- ID:
- ivo://CDS.VizieR/J/A+A/649/A94
- Title:
- A universal pattern in halo magnetic fields
- Short Name:
- J/A+A/649/A94
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Magnetic fields in galaxy halos are in general very difficult to observe. Most recently, the Continuum HAlos in Nearby Galaxies - an EVLA Survey (CHANG-ES) collaboration investigated the radio halos of 35 nearby edge-on spiral galaxies in detail and detected large-scale magnetic fields in 16 of them. We used the CHANG-ES radio polarization data to create rotation measure (RM) maps for all galaxies in the sample and stack them with the aim of amplifying any underlying universal toroidal magnetic field pattern in the halo above and below the disk of the galaxy. We discovered a large-scale magnetic field in the central region of the stacked galaxy profile, which is attributable to an axial electric current that universally outflows from the center, both above and below the plane of the disk. A similar symmetry-breaking has also been observed in astrophysical jets, but never before in galaxy halos. This is an indication that galaxy halo magnetic fields are probably not generated by pure magnetohydrodynamic (MHD) processes in the central regions of galaxies. One such promising physical mechanism is the Cosmic Battery operating in the innermost accretion disk around the central supermassive black hole. We anticipate that our discovery will stimulate a more general discussion on the origin of astrophysical magnetic fields.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/463/2939
- Title:
- Automatic galaxy detection & classification
- Short Name:
- J/MNRAS/463/2939
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study on galaxy detection and shape classification using topometric clustering algorithms. We first use the DBSCAN algorithm to extract, from CCD frames, groups of adjacent pixels with significant fluxes and we then apply the DENCLUE algorithm to separate the contributions of overlapping sources. The DENCLUE separation is based on the localization of pattern of local maxima, through an iterative algorithm, which associates each pixel to the closest local maximum. Our main classification goal is to take apart elliptical from spiral galaxies. We introduce new sets of features derived from the computation of geometrical invariant moments of the pixel group shape and from the statistics of the spatial distribution of the DENCLUE local maxima patterns. Ellipticals are characterized by a single group of local maxima, related to the galaxy core, while spiral galaxies have additional groups related to segments of spiral arms. We use two different supervised ensemble classification algorithms: Random Forest and Gradient Boosting. Using a sample of ~=24000 galaxies taken from the Galaxy Zoo 2 main sample with spectroscopic redshifts, and we test our classification against the Galaxy Zoo 2 catalogue. We find that features extracted from our pipeline give, on average, an accuracy of ~=93 per cent, when testing on a test set with a size of 20 per cent of our full data set, with features deriving from the angular distribution of density attractor ranking at the top of the discrimination power.
- ID:
- ivo://CDS.VizieR/J/A+A/497/41
- Title:
- Average Early-type galaxies NIR spectrum
- Short Name:
- J/A+A/497/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared (hereafter NIR) data may provide complementary information to the traditional optical population synthesis analysis of unresolved stellar populations because the spectral energy distribution of the galaxies in the 1-2.5um range is dominated by different types of stars than at optical wavelengths. Furthermore, NIR data are less affected by dust absorption and hence could constrain the stellar populations in dust-obscured galaxies. We attempt to develop observational constraints on the stellar populations of unresolved stellar systems in the NIR.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A94
- Title:
- Avg pitch angles & spiral amplitudes in S4G
- Short Name:
- J/A+A/631/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spiral galaxies are very common in the local Universe, but their formation, evolution, and interplay with bars remain poorly understood after more than a century of astronomical research on the topic. We use a sample of 391 nearby galaxies from the S4G survey to characterise the winding angle and amplitude of spiral arms as a function of disc properties, such as bar strength, in all kinds of spirals (grand-design, multi-armed, and flocculent). We derived global pitch angles in 3.6um de-projected images from i) average measurements of individual logarithmic spiral segments, and ii) for a subsample of 32 galaxies, from 2-D Fourier analyses. The strength of spirals was quantified from the tangential-to-radial force ratio and from the normalised m=2 Fourier density amplitudes. In galaxies with more than one measured logarithmic segment, the spiral pitch angle varies on average by ~10{deg} between segments, but by up to >=15-20{deg}. The distribution of the global pitch angle versus Hubble type (T) is very similar for barred and non-barred galaxies when 1<=T<=5. Most spiral galaxies (>90%) are barred for T>5. The pitch angle is not correlated with bar strength, and only weakly with spiral strength. The amplitude of spirals is correlated with bar strength (and less tightly, with bar length) for all types of spirals. The mean pitch angle is hardly correlated with the mass of the supermassive black hole (estimated from central stellar velocity dispersion), with central stellar mass concentration, or with shear, questioning previous results in the literature using smaller samples. We do not find observational evidence that spiral arms are driven by stellar bars or by invariant manifolds. Most likely, discs that are prone to the development of strong bars are also reactive to the formation of prominent spirals, explaining the observed coupling between bar and spiral amplitudes.
- ID:
- ivo://CDS.VizieR/J/A+AS/93/255
- Title:
- Axial ratios of edge-on spirals
- Short Name:
- J/A+AS/93/255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJS/244/24
- Title:
- A z=0 Multiwavelength Galaxy Synthesis (z0MGS). I.
- Short Name:
- J/ApJS/244/24
- Date:
- 14 Mar 2022 07:45:54
- Publisher:
- CDS
- Description:
- We present an atlas of ultraviolet and infrared images of ~15750 local (d<~50Mpc) galaxies, as observed by NASA's Wide-field Infrared Survey Explorer (WISE) and Galaxy Evolution Explorer (GALEX) missions. These maps have matched resolution (FWHM 7.5" and 15"), matched astrometry, and a common procedure for background removal. We demonstrate that they agree well with resolved intensity measurements and integrated photometry from previous surveys. This atlas represents the first part of a program (the z=0 Multiwavelength Galaxy Synthesis) to create a large, uniform database of resolved measurements of gas and dust in nearby galaxies. This atlas allows us estimate local and integrated star formation rates (SFRs) and stellar masses (M_*_) across the local galaxy population in a uniform way. In the appendix, we use the population synthesis fits of Salim+ (2016ApJS..227....2S and 2018ApJ...859...11S) to calibrate integrated M_*_ and SFR estimators based on GALEX and WISE. Because they leverage a Sloan Digital Sky Survey (SDSS)-based training set of >100000 galaxies, these calibrations have high precision and allow us to rigorously compare local galaxies to SDSS results. We provide these SFR and M_*_ estimates for all galaxies in our sample and show that our results yield a "main sequence" of star-forming galaxies comparable to previous work. We also show the distribution of intensities from resolved galaxies in NUV-to-WISE1 versus WISE1-to-WISE3 space, which captures much of the key physics accessed by these bands.
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/3462
- Title:
- AzTEC/ASTE 1.1mm survey of SSA22
- Short Name:
- J/MNRAS/440/3462
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a 1.1-mm imaging survey of the SSA22 field, known for having an overdensity of z=3.1 Lyman{alpha} emitting galaxies (LAEs), taken with the astronomical thermal emission camera (AzTEC) on the Atacama Submillimeter Telescope Experiment (ASTE). We imaged a 950-arcmin2 field down to a 1{sigma} sensitivity of 0.7-1.3mJy/beam to find 125 submillimetre galaxies (SMGs) with a signal-to-noise ratio >=3.5. Counterpart identification using radio and near/mid-infrared data was performed and one or more counterpart candidates were found for 59 SMGs. Photometric redshifts based on optical to near-infrared images were evaluated for 45 of these SMGs with Spitzer/IRAC data and the median value is found to be z=2.4. By combining these estimations with estimates from the literature, we determined that 10 SMGs might lie within the large-scale structure at z=3.1. The two-point angular cross-correlation function between LAEs and SMGs indicates that the positions of the SMGs are correlated with the z=3.1 protocluster. These results suggest that the SMGs were formed and evolved selectively in the high dense environment of the high-redshift Universe. This picture is consistent with the predictions of the standard model of hierarchical structure formation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/3831
- Title:
- AzTEC/ASTE source catalogue
- Short Name:
- J/MNRAS/415/3831
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 0.72deg^2^ contiguous 1.1-mm survey in the central area of the Cosmological Evolution Survey field carried out to a 1{sigma}~1.26mJy/beam depth with the AzTEC camera mounted on the 10-m Atacama Submillimeter Telescope Experiment. We have uncovered 189 candidate sources at a signal-to-noise ratio (S/N)>=3.5, out of which 129, with S/N>=4, can be considered to have little chance of being spurious (<~2 per cent). We present the number counts derived with this survey, which show a significant excess of sources when compared to the number counts derived from the ~0.5deg^2^ area sampled at similar depths in the Submillimetre Common-User Bolometer Array (SCUBA) HAlf Degree Extragalactic Survey (SHADES).
- ID:
- ivo://CDS.VizieR/J/MNRAS/423/529
- Title:
- AzTEC deep-field observations
- Short Name:
- J/MNRAS/423/529
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Instruments using arrays of many bolometers have become increasingly common in the past decade. The maps produced by such instruments typically include the filtering effects of the instrument as well as those from subsequent steps performed in the reduction of the data. Therefore interpretation of the maps is dependent upon accurately calculating the transfer function of the chosen reduction technique on the signal of interest. Many of these instruments use non-linear and iterative techniques to reduce their data because such methods can offer an improved signal-to-noise ratio over those that are purely linear, particularly for signals at scales comparable to that subtended by the array. We discuss a general approach for measuring the transfer function of principal component analysis on point sources that are small compared to the spatial extent seen by any single bolometer within the array. The results are applied to previously released AzTEC catalogues of the Cosmic Evolution Survey (COSMOS), Lockman Hole, Subaru XMM-Newton Deep Field, Great Observatories Origins Deep Survey (GOODS)-North and GOODS-South fields. Source flux density and noise estimates increase by roughly +10 per cent for fields observed while AzTEC was installed at the Atacama Submillimeter Telescope Experiment and +15-25 per cent while AzTEC was installed at the James Clerk Maxwell Telescope. Detection significance is, on average, unaffected by the revised technique. The revised photometry technique will be used in subsequent AzTEC releases.