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- ID:
- ivo://CDS.VizieR/J/A+A/572/A40
- Title:
- Outflow of H_2_ gas from NGC3256
- Short Name:
- J/A+A/572/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nuclei of merging galaxies are often deeply buried in dense layers of gas and dust. In these regions, gas outflows driven by starburst and active galactic nuclear activity are believed to play a crucial role in the evolution of these galaxies. However, to fully understand this process it is essential to resolve the morphology and kinematics of such outflows. Using near-infrared integral-field spectroscopy obtained with SINFONI on the Very Large Telescope, we detect a kpc-scale structure of high-velocity molecular hydrogen (H_2_) gas associated with the deeply buried secondary nucleus of the infrared-luminous merger-galaxy NGC 3256. We show that this structure is most likely the hot component of a molecular outflow, which was recently also detected in the cold molecular gas through CO emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/91
- Title:
- Outflows in sodium excess objects
- Short Name:
- J/ApJ/809/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Van Dokkum and Conroy (2010Natur.468..940V) revisited the unexpectedly strong NaI lines at 8200{AA} found in some giant elliptical galaxies and interpreted them as evidence for an unusually bottom-heavy initial mass function. Jeong et al. (2013, J/ApJS/208/7) later found a large population of galaxies showing equally extraordinary Na D doublet absorption lines at 5900{AA} (Na D excess objects: NEOs) and showed that their origins can be different for different types of galaxies. While a Na D excess seems to be related to the interstellar medium (ISM) in late-type galaxies, smooth-looking early-type NEOs show little or no dust extinction and hence no compelling signs of ISM contributions. To further test this finding, we measured the Doppler components in the Na D lines. We hypothesized that the ISM would have a better (albeit not definite) chance of showing a blueshift Doppler departure from the bulk of the stellar population due to outflow caused by either star formation or AGN activities. Many of the late-type NEOs clearly show blueshift in their Na D lines, which is consistent with the former interpretation that the Na D excess found in them is related to gas outflow caused by star formation. On the contrary, smooth-looking early-type NEOs do not show any notable Doppler components, which is also consistent with the interpretation of Jeong et al. that the Na D excess in early-type NEOs is likely not related to ISM activities but is purely stellar in origin.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/4530
- Title:
- outlier detection algorithm for SDSS galaxies
- Short Name:
- J/MNRAS/465/4530
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- How can we discover objects we did not know existed within the large data sets that now abound in astronomy? We present an outlier detection algorithm that we developed, based on an unsupervised Random Forest. We test the algorithm on more than two million galaxy spectra from the Sloan Digital Sky Survey and examine the 400 galaxies with the highest outlier score. We find objects which have extreme emission line ratios and abnormally strong absorption lines, objects with unusual continua, including extremely reddened galaxies. We find galaxy-galaxy gravitational lenses, double-peaked emission line galaxies and close galaxy pairs. We find galaxies with high ionization lines, galaxies that host supernovae and galaxies with unusual gas kinematics. Only a fraction of the outliers we find were reported by previous studies that used specific and tailored algorithms to find a single class of unusual objects. Our algorithm is general and detects all of these classes, and many more, regardless of what makes them peculiar. It can be executed on imaging, time series and other spectroscopic data, operates well with thousands of features, is not sensitive to missing values and is easily parallelizable.
- ID:
- ivo://CDS.VizieR/J/AJ/139/279
- Title:
- Outlying HII regions in HI-selected galaxies
- Short Name:
- J/AJ/139/279
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the first systematic search for outlying HII regions, as part of a sample of 96 emission-line point sources (referred to as ELdots-emission-line dots) derived from the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). Our automated ELdot finder searches SINGG narrowband and continuum images for high equivalent width point sources outside the optical radius of the target galaxy (>2xr_25_ in the R band). Follow-up long-slit spectroscopy and deep Galaxy Evolution Explorer (GALEX) images (exposure time >1000s) distinguish outlying HII regions from background galaxies whose strong emission lines ([OIII], H{beta], or [OII]) have been redshifted into the SINGG bandpass.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/121
- Title:
- Overdensities of 0<z<3 COSMOS galaxies
- Short Name:
- J/ApJ/805/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well-known that a galaxy's environment has a fundamental influence in shaping its properties. We study the environmental effects on galaxy evolution, with an emphasis on the environment defined as the local number density of galaxies. The density field is estimated with different estimators (weighted adaptive kernel smoothing, 10th and 5th nearest neighbors, Voronoi and Delaunay tessellation) for a K_s_<24 sample of ~190000 galaxies in the COSMOS field at 0.1<z<3.1. The performance of each estimator is evaluated with extensive simulations. We show that overall there is a good agreement between the estimated density fields using different methods over ~2dex in overdensity values. However, our simulations show that adaptive kernel and Voronoi tessellation outperform other methods. Using the Voronoi tessellation method, we assign surface densities to a mass complete sample of quiescent and star-forming galaxies out to z~3. We show that at a fixed stellar mass, the median color of quiescent galaxies does not depend on their host environment out to z~3. We find that the number and stellar mass density of massive (>10^11^M_{sun}_) star-forming galaxies have not significantly changed since z~3, regardless of their environment. However, for massive quiescent systems at lower redshifts (z<~1.3), we find a significant evolution in the number and stellar mass densities in denser environments compared to lower density regions. Our results suggest that the relation between stellar mass and local density is more fundamental than the color-density relation and that environment plays a significant role in quenching star-formation activity in galaxies at z<~1.
2697. Overmassive black holes
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/2330
- Title:
- Overmassive black holes
- Short Name:
- J/MNRAS/446/2330
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Semi-analytical models in a {Lambda} cold dark matter cosmology have predicted the presence of outlying, 'overmassive' black holes at the high-mass end of the (black hole mass-galaxy velocity dispersion) M_BH_-{sigma} diagram (which we update here with a sample of 89 galaxies). They are a consequence of having experienced more dry mergers - thought not to increase a galaxy's velocity dispersion - than the 'main-sequence' population. Wet mergers and gas-rich processes, on the other hand, preserve the main correlation. Due to the scouring action of binary supermassive black holes, the extent of these dry mergers (since the last significant wet merger) can be traced by the ratio between the central stellar mass deficit and the black hole mass (M_def,*_/M_BH_). However, in a sample of 23 galaxies with partially depleted cores, including central cluster galaxies, we show that the 'overmassive' black holes are actually hosted by galaxies that appear to have undergone the lowest degree of such merging. In addition, the rotational kinematics of 37 galaxies in the M_BH_-{sigma} diagram reveals that fast and slow rotators are not significantly offset from each other, also contrary to what is expected if these two populations were the product of wet and dry mergers, respectively. The observations are thus not in accordance with model predictions and further investigation is required.
- ID:
- ivo://CDS.VizieR/J/MNRAS/455/2627
- Title:
- Oxygen abundance gradient in M81
- Short Name:
- J/MNRAS/455/2627
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the sensitivity of the methods available for abundance determinations in HII regions to potential observational problems. We compare the dispersions they introduce around the oxygen and nitrogen abundance gradients when applied to five different sets of spectra of HII regions in the galaxy M81. Our sample contains 116 HII regions with galactocentric distances of 3 to 33kpc, including 48 regions observed by us with the OSIRIS long-slit spectrograph at the 10.4-m Gran Telescopio Canarias telescope. The direct method can be applied to 31 regions, where we can get estimates of the electron temperature. The different methods imply oxygen abundance gradients with slopes of -0.010 to -0.002dex/kpc, and dispersions in the range 0.06-0.25dex. The direct method produces the shallowest slope and the largest dispersion, illustrating the difficulty of obtaining good estimates of the electron temperature. Three of the strong-line methods, C, ONS, and N2, are remarkably robust, with dispersions of ~0.06dex, and slopes in the range -0.008 to -0.006dex/kpc. The robustness of each method can be directly related to its sensitivity to the line intensity ratios that are more difficult to measure properly. Since the results of the N2 method depend strongly on the N/O abundance ratio and on the ionization parameter, we recommend the use of the C and ONS methods when no temperature estimates are available or when they have poor quality, although the behaviour of these methods when confronted with regions that have different properties and different values of N/O should be explored.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A7
- Title:
- Oxygen abundance in disk galaxies
- Short Name:
- J/A+A/623/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the possible dependence of the radial oxygen abundance distribution on non-axisymmetrical structures (bar/spirals) and other macroscopic parameters such as the mass, the optical radius R25, the color g-r, and the surface brightness of the galaxy. A sample of disk galaxies from the third data release of the Calar Alto Legacy Integral Field Area Survey (CALIFA DR3) is considered. We adopted the Fourier amplitude A2 of the surface brightness as a quantitative characteristic of the strength of nonaxisymmetric structures in a galactic disk, in addition to the commonly used morphologic division for A, AB, and B types based on the Hubble classification. To distinguish changes in local oxygen abundance caused by the non-axisymmetrical structures, the multiparametric mass-metallicity relation was constructed as a function of parameters such as the bar/spiral pattern strength, the disk size, color index g-r in the Sloan Digital Sky Survey (SDSS) bands, and central surface brightness of the disk. The gas-phase oxygen abundance gradient is determined by using the R calibration We find that there is no significant impact of the non-axisymmetric structures such as a bar and/or spiral patterns on the local oxygen abundance and radial oxygen abundance gradient of disk galaxies. Galaxies with higher mass, however, exhibit flatter oxygen abundance gradients in units of dex/kpc, but this effect is significantly less prominent for the oxygen abundance gradients in units of dex/R25 and almost disappears when the inner parts are avoided (R>0.25R25). We show that the oxygen abundance in the central part of the galaxy depends neither on the optical radius R25 nor on the color g-r or the surface brightness of the galaxy. Instead, outside the central part of the galaxy, the oxygen abundance increases with g-r value and central surface brightness of the disk.
2700. Oxygen abundance in M83
- ID:
- ivo://CDS.VizieR/J/ApJ/695/580
- Title:
- Oxygen abundance in M83
- Short Name:
- J/ApJ/695/580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained deep multiobject optical spectra of 49 HII regions in the outer disk of the spiral galaxy M83 (=NGC 5236) with the FORS2 spectrograph at the Very Large Telescope. The targets span the range in galactocentric distance between 0.64 and 2.64 times the R_25_ isophotal radius (5.4-22.3kpc), and 31 of them are located at R>R_25_, thus belonging to the extreme outer disk of the galaxy, populated by UV complexes revealed recently by the Galaxy Evolution Explorer satellite. In order to derive the nebular chemical abundances, we apply several diagnostics of the oxygen abundance, including R_23_, [NII]/[OII], and the [OIII]{lambda}4363 auroral line, which was detected in four HII regions.
