- BETA pilot multi-epoch continuum survey
- Short Name:
- J/MNRAS/457/4160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Boolardy Engineering Test Array is a 6x12m dish interferometer and the prototype of the Australian Square Kilometre Array Pathfinder (ASKAP), equipped with the first generation of ASKAP's phased array feed (PAF) receivers. These facilitate rapid wide-area imaging via the deployment of simultaneous multiple beams within an ~30deg^2^ field of view. By cycling the array through 12 interleaved pointing positions and using nine digitally formed beams, we effectively mimic a traditional 1hx108 pointing survey, covering ~150deg^2^ over 711-1015MHz in 12h of observing time. Three such observations were executed over the course of a week. We verify the full bandwidth continuum imaging performance and stability of the system via self-consistency checks and comparisons to existing radio data. The combined three epoch image has arcminute resolution and a 1{sigma} thermal noise level of 375{mu}Jy/beam, although the effective noise is a factor of ~3 higher due to residual sidelobe confusion. From this we derive a catalogue of 3722 discrete radio components, using the 35 per cent fractional bandwidth to measure in-band spectral indices for 1037 of them. A search for transient events reveals one significantly variable source within the survey area. The survey covers approximately two-thirds of the Spitzer South Pole Telescope Deep Field. This pilot project demonstrates the viability and potential of using PAFs to rapidly and accurately survey the sky at radio wavelengths.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A135
- Title:
- Beyond the exoplanet mass-radius relation
- Short Name:
- J/A+A/630/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass and radius are two fundamental properties to characterize exoplanets but only for a relatively small fraction of exoplanets are they both available. The mass is often derived from radial velocity measurements while the radius is almost always measured with the transit method. For a large number of exoplanets, either the radius or the mass is unknown, while the host star has been characterized. Several mass-radius relations dependent on the planet's type have been published which often allow to predict the radius, as well as a bayesian code which forecasts the radius of an exoplanet given the mass or vice versa. Our goal is to derive the radius of exoplanets using only observables extracted from spectra used primarily to determine radial velocities and spectral parameters. Our objective is to obtain a mass-radius relation that is independent of the planet's type. We work with a database of confirmed exoplanets with known radii and masses as well as the planets from our Solar System. Using random forests, a machine learning algorithm, we compute the radius of exoplanets and compare the results to the published radii. Our code, BEM, is available online. On top of this, we also explore how the radius estimates compare to previously published mass-radius relations. The estimated radii reproduces the spread in radius found for high mass planets better than previous mass-radius relations. The average error on the radius is 1.8R_Earth_ across the whole range of radii from 1 to 22R_Earth_. We found that a random forest algorithm is able to derive reliable radii especially for planets between 4 and 20R_Earth_, for which the error is smaller than 25%. The algorithm has a low bias but still a high variance, which could be reduced by limiting the growth of the forest or adding more data. The random forest algorithm is a promising method to derive exoplanet properties. We show that the exoplanet's mass and equilibrium temperature are the relevant properties which constrain the radius, and do it with higher accuracy than the previous methods.
