Search

Invited talk about double-barred galaxiesfor the conference "Galactic bars: driving and decoding galaxy evolution" (Granada, 3-7 July, 2023).

We present part 2 of the sixth and final Data Release (DR6) of the Radial Velocity Experiment (Rave), a magnitude-limited spectroscopic survey of Galactic stars randomly selected in Earth's southern hemisphere. The Rave medium-resolution spectra (R ∼ 7500) cover the Ca triplet region (8410-8795 Å) and span the complete time frame from the start of Rave observations on 2003 April 12 to their completion on 2013 April 4. In the second of two publications, we present the data products derived from 518,387 observations of 451,783 unique stars using a suite of advanced reduction pipelines focusing on stellar atmospheric parameters, in particular purely spectroscopically derived stellar atmospheric parameters, and the overall metallicity), enhanced stellar atmospheric parameters inferred via a Bayesian pipeline using Gaia DR2 astrometric priors, and asteroseismically calibrated stellar atmospheric parameters for giant stars based on asteroseismic observations for 699 K2 stars. In addition, we provide abundances of the elements Fe, Al, and Ni, as well as an overall [α/Fe] ratio obtained using a new pipeline based on the GAUGUIN optimization method that is able to deal with variable signal-to-noise ratios. The Rave DR6 catalogs are cross-matched with relevant astrometric and photometric catalogs, and are complemented by orbital parameters and effective temperatures based on the infrared flux method. The data can be accessed via the Rave website (http://rave-survey.org) or the Vizier database., Funding for Rave has been provided by: the Leibniz-Institut f¨ur Astrophysik Potsdam (AIP); the Australian Astronomical Observatory; the Australian National University; the Australian Research Council; the French National Research Agency (Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES); the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency (research core funding no. P1-0188); the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Basel, Groningen, Heidelberg, and Sydney. PJM is supported by grant 2017-03721 from the Swedish Research Council. LC is the recipient of the ARC Future Fellowship FT160100402. RAG acknowledges the support from the PLATO CNES grant. SM would like to acknowledge support from the Spanish Ministry with the Ramon y Cajal fellowship number RYC-2015-17697. MS thanks the Research School of Astronomy & Astrophysics in Canberra for support through a Distinguished Visitor Fellowship. RFGW thanks the Kavli Institute for Theoretical Physics and the Simons Foundation for support as a Simons Distinguished Visiting Scholar. This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958 to KITP.

The process that leads to the formation of the bright star forming sites observed along prominent spiral arms remains elusive. We present results of a multi-wavelength study of a spiral arm segment in the nearby grand-design spiral galaxy M51 that belongs to a spiral density wave and exhibits nine gas spurs. The combined observations of the(ionized, atomic, molecular, dusty) interstellar medium (ISM) with star formation tracers (HII regions, young, 52 pages, 9 figures, 8 tables, accepted to ApJ

We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep HST photometry obtained with the Legacy ExtraGalactic UV Survey (LEGUS). We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95% being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviors, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of ~1.7 for length-scales between ~20 pc and 2.5 kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances between 1 and 2.5 kpc. About 60% of the young stars belong to the detected stellar structures, while the remaining stars are distributed among the complexes, still inside the ring of the galaxy. The analysis of the time-dependent clustering of young populations shows a significant change from a more clustered to a more distributed behavior in a time-scale of ~60 Myr. The observed hierarchy in stellar clustering is consistent with star formation being regulated by turbulence across the ring. The rotational velocity difference between the edges of the ring suggests shear as the driving mechanism for this process. Our findings reveal the interesting case of an inner ring forming stars in a hierarchical fashion., MNRAS Accepted 2015 June 11; in original form 2015 May 04 (21 pages, 21 figures, 4 tables)

We present observations of the stellar and gas kinematics for a representative sample of 24 Sa galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data have been homogeneously reduced and analysed by means of a dedicated pipeline. All resulting data cubes were spatially binned to a minimum mean signal-to-noise ratio of 60 per spatial and spectral resolution element. Our maps typically cover the bulge-dominated region. We find a significant fraction of kinematically decoupled components (12/24), many of them displaying central velocity dispersion minima. They are mostly aligned and co-rotating with the main body of the galaxies, and are usually associated with dust discs and rings detected in unsharp-masked images. Almost all the galaxies in the sample (22/24) contain significant amounts of ionized gas which, in general, is accompanied by the presence of dust. The kinematics of the ionized gas are consistent with circular rotation in a disc co-rotating with respect to the stars. The distribution of mean misalignments between the stellar and gaseous angular momenta in the sample suggests that the gas has an internal origin. The [O-III]/H beta ratio is usually very low, indicative of current star formation, and shows various morphologies (ring-like structures, alignments with dust lanes or amorphous shapes). The star formation rates (SFRs) in the sample are comparable with that of normal disc galaxies. Low gas velocity dispersion values appear to be linked to regions of intense star formation activity. We interpret this result as stars being formed from dynamically cold gas in those regions. In the case of NGC 5953, the data suggest that we are witnessing the formation of a kinematically decoupled component from cold gas being acquired during the ongoing interaction with NGC 5954.

Detailed neutral hydrogen observations have been obtained of the large barred spiral galaxy NGC 3992 and its three small companion galaxies, UGC 6923, UGC 6940, and UGC 6969. For the main galaxy, the HI distribution is regular with a low level radial extension outside the stellar disc. However, at exactly the region of the bar, there is a pronounced central HI hole in the gas distribution. Likely gas has been transported inwards by the bar and because of the emptyness of the hole no large accretion events can have happened in recent galactic times. The gas kinematics is very regular and it is demonstrated that the influence of the bar potential on the velocity field is negligible. A precise and extended rotation curve has been derived showing some distinct features which can be explained by the non-exponential radial light distribution of NGC 3992. The decomposition of the rotation curve gives a slight preference for a sub maximal disc, though a range of disc contributions, up to a maximum disc situation fits nearly equally well. For such a maximum disc contribution, which might be expected in order to generate and maintain the bar, the required mass-to-light ratio is large but not exceptional., Comment: accepted for publication in Astronomy and Astrophysics. A copy with high resolution graphics will shortly become available at http://www.astro.rug.nl/Preprints/preprints.html

Stellar rotation curves, velocity dispersion profiles, and line-of-sight velocity distributions (LOSVD) as derived from absorption lines are presented for the major axes of 18 S0 and two elliptical galaxies. Ionized gas rotation curves and dispersions were measured from the [O III] 5007 Angstrom emission line in the 9 S0 galaxies displaying this feature. Minor-axis results are given for 14 of the S0 galaxies and one of the ellipticals. A wide range of behaviors are observed in the rotation and velocity dispersion profiles. These variations could be the result of the superposition of stars and gas belonging to the disks and bulges as well as the possible influences of bars, nuclear disks, and warps. Deviations from a Gaussian LOSVD are found along the major axes of all the galaxies in our sample. As parametrized by the Gauss-Hermite series of orthogonal functions, asymmetric deviations are always found in the inner regions of the S0 galaxies such that the prograde wing of the LOSVD is steeper than the retrograde wing. This is similar to the behavior observed in elliptical galaxies. However, at larger radii these asymmetries can change their sign. We find that in 9 of the 18 S0 galaxies a high-speed tail to the LOSVD develops along the major axis beyond the central regions. In 3 of these 9 objects the LOSVD asymmetries display a second change of sign with radius such that a low-speed tail is again present and persists to our last measured values. No correlations were found between the sizes of the stellar velocity dispersion gradients and either central velocity dispersion, absolute magnitude, disk-to-bulge ratio, Mg-2 or Fe line strength gradients. For the objects in our sample with edge-on orientations a comparison between the minor-axis 'bulge' velocity dispersion gradients and those found in elliptical galaxies indicates that the S0 bulges display, on average, logarithmic gradients approximately 4 times steeper than those found in normal luminous ellipticals. A number of galaxies show particularly interesting features. For the LINER S0 galaxy NGC 3998 we find that the velocity dispersion profiles of both the stars and gas rise sharply towards the center reaching nuclear values of sigma approximate to 320 km s(-1) Nuclear disks of rapidly rotating gas are found in NGC 4350 and NGC 4762, A nuclear stellar disk is apparent in the edge-on galaxy NGC 4111 and an extended disk of counterrotating gas is observed in the barred S0 NGC 3941. (C) 1996 American Astronomical Society.

The morphology and kinematics of interstellar gas in the nearby disc galaxies NGC 4736 (= Messier 94) and NGC 3310 (= Arp 217), derived from observations in the 21 cm line of neutral hydrogen and in the H alpha line, are compared to the results of simulations of the dynamics of an ensemble of gas clouds in an external potential. The form of the potential was derived from broadband optical photometry. For NGC 4736, good fits are obtained, for HI and H alpha data alike, to both the morphology and the kinematics of the inner ring of HII regions (R approximate to 50('')) when using a potential which is mildly non-axisymmetric at intermediate radii (b/a = 0.8 for R between 16('') and 180('')) further assuming an inclination of 35 degrees and setting the major-axis position angle to 115 degrees +/- 3 degrees. Residual velocity differences between the best-fitting model and observed velocity fields are at most 2 times the observational velocity resolutions. For NGC 3310, the potential was derived from a wide-field I-band image, assuming a reasonable run of mass-to-light ratio with radius, such that the rotation curve measured in HI was reproduced. While not as precise as those for NGC 4736, reasonable fits to the observed gas morphology and kinematics could be found. The pattern speed of the m = 2 perturbation is found in the modeling process. In both cases, the corotation is located at half the outer radius of the simulations of the optical disc.

Stellar rotation curves, velocity dispersion profiles, and line-of-sight velocity distributions (LOSVD) as derived from absorption lines are presented for the major axes of 18 S0 and two elliptical galaxies. Ionized gas rotation curves and dispersions were measured from the [O III] 5007 Angstrom emission line in the 9 S0 galaxies displaying this feature. Minor-axis results are given for 14 of the S0 galaxies and one of the ellipticals. A wide range of behaviors are observed in the rotation and velocity dispersion profiles. These variations could be the result of the superposition of stars and gas belonging to the disks and bulges as well as the possible influences of bars, nuclear disks, and warps. Deviations from a Gaussian LOSVD are found along the major axes of all the galaxies in our sample. As parametrized by the Gauss-Hermite series of orthogonal functions, asymmetric deviations are always found in the inner regions of the S0 galaxies such that the prograde wing of the LOSVD is steeper than the retrograde wing. This is similar to the behavior observed in elliptical galaxies. However, at larger radii these asymmetries can change their sign. We find that in 9 of the 18 S0 galaxies a high-speed tail to the LOSVD develops along the major axis beyond the central regions. In 3 of these 9 objects the LOSVD asymmetries display a second change of sign with radius such that a low-speed tail is again present and persists to our last measured values. No correlations were found between the sizes of the stellar velocity dispersion gradients and either central velocity dispersion, absolute magnitude, disk-to-bulge ratio, Mg-2 or Fe line strength gradients. For the objects in our sample with edge-on orientations a comparison between the minor-axis 'bulge' velocity dispersion gradients and those found in elliptical galaxies indicates that the S0 bulges display, on average, logarithmic gradients approximately 4 times steeper than those found in normal luminous ellipticals. A number of galaxies show particularly interesting features. For the LINER S0 galaxy NGC 3998 we find that the velocity dispersion profiles of both the stars and gas rise sharply towards the center reaching nuclear values of sigma approximate to 320 km s(-1) Nuclear disks of rapidly rotating gas are found in NGC 4350 and NGC 4762, A nuclear stellar disk is apparent in the edge-on galaxy NGC 4111 and an extended disk of counterrotating gas is observed in the barred S0 NGC 3941. (C) 1996 American Astronomical Society.

The morphology and kinematics of interstellar gas in the nearby disc galaxies NGC 4736 (= Messier 94) and NGC 3310 (= Arp 217), derived from observations in the 21 cm line of neutral hydrogen and in the H alpha line, are compared to the results of simulations of the dynamics of an ensemble of gas clouds in an external potential. The form of the potential was derived from broadband optical photometry. For NGC 4736, good fits are obtained, for HI and H alpha data alike, to both the morphology and the kinematics of the inner ring of HII regions (R approximate to 50('')) when using a potential which is mildly non-axisymmetric at intermediate radii (b/a = 0.8 for R between 16('') and 180('')) further assuming an inclination of 35 degrees and setting the major-axis position angle to 115 degrees +/- 3 degrees. Residual velocity differences between the best-fitting model and observed velocity fields are at most 2 times the observational velocity resolutions. For NGC 3310, the potential was derived from a wide-field I-band image, assuming a reasonable run of mass-to-light ratio with radius, such that the rotation curve measured in HI was reproduced. While not as precise as those for NGC 4736, reasonable fits to the observed gas morphology and kinematics could be found. The pattern speed of the m = 2 perturbation is found in the modeling process. In both cases, the corotation is located at half the outer radius of the simulations of the optical disc.